The degree of T cell stemness differentially impacts the potency of adoptive cancer immunotherapy in a Lef-1 and Tcf-1 dependent manner.

Generating stem memory T cells (TSCM) is a key goal for improving cancer immunotherapy. Yet, the optimal way to modulate signaling pathways that enrich TSCM properties remains elusive. Here, we discovered that the degree to which the PI3K{delta} pathway is blocked pharmaceutically can generate T cells with differential levels of stemness properties. This observation was based on the progressive enrichment of transcriptional factors of stemness (Tcf-1 and Lef-1). Additional investigation revealed that T cells with high stemness features had enhanced metabolic plasticity, marked by heightened mitochondrial function and glucose uptake. Conversely, T cells with low or medium features of stemness expressed more inhibitory checkpoint receptors (Tim-3, CD39) and were vulnerable to antigen-induced cell death. Only TCR-antigen specific T cells with high stemness persisted following adoptive transfer in vivo and mounted protective immunity to melanoma tumors. Likewise, the strongest level of PI3K{delta} blockade in vitro generated human tumor infiltrating lymphocytes (TILs) and CAR T cells with heightened stemness properties, in turn bolstering their capacity to regress human mesothelioma tumors. We find that the level of stemness T cells possess in vitro differentially impacts their potency upon transfer in three tumor models. Mechanistically, both Lef-1 and Tcf-1 sustain anti-tumor protection by high TSCM, as deletion of either one compromised cellular therapy. Collectively, these findings highlight the therapeutic potential of carefully modulating PI3K{delta} signaling in T cells to confer high stemness and mediate protective responses to solid tumors.