Myeloid Regulatory Cells: New and Exciting Players in the Immunology of Lung Cancer

Cisplatin-induced oxPAPC release enhances MDSCs infiltration into LL2 tumour tissues through MCP-1/CCL2 and LTB4/LTB4R pathways

Lung cancer is the leading global cause of cancer-related death, however, resistance to chemotherapy drugs remains a huge barrier to effective treatment. The elevated recruitment of myeloid derived suppressor cells (MDSCs) to tumour after chemotherapy has been linked to resistance of chemotherapy drugs. Nevertheless, the specific mechanism remains unclear. oxPAPC is a bioactive principal component of minimally modified low-density lipoproteins and regulates inflammatory response. In this work, we found that cisplatin, oxaliplatin and ADM all increased oxPAPC release in tumour. Treating macrophages with oxPAPC in vitro stimulated the secretion of MCP-1 and LTB4, which strongly induced monocytes and neutrophils chemotaxis, respectively. Injection of oxPAPC in vivo significantly upregulated the percentage of MDSCs in tumour microenvironment (TME) of wild-type LL2 tumour-bearing mice, but not CCL2-/- mice and LTB4R-/- mice. Critically, oxPAPC acted as a pro-tumor factor in LL2 tumour model. Indeed, cisplatin increased oxPAPC level in tumour tissues of WT mice, CCL2-/- and LTB4R-/- mice, but caused increased infiltration of Ly6Chigh monocytes and neutrophils only in WT LL2-bearing mice. Collectively, our work demonstrates cisplatin treatment induces an overproduction of oxPAPC and thus recruits MDSCs infiltration to promote the tumour growth through the MCP-1/CCL2 and LTB4/LTB4R pathways, which may restrict the effect of multiple chemotherapy. This provides evidence for a potential strategy to enhance the efficacy of multiple chemotherapeutic drugs in the treatment of lung cancer by targeting oxPAPC.

Importance of myeloid derived suppressor cells in cancer from a biomarker perspective

Myeloid derived suppressor cells (MDSC) are a heterogenous population of immature myeloid cells that accumulate in tumor bearing host and migrate to lymphoid organs and tumor tissues. This process is controlled by a set of defined pro-inflammatory cytokines and chemokines, which are upregulated in malignancies. MDSC have strong immunosuppressive potential and constitute a major component of the tumor microenvironment (TME). Tumor cells take advantage of the suppressive mechanisms of MDSC to establish an immunosuppressive TME which inhibits antitumor immune responses thereby promoting cancer progression. An immunosuppressive TME acts as a significant barrier to immunotherapeutic interventions. Pre-clinical and clinical studies have demonstrated that enrichment and activation of MDSC is correlated with tumor progression, recurrence and metastasis. In this review we discuss the potential impact of MDSC on tumor progression and its role as a biomarker of prognostic significance in cancer with a special focus on hepatocellular cancer (HCC).