Table 1.

The role of different sEVs in the tumor microenvironment with corresponding immune cell populations

sEVs	Acting cell	Role in the formation of immunosuppressive environments	References
High expression of miR—203	Dendritic cells	Down-regulation of TLR4 and downstream cytokines, thereby inhibiting the immune response	[57]
High expression of miR-212-3p	Dendritic cells	Inhibit the expression of regulatory factor X-associated protein (RFXAP), reduce the expression of MHC II, and produce immune tolerance	[58]
High expression of CD63	T lymphocyte	Activate p38 mitogen-activated protein kinase (MAPK), induce cell apoptosis, and eventually lead to immunosuppression	[56]
High expression of tumor-associated antigens (TAAs)	B cell	As a bait for complement, it produces cytotoxicity and inhibits specific immune response	[60]
High expression of macrophage migration inhibitory factor (MIF)	Bone marrow-derived macrophages	Immunosuppressive cells are recruited to form an immunosuppressive environment	[40]
High expression of miR153	NK cells	Natural killer group 2 member D (NKG2D) was reduced by upregulation of hypoxia inducible factor 1-α (Hi1FA), and NK cells cleavage	[79]
High expression of miR-338-3p	Neutrophils	At present, the mechanism of action is not clear, biochemistry analysis indicated that it can inhibit the function of immune cells	[80]
High expression of miR-199b-5p	Neutrophils	At present, the mechanism of action is not clear, biochemistry analysis indicated that it can inhibit the function of immune cells	[80]
Lower expression of miR-340	Macrophages	At present, the mechanism of action is not clear, inhibits macrophages from becoming M1-like phenotype polarization in the peripheral and tumor immune microenvironment, and reduces T cells, especially CD8 + T cells	[81]
Lower expression of miR-128	All kinds of immune cells	At present, the mechanism of action is not clear, biochemistry analysis indicated that it can inhibit the function of immune cells	[64]