Intravital mucosal imaging of CD8 resident memory T cells shows tissue-autonomous recall responses that amplify secondary memory.

CD8 T cell immunosurveillance dynamics influence the outcome of intracellular infections and cancer. Here we used two-photon intravital microscopy to visualize the responses of CD8 resident memory T cells (T cells) within the reproductive tracts of live female mice. We found that mucosal T cells were highly motile, but paused and underwent in situ division after local antigen challenge. T cell reactivation triggered the recruitment of recirculating memory T cells that underwent antigen-independent T cell differentiation in situ. However, the proliferation of pre-existing T cells dominated the local mucosal recall response and contributed most substantially to the boosted secondary T cell population. We observed similar results in skin. Thus, T cells can autonomously regulate the expansion of local immunosurveillance independently of central memory or proliferation in lymphoid tissue.