Stable mixed chimerism and tolerance using a nonmyeloablative preparative regimen in a large-animal model

Bone marrow transplantation (BMT) has considerable potential for the treatm ent of malignancies, hemoglobinopathies, and autoimmune diseases, as well a s the induction of transplantation allograft tolerance. Toxicities associat ed with standard preparative regimens for bone marrow transplantation, howe ver make this approach unacceptable for all but the most severe of these cl inical situations. Here, we demonstrate that stable mixed hematopoietic cel l chimerism and donor-specific tolerance can be established in miniature sw ine, using a relatively mild, non-myeloablative preparative regimen. We con ditioned recipient swine with whole-body and thymic irradiation, and we dep leted their T-cells by CD3 immunotoxin-treatment. Infusion of either bone m arrow cells or cytokine-mobilized peripheral blood stem cells from leukocyt e antigen-matched animals resulted in stable mixed chimerism, as detected b y flow cytometry in the peripheral blood, thymus, and bone marrow, without any clinical evidence of graft-versus-host disease (GvHD). Long-term accept ance of donor skin and consistent rejection of third-party skin indicated t hat the recipients had developed donor-specific tolerance.