Allogeneic BM-MSC are immune rejected by MHC-mismatched colitis mice. (A) Experimental schemes for results shown in panels B-E. Mice (N = 5 per test group) received 4.0% (w/v) of DSS orally for 6 days and normal drinking water afterward until day 15. For the second cycle of colitis induction, the same mice were administered DSS starting on day 16 and continued until day 22 following normal drinking water afterward until day 30. On days 2 and 4 of the first cycle, allogenic or syngenic fresh BM-MSCs (10 × 10⁶ cells) were delivered via IP (N = 5 per group) injection and the mice were treated with the second challenge of fresh MSC administration on days 18 and 20. After 30 days of complete cycle, all mice were sacrificed. The development of colitis is monitored by measuring body weight change relative to the initial body weight at day 0 (B), disease activity index (C), H&E staining (D), and histological score (E). BM-MSC transfusion into B6 mice served as positive control. Error bars represent the mean ± SEM (N = 5 for all experiments). (D) Bars represents 100 μm. Statistical analysis was performed by Student t test (E) and by 2-way ANOVA (Tukey test) (B-C). **P < .01, ***P < .001, ****P < .0001.