Abstract
In this review, we identify important challenges facing physicians responsible for renal and cardiac transplantation in children based on a review of the contemporary medical literature. Regarding pediatric renal transplantation, we discuss the challenge of antibody-mediated rejection, focusing on both acute and chronic antibody-mediated rejection. We review new diagnostic approaches to antibody-mediated rejection, such as panel-reactive antibodies, donor-specific cross-matching, antibody assays, risk assessment and diagnosis of antibody-mediated rejection, the pathology of antibody-mediated rejection, the issue of ABO incompatibility in renal transplantation, new therapies for antibody-mediated rejection, inhibiting of residual antibodies, the suppression or depletion of B-cells, genetic approaches to treating acute antibody-mediated rejection, and identifying future translational research directions in kidney transplantation in children. Regarding pediatric cardiac transplantation, we discuss the mechanisms of cardiac transplant rejection, including the role of endomyocardial biopsy in detecting graft rejection and the role of biomarkers in detecting cardiac graft rejection, including biomarkers of inflammation, cardiomyocyte injury, or stress. We review cardiac allograft vasculopathy. We also address the role of genetic analyses, including genome-wide association studies, gene expression profiling using entities such as AlloMap®, and adenosine triphosphate release as a measure of immune function using the Cylex® ImmuKnow™ cell function assay. Finally, we identify future translational research directions in heart transplantation in children.
Child; Translational Medical Research; Transplantation; Kidney Transplantation; Renal Transplantation; Heart Transplantation; Cardiac
INTRODUCTION
Solid-organ transplantation is an accepted treatment for end-stage renal and cardiac diseases in children. Over the past few decades, better methods of matching donor-recipient pairs and newer immunosuppressive drugs have substantially improved the overall survival of transplant recipients. Consequently, the number of children receiving solid-organ transplants has increased tremendously. However, improving the long-term management and quality of life of recipients continues to be a challenge. The main challenges are allograft rejection, the deleterious effects of the immunosuppressive drugs, infections, malignancies, nephrotoxicity, post-transplant lymphoproliferative disorders, and, in some cases, recurrence of the primary disease.
The University of Miami's Miller School of Medicine is deeply involved in caring for a large number of children receiving solid-organ transplants. In this article, we review many of the challenges in caring for these children, which we accomplish with an interdisciplinary team of pediatric cardiologists, pediatric nephrologists, pediatric immunologists, cell biologists, molecular biologists, transplant surgeons, pathologists, epidemiologists, and computational scientists.
We focus on antibody-mediated rejection (AMR) and the recurrence of focal segmental glomerulosclerosis (FSGS) in the renal section and on biomarkers for rejection and immunotolerance in the cardiology section. At the end of this review, we propose future research directions to identify the most appropriate children to list for transplantation and to improve the post-transplant care of these children.
TRANSLATIONAL RESEARCH IN PEDIATRIC RENAL TRANSPLANTATION
The Challenge of Antibody-Mediated Rejection
Kidney transplantation has had a long and successful history since the human leukocyte antigen
(HLA) was discovered in the 1960s. The realization that graft rejection was an immunological
phenomenon resulted in the development of immunosuppressive drugs, which allowed for organ
transplantation from genetically different donors (11. Fuggle SV, Taylor CJ. Histocompatibility in renal transplantation. In: Morris PJ,
J. KS, editors. Kidney Transplantation: Principles and Practice. Philadelphia: Saunders Elsevier;
2008. p. 140-57.).
Although the primary consideration in tissue and organ transplantation is to ensure ABO blood group
compatibility, large national databases suggest that graft survival improves with better HLA antigen
matching and that this matching is an important factor in long-term graft survival (22. Hariharan S, Johnson CP, Bresnahan BA, Taranto SE, McIntosh MJ, Stablein D.
Improved graft survival after renal transplantation in the United States, 1988 to 1996.
N Engl J Med. 2000;342(9):605-12.,33. Zhou YC, Cecka JM. Effect of HLA matching on renal transplant survival. Clin
Transpl. 1993;499-510.). The establishment of
the International Histocompatibility Workshop in 1965 set the stage for histocompatibility testing
in transplantation. In the ensuing years, the techniques and standardization of HLA typing evolved,
and new antigens were characterized. In recent years, molecular technology has improved the accuracy
and reproducibility of tissue typing, cross-matching, and detection of anti-HLA antibodies (44. Taylor CJ, Kosmoliaptsis V, Summers DM, Bradley JA. Back to the future:
application of contemporary technology to long-standing questions about the clinical relevance of
human leukocyte antigen-specific alloantibodies in renal transplantation. Hum Immunol.
2009;70(8):563-8, http://dx.doi.org/10.1016/j.humimm.2009.05.001.
http://dx.doi.org/10.1016/j.humimm.2009....
,55. Fuggle SV, Martin S. Tools for human leukocyte antigen antibody detection and
their application to transplanting sensitized patients. Transplantation. 2008;86(3):384-90,
http://dx.doi.org/10.1097/TP.0b013e31817c90f5.
http://dx.doi.org/10.1097/TP.0b013e31817...
).
In the 1960s, immediate allograft failure was found to decrease markedly with negative
cross-matching between donor lymphocytes and recipient serum. This finding eventually resulted in
the development of the complement-dependent cytotoxicity assay (66. Terasaki PI. Humoral theory of transplantation. Am J Transplant.
2003;3(6):665-73.,77. Kissmeyer-Nielsen F, Olsen S, Petersen VP, Fjeldborg O. Hyperacute rejection of
kidney allografts, associated with pre-existing humoral antibodies against donor cells. Lancet.
1966;2(7465):662-5, http://dx.doi.org/10.1016/S0140-6736(66)92829-7.
http://dx.doi.org/10.1016/S0140-6736(66)...
). Although immunosuppressive therapy regimens and
the short-term survival of kidney allografts have improved substantially since then, acute rejection
in the first year and chronic allograft nephropathy continue to be major determinants of long-term
graft survival (88. Pirsch JD, Miller J, Deierhoi MH, Vincenti F, Filo RS. A comparison of tacrolimus
(FK506) and cyclosporine for immunosuppression after cadaveric renal transplantation. FK506 Kidney
Transplant Study Group. Transplantation. 1997;63(7):977-83,
http://dx.doi.org/10.1097/00007890-199704150-00013.
http://dx.doi.org/10.1097/00007890-19970...
). Traditionally, transplant rejection has
been considered to be predominantly mediated by T-cells. However, increasing evidence suggests that
inadequate control of the humoral arm of the immune system contributes to chronic allograft
nephropathy (99. Loupy A, Hill GS, Jordan SC. The impact of donor-specific anti-HLA antibodies on
late kidney allograft failure. Nat Rev Nephrol. 2012;8(6):348-57,
http://dx.doi.org/10.1038/nrneph.2012.81.
http://dx.doi.org/10.1038/nrneph.2012.81...
).
Halloran et al. first described an atypical form of acute rejection occurring a few days to weeks
after transplantation that was characterized by a rapid deterioration in renal function and a high
incidence of failure in a previously functioning graft. Pathologic features were similar to
hyperacute rejection and were associated with donor-specific HLA antibodies (1010. Halloran PF, Wadgymar A, Ritchie S, Falk J, Solez K, Srinivasa NS. The
significance of the anti-class I antibody response. I. Clinical and pathologic features of
anti-class I-mediated rejection. Transplantation. 1990;49(1):85-91,
http://dx.doi.org/10.1097/00007890-199001000-00019.
http://dx.doi.org/10.1097/00007890-19900...
,1111. Halloran PF, Schlaut J, Solez K, Srinivasa NS. The significance of the
anti-class I response. II. Clinical and pathologic features of renal transplants with anti-class
I-like antibody. Transplantation. 1992;53(3):550-5,
http://dx.doi.org/10.1097/00007890-199203000-00011.
http://dx.doi.org/10.1097/00007890-19920...
). This phenomenon has since been
termed AMR (1212. Takemoto SK, Zeevi A, Feng S, Colvin RB, Jordan S, Kobashigawa J, et al.
National conference to assess antibody-mediated rejection in solid organ transplantation.
Am J Transplant. 2004;4(7):1033-41.,1313. Mauiyyedi S, Colvin RB. Humoral rejection in kidney transplantation: new
concepts in diagnosis and treatment. Curr Opin Nephrol Hypertens. 2002;11(6)609-18,
http://dx.doi.org/10.1097/00041552-200211000-00007.
http://dx.doi.org/10.1097/00041552-20021...
).
Traditionally, the complement-dependent cytotoxicity cell-based assay was used to detect
donor-specific anti-HLA antibodies and was useful in predicting hyperacute rejection. However, this
assay is not sensitive enough to detect low or marginal titers of antibodies, which are relevant to
the early outcomes of the transplant. The advent of solid-phase assays (SPA), which have greater
sensitivity and specificity, has resulted in increased identification of AMR (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
). The incidence of AMR is less than 5% in unsensitized patients but between 40%
and 90% in sensitized patients (1515. van den Berg-Loonen EM, Billen EV, Voorter CE, van Heurn LW, Claas FH, van Hooff
JP, et al. Clinical relevance of pretransplant donor-directed antibodies detected by single antigen
beads in highly sensitized renal transplant patients. Transplantation. 2008;85(8):1086-90,
http://dx.doi.org/10.1097/TP.0b013e31816b3ed1.
http://dx.doi.org/10.1097/TP.0b013e31816...
). The strength of the
antibody response appears to be strongly associated with the risk of rejection (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
15. van den Berg-Loonen EM, Billen EV, Voorter CE, van Heurn LW, Claas FH, van Hooff
JP, et al. Clinical relevance of pretransplant donor-directed antibodies detected by single antigen
beads in highly sensitized renal transplant patients. Transplantation. 2008;85(8):1086-90,
http://dx.doi.org/10.1097/TP.0b013e31816b3ed1.
http://dx.doi.org/10.1097/TP.0b013e31816...
16. Reinsmoen NL, Lai CH, Vo A, Cao K, Ong G, Naim M, et al. Acceptable
donor-specific antibody levels allowing for successful deceased and living donor kidney
transplantation after desensitization therapy. Transplantation. 2008;86(6):820-5,
http://dx.doi.org/10.1097/TP.0b013e3181856f98.
http://dx.doi.org/10.1097/TP.0b013e31818...
-1717. Riethmuller S, Ferrari-Lacraz S, Muller MK, Raptis DA, Hadaya K, Rusi B, et al.
Donor-specific antibody levels and three generations of crossmatches to predict antibody-mediated
rejection in kidney transplantation. Transplantation. 2010;90(2):160-7,
http://dx.doi.org/10.1097/TP.0b013e3181e36e08.
http://dx.doi.org/10.1097/TP.0b013e3181e...
). Occurring from
preformed or new anti-HLA antibodies, AMR generally has a worse prognosis and requires different
management than does T-cell-related rejection (1818. Fehr T, Gaspert A. Antibody-mediated kidney allograft rejection: therapeutic
options and their experimental rationale. Transpl Int. 2012;25(6):623-32,
http://dx.doi.org/10.1111/j.1432-2277.2012.01453.x.
http://dx.doi.org/10.1111/j.1432-2277.20...
).
A higher degree of HLA mismatches, acute rejection episodes, patient nonadherence to treatment,
inadequate immune suppression, previous organ transplantation, blood transfusion, and pregnancy
result in sensitization and increased risk for AMR. The first six causes are important in children
(1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
,1818. Fehr T, Gaspert A. Antibody-mediated kidney allograft rejection: therapeutic
options and their experimental rationale. Transpl Int. 2012;25(6):623-32,
http://dx.doi.org/10.1111/j.1432-2277.2012.01453.x.
http://dx.doi.org/10.1111/j.1432-2277.20...
,1919. Billing H, Rieger S, Susal C, Waldherr R, Opelz G, Wuhl E, et al. IVIG and
rituximab for treatment of chronic antibody-mediated rejection: a prospective study in paediatric
renal transplantation with a 2-year follow-up. Transpl Int. 2012;25(11):1165-73,
http://dx.doi.org/10.1111/j.1432-2277.2012.01544.x.
http://dx.doi.org/10.1111/j.1432-2277.20...
). Currently, 17% of patients with end-stage kidney disease on
the waiting list for kidney transplants have had previous transplants. Given that 50% of all
childhood kidney transplant recipients will receive a second kidney transplant by the age of 25
years, a substantial proportion of children will be sensitized as young adults (2020. Rees L. Long-term outcome after renal transplantation in childhood. Pediatr
Nephrol. 2009;24(3):475-84, http://dx.doi.org/10.1007/s00467-007-0559-2.
http://dx.doi.org/10.1007/s00467-007-055...
). The true incidence and prevalence of AMR in children is not
known.
Clinical Features of Acute and Chronic Antibody-Mediated Rejection
In acute AMR, patients present with an acute loss of graft function, most often in
the first few weeks after transplantation. The clinical presentation is indistinguishable from acute
cellular rejection. It can also occur years after transplantation when immune suppression is
decreased or stopped, either iatrogenically or because of nonadherence by the patient (2121. Colvin RB. Antibody-mediated renal allograft rejection: diagnosis and
pathogenesis. J Am Soc Nephrol. 2007;18(4):1046-56,
http://dx.doi.org/10.1681/ASN.2007010073.
http://dx.doi.org/10.1681/ASN.2007010073...
). It can occur in both sensitized patients and in those with a
negative pre-transplant cross-match.
Chronic AMR is an insidious process associated with fluctuating levels of donor-specific antibodies (DSAs) and results in irreversible structural damage. Clinically, it manifests as proteinuria, hypertension, and declining graft function over time.
New Diagnostic Approaches to Antibody-Mediated Rejection
In the past decade, there have been major technologic advances in assays that detect anti-HLA
antibodies. Solid-phase assays and the use of single HLA antigen beads have increased the
sensitivity and specificity of detection. Knowing the presence and specificity of anti-HLA
antibodies in organ transplant candidates is important for identifying compatible donors,
interpreting cross-match results, and assessing the risk of post-transplant rejection. After
transplantation, knowledge of anti-HLA antibodies aids in diagnosing AMR and in monitoring
alloreactive antibodies (44. Taylor CJ, Kosmoliaptsis V, Summers DM, Bradley JA. Back to the future:
application of contemporary technology to long-standing questions about the clinical relevance of
human leukocyte antigen-specific alloantibodies in renal transplantation. Hum Immunol.
2009;70(8):563-8, http://dx.doi.org/10.1016/j.humimm.2009.05.001.
http://dx.doi.org/10.1016/j.humimm.2009....
,2222. Eng HS, Leffell MS. Histocompatibility testing after fifty years of
transplantation. J Immunol Methods. 2011;369(1-2):1-21,
http://dx.doi.org/10.1016/j.jim.2011.04.005.
http://dx.doi.org/10.1016/j.jim.2011.04....
). Therefore, these assays are useful for the preemptive management of sensitized
patients, who are at high risk for AMR, and for managing AMR when it occurs.
Panel Reactive Antibodies
Highly sensitized patients are less likely to have a cross-match-compatible donor and therefore
have longer waiting times on the deceased donor waiting list. The panel reactive antibody test
estimates the likelihood of finding a cross-match-compatible donor using a panel of normal blood
donors. The calculated score is the percentage of donors in this pool to whom a patient has reactive
antibodies. Analysis of antibody specificity by SPAs has helped determine unacceptable donor
antigens to which the patient has previously been sensitized and forms the basis for the calculated
panel reactive antibody (cPRA) and virtual cross-match. The cPRA represents the percentage of donors
that will be preemptively declined because of the presence of unacceptable antigens and has been
found to increase the efficiency of organ allocation, increase the identification of compatible
donors, and increase the likelihood of successful transplantation in sensitized patients (2323. Cecka JM. Calculated PRA (CPRA): the new measure of sensitization for transplant
candidates. Am J Transplant. 2010;10(1):26-9.,2424. Nikaein A, Cherikh W, Nelson K, Baker T, Leffell S, Bow L, et al. Organ
procurement and transplantation network/united network for organ sharing histocompatibility
committee collaborative study to evaluate prediction of crossmatch results in highly sensitized
patients. Transplantation. 2009;87(4):557-62,
http://dx.doi.org/10.1097/TP.0b013e3181943c76.
http://dx.doi.org/10.1097/TP.0b013e31819...
). Knowledge of the HLA
antibody specificity of the recipient and the HLA type of the potential donor can predict
compatibility, a process called the “virtual cross-match.”
Donor-Specific Cross-matching
Donor-specific cross-matching directly measures the reactivity of the patient's serum to the donor cells. The development of flow cytometry has increased the sensitivity of cross-match testing.
-
The complement-dependent cytotoxicity assay is a traditional cell-based assay that determines whether the donor and recipient are compatible and helps predict immediate graft loss from hyperacute or accelerated rejection. The limitations are that it may detect non-HLA antibodies that are not necessarily harmful, such as autoantibodies and IgM antibodies. The sensitivity is low, so there are false negative reactions, and distinguishing class I and class II antibody specificities is difficult (44. Taylor CJ, Kosmoliaptsis V, Summers DM, Bradley JA. Back to the future: application of contemporary technology to long-standing questions about the clinical relevance of human leukocyte antigen-specific alloantibodies in renal transplantation. Hum Immunol. 2009;70(8):563-8, http://dx.doi.org/10.1016/j.humimm.2009.05.001.
http://dx.doi.org/10.1016/j.humimm.2009.... ,2222. Eng HS, Leffell MS. Histocompatibility testing after fifty years of transplantation. J Immunol Methods. 2011;369(1-2):1-21, http://dx.doi.org/10.1016/j.jim.2011.04.005.
http://dx.doi.org/10.1016/j.jim.2011.04.... ). -
Flow cytometry cross-matching is an antibody-binding assay that detects antibodies to HLA antigens on the surface of target cells. It is more sensitive than the complement-dependent cytotoxicity assay in detecting low-titer complement-fixing and non-fixing antibodies and IgG sub-types associated with an increased risk of allograft rejection. Some centers have abandoned the complement-dependent cytotoxicity cross-match and instead use flow cytometry and solid-phase binding assays exclusively.
-
The ELISA cross-match test with donor antigen uses purified HLA molecules from the donor, which are bound to a well in a microtiter plate. HLA antibody is then detected by an enzyme-linked immunosorbent assay.
Antibody Assays
Solid-phase assays (SPAs), such as flow PRA and flow-specific beads that use purified HLA antigens attached to microparticles, can detect anti-HLA antibodies missed by the complement-dependent cytotoxicity assay. They allow for better definition of B-cell cross-matches, which have been attributed to non-HLA-specific autoantibodies in the past. A positive B-cell cross-match from class I and II HLA antibodies can result in acute AMR. Antibodies to HLA DP antigens have been associated with acute rejection. SPAs help identify these antigens because donors are not routinely typed for HLA-DP antigens.
In summary, techniques more sensitive to anti-HLA antibodies allow for early recognition of the
risk of allograft injury from AMR and for preemptive management. A concern with SPAs is the clinical
relevance of the low-level anti-HLA antibodies that they detect, which may not always be harmful.
