CD132 blockade reduces JAK3 and STAT5 phosphorylation in activated T cells, and JAK3 deficiency in donor T cells reduces GVHD. (A) western blot analysis is shown for pJAK3, tJAK3, and β-actin on the protein derived from splenic CD4 and CD8 T cells (C57BL/6) and enriched by MACS that had been exposed to CD3/CD28 beads, IL-2 (50 ng/mL), and anti-CD132 (100 nm) for 48 hours when indicated. Left panel, One representative western blot is shown; right panel, quantification of the pJAK3/tJAK3 ratio is shown. (B) Flow cytometry–based analysis is shown for pSTAT5 (y-axis), in splenic CD4 T cells (C57BL/6) that were exposed to increasing levels of IL-2 for 15 minutes (x-axis). (C) Flow cytometry–based analysis is shown for pSTAT5 (y-axis), in splenic CD4 T cells (C57BL/6) that were exposed to IL-2 (100 IU/mL) for 15 minutes and increasing levels of anti-CD132 (x-axis). (D) Western blot analysis is shown for pSTAT5, tSTAT5, and β-actin on the protein derived from splenic CD4 and CD8 T cells (C57BL/6) enriched by MACS that had been exposed to CD3/CD28 beads, IL-2 (50 ng/mL), and anti-CD132 (100 nm) for 48 hours when indicated. Top panel, One representative western blot is shown; lower panel, quantification of the pSTAT5/tSTAT5 ratio is shown. (E-F) Sublethally irradiated bm12 recipient mice received IV infusions of either 3 × 10⁴ (E) or 10⁵ (F) T cells derived from Jak3^−/− or WT (both C57BL/6 background) mice (n = 5 per group) and survival was measured over time. Survival was improved in the groups receiving T cells derived from Jak3^−/− compared with WT mice at both T-cell dosages (P < .001).