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

Snakebite envenoming is a neglected tropical disease, with neurotoxic elapid venoms in particular 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 overcome 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 subclass-specific antibody responses 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 4× 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, although this may have been influenced by the substantially lower toxin antigen dose received by VLP-immunised sheep and should not be interpreted as definitive evidence against the VLP platform. Overall, these findings further demonstrate that consensus α-neurotoxin immunogens can generate broad subclass-specific antibody recognition, but that neutralisation remains difficult. This study highlights the importance of antigen presentation, immunisation strategy and functional epitope targeting in the development of next-generation recombinant antivenoms.