CD33 and head and neck squamous cell carcinoma: A comparison of ARG-1, iNOS, and NOX2-component NCF1 gene expression in CD33+ and CD11b+ human MDSC induced by HNSCC or breast and lung carcinoma cell lines, respectively, revealed similar levels of expression between these subsets with a trend toward increased ARG-1 and NOX2 expression in CD33+ MDSC (Figure 6C).