A single cell sequencing approach to understand the nature of myeloid-derived suppressor cells in tumor-bearing mice

Abstract

Abstract Peripheral T Cell Lymphoma (PTCL), a type of non-Hodgkin’s lymphoma, is a heterogeneous group of mature T cells that have undergone transformation into a malignant form. The tumor microenvironment (TME) is very heterogeneous and is comprised of different cell types. Myeloid-derived suppressor cells (MDSC) are one of the vital components of the TME. Further, MDSC are associated with tumor growth, angiogenesis and enhanced metastasis. The aim of this study was to compare MSDCs isolated from TME and splenic MDSCs from tumor-bearing hosts (TBHs) as well as splenic MDSCs from naïve mice by using single cell RNA sequencing (scRNASeq). For this reason, C57BL/6 mice were injected with 1×106 EL4 cancer cells subcutaneously to induce tumor growth and 14 days later, cells were isolated from these three tissues, and flow cytometry and scRNASeq were performed. The flow cytometry results showed an increase in MDSC recruitment in the spleens from TBHs in comparison with spleens from naïve mice. scRNASeq analysis showed most of the genes upregulated in MDSCs from TME and spleen of TBHs were responsible for generation, recruitment and proliferation of MDSCs (Lgals5, CXCL10, Alox5ap, CCL6, IL1b, S100A8/A9/A11, CCL4, CCL5). Furthermore, we found several genes overexpressed in MDSCs promoted the proliferation and migration of cancer cells as well as tumor formation (Lyz2, Plac8, Ifitm3, Vim, S100A6, Crip1). In addition, we found some genes have anti-tumor effects by suppressing T and B cells (Lgals5, Ly6c2). In summary, these studies demonstrated that MDSCs from TME and spleens of TBHs have unique features for inducing immunosuppression, as well as recruitment and expansion of MDSCs in TBHs, which make these cells critical for target for immunotherapy.