Immune monitoring and biomarkers to predict chronic allograft dysfunction
2010; Elsevier BV; Volume: 78; Linguagem: Inglês
10.1038/ki.2010.425
ISSN1523-1755
Autores Tópico(s)Liver Disease and Transplantation
ResumoLate failure of a kidney transplant continues to be a major problem after transplantation, in spite of more potent immunosuppressive strategies and the focus of clinical management shifting toward prolonging long-term graft survival. It is now recognized that graft failure occurs because of two major complications: death with a functioning graft and intrinsic allograft failure. Recent studies of late kidney graft loss have indicated a complexity of findings, including etiologies that are both immune and non-immune. These studies suggest that late graft failure is not an inevitable fact and that further investigation into the etiology of transplant graft failure may lead to a new understanding of the biology that will provide novel therapeutic strategies and biomarkers. In this review, we will focus on late allograft failure due to intrinsic injury to the transplant. The role of immune monitoring will be discussed in the context of monitoring for ongoing injury or for identifying late injury. A variety of methodologies have been used, including genomics, proteomics, and metabolomics, not only for monitoring allograft injury but also for identifying markers of graft failure that are more sensitive than serum creatinine. The available studies, as they relate to late or chronic graft injury, will also be reviewed. Late failure of a kidney transplant continues to be a major problem after transplantation, in spite of more potent immunosuppressive strategies and the focus of clinical management shifting toward prolonging long-term graft survival. It is now recognized that graft failure occurs because of two major complications: death with a functioning graft and intrinsic allograft failure. Recent studies of late kidney graft loss have indicated a complexity of findings, including etiologies that are both immune and non-immune. These studies suggest that late graft failure is not an inevitable fact and that further investigation into the etiology of transplant graft failure may lead to a new understanding of the biology that will provide novel therapeutic strategies and biomarkers. In this review, we will focus on late allograft failure due to intrinsic injury to the transplant. The role of immune monitoring will be discussed in the context of monitoring for ongoing injury or for identifying late injury. A variety of methodologies have been used, including genomics, proteomics, and metabolomics, not only for monitoring allograft injury but also for identifying markers of graft failure that are more sensitive than serum creatinine. The available studies, as they relate to late or chronic graft injury, will also be reviewed. Over the last decade, graft failure more than 3 months after transplantation has been ascribed to an entity called chronic allograft nephropathy. This term came into use through the Banff classification schema, which organized biopsy specimens into those with acute and chronic injuries.1Racusen L.C. Solez K. Colvin R.B. et al.The Banff 97 working classification of renal allograft pathology.Kidney Int. 1999; 55: 713-723Abstract Full Text Full Text PDF PubMed Scopus (2771) Google Scholar This histological picture included fibrosing changes in the biopsy interstitium, as well as tubular atrophy (TA). Inflammation, when present, was only assessed in regions of biopsy viability and was often referred to as 'chronic rejection'.2Azuma H. Tilney N.L. Immune and nonimmune mechanisms of chronic rejection of kidney allografts.J Heart Lung Transplant. 