Virus-like particle display of consensus α-neurotoxins does not enhance neutralising antibody responses against elapid venoms

Abstract

Snakebite envenoming is a neglected tropical disease, with neurotoxic elapid venoms in particular posing a major therapeutic challenge due to the rapid action and inter-species diversity of α-neurotoxins. Consensus toxin approaches have emerged as a promising strategy for generating broadly cross-reactive antibodies, while virus-like particles (VLPs) have been proposed to help overcome inherent antigen immunogenicity challenges. Here, consensus short-chain (sc3FTx) and long-chain (lc3FTx) α-neurotoxins were evaluated as immunogens in sheep either alone or displayed on a VLP platform. Both toxin-only and VLP-displayed immunogens elicited antibody responses that were subclass-specific with broad geographical and taxonomic recognition of medically important elapids. A functional in vitro neurotoxicity assay successfully differentiated neutralising from non-neutralising binding responses and indicated superior efficacy of toxin-only antisera relative to VLP-toxin immunogens. However, despite promising in vitro neutralisation, translation to in vivo protection was limited with only modest improvements in murine survival observed following a 4x LD50 venom challenge. Increased concentrations of toxin-only experimental antivenom did, however, substantially improve protection relative to venom-only and VLP-toxin derived antivenom groups. In these experiments, VLP presentation did not enhance immunogenicity or protective efficacy under the conditions tested, which is a possible reflection of the substantially lower toxin exposure received by VLP-immunised sheep. Overall, these findings further demonstrate that consensus α-neurotoxin immunogens can generate broad subclass-specific antibody recognition, but that neutralisation remains difficult to achieve. This study highlights the importance of antigen presentation, immunisation strategy and functional epitope targeting in the development of next-generation recombinant antivenoms.