In vivo CRISPR screening reveals nutrient signaling processes underpinning CD8⁺ T cell fate decisions

How early events in effector T cell (T_EFF) subsets tune memory T cell (T_MEM) responses remains incompletely understood. Here, we systematically investigated metabolic factors in fate determination of T_EFF and T_MEM cells using in vivo pooled CRISPR screening, focusing on negative regulators of T_MEM responses. We found that amino acid transporters Slc7a1 and Slc38a2 dampened the magnitude of T_MEM differentiation, in part through modulating mTORC1 signaling. By integrating genetic and systems approaches, we identified cellular and metabolic heterogeneity among T_EFF cells, with terminal effector differentiation associated with establishment of metabolic quiescence and exit from the cell cycle. Importantly, Pofut1 (protein-O-fucosyltransferase-1) linked GDP-fucose availability to downstream Notch-Rbpj signaling, and perturbation of this nutrient signaling axis blocked terminal effector differentiation but drove context-dependent T_EFF proliferation and T_MEM development. Our study establishes that nutrient uptake and signaling are key determinants of T cell fate and shape the quantity and quality of T_MEM responses.