Radiation Dose as a Factor in Host Preparation for Bone Marrow Transplantation Across Different Genetic Barriers

Abstract

Engraftment of donor bone marrow in relation to total body irradiation (TBI) dose was studied in syngeneic (B6→B6), MHC-compatible (BALB.B→B6) and MHC-incompatible allogeneic (BALB/c→B6) murine bone marrow transplantation (BMT) models. For each BMT combination radiation dose-response curves were obtained from stable longterm bone-marrow chimerism using Gpi-1 phenotyping and this was compared with the growth of exogenous CFU-S. Syngeneic engraftment required the lowest TBI doses limited to ablation of host haemopoietic stem cells. Resistance against H-2-compatible allogeneic engraftment was evident at low radiation doses (< 5·5 Gy) but at 6 Gy and above the level of chimerism was comparable to syngeneic transplants, which indicated effective immunosuppression. Higher TBI doses were needed for engraftment as the immunological barrier was increased using fully H-2-incompatible allogeneic transplants. The high TBI dose (9·5 Gy) needed for suppression of spleen endocolonies in the CFU-S assay meant that rejection of exogenous bone marrow was evident only across the larger immunological barriers. When the fully allogeneic combination was reversed (B6→BALB/c) both CFU-S and chimerism data showed less rejection. The steep dose-response relationships show how engraftment is critically dependent on TBI dose, as well as the genetic disparity between donor and host.