Adoptive transfer of double negative T regulatory cells induces B-cell death in vivo and alters rejection pattern of rat-to-mouse heart transplantation

Background: Antibody-mediated hyperacute and acute graft rejection are major obstacles in achieving long-term graft survival in xenotransplantation. It is well documented that regulatory T (Treg) cells play a very important role in regulating immune responses to self and non-self antigens. Our previous studies have shown that TCR alpha beta(+)CD3(+)CD4(-)CD8(-) (double negative, DN)-Treg cells can suppress anti-donor T-cell responses and prolong graft survival in allo- and xenotransplantation models. We have demonstrated that DN-Treg cells can induce B-cell apoptosis in vitro through a perforin-dependent pathway. Methods: B6 mice received rat heart grafts, followed by 14 days of LF15-0195 treatment. Some mice received Lewis rat cell activated DN-Treg cells after LF treatment. DN-Treg cells, purified from perforin(-/-) mice and from B6 mice pre-immunized with third party rat cells, were used as controls. Results: In this study, we investigated the possibility that adoptive transfer of xenoreactive DN-Treg cells could suppress B cells in vivo, thus prolonging xenograft survival. We found that apoptotic death of B cells significantly increased after adoptive transfer of DN-Treg cells. In addition, anti-donor IgG subtypes were significantly inhibited in the DN-Treg cell-treated group, in which the rejection pattern was altered towards cellular-mediated rejection rather than antibody-mediated acute vascular rejection. However, perforin-deficient DN-Treg cells failed to induce B-cell death and to prolong heart graft survival, indicating a perforin-dependent mechanism contributes to B-cell death in vivo. Conclusion: This study suggests that adoptive transfer of xenoreactive DN-Treg cells can inhibit B-cell responses in vivo. DN-Treg cells may be valuable in controlling B-cell responses in xenotransplantation.