Reducing PI3Kδ signaling in a dose-dependent manner promotes human T cell stemness

Abstract

Abstract Adoptive T Cell Therapy (ACT) is a promising type of highly personalized immunotherapy against cancer. However, during the clinical production of T cell products for ACT, the cells experience cues that lead to early senescence and poor quality. Thus, ways to improve T cell quality for ACT is warranted. Previous mouse data indicate that inhibiting the PI3Kδ pathway in T cells using Idelalisib, an FDA-approved selective inhibitor of the δ subunit of PI3K, produces less differentiated T cells with enhanced efficacy against cancer. We hypothesized that Idelalisib treatment in human T cells would recapitulate a dose-dependent acquisition of stemness features. Mouse T cells, bulk donor human peripheral blood mononuclear cells (PBMCs), and isolated human CD3+ T cells were cultured in vitrofor seven days with dose escalation of Idelalisib. We counted the number of T cells to track expansion and assessed the phenotype through flow cytometry. Reducing PI3Kδ signaling produced a less differentiated phenotype in both murine and human CD3+ T cells. Human CD3+ T cells had lower expression of TCF-1 and LEF-1, transcription factors regulating stemness, due to Idelalisib. However, other markers (CD62L and CD45RA) still suggested dose escalation up to 25 μM led to less differentiation. PBMCs and CD3+ T cells treated with dosages of Idelalisib above 10 μM had limited expansion and decreased viability compared to mouse T cells. Altogether, our data demonstrate that blocking PI3Kδ with Idelalisib in human T cells supports acquisition of stemness features.