Induction of type 2 T cells is required for MDSC-mediated GVHD suppression. (A-D) Lethally irradiated B6.bm1 recipient mice were reconstituted with TCD-BM from B6 mice without or with B6-derived SCs or SCs derived from STAT6^−/− animals in the absence or presence of 1 × 10⁷ B6-derived MDSCs. Survival (A) and GVHD scores (B) were determined. (A) TCD-BM + SC (B6) vs TCD-BM + SC (B6) + 1 × 10⁷ MDSCs, *P ≤ .05; TCD-BM + SC (STAT6^−/−) vs TCD-BM + SC (STAT6^−/−) + 1 × 10⁷ MDSCs, P = .94. Surviving animals/total animals treated are indicated in brackets. (B) Error bars indicate ± SEM. TNF-α, IFN-γ, and IL-5 concentrations were determined in the serum of transplanted animals 10 days after BMT (C). Ten days after transplantation, mice were euthanized and CD3⁺ T cells were isolated. qRT-PCRs for the expression of cytokines IL-4, -5, -13, -17, TNF-α, and IFN-γ were performed, and relative expression to AIP was calculated (D). (E) Lethally irradiated B6.bm1 recipient mice were reconstituted with TCD-BM from B6 mice, together with B6.SJL-derived SCs or SCs derived from STAT6^−/− animals, in the absence or presence of 1 × 10⁷ B6-derived MDSCs. Different days after BMT, spleen, blood, liver, and colon cells were analyzed for numbers of infiltrating CD3⁺ T cells in spleen and liver, whereas the percentage of CD3⁺ T cells was calculated in blood and colon. B6.SJL-derived allogeneic T cells were detected by gating on CD45.1⁺CD3⁺ T cells, whereas STAT6^−/−-derived allogeneic T cells were detected by gating on STAT6^−/−CD3⁺ T cells. Data represent the mean value ± SD analyzed of triplicates from spleens of at least 5 mice pooled (D) or of 3 mice analyzed on each time point (E). *P ≤ .05; **P ≤ .01; n.s. = not significant. No significant statistical differences were detected in T-cell numbers between the different treatment groups (E). n.s, not significant.