When either CD4+ or CD8+ T cells and BM cells from wild-type B6 were injected into lethally irradiated Bm1 and Bm12 recipients, donor CD4+ T cells induced lethal GVHD in only Bm12 recipients, and donor CD8+ T cells did so only in Bm1 recipients (67). The gene discussed is CD4; the disease is graft versus host disease.