Regulatory functions of alloreactive Th2 clones in human renal transplant recipients

Background. Chronic allograft rejection is the major clinical problem in organ transplantation. There is evidence that indirect T cell recognition of donor-specific HLA peptides may play an important role in the immunopathogenesis of chronic allograft rejection. We have recently shown that HLA allopeptide-specific T cell clones generated from renal transplant recipients with chronic allograft nephropathy are of the Th1 phenotype, while those from stable patients are Th2. There is evidence in experimental animal models of autoimmunity and transplantation that Th2 cells may function to regulate immune responses, but the biological relevance of these observations in humans has not been reported. Methods. The purpose of this study was to investigate the putative regulatory functions of alloreactive human Th2 clones. HLA-DR allopeptide-specific Th1 and Th2 cell clones were generated from peripheral blood lymphocytes of human renal allograft recipients with chronic allograft nephropathy (CAN) or with stable renal function (SRF), respectively. Results. An in vitro co-culture system showed that the proliferative responses of Th1 clones from patients with CAN were significantly inhibited by the Th2 clones in response to the donor-derived HLA allopeptides. In addition, co-culture of the Th2 clones inhibited cytokine production (IFN-γ) by the Th1 clones in response to the donor-specific peptides. The regulatory functions of Th2 clones were antigen-specific since they only occurred when both the Th1 and Th2 clones were reactive to the same HLA-DR allopeptide, and were mediated by IL-4 and IL-10. Conclusions. This is the first demonstration, to our knowledge, indicating that Th2 cells may function to regulate indirect Th1 alloimmune responses that are critical for the progression of CAN in humans.