Abstract Text: Impressive progress has been made during the COVID-19 pandemic to deliver effective and safe vaccines for SARS-CoV2. However, while current vaccines can reduce disease severity, they are still not entirely able to prevent infection and transmission. In this context, immunity at barrier sites may play an important role. We are investigating mucosal vaccination approaches to improve the generation of tissue resident memory T cells (TRM) at the respiratory mucosa. Mice were immunized intramuscularly (i.m.) with Spike protein and poly I:C followed by an intranasal (i.n.) boost with the same formulation 3 weeks later and viral spike epitope-specific T cells analyzed using fluorescently labeled MHC class I and II tetramers for CD8+ and CD4+ T cells, respectively. After i.m. priming, we observed modest expansion of antigen-specific T cells in the iliac lymph nodes (ilLN) as well as lower levels of expansion in the lungs, nasal mucosa (NM) and mediastinal and mandibular lymph nodes (medLN/mandLNs), but they all waned after 21 days. After i.n. boosting, spike-specific T cells increased in ilLNs to levels similar to that during priming, while in the lungs, NM, medLNs and mandLNs, their expansion was much more robust, with the cells persisting in these tissues for at least 65 days. Most of the spike-specific CD4+ and CD8+ T cells had a TRM phenotype. Our data suggest that antigen exposure in the respiratory tract is necessary for the generation of local viral-specific T cells that will persist long term in the respiratory mucosa.
