CD28 and head and neck squamous cell carcinoma: To do this, isolated MDSCs from the tumors of MOC2 HNSCC tumor-bearing mice that had been treated with anti-PD-L1, IPI-549, anti-PD-L1 + IPI-549, or vehicle control were co-cultured with CD3/CD28 activated CFSE labeled T-cells isolated from C57BL/6 mice, and T-cell proliferation was measured by flow cytometry.