Therapy with monoclonal antibodies can also interfere with the assays. These tests have to be
interpreted in the context of the clinical presentation (44. Taylor CJ, Kosmoliaptsis V, Summers DM, Bradley JA. Back to the future:
application of contemporary technology to long-standing questions about the clinical relevance of
human leukocyte antigen-specific alloantibodies in renal transplantation. Hum Immunol.
2009;70(8):563-8, http://dx.doi.org/10.1016/j.humimm.2009.05.001.
http://dx.doi.org/10.1016/j.humimm.2009....
).
The HLA Matchmaker program was developed to review each HLA antigen as a string of epitopes.
Because antibodies are induced only against a small proportion of immunogenic epitopes, this
information is useful in determining HLA compatibility at a molecular level and can identify
acceptable mismatches (2525. Valentini RP, Nehlsen-Cannarella SL, Gruber SA, Mattoo TK, West MS, Lang C, et
al. Intravenous immunoglobulin, HLA allele typing and HLAMatchmaker facilitate successful
transplantation in highly sensitized pediatric renal allograft recipients. Pediatr Transplant.
2007;11(1):77-81, http://dx.doi.org/10.1111/j.1399-3046.2006.00617.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
,2626. Duquesnoy RJ, Askar M. HLAMatchmaker: a molecularly based algorithm for
histocompatibility determination. V. Eplet matching for HLA-DR, HLA-DQ, and HLA-DP. Hum Immunol.
2007;68(1):12-25, http://dx.doi.org/10.1016/j.humimm.2006.10.003.
http://dx.doi.org/10.1016/j.humimm.2006....
).
Risk Assessment and Diagnosis of Antibody-Mediated Rejection
Donor-specific antibodies can occur in the sensitized individual (before transplant) or in the
unsensitized individual after transplant. In living donors, preformed antibodies can be detected
before transplant, whereas in deceased donors, the target antigens may not be known in advance,
although they can be detected retrospectively. Kidney transplant recipients can also develop new
(de novo) HLA and non-HLA antibodies after transplantation, even when they were at
low immunological risk before transplant (99. Loupy A, Hill GS, Jordan SC. The impact of donor-specific anti-HLA antibodies on
late kidney allograft failure. Nat Rev Nephrol. 2012;8(6):348-57,
http://dx.doi.org/10.1038/nrneph.2012.81.
http://dx.doi.org/10.1038/nrneph.2012.81...
,1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
,2727. Vasilescu ER, Ho EK, Colovai AI, Vlad G, Foca-Rodi A, Markowitz GS, et al.
Alloantibodies and the outcome of cadaver kidney allografts. Hum Immunol. 2006;67(8):597-604,
http://dx.doi.org/10.1016/j.humimm.2006.04.012.
http://dx.doi.org/10.1016/j.humimm.2006....
,2828. Ginevri F, Nocera A, Comoli P, Innocente A, Cioni M, Parodi A, et al.
Posttransplant de novo donor-specific hla antibodies identify pediatric kidney recipients at risk
for late antibody-mediated rejection. Am J Transplant.
2012;12(12):3355-62.).
The development of de novo antibodies increases the risk of acute and chronic
graft injury, which occurs at a median of 2 years after transplant in children (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
,2828. Ginevri F, Nocera A, Comoli P, Innocente A, Cioni M, Parodi A, et al.
Posttransplant de novo donor-specific hla antibodies identify pediatric kidney recipients at risk
for late antibody-mediated rejection. Am J Transplant.
2012;12(12):3355-62.). The frequency of
occurrence is variable and depends on the sensitivity of the assay, the type of immune suppression,
and the patient. Anti-HLA antibodies often develop before allograft injury (2828. Ginevri F, Nocera A, Comoli P, Innocente A, Cioni M, Parodi A, et al.
Posttransplant de novo donor-specific hla antibodies identify pediatric kidney recipients at risk
for late antibody-mediated rejection. Am J Transplant.
2012;12(12):3355-62.). Patients with de novo DSAs have a higher risk of acute
rejection, higher creatinine concentrations, proteinuria, and a higher incidence of graft loss
(1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
). De novo DSAs are usually class II
antibodies and are associated with a worse prognosis than are class I HLA antibodies (99. Loupy A, Hill GS, Jordan SC. The impact of donor-specific anti-HLA antibodies on
late kidney allograft failure. Nat Rev Nephrol. 2012;8(6):348-57,
http://dx.doi.org/10.1038/nrneph.2012.81.
http://dx.doi.org/10.1038/nrneph.2012.81...
,2828. Ginevri F, Nocera A, Comoli P, Innocente A, Cioni M, Parodi A, et al.
Posttransplant de novo donor-specific hla antibodies identify pediatric kidney recipients at risk
for late antibody-mediated rejection. Am J Transplant.
2012;12(12):3355-62.).
Studies in animals and humans have found that T-cell recognition of the processed antigen through
the indirect pathway activates the humoral response (2929. Baldwin WM, 3rd, Valujskikh A, Fairchild RL. Antibody-mediated rejection:
emergence of animal models to answer clinical questions. Am J Transplant.
2010;10(5):1135-42.).
However, not all patients with anti-HLA antibodies have acute rejection or graft loss. Sutherland et
al. developed a C1q assay that detects complement binding DSAs, and they hypothesized that
complement activation by DSAs may be important in initiating tissue injury (3030. Sutherland SM, Chen G, Sequeira FA, Lou CD, Alexander SR, Tyan DB.
Complement-fixing donor-specific antibodies identified by a novel C1q assay are associated with
allograft loss. Pediatr Transplant. 2012;16(1):12-7,
http://dx.doi.org/10.1111/j.1399-3046.2011.01599.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
). Patients with C1q-binding DSAs were more likely to have allograft injury and
loss than were patients with non-C1q-binding DSAs (3030. Sutherland SM, Chen G, Sequeira FA, Lou CD, Alexander SR, Tyan DB.
Complement-fixing donor-specific antibodies identified by a novel C1q assay are associated with
allograft loss. Pediatr Transplant. 2012;16(1):12-7,
http://dx.doi.org/10.1111/j.1399-3046.2011.01599.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
).
Antibody-mediated rejection can be caused by antibodies to major histocompatibility complex (MHC)
class I chain-related gene A and gene B (MICA and MICB), angiotensin type I receptors, endothelial
antigens, and vimentin, which is a cytosolic protein (Table 1) (3131. Dragun D. Humoral responses directed against non-human leukocyte antigens in
solid-organ transplantation. Transplantation. 2008;86(8):1019-25,
http://dx.doi.org/10.1097/TP.0b013e3181889748.
http://dx.doi.org/10.1097/TP.0b013e31818...
).
Pathology of Antibody-Mediated Rejection
In AMR, alloantibodies preferentially attack the peritubular capillaries and glomerular
capillaries; by contrast, T cell-mediated rejection involves tubular, interstitial, and intimal
infiltration of inflammatory cells (3232. Racusen LC, Haas M. Antibody-mediated rejection in renal allografts: lessons
from pathology. Clin J Am Soc Nephrol. 2006;1(3):415-20,
http://dx.doi.org/10.2215/CJN.01881105.
http://dx.doi.org/10.2215/CJN.01881105...
33. Trpkov K, Campbell P, Pazderka F, Cockfield S, Solez K, Halloran PF. Pathologic
features of acute renal allograft rejection associated with donor-specific antibody, Analysis using
the Banff grading schema. Transplantation. 1996;61(11):1586-92,
http://dx.doi.org/10.1097/00007890-199606150-00007.
http://dx.doi.org/10.1097/00007890-19960...
-3434. Mauiyyedi S, Crespo M, Collins AB, Schneeberger EE, Pascual MA, Saidman SL, et
al. Acute humoral rejection in kidney transplantation: II. Morphology, immunopathology, and
pathologic classification. J Am Soc Nephrol. 2002;13(3):779-87.). Acute cellular rejection can coexist with acute AMR. In many circumstances,
AMR is mediated by activation of the classical complement pathway. The C4d biomarker is a
degradation product of activated C4b, which is a classical component of complement. It is covalently
bound to tissues and deposited in peritubular capillaries in AMR. C4d is diagnosed by
immunohistologic staining. It is strongly associated with DSAs, helps confirm the diagnosis, and is
the best marker of complement-fixing circulating antibodies [Figure 1A and 1B (3434. Mauiyyedi S, Crespo M, Collins AB, Schneeberger EE, Pascual MA, Saidman SL, et
al. Acute humoral rejection in kidney transplantation: II. Morphology, immunopathology, and
pathologic classification. J Am Soc Nephrol. 2002;13(3):779-87.
35. Platt JL. C4d and the fate of organ allografts. J Am Soc Nephrol.
2002;13(3):2417-9, http://dx.doi.org/10.1097/01.ASN.0000030140.74450.0B.
http://dx.doi.org/10.1097/01.ASN.0000030...
-3636. Sund S, Hovig T, Reisaeter AV, Scott H, Bentdal O, Mollnes TE. Complement
activation in early protocol kidney graft biopsies after living-donor transplantation.
Transplantation. 2003;75(8):1204-13,
http://dx.doi.org/10.1097/01.TP.0000062835.30165.2C.
http://dx.doi.org/10.1097/01.TP.00000628...
)].
A) A 4-year-old child who had good allograft function initially and then developed acute antibody-mediated rejection 2 weeks after deceased donor kidney transplantation. Renal biopsy reveals marked acute tubular necrosis and interstitial hemorrhage. There is evidence of glomerulitis and tubulitis (H&E, 40×). B) Immunofluorescence in this patient reveals diffuse C4d staining of the peritubular capillaries, supporting the diagnosis of acute antibody-mediated rejection.
Antibodies to class I and II HLA antigens are found in 88% to 95% of patients with C4d deposition
and acute graft dysfunction (3636. Sund S, Hovig T, Reisaeter AV, Scott H, Bentdal O, Mollnes TE. Complement
activation in early protocol kidney graft biopsies after living-donor transplantation.
Transplantation. 2003;75(8):1204-13,
http://dx.doi.org/10.1097/01.TP.0000062835.30165.2C.
http://dx.doi.org/10.1097/01.TP.00000628...
). The deposition of C4d
without circulating antibodies can be the result of absorption by the graft, as was proven by
eluting anti-HLA antibodies from rejected grafts (2121. Colvin RB. Antibody-mediated renal allograft rejection: diagnosis and
pathogenesis. J Am Soc Nephrol. 2007;18(4):1046-56,
http://dx.doi.org/10.1681/ASN.2007010073.
http://dx.doi.org/10.1681/ASN.2007010073...
).
Additional staining with C3d, a cleavage product of the complement component C3, may be useful in
some cases (3737. Kuypers DR, Lerut E, Evenepoel P, Maes B, Vanrenterghem Y, Van Damme B. C3D
deposition in peritubular capillaries indicates a variant of acute renal allograft rejection
characterized by a worse clinical outcome. Transplantation. 2003;76(1):102-8,
http://dx.doi.org/10.1097/01.TP.0000069040.16457.06.
http://dx.doi.org/10.1097/01.TP.00000690...
). C4d deposition can occur beginning several
years after transplantation, even though previous biopsies were C4d negative (3434. Mauiyyedi S, Crespo M, Collins AB, Schneeberger EE, Pascual MA, Saidman SL, et
al. Acute humoral rejection in kidney transplantation: II. Morphology, immunopathology, and
pathologic classification. J Am Soc Nephrol. 2002;13(3):779-87.,3838. Regele H, Bohmig GA, Habicht A, Gollowitzer D, Schillinger M, Rockenschaub S, et
al. Capillary deposition of complement split product C4d in renal allografts is associated with
basement membrane injury in peritubular and glomerular capillaries: a contribution of humoral
immunity to chronic allograft rejection. J Am Soc Nephrol. 2002;13(9):2371-80,
http://dx.doi.org/10.1097/01.ASN.0000025780.03790.0F.
http://dx.doi.org/10.1097/01.ASN.0000025...
). C4d deposition is found in 2% to 26%
of ABO-compatible, histologically normal renal allografts. The long-term importance of this
deposition is unknown (3939. Mengel M, Bogers J, Bosmans JL, Seron D, Moreso F, Carrera M, et al. Incidence
of C4d stain in protocol biopsies from renal allografts: results from a multicenter trial.
Am J Transplant. 2005;5(5):1050-6.). Antibody-mediated rejection has
been detected in C4d-negative grafts, and in such cases, evidence of microcirculatory injury and the
presence of class II DSAs portend a bad outcome (4040. Loupy A, Hill GS, Suberbielle C, Charron D, Anglicheau D, Zuber J, et al.
Significance of C4d Banff scores in early protocol biopsies of kidney transplant recipients with
preformed donor-specific antibodies (DSA). Am J Transplant.
2011;11(1):56-65.).
The Banff criteria for diagnosing AMR are (4141. Solez K, Colvin RB, Racusen LC, Haas M, Sis B, Mengel M, et al. Banff 07 classification of renal allograft pathology: updates and future directions. Am J Transplant. 2008;8(4):753-60.):
-
Circulating antibodies to donor MHC antigens,
-
Diffuse deposition of the complement split product C4d in peritubular capillaries as an indicator of antibody activity (>50% of peritubular capillaries),
-
Morphologic indications of acute tissue injury, and
-
Clinical evidence of graft dysfunction.
Morphologic evidence of acute tissue injury includes 1) acute tubular injury, 2) neutrophils or
monocytes in the peritubular capillaries or glomeruli, and 3) intimal arteritis, intramural or
transmural inflammation, or fibrinoid necrosis of the arteries. Antibody-mediated rejection is
diagnosed in 1% to 6% of protocol renal biopsies in unsensitized patients and in 60% to 70% of
patients with suspected acute rejection (3434. Mauiyyedi S, Crespo M, Collins AB, Schneeberger EE, Pascual MA, Saidman SL, et
al. Acute humoral rejection in kidney transplantation: II. Morphology, immunopathology, and
pathologic classification. J Am Soc Nephrol. 2002;13(3):779-87.,3838. Regele H, Bohmig GA, Habicht A, Gollowitzer D, Schillinger M, Rockenschaub S, et
al. Capillary deposition of complement split product C4d in renal allografts is associated with
basement membrane injury in peritubular and glomerular capillaries: a contribution of humoral
immunity to chronic allograft rejection. J Am Soc Nephrol. 2002;13(9):2371-80,
http://dx.doi.org/10.1097/01.ASN.0000025780.03790.0F.
http://dx.doi.org/10.1097/01.ASN.0000025...
). Protocol biopsies have revealed diffuse peritubular capillary
staining with C4d and DSAs with no histological evidence of injury. The importance of this finding
is not clear, but some authors postulate that there may be accommodation to the graft (3232. Racusen LC, Haas M. Antibody-mediated rejection in renal allografts: lessons
from pathology. Clin J Am Soc Nephrol. 2006;1(3):415-20,
http://dx.doi.org/10.2215/CJN.01881105.
http://dx.doi.org/10.2215/CJN.01881105...
,3535. Platt JL. C4d and the fate of organ allografts. J Am Soc Nephrol.
2002;13(3):2417-9, http://dx.doi.org/10.1097/01.ASN.0000030140.74450.0B.
http://dx.doi.org/10.1097/01.ASN.0000030...
). Accommodation is the
acquired resistance of the allograft to immune-mediated injury (4242. Tang AH, Platt JL. Accommodation of grafts: implications for health and disease.
Hum Immunol. 2007;68(8):645-51, http://dx.doi.org/10.1016/j.humimm.2007.04.003.
http://dx.doi.org/10.1016/j.humimm.2007....
).
Chronic AMR is characterized by injury to the glomerular and tubular basement membrane. Capillary injury is considered the initiating event, as evidenced by an up-regulation of the endothelial antigen, PV1 (plasmalemmal vesicle associated protein 1) (4343. Yamamoto I, Horita S, Takahashi T, Tanabe K, Fuchinoue S, Teraoka S, et al. Glomerular expression of plasmalemmal vesicle-associated protein-1 in patients with transplant glomerulopathy. Am J Transplant. 2007;7(8):1954-60.). The glomerular lesion is termed “transplant glomerulopathy” and is characterized by thickened capillary loops and double contours. On electron microscopy, the glomerular basement membrane (GBM) shows reduplication and lamination. There are peritubular basement membrane multilayers with margination of mononuclear leukocytes. Ultimately, the peritubular capillaries are destroyed, resulting in tubular atrophy and interstitial fibrosis (4444. Sis B, Campbell PM, Mueller T, Hunter C, Cockfield SM, Cruz J, et al. Transplant glomerulopathy, late antibody-mediated rejection and the ABCD tetrad in kidney allograft biopsies for cause. Am J Transplant. 2007;7(7):1743-52.,4545. Cosio FG, Gloor JM, Sethi S, Stegall MD. Transplant glomerulopathy. Am J Transplant. 2008;8(3):492-6.).
Transplant glomerulopathy has been described as the “ABCD” tetrad: Anti-donor antibodies, capillary Basement membrane multilayering, C4d deposition, and GBM Duplication (4444. Sis B, Campbell PM, Mueller T, Hunter C, Cockfield SM, Cruz J, et al. Transplant glomerulopathy, late antibody-mediated rejection and the ABCD tetrad in kidney allograft biopsies for cause. Am J Transplant. 2007;7(7):1743-52.). C4d deposition may or may not be present in chronic AMR, and donor-specific antibody concentrations usually fluctuate.
Other than these findings, complement-independent mechanisms caused by antibodies with
specificities to MHC class II (expressed constitutively in the endothelial cells of capillaries in
human kidneys) or a mixture of class I and II anti-HLA antibodies are also associated with AMR
(4646. Denton MD, Davis SF, Baum MA, Melter M, Reinders ME, Exeni A, et al. The role of
the graft endothelium in transplant rejection: evidence that endothelial activation may serve as a
clinical marker for the development of chronic rejection. Pediatr Transplant. 2000;4(4):252-60,
http://dx.doi.org/10.1034/j.1399-3046.2000.00031.x.
http://dx.doi.org/10.1034/j.1399-3046.20...
,4747. Valenzuela NM, Reed EF. The link between major histocompatibility complex
antibodies and cell proliferation. Transplant Rev (Orlando). 2011;25(4):154-66,
http://dx.doi.org/10.1016/j.trre.2011.04.001.
http://dx.doi.org/10.1016/j.trre.2011.04...
). Platelet
activation upregulates MHC class I and II antigens on endothelial cells, which then release factors
that activate T-cells (4848. Morrell CN, Murata K, Swaim AM, Mason E, Martin TV, Thompson LE, et al. In vivo
platelet-endothelial cell interactions in response to major histocompatibility complex alloantibody.
Circ Res. 2008;102(7):777-85, http://dx.doi.org/10.1161/CIRCRESAHA.107.170332.
http://dx.doi.org/10.1161/CIRCRESAHA.107...
). Elevated endothelial- and
adhesion-molecule-associated gene transcripts and antibodies against the GBM are implicated in the
morphologic lesion of transplant glomerulopathy (4949. Joosten SA, Sijpkens YW, van Ham V, Trouw LA, van der Vlag J, van den Heuvel B,
et al. Antibody response against the glomerular basement membrane protein agrin in patients with
transplant glomerulopathy. Am J Transplant. 2005;5(2):383-93.,5050. Sis B, Jhangri GS, Bunnag S, Allanach K, Kaplan B, Halloran PF. Endothelial gene
expression in kidney transplants with alloantibody indicates antibody-mediated damage despite lack
of C4d staining. Am J Transplant. 2009;9(10):2312-23.).
