Human C5-specific single-chain variable fragment ameliorates brain injury in a model of NMOSD.

Objective: Using phage display, we sought to screen single-chain variable fragments (scFvs) against complement C5 to treat neuromyelitis optica spectrum disorder (NMOSD). Methods: After 5 rounds of phage display, we isolated individual clones and identified phage clones specifically binding to C5 using ELISA. Using aquaporin-4 (AQP4)-transfected cells in vitro, we confirmed whether these scFvs prevented complement-dependent cytotoxicity (CDC) caused by the serum of patients with NMOSD and human complement (hC). We selected an NMOSD mouse model, in which intracerebral NMOSD immunoglobulin G (IgG) and hC injections induce NMOSD-like lesions in vivo. Results: We obtained scFvs to test specificity and blocking efficiency. The scFv C5B3 neutralized C5 in the complement activation pathway, which prevented AQP4-IgG-mediated CDC in AQP4-transfected cells. In an NMOSD mouse model, C5B3 prevented AQP4 and astrocyte loss, decreased demyelination, and reduced inflammatory infiltration and membrane attack complex formation in lesions. Conclusions: We used phage display to screen C5B3 against C5, which was effective in inhibiting cytotoxicity in vitro and preventing CNS pathology in vivo.