1995; 14: S136-S142PubMed Google Scholar These changes could also be accompanied by arterial thickening and, more recently, may have included the entity of transplant glomerulopathy.1Racusen L.C. Solez K. Colvin R.B. et al.The Banff 97 working classification of renal allograft pathology.Kidney Int. 1999; 55: 713-723Abstract Full Text Full Text PDF PubMed Scopus (2771) Google Scholar Thus, establishing criteria for allograft pathology could facilitate agreement and establish diagnostic standards to support clinical trials and the study of specific entities. However, it was recognized that many factors could contribute to allograft fibrosis, including hypertension, recurrent disease, ischemic injury, drug toxicity, infection such as BK nephropathy, and ongoing alloimmune injury; however, all these became synonymous with one term, 'chronic allograft nephropathy'. As such, various entities with different etiologies were lumped together, and various animal models were studied to simulate different aspects of human disease, all seemingly used to describe one entity.3Halloran P.F. Call for revolution: a new approach to describing allograft deterioration.Am J Transplant. 2002; 2: 195-200Crossref PubMed Scopus (94) Google Scholar The results were another revision of the Banff criteria, classifying in an isolated manner both interstitial fibrosis (IF) and TA in the absence of etiological factors in a biopsy as IF/TA.4Racusen L.C. Solez K. Colvin R. Fibrosis and atrophy in the renal allograft: interim report and new directions.Am J Transplant. 2002; 2: 203-206Crossref PubMed Scopus (67) Google Scholar Other 'chronic' lesions included chronic T-cell-mediated rejection, chronic antibody-mediated rejection,5Racusen L.C. Colvin R.B. Solez K. et al.Antibody-mediated rejection criteria – an addition to the Banff 97 classification of renal allograft rejection.Am J Transplant. 2003; 3: 708-714Crossref PubMed Scopus (947) Google Scholar as well as contributory entities to graft failure ('other'). Although these changes supported the notion that not all chronic allograft nephropathy was rejection, it continued to de-emphasize the need to understand the causes of injury that could be reversed or ameliorated. Recent studies, however, have suggested that individual diseases can be identified as the causes of late graft failure. These insights are critical if we are to formulate strategies for prevention and disease identification. A large single-center study of over 1000 recipients reviewed allograft biopsies over a 10-year period.6El-Zoghby Z.M. Stegall M.D. Lager D.J. et al.Identifying specific causes of kidney allograft loss.Am J Transplant. 2009; 9: 527-535Crossref PubMed Scopus (616) Google Scholar A total of 330 allografts were lost during this period, and of these, 46% were because of allograft failure. Nearly all of these individuals had an allograft biopsy in a median of 4.7 months before graft loss. In all, 95% of individuals with failing allografts had an identifiable diagnosis—this included 37% of such failures due to transplant glomerulopathy and recurrent disease, 12% with acute rejection, and 31% with a diagnosis of IF/TA. Of those with IF/TA, 80% of biopsy samples had an ascribable cause to their fibrosis, including such entities as BK polyomavirus nephropathy, ongoing cellular or antibody-mediated rejection, or recurrent pyelonephritis. Another surprising feature of these data was the lack of frequency of calcineurin inhibitor toxicity. Although calcineurin inhibitor use has been attributed to be commonly seen in kidney allograft recipients, and is a key factor to graft loss,7Nankivell B.J. Borrows R.J. Fung C.L. et al.The natural history of chronic allograft nephropathy.N Engl J Med. 2003; 349: 2326-2333Crossref PubMed Scopus (1661) Google Scholar only 0.6% of allografts failed because of calcineurin inhibitor toxicity. Thus, allograft failure, in the current generation of immunosuppression, can take on many etiologies, and immune-mediated injury is one of them. Strategies that can assist in diagnosis of these etiologies are important adjuncts to biopsy diagnosis and are discussed below. A recent consortium study of failing allografts and their biopsies (the Decline in Kidney Allograft Function (DeKAF) study) has suggested that, although IF/TA may be uniformly present on biopsy, histopathological subscoring by cluster analysis can identify groups of patients with varying outcomes.8Matas A.J. Leduc R. Rush D. et al.Histopathologic clusters differentiate subgroups within the nonspecific diagnoses of CAN or CR: preliminary data from the DeKAF Study.Am J Transplant. 