CD33 and head and neck cancer: To further confirm the upregulated expression of cluster 6 proteins in MDSC-like cells, we examined their expression at the single-cell mRNA level in a human MDSC single-cell RNA-Seq dataset, which profiled CD11b+ CD33+ HLA-DRlo/− MDSCs isolated from five patients with cancer (three with melanoma, one with head and neck cancer, and one with breast cancer) [33].