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

Tissue-resident memory T cells (T-RM) reside in barrier tissues and provide local immediate protective immunity. Here, we show that the salivary gland (SG) most-effectively induces CD8(+) and CD4(+) T-RM cells against murine cytomegalovirus (MCMV), which persists in and spreads from this organ. T-RM generation depended on local antigen for CD4(+), but not CD8(+), T-RM cells, highlighting major differences in T cell subset-specific demands for T-RM 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.