Bone marrow failure in tertiary recipients. Lethally irradiated wild-type mice received transplants of 100% MSH2^–/– cells (P1). Three weeks later mice were treated with TMZ (□) at 80 mg/kg daily times 3 or left untreated (▪). Bone marrow was harvested from P1 recipients and transplanted into P2 and P3 recipients at 8-week intervals. Mice were treated again at P2 with TMZ or left untreated. P3 recipients were killed 18 days after transplantation. Bone marrow mononuclear cells (A) were measured, and CFUs were assessed by methylcellulose assay (B). There was a significant decrease in total cells and CFUs recovered from the marrow of treated versus untreated mice; P < .0001 (Fisher exact test).