CD28 and neoplasm: To evaluate if the downregulated PD-L1 expression contributes to reversed immunosuppressive phenotype of tumor-infiltrating MDSCs, we sorted Gr-1+Ly-6G+ MDSCs from C44/mcr84-treated tumors using an MDSC isolation kit and cocultured with anti-CD3/CD28-stimulated wild-type CD8+ T cells at different ratios.