Hybrid Resistance to Parental Bone Marrow Transplantation: Adaptive Modification of Hemopoietic Stem Cell in a Nonsyngeneic Environment

Defective growth of parental bone marrow in an F1hybrid is associated with delay of the exponential growth phase of injected hemopoietic stem cells rather than with their rejection. This is demonstrated both by parental hemopoietic stem cell kinetics in the irradiated hybrid and by the increase in the number of spleen colonies with time after hemopoietic cell injection. After passage through an F1hybrid the parental hemopoietic stem cells acquire ability for better growth in the same F1host. This phenomenon, which we designated ``adaptive modification of hemopoietic stem cells,'' is associated with the appearance, on their surface, of histocompatibility molecules carrying H-2 determinants of the recipient. Treatment of the modified cells with antiserum against the second parental strain abrogates the state of adaptive modification.