Circulating and tumor-infiltrating arginase 1-expressing cells in gastric adenocarcinoma patients were mainly immature and monocytic Myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSCs) are a group of heterogeneous cells derived from immature myeloid cells (IMCs). MDSCs are known to play important roles in tumor immune evasion. While we know that there are a large number of circulating and tumor-infiltrating MDSCs existing in gastric cancer (GC) patients, the phenotypic characteristics and arginase 1 (ARG1) expression levels of these MDSCs remain very unclear. In our study, flow cytometric analysis of circulating MDSCs from 20 gastric adenocarcinoma (GAC) patients found that ≥80% ARG1-expressing MDSCs were mainly early-stage MDSCs (HLA-DR ^- CD33 ⁺ CD14 ^- CD15 ^- MDSCs). In addition, our investigation showed that tumor-infiltrating MDSCs from 6 GAC patients consisted of >35% ARG1-expressing naïve MDSCs (HLA-DR ^- CD33 ^- CD11b ^- CD14 ^- CD15 ^- MDSCs), >15% early-stage MDSCs and >40% monocytic MDSCs (HLA-DR ^- CD14 ⁺ MDSCs). This preliminary study describes the phenotypic characteristics and ARG1 expression levels of MDSCs from GAC patients and shows that circulating and tumor-infiltrating ARG1-expressing cells were mainly immature and monocytic MDSCs, which provides information to better understand the mechanisms that allow gastric cancer cells to evade the immune system.