Background: Development of inhibitory antibodies (inhibitors) against FVIII is a significant complication of protein replacement therapy in hemophilia A (HA). Platelets, traditionally viewed as mediators of hemostasis, also modulate immune responses through cytokine release and interactions with immune cells. Harnessing these immunomodulatory properties may provide a novel strategy to prevent or suppress inhibitor formation. Objective: To investigate whether FVIII-engineered platelets and related platelet-based products modulate FVIII immune responses in HA mice. Methods: FVIII-containing platelets were isolated from 2bF8 transgenic mice. FVIII-deficient mice were infused with intact FVIII-containing platelets, desialylated FVIII-containing platelets (dPlts), or acidified platelet lysates in combination with or before recombinant human FVIII (rhF8) exposure. Anti-FVIII antibody titers were determined by the Bethesda assay and ELISA, and T cell responses were analyzed by flow cytometry and proliferation assays. Results: Co-infusion of FVIII platelets with rhF8 significantly reduced inhibitor titers compared with rhF8 alone. Acidified FVIII platelet lysates were potent, decreasing inhibitor titers by >20-fold when co-infused with rhF8. In contrast, co-infusion of dPlts with rhF8 did not suppress immune responses. However, repeated pre-sensitization with dPlts alone promoted immune tolerance to FVIII, evidenced by reduced inhibitor titers upon rhF8 immunization and attenuated CD4ô€€€ T cell proliferation upon subsequent rhF8 exposure. These findings reveal a hierarchy of immune modulation, with intact platelets providing partial protection, lysates strongly suppressing immune responses, and dPlts inducing immune tolerance. Conclusions: FVIII-engineered platelets and platelet-derived products are potent immune modulators. These strategies offer novel and translatable approaches to both restore hemostasis and prevent or eradicate inhibitors in HA.
Chen et al. (Thu,) studied this question.