2009; 9: 315-323Google Scholar Indeed, the presence of tubulitis, interstitial inflammation, and vascular lesions was associated with worse prognosis. Similarly, a study of 234 biopsy samples for cause associated Banff's scoring patterns into patterns of disease, including microcirculation change, tubulointerstitial inflammation, and tubulointerstitial scarring, supporting the notion that grouping of related lesions into diagnoses can explain the stress on various compartments in the kidney and may guide the interpretation of the biology of the lesion by acknowledging their relationships.9Sis B. Einecke G. Chang J. et al.Cluster analysis of lesions in nonselected kidney transplant biopsies: microcirculation changes, tubulointerstitial inflammation and scarring.Am J Transplant. 2010; 10: 421-430Crossref PubMed Scopus (72) Google Scholar The development of donor-specific alloantibody has long been recognized as a negative prognostic factor in graft survival.10Halloran P.F. Schlaut J. Solez K. et al.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: 550-555Crossref PubMed Scopus (305) Google Scholar With the detection of C4d deposition in the allograft as a marker of antibody deposition and complement activation, it is now recognized that alloantibody can be a critical cause of late graft failure (reviewed by Colvin and Smith11Colvin R.B. Smith R.N. Antibody-mediated organ-allograft rejection.Nat Rev Immunol. 2005; 5: 807-817Crossref PubMed Scopus (393) Google Scholar). Although controversy still exists about the association of C4d and transplant glomerulopathy,12Akalin E. Dinavahi R. Dikman S. et al.Transplant glomerulopathy may occur in the absence of donor-specific antibody and C4d staining.Clin J Am Soc Nephrol. 2007; 2: 1261-1267Crossref PubMed Scopus (55) Google Scholar the use of molecular analysis of allograft biopsies suggests that endothelial cell activation detected by gene expression is strongly associated with graft failure, even in the absence of C4d staining.13Sis B. Jhangri G.S. Bunnag S. et al.Endothelial gene expression in kidney transplants with alloantibody indicates antibody-mediated damage despite lack of C4d staining.Am J Transplant. 2009; 9: 2312-2323Crossref PubMed Scopus (388) Google Scholar Thus, it is becoming apparent that screening for alloantibody is critical if we are to make any impact on antibody-mediated late injury. This will be discussed in more depth below. A number of studies have indicated that inflammation in the allograft is strongly associated with poorer graft outcome. In an analysis of nearly 300 protocol biopsy samples at 1-year after transplantation, Cosio et al.14Cosio F.G. Grande J.P. Wadei H. et al.Predicting subsequent decline in kidney allograft function from early surveillance biopsies.Am J Transplant. 2005; 5: 2464-2472Crossref PubMed Scopus (263) Google Scholar demonstrated that fibrosis and changes in inflammation, even in the absence of meeting criteria for acute rejection, together had a 8.5-fold higher risk of graft failure than did biopsies showing no histological abnormalities. Similarly, the presence of subclinical rejection, identified as Banff's acute cellular rejection or borderline inflammation, in 435 biopsies performed in recipients with normal function and without proteinuria at 6 months after transplantation, in association with IF/TA, was an independent risk factor for graft failure.15Moreso F. Ibernon M. Goma M. et al.Subclinical rejection associated with chronic allograft nephropathy in protocol biopsies as a risk factor for late graft loss.Am J Transplant. 2006; 6: 747-752Crossref PubMed Scopus (266) Google Scholar These types of studies, as well as recent data implicating that inflammation in areas of scarring and atrophy may contribute to graft failure,16Mengel M. Reeve J. Bunnag S. et al.Scoring total inflammation is superior to the current Banff inflammation score in predicting outcome and the degree of molecular disturbance in renal allografts.Am J Transplant. 2009; 9: 1859-1867Crossref PubMed Scopus (127) Google Scholar emphasize the need to identify ongoing inflammation in the allograft even in the absence of functional impairment or abnormality. Using allograft histology as the 'gold standard', a number of approaches have been suggested as non-invasive strategies for diagnosis and monitoring.17Cravedi P. Mannon R.B. Non-invasive methods to assess the risk of kidney transplant rejection.Expert Rev Clin Immunol. 