Engraftment of either Atm^-/- or Atm^+/+ donor bone marrow in conditioned recipients results in stable multilineage chimerism. Lethally irradiated C3H mice were reconstituted with 10⁷ bone marrow cells from either Atm^-/- (solid line; n = 6) mutant mice or wild-type littermate controls (dashed line; n = 6). Six weeks after BMT, PBMCs were stained with donor-specific anti-H-2K^b antibodies and analyzed by flow cytometry. Twenty-two weeks after transplantation, blood cells were stained with donor-specific anti-H-2K^b and lineage-specific antibodies and were analyzed by flow cytometry for the presence of donor-derived CD3⁺, B220⁺,or CD11b⁺ after gating. In all experiments, PBMCs from untreated C3H mice were used as negative controls (dotted line).