B-cell-dependent memory T cells impede nonmyeloablative mixed chimerism induction in presensitized mice.

Presensitization to HLA antigens limits the success of organ transplantation. The achievement of donor-specific tolerance via mixed chimerism could improve outcomes of transplantation in presensitized patients. In presensitized B-cell-deficient μMT B6 mice, we developed nonmyeloablative bone marrow transplantation (BMT) regimens that successfully tolerized presensitized T cells, achieving long-term (LT) multilineage chimerism and tolerance to donor-type skin. To apply these regimens in wild-type (WT) animals while avoiding antibody-mediated destruction of donor bone marrow cells, presensitized WT B6 mice were rested >2 years to allow alloantibody clearance. However, chimerism and tolerance were not reliably achieved in LT presensitized WT B6 mice in which alloantibody had declined to minimal or undetectable levels before BMT. Strong antidonor memory T-cell responses were detected in LT presensitized WT B6 mice after rejection of donor bone marrow (BM) occurred, whereas levels of alloantibody remained consistently low. In contrast, presensitized μMT B6 mice had diminished memory T-cell responses compared to WT B6 mice. These data implicate T-cell memory, but not alloantibody, in rejection of donor BM in LT presensitized WT mice.