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

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 in MDSCs (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.