To this end, M-MDSCs and G-MDSCs were isolated from the spleen of control and αPD-L1-treated melanoma-bearing mice and were co-cultured with CellTrace CFSE-labeled T effector (CD4+Foxp3−) cells sorted from naive Foxp3EGFP mice in the presence of anti-CD3/anti-CD28 activation beads (Supplementary Figure 2A). Here, CD4 is linked to melanoma.