Inactivation of Notch signaling in donor CD4⁺ T cells inhibits acute GVHD in irradiated MHC-mismatched hosts. (A) Lethally irradiated BALB/c mice (1000 rads) were transplanted with 5 × 10⁶ TCD BM from B6-SJL mice (n = 10, ♦), with or without 2 × 10⁶ WT B6 CD4⁺ T cells (WT CD4, n = 15, ■) or B6 DNMAML CD4⁺ T cells (DNMAML CD4, n = 19, ▴). Survival was assessed over time (P < .001, ■ versus ▴). Data shown are pooled from 3 independent experiments (left panel). Right panel, clinical GVHD score (*P < .05, ■ versus ▴), determined as described.³²  Representative data from 1 of 2 independent experiments are presented. (B) Histological GVHD score.^33,34  Tissues were collected at day 10 (n = 4 for each group) or > 20 days (range 20-40; WT, n = 8; DNMAML, n = 9) after transplantation (850 rads; left). Int, intestine; Liv, liver; Sk, skin. Right panel, histological analysis of intestine, liver, and skin after transplantation of WT (n = 8) or DNMAML (n = 9) CD4⁺ B6 T cells (×100),^33,34  which is representative of 2 independent experiments. (C) Dose-response ex-periment. Lethally irradiated BALB/c mice were transplanted with 5.0 × 10⁶ TCD BM from B6-SJL mice (n = 13, ♦), or TCD BM with 0.5 × 10⁶ (□) or 2.0 × 10⁶ (■) WT B6 CD4⁺ T cells (WT CD4, n =10/group) versus 2.0 × 10⁶ (▴) or 5.0 × 10⁶ B6 DNMAML (r) CD4⁺ T cells (DNMAML CD4, n = 10/group). Survival (left panel) and clinical GVHD score (right panel) were assessed over time, as described.³²  Survival (P = .012) and GVHD severity (P < .01) were worse after administration of 0.5 × 10⁶ WT CD4⁺ than 5.0 × 10⁶ DNMAML CD4⁺ T cells (□ versus ▵).