Skin vaccination and generation of protective lung-tropic memory T cells - Respiratory viral pathogens have been responsible for major pandemics over the past two centuries with extraordinary human and economic cost. While most vaccines have focused on antibody neutralization of virus, there has been growing interest in targeting CD8 T cell immunity for more durable protective immune memory. Specifically, there has been interest in vaccines that generate tissue resident memory T cells (TRM), but one issue complicating this approach is the observed lack of durability of lung TRM, whether generated by pulmonary viral infection or targeted vaccination. Unlike TRM in other tissues, which accumulate and survive for years, lung TRM have half-lives measured in days. We have discovered an alternative population of CD8 TM that can mediate lung-focused T cell memory and protection from morbidity and mortality after skin vaccination. The durability of this immunity appears to be provided by a unique population of lung tropic CD8 T cells concentrated in the intravascular space of the lung (rather than the parenchyma). Using IAV as a model viral respiratory pathogen, these CD8 T cells appear to rapidly extravasate and enter lung parenchyma within hours after infection, providing a rapid on demand protective memory response with kinetics comparable to lung TRM. Their activity does not require CD4 T cells, and elimination of these CD8 TM cells completely abrogates robust vaccine protection. Analysis of these cells by scRNAseq reveals that they have circulatory markers, but also immediate-early genes reminiscent of skin TRM generated from the same vaccination. They are transcriptionally distinct from spleen TEM and LN TCM generated by the same vaccination and appear to be robust >6 months later. Most importantly, they provide complete protection from morbidity and mortality from viral lung challenge and function independently of antibodies and B cells. Using defined genetic models, scRNA seq, ATACseq, multidimensional flow cytometry, and lung intravital microscopy, we will test key hypotheses about the mode of generation, in vivo biological behavior, and protective immunity of these cells. We have assembled expert collaborators in each of these areas to fully explore the biology of these cells and the potential of generating these cells by epidermal disruption (ed) vaccination. We believe that these TM cells are an important and unstudied component of normal T cell memory designed to provide superior and long-lasting lung immunity without occupying valuable lung parenchymal space. We believe that optimized generation of these cells by improved vaccination approaches will provide a superior way to combat respiratory viral pathogens.
