iNKT cell activation plus T‐cell transfer establishes complete chimerism in a murine sublethal bone marrow transplant model

Transplant tolerance induction makes it possible to preserve functional grafts for a lifetime without immunosuppressants. One powerful method is to generate mixed hematopoietic chimeras in recipients by adoptive transfer of donor‐derived bone marrow cells (BMCs). In our murine transplantation model, we established a novel method for mixed chimera generation using sublethal irradiation, CD40‐CD40L blockade, and invariant natural killer T‐cell activation. However, numerous BMCs that are required to achieve stable chimerism makes it difficult to apply this model for human transplantation. Here, we show that donor‐derived splenic T cells could contribute to not only the reduction of BMC usage but also the establishment of complete chimerism in model mice. By cotransfer of T cells together even with one‐fourth of the BMCs used in our original method, the recipient mice yielded complete chimerism and could acquire donor‐specific skin‐allograft tolerance. The complete chimeric mice did not show any remarks of graft versus host reaction in vivo and in vitro. Inhibition of the apoptotic signal resulted in increase in host‐derived CD8⁺ T cells and chimerism brake. These results suggest that donor‐derived splenic T cells having veto activity play a role in the depletion of host‐derived CD8⁺ T cells and the facilitation of complete chimerism.