Integrin αvβ8-mediated TGF-β1 activation regulates sustained response in immune thrombocytopenia after TPO-RA withdrawal

Only 30-50% of patients with immune thrombocytopenia (ITP) exhibit a sustained response upon thrombopoietin receptor agonists (TPO-RAs) withdrawal, underscoring the necessity for mechanistic elucidation. We enrolled 49 patients treated with TPO-RAs for four months and performed a follow-up study for three months, classifying them into sustained responders (ITP-sus, n=21), and non-sustained responders (ITP-non-sus, n=28). Compared with total TGF-β1 levels, activated TGF-β1 levels (3854±4380 vs. 943±1500 pg/ml, p＜0.001) were significantly elevated in sustained responders, with integrin αvβ8 regulating TGF-β1 activation and restoring immune tolerance. We established a passive ITP model using PF4-TGF-β1 conditional knockout (CKO) mice, which exhibited a shorter duration of sustained response compared to WT mice. CKO mice demonstrated a reduced Treg population, an increased M1/M2 macrophage ratio, and more severe megakaryocyte destruction following anti-CD41 injection. Exogenous administration of αvβ8 (250 ng/kg) effectively activated TGF-β1 and prolonged remission after TPO discontinuation in WT mice. Additionally, CD4+ T cells were transfected with lentiviral siRNA or shRNA to modulate integrin β8 expression and these were injected into SCID mice undergoing an active model of ITP. Results showed that β8 overexpression increased Treg cells and reduced megakaryocyte damage. Mechanistically, TPO-RAs modulated αvβ8-mediated TGF-β1 activation through the activator protein-1(AP-1) family and Smad-2 signaling pathways. Furthermore, D-mannose combined with TPO prolonged the response in ITP mice by upregulating αvβ8 and activating TGF-β1. Overall, the integrin αvβ8-mediated activation of TGF-β1 pathway represents a promising therapeutic target for ITP, with substantial potential for clinical application.