SIRT1−/− BM cells confer stable reconstitution in competitive and serial transplantation experiments. (A) Percentages of CD45.2+ WBCs derived from 2- (left), 6- (middle), and 16 (right)–month-old SIRT1−/− (black) and SIRT1+/+ (gray) donors in the blood of lethally irradiated CD45.1+ recipients, as measured 4, 8, and 16 weeks after transplantation. Dots represent means ± SEM (n = 8-11 per age group). Recipients were transplanted with 2 × 105 whole BM donor cells together with 1 × 105 competitor recipient cells. (B) Percentages of donor-derived cells within B-cell (CD19+), T-cell (CD3+), neutrophil (Gr1+), and monocyte (F4/80+) populations in recipient bloods 16 weeks after transplantation. Each data point represents an individual animal; lines represent means ± SEM. The groups are as described in panel A. (C) Design of the serial transplantation experiment (left). BMs from 3 mice older than 18 months were pooled and transplanted into lethally irradiated CD45.1+ recipients (n = 7) at a dose of 2 × 106 cells without BM rescue cells. Four months later, recipient peripheral blood was analyzed by FACS, followed by harvesting whole BM cells and transplanting them individually into a new set of lethally irradiated hosts (n = 7) at the same cell dose (secondary transplantations). The same procedure was repeated after another 16-week period (tertiary transplantations). Also shown (C right) are survival rates for recipient mice transplanted with SIRT1−/− (black) and SIRT1+/+ (gray) BM cells. Bars represent the percentage of mice surviving at 16 weeks after transplantation. (D) Percentages of CD45.2+ donor cells in each WBC compartment of lethally irradiated CD45.1+ recipients 4 months after primary (left), secondary (middle), and tertiary (right) transplantation; each data point represents an individual animal; lines represent means ± SEM (n = 7 per group). The fraction of circulating donor cells gradually decreases during subsequent transplantations, indicating that donor cells are competing with the recipient cells that have survived irradiation.