Fig. 3

MDSC-mediated T cell suppression and MDSC-targeted therapies. a MDSC-mediated T cell suppression. Although MDSCs have been implicated in undermining the functions of multiple immune cells, their main targets are T cells. MDSCs cause immune suppression by upregulating TGF-β, IL-10, IDO, iNOS, ARG1, ROS, PD-L1, and depleting cystine and cysteine in the TME. Besides, the ADAM17 on MDSCs exerts immunosuppressive effects by downregulating L-selectin (T cell homing receptor) on naïve T cells. b MDSC-targeted therapies can be categorized into four groups: suppressing the recruitment and expansion of MDSCs; facilitating the differentiation of MDSCs into mature myeloid cells; counteracting the functions of MDSCs; and directly depleting MDSCs. Abbreviations: MDSC, myeloid-derived suppressor cell; ASC, asc­type amino acid transporter; CAT-2B, cationic amino acid transporter 2B; Xc⁻, cystine-glutamate transporter; IDO, indole-2,3 dioxygenase; NO, nitric oxide; iNOS, inducible nitric oxide synthase; TCR, T cell receptor; ROS, reactive oxygen species