MMC hypersensitivity of Fac^−/−hematopoietic progenitor cells. BM LDMNC fromFac^−/− (▪) and Fac^+/+(•) animals were cultured in clonogenic methylcellulose progenitor assays at 1 × 10⁴ cells/mL with increasing concentrations of MMC. Each condition was plated in triplicate. The total number of colony-forming units (CFU) per 1 × 10⁴ LDMNC was determined on day 7 of culture. Error bars represent standard error of the means (SEM). Fac^−/− hematopoietic progenitor cells were significantly more sensitive to MMC at 5-, 10-, 50-, and 100-nmol concentrations. n = 6 for each group. *P< .05.