Biophysics in Africa: Monoclonal antibodies neutralizing snake venom long & short chain three finger neurotoxins

Snakebite envenomation is a neglected tropical disease killing >135,000 people annually, predominantly in developing countries. Polyvalent antivenom is the only treatment, but it’s made through outdated technology. Monoclonal antibodies (mAbs) are the logical alternative for developing next-generation antivenom medicines.Here, we isolated a pair of antivenom mAbs that broadly cross-neutralized long and short chain three finger neurotoxins from elapids. Stored peripheral blood mononuclear cells from a hyperimmunised horse were fluorescently stained with long and short chain neurotoxins from Dendroaspis polylepis to select toxin binding memory B cells. Antibody variable genes were identified by RT-PCR and Sanger sequencing, then cloned and expressed in expiCHO. Binding was measured by ELISA and neutralization was assessed with a TE671 cell assay.Data for two crystal structures of Fab-Toxin complexes were collected at Diamond Light Source. Eight of the isolated antibodies bound snake neurotoxins and were 5%-14% mutated with human-like complementarity determining region 3 (CDR3) lengths.Two somatically related mAbs (Eq4.Dp46-3A/-3D) completely neutralized long and short chain α-neurotoxins and broadly bound neurotoxins from Africa, Asia, and the Americas.Crystal structures revealed an epitope between Fingers II and III that overlapped with the n-acetylcholine receptor (nAChR) F loop, explaining broad binding activity. Indels in heavy chain CDR1/2 were shown to determine monomeric or dimeric toxin binding, while the angle of approach completely occluded nAChR, providing a neutralization mechanism.Our data is the first to describe broadly cross-reactive mAbs with the ability to neutralise long and short chain α-neurotoxins, identifying a lead candidate for next-generation antivenom in the developing world.