Project 3 (Goldrath) In response to infection, many cellular factors cooperate to direct T cells through their expansion and differentiation to effector cells that mediate pathogen clearance and memory cells that persist to provide long- lived host protection from reinfection. Harnessing the functionality and longevity of memory T cells is the basis for some vaccines and has become an attractive approach in cancer immunotherapy. However, the memory T cell pool is heterogeneous, and it is currently unclear which subsets confer optimal protection during malignancy or infection and how these subsets are transcriptionally programmed. We propose to define the transcriptional and chromatin regulatory factors of memory T cell subset differentiation following infection and identify those that promote accumulation and function of anti-tumor cytotoxic lymphocytes. Further, we will explore the relationship between changes in chromatin configuration and memory T cell-specific transcriptional programs. We propose highly collaborative Aims which leverage the expertise, infrastructure and technologies unique to the Crotty- Pipkin-Goldrath laboratories and Cores. Specifically, we will: (1) Resolve the functional heterogeneity and transcriptional programming of circulating CD8 memory T cell populations. (2) Define the transcriptional and epigenetic programming of stem-like memory, effector, and tissue-resident CD8 T cell subsets in tumors. (3) Resolve the roles of Blimp1 and Bcl6 in programming distinct CD4 memory T cell populations. (4) Dissect the mechanism(s) by which the chromatin regulatory factor CTCF instructs memory T cell differentiation. By developing an understanding of the factors that control differentiation and function of memory T cell subsets, it may be possible to induce or regulate their activity in the context of infection, malignancy, and immunopathology.