Defining the Immune Profile of Radiation Necrosis Through Single-cell Analysis of Intracranial Lesions

INTRODUCTION: The incidence of radiation necrosis (RN), a common and morbid side effect of radiosurgical management of brain metastases, is growing as patient survival and use of immunotherapy increases. RN is thought to be immunologically driven; however, its pathophysiology remains poorly understood. Further, difficulty distinguishing it radiographically from recurrent metastatic disease often necessitates invasive brain biopsies for diagnosis. METHODS: Over 12 months, we collected intraoperative samples from patients undergoing craniotomy for RN and/or metastatic tumor. We created a bank of these 16 patient samples and processed them for scRNAseq analysis. Using fluorescence-activated cell sorting (FACS) and 10x Genomics single cell RNA sequencing, we analyzed the cellular immune profile of lesional tissue and time-matched blood from each patient. RESULTS: Compared to metastases, RN demonstrates decreased expression of FOXP3, NKG7, and GZMB, markers of regulatory and cytotoxic T cells, and natural killer (NK) cells, and increased expression of interleukin 7 receptor (IL7R), a marker of naÏve and memory T cells – profiles reflective of bystander transcriptional signatures. In contrast, metastases demonstrate an antigen-reactive profile, including commonly observed exhaustion signatures. Importantly, blood samples from patients reflect these differences as well. Interestingly, increased IL7R is implicated in autoimmune disorders, suggesting an iatrogenically-induced autoreactive process underlying RN. CONCLUSIONS: These findings demonstrate, firstly, the feasibility of extracting live cells from RN tissue, and, secondly, suggest RN and metastases have unique immune profiles that can be detected in patient blood. Therefore, in addition to beginning to define the immune landscape of this poorly understood pathology, this work has the potential to open new avenues for the development of improved diagnostic and therapeutic approaches to allow for earlier detection and more effective treatment of RN in metastatic brain tumors patients.