PI3K Delta Inhibition Alters CD8 T Cell Différentiation and Reprograms the Tumor Microenvironment Following Adoptive Immunotherapy 2247548
T cell exhaustion limits the durability of adoptive cell therapy (ACT) in solid tumors. Because PI3Kδ signaling governs T cell differentiation, we hypothesized that transient, high-dose PI3Kδ inhibition would endow T cells with durable stemness and metabolic fitness to resist terminal exhaustion and alter the immune composition of the tumor microenvironment (TME). Mouse and human T cells were treated in vitro with the PI3Kδ inhibitor CAL-101 (30 uM) prior to chronic antigen stimulation and ACT into B16 melanoma. Metabolic fitness was assessed by mitochondrial dependence and spare respiratory capacity. Single-cell RNA sequencing and spatial transcriptomics profiled T cell states, spatial localization, and TME remodeling post ACT. Pathway analyses interrogated oxidative phosphorylation (OXPHOS), glycolysis, proliferation, inflammatory signaling, and myeloid composition. CAL-101—treated T cells acquired enhanced stemness and metabolic fitness, with increased mitochondrial dependence and spare respiratory capacity while maintaining normal basal metabolism. Under chronic stimulation, including in human T cells, they resisted terminal exhaustion and preserved stem-like properties. In tumors, treated cells preferentially differentiated into progenitor exhausted T cells (Tpex), displayed superior infiltration, and upregulated the Cxcl10/Cxcr3 axis. Tumors harboring CAL-101—treated T cells showed reduced glycolysis, OXPHOS, and proliferation alongside increased pro-inflammatory signaling and fewer immunosuppressive tumor-associated macrophages. Single-cell analysis revealed CAL-101 treated T cells concurrently increased OXPHOS, proliferation, and immune signaling pathways. Brief PI3Kδ inhibition programs T cells with stemness and metabolic fitness that favor Tpex differentiation, resist terminal exhaustion, and remodel the TME toward an inflammatory state, supporting a practical strategy to improve ACT efficacy in solid tumors. NIH RO1 grant: CA257954, Dartmouth TQCR Training Grant: T32CA260626 Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)