The COVID-19 pandemic has highlighted the importance of vaccination as a critical public health tool against current and emerging pathogens. While vaccines have traditionally been delivered via needle-and-syringe injection, much work into alternative delivery systems has been conducted. The immunologically active microenvironment and the high density of antigen-presenting cells make the skin an attractive target for vaccination. The use of microarray patches to deliver vaccines directly to these layers of the skin presents a promising alternative to traditional vaccine delivery mechanisms. One such microarray patch is the Vaxxas High-Density Microarray patch (HD-MAP). Delivery of vaccines via the HD-MAP has shown dramatic improvements in immunogenicity in terms of magnitude, breadth and quality of the immune response. We used newly available spatial transcriptomics tools to examine the immunological mechanisms underpinning the immune enhancement phenomena associated with HD-MAP vaccine delivery, including the nanoString GeoMx and 10x Genomics Xenium. Using these techniques, we investigated the response to HD-MAPs at the transcriptome level in both mice and humans temporally and spatially in the skin. Analysis revealed the HD-MAP triggers a localised enhanced inflammatory state in the skin within 1 hour, characterised by TNF and IL-17 signalling, resulting in rapid infiltration of multiple immune cells. Distinct cell infiltrates into the epidermis and dermis were observed with the 10x Xenium platform.
Next, we immunised mice via HD-MAP or intradermal injection using prefusion stabilised Spike protein (hexapro), derived from the ancestral SARS-CoV-2 strain, and adjuvanted with QS21 to analyse the B cell receptor repertoire of vaccinated mice. Analysis of this nature is required to understand further the advantages associated with functional immune outcomes following HD-MAP vaccination. Individual, isotype-switched (IgD-) and receptor-binding domain-specific B cells from germinal centres of draining lymph nodes were isolated after vaccination, and the B cell receptor (paired heavy and light chain) sequenced. Initial findings suggest HD-MAP vaccination increased the repertoire/diversity of the B cell response compared to intradermal injection. Using the sequencing data, we also expressed and analysed a panel of monoclonal antibodies elicited following HD-MAP vaccination. Analysis revealed that these antibodies had strong avidity for the spike protein and neutralisation potency across multiple variants (Wuhan, Alpha, Delta, Gamma, Omicron BA1 and BA2). This work provides unprecedented detail into the precise transcriptional mechanisms and functional antibody responses following HD-MAP vaccination. These findings have implications for future microarray patch-delivered vaccine development and design.