Abstract LB310: Single-cell transcriptomics and TCR clonality reveal a role for immunotherapy in pediatric brain tumors

Abstract Central nervous system tumors are the most common solid tumors and the leading cause of cancer-related deaths in children. Outcomes remain dismal for a significant proportion of patients despite aggressive multimodal therapy and survivors suffer from treatment-related morbidity and neurological deficits. Despite their remarkable success in adult cancers, immunotherapies are not approved for pediatric brain tumors. Several factors like the relatively smaller patient population, a tumor location that makes them difficult to access through biopsies and poorly-studied tumor immune microenvironment (TME) have posed challenges in advancing immunotherapeutic options for these patients. Immune checkpoint blockers (ICB) tested in unstratified cohorts of children with brain tumors have not shown promising results; therefore, the role of immunotherapy remains unclear. Because the magnitude and nature of pre-existing T cell responses in the tumor has been shown to correlate with response to ICB, we asked if pediatric brain tumors show evidence of such favorable T cell responses. In the current study, we address this question using an unbiased approach to analyze the clonal relationship and transcriptional status of T cells present in tumor tissue of children with brain tumors using paired single-cell RNA-sequencing and TCR-sequencing. Our results demonstrate that a large fraction of T cells in the tumor tissue are clonally expanded with potential to recognize tumor antigens. Such clonally-expanded T cells display states linked to anti-tumor immunity, express higher levels of transcripts encoding for molecules linked to T cell activation, effector functions, immune cell recruitment, tissue-residency, immune checkpoints, and importantly, show significant enrichment of signatures linked to neoantigen-specific T cells and immunotherapy response. Notably, we identify several neoantigens in pediatric brain tumors, and show that neoantigen-specific T cell gene signatures are linked to better survival outcomes in high-grade glioma. We further show that PD1-expressing CD8+ T cells in pediatric brain tumors are indeed functional as evidenced by their capacity for cytotoxicity, cytokine production and proliferation. Among the patients in our cohort, we observe substantial heterogeneity in the degree of clonal expansion and expression of transcripts encoding immune checkpoints in tumor-infiltrating T cells. Overall, our findings suggest that accurate characterization of intra-tumoral T cell responses for features linked to immune check point therapy (ICB) response may enable selection of patients where immunotherapy is likely to be beneficial, an approach that requires prospective validation in future clinical trials. Citation Format: Anusha Preethi Ganesan, Aditi Upadhye, Kevin Meza Landeros, Ciro Ramírez-Suástegui1, Benjamin Schmiedel, Edwin Woo, Serena J. Chee, Denise Malicki, Nicole Coufal, David Gonda, Michael Levy, Jason Greenbaum, Gregory Seumois, John Crawford, William Roberts, Stephen Schoenberger, Hilde Cheroutre, Christian Ottensmeier, Pandurangan Vijayanand. Single-cell transcriptomics and TCR clonality reveal a role for immunotherapy in pediatric brain tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB310.