Small animal models of cardiac transplantation are frequently used because of the ease of surgery
and vigor of rejection, although the concept of AMR is controversial in cardiac transplantation.
Animal models suggest that the lesions occur because of chronic endothelial cell injury, and
B-cell-deficient mice do not develop fibrous chronic allograft nephropathy (5151. Russell PS, Chase CM, Colvin RB. Alloantibody- and T cell-mediated immunity in
the pathogenesis of transplant arteriosclerosis: lack of progression to sclerotic lesions in B
cell-deficient mice. Transplantation. 1997;64(11):1531-6,
http://dx.doi.org/10.1097/00007890-199712150-00005.
http://dx.doi.org/10.1097/00007890-19971...
). However, these models are limited by antigenic differences between murine and
human organs (2929. Baldwin WM, 3rd, Valujskikh A, Fairchild RL. Antibody-mediated rejection:
emergence of animal models to answer clinical questions. Am J Transplant.
2010;10(5):1135-42.,5252. Minami K, Murata K, Lee CY, Fox-Talbot K, Wasowska BA, Pescovitz MD, et al. C4d
deposition and clearance in cardiac transplants correlates with alloantibody levels and rejection in
rats. Am J Transplant. 2006;6(5 Pt 1):923-32.).
ABO-Incompatible Renal Transplant
Historically, one of the main barriers to living kidney donation has been ABO incompatibility. In
Japan, because of the lack of deceased donors, ABO-incompatible donors have been used in kidney
transplantation, spurring the development of aggressive immunosuppressive protocols (5353. Takahashi K, Saito K, Takahara S, Okuyama A, Tanabe K, Toma H, et al. Excellent
long-term outcome of ABO-incompatible living donor kidney transplantation in Japan.
Am J Transplant. 2004;4(7):1089-96.). The three-year survival in ABO-incompatible transplants in
adults is similar to that of ABO-compatible kidney transplants. According to the 2010 report of the
North American Pediatric Renal Trials and Collaborative Studies, 0.6% of childhood transplants are
across ABO barriers (5454. NAPRTCS 2010 Annual Transplant Report. [cited 2012 October 10 ].
Available from: https://web.emmes.com/study/ped/annlrept/2010_Report.pdf.
https://web.emmes.com/study/ped/annlrept...
). The main problem with
ABO-incompatible transplants is the development of hemagglutinin antibodies to blood groups not
present in the recipient (5353. Takahashi K, Saito K, Takahara S, Okuyama A, Tanabe K, Toma H, et al. Excellent
long-term outcome of ABO-incompatible living donor kidney transplantation in Japan.
Am J Transplant. 2004;4(7):1089-96.,5555. Schaefer B, Tonshoff B, Schmidt J, Golriz M, Mehrabi A, Gombos P, et al.
Bleeding complications in pediatric ABO-incompatible kidney transplantation. Pediatr Nephrol.
2013;28(2):327-32, http://dx.doi.org/10.1007/s00467-012-2302-x
http://dx.doi.org/10.1007/s00467-012-230...
,5656. Shishido S, Asanuma H, Tajima E, Hoshinaga K, Ogawa O, Hasegawa A, et al.
ABO-incompatible living-donor kidney transplantation in children. Transplantation.
2001;72(6):1037-42, http://dx.doi.org/10.1097/00007890-200109270-00010.
http://dx.doi.org/10.1097/00007890-20010...
).
Decreasing hemagglutinin antibody titers, caused by B-cell depletion therapies before transplantation, has improved the short- and mid-term survival of children with kidney transplants (5353. Takahashi K, Saito K, Takahara S, Okuyama A, Tanabe K, Toma H, et al. Excellent long-term outcome of ABO-incompatible living donor kidney transplantation in Japan. Am J Transplant. 2004;4(7):1089-96.). Strategies to decrease these titers include treatment with rituximab, splenectomy, immunoadsorption of hemagglutinin antibodies, and intravenous immunoglobulin (IVIG) before transplant. However, acute rejection rates are higher than with ABO-compatible transplants, and long-term outcomes remain to be established (5757. Haas M, Rahman MH, Racusen LC, Kraus ES, Bagnasco SM, Segev DL, et al. C4d and C3d staining in biopsies of ABO- and HLA-incompatible renal allografts: correlation with histologic findings. Am J Transplant. 2006;6(8):1829-40.).
New Therapies for Antibody-Mediated Rejection
Sensitization to HLA antigens limits access to and the success of transplantation. Pre-transplant
desensitization protocols have made it possible to convert positive anti-HLA cross-matches to
negative, thus enabling transplantation in patients who otherwise could not have undergone
transplantation. These patients can be managed with desensitization before transplant and treatment
of AMR after transplant. Apheresis and IVIG-based protocols can convert a positive lymphocytotoxic
cross-match to a negative one before transplant. These protocols have led to higher transplantation
rates and improved short-term graft survival. Despite such protocols, however, many patients
continue to experience clinical and subclinical AMR after transplant (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
).
The protocols used for pre-transplant desensitization and post-transplant treatment of acute AMR are similar and are based on four concepts.
-
Eliminating or reducing circulating antibodies
-
Inhibiting residual antibodies
-
Suppressing or depleting B-cells
-
Suppressing T-cell response
Plasmapheresis can reduce the total IgG HLA antibodies. In one case series, some patients
required 15 to 30 sessions of plasmapheresis, alternating with IVIG, to substantially lower antibody
titers (5858. Montgomery RA, Zachary AA, Racusen LC, Leffell MS, King KE, Burdick J, et al.
Plasmapheresis and intravenous immune globulin provides effective rescue therapy for refractory
humoral rejection and allows kidneys to be successfully transplanted into cross-match-positive
recipients. Transplantation. 2000;70(6):887-95,
http://dx.doi.org/10.1097/00007890-200009270-00006.
http://dx.doi.org/10.1097/00007890-20000...
). However, these treatments also remove clotting
factors and require replacement with fresh frozen plasma and albumin. Anemia requiring packed red
cell transfusion, bleeding diathesis, allergic reactions, and blood-borne infections are some of the
complications associated with plasmapheresis. A Sepharose-bound staphylococcal protein A column with
a high affinity for binding IgG is used in immunoadsorption. This technique has higher specificity
compared with plasmapheresis and does not require replacing large volumes of plasma. Most columns
used in Europe and Japan are not approved by the FDA (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
).
However, anti-HLA antibodies may rebound to baseline or higher levels a few weeks after both
plasmapheresis and immunoadsorption.
Inhibiting Residual Antibodies
Intravenous immunoglobulin inhibits the immune resfoponse in several ways, including neutralizing
anti-HLA antibodies and inhibiting complement (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
). Various
protocols have been used to inhibit antibodies. Montgomery et al. used low-dose IVIG (100
mg/kg/day), alternating with plasmapheresis, as part of their desensitization and treatment protocol
(5858. Montgomery RA, Zachary AA, Racusen LC, Leffell MS, King KE, Burdick J, et al.
Plasmapheresis and intravenous immune globulin provides effective rescue therapy for refractory
humoral rejection and allows kidneys to be successfully transplanted into cross-match-positive
recipients. Transplantation. 2000;70(6):887-95,
http://dx.doi.org/10.1097/00007890-200009270-00006.
http://dx.doi.org/10.1097/00007890-20000...
). The University of Maryland protocol uses 6 sessions of
plasmapheresis, triple immune suppression, and low-dose IVIG after each plasmapheresis in living
kidney donors (5959. Schweitzer EJ, Wilson JS, Fernandez-Vina M, Fox M, Gutierrez M, Wiland A, et al.
A high panel-reactive antibody rescue protocol for cross-match-positive live donor kidney
transplants. Transplantation. 2000;70(10):1531-6,
http://dx.doi.org/10.1097/00007890-200011270-00023.
http://dx.doi.org/10.1097/00007890-20001...
).
Jordan et al. initially used high-dose IVIG at 2 g/kg/month until cross-matching was negative
(6060. Tyan DB, Li VA, Czer L, Trento A, Jordan SC. Intravenous immunoglobulin
suppression of HLA alloantibody in highly sensitized transplant candidates and transplantation with
a histoincompatible organ. Transplantation. 1994;57(4):553-62.,6161. Jordan SC, Vo AA, Toyoda M, Tyan D, Nast CC. Post-transplant therapy with
high-dose intravenous gammaglobulin: Applications to treatment of antibody-mediated rejection.
Pediatr Transplant. 2005; 9(2):155-61,
http://dx.doi.org/10.1111/j.1399-3046.2005.00256.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
). However, they
subsequently modified the protocol to 2 doses of IVIG and 1 dose of rituximab (6262. Vo AA, Lukovsky M, Toyoda M, Wang J, Reinsmoen NL, Lai CH, et al. Rituximab and
intravenous immune globulin for desensitization during renal transplantation.
N Engl J Med. 2008;359(3):242-51.). The advantage of this method is its applicability to patients on the deceased
donor list. A report of the use of high-dose IVIG in 2 highly sensitized patients showed both to be
rejection-free with excellent renal function at 15 and 19 months, respectively (2525. Valentini RP, Nehlsen-Cannarella SL, Gruber SA, Mattoo TK, West MS, Lang C, et
al. Intravenous immunoglobulin, HLA allele typing and HLAMatchmaker facilitate successful
transplantation in highly sensitized pediatric renal allograft recipients. Pediatr Transplant.
2007;11(1):77-81, http://dx.doi.org/10.1111/j.1399-3046.2006.00617.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
).
Despite these desensitization protocols, the incidence of AMR remains high in the first year after transplant because these protocols have no effect on memory B-cells.
Suppressing or Depleting B-cells
Rituximab is a chimeric humanized monoclonal antibody against the cell surface marker, CD20,
which is expressed in pre-B and mature B-cells. Rituximab destroys CD20-positive cells in several
ways, including antibody-dependent cell-mediated cytotoxicity, complement-mediated cytotoxicity, and
apoptosis. Rituximab is generally combined with plasmapheresis, IVIG, or both because it is not
effective against antibody-producing plasma cells if used alone (1313. Mauiyyedi S, Colvin RB. Humoral rejection in kidney transplantation: new
concepts in diagnosis and treatment. Curr Opin Nephrol Hypertens. 2002;11(6)609-18,
http://dx.doi.org/10.1097/00041552-200211000-00007.
http://dx.doi.org/10.1097/00041552-20021...
,1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
,1818. Fehr T, Gaspert A. Antibody-mediated kidney allograft rejection: therapeutic
options and their experimental rationale. Transpl Int. 2012;25(6):623-32,
http://dx.doi.org/10.1111/j.1432-2277.2012.01453.x.
http://dx.doi.org/10.1111/j.1432-2277.20...
,2121. Colvin RB. Antibody-mediated renal allograft rejection: diagnosis and
pathogenesis. J Am Soc Nephrol. 2007;18(4):1046-56,
http://dx.doi.org/10.1681/ASN.2007010073.
http://dx.doi.org/10.1681/ASN.2007010073...
). The response to rituximab in chronic
antibody-mediated-rejection is variable, and there is currently no way to distinguish responders
from nonresponders (6363. Smith RN, Malik F, Goes N, Farris AB, Zorn E, Saidman S, et al. Partial
therapeutic response to Rituximab for the treatment of chronic alloantibody mediated rejection of
kidney allografts. Transpl Immunol. 2012;27(2-3):107-13,
http://dx.doi.org/10.1016/j.trim.2012.08.005.
http://dx.doi.org/10.1016/j.trim.2012.08...
). Infectious complications can
increase when rituximab is used with other powerful immunosuppressive agents, such as anti-thymocyte
globulin.
Splenectomy immediately reduces the B-cell and plasma cell pool and has been used as a last
resort for salvaging transplanted kidneys (6464. Tzvetanov I, Spaggiari M, Jeon H, Roca RG, Bhati C, Oberholzer J, et al. The
role of splenectomy in the setting of refractory humoral rejection after kidney transplantation.
Transplant Proc. 2012;44(5):1254-8,
http://dx.doi.org/10.1016/j.transproceed.2012.01.109.
http://dx.doi.org/10.1016/j.transproceed...
,6565. Roberti I, Geffner S, Vyas S. Successful rescue of refractory acute
antibody-mediated renal allograft rejection with splenectomy--a case report. Pediatr Transplant.
2012;16(2):E49-52, http://dx.doi.org/10.1111/j.1399-3046.2011.01518.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
). It has also been used in highly sensitized patients in whom
desensitization therapy has failed.
Other Therapies
Bortezomib, a proteosome inhibitor, is effective against antibody-producing plasma cells that
induce apoptosis and has been successfully used with plasmapheresis and rituximab to treat children
undergoing heart transplant (6666. Morrow WR, Frazier EA, Mahle WT, Harville TO, Pye SE, Knecht KR, et al. Rapid
reduction in donor-specific anti-human leukocyte antigen antibodies and reversal of
antibody-mediated rejection with bortezomib in pediatric heart transplant patients. Transplantation.
2012;93(3):319-24, http://dx.doi.org/10.1097/TP.0b013e31823f7eea.
http://dx.doi.org/10.1097/TP.0b013e31823...
). Plasmapheresis removes only
some of the alloantibodies, and re-equilibration with extra vascular antibodies occurs in 48 to 72
hours. Rituximab blocks CD20-positive cells, and plasma cells do not express this marker. Therefore,
bortezomib is useful in blocking anti-HLA antibody production. However, bortezomib alone may not be
sufficient to reduce anti-HLA antibody levels because it requires activated plasma cells, such as
those present in acute AMR (6767. Guthoff M, Schmid-Horch B, Weisel KC, Haring HU, Konigsrainer A, Heyne N.
Proteasome inhibition by bortezomib: effect on HLA-antibody levels and specificity in sensitized
patients awaiting renal allograft transplantation. Transpl Immunol. 2012;26(4):171-5,
http://dx.doi.org/10.1016/j.trim.2012.01.002.
http://dx.doi.org/10.1016/j.trim.2012.01...
). Moreover, it may not
sufficiently target memory B-cells.
Eculizumab is an anti-complement C5 humanized mouse monoclonal antibody that prevents the
formation of the membrane attack complex. It is based on evidence that activation of the terminal
component of complement is necessary for the development of acute antibody-mediated rejection. It
has been used as a rescue therapy in patients not responding to other treatments for AMR (6868. Locke JE, Magro CM, Singer AL, Segev DL, Haas M, Hillel AT, et al. The use of
antibody to complement protein C5 for salvage treatment of severe antibody-mediated rejection.
Am J Transplant. 2009;9(1):231-5.,6969. Stegall MD, Diwan T, Raghavaiah S, Cornell LD, Burns J, Dean PG, et al. Terminal
complement inhibition decreases antibody-mediated rejection in sensitized renal transplant
recipients. Am J Transplant. 2011;11(11):2405-13.). Infectious
complications, such as polyoma virus type BK nephritis, have been reported after its use. Stegall et
al. reported decreased rates of acute and chronic AMR after treatment with eculizumab (6969. Stegall MD, Diwan T, Raghavaiah S, Cornell LD, Burns J, Dean PG, et al. Terminal
complement inhibition decreases antibody-mediated rejection in sensitized renal transplant
recipients. Am J Transplant. 2011;11(11):2405-13.). Eculizumab does not affect DSA or C4d deposition, but it does
decrease tissue injury and graft dysfunction (7070. Stegall MD, Chedid MF, Cornell LD. The role of complement in antibody-mediated
rejection in kidney transplantation. Nat Rev Nephrol. 2012;8(11):670-8,
http://dx.doi.org/10.1038/nrneph.2012.212.
http://dx.doi.org/10.1038/nrneph.2012.21...
). Experience
with this drug is currently limited.
C1 inhibitor therapy may eventually be an option for treating refractory AMR. Its use is based on
the theory that C1q-binding DSAs harm the allograft (7171. Tillou X, Poirier N, Le Bas-Bernardet S, Hervouet J, Minault D, Renaudin K, et
al. Recombinant human C1-inhibitor prevents acute antibody-mediated rejection in alloimmunized
baboons. Kidney Int. 2010;78(2):152-9, http://dx.doi.org/10.1038/ki.2010.75.
http://dx.doi.org/10.1038/ki.2010.75...
).
Secondary Immunodeficiency
While several reports have concluded that immunomodulatory therapies, such as IVIG-rituximab
desensitization, do not significantly hinder cell-mediated or humoral immunity (7272. Ge S, Pao A, Vo A, Deer N, Karasyov A, Petrosyan A, et al. Immunologic
parameters and viral infections in patients desensitized with intravenous immunoglobulin and
rituximab. Transpl Immunol. 2011;24(3):142-8,
http://dx.doi.org/10.1016/j.trim.2010.11.006.
http://dx.doi.org/10.1016/j.trim.2010.11...
,7373. Kahwaji J, Sinha A, Toyoda M, Ge S, Reinsmoen N, Cao K, et al. Infectious
complications in kidney-transplant recipients desensitized with rituximab and intravenous
immunoglobulin. Clin J Am Soc Nephrol. 2011;6(12):2894-900,
http://dx.doi.org/10.2215/CJN.03710411.
http://dx.doi.org/10.2215/CJN.03710411...
), the potential
immunologic consequences of these and newer therapies used in desensitization or “antibody
reduction therapies” (7474. Jordan SC, Toyoda M, Kahwaji J, Vo AA. Clinical aspects of intravenous
immunoglobulin use in solid organ transplant recipients. Am J Transplant.
2011;11(2):196-202.) should not be overlooked,
especially with long-term immunosuppression. Secondary immunodeficiency can be clinically
significant, and it presents with recurrent fungal, bacterial, or viral infections, usually of the
respiratory tract; however, it may include gastrointestinal infections and increased autoimmune
complications, depending on the extent of the immune suppression. Infections, including CMV, BK
virus, and parvovirus B19, have been treated with IVIG in the post-transplant setting (7474. Jordan SC, Toyoda M, Kahwaji J, Vo AA. Clinical aspects of intravenous
immunoglobulin use in solid organ transplant recipients. Am J Transplant.
2011;11(2):196-202.). The role of IVIG is both immunomodulatory at high doses and
immune replacing at lower doses and may be required in the case of secondary hypogammaglobulinemia.
Immune replacement with IVIG or subcutaneous immunoglobulin plays an important role in the
post-transplant period for patients with recurrent infection because of secondary immunodeficiency.
A consultation with an immunologist to coordinate replacement therapy may be an important part of
the multidisciplinary approach. With regard to IVIG protocols to prepare “sensitized”
patients for transplant, a consensus approach does not yet exist. However, IVIG has certainly become
a keystone of many empirically derived protocols, and a recent review of IVIG use in solid organ
transplantation endorsed its use in high-risk groups (7575. Shehata N, Palda VA, Meyer RM, Blydt-Hansen TD, Campbell P, Cardella C, et al.