2009; 5: 535-546Crossref PubMed Scopus (15) Google Scholar,18Mannon R.B. Kirk A.D. Beyond histology: novel tools to diagnose allograft dysfunction.Clin J Am Soc Nephrol. 2006; 1: 358-366Crossref PubMed Scopus (28) Google Scholar A major issue in the literature is that many of the studies are single center or consist of small numbers of patients from multiples centers and have yet to be validated in large patient populations. The recently conducted Clinical Trials in Organ Transplantation is a series of consortium studies in immune monitoring sponsored by the National Institute of Allergy and Infectious Diseases. Insights from these studies have to date been published in abstract format only, but suggest that, rather than an individual analyte, analysis should take into account a number of methodologies simultaneously to identify those at risk of ongoing immune injury.19Anglicheau D. Suthanthiran M. Noninvasive prediction of organ graft rejection and outcome using gene expression patterns.Transplantation. 2008; 86: 192-199Crossref PubMed Scopus (80) Google Scholar The opportunities for monitoring immune responses are plenty in kidney transplant recipients. These include assaying the serum, peripheral blood mononuclear cells (PBMCs), urine, and of course the allograft through biopsy. A distinct advantage for an assay is the utilization of a non-invasive method that may ultimately be easy to use and with limited risk or side effects when performing such tests. Methodology may be further affected by the immunosuppressive strategy. For example, with the increasing frequency of use of depletional induction therapy, PBMC availability may be limited, at least in the first 6 months after induction. As already noted, with inflammation in the first 6–12 months correlating with poor outcome, the lack of ability to survey this cell population is a limitation of this approach. Urine markers seem ideal as urine is in close contact with the microenvironment of the kidney. This approach may be complicated by the presence of proteinuria, an obvious marker of renal injury, or if there is severe allograft dysfunction. Thus, defining an approach needs to take into account not only reproducibility, cost, and ease but also the limitations of a specific site of sampling. A critical feature of late graft failure, as noted above, is an ongoing alloimmune response. This may be cellular or antibody mediated and may be observed as proinflammatory markers such as chemokines and cytokines, and as the presence of donor-specific antibody. Other contributory factors in late allograft failure may include elevated growth factor expression supporting a profibrotic milieu.20Mannon R.B. Therapeutic targets in the treatment of allograft fibrosis.Am J Transplant. 2006; 6: 867-875Crossref PubMed Scopus (68) Google Scholar Thus, we will review approaches taken on the basis of sample location, recognizing that an approach that uses multiple methods and biological specimens may ultimately be the required approach. The detection and monitoring of antibody-mediated injury has become a primary focus of postrenal transplant management, as evidence of the contribution of donor-specific antibody to injury continues to mount. In addition to the association of transplant glomerulopathy with endothelial cell injury and complement activation,21Einecke G. Sis B. Reeve J. et al.Antibody-mediated microcirculation injury is the major cause of late kidney transplant failure.Am J Transplant. 2009; 9: 2520-2531Crossref PubMed Scopus (536) Google Scholar graft failure has been associated strongly with alloantibody development.22Gerbase-DeLima M. Campos E.F. Tedesco-Silva H. et al.Anti-HLA class II antibodies and chronic allograft nephropathy.Clin Transpl. 2006; : 201-205PubMed Google Scholar, 23Lee P.C. Terasaki P.I. Takemoto S.K. et al.All chronic rejection failures of kidney transplants were preceded by the development of HLA antibodies.Transplantation. 2002; 74: 1192-1194Crossref PubMed Scopus (296) Google Scholar, 24Mao Q. Terasaki P.I. Cai J. et al.Extremely high association between appearance of HLA antibodies and failure of kidney grafts in a five-year longitudinal study.Am J Transplant. 2007; 7: 864-871Crossref PubMed Scopus (185) Google Scholar, 25Terasaki P.I. Ozawa M. Predicting kidney graft failure by HLA antibodies: a prospective trial.Am J Transplant. 