Mortality and Skin Transplantability in X-Irradiated Mice Receiving Isologous, Homologous or Heterologous Bone Marrow.∗ †

Summary The degree and duration of protection afforded by isologous, homologous and heterologous sources of bone marrow administered after lethal doses of x-irradiation in mice was directly proportional to the closeness of genetic relationship of the marrow donor to the irradiated mice. Uninijected controls were all dead by the 12th day. Mouse marrow from the same strain or from an F1 hybrid of the irradiated strain, or from a foreign strain, all gave excellent and essentially equal protection as late as 21 days post-irradiation. While mice receiving marrow from the same strain remained well protected beyond 100 days, those receiving marrow from a foreign strain showed considerable late mortality between the 21st and 60th days. Mortality in mice receiving F1 hybrid marrow was intermediate at 60 days. Guinea pig and rabbit marrow elicited a very low degree and duration of protection. Rat marrow permitted 55% of the irradiated mice to survive beyond the longest survival of the untreated controls. The duration of protection however was short, only 6% at 60 days. Irradiated mice protected with marrow from an F1 hybrid of the irradiated strain showed a high degree and long duration of tolerance of skin homografts from the F1 hybrid or from the other parent strain. Irradiated mice protected with foreign strain mouse marrow showed a high degree and long duration of tolerance for skin homografts from the same foreign strain. Irradiated mice protected with marrow from the same strain did not tolerate skin homo-grafts from a foreign strain or from an F1 hybrid.