154 Elucidating the Immune Landscape of Radiation Necrosis Through Single Cell Analysis of Recurrent Brain Lesions in Patients After Stereotactic Radio Surgery

Abstract

INTRODUCTION: Radiation necrosis (RN), a common and morbid side effect of radiosurgical treatment of brain metastasis, is becoming more prevalent as immunotherapy options and patient survival improve. Thought to be immunologically driven, the pathophysiology of RN remains poorly defined. Further, RN is often indistinguishable from regrowing metastases after stereotactic radiosurgery (SRS), requiring invasive brain biopsy for diagnosis. METHODS: We collected 20 intraoperative samples from patients undergoing craniotomy for RN and/or metastatic tumor, as well as time-matched blood and CSF. We created a tissue bank, processed samples, and using fluorescence-activated cell sorting (FACS) and 10x Genomics single cell RNA sequencing, analyzed the cellular immune profile of lesional tissue, blood, and CSF. RESULTS: RN tissue demonstrates a robust, detectable expression of immune cells, including CD8+ and CD4+ T cells, natural killer (NK) and myeloid cells. Importantly, clustering of RN-derived immune cells (including T cells, myeloid cells, and NK cells) is reflected in the blood and CSF, with similar immune profiles. We demonstrate a subpopulation of myeloid cells with a microglia signature (CD14+, LYZ-, MS4A7+), and a separate population expressing interferon-stimulated gene (ISG). Supporting these findings, pathway analysis of top blood markers reveals pathways involved in innate and inflammatory immune responses in the blood of RN patients. CONCLUSIONS: These findings demonstrate the feasibility of extracting live cells from RN tissue for scRNAseq analysis and suggest that there are unique signatures of RN that can be detected in the blood and CSF of patients. This work has the potential to open new avenues for improved diagnostic and therapeutic approaches to allow earlier detection and more effective treatment of RN in patients with metastatic brain tumors.