Memory T cells do not cause GVHD. Sorted 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 and weight curves. Body weight data are presented as mean + SD. For survival, P < .05 (memory versus bulk or naive). For body weight, P was not significant (memory versus TCD BM only in all time points after day 7). No signs of GVHD were observed in the single memory T-cell recipient (C57BL/6→C3H/HeJ) that died during observation. Data were pooled from several independent similar experiments (3 for C57BL/6→BALB/c, 1 for BALB/c→C57BL/6, 2 for C57BL/6→C3H/HeJ). (B) Histological analysis (hematoxylin and eosin stain, × 100). Biopsy specimens were obtained from BALB/c recipients of C57BL/6 T cells on day 32 for bulk and naive T-cell groups and day 120 for TCD BM only and memory T-cell groups. (C) Dose-dependent T-cell response in GVHD. Graded numbers of purified C57BL/6 T cells were transplanted into lethally irradiated BALB/c recipients along with T-cell–depleted BM. Mice were monitored for the development of GVHD. For survival, P < .05 (1 × 10⁶ versus other groups). For body weight, P < .05 (TCD BM only versus 1 × 10⁴, 1 × 10⁵, and 1 × 10⁶ at all time points later than day 14 except 1 × 10⁴ on day 70). *P < .05 (1 × 10³ versus TCD BM only on days 77, 84, and 98). TCD BM indicates T-cell–depleted BM.