Mechanism of early tissue response in vaccination with lipid encapsulated non-amplifying mRNA (MechRNA)

Context: Lipid nanoparticle encapsulated mRNA (mRNA) is an innovative new vaccine platform technology with the potential for multiple clinical applications. Whilst the paradigm COVID-19 non-amplifying mRNA vaccines have proven successful in the immediate response to the pandemic, they fall short in subsequent control; on-going susceptibility to infection with waning antibody titres, lower responses in immunocompromised and older people, and off-target responses remain major challenges. Solving these problems for the construction of next generation mRNA vaccines requires an understanding of the mechanism of action (MoA) at the cellular level in responding issue. Challenge the project addresses: The in vivo tissue based MoA of mRNA vaccines has only been partially studied in humans, with few indicators as to how to improve vaccine design. To address this, we propose to study the in vivo lymph node MoA of a paradigm mRNA COVID-19 vaccine where responses are optimal (healthy volunteers) and suboptimal (participants on anti-TNF and older people). These comparator groups have been selected to provide a reductionist model (anti-TNF) and a highly clinically relevant patient model with an overlapping, functionally impaired, waning response phenotype (older people). Observational studies in humans receiving anti-TNF indicate persistence of the response to mRNA vaccines to be TNF dependent. Our studies in TNF deficient (TNFRDKO ) mice showed that cellular infiltration into the draining lymph node and formation of GCs is critical to mRNA vaccine function, and that this is TNF mediated. Together these data indicate that TNF signalling in the responding secondary lymphoid tissue is critical to mRNA vaccine function. This TNF dependence could explain suboptimal responses in older people, given pro-inflammatory changes with age that dysregulate TNF signalling. We hypothesise that directly examining the draining secondary lymphoid tissue in health and in settings of impaired immunity will provide key insights into MoA of mRNA vaccines. Aims and objectives: We will dissect the cellular mechanism of a first-generation mRNA vaccine (Spikevax, Moderna) in an established experimental medicine setting in clinically relevant groups. The response to intramuscular injection with mRNA vaccine encoding the seasonally updated SARS-CoV-2 spike protein will be measured in draining lymph nodes in the axilla imaged by ultrasound (US) and sampled using fine needle aspiration (FNA), coupled with measurements in the blood. This approach is suited to analysis with single-cell sequencing technologies (scRNA-seq, TCR- and BCR-seq, CITE-seq) yielding multiple data streams with which to test our hypotheses and to generate downstream avenues for research. Aim 1: To dissect the TNF-dependent cell signalling pathways in secondary lymphoid tissue in response to lipid encapsulated mRNA immunisation in participants with and without inhibition of TNF signalling. Aim 2: To measure cellular responses in secondary lymphoid tissue to mRNA vaccination dependent on TNF-signalling in older participants compared with controls. Our scientific objectives are designed to measure the specialised lymph node cells that respond to mRNA vaccines. Potential applications and benefits: Demonstration of tissue-based immunological function of mRNA will be a significant step forward in mRNA science. If our hypothesis is correct, it will open a major signalling pathway (TNF/TNFR1/TNFR2) as an avenue for the construction of next generation mRNA vaccines, and the unsupervised approach of scRNA-seq will yield alternate hypotheses for investigation. Our experiments will provide proof-of-principle for the cellular targets for novel mRNA vaccine discovery and establish our experimental medicine model for testing future constructs.