Table 1.

Immunomodulatory cells in cancer and their mechanisms of immune regulation.

Cells	Mechanisms	Effects	Ref
Regulatory T-cells (Tregs)	IL-10	T-cell suppression	[14]
	IL-2 consumption	T-cell suppression	[15]
	COX-2 and PGE2	T-cell suppression	[16]
	Adenosine	T-cell suppression	[17]
Myeloid-derived suppressor cells (MDSCs)	ARG1	T-cell suppression	[18]
	IDO	T-cell suppression Tregs induction NK cell suppression	[19,20]
	PD-L1/PD-1	T-cell suppression	[21]
	IL-10	Tregs induction	[22]
	TGF-β	Tregs induction	[22]
	CD40/CD40L	Tregs activation	[23]
	Depletion of cystine and cysteine	T-cell suppression	[24]
	ROS	T-cell suppression	[25]
	Free radical peroxynitrite	Resistance to cytotoxic T-cells	[26]
Tumor associated macrophages (TAMs)	PD-L1/PD-1	Decreased phagocytosis	[27]
	ARG1	T-cell suppression	[28]
	IL-10	T-cell suppression	[29]
	IL-1β	MDSC infiltration Induction of the protumor phenotype	[30,31]
	IL-12	Induction of T-cell response	[32]
	TNF-α	Induction of anti-tumor response	[33]
Tumor associated neutrophils (TANs)	ARG1	T-cell suppression	[18,28]
	NOS	T-cell suppression T-cell apoptosis	[34,35]
	PD-L1/PD-1	T-cell suppression	[36]
Cancer associated fibroblasts (CAFs)	PD-L1/PD-1	T-cell suppression	[37]
	FasL, PD-L2	T-cell suppression	[38]
	IL-6	Induction of PD-L1+ TANs	[39]
	Chemokines	MDSC infiltration	[40]
Erythroid progenitor cells (EPCs)	ROS	T-cell suppression	[41,42]
	IL-10	T-cell suppression	[42]
	PD-L1/PD-1	T-cell suppression	[43]
	TGF-β	T-cell suppression	[42]

ARG1—arginase 1, COX-2—cyclooxygenase-2, FasL—Fas ligand (CD95L, CD178), IDO—Indoleamine-pyrrole 2,3-dioxygenase, IL—interleukin, NK—natural killer, NOS—nitric oxide synthase, PD-1—programmed cell death 1, PD-L1—programmed death-ligand 1, PGE2—Prostaglandin E₂, ROS—reactive oxygen species, TGF-β—transforming growth factor β, TNF-α—tumor necrosis factor α.