Th2 cell abrogation of rejection requires donor Th2 cell IL-4 and host T-cell STAT6. BALB/c-into-B6 transplantation consisted of lethal host irradiation (1100 cGy; day −2), and some combination, as indicated, of WT, STAT6^−/−, or IL-4^−/− host T cells (day −1, “HT”) and BALB/c donor BM (WT or IL-4^−/−) with or without donor Th2R cells generated from WT or IL-4^−/− donors (day 0). The ratio of donor Th2R cells to host T cells was 100:1 (10 × 10⁶ cells: 0.1 × 10⁶ cells); donor Th2 cells were generated in the presence or absence of rapamycin (Th2R or Th2 cells, respectively). Transplant recipients were monitored until day 45 for survival (A) and weight loss (panel B right); surviving mice were evaluated at day 45 for donor chimerism in the spleen and BM (panel B left). On day 8 after BMT, spleen cells were isolated and stimulated with syngeneic (B6) or allogeneic (BALB/c) DCs for 24 hours. The total number of host CD4⁺ and CD8⁺ cells in the spleen producing allospecific IFN-γ was determined by flow cytometry. Results from molecule-deficient host and donor cells are shown in panels C and D, respectively; results shown are mean plus or minus SEM of n = 10 per cohort. *P < .05; **P < .01; ***P < .001.