Abstract 1671: Immunosuppressive myeloid-derived suppressor cells expressing PDL1 are increased in human melanoma tumor tissue

Despite the ability to elicit active immune responses, most immunotherapies fail to eliminate tumors in human cancer patients. One reason immunotherapy has not met expectations may be due to immunosuppression in the local environment of the tumor. Immunosuppressive myeloid-derived suppressor cells (MDSCs) are increased in the peripheral blood of melanoma patients and the frequency of MDSCs correlates with overall survival and disease progression. Furthermore, cytokines related to the recruitment and differentiation of MDSCs are also increased in melanoma patient serum and changes in these cytokine levels may correlate with disease progression. We find an increased frequency of regulatory T cells, PD-1-expressing T cells, and PD-L1 expressing MDSCs in primary melanoma tumors, suggesting that PD-1/PD-L1 interactions may play a role in immunosuppression in the microenvironment of the tumor. We are currently investigating the mechanisms of immunosuppression used by human MDSCs and whether the suppressive function of MDSCs can be blocked with antibodies targeting PD-L1. In conclusion, we have established MDSCs as an important player in immunosuppression in melanoma patients suggesting that combinatorial treatments that reduce the frequency or activity of MDSCs may improve the effectiveness of future immunotherapies. Citation Format: Kimberly Rae Jordan, Virginia Borges, Martin D. McCarter. Immunosuppressive myeloid-derived suppressor cells expressing PDL1 are increased in human melanoma tumor tissue. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1671. doi:10.1158/1538-7445.AM2014-1671