Treatment with Ex-527 attenuates cGVHD. Lethally irradiated (700 cGy) BALB/c mice underwent transplantation with 5 × 10⁶ TCD-BM of B10.D2 BM plus 5 × 10⁶ whole splenocytes containing CD25 per mouse isolated from WT donor. The recipients were treated either prophylactically on day 0 or day 28 posttransplant for 21 days with 2 mg/kg/mouse/day Ex-527. (A) Survival (B) cGVHD clinical scores. (C-D) Analysis of IFN-γ and IL-17 expressions on donor CD4 in spleen. (E-F) BCL6 expression and IL-21 secretion by donor CD4 were determined on day 50. (G-H) Analysis of Foxp3 expression and frequency of Tfh (Foxp3⁻CXCR5⁺PD-1⁺) and PD-1⁺CD8⁺ were measured on donor T cells. Splenic B cells were analyzed for B220⁺, B220^-CD138⁺, and MHCII. Data were combined from 2 independent experiments (n = 5-7 mice/group). Student t test was used for statistical analysis. *P < .05; **P < .01.