The use of immunoglobulin therapy for patients undergoing solid organ transplantation: an
evidence-based practice guideline. Transfus Med Rev. 2010;24 Suppl 1:S7-S27,
http://dx.doi.org/10.1016/j.tmrv.2009.09.010.
http://dx.doi.org/10.1016/j.tmrv.2009.09...
). An
earlier review published in the US also recognized the use of IVIG in solid organ transplantation
but cautioned that further studies are necessary to optimize use for this indication (7676. Orange JS, Hossny EM, Weiler CR, Ballow M, Berger M, Bonilla FA, et al. Use of
intravenous immunoglobulin in human disease: a review of evidence by members of the Primary
Immunodeficiency Committee of the American Academy of Allergy, Asthma and Immunology. J Allergy
Clin Immunol. 2006;117(4 Suppl):S525-53,
http://dx.doi.org/10.1016/j.jaci.2006.01.015.
http://dx.doi.org/10.1016/j.jaci.2006.01...
).
General Approach to Treating Acute Antibody-Mediated Rejection
Data from children treated with AMR are scarce (1919. Billing H, Rieger S, Susal C, Waldherr R, Opelz G, Wuhl E, et al. IVIG and
rituximab for treatment of chronic antibody-mediated rejection: a prospective study in paediatric
renal transplantation with a 2-year follow-up. Transpl Int. 2012;25(11):1165-73,
http://dx.doi.org/10.1111/j.1432-2277.2012.01544.x.
http://dx.doi.org/10.1111/j.1432-2277.20...
,7777. Zarkhin V, Li L, Kambham N, Sigdel T, Salvatierra O, Sarwal MM. A randomized,
prospective trial of rituximab for acute rejection in pediatric renal transplantation.
Am J Transplant. 2008;8(12):2607-17.,7878. Kranz B, Kelsch R, Kuwertz-Broking E, Brocker V, Wolters HH, Konrad M. Acute
antibody-mediated rejection in paediatric renal transplant recipients. Pediatr Nephrol.
2011;26(7):1149-56, http://dx.doi.org/10.1007/s00467-011-1864-3.
http://dx.doi.org/10.1007/s00467-011-186...
). In highly sensitized
patients, graft survival is better after desensitization and transplantation. The KDIGO (Kidney
disease: improving global outcomes) guidelines (strength of evidence 2C) suggest treating acute AMR
with some combination of plasma exchange, IVIG, and anti-CD20 antibody, with or without
corticosteroids (7979. KDIGO clinical practice guideline for the care of kidney transplant recipients.
Am J Transplant. 2009;9 Suppl 3:S1-155.). Depending on the clinical response, a
tiered approach to management has been suggested by various authors (Figure 2).
Schematic diagram depicting a suggested algorithm for the management of acute antibody-mediated rejection. T cell-mediated and antibody-mediated rejection can often coexist, and treatment may need to address both. Surveillance for viral infections should be intensified, and the use of anti-viral and antibiotic prophylaxis is important during treatment. The benefits of escalating treatment should be weighed against the risk of infection and malignancy.
During treatment, antibody strength is monitored using an SPA. Threshold values for antibody
levels depend on technical and immunosuppression protocols and are established by individual
transplant centers (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
15. van den Berg-Loonen EM, Billen EV, Voorter CE, van Heurn LW, Claas FH, van Hooff
JP, et al. Clinical relevance of pretransplant donor-directed antibodies detected by single antigen
beads in highly sensitized renal transplant patients. Transplantation. 2008;85(8):1086-90,
http://dx.doi.org/10.1097/TP.0b013e31816b3ed1.
http://dx.doi.org/10.1097/TP.0b013e31816...
16. Reinsmoen NL, Lai CH, Vo A, Cao K, Ong G, Naim M, et al. Acceptable
donor-specific antibody levels allowing for successful deceased and living donor kidney
transplantation after desensitization therapy. Transplantation. 2008;86(6):820-5,
http://dx.doi.org/10.1097/TP.0b013e3181856f98.
http://dx.doi.org/10.1097/TP.0b013e31818...
-1717. Riethmuller S, Ferrari-Lacraz S, Muller MK, Raptis DA, Hadaya K, Rusi B, et al.
Donor-specific antibody levels and three generations of crossmatches to predict antibody-mediated
rejection in kidney transplantation. Transplantation. 2010;90(2):160-7,
http://dx.doi.org/10.1097/TP.0b013e3181e36e08.
http://dx.doi.org/10.1097/TP.0b013e3181e...
). Antibody strength is measured by Luminex and is expressed as the mean fluorescence
intensity or molecules of equivalent soluble fluorochrome. Antibody strengths are expressed as
medium channel shifts in flow cytometry. In acute AMR, the mean fluorescence intensity values were
greater than 5200 in most patients (1414. Marfo K, Lu A, Ling M, Akalin E. Desensitization protocols and their outcome.
Clin J Am Soc Nephrol. 2011;6(4):922-36,
http://dx.doi.org/10.2215/CJN.08140910.
http://dx.doi.org/10.2215/CJN.08140910...
,1717. Riethmuller S, Ferrari-Lacraz S, Muller MK, Raptis DA, Hadaya K, Rusi B, et al.
Donor-specific antibody levels and three generations of crossmatches to predict antibody-mediated
rejection in kidney transplantation. Transplantation. 2010;90(2):160-7,
http://dx.doi.org/10.1097/TP.0b013e3181e36e08.
http://dx.doi.org/10.1097/TP.0b013e3181e...
). Treatment is aimed at lowering the strength of the antibody.
Treating chronic AMR is difficult, and the optimal approach has yet to be identified because of
its indolent course. High-dose IVIG and rituximab given to children with chronic AMR slowed the rate
of decline in renal function in a single-center study (1919. Billing H, Rieger S, Susal C, Waldherr R, Opelz G, Wuhl E, et al. IVIG and
rituximab for treatment of chronic antibody-mediated rejection: a prospective study in paediatric
renal transplantation with a 2-year follow-up. Transpl Int. 2012;25(11):1165-73,
http://dx.doi.org/10.1111/j.1432-2277.2012.01544.x.
http://dx.doi.org/10.1111/j.1432-2277.20...
).
Other Pre-emptive Measures
Paired organ sharing, such as kidney-paired donation, is a viable option when two donor-recipient
pairs are blood type or cross-match incompatible with their intended recipients. The exchange of
donor kidneys allows each donor to donate a kidney and each recipient to receive a compatible
transplant. If this exchange works for specific donor-recipient pairs, less-intense immune
suppression and better graft outcomes are expected (8080. Segev DL, Kucirka LM, Gentry SE, Montgomery RA. Utilization and outcomes of
kidney paired donation in the United States. Transplantation. 2008;86(4):502-10,
http://dx.doi.org/10.1097/TP.0b013e3181812f85.
http://dx.doi.org/10.1097/TP.0b013e31818...
).
Combined liver-kidney transplantation with a liver allograft decreases rejection rates and promotes rejection-free survival of the transplanted organs, even if the cross-match is positive before surgery (8181. Flye MW, Duffy BF, Phelan DL, Ratner LE, Mohanakumar T. Protective effects of liver transplantation on a simultaneously transplanted kidney in a highly sensitized patient. Transplantation. 1990;50(6):1051-4.). Combined organ transplantation has been extended to include partial auxiliary liver transplantation to make kidney transplantation possible (8282. Olausson M, Mjornstedt L, Norden G, Rydberg L, Molne J, Backman L, et al. Successful combined partial auxiliary liver and kidney transplantation in highly sensitized cross-match positive recipients. Am J Transplant. 2007;7(1):130-6.). However, AMR has been reported in the renal allograft in highly sensitized patients (8383. Reichman TW, Marino SR, Milner J, Harland RC, Cochrane A, Millis JM, et al. Acute humoral rejection in an ABO compatible combined liver-kidney transplant--the kidney is not always protected. Am J Transplant. 2009;9(8):1957-60.).
Summary and Future Translational Research Directions in Kidney Transplantation
Advances in molecular technology have increased our knowledge and ability to manage sensitized
individuals and to recognize AMR. These advances have prompted the evolution of various protocols to
preemptively manage the sensitized patient and have given us several options for treating acute AMR.
However, the persistence of memory cells is a substantial barrier to management. We need to better
understand graft accommodation and therapies that will increase tolerance to the graft. Appropriate
management of acute AMR and the sensitized patient may slow the development of chronic AMR.
Reprogrammed pluripotent stem cells may also have enormous therapeutic potential (8484. Song B, Niclis JC, Alikhan MA, Sakkal S, Sylvain A, Kerr PG, et al. Generation
of induced pluripotent stem cells from human kidney mesangial cells. J Am Soc Nephrol.
2011;22:1213-20, http://dx.doi.org/10.1681/ASN.2010101022.
http://dx.doi.org/10.1681/ASN.2010101022...
). Because endothelial injury is a prominent feature of AMR,
drugs like mycophenolate mofetil, angiotensin-converting enzyme inhibitors, statins, and aspirin
could potentially modulate endothelial cell function (8585. Nickel T, Schlichting CL, Weis M. Drugs modulating endothelial function after
transplantation. Transplantation. 2006;82:S41-6,
http://dx.doi.org/10.1097/01.tp.0000231505.91988.26.
http://dx.doi.org/10.1097/01.tp.00002315...
). We
also need to develop more sensitive, specific, and noninvasive biomarkers of the onset of AMR.
Bench to Bedside in Recurrent FSGS
The role of translational science in bridging the gap between “bench and bedside”
is best demonstrated by the progress in unraveling the mechanisms of recurrent disease in renal
transplantation. Perhaps the most ominous mechanism has been recurrent FSGS, a non-immune
podocytopathy that is characterized by nephrotic-range proteinuria and variable progression to
end-stage renal disease. Approximately 10% of children undergoing renal transplantation have FSGS as
the primary diagnosis (8686. Fine RN. Recurrence of nephrotic syndrome/focal segmental glomerulosclerosis
following renal transplantation in children. Pediatr Nephrol. 2007;22(7):496-502,
http://dx.doi.org/10.1007/s00467-006-0361-6.
http://dx.doi.org/10.1007/s00467-006-036...
,8787. NAPRTCS 2011 Annual Report. [cited 2012 October 19]. Available from:
https://web.emmes.com/study/ped/annlrept/2010_Report.pdf.
https://web.emmes.com/study/ped/annlrept...
). Since FSGS was first recognized in 1972, the incidence in various ethnic populations
has remained approximately 30% (range, 20% to 67%) (8686. Fine RN. Recurrence of nephrotic syndrome/focal segmental glomerulosclerosis
following renal transplantation in children. Pediatr Nephrol. 2007;22(7):496-502,
http://dx.doi.org/10.1007/s00467-006-0361-6.
http://dx.doi.org/10.1007/s00467-006-036...
,8888. Hoyer JR, Vernier RL, Najarian JS, Raij L, Simmons RL, Michael AF. Recurrence of
idiopathic nephrotic syndrome after renal transplantation. Lancet. 1972;2(7773):343-8,
http://dx.doi.org/10.1016/S0140-6736(72)91734-5.
http://dx.doi.org/10.1016/S0140-6736(72)...
,8989. Baum MA, Stablein DM, Panzarino VM, Tejani A, Harmon WE, Alexander SR. Loss of
living donor renal allograft survival advantage in children with focal segmental glomerulosclerosis.
Kidney Int. 2001;59(1):328-33, http://dx.doi.org/10.1046/j.1523-1755.2001.00494.x.
http://dx.doi.org/10.1046/j.1523-1755.20...
). Although
“late” recurrence may occur years after transplantation, the most frequent and marked
recurrence of FSGS is with massive proteinuria when the graft is reperfused at the time of surgery.
If remission cannot be achieved by medical intervention, the rate of graft loss increases to more
than 50% within the first year (9090. Ponticelli C, Glassock RJ. Posttransplant recurrence of primary
glomerulonephritis. Clin J Am Soc Nephrol. 2010;5(12):2363-72,
http://dx.doi.org/10.2215/CJN.06720810.
http://dx.doi.org/10.2215/CJN.06720810...
).
Early speculation that a “circulating permeability factor” (cPF) caused recurrent
FSGS (R-FSGS) led to plasmapheresis as a primary treatment with mixed success (9191. Artero ML, Sharma R, Savin VJ, Vincenti F. Plasmapheresis reduces proteinuria
and serum capacity to injure glomeruli in patients with recurrent focal glomerulosclerosis.
Am J Kidney Dis. 1994;23(4):574-81.
92. Savin VJ, Sharma R, Sharma M, McCarthy ET, Swan SK, Ellis E, et al. Circulating
factor associated with increased glomerular permeability to albumin in recurrent focal segmental
glomerulosclerosis. N Engl J Med. 1996;334(14):878-83.-9393. Hubsch H, Montane B, Abitbol C, Chandar J, Shariatmadar S, Ciancio G, et al.
Recurrent focal glomerulosclerosis in pediatric renal allografts: the Miami experience. Pediatr
Nephrol. 2005;20(2):210-6, http://dx.doi.org/10.1007/s00467-004-1706-7.
http://dx.doi.org/10.1007/s00467-004-170...
). Plasmapheresis continues to be a
component of both pre-emptive and maintenance treatment for R-FSGS and has led to the quest to
identify circulating factors as new targets for more effective treatments (9292. Savin VJ, Sharma R, Sharma M, McCarthy ET, Swan SK, Ellis E, et al. Circulating
factor associated with increased glomerular permeability to albumin in recurrent focal segmental
glomerulosclerosis. N Engl J Med. 1996;334(14):878-83.
93. Hubsch H, Montane B, Abitbol C, Chandar J, Shariatmadar S, Ciancio G, et al.
Recurrent focal glomerulosclerosis in pediatric renal allografts: the Miami experience. Pediatr
Nephrol. 2005;20(2):210-6, http://dx.doi.org/10.1007/s00467-004-1706-7.
http://dx.doi.org/10.1007/s00467-004-170...
94. Gonzalez E, Ettenger R, Rianthavorn P, Tsai E, Malekzadeh M. Preemptive
plasmapheresis and recurrence of focal segmental glomerulosclerosis in pediatric renal
transplantation. Pediatr Transplant. 2011;15(5):495-501,
http://dx.doi.org/10.1111/j.1399-3046.2011.01478.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
-9595. Ohta T, Kawaguchi H, Hattori M, Komatsu Y, Akioka Y, Nagata M, et al. Effect of
pre-and postoperative plasmapheresis on posttransplant recurrence of focal segmental
glomerulosclerosis in children. Transplantation. 2001;71(5):628-33,
http://dx.doi.org/10.1097/00007890-200103150-00008.
http://dx.doi.org/10.1097/00007890-20010...
).
Efforts to identify cPF(s) have been arduous and have involved the complex collaboration of basic
and clinical physician scientists (9696. McCarthy ET, Sharma M, Savin VJ. Circulating permeability factors in idiopathic
nephrotic syndrome and focal segmental glomerulosclerosis. Clin J Am Soc Nephrol.
2010;5(11):2115-21, http://dx.doi.org/10.2215/CJN.03800609.
http://dx.doi.org/10.2215/CJN.03800609...
,9797. D'Agati VD, Kaskel FJ, Falk RJ. Focal segmental glomerulosclerosis.
N Engl J Med. 2011;365(25):2398-411.). Evidence for circulating factor(s) include:
-
The immediate recurrence of proteinuria when the graft is reperfused (9797. D'Agati VD, Kaskel FJ, Falk RJ. Focal segmental glomerulosclerosis. N Engl J Med. 2011;365(25):2398-411.,9898. Vinai M, Waber P, Seikaly MG. Recurrence of focal segmental glomerulosclerosis in renal allograft: an in-depth review. Pediatr Transplant. 2010;14(3):314-25, http://dx.doi.org/10.1111/j.1399-3046.2009.01261.x.
http://dx.doi.org/10.1111/j.1399-3046.20... ). -
The improvement in proteinuria when the presumed cPF is removed with plasmapheresis or immunoadsorption (9999. Deegens JK, Andresdottir MB, Croockewit S, Wetzels JF. Plasma exchange improves graft survival in patients with recurrent focal glomerulosclerosis after renal transplant. Transpl Int. 2004;17(3):151-7, http://dx.doi.org/10.1111/j.1432-2277.2004.tb00420.x.
http://dx.doi.org/10.1111/j.1432-2277.20... ,100100. Dantal J, Bigot E, Bogers W, Testa A, Kriaa F, Jacques Y, et al. Effect of plasma protein adsorption on protein excretion in kidney-transplant recipients with recurrent nephrotic syndrome. N Engl J Med. 1994;330(1):7-14.). -
The regression of FSGS when a kidney with recurrent FSGS is re-transplanted into a patient without FSGS (101101. Gallon L, Leventhal J, Skaro A, Kanwar Y, Alvarado A. Resolution of recurrent focal segmental glomerulosclerosis after retransplantation. N Engl J Med. 2012;366(17):1648-9.).
-
The induction of proteinuria in animals injected with a patient's sera or with specific cPF (102102. Sharma M, Sharma R, Reddy SR, McCarthy ET, Savin VJ. Proteinuria after injection of human focal segmental glomerulosclerosis factor. Transplantation. 2002;73(3):366-72, http://dx.doi.org/10.1097/00007890-200202150-00009.
http://dx.doi.org/10.1097/00007890-20020...
103. Zimmerman SW. Increased urinary protein excretion in the rat produced by serum from a patient with recurrent focal glomerular sclerosis after renal transplantation. Clin Nephrol. 1984;22(1):32-8.-104104. Avila-Casado Mdel C, Perez-Torres I, Auron A, Soto V, Fortoul TI, Herrera-Acosta J. Proteinuria in rats induced by serum from patients with collapsing glomerulopathy. Kidney Int. 2004;66(1):133-43, http://dx.doi.org/10.1111/j.1523-1755.2004.00715.x.
http://dx.doi.org/10.1111/j.1523-1755.20... ). -
The destruction of the podocyte foot process observed in transplanted kidneys biopsied within 1 to 2 hours after reperfusion in patients with recurrent proteinuria (105105. Chang JW, Pardo V, Sageshima J, Chen L, Tsai HL, Reiser J, et al. Podocyte Foot Process Effacement in Postreperfusion Allograft Biopsies Correlates With Early Recurrence of Proteinuria in Focal Segmental Glomerulosclerosis. Transplantation. 2012;93(12):1238-44, http://dx.doi.org/10.1097/TP.0b013e318250234a.
http://dx.doi.org/10.1097/TP.0b013e31825... ). -
The disruption of the actin cytoskeleton in normal human podocytes exposed to sera from patients with R-FSGS or to currently suspected cPFs (106106. Wei C, Moller CC, Altintas MM, Li J, Schwarz K, Zacchigna S, et al. Modification of kidney barrier function by the urokinase receptor. Nat Med. 2008;14(1):55-63, http://dx.doi.org/10.1038/nm1696.
http://dx.doi.org/10.1038/nm1696... ,107107. Wei C, El Hindi S, Li J, Fornoni A, Goes N, Sageshima J, et al. Circulating urokinase receptor as a cause of focal segmental glomerulosclerosis. Nat Med. 2011;17(8):952-60, http://dx.doi.org/10.1038/nm.2411.
http://dx.doi.org/10.1038/nm.2411... ).
