Serial bone marrow transplantations.

Serial bone marrow transplantations demonstrate a significant defect in HSC competition and self-renewal bySca-1^−/−mice. Sca-1^+/+BM was able to completely repopulate Sca-1^−/− mice in both primary and secondary recipients. However, when Sca-1^−/−bone marrow was used to repopulate lethally irradiated Sca-1^+/+mice, endogenous Sca-1^+/+HSCs were able to compete against donor stem cells in the primary repopulations (▨). In secondary transplantations using bone marrow from primary recipients to repopulate lethally irradiated Sca-1^+/+mice (▪), the donor bone marrow could not rescue one-third of the recipients from irradiation-induced anemia. Of the remaining recipients, the Sca-1^−/−bone marrow contributed approximately 45% to the recipient bone marrow 4 months following repopulation. Three of 9 secondary recipients died.