Identifying transplant recipients in whom immunological tolerance is established or is developing would allow an individually tailored approach to their posttransplantation management. In this study, we aimed to develop reliable and reproducible in vitro assays capable of detecting tolerance in renal transplant recipients. Several biomarkers and bioassays were screened on a training set that included 11 operationally tolerant renal transplant recipients, recipient groups following different immunosuppressive regimes, recipients undergoing chronic rejection, and healthy controls. Highly predictive assays were repeated on an independent test set that included 24 tolerant renal transplant recipients. Tolerant patients displayed an expansion of peripheral blood B and NK lymphocytes, fewer activated CD4 + T cells, a lack of donor-specific antibodies, donor-specific hyporesponsiveness of CD4 + T cells, and a high ratio of forkhead box P3 to α-1,2-mannosidase gene expression. Microarray analysis further revealed in tolerant recipients a bias toward differential expression of B cell-related genes and their associated molecular pathways. By combining these indices of tolerance as a cross-platform biomarker signature, we were able to identify tolerant recipients in both the training set and the test set. This study provides an immunological profile of the tolerant state that, with further validation, should inform and shape drug-weaning protocols in renal transplant recipients.

No abstract

No abstract

Long-term allograft survival generally requires lifelong immunosuppression (IS). Rarely, recipients display spontaneous ''operational tolerance'' with stable graft function in the absence of IS. The lack of biological markers of this phenomenon precludes identification of potentially tolerant patients in which IS could be tapered and hinders the development of new tolerance-inducing strategies. The objective of this study was to identify minimally invasive blood biomarkers for operational tolerance and use these biomarkers to determine the frequency of this state in immunosuppressed patients with stable graft function. Blood gene expression profiles from 75 renal-transplant patient cohorts (operational tolerance/acute and chronic rejection/stable graft function on IS) and 16 healthy individuals were analyzed. A subset of samples was used for microarray analysis where three-class comparison of the different groups of patients identified a ''tolerant footprint'' of 49 genes. These biomarkers were applied for prediction of operational tolerance by microarray and real-time PCR in independent test groups. Thirty-three of 49 genes correctly segregated tolerance and chronic rejection phenotypes with 99% and 86% specificity. The signature is shared with 1 of 12 and 5 of 10 stable patients on triple IS and low-dose steroid monotherapy, respectively. The gene signature suggests a pattern of reduced costimulatory signaling, immune quiescence, apoptosis, and memory T cell responses. This study identifies in the blood of kidney recipients a set of genes associated with operational tolerance that may have utility as a minimally invasive monitoring tool for guiding IS titration. Further validation of this tool for safe IS minimization in prospective clinical trials is warranted.kidney transplantation ͉ microarray ͉ tolerant ͉ genomics ͉ immunosuppression titration D espite continuous improvement in renal allograft survival over the last decade, the half-life of renal allografts has increased marginally because of accrual of chronic graft nephropathy from drug-related nephrotoxicity and chronic rejection (1, 2). Patients facing life-long immunosuppression (IS) have increased risk of infection and malignancy (3), whereas insufficient immunosuppressive drug exposure or interruption usually increases rejection risk (4). However, spontaneous and long-term graft acceptance is observed in a small number of patients after solid-organ transplantation (5, 6), years after total withdrawal of immunosuppressive drugs, confirming that a clinical operational state of tolerance to a mismatched graft, described as ''a state of quiescence of the transplanted organ, functioning without a destructive immune response'' (7), can indeed occur and exist in humans. However, the frequency of this observation in the kidney transplant population is unknown and, currently, we cannot identify patients primed to develop this immune adaptation or monitor for the stability of this status of ''operational tolerance.'' The operationally tolerant kidney transpla...