Regression of Grafted Bone Marrow in Homologous Irradiated Mouse Chimeras

Abstract

Lethally irradiated (C57BL × 101)F₁ mice receiving injections of C57BL bone marrow exhibited only a transitory production of graft-derived erythrocytes, the tendency for regression of the grafted marrow apparently varying with the X-ray dose and number of marrow cells infused. Judged on the basis of circulating erythrocytes, the grafted marrow persisted longer and regressions occurred later and less frequently in lethally than in midlethally irradiated recipients of 75 × 10⁶ cells. Regression of grafted 101 marrow was not observed in lethally irradiated (C57BL × 101)F₁ mice, though such marrow did regress in midlethally irradiated hybrid recipients. The delayed mortality of the irradiated recipients was not consistently correlated with persistence or regression of the grafted marrow. The regression of grafted parental marrow noted under these conditions cannot as yet be conclusively explained, but might have resulted from an immunological rejection of the grafted cells. Genetic mechanisms for such a phenomenon are discussed, along with other mechanisms that might favor the selective growth of autologous hematopoietic cells.