Table 1.

Known effectors or regulators of MDSC biology.

Effectors	Mechanisms	References
STAT3	Stimulates inflammatory cytokines, activates transcription of immunosuppressive enzymes with C/EBPß. Downregulates IRF8	(23, 33, 34)
STAT5	Downregulates IRF8, promoting aberrant myeloid differentiation	(23)
C/EBPß	Master regulator. Promotes transcription of immunosuppressive enzymes and inflammatory cytokines in tumor microenvironment	(27, 35–37)
IRF8	Crucial for normal myeloid differentiation. Negative regulator of MDSCs. Downregulated by STAT3/5	(23)
S100A8/9	Produced by tumors. Binds to RAGE receptors in myeloid precursors and activates immunosuppressive NF-κB-C/EBPß-STAT3 signaling axis.	(29)
RB	Epigenetically silenced by HDAC6 in MDSCs. Negatively regulates myeloid differentiation into PMN-MDSCs.	(38)
TIPE2	Induced by IL-6 and high ROS in tumor microenvironment. Activates C/EBPß and STAT3 which promote immunosuppressive activity.	(30, 31)
GCN2	Polarity switch. Expression correlates with immunosuppressive activity. Induces C/EBPß and CREB2/ATF4 promoting immunosuppression.	(31)