An innovative AQP4 loop C-targeted monoclonal antibody reduces complement-dependent cytotoxicity and lessens experimental neuromyelitis optica

Neuromyelitis optica spectrum disorder (NMOSD) is a neuroinflammatory disease caused by an autoantibody that targets the extracellular domain (ECD) of the astrocytic water channel aquaporin-4 (AQP4-IgG or NMO-IgG). The generation of AQP4-IgG leads to the loss of AQP4 function, destruction of astrocytes via complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity, and subsequent inflammatory nerve damage. Therefore, preventing NMO-IgG-AQP4 binding may represent a feasible therapeutic strategy for NMOSD. In this study, we generated a monoclonal antibody targeting the AQP4 ECD loop C (named A001). We examined its binding affinity for AQP4 and its ability to prevent NMO-IgG from binding to AQP4, inhibit CDC in culture, and mitigate NMO-like pathology in a mouse model. Fluorophore-tagged A001 displayed a staining pattern in AQP4-overexpressing HEK293 cells that overlapped the staining pattern of fluorophore-tagged NMO-IgG. Preincubation or coincubation with A001 effectively blocked NMO-IgG immunostaining. Furthermore, A001 inhibited NMO-IgG-induced damage to AQP4-overexpressing HEK293 cells in the presence of human or mouse complement. Intrathecal A001 injection also reduced demyelination and immunocyte infiltration in the optic nerve and spinal cord in an NMO-IgG-induced mouse model of NMOSD. Competitive blockade of autoantibody binding to APQ4 using an ECD peptide-specific antibody is a potentially promising therapeutic strategy for NMOSD.