Figure 4. Prevention of acute GVHD by STAT3 deficiency in donor T cells requires PD-1 signaling triggered by GVHD target tissue expression of PD-L1.

(A) Lethally irradiated BALB/c recipients were engrafted with TCD-BM cells (5 × 10⁶) and CD90.2⁺ T cells (2.5 × 10⁶) from STAT3^–/– C57BL/6 donors. Anti–PD-1 (29F.1A12; 200 μg/mouse) or anti–PD-L1 (10F.9G2; 200 μg/mouse) was given i.p. on days 4, 6, 8, and 10. Curves of percentages of original body weight, clinical GVHD score, and percentage survival are shown. (B, D, and E) Lethally irradiated WT or PD-L1^–/– BALB/c recipients were engrafted with TCD-BM cells (5 × 10⁶) from WT C57BL/6 donors and CD90.2⁺ T cells (2.5 × 10⁶) from STAT3^–/– C57BL/6 donors. (B) Curves of percentage original body weight, clinical GVHD score, and percentage survival are shown. (C and F–G) Lethally irradiated WT BALB/c recipients were engrafted with TCD-BM cells (5 × 10⁶) from WT C57BL/6 donors and CD90.2⁺ T cells (1 × 10⁶) from STAT3^–/– or STAT3^–/–PD-1^–/– C57BL/6 donors. (C) Curves of percentage original body weight, clinical GVHD score, and percentage survival are shown. Data combined from 2 independent experiments. (D and F) Histopathology of liver, small intestine, and colon was evaluated on day 6 after HCT, and the histopathological scores are shown. n =4–5 combined from 2 replicate experiments. (E and G) Spleen, liver, small intestine, and colon samples were collected on day 6 after HCT, and yields of H-2Kb⁺TCR-β⁺ T cells are shown. n = 6–7 combined from 2 replicated experiments. Crosses indicate deaths. Data are represented as mean ± SEM. Two-tailed P values were calculated by nonlinear regression (curve fit) for comparison of body weights and clinical GVHD scores (A–C), log-rank test for survival comparisons (A–C), and unpaired Student’s t tests for other comparisons (D–G). *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.