Savin et al. pioneered the development of an assay to identify the character and function of the
cPF by studying the sera from patients with R-FSGS (9696. McCarthy ET, Sharma M, Savin VJ. Circulating permeability factors in idiopathic
nephrotic syndrome and focal segmental glomerulosclerosis. Clin J Am Soc Nephrol.
2010;5(11):2115-21, http://dx.doi.org/10.2215/CJN.03800609.
http://dx.doi.org/10.2215/CJN.03800609...
). They
developed an in vitro biological assay of glomerular permeability (9191. Artero ML, Sharma R, Savin VJ, Vincenti F. Plasmapheresis reduces proteinuria
and serum capacity to injure glomeruli in patients with recurrent focal glomerulosclerosis.
Am J Kidney Dis. 1994;23(4):574-81.,9292. Savin VJ, Sharma R, Sharma M, McCarthy ET, Swan SK, Ellis E, et al. Circulating
factor associated with increased glomerular permeability to albumin in recurrent focal segmental
glomerulosclerosis. N Engl J Med. 1996;334(14):878-83.,9696. McCarthy ET, Sharma M, Savin VJ. Circulating permeability factors in idiopathic
nephrotic syndrome and focal segmental glomerulosclerosis. Clin J Am Soc Nephrol.
2010;5(11):2115-21, http://dx.doi.org/10.2215/CJN.03800609.
http://dx.doi.org/10.2215/CJN.03800609...
). Isolated rat glomeruli are incubated with a patient's serum, plasma, or
plasma fraction. The permeability of albumin to the glomerular membrane is determined and expressed
as the “albumin permeability index” (Palb), which ranges from zero in
normal control serum to 1.0 for maximal induced injury. A Palb greater than 0.5 indicates
marked injury to the glomerular protein barrier and is not specific to FSGS (9292. Savin VJ, Sharma R, Sharma M, McCarthy ET, Swan SK, Ellis E, et al. Circulating
factor associated with increased glomerular permeability to albumin in recurrent focal segmental
glomerulosclerosis. N Engl J Med. 1996;334(14):878-83.). For example, circulating cytokines and inflammatory markers, such as
TNFα and β-1-integrin, may also generate a Palb greater than 0.5. In patients
at high risk for recurrence and in those with rapid progression to end-stage renal disease, a
Palb greater than 0.5 has been highly predictive of outcomes (9292. Savin VJ, Sharma R, Sharma M, McCarthy ET, Swan SK, Ellis E, et al. Circulating
factor associated with increased glomerular permeability to albumin in recurrent focal segmental
glomerulosclerosis. N Engl J Med. 1996;334(14):878-83.,9696. McCarthy ET, Sharma M, Savin VJ. Circulating permeability factors in idiopathic
nephrotic syndrome and focal segmental glomerulosclerosis. Clin J Am Soc Nephrol.
2010;5(11):2115-21, http://dx.doi.org/10.2215/CJN.03800609.
http://dx.doi.org/10.2215/CJN.03800609...
). The cPF was further characterized by
concentrating patient samples and applying protein isolation and fractionation techniques to obtain
a molecular weight between 30 and 50 kD (108108. Sharma M, Sharma R, McCarthy ET, Savin VJ. "The FSGS factor:" enrichment and in
vivo effect of activity from focal segmental glomerulosclerosis plasma. J Am Soc Nephrol.
1999;10(3):552-61.). More
recently, the Savin group has identified cardiotrophin-like cytokine-1 (CLC-1) as a potential
candidate cPF protein, but further studies are required (109109. Sharma R, Sharma M, McCarthy ET, Ge XL, Savin VJ. Components of normal serum
block the focal segmental glomerulosclerosis factor activity in vitro. Kidney Int.
2000;58(5):1973-9, http://dx.doi.org/10.1111/j.1523-1755.2000.00369.x.
http://dx.doi.org/10.1111/j.1523-1755.20...
).
A parallel effort using research in molecular biology, genetics, and clinically applicable
mechanistic studies has been directed to understand the pathophysiology of proteinuria and is
grounded in the work of Mundel and of Reiser and colleagues (106106. Wei C, Moller CC, Altintas MM, Li J, Schwarz K, Zacchigna S, et al.
Modification of kidney barrier function by the urokinase receptor. Nat Med. 2008;14(1):55-63,
http://dx.doi.org/10.1038/nm1696.
http://dx.doi.org/10.1038/nm1696...
,107107. Wei C, El Hindi S, Li J, Fornoni A, Goes N, Sageshima J, et al. Circulating
urokinase receptor as a cause of focal segmental glomerulosclerosis. Nat Med. 2011;17(8):952-60,
http://dx.doi.org/10.1038/nm.2411.
http://dx.doi.org/10.1038/nm.2411...
,110110. Reiser J, von Gersdorff G, Loos M, Oh J, Asanuma K, Giardino L, et al.
Induction of B7-1 in podocytes is associated with nephrotic syndrome. J Clin Invest.
2004;113(10):1390-7.,111111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
). Much of this research has taken place at
the University of Miami Transplant Institute during the past decade and has led to an intense global
collaboration with physician scientists caring for patients with both primary and recurrent FSGS
(110110. Reiser J, von Gersdorff G, Loos M, Oh J, Asanuma K, Giardino L, et al.
Induction of B7-1 in podocytes is associated with nephrotic syndrome. J Clin Invest.
2004;113(10):1390-7.
111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
112. Faul C, Donnelly M, Merscher-Gomez S, Chang YH, Franz S, Delfgaauw J, et al.
The actin cytoskeleton of kidney podocytes is a direct target of the antiproteinuric effect of
cyclosporine A. Nat Med. 2008;14(9):931-8, http://dx.doi.org/10.1038/nm.1857.
http://dx.doi.org/10.1038/nm.1857...
113. Zhang B, Shi W, Ma J, Sloan A, Faul C, Wei C, et al. The calcineurin-NFAT
pathway allows for urokinase receptor-mediated beta3 integrin signaling to cause podocyte injury.
J Mol Med (Berl). 2012;90(12):1407-20,
http://dx.doi.org/10.1007/s00109-012-0960-6.
http://dx.doi.org/10.1007/s00109-012-096...
114. Trachtman H, Gipson DS, Kaskel F, Ghiggeri GM, Faul C, Gupta V, et al.
Regarding Maas's editorial letter on serum suPAR levels. Kidney Int. 2012;82(4):492,
http://dx.doi.org/10.1038/ki.2012.230.
http://dx.doi.org/10.1038/ki.2012.230...
-115115. Fornoni A, Sageshima J, Wei C, Merscher-Gomez S, Aguillon-Prada R, Jauregui AN,
et al. Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis. Sci Transl Med.
2011;3(85):85ra46.).
The integrity of the podocyte is paramount in maintaining the “barrier” against
proteinuria and in the evolution of many progressive kidney diseases (110110. Reiser J, von Gersdorff G, Loos M, Oh J, Asanuma K, Giardino L, et al.
Induction of B7-1 in podocytes is associated with nephrotic syndrome. J Clin Invest.
2004;113(10):1390-7.,111111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
). This complex genetic, anatomic,
and physiologic pathogenesis has become better understood during the past decade. The fundamental
research began with Reiser et al. (110110. Reiser J, von Gersdorff G, Loos M, Oh J, Asanuma K, Giardino L, et al.
Induction of B7-1 in podocytes is associated with nephrotic syndrome. J Clin Invest.
2004;113(10):1390-7.), who discovered the
relationship between the stimulation of a receptor on the podocyte, termed the “B7-1”
(also known as CD80), that, when stimulated in various pathologic settings, disrupted the integrity
of the podocyte cytoskeleton and led to pathologic proteinuria and nephrotic syndrome (110110. Reiser J, von Gersdorff G, Loos M, Oh J, Asanuma K, Giardino L, et al.
Induction of B7-1 in podocytes is associated with nephrotic syndrome. J Clin Invest.
2004;113(10):1390-7.).
In a summary of recent discoveries, Mundel and Reiser emphasize the basic physiology involved in
the proteinuria and identify potential therapeutic targets (111111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
). They hypothesize that there may be a common pathologic pathway involving the enzymatic
cleavage of regulators of the podocyte actin cytoskeleton by cytosolic cathepsin L (111111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
). This cleavage disrupts the podocyte actin cytoskeleton and
causes the clinical syndrome of nephrotic proteinuria. In the early stages of nephrotic proteinuria,
as in R-FSGS, these changes are potentially reversible. In essence, this work forms the basis of new
discoveries in the pathogenesis and development of therapeutic targets for early intervention (116116. Reiser J, Wei C, Tumlin J. Soluble urokinase receptor and focal segmental
glomerulosclerosis. Curr Opin Nephrol Hypertens. 2012;21(4):428-32,
http://dx.doi.org/10.1097/MNH.0b013e328354a681.
http://dx.doi.org/10.1097/MNH.0b013e3283...
).
With this active translational research, the microanatomy of the podocyte has been elaborated,
and a number of genetic, immune, and nonimmune diseases of the podocyte have been described (117117. Tryggvason K, Patrakka J, Wartiovaara J. Hereditary proteinuria syndromes and
mechanisms of proteinuria. N Engl J Med. 2006;354(13):1387-401.,118118. Winkler CA, Nelson G, Oleksyk TK, Nava MB, Kopp JB. Genetics of focal segmental
glomerulosclerosis and human immunodeficiency virus-associated collapsing glomerulopathy: the role
of MYH9 genetic variation. Semin Nephrol. 2010;30(2):111-25,
http://dx.doi.org/10.1016/j.semnephrol.2010.01.003.
http://dx.doi.org/10.1016/j.semnephrol.2...
). In concert with
these discoveries has been the rapid and exciting evolution of potential therapies (109109. Sharma R, Sharma M, McCarthy ET, Ge XL, Savin VJ. Components of normal serum
block the focal segmental glomerulosclerosis factor activity in vitro. Kidney Int.
2000;58(5):1973-9, http://dx.doi.org/10.1111/j.1523-1755.2000.00369.x.
http://dx.doi.org/10.1111/j.1523-1755.20...
110. Reiser J, von Gersdorff G, Loos M, Oh J, Asanuma K, Giardino L, et al.
Induction of B7-1 in podocytes is associated with nephrotic syndrome. J Clin Invest.
2004;113(10):1390-7.
111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
112. Faul C, Donnelly M, Merscher-Gomez S, Chang YH, Franz S, Delfgaauw J, et al.
The actin cytoskeleton of kidney podocytes is a direct target of the antiproteinuric effect of
cyclosporine A. Nat Med. 2008;14(9):931-8, http://dx.doi.org/10.1038/nm.1857.
http://dx.doi.org/10.1038/nm.1857...
113. Zhang B, Shi W, Ma J, Sloan A, Faul C, Wei C, et al. The calcineurin-NFAT
pathway allows for urokinase receptor-mediated beta3 integrin signaling to cause podocyte injury.
J Mol Med (Berl). 2012;90(12):1407-20,
http://dx.doi.org/10.1007/s00109-012-0960-6.
http://dx.doi.org/10.1007/s00109-012-096...
114. Trachtman H, Gipson DS, Kaskel F, Ghiggeri GM, Faul C, Gupta V, et al.
Regarding Maas's editorial letter on serum suPAR levels. Kidney Int. 2012;82(4):492,
http://dx.doi.org/10.1038/ki.2012.230.
http://dx.doi.org/10.1038/ki.2012.230...
-115115. Fornoni A, Sageshima J, Wei C, Merscher-Gomez S, Aguillon-Prada R, Jauregui AN,
et al. Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis. Sci Transl Med.
2011;3(85):85ra46.). New insights
into the cause-effect relationship between cPF and podocyte injury in recurrent FSGS have come from
identifying the soluble urokinase receptor (suPAR) as a cPF that can cause podocyte injury in
recurrent FSGS (106106. Wei C, Moller CC, Altintas MM, Li J, Schwarz K, Zacchigna S, et al.
Modification of kidney barrier function by the urokinase receptor. Nat Med. 2008;14(1):55-63,
http://dx.doi.org/10.1038/nm1696.
http://dx.doi.org/10.1038/nm1696...
,107107. Wei C, El Hindi S, Li J, Fornoni A, Goes N, Sageshima J, et al. Circulating
urokinase receptor as a cause of focal segmental glomerulosclerosis. Nat Med. 2011;17(8):952-60,
http://dx.doi.org/10.1038/nm.2411.
http://dx.doi.org/10.1038/nm.2411...
) and from the discovery that sphingolipid-related enzymes are markedly affected in
podocytes in R-FSGS (115115. Fornoni A, Sageshima J, Wei C, Merscher-Gomez S, Aguillon-Prada R, Jauregui AN,
et al. Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis. Sci Transl Med.
2011;3(85):85ra46.). Other discoveries include the
nonimmune target mechanism of action of cyclosporine (111111. Mundel P, Reiser J. Proteinuria: an enzymatic disease of the podocyte? Kidney
Int. 2010;77(7):571-80, http://dx.doi.org/10.1038/ki.2009.424.
http://dx.doi.org/10.1038/ki.2009.424...
,112112. Faul C, Donnelly M, Merscher-Gomez S, Chang YH, Franz S, Delfgaauw J, et al.
The actin cytoskeleton of kidney podocytes is a direct target of the antiproteinuric effect of
cyclosporine A. Nat Med. 2008;14(9):931-8, http://dx.doi.org/10.1038/nm.1857.
http://dx.doi.org/10.1038/nm.1857...
) and rituximab (115115. Fornoni A, Sageshima J, Wei C, Merscher-Gomez S, Aguillon-Prada R, Jauregui AN,
et al. Rituximab targets podocytes in recurrent focal segmental glomerulosclerosis. Sci Transl Med.
2011;3(85):85ra46.) in preventing and modulating FSGS recurrence. Most recently, in our
institution, four patients with severe R-FSGS who were nonresponsive to multiple interventions with
plasmapheresis, rituximab, and calcineurin inhibitors responded to the specific B7-1 receptor
inhibitor, abatacept, with resolution of their proteinuria (119119. Yu CC, Fornoni A, Weins A, Hakroush S, Maiguel D, Sageshima J, et al. Abatacept
in B7-1-Positive Proteinuric Kidney Disease. N Engl J Med. 2013 Nov8.).
Despite recent advances in research related to primary and recurrent FSGS, observational and
therapeutic trials are needed to better understand and treat this complex disease. Among the current
studies are the NEPTUNE and FONT2 trials. The NEPTUNE (Nephrotic Syndrome Study Network) is a
multicenter, observational trial whose purpose is to characterize the complex disease known as
“steroid-resistant nephrotic syndrome.” The National Institutes of Health and private
foundations, including the NephCure Foundation, fund it. FONT2 is a randomized, phase II trial
comparing the efficacy of galactose with that of adalimumab for treating steroid-resistant FSGS
(120120. FONT 2 Novel Therapies in resistant Focal segmental glomerulosclerosis.
[cited 2012 October 23]. Available from: http://www.fonttrial.org/.
http://www.fonttrial.org/...
).
In summary, scientific advances in understanding the pathogenesis of FSGS and its recurrence after kidney transplant during the past decade have enabled the introduction of targeted therapies designed to improve patient outcomes.
TRANSLATIONAL RESEARCH IN PEDIATRIC CARDIAC TRANSPLANTATION
Allograft rejection and complications related to the immunosuppression necessary for the survival
of the transplanted organ remain the major causes of morbidity and mortality in cardiac transplant
recipients. The mechanisms of cardiac transplant rejection are similar to those of other solid-organ
rejections and can be manifested through three modalities (121121. Labarrere CA, Jaeger BR. Biomarkers of heart transplant rejection: the good,
the bad, and the ugly! Transl Res. 2012;159(4):238-51,
http://dx.doi.org/10.1016/j.trsl.2012.01.018.
http://dx.doi.org/10.1016/j.trsl.2012.01...
).
-
Acute cellular rejection mediated through T-cells invading and destroying allograft tissue.
-
AMR mediated through complement activation and triggered by antibodies directed against the HLA antigens of the donor.
-
Cardiac allograft vasculopathy (CAV) characterized by intimal thickening and remodeling of the coronary arteries. This type of rejection usually occurs many years after transplantation and is a major limiting factor in long-term allograft survival.
Currently, endomyocardial biopsy is the reference standard for detecting graft rejection.
However, it is invasive and limited by sampling error and interobserver variability. Additionally,
Nakhleh et al. have established that histological expression of rejection is patchy in autopsied
heart allografts; the foci of rejection were surrounded by large areas of intact myocardium (122122. Nakhleh RE, Jones J, Goswitz JJ, Anderson EA, Titus J. Correlation of
endomyocardial biopsy findings with autopsy findings in human cardiac allografts. J Heart Lung
Transplant. 1992;11(3 Pt 1):479-85.). Other drawbacks of endomyocardial biopsy include the need
for multiple samples to increase sensitivity, the inability to detect graft events in the period
between biopsies, and its high cost (121121. Labarrere CA, Jaeger BR. Biomarkers of heart transplant rejection: the good,
the bad, and the ugly! Transl Res. 2012;159(4):238-51,
http://dx.doi.org/10.1016/j.trsl.2012.01.018.
http://dx.doi.org/10.1016/j.trsl.2012.01...
). Endomyocardial
biopsy also has complications, albeit rare, such as damage to the vessels, arrhythmias, conduction
abnormalities, biopsy-induced tricuspid regurgitation, and even cardiac perforation (123123. Baraldi-Junkins C, Levin HR, Kasper EK, Rayburn BK, Herskowitz A, Baughman KL.
Complications of endomyocardial biopsy in heart transplant patients. J Heart Lung Transplant.
1993;12(1 Pt 1):63-7.
124. Williams MJ, Lee MY, DiSalvo TG, Dec GW, Picard MH, Palacios IF, et al.
Biopsy-induced flail tricuspid leaflet and tricuspid regurgitation following orthotopic cardiac
transplantation. Am J Cardiol. 1996;77(15):1339-44,
http://dx.doi.org/10.1016/S0002-9149(96)00202-0.
http://dx.doi.org/10.1016/S0002-9149(96)...
125. Oldham N, Ott RA, Allen BA, Fopiano P, Dwyer M. Ventricular fibrillation
complicating endomyocardial biopsy of a cardiac allograft. Cathet Cardiovasc Diagn.
1991;23(4):300-1, http://dx.doi.org/10.1002/ccd.1810230415.
http://dx.doi.org/10.1002/ccd.1810230415...
126. Bhat G, Burwig S, Walsh R. Morbidity of endomyocardial biopsy in cardiac
transplant recipients. Am Heart J. 1993;125(4):1180-1,
http://dx.doi.org/10.1016/0002-8703(93)90138-Y.
http://dx.doi.org/10.1016/0002-8703(93)9...
-127127. Hamour IM, Burke MM, Bell AD, Panicker MG, Banerjee R, Banner NR. Limited
utility of endomyocardial biopsy in the first year after heart transplantation. Transplantation.
2008;85(7):969-74, http://dx.doi.org/10.1097/TP.0b013e318168d571.
http://dx.doi.org/10.1097/TP.0b013e31816...
