Induction of donor-specific tolerance in sublethally irradiated recipients by gene therapy.

Donor-specific transplantation tolerance can be established through the induction of molecular chimerism following reconstitution of lethally irradiated mice with autologous bone marrow expressing retrovirally transduced allogeneic MHC antigens. Here, we set out to define nonmyeloablative host conditioning regimens that would allow for establishment of molecular chimerism and the induction of donor-specific tolerance. Recipient mice received various doses of whole-body irradiation, together with costimulatory blockade using anti-CD154 monoclonal antibody prior to reconstitution with syngeneic bone marrow cells transduced with retroviruses carrying the gene encoding H-2K(b). Conditioning consisting of 3 Gy whole-body irradiation and treatment with anti-CD154 was sufficient to induce molecular chimerism resulting in stable multilineage expression of K(b) on hematopoietic cells. T cells from molecular chimeras were unable to lyse allogeneic targets expressing K(b) and contained substantially fewer K(b)-reactive IL-2- and IFN-gamma-producing CD4 T cells than controls receiving mock-transduced bone marrow. Induction of molecular chimerism using nonmyeloablative host conditioning allowed for permanent survival of K(b)-disparate allogeneic skin grafts. These data suggest that nonmyeloablative host conditioning can be used effectively to induce molecular chimerism resulting in transplantation tolerance.