P1.055. Combination of CAR-T Cell Therapy With Immune Checkpoint Inhibition Enhances Anti-Tumor Efficacy in Esophageal Squamous Cell Carcinoma

Abstract Topic Esophageal Cancer: Adjuvant and Neo-Adjuvant Therapies Background Chimeric antigen receptor (CAR)-T cell therapy has limited efficacy in solid tumors like esophageal squamous cell carcinoma (ESCC). This study investigates whether combining CAR-T cells with an anti-PD-1 antibody can overcome immunosuppression and improve therapeutic outcomes by remodeling the tumor microenvironment (TME). Methods We constructed second-generation CAR-T cells targeting mesothelin, an antigen overexpressed in ESCC. Using a patient-derived xenograft (PDX) mouse model of ESCC, animals were randomized into four groups: control, anti-PD-1 monotherapy, CAR-T monotherapy, and combination therapy. Tumor growth was monitored, and tumors were analyzed by flow cytometry for immune cell infiltration, multiplex immunofluorescence for spatial distribution of T cells and PD-L1 expression, and RNA sequencing to identify altered signaling pathways. Results The combination therapy group showed superior tumor suppression compared to all other groups (p<0.001). Flow cytometry revealed a 2.5-fold increase in tumor-infiltrating CAR-T cells and a significant reduction in regulatory T cells and myeloid-derived suppressor cells in the combination group. Spatial analysis confirmed enhanced CAR-T cell penetration and decreased PD-L1+ immunosuppressive niches. RNA-seq indicated upregulation of interferon-gamma and T cell receptor signaling pathways and downregulation of TGF-β-mediated immunosuppression in the combination therapy group. Conclusion Combining mesothelin-targeted CAR-T cells with PD-1 blockade effectively reprograms the immunosuppressive TME, enhances CAR-T cell infiltration and function, and achieves significantly greater anti-tumor activity in ESCC. This combination strategy represents a promising translational approach to improve CAR-T cell efficacy in solid tumors.