TABLE 1.

Myeloid-derived suppressor cells in a variety of tumors.

Tumor	Contribution of MDSCs to tumor development	Regulatory effect of factors on MDSC	Reference
Prostate cancer	MDSCs promoted tumor survival	Tumor-derived G-CSF promoted the proliferation of MDSCs via a STAT3-dependent pathway	Yu et al., 2015
	MDSCs promoted tumor progression	Chemokines promoted the expansion of CCR5+PMN-MDSCs at the BM, and potentiated their immunosuppression at the tumor site	Hawila et al., 2017
	MDSCs promoted tumor angiogenesis	CSF1R signaling promoted tumor recruitment of M-MDSC recruitment from peripheral blood	Priceman et al., 2010
Breast cancer	MDSCs promoted tumor growth	TEXs with abundant PGE2 and TGF-β enhanced the expansion and immunosuppression of MDSCs	Xiang et al., 2009
	MDSCs promoted tumor progression	Transmembrane Tm-TNF-α induced the immunosuppression of MDSCs	Hu et al., 2014
	MDSCs promoted tumor growth and metastasis	Mir-494 induced the expansion of MDSCs in tumor tissues by increasing the activity of the Akt pathway	Liu et al., 2012
	MDSCs stimulated tumor cell metastasis to distant sites	IL-6 secreted from breast cancer cells facilitated MDSC recruitment	Oh et al., 2013
Melanoma	MDSCs promoted tumor growth	Lnc-chop encouraged the activity of C/EBP β, improved the immunosuppression of MDSCs	Gao et al., 2018
	MDSCs promoted tumor progression	Tumor-derived chemokines CCL3, CCL4, and CCL5 recruited CCR5+ MDSCs to the tumor site	Blattner et al., 2018
	PMN-MDSCs induced the proliferation and EMT of tumor cells	Tumor-derived chemokines CXCL1, CXCL2, and CXCL5 recruited CXCR2+ MDSC to the tumor site	Toh et al., 2011
Colon cancer	MDSCs promoted tumor growth	HMGB1 promoted the differentiation of MDSCs from bone marrow progenitor cells, and activated the immunosuppression of MDSCs via the NF-κB pathway	Parker et al., 2014
	MDSCs promoted tumor growth	MiR-200c promoted immunosuppression of MDSCs by targeting PTEN/FOG2, which led to STAT3 and PI3K/Akt activation	Mei et al., 2015
	MDSCs formed PMN in the pre-metastatic liver	VEGFA secreted by colon cancer cells stimulated CXCL1 production by TAMs, which recruited CXCR2+ MDSCs to promote liver metastasis.	Wang et al., 2017