T follicular helper and memory cell responses and the mTOR pathway in murine heart transplantation

BACKGROUND The mammalian target of rapamycin (mTOR) inhibitors are valuable immunosuppressants in clinical transplantation; however, the mTOR regulation of allogeneic T-cell responses is not fully understood yet. Therefore, the objective of this study is to investigate the effects of T-cell-specific mTOR deletion on the allogeneic T-cell responses and heart transplant survival . METHODS BALB/c heart allografts , with or without BALB/c skin sensitization , were transplanted in the wild-type C57BL/6, Mtorfl/fl Cd4-Cre, Stat3 fl/flCd4-Cre, and Mtorfl/flStat3fl/flCd4-Cre mice. Graft survival and histology, as well as T-cell frequencies and phenotypes, were evaluated after transplantation. RESULTS In the absence of donor skin sensitization, long-term heart allograft survival was achieved in the Mtorfl/flCd4-Cre recipients, which was associated with significantly decreased frequencies of CD62L–CD44+ effector T cells and BCL-6+CXCR5+ T follicular helper (Tfh) cells in the periphery. Long-term heart allograft survival was also achieved in the donor skin-sensitized Mtorfl/flStat3fl/flCd4-Cre mice, whereas the heart allograft survival was prolonged in the donor skin-sensitized Mtorfl/flCd4-Cre and Stat3fl/flCd4-Cre mice. CONCLUSIONS mTOR is required for Tfh cell response in murine heart transplantation. T-cell-specific deletion of both mTOR and Stat3 abrogates the memory response to heart transplants . These findings help us to better understand the molecular mechanisms underlying the T cell immunity to transplanted organs.