Rational design of a novel engineered factor X with chimeric activation peptide as bypassing agent for haemophilia

BACKGROUND: While replacement therapy in Haemophilia A (HA) and B (HB) has provided remarkable improvements, the development of neutralizing antibodies remains a significant complication, with rational engineering of bypassing molecules being a relevant issue. OBJECTIVES: To develop a human factor X (FX) variant containing a FIX-derived chimeric activation peptide (AP) driving FVIII or FIX deficiency bypass. METHODS: Engineered variants were expressed and purified, and activation/activity properties were evaluated through functional assays, also in plasma with inhibitors from HA and HB patients. RESULTS: significantly shortened the clotting time in plasma from patients with high-titer anti-FVIII or anti-FIX inhibitory antibodies, with efficacy levels comparable with those of well-established bypassing agents. CONCLUSIONS: as a promising and versatile bypassing agent able to sustain coagulation across multiple haemophilic contexts including inhibitors presence, while maintaining favourable activation profiles.