Lytic polyplex vaccines enhance antigen-specific cytotoxic T cell response through induction of local cell death

Endosomolytic vaccine nanocarriers can potentiate cellular immune responses by enhancing cross-presentation. We recently developed a cationic polymer-lytic peptide conjugate (VIPER) that greatly improves endosomal escape and intracellular activity of nucleic acid cargoes; furthermore, we hypothesize that VIPER's unique mechanism of endosomal disruption can increase cytoplasmic delivery of other biomacromolecules (e.g., peptides). Herein, we formulate VIPER as a polyplex subunit vaccine composed of conjugated peptide antigens and electrostatically complexed poly(I:C) nucleic acid adjuvant and evaluate whether the presence of the lytic peptide melittin conjugated to the pH-responsive micelle core improves vaccination outcomes. Although VIPER delivers peptide antigens intracellularly, disrupts endosomes in antigen-presenting cells (APCs) in vitro, and generates strong antigen-specific cytotoxic T cell responses in vivo, significantly enhanced cross-presentation is only observed in conjunction with VIPER-induced local cell death. While these results demonstrate that VIPER is a useful platform technology for the study of vaccine delivery, full elucidation of how endosomal disruption by VIPER improves vaccination outcomes will require decoupling of endosomolysis from cytotoxicity, as well as precise targeting of VIPER vaccine formulations to APC populations in vivo.