Christoffer Gebhardt, Alexandra Sevko, Huanhuan Jiang, Ramtin Lichtenberger, Maike Reith, Kathrin Tarnanidis, Tim Holland-Letz, Ludmila Umansky, Philipp Beckhove, Antje Sucker, Dirk Schadendorf, Jochen Utikal, Viktor Umansky

Immunotherapy with ipilimumab improves the survival of patients with metastatic melanoma. Since 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. 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 multi-color flow cytometry. In addition, the production of related inflammatory factors was evaluated by ELISA or bio-plex assays. 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 (moMDSCs), neutrophils, and monocytes were found in non-responders (n=36) as compared to basal levels and to responding patients (n=23). Moreover, in non-responders, 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, non-responders displayed elevated serum concentrations of S100A8/A9 and HMGB1 that attract and activate MDSCs. 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.