Anti-CD137 induces aGVHD when treated during the induction phase of cGVHD. On day 0, Balb/c recipient mice were sublethally irradiated and reconstituted with 5 × 106 BM cells alone or together with 1 × 107 purified CD4+ T cells from B10.D2 donor mice. Anti-CD137 (200 μg per mouse) was administered immediately after transfer of donor cells (n = 10 per group). (A) Change of body weight. Data indicate percentage of body weight at each time point divided by original body weight at day 0. (B) Percentage of survival. ***P < .001, between the group of mice that received donor BM, CD4+ T cells, and anti-CD137 and the other 3 groups. The results are representative of more than 3 independent experiments.