The Salivary Gland Acts as a Sink for Tissue-Resident Memory CD8+ T Cells, Facilitating Protection from Local Cytomegalovirus Infection

• MCMV infection leads to effective generation of CD8+ and CD4+ TRM cells in the SG
• TRM generation in the SG depends on cognate antigen for CD4+, but not CD8+, T cells
• Memory CD8+ T cells protect from localized MCMV challenge infection
• Early target cells of intraglandular infection resist MHC I downregulation

SummaryTissue-resident memory T cells (TRM) reside in barrier tissues and provide local immediate protective immunity. Here, we show that the salivary gland (SG) most-effectively induces CD8+ and CD4+ TRM cells against murine cytomegalovirus (MCMV), which persists in and spreads from this organ. TRM generation depended on local antigen for CD4+, but not CD8+, TRM cells, highlighting major differences in T cell subset-specific demands for TRM development. CMV-specific CD8+ T cells fail to control virus replication upon primary infection in the SG due to CMV-induced MHC I downregulation in glandular epithelial cells. Using intraglandular infection, we challenge this notion and demonstrate that memory CD8+ T cells confer immediate protection against locally introduced MCMV despite active viral immune evasion, owing to early viral tropism to cells that largely withstand MHC I downregulation. Thus, we unravel a yet-unappreciated role for memory CD8+ T cells in protecting mucosal tissues against CMV infection.

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