).
Over the past few years, clinicians have looked into other noninvasive diagnostic tools, such as
Doppler echocardiography (128128. Moidl R, Chevtchik O, Simon P, Grimm M, Wieselthaler G, Ullrich R, et al.
Noninvasive monitoring of peak filling rate with acoustic quantification echocardiography accurately
detects acute cardiac allograft rejection. J Heart Lung Transplant. 1999;18(3):194-201,
http://dx.doi.org/10.1016/S1053-2498(98)00031-X.
http://dx.doi.org/10.1016/S1053-2498(98)...
,129129. Mankad S, Murali S, Kormos RL, Mandarino WA, Gorcsan J, 3rd. Evaluation of the
potential role of color-coded tissue Doppler echocardiography in the detection of allograft
rejection in heart transplant recipients. Am Heart J. 1999;138(4 Pt 1):721-30,
http://dx.doi.org/10.1016/S0002-8703(99)70188-2.
http://dx.doi.org/10.1016/S0002-8703(99)...
), high-resolution electrocardiography (130130. Graceffo MA, O'Rourke RA. Cardiac transplant rejection is associated with
a decrease in the high-frequency components of the high-resolution, signal-averaged
electrocardiogram. Am Heart J. 1996;132(4):820-6,
http://dx.doi.org/10.1016/S0002-8703(96)90317-8.
http://dx.doi.org/10.1016/S0002-8703(96)...
), intramyocardial electrography (131131. Bourge R, Eisen H, Hershberger R, Keller A, Radovancevic B, Schreier G, et al.
Noninvasive rejection monitoring of cardiac transplants using high resolution intramyocardial
electrograms: initial US multicenter experience. Pacing Clin Electrophysiol. 1998;21(11 Pt
2):2338-44, http://dx.doi.org/10.1111/j.1540-8159.1998.tb01178.x.
http://dx.doi.org/10.1111/j.1540-8159.19...
),
scintigraphy to detect antimyosin antibodies (132132. Hesse B, Mortensen SA, Folke M, Brodersen AK, Aldershvile J, Pettersson G.
Ability of antimyosin scintigraphy monitoring to exclude acute rejection during the first year after
heart transplantation. J Heart Lung Transplant. 1995;14(1 Pt 1):23-31.), and gene
expression profiling in peripheral blood lymphocytes (133133. Deng MC, Eisen HJ, Mehra MR, Billingham M, Marboe CC, Berry G, et al.
Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression
profiling. Am J Transplant. 2006;6(1):150-60.).
Narula et al. studied the imaging of technetium-labeled annexin V using gamma cameras. Annexin V is
an endogenous protein with a high affinity to phosphatidylserine, which is a phospholipid released
during apoptotic cell death. The uptake of annexin V by the myocardium was associated with moderate
grades of allograft rejection, suggesting the use of this imaging technique to detect rejection
(134134. Narula J, Acio ER, Narula N, Samuels LE, Fyfe B, Wood D, et al. Annexin-V
imaging for noninvasive detection of cardiac allograft rejection. Nat Med. 2001;7(12):1347-52,
http://dx.doi.org/10.1038/nm1201-1347.
http://dx.doi.org/10.1038/nm1201-1347...
). However, although they may be able to detect
rejection, these methods are not as effective as endomyocardial biopsy.
Identifying biological markers that can quickly, accurately, and noninvasively detect different types of rejection may improve the management of cardiac transplant patients. Biomarkers are becoming more important because they are effective in monitoring biological processes, helpful in diagnosing and monitoring disease progression, and useful in assessing the response to treatment. Characterizing a disease process through biomarkers may help tailor treatment to individual patients and indicate their prognosis.
Biomarkers are anatomic, biochemical, or molecular characteristics of body fluids or tissues that
indicate or are associated with clinically meaningful changes in physiology (135135. Cravedi P, Heeger PS. Immunologic monitoring in transplantation revisited. Curr
Opin Organ Transplant. 2012;17(1):26-32,
http://dx.doi.org/10.1097/MOT.0b013e32834ee402.
http://dx.doi.org/10.1097/MOT.0b013e3283...
). To be clinically useful, they should be easily acquired and measured, valid,
and have a sensitivity and specificity greater than other relevant technologies. They should also be
relatively inexpensive and directly related to treatment decisions. Their validity should be
established in prospective multicenter studies (136136. Morrow DA, de Lemos JA. Benchmarks for the assessment of novel cardiovascular
biomarkers. Circulation. 2007;115(8):949-52,
http://dx.doi.org/10.1161/CIRCULATIONAHA.106.683110.
http://dx.doi.org/10.1161/CIRCULATIONAHA...
).
In the field of transplantation, the use of biomarkers is rapidly evolving in two areas: 1)
predicting and detecting allograft rejection and 2) detecting allograft tolerance for directing the
weaning and proper adjustment of immunosuppression (135135. Cravedi P, Heeger PS. Immunologic monitoring in transplantation revisited. Curr
Opin Organ Transplant. 2012;17(1):26-32,
http://dx.doi.org/10.1097/MOT.0b013e32834ee402.
http://dx.doi.org/10.1097/MOT.0b013e3283...
).
Overview of Rejection and Cardiac Biomarkers
Rejection of the transplanted heart starts as a proinflammatory state that ultimately leads to
graft failure marked by the signs and symptoms of heart failure. The immunological mechanism of
rejection begins when recipient T-cells recognize the graft antigens by non-self MHC type I and type
II antigens and by the recruitment of cytotoxic T-lymphocytes. The CD4+ T-cells then help the
B-lymphocytes to produce antibodies against the MCH antigens. This step is followed by the release
of chemical mediators and cytokines and the further proliferation and differentiation of T- and
B-lymphocytes, which creates a vicious cycle of inflammation and alloreactivity. The combined
actions of the T-cells, antibodies, and natural killer cells cause inflammation, necrosis, and
fibrosis in the myocardium (137137. Law YM. Pathophysiology and diagnosis of allograft rejection in pediatric heart
transplantation. Curr Opin Cardiol. 2007;22(2):66-71,
http://dx.doi.org/10.1097/HCO.0b013e328028fd68.
http://dx.doi.org/10.1097/HCO.0b013e3280...
).
The current knowledge about biomarkers for detecting allograft rejection is derived from markers of different pathophysiologic processes, such as cardiac failure. We review below some of the biomarkers for inflammation, cardiomyocyte injury, and cardiomyocyte stress that have some potential to detect early rejection episodes in cardiac transplantation.
Inflammation
The first biomarker of inflammation was C-reactive protein (CRP), discovered in 1954 (66. Terasaki PI. Humoral theory of transplantation. Am J Transplant.
2003;3(6):665-73.). A member of the pentraxin superfamily, CRP is a prototypical
“acute phase” protein that is synthesized at a low rate under physiologic conditions
but that is markedly induced and secreted after tissue injury and inflammation (138138. Frangogiannis NG. Monomeric C-reactive protein and inflammatory injury in
myocardial infarction. Cardiovasc Res. 2012;96(1):4-6,
http://dx.doi.org/10.1093/cvr/cvs265.
http://dx.doi.org/10.1093/cvr/cvs265...
). It is produced predominantly by hepatocytes under the
influence of cytokines, such as IL-6 or TNF-alpha.
In 1956, Elster et al. found elevated concentrations of CRP in patients with heart failure, and
those with higher concentrations had more severe disease (139139. Elster SK, Braunwald E, Wood HF. A study of C-reactive protein in the serum of
patients with congestive heart failure. Am Heart J. 1956;51(4):533-41,
http://dx.doi.org/10.1016/0002-8703(56)90099-0.
http://dx.doi.org/10.1016/0002-8703(56)9...
). Since then, many studies have verified that CRP is an important biomarker of
inflammation. It became widely used when Ridker developed a low-cost and high-sensitivity assay in
2001 (140140. Ridker PM. High-sensitivity C-reactive protein: potential adjunct for global
risk assessment in the primary prevention of cardiovascular disease. Circulation.
2001;103(13):1813-8, http://dx.doi.org/10.1161/01.CIR.103.13.1813.
http://dx.doi.org/10.1161/01.CIR.103.13....
).
Venugopal et al. determined that CRP directly affects vascular endothelium by reducing nitric
oxide release, increasing endothelin-1 production, and inducing the expression of endothelial
adhesion molecule (141141. Venugopal SK, Devaraj S, Jialal I. Effect of C-reactive protein on vascular
cells: evidence for a proinflammatory, proatherogenic role. Curr Opin Nephrol Hypertens.
2005;14(1):33-7, http://dx.doi.org/10.1097/00041552-200501000-00006.
http://dx.doi.org/10.1097/00041552-20050...
).
More recently, in a prospective observational study of 79 cardiac transplant recipients, Dolz et
al. measured various inflammatory markers, such as fibrinogen, IL-6, TNF-alpha, sialic acid
determinants, and CRP in endomyocardial biopsies performed during the first year after transplant.
They concluded that CRP had the largest area under the ROC curve, with concentrations less than 0.87
mg/dL being 90% specific for rejection and concentrations greater than 7.3 mg/dL being 100%
sensitive for rejection. They identified CRP as the most useful biomarker for the noninvasive
screening of acute cellular rejection in the first year after heart transplantation (142142. Martinez-Dolz L, Almenar L, Reganon E, Vila V, Sanchez-Soriano R,
Martinez-Sales V, et al. What is the best biomarker for diagnosis of rejection in heart
transplantation? Clin Transplant. 2009;23(5):672-80,
http://dx.doi.org/10.1111/j.1399-0012.2009.01074.x.
http://dx.doi.org/10.1111/j.1399-0012.20...
). However, because its level is elevated in many inflammatory
states, CRP is a nonspecific marker and does not always indicate cardiac rejection alone.
Cardiomyocyte Injury
Cardiomyocyte injury results from a variety of factors, such as ischemia, inflammation, neurohormonal activation, and oxidative stress. Over the past two decades, myofibrillar proteins —the cardiac troponins I and T—have emerged as sensitive and specific markers of cardiomyocyte injury and have proven useful in stratifying the risk of coronary syndromes.
In a recent pilot study, Dyer et al. evaluated the use of a high-sensitivity assay for cardiac
troponin to detect acute graft rejection (AR) in children with heart transplants. Plasma samples for
measuring cardiac troponin T were drawn at the same time as endomyocardial biopsy. Children with AR
had much higher cardiac troponin T levels than those without AR. On follow-up, troponin
concentrations decreased as the rejection was resolving. These researchers concluded that cardiac
troponin could be a useful biomarker for monitoring rejection in transplant recipients (143143. Dyer AK, Barnes AP, Fixler DE, Shah TK, Sutcliffe DL, Hashim I, et al. Use of a
highly sensitive assay for cardiac troponin T and N-terminal pro-brain natriuretic peptide to
diagnose acute rejection in pediatric cardiac transplant recipients. Am Heart J.
2012;163(4):595-600, http://dx.doi.org/10.1016/j.ahj.2012.02.003.
http://dx.doi.org/10.1016/j.ahj.2012.02....
).
Cardiomyocyte Stress
Several other biomarkers of myocardial stress have been studied. Brain natriuretic peptide (BNP) is a 134-amino acid molecule synthesized by cardiomyocytes in response to ventricular dilatation and increased wall tension. It is then cleaved into pro-hormone BNP, which consists of 108 amino acids. A circulating endoprotease, termed “corin,” further cleaves the pro-hormone into two polypeptides: the inactive N-terminal proBNP (NT-proBNP) and the bioactive peptide BNP (144144. Braunwald E. Biomarkers in heart failure. N Engl J Med. 2008;358(20):2148-59.).
The physiologic effects of BNP include arterial vasodilatation, diuresis, natriuresis, inhibition of the renin-angiotensin-aldosterone system, and inhibition of sympathetic nervous activity (144144. Braunwald E. Biomarkers in heart failure. N Engl J Med. 2008;358(20):2148-59.). Today, BNP and NT-proBNP are the most widely used biomarkers for heart failure and are being evaluated for their ability to detect graft rejection in patients with cardiac transplants.
In a retrospective study of 85 children with heart transplants, Rossano et al. evaluated BNP as a
screening tool for acute rejection. They measured BNP concentrations at the time of endomyocardial
biopsy. In the first year after transplant, the median BNP concentration in children with acute
rejection was 387 pg/mL, whereas children without rejection had a median concentration of 66 pg/mL.
A concentration of 100 pg/mL corresponded to 85% sensitivity and a 97% negative predictive value for
detecting rejection. At BNP levels above 100 pg/mL, the sensitivity and negative predictive value
for detecting acute rejection 1 year after transplantation increased to 95% and 99%, respectively.
The authors conclude at that more than 1 year after transplantation, children with a BNP level of
greater than 100 pg/mL had less than a 1% chance of experiencing acute rejection and that BNP can
eliminate the need for endomyocardial biopsies for surveillance in some cases (145145. Rossano JW, Denfield SW, Kim JJ, Price JF, Jefferies JL, Decker JA, et al.
B-type natriuretic peptide is a sensitive screening test for acute rejection in pediatric heart
transplant patients. J Heart Lung Transplant. 2008;27(6):649-54,
http://dx.doi.org/10.1016/j.healun.2008.03.008.
http://dx.doi.org/10.1016/j.healun.2008....
).
Dyer et al. were the first to study NT-proBNP as a biomarker of graft rejection in children
receiving transplants. In this prospective observational study of 42 children (mean age, 11 years),
high-sensitive cardiac troponin T (hscTnT) and NT-proBNP were assayed at the time of endomyocardial
biopsy. Acute rejection was defined as an International Society for Heart & Lung
Transplantation (ISHLT) grade of 2 or higher. Median (25th to 75th percentile)
hscTnT and NT-proBNP concentrations were higher in children with acute rejection than in those
without: hscTnT, 66 (45 to 139) vs. 7 (2 to 13) pg/mL;
p = 0.001 and NT-proBNP, 11,169 (280 to 23,317) vs.
334 (160 to 650) pg/mL; p<0.01). They concluded that elevations in NT-proBNP
concentrations are associated with episodes of rejection in these children (143143. Dyer AK, Barnes AP, Fixler DE, Shah TK, Sutcliffe DL, Hashim I, et al. Use of a
highly sensitive assay for cardiac troponin T and N-terminal pro-brain natriuretic peptide to
diagnose acute rejection in pediatric cardiac transplant recipients. Am Heart J.
2012;163(4):595-600, http://dx.doi.org/10.1016/j.ahj.2012.02.003.
http://dx.doi.org/10.1016/j.ahj.2012.02....
).
Chronic Rejection and Cardiac Allograft Vasculopathy
Allograft vasculopathy is a form of chronic rejection that is associated with graft failure and
re-transplantation in both adults and children after heart transplantation (146146. Schmauss D, Weis M. Cardiac allograft vasculopathy: recent developments.
Circulation. 2008;117(16):2131-41,
http://dx.doi.org/10.1161/CIRCULATIONAHA.107.711911.
http://dx.doi.org/10.1161/CIRCULATIONAHA...
,147147. Kirk R, Edwards LB, Aurora P, Taylor DO, Christie J, Dobbels F, et al. Registry
of the International Society for Heart and Lung Transplantation: eleventh official pediatric heart
transplantation report--2008. J Heart Lung Transplant. 2008;27(9):970-7,
http://dx.doi.org/10.1016/j.healun.2008.06.016.
http://dx.doi.org/10.1016/j.healun.2008....
). There is clearly a need to
understand and detect this process as early as possible.
Allograft vasculopathy is characterized by remodeling of the coronary arteries through diffuse
fibromuscular intimal hyperplasia and focal atherosclerosis. Endothelial damage is caused by a
combination of alloimmune and non-alloimmune responses and other factors that induce endothelial
activation and death. Endothelial damage is concomitant with endothelial repair. During this process
of damage and repair, apoptotic circulating endothelial cells and endothelial microparticles are
released into the circulation. During the regeneration process, endothelial progenitor cells are
released. All these circulating endothelial components may become useful biomarkers of CAV (148148. Singh N, Van Craeyveld E, Tjwa M, Ciarka A, Emmerechts J, Droogne W, et al.
Circulating apoptotic endothelial cells and apoptotic endothelial microparticles independently
predict the presence of cardiac allograft vasculopathy. J Am Coll Cardiol. 2012;60(4):324-31,
http://dx.doi.org/10.1016/j.jacc.2012.02.065.
http://dx.doi.org/10.1016/j.jacc.2012.02...
).
Singh et al. studied 52 cardiac transplant patients undergoing coronary angiography between 5 and 15 years after transplant. In a logistic regression model, apoptotic circulating endothelial cells (p = 0.011) and apoptotic endothelial microparticle concentrations (p = 0.014) were independent predictors of vasculopathy (C statistic, 0.86; 95% confidence interval, 0.76 to 0.95). This research is an initial step in predicting CAV and in determining the need for coronary angiography and intravascular ultrasound when it is suspected.
Biomarkers of rejection have been evaluated in several studies. However, the need for larger, multicenter trials remains. Validated biomarkers will detect allograft rejection before acute clinical decompensation and graft failure. However, few biomarkers have yet become commercially available.
In addition to detecting early rejection, clinicians must also manage the severe immunosuppression required for these transplant recipients. In the next sections, we review the present and future efforts being made to address this challenge.
Tolerance in Transplantation
Rejection of a transplanted allograft is an immunologically mediated process that occurs because
of differences between donor and recipient concentrations in HLA. Allorecognition is the term for
the immunological recognition of histo-incompatible antigens between genetically disparate
individuals from the same species. Alloresponse in transplantation is the beginning of an adaptive
immune response in which allospecific T-cells are recruited. This alloresponse rejects the
transplanted organ in nontolerant or inadequately immunosuppressed individuals (149149. Afzali B, Lombardi G, Lechler RI. Pathways of major histocompatibility complex
allorecognition. Curr Opin Organ Transplant. 2008;13(4):438-44,
http://dx.doi.org/10.1097/MOT.0b013e328309ee31.
http://dx.doi.org/10.1097/MOT.0b013e3283...
).
To protect against alloresponse, cardiac transplant recipients must take immunosuppressive medications, which in the long run increase their susceptibility to infection, malignancy, and accelerated cardiovascular disease, thereby increasing their morbidity and mortality.
A new direction in preventing alloresponse has been to induce “transplant
tolerance,” which would avoid the need for immunosuppression and its associated adverse
effects. Transplant tolerance is defined as a well-functioning graft that lacks histological signs
of rejection in an immunocompetent host in the absence of any immunosuppressive drugs (150150. Hernandez-Fuentes MP, Lechler RI. A 'biomarker signature' for
tolerance in transplantation. Nat Rev Nephrol. 2010;6(10):606-13,
http://dx.doi.org/10.1038/nrneph.2010.112.
http://dx.doi.org/10.1038/nrneph.2010.11...
).
“Operational transplant tolerance” is a clinical situation defined as stable graft
function without clinical features of chronic rejection and in the absence of any immunosuppressive
drugs, usually for longer than 1 year (151151. Roussey-Kesler G, Giral M, Moreau A, Subra JF, Legendre C, Noel C, et al.
