ESTRO 2025 - Abstract Book

S3876

Radiobiology - Immuno-radiobiology

ESTRO 2025

Germany. 3 National Center for Tumor Diseases (NCT), Partner Site Dresden; German Cancer Research Center (DKFZ), Heidelberg, Germany, Dresden, Germany. 4 Department of Oral and Maxillofacial Surgery, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany. 5 Department of Otorhinolaryngology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany. 6 German Cancer Consortium (DKTK), partner site Dresden and German Cancer Research Center (DKFZ), Heidelberg, Germany. 7 Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany Purpose/Objective: Most patients with head and neck squamous cell carcinoma (HNSCC) are diagnosed at the locally advanced (LA) stage. Despite treatment advances, LA HNSCC has a high risk of local and distant recurrence, and the reliable stratification of HPV-negative patients for prediction of treatment outcomes is yet missing. We aim to identify the key biological regulators of HNSCC radioresistance and immune evasion, validate their relevance in the retrospective cohorts of LA HNSCC, and target them in vitro and in animal models using CD98hc-targeted immune therapy with a switchable universal CAR (UniCAR) T cells in combination with radio(chemo)therapy. Material/Methods: The role of CD98hc and the CD98hc-dependent amino acid transporters (AATs) LAT1, LAT2, and xCT in the regulation of tumor radioresistance, immune activation, and tumor metabolism was analyzed by radiobiological assays, RNAseq, Seahorse assay, luciferase reporters, ROS measurement and ChIP analysis and other standard laboratory methods. The efficacy of CD98hc-targeted UniCARs in combination with radiotherapy was analyzed in 3D tumor spheroid cultures, patient-derived organoids, and murine HNSCC xenograft models. To delineate the subsets of the tumor infiltrating UniCAR T cells, we conducted a single-nuclear RNA sequencing (snRNAseq). The levels of protein expression in tumor tissues from patients with LA HNSCC treated with postoperative radio(chemo)therapy (PORT-C) (n=128) were evaluated by immunohistochemical analysis and correlated with locoregional control (LRC) rates. Results: The retrospective analyses in patients with locally advanced HNSCC treated with PORT-C revealed that combined protein expression signature for the CD98hc-related AATs is associated with lower LRC rates (p=0.005). Genetic or chemical inhibition of AATs in several HNSCC cell lines decreased stemness, anti-oxidative capacity, clonogenic cell survival, DNA repair efficiency, and induced immune-activating pathways. The efficacy of CD98hc-targeting UniCAR T cells for eradicating HNSCC was first validated in 3D tumor models. The synergistic effect of this treatment with radiotherapy in vitro has also been confirmed in vivo . The tumor-bearing mice treated with a combination of UniCAR immunotherapy and cisplatin-based radiochemotherapy had delayed tumor growth and improved tumor-free survival as compared to radiochemotherapy (p=0.02) or immunotherapy (p=0.0002) alone. No toxicity was observed for combination therapy. The UniCAR infiltration into experimental tumors has been confirmed by immunohistochemical analysis and snRNA-seq. Conclusion: The expression of CD98hc-AATs is associated with HNSCC radioresistance, stemness, and immune evasion. The CD98hc-targeted UniCAR-T immunotherapy synergies with radiotherapy in vitro and in vivo . The CD98hc-AATs are clinically relevant biomarkers of HNSCC radioresistance and a promising target for further clinical trials. References: 1. Digomann D, et al. The CD98 Heavy Chain Is a Marker and Regulator of Head and Neck Squamous Cell Carcinoma Radiosensitivity. Clin Cancer Res. 2019;25: 3152-3163. 2. Koseer AS, et al. Validation of CD98hc as a Therapeutic Target for a Combination of Radiation and Immunotherapies in Head and Neck Squamous Cell Carcinoma. Cancers (Basel). 2022;14. 3. Arndt C, et al. UniCAR T cell immunotherapy enables efficient elimination of radioresistant cancer cells. Oncoimmunology. 2020;9: 1743036. Keywords: HNSCC, PORT-C, UniCARs