ABSTRACT
The still ongoing pandemic has highlighted the unmet need for more innovative and rapidly adaptable vaccine platforms. Here, we introduce a novel vaccine platform which uses adenoassociated virus (AAV) capsids as scaffolds for large immunogenic epitopes to induce strong and specific immune responses. The structural viral proteins (VP) of AAVs are known to allow small peptide insertions in specific surface exposed regions. In order to allow for a better immune response, we introduced larger insertions of approximately 200 amino acids in the variable loop IV of the AAV2 or the AAV9 capsid. We produced and characterised AAV particles with or without genome. Empty, viruslike particles (VLP) were administered intramuscularly in adult rabbits and tested for their ability to induce an immune response delivered against the immunogenic protein sequence presented on the capsid surface. The immunised rabbits showed elevated levels of binding and neutralising IgG antibodies against the administered antigen. Moreover, VLPs presenting a large SARS-CoV-2 antigenic protein on the capsid surface were efficiently neutralised by serum from Comirnaty mRNA-vaccinated individuals. These VLPs also strongly activated T- and B-cell responses in PBMCs of individuals vaccinated with mRNA-based vectors as evident by the induction of CD4, CD8 and CD19 markers. This next-generation vaccine platform based on AAV capsids with large insertions of immunogenic sequences enables strong and specific immune responses without the need for genomically encoded immunogens, thus reducing the risk of potentially pathogenic intracellular processes associated with viral vector genomes and prolonged transgene expression.