Decreased Circulating Myeloid Derived Suppressor Cells at First Follow-up Predict Favorable Response to Immunotherapy in a Randomized Trial of Nivolumab and Bevacizumab in Recurrent GBM

Abstract

INTRODUCTION: A potential barrier to successful immunotherapy response in glioblastoma (GBM) is myeloid-derived suppressor cells (MDSCs): an immature immunosuppressive cell elevated in the circulation and tumor of GBM patients. Given a limited set of biomarkers predictive of response to immunotherapy in GBM, we explored the change in MDSC levels with immunotherapy to predict treatment response. METHODS: A retrospective analysis was performed on patients in a randomized, phase 2 study of nivolumab and bevacizumab at GBM first recurrence. Clinical and radiographic data were analyzed for disease progression or treatment response via Response Assessment in Neuro- Oncology (RANO) criteria. Blood was collected prior to treatment and at first imaging follow-up. Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood samples and analyzed. Characterization of circulating immune cells was performed using flow cytometry. RESULTS: A total of 9 patients were identified as responders or nonresponders at a median time of 8.7 wk (range 6.9-10.0) after therapy initiation. MDSCs, as a percentage of total PBMCs, were elevated at baseline in responders compared to nonresponders (4.9% ± 0.7 vs 2.6% ± 0.2, P = .019), which reversed at follow up (1.8% ± 0.4 vs 5.8% ± 1.1, P = .032). There was a 6.4 fold decrease in MDSCs as a percentage of total PBMCs between baseline and first imaging follow-up in responders as compared to nonresponders (P = .001). When looking at subtypes of MDSCs, a 4.9 fold decrease in granulocytic MDSCs (G-MDSCs) was noted in responders over nonresponders (P = .010). Further investigation of this cohort by simultaneous single-cell analysis of transcriptome and surface epitopes is ongoing. CONCLUSION: Differences in circulating MDSC levels that were specific to responders and nonresponders were seen both before and after therapy initialization, with decreases inMDSCs (specifically G-MDSCs) being correlated with treatment response. Characterization of MDSCs in the peripheral blood may be helpful in identifying GBM patients likely to benefit from immunotherapy.