Engraftment following T cell-depleted bone marrow transplantation: Differential effects of increased total-body irradiation on semiallogeneic and allogeneic recipients

Three different doses of total-body irradiation (TBI) (1100, 1300, 1500 cGy) have been analyzed as conditioning regimens for semiallogeneic B6AF1 (H-2bxH-2a) and allogeneic A/J (H-2a) recipients of T cell-depleted C57BL6 (H-2b) bone marrow transplants. Recipient survival and engraftment of both donor erythrocytes and lymphocytes were examined in each group. The large majority of allogeneic mice prepared with 1100 cGy rejected their grafts, which resulted in poor survival (<30%); improved survival (up to 80%) and complete donor engraftment were noted as the TBI dose was increased. By contrast, survival in semiallogeneic B6AF1 recipients was independent of TBI dose and was greater than 80% in all groups. Outright failure of marrow grafts (<10% donor hematopoiesis) did not occur in these recipients, but mixed chimerism (simultaneous occurrence of both donor and host cells) was frequently observed at lower TBI doses. Complete (>90%) donor engraftment was noted for erythrocytes but not for lymphocytes. Possible mechanisms accounting for these differences between semiallogeneic and allogeneic recipients of marrow transplants are discussed.