TOL and MONO patients exhibit very similar indirect pathway responses whereas the levels of circulating nave B cells were very different. == The tvDTH assay measures indirect pathway T-cell regulation in a B-cell-independent manner == Because nave B cells are elevated and linked-suppression is strongest in the TOL patients, we next sought to determine if B cells played any role in linked-suppression of cell-mediated immunity detected in the tvDTH assay. > CR; p < 0.005). This pattern differed from that seen in circulating nave B-cell numbers and in a cross-platform biomarker analysis, where patients on monotherapy were not ranked closest to TOL patients, but rather were indistinguishable from chronically rejecting patients. Cross-sectional analysis of the indirect pathway revealed a spectrum in T-regulatory:T-effector balance, ranging from TOL patients having predominantly regulatory responses to CR patients having predominantly effector responses. Therefore, the indirect pathway measurements reflect a distinct aspect of tolerance from the recently reported elevation of circulating nave B cells, which was apparent only in recipients off immunosuppression. Keywords:DTH assay, human, immunological monitoring, indirect pathway, renal transplantation, transplant tolerance == Introduction == We have cFMS-IN-2 previously reported TGF- or IL10-producing regulatory indirect pathway T-cell responses in patients with long-term excellent graft function after kidney or liver transplantation and withdrawal of all immunosuppression (1). However, the Th3/TGF-dependent form of tolerance to a kidney transplant in monkeys and humans was found to be metastable (24) and eventually some grafts underwent acute cellular, antibody-mediated or chronic rejection (CR). It is now well established that Th17 responses are induced when cells are exposed to TGF in the presence of IL6, so metastable tolerance to allografts based on Th3/TGF cells may be prone to develop into Th17-driven CR, a phenomenon most clearly demonstrated in clinical lung transplants (5). A more stable form of tolerance may therefore involve both Th3/TGF- and Tr1/IL10-T regulatory (Treg)-cell responses (6). How tolerance at the T- and B-cell levels are interconnected is not yet clear. Much interest in the possible role of B regulatory cells (Bregs; Ref.7) has been generated by the recent discovery that renal cFMS-IN-2 transplant tolerance in rodents (8,9) and humans (1012) is characterized by an increase in both intragraft and systemic B cells. Whether this increase is a driving force for tolerance induction or whether it simply helps to stabilize tolerance in the absence of immunosuppression has not been established. We hypothesized that the regulatory indirect pathway T-cell response to donor alloantigens in kidney transplant recipients is a progressive indicator of tolerance, that is, one which becomes more pronounced in a patient population that receives less immunosuppression while maintaining excellent graft function. We studied patients in categories ranging from most tolerant (identical twin isograft) to least tolerant (chronic allograft rejection) and including three in between groups: patients with well-functioning renal allografts who were taking standard, minimal or zero (functionally tolerant) immunosuppressive medications. We compared the results of indirect pathway monitoring with the analysis of circulating B cells and Bcell-biased probability of being tolerant (POT) scores (10,11). == Materials and Methods == == Source of cells and reagents == Renal transplant recipients and living donors from three transplant centers (Emory University, Atlanta, GA, USA; University of WisconsinMadison, WI, USA and Swedish Medical Center, Seattle, WA, USA) were enrolled in the ITN507ST Mouse monoclonal to ERBB3 observational trial, Identification and Mechanistic Investigations of Tolerant Kidney Transplant Patients (Clinicaltrials.gov identifierNCT01338779) using institutional review board-approved informed written consent procedures at each institution. Patients were assigned to groups based on clinical status as previously described (10). Patients enrolled in four of the groupsidentical twin (TWINtransplant from an identical twin donor), clinically tolerant (TOLno immunosuppression medication for >1 year), steroid monotherapy (MONO, 10 mg/day of prednisone) and standard immunosuppression (SIincluding any combination of standard post-transplant immunosuppression) all had stable and normal renal function (within 25% of baseline) at the time of enrollment. All patients in the CR group had moderately impaired or gradually deteriorating renal function (GFR < 40 mL/min or creatinine >50% above baseline value), had a previous biopsy showing chronic allograft nephropathy (BANFF 1997 criteria) and continued to receive immunosuppressive medications, but were not on dialysis. Peripheral blood samples were collected in citrate and processed using Ficoll-Hypaque to isolate peripheral blood mononuclear cells (PBMC). PBMC were either used immediately or cryopreserved before analysis. Antigens used to test for indirect pathway responses included: donor PBMC or spleen cell sonicates, as cFMS-IN-2 described elsewhere (1); HLA-A1, HLA-B62 and HLA-B57 single antigen Luminex beads (One Lambda, Inc., Canoga Park, CA, USA), a kind gift of Dr. Junchao Cai, Paul Terasaki Foundation, Los Angeles, CA, USA and HLA-B allopeptides p37MA (DSDAASPRMAPRAPWIEQ) and p37TE (DSDAASPRTEPRAPWIEQ), described elsewhere (4). Antibodies co-injected with PBMC: rabbit anti-human TGF-, goat anti-human IL-10 or control normal rabbit IgG or goat IgG (all R&D Systems, Minneapolis, MN, USA, all at 25 g/injection), anti-human IFN (eBioscience, San Diego, CA, USA, 5 g/injection) or anti-human IL17 (R&D Systems, 5.