Role of the Hemopoietic Inductive Microenvironments (Him) in Xenogeneic Bone Marrow Transplantation

SUMMARY Isologous mouse marrow transfused into lethally irradiated mice gave erythroid, granuloid, and megakaryocytic spleen colonies, with an erythroid to granuloid (E:G) spleen colony ratio of 2.2:1 for 600 colonies in four different mouse strains. Isologous rat marrow transfused into lethally irradiated rats gave rise only to erythroid and un-differentiated colonies (E:G colony ratio = 490:0). However, rat marrow transfused into lethally irradiated mice gave rise to both erythroid and granuloid colonies (E:G eolony ratio approximately 3:1 for 303 colonies). These results further support the concept of the determining influence of the hemopoietic inductive microenvironments (HIM) with respect to the direction of differentiation of pluripotent hemopoietic stem cells. They indicate that the mouse spleen HIM can influence the direction of differentiation of rat pluripotent hemopoietic stem cells. The fact that hemopoietic colonies of rat origin grew more rapidly in mouse spleens than in rat spleens, and at a rate comparable to isologous mouse spleen colonies, suggests that the mouse HIM, or other host factors, also regulate the rate of growth of spleen colonies.