Clinical operational tolerance after kidney transplantation. Am J Transplant.
2006;6(4):736-46.). However,
current tests and biomarkers cannot indicate tolerance to the graft. Validated indicators or
biomarkers of immunologic tolerance and biomarkers able to predict and diagnose graft dysfunction,
acute and chronic rejection, and the level of immunosuppression potentially allow for individualized
therapy and the safe minimization or withdrawal of immunosuppressive therapy in certain transplant
recipients (150150. Hernandez-Fuentes MP, Lechler RI. A 'biomarker signature' for
tolerance in transplantation. Nat Rev Nephrol. 2010;6(10):606-13,
http://dx.doi.org/10.1038/nrneph.2010.112.
http://dx.doi.org/10.1038/nrneph.2010.11...
).
Experimental models of the immune system's response to transplantation have identified two
key events that lead to tolerance in the recipient: the deletion of a considerable fraction of
alloreactive T-cells and the development of T-regulatory cells that protect the graft from being
attacked by the immune system (150150. Hernandez-Fuentes MP, Lechler RI. A 'biomarker signature' for
tolerance in transplantation. Nat Rev Nephrol. 2010;6(10):606-13,
http://dx.doi.org/10.1038/nrneph.2010.112.
http://dx.doi.org/10.1038/nrneph.2010.11...
). Some evidence indicates
that the terminal pathway in destroying the transplanted organ, as occurs in acute rejection, is the
same pathway that destroys tissues in many other inflammatory processes, such as immune-mediated
tumor rejection, autoimmune disease, cardiovascular events, chronic obstructive pulmonary disease,
and infection clearance. This common pathway has been called the “immunologic constant of
rejection” (152152. Wang E, Worschech A, Marincola FM. The immunologic constant of rejection.
Trends Immunol. 2008;29(6):256-62, http://dx.doi.org/10.1016/j.it.2008.03.002.
http://dx.doi.org/10.1016/j.it.2008.03.0...
).
Microarrays that quickly analyze thousands of genes have been used to study the mechanisms and
pathways of acute rejection in organ transplantation. In an interesting meta-analysis, Spivey et al.
reviewed the literature for all the most common pathways of acute allograft rejection in humans, as
determined by microarray technology. The pathways reported in the immunologic constant of rejection
hypothesis are the same pathways as those occurring in acute allograft rejection. Microarray
analysis may help to determine the mechanism that controls the balance between tolerance and
rejection (153153. Spivey TL, Uccellini L, Ascierto ML, Zoppoli G, De Giorgi V, Delogu LG, et al.
Gene expression profiling in acute allograft rejection: challenging the immunologic constant of
rejection hypothesis. J Transl Med. 2011;9:174,
http://dx.doi.org/10.1186/1479-5876-9-174.
http://dx.doi.org/10.1186/1479-5876-9-17...
). Because of the large number of genes that
can be analyzed, the microarray technique can be used to study the mechanism of activation of the
immunosystem directly in the human body, bypassing experiments in animal models.
Currently, new techniques that can rapidly measure and analyze large amounts of different biological substances and that will help identify new biomarkers include the following:
-
Genetic analysis with real-time PCR, microarrays, and genome-wide association.
-
Flow cytometry and Luminex-based techniques for measuring large numbers of cells and their products.
-
Mass spectrometry for measuring and identifying proteins.
Genetic Analysis
Real-time PCR can test a small number of genes with high sensitivity and specificity. Microarrays
can quickly analyze thousands of genes and determine whether they are activated or suppressed.
Microarray analysis is more cost-effective then real-time PCR for studying a large number of genes,
but its sensitivity and specificity are lower. Since 2001, microarrays have been used in various
solid-organ transplant studies to identify specific patterns of gene expression that can predict and
characterize acute and chronic rejection and transplant tolerance (154154. Khatri P, Sarwal MM. Using gene arrays in diagnosis of rejection. Curr Opin
Organ Transplant. 2009;14(1):34-9, http://dx.doi.org/10.1097/MOT.0b013e32831e13d0.
http://dx.doi.org/10.1097/MOT.0b013e3283...
). Chen et al. used microarray analysis of the biopsies of transplanted hearts in acute
rejection to identify 45 upregulated genes that may be correlated with rejection (155155. Chen R, Sigdel TK, Li L, Kambham N, Dudley JT, Hsieh SC, et al. Differentially
expressed RNA from public microarray data identifies serum protein biomarkers for cross-organ
transplant rejection and other conditions. PLoS Comput Biol. 2010;6.).
Genome-wide association studies can be described as whole-genome scans that can identify single
nucleotide polymorphisms in a small amount of DNA (156156. Peltonen L, McKusick VA. Genomics and medicine. Dissecting human disease in the
postgenomic era. Science. 2001;291(5507):1224-9,
http://dx.doi.org/10.1126/science.291.5507.1224.
http://dx.doi.org/10.1126/science.291.55...
). The
theory is that the association between a polymorphism and a disease phenotype can be used as a
genetic marker to aid in diagnosis and prognosis. Transplant centers in the UK and Ireland are
currently using this type of analysis to identify genes for kidney transplant failure (157157. The United Kingdom and Ireland Renal Transplant Consortium Defining the Genetic
Basis of interactions between Donor and Recipient DNA that Determine Early and Late Renal Transplant
Dysfunction. [cited 2012 October 14]. Available from:
http://www.ukirtc.org/site/.
http://www.ukirtc.org/site/...
). If this technique is applied to a cardiac transplantation
population, it may also identify clinically useful biomarkers in that population.
Gene Expression Profiling
Applying genetic testing to cardiac transplantation has brought about a new, noninvasive test for
detecting acute cellular rejection. Gene expression profiling (GEP) is being investigated as a
potential adjunct to, or even substitute for, endomyocardial biopsy for monitoring acute cellular
rejection of cardiac allografts in certain clinical situations. Among the more than 15,000
biomarkers studied so far in relation to solid-organ transplantation, only 2 are approved by the FDA
and are commercially available: the AlloMap® and Cylex®
ImmuKnow™ tests (121121. Labarrere CA, Jaeger BR. Biomarkers of heart transplant rejection: the good,
the bad, and the ugly! Transl Res. 2012;159(4):238-51,
http://dx.doi.org/10.1016/j.trsl.2012.01.018.
http://dx.doi.org/10.1016/j.trsl.2012.01...
).
The AlloMap® test uses quantitative real-time PCR to measure the expression of 20
genes (11 informative, 9 control and normalization) in peripheral blood mononuclear cells (133133. Deng MC, Eisen HJ, Mehra MR, Billingham M, Marboe CC, Berry G, et al.
Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression
profiling. Am J Transplant. 2006;6(1):150-60.,158158. Pham MX, Teuteberg JJ, Kfoury AG, Starling RC, Deng MC, Cappola TP, et al.
Gene-expression profiling for rejection surveillance after cardiac transplantation.
N Engl J Med. 2010;362(20):1890-900.). The test was
developed on the premise that peripheral blood mononuclear cells may reflect host responses to the
allograft. It has been available for clinical use through the Clinical Laboratory Improvement
Amendment certified XDx, Inc. reference laboratory since January 2005 (159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
).
The AlloMap® test was developed using DNA microarray technology and validated with quantitative real-time PCR. The 11 informative genes represent several biologic pathways, including T-cell activation (PDCD1), T-cell migration (ITGA4), mobilization of hematopoietic precursors (WDR40A and cMIR), and steroid-responsive genes (ILIR2, FLT3, and ITGAM). The remaining nine AlloMap® genes are controls for test accuracy and reproducibility (133133. Deng MC, Eisen HJ, Mehra MR, Billingham M, Marboe CC, Berry G, et al. Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression profiling. Am J Transplant. 2006;6(1):150-60.,158158. Pham MX, Teuteberg JJ, Kfoury AG, Starling RC, Deng MC, Cappola TP, et al. Gene-expression profiling for rejection surveillance after cardiac transplantation. N Engl J Med. 2010;362(20):1890-900.). A score from 0 to 40 is generated using a multigene algorithm. The test was developed and validated through the Cardiac Allograft Rejection Gene Expression Observational (CARGO) study, with the aim to distinguish between a quiescent state (grade 0R by the revised ISHLT grading) and moderate-to-severe rejection (a grade of 3A/2R or higher by the original and revised ISHLT grading of rejection, respectively). Importantly, GEP could detect the absence of moderate-to-severe rejection and thus identify a state of quiescence, with score thresholds varying with the time after transplant (>2 to ≤6 months, >6 to ≤12 months, or >12 months).
The test has a high negative predictive value, which ranges from approximately 98% to 99% for
scores considered to be appropriate thresholds in each of the three time periods after transplant
(133133. Deng MC, Eisen HJ, Mehra MR, Billingham M, Marboe CC, Berry G, et al.
Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression
profiling. Am J Transplant. 2006;6(1):150-60.,158158. Pham MX, Teuteberg JJ, Kfoury AG, Starling RC, Deng MC, Cappola TP, et al.
Gene-expression profiling for rejection surveillance after cardiac transplantation.
N Engl J Med. 2010;362(20):1890-900.,159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
). One year after transplantation, scores of less than 34 were
associated with a negative predictive value of more than 99% for grade 3A/2R rejection, suggesting
the clinical utility of this test is its ability to rule out acute cellular rejection (158158. Pham MX, Teuteberg JJ, Kfoury AG, Starling RC, Deng MC, Cappola TP, et al.
Gene-expression profiling for rejection surveillance after cardiac transplantation.
N Engl J Med. 2010;362(20):1890-900.,159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
). The positive
predictive values for GEP of 34 or more were low, however, with values decreasing from 20% to 40%
during the first 6 months after transplant to approximately 7.8% at 1 year after transplantation.
This decline in PPV is thought to be related to the decrease in the incidence of acute rejection
with time from transplantation (133133. Deng MC, Eisen HJ, Mehra MR, Billingham M, Marboe CC, Berry G, et al.
Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression
profiling. Am J Transplant. 2006;6(1):150-60.,158158. Pham MX, Teuteberg JJ, Kfoury AG, Starling RC, Deng MC, Cappola TP, et al.
Gene-expression profiling for rejection surveillance after cardiac transplantation.
N Engl J Med. 2010;362(20):1890-900.,159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
). These findings indicate that GEP
has a high sensitivity and low PPV for detecting acute cellular rejection over time.
AlloMap® scores and the histologic results of cardiac biopsies sometimes differ.
High GEP scores in the setting of negative biopsy results is the more common phenomenon and may be
caused by early or focal rejection that may be missed on biopsy as a result of sampling error.
Additionally, immune processes related to conditions other than acute cellular rejection
(e.g., AMR, infection, cardiac allograft vasculopathy, or chronic rejection) may be
associated with higher AlloMap® scores. AlloMap® scores also tend to
increase with time after transplantation, even with quiescence, and values must be interpreted in
this context. Higher GEP scores in the setting of quiescence are thought to be related to
down-titration of corticosteroids and other immunosuppression. However, the clinical importance of
an AlloMap® score above a threshold in the setting of quiescence is as yet unknown
(133133. Deng MC, Eisen HJ, Mehra MR, Billingham M, Marboe CC, Berry G, et al.
Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression
profiling. Am J Transplant. 2006;6(1):150-60.,158158. Pham MX, Teuteberg JJ, Kfoury AG, Starling RC, Deng MC, Cappola TP, et al.
Gene-expression profiling for rejection surveillance after cardiac transplantation.
N Engl J Med. 2010;362(20):1890-900.,159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
).
AlloMap® testing is currently being used in clinically stable cardiac transplant
recipients aged 15 years or older at 6 months or more after transplantation to identify those at
low-risk for moderate or severe (Grade ≥3A/2R) cellular rejection. The test has also been
used as an adjunct to clinical evaluation and endomyocardial biopsy in monitoring for rejection and
in lieu of biopsy in patients 6 months or more after transplant who are at low risk of rejection
(159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
,160160. Mehra MR, Kobashigawa JA, Deng MC, Fang KC, Klingler TM, Lal PG, et al.
Clinical implications and longitudinal alteration of peripheral blood transcriptional signals
indicative of future cardiac allograft rejection. J Heart Lung Transplant. 2008;27(3):297-301,
http://dx.doi.org/10.1016/j.healun.2007.11.578.
http://dx.doi.org/10.1016/j.healun.2007....
). Its
application should be individualized and the results interpreted in the context of the
patient's overall clinical status and risk of acute rejection. The frequency of surveillance
should be individualized and a thorough clinical evaluation performed at the time of testing,
including echocardiographic assessment of allograft function (159159. Starling RC, Pham M, Valantine H, Miller L, Eisen H, Rodriguez ER, et al.
Molecular testing in the management of cardiac transplant recipients: initial clinical experience.
J Heart Lung Transplant. 2006;25(12):1389-95,
http://dx.doi.org/10.1016/j.healun.2006.10.002.
http://dx.doi.org/10.1016/j.healun.2006....
). Thresholds should also be individualized and decisions regarding biopsy or changes in
immunosuppression made according to each patient's risk for acute rejection.
AlloMap® is not recommended for use in patients who are at high risk for acute rejection or graft failure, including pregnant women, patients who have received blood transfusions in the prior 30 days, patients who have received hematopoietic growth factors affecting leukocytes within the prior 30 days, and patients who have received high-dose steroids within the past 21 days or who are taking 20 mg/day or more of prednisone equivalent. The test has not been validated for use in children less than 15 years of age.
The AlloMap® test has distinct advantages over biopsy in that it is a
less-invasive method for monitoring acute cellular rejection in cardiac allograft recipients. Its
genetic basis also has the advantage of having the potential to predict episodes of acute rejection,
which may help to guide risk stratification, monitoring, and treatment (161161. Mehra MR, Kobashigawa JA, Deng MC, Fang KC, Klingler TM, Lal PG, et al.
Transcriptional signals of T-cell and corticosteroid-sensitive genes are associated with future
acute cellular rejection in cardiac allografts. J Heart Lung Transplant. 2007;26(12):1255-63,
http://dx.doi.org/10.1016/j.healun.2007.09.009.
http://dx.doi.org/10.1016/j.healun.2007....
,162162. Cadeiras M, Burke E, Dedrick R, Gangadin A, Latif F, Shahzad K, et al. Gene
expression profiles of patients with antibody-mediated rejection after cardiac transplantation.
J Heart Lung Transplant. 2008;27(8):932-4,
http://dx.doi.org/10.1016/j.healun.2008.05.001.
http://dx.doi.org/10.1016/j.healun.2008....
). The clinical usefulness also
extends to its applicability in managing immunosuppressive regimes to minimize the risk and
complications of toxicity while also minimizing the risk of rejection.
The importance of GEP scores in cardiac allograft vasculopathy and in AMR are also areas of
investigation (163163. Roedder S, Vitalone M, Khatri P, Sarwal MM. Biomarkers in solid organ
transplantation: establishing personalized transplantation medicine. Genome Med. 2011;3(6):37,
http://dx.doi.org/10.1186/gm253.
http://dx.doi.org/10.1186/gm253...
). These studies are, however, limited by
small patient numbers, and their usefulness in children is limited by the fact that most results are
from data in adults. AlloMap® scores in patients less than age 15 years remain to be
validated.
Adenosine Triphosphate Release as a Measure of Immune Function
The Cylex® ImmuKnow™ cell function assay (CICFA) has been promoted as a
way to monitor the integrity of cell-mediated immunity. The assay measures the adenosine
triphosphate (ATP) concentrations in CD4+ T-cell lymphocytes after stimulation with
phytohemagglutinin-L. High CICFA concentrations correspond with immune competence and low
concentrations with immune suppression (164164. Kowalski R, Post D, Schneider MC, Britz J, Thomas J, Deierhoi M, et al. Immune
cell function testing: an adjunct to therapeutic drug monitoring in transplant patient management.
Clin Transplant. 2003;17(2):77-88,
http://dx.doi.org/10.1034/j.1399-0012.2003.00013.x.
http://dx.doi.org/10.1034/j.1399-0012.20...
). In adult
solid-organ transplant patients, low CICFA concentrations were associated with a risk of infection,
and high CICFA concentrations were associated with a risk of acute organ rejection (165165. Kowalski RJ, Post DR, Mannon RB, Sebastian A, Wright HI, Sigle G, et al.
Assessing relative risks of infection and rejection: a meta-analysis using an immune function assay.
Transplantation. 2006;82(5):663-8,
http://dx.doi.org/10.1097/01.tp.0000234837.02126.70.
http://dx.doi.org/10.1097/01.tp.00002348...
). In an observational study of 296 heart transplant patients,
Kobashigawa et al. found that patients with assay results below normal were at higher risk for
infectious complication related to elevated immunosuppression, but attempts to predict rejection
were inconclusive (166166. Kobashigawa JA, Kiyosaki KK, Patel JK, Kittleson MM, Kubak BM, Davis SN, et al.
Benefit of immune monitoring in heart transplant patients using ATP production in activated
lymphocytes. J Heart Lung Transplant. 2010;29(5):504-8,
http://dx.doi.org/10.1016/j.healun.2009.12.015.
http://dx.doi.org/10.1016/j.healun.2009....
).
There have, however, been conflicting results. A retrospective study of 111 adult heart
transplant patients found that CICFA did not predict either infection or rejection (167167. Gupta S, Mitchell JD, Markham DW, Mammen PP, Patel PC, Kaiser PA, et al.
Utility of the Cylex assay in cardiac transplant recipients. J Heart Lung Transplant.
2008;27(8):817-22, http://dx.doi.org/10.1016/j.healun.2008.05.014.
http://dx.doi.org/10.1016/j.healun.2008....
). In this study, two patients had three episodes of cellular
rejection, and the Cylex® response did not correlate with these periods of
rejection. Few studies have evaluated the use of CICFA in children. Hooper et al. established the
normal ranges of immune assay concentrations in healthy children, both those less than and greater
than 12 years old, and in stable renal transplant recipients greater than 12 years old (168168. Hooper E, Hawkins DM, Kowalski RJ, Post DR, Britz JA, Brooks KC, et al.
Establishing pediatric immune response zones using the Cylex ImmuKnow assay. Clin Transplant.
2005;19(6):834-9, http://dx.doi.org/10.1111/j.1399-0012.2005.00429.x.
http://dx.doi.org/10.1111/j.1399-0012.20...
). These ranges are the basis for studying
Cylex® ImmuKnow™ assays in children. Gautam et al. used the ImmuKnow™
assay to adjust the dosing of immunosuppressive medications in a child with lymphoproliferative
disorder after kidney transplantation (169169. Gautam A, Morrissey PE, Brem AS, Fischer SA, Gohh RY, Yango AF, et al. Use of
an immune function assay to monitor immunosuppression for treatment of post-transplant
lymphoproliferative disorder. Pediatr Transplant. 2006;10(5):613-6,
http://dx.doi.org/10.1111/j.1399-3046.2006.00510.x.
http://dx.doi.org/10.1111/j.1399-3046.20...
). The assay can
thus be used to predict the degree of immunosuppression and to adjust medications in young
transplant recipients.
