Hypoxia-induced autophagy in pancreatic cancer counteracts the cytotoxicity of CD8+ T cells by inhibiting the expression of MHC-I.

Abstract

The hypoxic microenvironment is an essential feature of solid tumors. Autophagy has been controversial in its role in immune regulation. This project aims to elucidate the impact of autophagy in pancreatic cancer (PC) under specific conditions (hypoxia) on CD8⁺ T cells and the regulatory mechanisms behind it.The levels of HIF1α and autophagy were analyzed by western blot (WB) and immunofluorescence (IF). The effects of HIF1α on cell autophagy were assessed in normoxic or hypoxic treatments using KC7F2 (HIF-1 channel inhibitor) or chloroquine (autophagy inhibitor). CD8⁺ T cells were co-cultured with PC cells to assess the cytotoxicity using lactate dehydrogenase (LDH) and Hoechst/PI staining. The content of cytokines and the activation level of CD8⁺ T cells were measured by enzyme-linked immunosorbent assay (ELISA) and flow cytometry. MHC-I expression in PC cells (membranes) was analyzed using quantitative reverse transcription polymerase chain reaction (qRT-PCR), WB, IF, and flow cytometry. Humanized immune-reconstituted mice were applied to investigate the impact of HIF1α-induced autophagy on in vivo immunity.When cells were in hypoxia, the levels of HIF1α and autophagy were higher compared to normoxic conditions. Treatment with KC7F2 resulted in similar levels of HIF1α and autophagy as those in normoxic state. Chloroquine treatment reversed the autophagy level to the normoxic state. The autophagy level of PC cells transfected with oe-HIF1α was increased, with reduced MHC-I expression on cells (membranes), which impaired the cytotoxicity of CD8⁺ T cells, and thus decreasing the probability of recognition and attack by CD8⁺ T cells when co-cultured with them. In mice, overexpression of HIF1α hindered the immune suppressive function of CD8⁺ T cells and facilitated the immune escape of PC by reducing antigen presentation of MHC-I.Under hypoxia, HIF1α-induced autophagy reduces the cytotoxicity of CD8⁺ T cells by repressing MHC-I expression.