CD28 and melanoma: To this end, highly pure M-MDSCs and G-MDSCs were isolated from the spleens of melanoma-bearing Nlrp3-/- and WT animals and co-cultured with CellTrace Violet (CTV)-labeled T effector (CD4+Foxp3-) cells sorted from naïve Foxp3GFP mice in the presence of anti-CD3/anti-CD28 activation beads (Figure 7A).