Combination of downregulating FEN1 and PD‐1 blockade enhances antitumor activity of CD8+ T cells against HNSCC cells in vitro

Abstract

AbstractBackgroundProgrammed cell death ligand 1 (PD‐L1) and human leukocyte antigen/major histocompatibility complex (HLA/MHC) are two main kinds of immunophenotypes affecting the susceptibility to anti‐PD therapy. Our previous study found that down‐regulation of flap endonuclease‐1 (FEN1) could not only inhibit PD‐L1 expression, but also upregulate HLA expression in head and neck squamous cell carcinoma (HNSCC). We aimed to clarify whether downregulating FEN1 cloud enhance the response to PD‐1 blockade, and possible mechanisms in HNSCC in vitro.MethodsDifferential expression of FEN1 in HNSCC tumor and normal tissues were explored in the TIMER and TISIDB datasets. A HNSCC cells/CD8+ T cells co‐culture model was established. HNSCC cell cycle and apoptosis were recorded by flow cytometry. Immune activity markers of granzyme A, granzyme B, and PRF1 expressed in the CD8+ T cells, and IFN‐γ, IL‐2, and TNF‐α secreted in the supernatants were detected by western blot, ELISA, respectively.ResultsFEN1 was highly expressed in HNSCC and associated with low immune infiltration. Downregulating FEN1 could induce HLA class I expression, and inhibit PD‐L1 expression in HNSCC cells. Functionally, FEN1 knockdown enhanced the response to αPD‐1 mAb by mediating G2/M phase arrest, apoptosis of HNSCC cells. Mechanistically, targeting FEN1 synergized with αPD‐1 mAb could reinforce the antitumor response of CD8+ T cells against HNSCC cells, as indicated by increasing granzyme A, granzyme B, and PRF1 expressions, and promoting IFN‐γ, IL‐2, and TNF‐α secretions.ConclusionThese findings might offer a potential combined strategy for patients resistant to anti‐PD therapy via combining FEN1 knockdown and PD‐1 blockade.