T_BM induce severe lethal GVHD. Lethally irradiated B6D2F₁ recipients were reconstituted with B6-derived HSCs (n = 8), HSCs plus 200 000 CD8⁺ T_BM (n = 9), or HSCs plus 200 000 T_SP (n = 14) and were assessed for survival. The inoculum containing CD8⁺T_BM resulted in death from lethal GVHD, similar to that seen with αβTCR⁺ T_SP used as a positive GVHD control (P = NS). Survival was markedly decreased for T_BM and T_SP compared with HSCs alone (P < .05 for both groups at 30 days).