Defining the niche for stem-like CD8 + T cell formation and function.

TCF-1 + CD8 + T cell populations have emerged as critical determinants for long-lived immunological memory. This cell population has stem-like properties and is implicated in improved disease outcomes by driving sustained killing of infected cells and maintaining the immune-cancer equilibrium. During an immune response, several factors, including antigen deposition and affinity, the inflammatory milieu, and T cell priming dynamics, aggregate to skew CD8 + T cell differentiation. Although these mechanisms are altered between acute and chronic disease settings, phenotypically similar stem-like TCF-1 + CD8 + T cell states are formed in each of these settings. Here, we characterize the specialized microenvironments within lymph nodes and the tumor microenvironment, which foster the generation or re-activation of stem-like TCF-1 + CD8 + T cell populations. We highlight the potential for targeting the stem-like CD8 + T cell niche to enhance vaccination and cancer immunotherapy and to track the trajectory of stem-like CD8 + T cells as biomarkers of therapeutic efficacy.