Th111 - Metastatic melanoma (MM) patients with stable disease display reduced Mo-MDSCs levels in peripheral blood

Introduction: Myeloid-derived suppressor cells (MDSCs) are increased in late-stage tumors promoting metastasis by exerting their immunosuppressive functions. Recently, treatment with anti-PD1 and/or anti-CTLA-4 has improved the prognosis of metastatic melanoma (MM). In this regard, the immune effect of cancer immunotherapy on MDSCs is poorly understood. The aim of this study was to examine Mo-MDSCs frequencies in peripheral blood in relation with clinical outcomes in MM patients under immunotherapy.

Material and methods: Peripheral blood from 38 MM patients included in a clinical trial authorised by the Ethics Committee of the University of Regensburg was collected before administration of the first dose of Nivolumab and/or Ipilimumab. Patients were classified according to the iRECIST criteria into complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD). Samples were acquired with a NaviosTM cytometer. Mo-MDSCs were defined as CD14⁺ CD33⁺ CD11b⁺ CD15^- HLA-DR^-/low lin^- cells.

Results: We found no association between Mo-MDSCs levels and checkpoint blockade adverse events (hepatitis and colitis), sex, presence of IgG anti-CMV and stage of the disease. On the contrary, we observed that Mo-MDSCs frequencies in patients with stable disease (n=7, median 50.92 IQR 49.63-71.49) were lower compared to those who progress (n=15, median 77.95 IQR 67.24-83.39) (p=0.026) and those who have partial response (n=11, median 78.98 IQR 66.84-80.35) (p= 0.0185).

Conclusion: Further studies are required to understand the immune response to immunotherapy and if MDSCs could serve as a biomarker to predict prognosis in MM patients under immunotherapy treatment.