UCSF

Pathogenesis in seropositive neuromyelitis optica spectrum disorders (herein called NMO) involves binding of IgG1 autoantibodies to aquaporin-4 (AQP4) on astrocytes in the central nervous system, which initiates complement and cellular injury. We previously developed an antibody blocking approach for potential therapy of NMO in which an engineered, monoclonal, anti-AQP4 antibody lacking cytotoxicity effector functions (called aquaporumab) blocked binding of NMO autoantibodies to astrocyte AQP4 (Tradtrantip et al. Ann. Neurol. 71, 314-322, 2012). Here, a high-affinity aquaporumab, which was generated by affinity maturation using saturation mutagenesis, was shown to block cellular injury caused by NMO patient sera. Anti-AQP4 antibody rAb-53, a fully human antibody with effector function neutralizing Fc mutations L234A/L235A and affinity-enhancing Fab mutations Y50R/S56R, called AQmab^AM, bound to AQP4 in cell cultures with K_d ~ 18 ng/ml (~0.12 nM), ~8-fold greater affinity than the original antibody. AQmab^AM, but without L234A/L235A Fc mutations, produced complement-dependent cytotoxicity (CDC) with EC₅₀ ~ 82 ng/ml. AQmab^AM prevented CDC produced by sera from eight NMO patients with IC₅₀ ranging from 40 to 80 ng/ml, and similarly prevented antibody-dependent cellular cytotoxicity (ADCC). Mechanistic studies demonstrated that AQmab^AM blocked binding of serum NMO autoantibodies to AQP4. AQmab^AM offers a targeted, non-immunosuppressive approach for therapy of seropositive NMO. Autoantibody blocking may be a useful therapeutic strategy for other autoimmune diseases as well.