Hematopoietic stem cell capacities are abrogated in ATM and TERT doubly null mice. (A) Primary bone marrow transplantation: repopulation ability is impaired in ATM^−/−TERT^−/− mice. Recipient mice were transplanted with 2 × 10³ LSKs from mice of the indicated genotypes and 2 × 10⁵ competitor BM-MNCs. Donor-derived chimerism of PB was analyzed monthly after transplantation. Data shown are the ratio (mean ratio: crossbar) of donor-derived cells in the competitive assay (*P < .05). (B) Second bone marrow transplantation: repopulation ability is again impaired in ATM^−/−TERT^−/− LSKs. The repopulating capacity of donor cells of the indicated genotypes was determined as for primary transplantation. (C) Impaired long-term repopulation capacity in ATM^−/−TERT^−/− LSKs during serial transplantation. Comparison of repopulation ability between primary and secondary transplantation for the indicated genotypes are represented. Data shown are the ratio (mean ratio: crossbar) of donor-derived cells in recipient BM (*P < .05).