Targeting p-FGFR1 Enhances CD8+ T Cells Infiltration and Overcomes Immunotherapy Resistance in Esophageal Squamous Cell Carcinoma by Regulating the CXCL8-CXCR2 Axis.

Esophageal squamous cell carcinoma (ESCC) is a fatal malignant tumor. Several studies have demonstrated that immune checkpoint inhibitors can provide clinical benefits to patients with ESCC. However, the single-agent efficacy of these agents remains limited. Although combination therapies (e.g., radiotherapy, chemotherapy) can help to overcome immunotherapy resistance in ESCC, their severe side effects limit clinical application. This study aimed to explore new resistance mechanisms to immunotherapy in ESCC and identify novel molecular targets to overcome immunotherapy resistance. We employed immunohistochemistry staining to examine the p-FGFR1 in tumor samples obtained from 103 patients with ESCC, in addition to evaluating CD8+ T cell infiltration. In vitro expression, western blotting, CCK-8, 5-bromo-2'-deoxyuridine incorporation assays, and migration assays were used to confirm the impact of AZD4547 on p-FGFR1 expression and the proliferation and migration in ESCC cell lines. Through RNA sequencing analysis, databases such as the Cancer Genome Atlas (TCGA) and Gene Set Cancer Analysis (GSCA), and the reconstruction of transgenic mice using the humanized immune system, we validated the correlation between the expression of p-FGFR1 and CD8+ T cell infiltration. We also explored how p-FGFR1 recruits myeloid-derived suppressor cells (MDSCs) through the CXCL8-CXCR2 axis to suppress the therapeutic efficacy of immunotherapy in ESCC. Finally, the tumor-suppressive effects of AZD4547 combined with immunotherapy were confirmed in vivo in tumor-bearing mice with a humanized immune system. We found that the inhibition of p-FGFR1 expression in ESCC can enhance CD8+ T cell infiltration by suppressing the CXCL8--XCR2 recruitment of MDSCs. AZD4547, combined with immunotherapy, further promotes immunotherapeutic efficacy in ESCC. In conclusion, our study presents a promising model for combination therapy in ESCC immunotherapy.