2004; 4: 438-443Crossref PubMed Scopus (380) Google Scholar, 26Worthington J.E. Martin S. Al Husseini D.M. et al.Posttransplantation production of donor HLA-specific antibodies as a predictor of renal transplant outcome.Transplantation. 2003; 75: 1034-1040Crossref PubMed Scopus (260) Google Scholar A recent prospective multicenter study of over 1100 recipients of deceased donor kidney transplants demonstrated that human leukocyte antigen (HLA) class I antibodies present before transplantation were associated with a higher rate of delayed graft function and acute rejection episodes during the first 3 months after transplantation, and ultimately in an increased risk of graft loss by 3 years after transplantation.27Susal C. Dohler B. Sadeghi M. et al.HLA antibodies and the occurrence of early adverse events in the modern era of transplantation: a collaborative transplant study report.Transplantation. 2009; 87: 1367-1371Crossref PubMed Scopus (38) Google Scholar Although the majority of these studies support donor-specific HLA antibodies, preclinical studies in rodents suggest that autoantibodies to kidney antigens may also be of functional significance.28Dragun D. Muller D.N. Brasen J.H. et al.Angiotensin II type 1-receptor activating antibodies in renal-allograft rejection.N Engl J Med. 2005; 352: 558-569Crossref PubMed Scopus (678) Google Scholar,29Joosten S.A. van Dixhoorn M.G. Borrias M.C. et al.Antibody response against perlecan and collagen types IV and VI in chronic renal allograft rejection in the rat.Am J Pathol. 2002; 160: 1301-1310Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar As yet, the role of alloantibody detection in allograft monitoring has not been fully defined. Key factors include detecting the onset of development and specificity of donor-reactive antibody, as well as correlating their presence with specific tissue damage. Using luminex technology, the ability to detect HLA antibodies has occurred in about a third of recipients at 5 years after transplantation, and of these, about 30% have donor-specific antibody.30Lachmann N. Terasaki P.I. Budde K. et al.Anti-human leukocyte antigen and donor-specific antibodies detected by luminex posttransplant serve as biomarkers for chronic rejection of renal allografts.Transplantation. 2009; 87: 1505-1513Crossref PubMed Scopus (301) Google Scholar Serial monitoring indicates that the occurrence of repeated negative results over 5 years is associated with a high rate of graft survival (95%) compared with those recipients with HLA antibody (79%). With the increased sensitivity to detect alloantibodies, there is also a significant rise in cost. A monitoring protocol following transplantation that incorporated such assays would potentially identify the development of donor-specific antibody; however, in non-sensitized first-graft recipients, the frequency may be so low that the assay may not be cost-effective. Another critical concern is the limited effect in therapeutics following a positive study. Studies in sensitized patients suggest that B-lymphocyte depletion31Vo A.A. Lukovsky M. Toyoda M. et al.Rituximab and intravenous immune globulin for desensitization during renal transplantation.N Engl J Med. 2008; 359: 242-251Crossref PubMed Scopus (551) Google Scholar or plasma cell inhibition32Trivedi H.L. Terasaki P.I. Feroz A. et al.Abrogation of anti-HLA antibodies via proteasome inhibition.Transplantation. 2009; 87: 1555-1561Crossref PubMed Scopus (135) Google Scholar may reduce the production of anti-HLA antibodies and might be therefore effective in limiting chronic antibody-mediated injuries. However, additional studies are needed in a broad clinical population to identify their cost-effectiveness and clinical utility. The analysis of serum proteins has been another focus of blood sample monitoring. The upregulation of transforming growth factor-β (TGFβ)33Campistol J.M. Inigo P. Larios S. et al.Role of transforming growth factor-beta1 in the progression of chronic allograft nephropathy.Nephrol Dial Transplant. 