Fig. 2

Immunosuppressive mechanisms and targets of MDSCs. MDSCs inhibit T-cell activity through distinct mechanisms, including loss of the TCR ζ-chain; nitration of the TCR complex; depletion of amino acids necessary for the T-cell response; the production of adenosine, high levels of NO, RNS, Arg1, and chemokines; the presence of immune checkpoint blockade; and impairment of T-cell homing. Moreover, MDSCs promote Treg and macrophage differentiation and increase FOXP3 expression. Additionally, MDSCs suppress NK cells and CD8⁺ T cells. Finally, tumor-infiltrating MDSCs promote the migration of tumor cells by interacting with cancer stem cells (CSCs).