Increased expression of ST2 on T cells augments T-cell function during aGVHD. (A) ST2 was measured by flow cytometry on murine CD4⁺ T cells isolated from naïve mice after in vitro stimulation with allogeneic DC. Data are representative of 2 experiments. (B) ST2 expression on human CD4⁺ IFN-γ⁺ T cells in the peripheral blood analyzed by flow cytometry. Each data point represents the MFI for ST2 of an individual patient or healthy volunteer donor. Myeloablative conditioning (cond.) was performed with busulfan/cyclophosphamide or fludarabin/BCNU/melphalan, and samples were collected within the range of 5 to 10 days after allogeneic HCT. This experiment was performed once. (C) Survival of mice after allo-HCT performed as described for the 129 into BALB/c combination with 5 × 10⁶ BM cells and 3 × 10⁵ WT T cells, or st2^−/− T cells as indicated. The experiment was performed 3 times and the data were pooled. (D-F) Survival (D), clinical GVHD scores (E), and weight (F) of mice after allo-HCT was performed as described for the BALB/c into C57BL/6 combination with 1 × 10⁷ BM cells and 2.5 × 10⁶ WT BALB/c T cells, or st2^−/− T cells as indicated. This experiment was performed twice and representative data shown. (G) Histopathologic GVHD severity of the intestines and liver isolated on day 8 from mice treated as described under (C) when quantified as mean + SEM. Data are pooled from 2 independent experiments. (H) Survival of WT C57Bl/6 mice after allo-HCT with 1 × 10⁷ BM cells and 2.5 × 10⁶ WT BALB/c T cells, or st2^−/− T cells, performed as described under (D) with prior deletion of CD25⁺ cells within the transferred donor T cells. This experiment was performed once (n = 10). MFI, mean fluorescence intensity.