ID #753 ESTABLISHMENT OF A HIGH-FIDELITY SYNGENEIC MODEL FOR ATYPICAL TERATOID/RHABDOID TUMOR (AT/RT) RESEARCH

Abstract

Atypical Teratoid/Rhabdoid Tumor (AT/RT) is the most common malignant brain tumor in infants <3 years, representing 10–15% of pediatric CNS malignancies. This lethal embryonic tumor is driven by biallelic inactivation of the chromatin-remodeling gene Smarcb1. Despite aggressive multimodal therapy (surgery, chemotherapy, radiotherapy), median overall survival remains <12 months. Current AT/RT research relies heavily on immunodeficient xenograft models, which fail to recapitulate the tumor microenvironment (TME) and cannot adequately evaluate immunotherapeutic strategies. Syngeneic immunocompetent models are essential for understanding TME composition and immune dynamics critical to developing next-generation treatments. Spontaneous AT/RT tumors were generated in an inducible Smarcb1fl/fl;Rosa26-CreERT2 mouse model (tamoxifen induction at E6–E7, Han et al., 2016) by Franck Bourdeaut’s laboratory at Institut Curie, Paris. Tumor explants were established as a stable syngeneic cell line and implanted orthotopically using the guide screw method into immunocompetent C57BL/6 hosts. Tumors were characterized by: (i) immunohistochemistry and western confirming biallelic SMARCB1 loss; (ii) in vivo growth kinetics and survival curves; and (iii) single-cell RNA sequencing (scRNA-seq) of tumor and immune compartments. The established cell line demonstrated 100% penetrance with aggressive growth kinetics. ScRNA-seq analysis revealed a macrophage-dominant tumor microenvironment (72% of immune infiltrate), with T-cell exhaustion markers (PD1+, TIM3+) and minimal lymphocyte infiltration. Notably, this immune phenotype closely mirrors observations in human AT/RT patient samples, establishing our model as a high-fidelity platform. This immunocompetent syngeneic AT/RT model recapitulates human disease immune architecture and provides a robust platform for studying tumor-immune interactions and evaluating immunotherapeutic strategies, including oncolytic virotherapy, checkpoint modulation, and adoptive cell therapies. This model will accelerate clinical translation of promising approaches for this uniformly fatal pediatric malignancy.