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

ABSTRACT: Only 30% to 50% of patients with immune thrombocytopenia (ITP) exhibit a sustained response upon thrombopoietin receptor agonists (TPO-RA) withdrawal, underscoring the necessity for mechanistic elucidation. We enrolled 49 patients treated with TPO-RA for 4 months and performed a follow-up study for 3 months, classifying them into sustained responders (n = 21), and nonsustained responders (n = 28). Compared with total transforming growth factor β1 (TGF-β1) levels, activated TGF-β1 levels (3854 ± 4380 vs 943 ± 1500 pg/mL; P< .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 platelet factor 4-TGF-β1 conditional knockout (CKO) mice, which exhibited a shorter duration of sustained response than wild-type (WT) mice. CKO mice demonstrated a reduced regulatory T-cell (Treg) population, an increased M1-to-M2 macrophage ratio, and more severe megakaryocyte destruction after 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 small interfering RNA or short hairpin RNA to modulate integrin β8 expression and these were injected into severe combined immunodeficiency mice undergoing an active model of ITP. Results showed that β8 overexpression increased Tregs and reduced megakaryocyte damage. Mechanistically, TPO-RA modulated αvβ8-mediated TGF-β1 activation through the activator protein 1family and Smad family member 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.