The role of cyclosporine-induced autoreactive T lymphocytes in solid organ allograft survival and chronic rejection

Cyclosporine (CsA) has profound but paradoxical effects on the immune system. CsA can facilitate the induction of transplantation tolerance in some animal systems but it inhibits the clonal deletion of MHC class II autoreactive T cells. The present studies evaluated whether the autoreactive T cells participate in the induction of facilitated graft acceptance after CsA treatment by recognizing and eliminating activated allograft responsive T cells that express MHC class II determinants. Transfer of autoreactive T cells into naive Lewis rats pretreated with cyclophosphamide significantly prolonged the survival of heterotopic cardiac allografts from MHC-disparate BN strain donors. Following transfer of the autoreactivc T cells, there was a marked reduction in the frequency of alloreac-tive T lymphocytes responsive to donor alloantigens. The role of MHC class II autoreactive CD8+ Vβ 8.5⁺ T cells in facilitated graft acceptance was also supported by the findings that (1) treatment with anti-MHC class II antibody abrogated prolonged allograft survival after CsA therapy and (2) Vβ 8.5⁺ lymphocytes infiltrate the allograft during CsA therapy but are absent in the graft in non-CsA-treated control animals. Although these data are consistent with the hypothesis that autoreactive T cells prolong cardiac allograft survival after CsA treatment, the autoaggres-eive cells failed to inhibit the development of chronic rejection of both heart and skin allografts. These data suggest either that the autoreactive T cells do not inhibit immune mechanisms responsible for chronic graft rejection or that the autoaggressive lymphocytes may participate in and exacerbate chronic rejection of allografts. Taken together, the induction of MHC class II autoreactive T cells may provide a common fundamental mechanism explaining the paradoxical effects of CsA.