Abstract: Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells at different stages of maturation. MDSCs mediate the suppression of the anti-tumor immunity，and play a crucial role in cancer tolerance through suppressing the activity of T cells and natural killer cells ,inducing T-regs and involving the angiogenesis, and then contribute to the tumor development and metastasis. Promoting the differentiation of MDSCs, reducing its quantity and inhibiting its function by using various methods may contribute to the recovery of  patients normal immune status, the tumor progression control, and improvement of the efficacy of other anti-neoplastic therapies. Therefore，possible novel therapeutic approaches targeted at MDSCs could be considered and developed rapidly now.

Key words: Myeloid cells, Immune tolerance, Immunotherapy