Engrafting efficiency of pitpα/β WT and pitpα^−/−/β^−/−BM as assessed by competitive BM transplantation and limiting dilution analysis. Donor BM cells (CD45.1⁻ CD45.2⁺) from pitpα/β WT and pitpα^−/−/β^−/− mice at various doses (25 000, 50 000, and 100 000) were mixed with 1 × 10⁵ competitor Boy/J BM cells (CD45.1⁺CD45.2⁻) and injected IV into lethally irradiated F1 host mice (CD45.1⁺CD45.2⁺). Following 1 (A), 2 (B), 3 (C), and 4 months (D), the percentage of donor-derived cells (referred to as CD45.2⁺) in the PB was determined by flow cytometry. (E) The percentage of donor-derived cells in the BM was determined at 4 months. (F) The myeloid (CD11b⁺)/ lymphoid (CD3⁺ and B220⁺) ratio in the PB at 4 months was determined by flow cytometry. (G-H) Limiting dilution analysis was performed. (G) Poisson statistical analysis of data from the limiting dilution transplantation. Each circle represents the percentage of negative mice for a specific dose of cells. Each solid line indicates best-fit linear model for the data set. Dotted lines represent 95% confidence intervals. (H) The number of CRUs in 1 × 10⁶ cells was calculated. See supplemental Table 1 for more details. Data represent the mean ± SEM of 6 to 10 host/recipient mice per group.