Autophagy regulates the function of myeloid-derived suppressor cells in tumor-induced immunosuppression

Abstract

Tumor-infiltrating MDSCs were isolated from syngeneic C57BL/6 mouse models bearing B16-F10 melanoma or EO771 breast carcinoma tumors. Immunofluorescence staining of LC3B and western blotting of p62/SQSTM1 were used to assess autophagic activity. T-cell suppression by MDSCs was evaluated using co-culture assays, including assessment of T-cell proliferation by CFSE dilution and T-cell cytokine production by ELISA. Pharmacological inhibition of autophagy was performed using chloroquine, whereas genetic inhibition was achieved by knockdown of Atg5 using CRISPR-Cas9. Tumor growth and immune-cell infiltration were assessed in vivo following autophagy inhibition. MDSCs from tumor-bearing mice showed markedly higher autophagic activity than MDSCs from controls, with LC3B puncta and p62 levels increased 2.4-fold (p < 0.001). In co-culture, MDSCs inhibited T-cell proliferation by 55%, and this effect was partially reversed by autophagy inhibition. ELISA results indicated that IL-10, TGF-β, and IL-6 secretion by tumor-derived MDSCs was increased 1.5-fold and was significantly reduced by autophagy inhibition (p < 0.01). In vivo chloroquine treatment reduced tumor volume by 32% (p < 0.05) and increased CD8 + T-cell infiltration by 3.4-fold. Autophagy plays an important role in maintaining the immunosuppressive activity of MDSCs in the tumor microenvironment. Inhibition of autophagy reduces MDSC-mediated immunosuppression, restores T-cell activity, and inhibits tumor progression. These findings suggest that autophagy may represent a promising target for cancer immunotherapy.