CRU numbers are similar inSHIP^-/-and wild-type mice, butSHIP^-/-CRUs have an increased sensitivity to 5-FU. (A) CRU levels were determined by injecting 4 to 8 recipients per group in 1 (PB) or 2 (BM and spleen) separate experiments. Cell doses used included the following: 5 × 10³ to 3 × 10⁴ (4-5 doses per group) for BM; 10⁴ to 2 × 10⁶ (6-9 doses per group) for spleen; and 10⁴ to 10⁶ (3 doses per group) for PB. Repopulation of the hematopoietic system in the recipients was evaluated by taking aliquots (200 μL) of PB from the tail veins at 16 weeks after transplantation, and analyzing samples for the presence of Ly5.2⁺ (donor) myeloid and B-lymphoid cells by FACS. CRU content, determined using Poisson statistics, in the BM (BM; number per femur × 16.6), spleen (SPL), or 1.5 mL PB are shown for the SHIP^+/+ (white bars) and SHIP^-/- (dark bars) mice. (B) Total BM CRU numbers remaining 2 days after a single injection or 6 days after 2 injections (days 0 and 5) of 150 mg/kg 5-FU, in SHIP^+/+ (white bars) and SHIP^-/- (dark bars) mice are shown. CRU numbers per femur were assayed in 2 separate experiments by limiting dilution analysis as described above. Each of the 9 cell doses (ranging from 2 × 10³ to 1.8 × 10⁵) was injected into 4 to 6 recipients. The normal range indicates the number of CRU ± 95% CI in untreated wild-type mice. All data are expressed as mean CRU number ± 95% confidence interval (CI). ^*P < .01; ^**P < .0001 versus SHIP^+/+ mice.