CD33 and colorectal carcinoma: To directly verify the expression of PKM2, PKM2 (p-Y105) and iNOS in MDSCs infiltrated by CRC, we further detected the expression of PKM2, PKM2 (p-Y105) and iNOS in MDSCs (HLA-DR−/low CD33+ CD14−/low CD66b+) from human CRC tissues and adjacent nontumor tissues by flow cytometry (Additional file 1: Fig. S6A).