DNA vaccination against Respiratory Syncytial Virus [RSV]

Abstract

Despite years of research, a vaccine for RSV is currently not available. One attractive platform for RSV vaccines is DNA vaccination, however to date DNA vaccines have been poorly immunogenic in humans. More understanding of the interplay between route of delivery, expression and immunogenicity of DNA vaccines is required. The aim of this project was to use the novel linear DNA construct developed by Touchlight Genetics Ltd to investigate the immune response to DNA vaccines. These constructs, or doggybones (dbDNA) because of their characteristic shape, are faster and easier to produce than conventional plasmid DNA vaccines, can be produced synthetically and only contain elements needed for gene expression. Initial studies investigated the relationship between expression and immunogenicity. dbDNA and circular plasmid vaccines were compared by evaluating the visible expression of a range of red fluorescent protein using in vivo imaging; immunogenicity was compared using vaccination models. Expression of dbDNA and plasmid vaccines was similar but there was a disconnect between expression and immunogenicity. dbDNA and plasmid vaccines of the RSV F, M2-1 and G genes were produced and efficacy evaluated after intramuscular, subcutaneous and tattoo delivery. The distinct immune profiles produced by RSV genes allowed for examination of immune response generated after delivery by various routes. dbDNA and plasmid vaccines had comparable immune responses, but no viable vaccine candidates were identified due to priming for vaccine enhanced disease. The route of delivery did not alter the immune phenotype of the antigen, but it did alter the magnitude. Intramuscular delivery produced strongest immune responses, followed by the tattooing route and with limited responses observed after subcutaneous delivery. The DNA vaccines generated in the project were immunogenic, generating strong T cell responses, but not protective. Better correlates of anti-RSV cellular protection are needed, therefore, the contribution of T cells to protection was investigated. Natural RSV infection induces tissue resident memory (TRM) populations in the airways which were not produced after intramuscular immunisation with DNA vaccines. Airway T cells from RSV exposed mice were able to protect naïve mice from RSV disease in a novel model of cell transfer. These studies provide evidence of protective roles of TRM cells and support the need to induce TRM with DNA vaccine strategies for protective immunogenicity.