T-cell development is normal in Atm^-/- mutant mice that receive C3H bone marrow cells. (A) Atm^-/- mice were treated with anti-CD4 and anti-CD8 antibodies and cyclophosphamide before receiving 10⁸ C3H bone marrow cells. Twelve weeks after BMT, mice were killed and thymi were analyzed by flow cytometry after cell surface staining. Shown is a flow cytometry profile from representative mice. (B) The total number of cells in each thymus was counted, and the absolute number of each thymocyte subset was calculated based on the frequency of each subset as determined by flow cytometry. Shown is the absolute number of cells in each thymocyte subset in Atm^-/- mice that were engrafted with C3H bone marrow (▪) and conditioned control Atm^-/- mice (□). Shown are the combined mean and standard deviation of 3 experiments.