Background While tumor infiltrating T-cells have a prognostic benefit in many tumor types1-8, the prognostic role of infiltrating immune cells is in patients with brain metastases (BrM) is poorly understood. While patients with 1-2 BrM are treated with resection and stereotactic radiosurgery (SRS), intracranial failure is common, and prognostic biomarkers are needed. Our group recently reported the T-cell response in renal tumors is beneficial for patient outcomes. This response is supported by TCF1+ stem-like CD8 T-cells residing in dense regions of closely clustered antigen presenting cells within the tumor known as the immune niche.9 Notably, these stem-like T cells are critical for a robust anti-PD-1 response. Here, we wished to determine whether: 1) TCF1+ stem-like CD8 T-cells are present, residing in immune niches, in BrM?, (2) the density of these niches is associated with patient outcomes? and (3) stem-like CD8 T-cells and immune niches persist following SRS?
Methods Tumor tissue was collected from 146 patients with BrM undergoing surgery at two clinical centers. Samples were analyzed by flow cytometry, single cell RNA sequencing, and immunofluorescence. Imaging data was analyzed using custom quantitative pipelines. Together, this allowed for evaluation of the BrM immune microenvironment at baseline or following pre-operative SRS.
Results We describe the presence of TCF1+ stem-like CD8 T-cells in BrM (figure 1A-B), regardless of histology, these stem-like cells reside in dense, antigen-presenting immune niches (figure 1C-D). We find that higher density of these immune niches in BrM correlates with improved local control of BrM (figure 1E). Pre-operative SRS did not decrease immune niche density (figure 1F-G), nor significantly alter the stem-like signature of this population of T-cells. Finally, we also find that a longer time from SRS to resection may lead to increased CD8+ T-cell density in BrM (figure 1H).
Conclusions We have shown that stem-like T-cells are present in BrM in immune niches. The density of this intratumoral immune organization is associated with improved patient outcomes regardless of primary tumor origin. These findings recapitulate the previously reported phenomena of immune organization in tumor tissue, underscoring the trans-tumor/trans-tissue importance of this biology in the anti-tumor immune response. Finally, this niche is maintained following SRS suggesting it is a relatively radioresistant compartment. This has significant implications for combinatorial strategies of immunotherapy and SRS for BrM.
Acknowledgements We would like to acknowledge NCI grant 1-F30-CA-243250 (to C.S. Jansen), the Yerkes NHP Genomics Core which is supported in part by NIH P51 OD011132, the Emory Flow Cytometry Core supported by the National Center for Georgia Clinical & Translational Science Alliance of the National Institutes of Health under award number UL1TR002378, the Intramural Research Program of the NIH, National Cancer Institute and the Emory University Integrated Cellular Imaging Microscopy Core of the Winship Cancer Institute of Emory University and NIH/NCI under award number 2P30CA138292-04.
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Ethics Approval Samples are collected under an approved IRB protocol (00001896).
Consent All patients provided informed consent.
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