2001; 16: 114-116Crossref PubMed Scopus (70) Google Scholar,34Sharma V.K. Bologa R.M. Xu G.P. et al.Intragraft TGF-beta 1 mRNA: a correlate of interstitial fibrosis and chronic allograft nephropathy.Kidney Int. 1996; 49: 1297-1303Abstract Full Text PDF PubMed Scopus (173) Google Scholar remains an inconsistent finding in recipients with biopsy-proven IF/TA.35Mas V. Maluf D. Archer K. et al.Establishing the molecular pathways involved in chronic allograft nephropathy for testing new noninvasive diagnostic markers.Transplantation. 2007; 83: 448-457Crossref PubMed Scopus (66) Google Scholar Indeed, our evaluation of connective tissue growth factor, a downstream effector of TGFβ, indicates that, although serum levels in a cohort of recipients were elevated compared with normal, healthy controls, these elevations did not distinguish acute from chronic allograft injury, whereas urinary levels had an excellent correlation to renal pathology.36Cheng O. Thuillier R. Sampson E. et al.Connective tissue growth factor is a biomarker and mediator of kidney allograft fibrosis.Am J Transplant. 2006; 6: 2292-2306Crossref PubMed Scopus (97) Google Scholar Other serum proteins upregulated in recipients with IF/TA include advanced glycation end products and oxidative stress proteins,37Raj D.S. Lim G. Levi M. et al.Advanced glycation end products and oxidative stress are increased in chronic allograft nephropathy.Am J Kidney Dis. 2004; 43: 154-160Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar C-reactive protein,38Sezer S. Akcay A. Ozdemir F.N. et al.Post-transplant C-reactive protein monitoring can predict chronic allograft nephropathy.Clin Transplant. 2004; 18: 722-725Crossref PubMed Scopus (22) Google Scholar sCD30 and neopterin,39Weimer R. Susal C. Yildiz S. et al.Post-transplant sCD30 and neopterin as predictors of chronic allograft nephropathy: impact of different immunosuppressive regimens.Am J Transplant. 2006; 6: 1865-1874Crossref PubMed Scopus (75) Google Scholar metzincins and related proteins,40Rodder S. Scherer A. Raulf F. et al.Renal allografts with IF/TA display distinct expression profiles of metzincins and related genes.Am J Transplant. 2009; 9: 517-526Crossref PubMed Scopus (55) Google Scholar and tribbles-1 protein, which is expressed by activated endothelial cells and antigen-presenting cells;41Ashton-Chess J. Giral M. Mengel M. et al.Tribbles-1 as a novel biomarker of chronic antibody-mediated rejection.J Am Soc Nephrol. 2008; 19: 1116-1127Crossref PubMed Scopus (68) Google Scholar however, these targets have not been validated in larger studies. Finally, proteomic approaches have largely focused on urine (see below) rather than serum in identifying, on a more global scale, proteins associated with chronic allograft injury. One approach to monitor and detect the extent of alloreactivity is the enzyme-linked immunosorbent spot, a variation of the standard enzyme-linked immunosorbent assay to detect cytokine produced by individual antigen-specific T cells. This assay has been studied over the past decade, providing a sensitive quantitation of antigen-specific T cells, and assessing immune responses in both animal models and in human solid organ transplant recipients (reviewed by Dinavahi and Heeger42Dinavahi R. Heeger P.S. T-cell immune monitoring in organ transplantation.Transplantation. 2009; 88: 1157-1158Crossref PubMed Scopus (7) Google Scholar). Enzyme-linked immunosorbent spot provides information on both cell frequency and cytokine function. Before transplantation, high frequencies of donor-reactive interferon-γ-producing cells have correlated with posttransplant acute rejection episodes.43Heeger P.S. Greenspan N.S. Kuhlenschmidt S. et al.Pretransplant frequency of donor-specific, IFN-gamma-producing lymphocytes is a manifestation of immunologic memory and correlates with the risk of posttransplant rejection episodes.J Immunol. 1999; 163: 2267-2275Crossref PubMed Google Scholar Serial monitoring after transplantation has also identified recipients at risk for acute rejection, with worse renal function in those with higher posttransplant frequencies of both donor and third-party responses.44Augustine J.J. Siu D.S. Clemente M.J. et al.Pre-transplant IFN-gamma ELISPOTs are associated with post-transplant renal function in African American renal transplant recipients.Am J Transplant. 2005; 5: 1971-1975Crossref PubMed Scopus (127) Google Scholar,45Hricik D.E. Rodriguez V. Riley J. et al.Enzyme linked immunosorbent spot (ELISPOT) assay for interferon-gamma independently predicts renal function in kidney transplant recipients.Am J Transplant. 