PROJECT SUMMARY Developing immunological memory is crucial for surviving deadly pandemics and while a better understanding of how memory B and T cells form and function is being gained, there are still many gaps in knowledge that limit our ability to create superior vaccines for several pathogens and new immunotherapies. CD8+ T cells differentiate into heterogeneous subsets that display diverse functions, migration patterns and long- term fates to protect against recurrent viral infection. How CD8+ T cells toggle between less-, intermediate- and terminally-differentiated states remains a major question because this can influence the number and quality of memory T cells that form. Great progress has been made in identifying transcription factors (TFs) and epigenetic writers and erasers that control CD8+ T cell differentiation states, particularly the long-lived, multi-potent memory precursor (MP) cells and shorter-lived, terminally-differentiated effector (TE) cells. But it is unclear what determines which enhancers open and close to permit the targeting of these factors to specific loci that ultimately creates the molecular foundation for a range of gene expression patterns and differentiation states in T cells. To address this question, we are focusing on the nucleosome remodeling BRG1/BRM associated factor (BAF) complexes because they sculpt the chromatin landscape by moving or evicting nucleosomes to control accessibility of TFs and other chromatin modifiers. There are three major BAF complexes (cBAF, ncBAF and PBAF), but BAF complexes lack intrinsic DNA- binding specificity, and therefore how their chromatin remodeling activities are targeted within the genome remains poorly understood. We hypothesize that lineage-specifying TFs target BAF complexes to discrete loci in activated T cells, allowing BAF in turn, to make enhancers and promoters accessible for other TFs and chromatin modifiers to regulate the spectrum of effector and memory CD8+ T cell fates that form during infection. Our preliminary data show that cBAF is critical for the differentiation of TE cells in viral infection, demonstrating that cBAF restricts CD8+ T cell plasticity and memory cell potential. This proposal aims to ‘map’ cBAF activity across the genome to decode how it controls enhancer accessibility for specific TFs and other epigenetic regulators such as CTCF and PRC2 in differentiating effector and memory CD8+ T cells. Conversely, we will identify how certain TFs control cBAF recruitment to open-up sites that permit new differentiation states to arise. This grant will also help us understand how nucleosome remodeling allows T cells to listen to certain signal inputs while insulating themselves from others during infection to adopt specific differentiation states. Lastly, this proposal will determine how the BAF complexes regulate the stability of or interconversion between T cell differentiation states, and establish if cBAF, ncBAF and PBAF play cooperative or oppos...