Antibodies against Elapidae and Viperidae snake venoms: in vivo neutralization and mechanistic insights

Snake envenomation results in a range of clinical sequelae, and effective therapy is yet to be discovered. Anti-snake venom antibodies are being considered as a potent strategy. We developed venom-neutralizing humanized antibody scFvs and elucidated biochemical and structural mechanisms associated with the inhibition of toxicity. Tomlinson I and J human antibody scFv libraries were screened against Naja naja and Echis carinatus venoms, and seven unique antibody scFvs were obtained. Further, specific toxins of snake venom interacting with each of these scFvs were identified, and phospholipase A2 (PLA2) was found to be prominently captured by the phage-anchored antibody scFvs. Proteomic analysis of whole venom also revealed PLA2 to be the most abundant toxin in both venom samples. The scFvs binding to PLA2 were used to perform in vivo survival assay using the mouse model and in vitro toxin inhibition assays. scFv N194, which binds to acidic PLA2, showed considerable survival in Naja naja venom-challenged mice and conferred up to 50% protection. A combination of two scFvs, E113 and E10, both interacting with basic PLA2, exhibited synergistically enhanced survival of 33% in Echis carinatus venom-challenged mice, compared to 16% survival conferred by an equal amount of individual scFvs. Furthermore, these scFvs demonstrated inhibition of venom-induced myotoxicity and hemolysis which corroborate the survival data. Structural studies highlighted possible modes of PLA2 neutralization by scFv through the engagement of CDRs with C-terminal myotoxic loop and interfacial region, which are crucial for PLA2 toxicity.