IT-32 * DIVERGENCE OF INTRATUMORAL AND SYSTEMIC T CELL REPERTOIRES REFLECTS LOCAL MONOCYTE PROFILES DURING GLIOMA PROGRESSION

Abstract

INTRODUCTION: Glioblastoma (GBM) remains prognostically dismal, with relatively modest gains in survival from conventional therapies motivating research into how its characteristic immunosuppression might be reversed with minimal damage to brain tissue. We sequenced the T cell receptor (TCR) repertoires of tumor tissue and peripheral lymphocytes from human low-grade gliomas (LGG) and GBM, and PDGF-driven murine gliomas at timepoints and with targeted signaling blockade, leveraging innovative whole-repertoire methods to elucidate the relationship between the microenvironment and systemic effector T cells. METHODS: TCR libraries were generated from cryfrozen tumor tissue and corresponding peripheral lymphocytes, using reverse transcription and PCR (iRepertoire) of the TCR-alpha and TCR-beta chains, then sequenced on an Illumina MiSeq. We developed a computational pipeline for V-J cassette mapping, in silico translation, and sequence error correction, and profiled gene expression in tumor samples by RNAseq. We calculated TCR repertoire divergence (Jensen-Shannon divergence metric) between matched brain and blood samples, and analyzed its correlation with pathway and cell type-specific gene expression in tumor tissue. RESULTS: While the blood-brain TCR divergence was characteristically low in healthy humans and mice, it was distinctively high with a strong contribution from amino acid identity, suggesting antigen-driven selection, in early-stage (D21) glioma-bearing mice which decreased and was more variable in late-stage (D42+) glioma mice. A similar trend was observed in human LGG and GBM. ComparingTCR divergence with local gene expression revealed anticorrelation with inflammation, immune response, and cytokine signaling pathways, which we attributed to microglia/monocytes. Blockade of CCL2-dependent monocyte chemoattraction/activation in mouse tumors prevented progressive decrease blood-brain TCR divergence. CONCLUSION: The divergence of the glioma TCR repertoire from the blood offers a novel, massively-parametric biomarker of tumor progression, mechanistically linked to monocyte/microglial states, both indicating a potential target for and providing a potential predictor of personalized immunotherapy for high- and low-grade glioma patients.