Increased RA levels and RAR signaling exacerbates GVHD. Survival and weight curves of lethally irradiated B10.BR recipients injected with 10⁷ BM cells and 5 × 10⁶ splenocytes from B6 mice are shown (n = 16/group). Subgroups were treated with vehicle (filled circles) or ATRA (open circles); P = .017. Data are combined from 2 experiments with similar results. **P > .01; ***P > .001.