Trafficking of Intra-Graft Donor T Cells After Skin Transplantation in Mice.: Abstract# B759

It is firmly established that the skin contains T lymphocytes including significant numbers of FoxP3+ regulatory T cells (Tregs). However, their role in skin transplantation is still unknown. Recent evidence has been provided by W. Burlingham's laboratory suggesting that intra-graft T cells may influence the alloresponse and rejection process (bi-directional alloimmunity). In this study, we investigated the trafficking of intra-graft donor T cells to the recipient's lymphoid organs after skin transplantation in mice. To test this C57BL/6 (B6) mice received a skin transplant from a double transgenic B6 donor whose T cells expressed DSred while FoxP3 expression was associated with GFP (Tregs being double positive). At different time points after transplantation, cell suspensions of recipients' lymph nodes, spleen and thymus were prepared. The presence and characterization of fluorescent donor cells was investigated using Image Stream (Amnis) technology. First, the presence of T cells (DSred+ FoxP3-) was detected only at d4-d7 posttransplantation i.e. after skin graft revascularization and essentially in the host's thymus. On the other hand, double positive (DSred+ FoxP3+) Tregs were found in all recipient's lymphoid organs. Surprisingly, high frequencies of single positive GFP+ cells were found in both ipsilateral lymph nodes and thymus. The nature of these cells is being investigated. In summary, our results show that most T cells leaving the graft are Tregs spreading through all recipient's lymphoid organs while intra-graft effector T cells migrate primarily to the host's thymus.