Differentiation and function of intestinal tissue-resident memory T cells

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T cells play a critical role eliminating pathogens and the generation of memory T cells is an important component in protection from secondary infection. Memory T cells can be divided into two groups based on their location, those that are capable of circulating throughout the body and those that are lodged in tissues, poised to respond rapidly to secondary infection. Tissue-resident memory T cells (Trm) cells remain in the tissue and are not replenished by circulating cells after infection is resolved. Circulating T cells are often not sufficient to protect from secondary infection; therefore, it is of significant interest to determine how Trm cells are generated and maintain their function over time. Only a small number of microbes need to breach the mucosal surface to initiate disease. The ability of adaptive immune cells to locate pathogens in large, complex tissues and eliminate them before they disseminate to deeper tissues is a necessary component of protective immunity. We have used infection with the intestinal pathogen Yersinia pseudotuberculosis to examine pathogen-specific CD8+ Trm during infection, and using this model we have uncovered significant phenotypic heterogeneity in intestinal Trm cells, with expression of the integrin CD103 defining these populations. Proximity of T cells to areas of infection within the intestinal tissue regulates Trm differentiation, with inflammation and activation of the transcription factor STAT4 leading to increased numbers of CD103 Trm cells. This proposal will identify the underlying mechanisms that regulate the differentiation and maintenance of the CD103 Trm subset. We have already shown a critical role for CD103 Trm cells in controlling pathogen replication during primary infection, and we have developed new tools to analyze the division of labor between Trm subsets during secondary infection. These findings will address a fundamental gap in our knowledge regarding the function of Trm cells in controlling intestinal colonization during secondary infection. Additionally, it is currently unclear whether either Trm subset alone is sufficient to confer protection, and we will determine if the full complement of Trm cells is necessary for robust immunity. This work will identify strategies to maximize the number and persistence of Trm cells, an important component of any successful vaccination strategy to target mucosal pathogens.