MDSC suppression assay

For the in vitro suppression assay, total spleen cells were isolated from healthy mice followed by red blood cell lysis. These cells were labelled with CFSE (Beyotime), cultured in a 96-well plate (1 × 10⁵ cells per well), and stimulated with Con A (4 μg mL⁻¹, Sigma-Aldrich). MDSCs were incubated with dextran, C-dextran or PEI for 6 hours. Then, the CFSE-labelled spleen cells were co-cultured with MDSCs at a 2:1 ratio. After 4 days, CFSE dye dilution after CD3 staining was analyzed with flow cytometry. In doing so, we assessed whether the polymers would affect the suppressive effect of MDSCs on T cell proliferation.