Figure. 1. Diverse functions of MDSCs in cancer.
MDSCs are generated from hematopoietic stem cells from the bone marrow under the influence of growth factors including GM-CSF and G-CSF, and COX-2. They acquire immunosuppressive potential on activation by cytokines including IL-6 and IL-4. COX-2 by itself can expand MDSCs and confer suppressive function. With Ly6C and Ly6G, MDSCs can be separated into M-MDSCs, I-MDSCs, and PMN-MDSCs. They suppress T cell function, promote expansion of Tregs and Th17 cells, modulate B cells by both suppressing B cells and promoting Bregs, and also produce inflammatory cytokines. Overall, MDSCs use these different mechanisms to promote tumor growth, angiogenesis, and metastasis.