Abstract: Myeloid-derived suppressor cells (MDSCs）are a group of heterogeneous and immature myeloid-derived cells, which accumulate largely in blood, lymphoid organs, spleen and tumor tissue and so on under the different pathogenic conditions such as infection, trauma, hematosepsis, especially tumor and so on. MDSCs can suppress tumor immune through many mechanisms. The number of MDSCs in periphery blood of patients is closely related with tumor stage, tumor burden, remote metastasis and prognosis. The major results are from laboratory mice. Because of the complexity of MDSCs in patients with tumor, there are many difficulties and debate on the research of them, and the researches of human MDSCs progress slowly.

Key words: Myeloid cells, Immune tolerance, Tumor escape