Inter-chain disulfide bond improved protein trans-splicing increases plasma coagulation activity in C57BL/6 mice following portal vein FVIII gene delivery by dual vectors

Protein trans-splicing based dual-vector factor VIII (FVIII) gene delivery is adversely affected by less efficiency of protein splicing. We sought to increase the amount of spliced FVIII protein and plasma coagulation activity in dual-vector FVIII transgene in mice by means of strengthening the interaction of inteins, protein splicing elements, thereby facilitating protein trans-splicing. Dual-vector delivery of the FVIII gene in cultured cells showed that replacement of Met226 in the heavy chain and Asp1828 in the light chain with Cys residues could facilitate inter-chain disulfide linking and improve protein trans-splicing, increasing the levels of spliced FVIII protein. In this study, C57BL/6 mice were coadministered dual vectors of intein-fused human FVIII heavy chain and light chain with Cys mutations via portal vein injection into the liver. Forty-eight hours post-injection, plasma was collected and analyzed for FVIII antigen concentration and coagulation activity. These mice showed increased circulating FVIII heavy chain polypeptide (442±151 ng m^L?1 vs. 305±103 ng mL^?1) and coagulation activity (1.46±0.37 IU m^?1 vs. 0.85±0.23 IU mL^?1) compared with control mice co-administered dual vectors expressing the heavy and light chains of wild-type FVIII. Moreover, coagulation activity was similar to that of mice receiving a single vector expressing FVIII (1.79±0.59 IU mL^?1). These findings indicate that improving protein trans-splicing by inter-chain disulfide bonding is a promising approach for increasing the efficacy of dual-vector based FVIII gene transfer.