Progressively Enhancing Stemness of Adoptively Transferred T Cells with PI3Kd Blockade Improves Metabolism and Antitumor Immunity

Generating stem-like memory T cells (T_SCM) is a potential strategy to improve adoptive immunotherapy. Elucidating optimal ways to modulate signaling pathways that enrich T_SCM properties could identify approaches to achieve this goal. We discovered herein that blocking the PI3Kd pathway pharmaceutically to varying degrees can generate T cells with increasingly heightened stemness properties, based on the progressive enrichment of the transcription factors Tcf1 and Lef1. T cells with enhanced stemness features exhibited metabolic plasticity, marked by improved mitochondrial function and glucose uptake after tumor recognition. Conversely, T cells with low or medium stemness were less metabolically dynamic, vulnerable to antigen-induced cell death, and expressed more inhibitory checkpoint receptors. Only T-cell receptor–specific or chimeric antigen receptor (CAR)-specific T cells with high stemness persisted in vivo and mounted protective immunity to tumors. Likewise, the strongest level of PI3Kd blockade in vitro generated human tumor-infiltrating lymphocytes and CAR T cells with elevated stemness properties, in turn bolstering their capacity to regress human solid tumors. The stemness level of T cells in vitro was important, ultimately impacting their efficacy in mice bearing three distinct solid tumors. Lef1 and Tcf1 sustained antitumor protection by donor high CD8^þ T_SCM or CD4^þ Th17_SCM, as deletion of either one compromised the therapeutic efficacy. Collectively, these findings highlight the importance of strategic modulation of PI3Kd signaling in T cells to induce stemness and lasting protective responses to solid tumors.