2003; 3: 878-884Crossref PubMed Scopus (165) Google Scholar The ability to predict those more at risk for immune injury may provide an opportunity to intervene in the peritransplant period, as well as encourage more intense clinical follow-up. Further testing is underway to establish its role in immune therapy management. As an alternative approach, Kurian et al.46Kurian S.M. Heilman R. Mondala T.S. et al.Biomarkers for early and late stage chronic allograft nephropathy by proteogenomic profiling of peripheral blood.PLoS One. 2009; 4: e6212Crossref PubMed Scopus (64) Google Scholar have reported some fascinating results using combined gene microarray with tandem mass spectroscopy of RNA and proteins extracted from PBMCs from a small set of recipients with either mild IF/TA changes on allograft biopsy or more severe IF/TA. In mild disease, 1066 genes falling into 27 networks were identified, including, most commonly, those related to toll-like receptor signaling, stress-activated protein kinase/c-Jun NH2-terminal kinase, apoptosis, notch, and death receptor and interferon signaling. Finding 1066 significantly differentially expressed genes is a first indication that peripheral blood leukocyte transcript profiling is capable of classifying subjects defined by chronic allograft nephropathy biopsy histology. In moderate-to-severe IF/TA, 62 differentially expressed genes were identified. Proteomic analysis by shotgun tandem mass spectroscopy of PBMCs identified 206 differentially expressed proteins between Banff 0 and Banff grade I changes, including those linked to program cell death, cell signaling, and post-translational protein modification. In more severe 2–3 IF/TA, 282 proteins were differentially identified compared with Banff 0 biopsies and 95 proteins with grade 1 IF/TA, including proteins linked to cellular morphology, growth, proliferation, and signaling through extracellular signal-regulated protein kinase/mitogen-activated protein kinase, acute-phase reactants, peroxisome proliferator-activated receptor-α/retinoid X receptor alpha, and insulin-like growth factor. Importantly, using only differentially expressed proteins, moderate-to-severe IF/TA was correctly classified 83% of the time. Thus, a series of potential candidate biomarkers has been proposed to provide near-perfect identification of biopsy pathology. These transcripts and proteins are undergoing further validation in a comprehensive multicenter prospective clinical trial and may be a source of potential therapeutic targets for chronic allograft failure. The use of proteomic technology has changed the focus from a specific factor related to outcome to the identification of multiple factors that may be interrelated in allograft failure. Initial studies have primarily studied acute cellular rejection, distinguishing this injury from stable functioning allografts.47Clarke W. Silverman B.C. Zhang Z. et al.Characterization of renal allograft rejection by urinary proteomic analysis.Ann Surg. 2003; 237: 660-664Crossref PubMed Google Scholar, 48O'riordan E. Orlova T.N. Mei J.J. et al.Bioinformatic analysis of the urine proteome of acute allograft rejection.J Am Soc Nephrol. 2004; 15: 3240-3248Crossref PubMed Scopus (120) Google Scholar, 49Wittke S. Haubitz M. Walden M. et al.Detection of acute tubulointerstitial rejection by proteomic analysis of urinary samples in renal transplant recipients.Am J Transplant. 2005; 5: 2479-2488Crossref PubMed Scopus (126) Google Scholar Although not directly detecting chronic injury, one could suggest that the detection of ongoing acute injury may be beneficial in identifying allografts at risk for later graft failure. One approach has been through the use of liquid chromatography and tandem mass spectroscopy of urine specimens. In their initial report, Quintana et al.51Quintana L.F. Campistol J.M. Alcolea M.P. et al.Application of label-free quantitative peptidomics for the identification of urinary biomarkers of kidney chronic allograft dysfunction.Mol Cell Proteomics. 2009; 8: 1658-1673Crossref PubMed Scopus (83) Google Scholar identified 6000 protein ions from 32 recipients with IF/T
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