Abstract 3445: Immuno-transcriptomic profiling identifies actionable genomic alterations in pediatric solid malignancies
Authors: Wei Jun S. , Brohl Andrew S. , Sindiri Sivasish , Milewski David , Song Young K. , Nagaraj Sushma , Gangalapudi Vineela , Wen Xinyu , Ladanyi Marc , Khan Javed 
Published: September 2020

Abstract
Malignancy remains the leading cause of disease-related death in children. To identify potential tumor-driving molecular targets and characterize immunogenomic profiles in pediatric cancers, we performed RNA-seq analysis on a cohort of 788 pediatric solid tumors across 14 different diagnoses in conjunction with additional 147 normal tissues for comparison. Sequencing data were analyzed for expressed mutations, fusion events, and expressional patterns, providing therapeutic targets and rich cancer biology for these childhood cancers. Furthermore, we describe a comprehensive and in-depth immunogenomic landscape of these solid tumors including immune cell infiltrate, neoepitope analysis from expressed mutations and fusions, expressional patterns of clinically relevant immune checkpoint genes, expression of tumor-specific genes as potential pharmacological or immunological targets, and T cell receptor repertoire. Across the cohort, we observed a striking correlation between the expressed neoepitope burden in tumors and enrichment of the effector immune signatures. Intriguingly, canonical fusions (e.g. EWS-FLI1) contribute a disproportionally large number of neoepitopes in these typically low mutational tumors. Histology-specific immunogenomic patterns are also apparent. Several of the pediatric cancers such as alveolar soft part sarcoma and osteosarcoma exhibit rich immune cell infiltration and evidence for activated T cell activities, whereas others such as Wilms tumors and synovial sarcoma generally have a very low T cell infiltration. In addition, we demonstrated a significant positive correlation between tumor-infiltrating CD8+ T cells and overall survival in patients with osteosarcoma, revealing the clinical importance of these tumor-infiltrating immune cells in these childhood cancers. Moreover, an orthogonal evaluation of immunopeptidome in osteosarcoma, a cancer type displaying high immune infiltrates, confirmed our transcriptomic findings on potential targetable tumor-specific genes. Finally, we took an adoptive cell therapy-based approach to target a tumor-specific gene PRAME identified by our transcriptomic and immunopeptidomic studies and showed significant in-vitro cytotoxicity using T cells expressing TCRs specifically targeting PRAME in osteosarcoma U2OS cells. Therefore, we demonstrate that RNA-seq is a powerful tool to identify clinically relevant and histology-specific genomic alterations and translationally relevant immunogenomic patterns for pediatric cancers. This study also represents one of the largest of its type to date and provides a framework for future translational efforts in pediatric cancer.
Citation Format: Jun S. Wei, Andrew S. Brohl, Sivasish Sindiri, David Milewski, Young K. Song, Sushma Nagaraj, Vineela Gangalapudi, Xinyu Wen, Marc Ladanyi, Javed Khan. Immuno-transcriptomic profiling identifies actionable genomic alterations in pediatric solid malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3445.