However, the use of the ImmuKnow™ assay in pediatric heart transplantation is very
limited. We found only one study that assessed its use in children with heart transplants. The
retrospective study by Rossano et al. of 83 children with heart transplants reported 20 episodes of
cellular rejection, but ATP concentrations measured by the ImmuKnow™ assay did not differ
between children with and without rejection. The authors concluded that CICFA concentrations did not
predict acute rejection or clinically important infections (170170. Rossano JW, Denfield SW, Kim JJ, Price JF, Jefferies JL, Decker JA, et al.
Assessment of the Cylex ImmuKnow cell function assay in pediatric heart transplant patients.
J Heart Lung Transplant. 2009;28(1):26-31,
http://dx.doi.org/10.1016/j.healun.2008.10.001.
http://dx.doi.org/10.1016/j.healun.2008....
). Thus, given these conflicting results, larger multicenter studies are needed to
determine whether ATP concentrations can aid in titrating immunosuppressive therapy and in reducing
adverse effects.
Genome Transplant Dynamic
Because rejection is associated with apoptosis and cell death and because free DNA is released
into plasma, Snyder et al. used single nucleotide polymorphism (SNP) technology to measure the
presence of free donor DNA as a percent of recipient DNA in the plasma of transplant recipients at
the time of endomyocardial biopsy. The correlation between the percentage of donor DNA and rejection
increased with the severity of the rejection. Furthermore, these investigators also found that an
elevation in donor DNA was detected even before biopsy-proven rejection and that it returned to
normal after treatment. On the ROC curve, a threshold of 1.70% donor DNA identified grade 2R
rejection with an 83% true positive rate and a 16% false positive rate (171171. Snyder TM, Khush KK, Valantine HA, Quake SR. Universal noninvasive detection of
solid organ transplant rejection. Proc Natl Acad Sci U S A. 2011;108(15):6229-34,
http://dx.doi.org/10.1073/pnas.1013924108.
http://dx.doi.org/10.1073/pnas.101392410...
). A test that directly measures the extent of cardiac damage, along with the
AlloMap® test, which measures the signal of the host immune system indicating
rejection, may further increase the sensitivity and specificity of detecting rejection.
Mass Spectrometry
Mass spectrometry can analyze proteins in different body fluids and now includes tandem
spectrometry to obtain new protein sequence information (172172. Diamandis EP. Mass spectrometry as a diagnostic and a cancer biomarker
discovery tool: opportunities and potential limitations. Mol Cell Proteomics. 2004;3(4):367-78,
http://dx.doi.org/10.1074/mcp.R400007-MCP200.
http://dx.doi.org/10.1074/mcp.R400007-MC...
). Mass spectrometry of bronchoalveolar lavage fluid has proved useful in diagnosing
bronchiolitis obliterans syndrome in lung transplant recipients with 94% specificity and 74%
sensitivity (173173. Zhang Y, Wroblewski M, Hertz MI, Wendt CH, Cervenka TM, Nelsestuen GL. Analysis
of chronic lung transplant rejection by MALDI-TOF profiles of bronchoalveolar lavage fluid.
Proteomics. 2006;6(3):1001-10, http://dx.doi.org/10.1002/pmic.200500105.
http://dx.doi.org/10.1002/pmic.200500105...
).
Flow Cytometry
Flow cytometry and Luminex-based techniques measure specific cells and their subsets along with
the production of cytokines and other cell functions. These techniques are useful in transplantation
(174174. Pei R, Lee JH, Shih NJ, Chen M, Terasaki PI. Single human leukocyte antigen
flow cytometry beads for accurate identification of human leukocyte antigen antibody specificities.
Transplantation. 2003;75(1):43-9,
http://dx.doi.org/10.1097/00007890-200301150-00008.
http://dx.doi.org/10.1097/00007890-20030...
). Measuring the concentrations of T- and B-lymphocytes
and their subsets can help determine the level of immunosuppression and the response to
immunosuppressive treatment. The diagnostic specificity and the amount of antibodies can also be
determined. Limitations include inter-laboratory variability and the inability to cover all the
alleles in the population. Antibodies against HLA in the transplanted organ are associated with
chronic rejection and a lower rate of organ survival. In 243 cardiac transplant patients with no
DSAs before transplantation, Smith et al. found that the development of DSAs was associated with a
marked decrease in survival (hazard ratio, 4.35), independent of the ability to fix complement. More
patients with DSAs died of CAV or acute rejection than did patients with non-DSAs. Although the
authors were not able to show a cause-effect relationship between DSAs and CAV, having both DSAs and
CAV was associated with a worse prognosis. The results of this study also emphasized the importance
of regular monitoring for the presence of DSAs, starting in the first year after transplantation
(175175. Smith JD, Banner NR, Hamour IM, Ozawa M, Goh A, Robinson D, et al. De novo
donor HLA-specific antibodies after heart transplantation are an independent predictor of poor
patient survival. Am J Transplant. 2011;11(2):312-9.).
Antibodies to non-HLA antigens are also associated with an increased risk of CAV. Kalache et al.
reported that the myosin-specific antibodies and T-cells were independently associated with the
development of CAV (odds ratio, 45; 95% CI, 4 to 500) and can be used as predictors of outcome in
cardiac transplant recipients (176176. Kalache S, Dinavahi R, Pinney S, Mehrotra A, Cunningham MW, Heeger PS.
Anticardiac myosin immunity and chronic allograft vasculopathy in heart transplant recipients.
J Immunol. 2011;187(2):1023-30, http://dx.doi.org/10.4049/jimmunol.1004195.
http://dx.doi.org/10.4049/jimmunol.10041...
).
Concentrations of alloreactive T-cells derived from the memory pool can also be used to predict
outcomes in transplant patients. Ongoing multicenter studies in heart and kidney transplant
recipients are assessing the feasibility and standardization of measuring memory T-cells to guide
the management of immunosuppressants. However, the high cost and complexity of this technique are
major obstacles to its widespread implementation (135135. Cravedi P, Heeger PS. Immunologic monitoring in transplantation revisited. Curr
Opin Organ Transplant. 2012;17(1):26-32,
http://dx.doi.org/10.1097/MOT.0b013e32834ee402.
http://dx.doi.org/10.1097/MOT.0b013e3283...
).
Summary and Future Translational Research Directions in Heart Transplantation
In this review, we have presented current challenges and approaches to the care of children who have received a heart transplant. Specifically, we have reviewed the mechanisms of cardiac transplant rejection and the roles of endomyocardial biopsy and biomarkers, such as biomarkers of inflammation, cardiomyocyte injury, or stress, in detecting cardiac graft rejection. We have also reviewed CAV. Lastly, we addressed the role of genetic analyses, including genome-wide association studies, gene expression profiling using entities like AlloMap®, and adenosine triphosphate release as a measure of immune function using the Cylex® ImmuKnow™ cell function assay.
Clearly, there has been significant progress in the care of post-transplant pediatric patients
using the approaches described above. One theme that has emerged is the importance of further
investigations of existing cardiac biomarkers, whether circulating proteins or genetic biomarkers,
and identifying novel cardiac biomarkers to better predict the clinical course after heart
transplantation in children. The goal is to minimize the need for resource-intense and potentially
risky myocardial biopsies and to better guide therapeutic interventions. Beyond 1 year of life, most
pediatric heart transplants occur in children with cardiomyopathy. Recent reports show the knowledge
gap regarding cardiac biomarkers in pediatric cardiomyopathy, heart failure, or congenital
cardiovascular malformations, which results from a lack of large multisite clinical trials (177177. Wilkinson JD, Diamond M, Miller TL. The promise of cardiovascular biomarkers in
assessing children with cardiac disease and in predicting cardiovascular events in adults. Progress
in Pediatric Cardiology. 2011;32(5):25-34,
http://dx.doi.org/10.1016/j.ppedcard.2011.06.006.
http://dx.doi.org/10.1016/j.ppedcard.201...
). If noninvasive biomarkers could reliably improve clinical
monitoring and prognosis, both before and after heart transplantation, they could serve as important
surrogate endpoints in both observational studies and clinical trials. New investigations into
mechanistic pathways, as identified by existing and novel cardiac biomarkers and recipient genotypes
as biomarkers (including the expression of genetic polymorphisms), could result in important
advances in the monitoring of these children and result in improved outcomes for children receiving
a heart transplant (178178. Kantor PF, Rusconi PG, Lipshultz SE, Mital S, Wilkinson JD, Burch M. Current
applications and future needs for biomarkers in pediatric cardiomyopathy and heart failure: Summary
from the second international conference on pediatric cardiomyopathy. Progress in Pediatric
Cardiology. 2011;32(1):11-4, http://dx.doi.org/10.1016/j.ppedcard.2011.06.003.
http://dx.doi.org/10.1016/j.ppedcard.201...
,179179. Kantor PF, Rusconi PG. Biomarkers in pediatric heart failure: Their role in
diagnosis and evaluating disease progression. Progress in Pediatric Cardiology. 2011;31(1):53-7,
http://dx.doi.org/10.1016/j.ppedcard.2010.11.012.
http://dx.doi.org/10.1016/j.ppedcard.201...
).
While continued translational research regarding mechanistic and genetic studies in children who
have received a heart transplant is vital to improved patient outcomes, there is a complementary
research approach that also needs to be vigorously pursued to result in the best evidence-based
approach to the evaluation, monitoring, and decision making regarding the listing of these children
for heart transplant. Many risk factors and outcome predictors in children eligible for cardiac
transplantation can be identified early in these children's clinical course. Since the
mid-1990s, the National Heart, Lung, and Blood Institute-funded Pediatric Cardiomyopathy Registry
(PCMR) has conducted epidemiological and longitudinal follow-up studies of thousands of children
with cardiomyopathy, which is the most common indication for heart transplantation after infancy
(180180. Grenier MA, Osganian SK, Cox GF, Towbin JA, Colan SD, Lurie PR, et al. Design
and implementation of the North American Pediatric Cardiomyopathy Registry. Am Heart J. 2000;139(2
Pt 3):S86-95.,181181. Lipshultz SE, Sleeper LA, Towbin JA, Lowe AM, Orav EJ, Cox GF, et al. The
incidence of pediatric cardiomyopathy in two regions of the United States.
N Engl J Med. 2003;348(17):1647-55.). During
this period, the PCMR has reported risk factors for either death or heart transplant using their
pre-transplant dataset. Additionally, the PCMR has combined their data with the peri- and
post-transplant data from the Pediatric Heart Transplant Study (PHTS) (182182. McGiffin DC, Naftel DC, Kirklin JK, Morrow WR, Towbin J, Shaddy R, et al.
Predicting outcome after listing for heart transplantation in children: comparison of Kaplan-Meier
and parametric competing risk analysis. Pediatric Heart Transplant Study Group. J Heart Lung
Transplant. 1997;16(7):713-22.
183. Canter C, Naftel D, Caldwell R, Chinnock R, Pahl E, Frazier E, et al. Survival
and risk factors for death after cardiac transplantation in infants. A multi-institutional
study. The Pediatric Heart Transplant Study. Circulation. 1997;96(1):227-31,
http://dx.doi.org/10.1161/01.CIR.96.1.227.
http://dx.doi.org/10.1161/01.CIR.96.1.22...
-184184. Shaddy RE, Naftel DC, Kirklin JK, Boyle G, McGiffin DC, Towbin JA, et al.
Outcome of cardiac transplantation in children. Survival in a contemporary
multi-institutional experience. Pediatric Heart Transplant Study. Circulation. 1996;94(9
Suppl):II69-73.) to better characterize the
clinical course and risk factors for the outcomes of these children from cardiomyopathy diagnosis to
post-cardiac transplant follow-up.
With regard to pediatric cardiomyopathy, the PCMR and the PCMR-PHTS collaborations have
identified the following predictors of the risk of transplant or death, which have not previously
been reported. These results could result in better evidence-based decisions regarding listing for
heart transplantation by pediatric cardiologists. In children with dilated cardiomyopathy, those
with a familial or myocarditis etiology had a very good survival experience versus
other etiologies, particularly idiopathic dilated cardiomyopathy (185185. Towbin JA, Lowe AM, Colan SD, Sleeper LA, Orav EJ, Clunie S, et al. Incidence,
causes, and outcomes of dilated cardiomyopathy in children. Jama. 2006;296(15):1867-76,
http://dx.doi.org/10.1001/jama.296.15.1867.
http://dx.doi.org/10.1001/jama.296.15.18...
). In a competing risk analysis of children with idiopathic dilated cardiomyopathy, age
>6 years at diagnosis, heart failure, left ventricular dilation, decreased left ventricular
function, and decreased height-for age predicted worse clinical outcomes (186186. Alvarez JA, Orav EJ, Wilkinson JD, Fleming LE, Lee DJ, Sleeper LA, et al.
Competing risks for death and cardiac transplantation in children with dilated cardiomyopathy:
results from the pediatric cardiomyopathy registry. Circulation. 2011;124(7):814-23,
http://dx.doi.org/10.1161/CIRCULATIONAHA.110.973826.
http://dx.doi.org/10.1161/CIRCULATIONAHA...
). However, in this same group, increased left ventricular dilation was
predictive of an increased risk of transplantation but not death. The conclusion was that left
ventricular dilation may be over emphasized in listing decisions in idiopathic cardiomyopathy
patients by pediatric cardiologists, whereas linear growth retardation may not be considered in
listing decisions, despite its risk for increased mortality.
In another PCMR study, it was found that children with myocarditis and impaired ejection function
at diagnosis and children without left ventricular dilation and increased septal thickness were most
likely to experience echocardiographic normalization (187187. Foerster SR, Canter CE, Cinar A, Sleeper LA, Webber SA, Pahl E, et al.
Ventricular remodeling and survival are more favorable for myocarditis than for idiopathic dilated
cardiomyopathy in childhood: an outcomes study from the Pediatric Cardiomyopathy Registry. Circ
Heart Fail. 2010;3(6):689-97,
http://dx.doi.org/10.1161/CIRCHEARTFAILURE.109.902833.
http://dx.doi.org/10.1161/CIRCHEARTFAILU...
).
Although hypertrophic cardiomyopathy is not regularly a criterion for cardiac transplantation
listing for children, PCMR results showed that children with hypertrophic cardiomyopathy who present
at less than 1 year of age have a very poor prognosis and should be considered for listing for heart
transplant (188188. Colan SD, Lipshultz SE, Lowe AM, Sleeper LA, Messere J, Cox GF, et al.
Epidemiology and cause-specific outcome of hypertrophic cardiomyopathy in children: findings from
the Pediatric Cardiomyopathy Registry. Circulation. 2007;115(6):773-81,
http://dx.doi.org/10.1161/CIRCULATIONAHA.106.621185.
http://dx.doi.org/10.1161/CIRCULATIONAHA...
). For those children with hypertrophic
cardiomyopathy in the setting of Noonan syndrome who present with heart failure at less than 6
months of age, the prognosis is even more dire. Although this group of patients is rarely listed or
transplanted, the PCMR data suggest a more aggressive clinical approach regarding listing for heart
transplant for these children in the absence of contraindications (189189. Wilkinson JD, Lowe AM, Salbert BA, Sleeper LA, Colan SD, Cox GF, et al.
Outcomes in children with Noonan syndrome and hypertrophic cardiomyopathy: A study from the
Pediatric Cardiomyopathy Registry. Am Heart J. 2012;164(3):442-8,
http://dx.doi.org/10.1016/j.ahj.2012.04.018.
http://dx.doi.org/10.1016/j.ahj.2012.04....
). For children with cardiomyopathy who have received a heart transplant, the combined
PCMR-PHTS pre- and post-transplant analyses are equally informative. These studies have determined
that a strategy of directing donors preferentially to the sickest children, as defined by the need
for intravenous inotropic or mechanical support, is appropriate (190190. Larsen RL, Canter CE, Naftel DC, Tressler M, Rosenthal DN, Blume ED, et al. The
impact of heart failure severity at time of listing for cardiac transplantation on survival in
pediatric cardiomyopathy. J Heart Lung Transplant. 2011;30(7):755-60,
http://dx.doi.org/10.1016/j.healun.2011.01.718.
http://dx.doi.org/10.1016/j.healun.2011....
). Finally, PCMR-PHTS analyses determined that children with myocarditis who received a
heart transplant had significantly higher mortality post-transplantation compared with children with
cardiomyopathy from a non-myocarditis etiology (191191. Pietra BA, Kantor PF, Bartlett HL, Chin C, Canter CE, Larsen RL, et al. Early
predictors of survival to and after heart transplantation in children with dilated cardiomyopathy.
Circulation. 2012;126(9):1079-86,
http://dx.doi.org/10.1161/CIRCULATIONAHA.110.011999.
http://dx.doi.org/10.1161/CIRCULATIONAHA...
). These
findings suggest that children with myocarditis listed for transplant should be maintained medically
until acute inflammation resolves before they undergo heart transplantation. All these results
suggest the importance of robust longitudinal clinical research studies, in combination with
immunologic, genetic, and circulation biomarker studies, in the pre- and peri-transplant period to
improve the outcomes of children with conditions that could be treated with cardiac
transplantation.
FINAL CONSIDERATIONS
As discussed here in the different sections, there has been some success in identifying limitations in solid-organ transplant-related issues. However, the potential to expand research and to resolve these issues is great. In terms of AMR, an area requiring further attention is the allograft injury caused by the binding of C1q to DSAs. Therefore, therapies that target C1q can help prevent chronic allograft injury. The recurrence of FSGS can be prevented by understanding the mechanism of proteinuria and identifying the cPF, which can then be targeted for therapy.
We speculate that a combination of genomics and proteomics will identify a large number of biomarkers and provide information that may further improve our ability to predict outcomes in transplantation, thereby facilitating a new branch of personalized medicine for transplant recipients.
At the bedside, the large amount of data generated by the techniques listed above should be combined with the subjective clinical information that is not always suitable for mathematical analysis. New statistical analyses may need to be created for accurate evaluation and to facilitate the transition of information to clinical practice.
Only through a strong interdisciplinary effort, as mentioned above, will a translational approach to patient care advance knowledge in the field of pediatric transplantation. To this aim, we have described the basis for a strong clinical research effort in transplantation that will generate new evidence-based tools. At the same time, we recommend the implementation of a “bedside to the bench” approach with the goal of evaluating and caring for each patient with individualized treatments. This approach will involve the development and validation of minimally invasive assays that can predict transplant outcomes and guide therapeutic decisions in each of these highly vulnerable children.
This study was supported in part by grants from the National Institutes of Health (HL072705, HL078522, HL053392, CA127642, CA068484, HD052104, AI50274, CA068484, HD052102, HL087708, HL079233, HL004537, HL087000, HL007188, HL094100, HL095127, HD80002), the Children's Cardiomyopathy Foundation, the Women's Cancer Association, the Lance Armstrong Foundation, the STOP Children's Cancer Foundation, the Scott Howard Fund, and the Michael Garil Fund. A.F. is supported by the US National Institutes of Health (NIH) (DK82636), the Forest County Potawatomi Community Foundation, the Max and Yetta Karasik Family Foundation, the Diabetes Research Institute Foundation (diabetesresearch.org), the Nephcure Foundation, and the Peggy and Harold Katz Family Foundation.
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