MUC5AC and cancer: For example, CD43 on the surface of leukemia cells selectively interacts with the glyco-immune checkpoint receptor Siglec-7 through its N-terminal mucin domain16; mucin domain-containing splice variants of CD44 (CD44v) serve as cancer cell markers relative to the ubiquitously expressed standard isoform17; CD45 mucin domains act as suppressors of T-cell activation18; mucin domain O-glycosylation on PSGL-1 is required for leukocyte-endothelial interactions19; and aberrant regulation of mucin domains in podocalyxin and SynCAM1 are implicated in a variety of cancers20,21.