Allospecific rejection of MHC class I-deficient bone marrow by CD8 T cells

摘要

Avoidance of long-term immunosuppression is a desired goal in organ transplantation. Mixed chimerism offers a promising approach to tolerance induction, and we have aimed to develop low-toxicity, non-immunodepleting approaches to achieve this outcome. In a mouse model achieving fully MHC-mismatched allogeneic bone marrow engraftment with minimal conditioning (3 Gy total body irradiation followed by anti-CD154 and T cell-depleted allogeneic bone marrow cells), CD4 T cells in the recipient are required to promote tolerance of pre-existing alloreactive recipient CD8 T cells and thereby permit chimerism induction. We now demonstrate that mice devoid of CD4 T cells and NK cells reject MHC class-I deficient and class I/class II-deficient marrow in a CD8 T cell-dependent manner. This rejection is specific for donor alloantigens, since recipient hematopoiesis is not affected by donor marrow rejection and MHC class-I deficient bone marrow that is syngeneic to the recipient is not rejected. Recipient CD8 T cells are activated and develop cytotoxicity against MHC class I-deficient donor cells in association with rejection. These data implicate a novel CD8 T cell-dependent bone marrow rejection pathway, wherein recipient CD8 T cells indirectly activated by donor alloantigens promote direct killing, in a TCR-independent manner, of class I-deficient donor cells.