Purpose: Immunotherapy with ipilimumab improves the survival of patients with metastatic melanoma. Because only around 20% of patients experience long-term benefit, reliable markers are needed to predict a clinical response. Therefore, we sought to determine if some myeloid cells and related inflammatory mediators could serve as predictive factors for the patients' response to ipilimumab.

Experimental Design: We performed an analysis of myeloid cells in the peripheral blood of 59 stage IV melanoma patients before the treatment and at different time points upon the therapy using a clinical laboratory analysis and multicolor flow cytometry. In addition, the production of related inflammatory factors was evaluated by ELISA or Bio-Plex assays.

Results: An early increase in eosinophil count during the treatment with ipilimumab was associated with an improved clinical response. In contrast, elevated amounts of monocytic myeloid-derived suppressor cells (moMDSC), neutrophils, and monocytes were found in nonresponders (n = 36) as compared with basal levels and with responding patients (n = 23). Moreover, in nonresponders, moMDSCs produced significantly more nitric oxide, and granulocytic MDSCs expressed higher levels of PD-L1 than these parameters at baseline and in responders, suggesting their enhanced immunosuppressive capacity. Upon the first ipilimumab infusion, nonresponders displayed elevated serum concentrations of S100A8/A9 and HMGB1 that attract and activate MDSCs.

Conclusions: These findings highlight additional mechanisms of ipilimumab effects and suggest levels of eosinophils, MDSCs, as well as related inflammatory factors S100A8/A9 and HMGB1 as novel complex predictive markers for patients who may benefit from the ipilimumab therapy. Clin Cancer Res; 21(24); 5453–9. ©2015 AACR.