Tumor-intrinsic PD-L1 regulates tumor initiating cell virulence and stemness genes, and TCF1+ stem-like T cells through Raptor in ovarian cancer, which correlates with survival in high grade serous ovarian cancer

Abstract

Abstract We reported that tumor intrinsic PD-L1 promotes tumor initiating cell (TIC) virulence and mTORC1. Others have focused on PI3K/AKT/mTOR in promoting TIC, but specific downstream mTOR regulators of tumor stemness are unknown. We knocked down Raptor (mTORC1 component, Rptorlo) in ID8agg cells (murine ovarian cancer). Rptorlo cells had reduced mTORC1 with no change in PD-L1 in total cells or CD44+CD24+ TIC. %TIC was reduced in Rptorlo cell cultures, and Rptorlo TIC were functionally defective for self-renewal by tumorosphere formation. Rapamycin (mTORC1 inhibitor) reduced ID8agg Rptor, tumorospheres, and the stemness and virulence genes Oct4 and Nanog. Oct4 knockin to PD-L1lo ID8agg restored TIC numbers and spheres. Together, data confirm PD-L1 drives stemness through Oct4 by increasing mTORC1. Rptorlo TIC formed significantly smaller tumors vs. control TIC in immunodeficient NSG mice, confirming TIC intrinsic Rptor drives immune independent virulence. In wild type mice, Rptorlo vs. control TIC produced less ascites and smaller tumors with lower %TIC in vivo (but similar PD-L1), significantly more recently-activated CD44hiCD62LloCD8+ cells in ascites and draining lymph nodes (DLN). CCR2+CD8+ T cells and CXCR5+TCF1+PD-1+Tim3− stem-like T cells were also increased in Rptorlo DLN. Thus, Rptorlo TIC influence systemic and tumor-associated immunity. In high grade serous ovarian tumors (The Cancer Genome Atlas) high Rptor expression predicted a significantly higher cancer stem cell signature, and lower median survival in late stage patients. Our work establishes tumor intrinsic Rptor driven by PD-L1 plays a key role in regulating TIC and stem like T cells and can be a prognostic marker for late stage ovarian cancer patients.