T_reg cells do not require granzyme B to rescue hosts from GVHD lethality or to prevent GVHD target organ damage. Lethally irradiated (900 cGy) Balb/c mice received 2 × 10⁶ 129/SvJ TCD BM cells with or without 4 × 10⁵ 129/SvJ CD25⁻ T_eff cells (both CD4⁺ and CD8⁺) and either (A) 4 × 10⁵ or (B) 2 × 10⁵ wild-type or Gzmb^−/− CD4⁺CD25⁺ T_reg cells. Kaplan-Meier survival curves of recipient mice, pooled from 2 independent experiments (n = 10 mice per group), are shown. (C) Seven days after transplantation, 3 mice per experimental group (as outlined in panel A) were killed, and portions of lung, liver, and gut were prepared for histopathologic analysis. There was no statistically significant difference between groups receiving WT or Gzmb^−/− T_reg cells.