编程细胞死亡配体1（PD-L1）和人类白细胞抗原/主要组织相容性复合体（HLA/MHC）是影响抗PD疗法易感性的两种主要免疫表型。我们以前的研究发现，下调剪切末端核酸内切酶-1（FEN1）不仅可以抑制PD-L1表达，还可以上调头颈部鳞状细胞癌（HNSCC）中HLA的表达。我们的目标是阐明是否通过下调FEN1可以增强对PD-1阻滞的反应，并研究其可能的机制在HNSCC细胞系中。在TIMER和TISIDB数据库中探索了HNSCC肿瘤和正常组织中FEN1的差异表达。建立了HNSCC细胞/CD8+ T细胞共培养模型。通过流式细胞术记录HNSCC细胞的细胞周期和凋亡。通过Western blot和ELISA检测CD8+ T细胞中的免疫活性标志物鳞状蛋白酶A、鳞状蛋白酶B和PRF1的表达，以及上清液中分泌的IFN-γ、IL-2和TNF-α。FEN1在HNSCC中高表达，与免疫浸润低相关。下调FEN1可以诱导HLA第一类的表达，并抑制HNSCC细胞中的PD-L1表达。功能上，FEN1敲下通过介导G2/M期阻滞和HNSCC细胞的凋亡增强了对αPD-1单抗的反应。在机制上，靶向FEN1与αPD-1单抗协同作用可以加强CD8+ T细胞对HNSCC细胞的抗肿瘤反应，如增加鳞状蛋白酶A、鳞状蛋白酶B和PRF1的表达，并促进IFN-γ、IL-2和TNF-α的分泌。这些发现可能为抗PD疗法耐药的患者提供了一种潜在的联合策略，即通过组合FEN1敲下和PD-1阻断。© 2023 John Wiley & Sons A/S. John Wiley & Sons Ltd. 发表

Programmed 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.Differential 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.FEN1 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.These findings might offer a potential combined strategy for patients resistant to anti-PD therapy via combining FEN1 knockdown and PD-1 blockade.© 2023 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.