CD33 and colorectal carcinoma: MDSCs were originally identified in tumor-bearing mice as cells that co-express CD11b and GR1, subpopulations have been shown to exist: polymorphonuclear (PMN)-MDSC (CD11b+Ly6G+Ly6Clo) and monocytic (M)-MDSC (CD11b+Ly6G-Ly6Chi); however, their phenotype in human cancer is rather diverse, MDSCs with the LIN−HLA−DR−CD33+CD11b+5,26, CD33+HLA-DR−28 and CD14+HLA-DR−/low phenotypes29 have been isolated from the blood of CRC patients.