CD4⁺ memory T cells do not cause GVHD. Sorted CD4⁺ T-cell subsets were transplanted into lethally irradiated recipients along with T-cell–depleted BM cells. Mice were monitored for the development of GVHD. (A) Survival. P < .05, CD4⁺ memory versus bulk or CD4⁺ naive; P < .05, bulk versus CD4⁺ naive. (B) Weight curve. P < .05, CD4⁺ memory versus TCD BM only after day 42.