RBIO-06. STEREOTACTIC RADIOSURGERY ENHANCES T-CELL RECEPTOR REPERTOIRES AND INDUCES IMMUNOGENICITY IN BRAIN METASTASIS

Abstract BACKGROUND Brain metastasis is a frequent and deadly complication of systemic malignancy. The incidence rate is increasing and the prognosis remains poor, in contrast to recent advances in the management of systemic malignancy. Our previous work revealed an immunosuppressive microenvironment in brain metastasis and correlation between T-cell status and patient outcomes, shared across the primary tumor histologies. Therefore, we hypothesize that induction of immunogenicity has potential to improve brain metastasis patient outcome. METHODS Pre-operative stereotactic radiosurgery (SRS) (n = 44) and post-operative SRS (n = 47) brain metastasis specimens were collected from an ongoing clinical trial (MDACC protocol 2018-0552) designed to determine optimal timing of SRS for the treatment of brain metastasis. The patient materials were extracted DNA and RNA, and subjected to T-cell receptor (TCR) repertoire sequencing and mRNA-seq to interrogate radiation-induced immunogenicity. RESULTS In a preliminary analysis of the first 21 specimens, Gene Set Enrichment Analysis revealed that SRS significantly enhanced multiple immune-related signaling pathways including interferon response, along with apoptotic pathways, in brain metastasis. We also found that TCR signaling and PD-1 signaling was upregulated by radiotherapy. TCR repertoire analysis further identified increased density and diversity of TCRs induced by SRS treatment. Profiling of the remaining sample set is currently ongoing. CONCLUSIONS In light of our previous finding regarding the correlation between immune status and outcomes of patients with brain metastases, reversing immunosuppression in brain metastasis could be a key factor on patient prognosis and treatment. Our TCR repertoire and mRNA sequencing analyses with pre-operative and post-operative SRS brain metastasis cohorts support a role for radiation-induced immunogenicity, pointing to a prospective therapeutic approach for brain metastasis management.