Platelet-derived TGF-β1 induced functional reprogramming of MDSCs in the ITP murine model. (A) Passive-ITP mice in group a, b, and c presented Pf4^cre–Tgfb1^fl/fl. Group a was injected with sterile water as a control. Group b was treated with TPO-RA (romiplostim, 30 μg/kg, once every 3 days). Group c was treated with TPO-RA and TGF-βi (SB431542, 10 mg/kg, once every 3 days). Mice in groups d and e were Pf4^cre+Tgfb1^fl/fl and treated with TPO-RA or not. Platelet counts detected every other day. Platelet counts among the groups differed significantly on day 6. (B) Percentage of MDSCs in bone marrow nucleated cells. (C) MDSC-mediated suppression of CD4⁺ T_eff proliferation measured according to the division index. Platelet counts (D) and percentage of MDSCs (E) of active-ITP mice after platelet transfusion. CFSE, carboxyfluorescein diacetate succinimidyl ester.