MUC5AC and cancer: Siglec-7 is considered a glyco-immune checkpoint that plays an important role in cancer.49 Recent findings have converged on Siglec-7 ligands being on sialylated core-1 mucin-type O-glycans.50 ST3GAL1/2 has been shown to be essential in creating O-glycans that are ligands of Siglec-7 but, interestingly, the affinity of sialyl T for Siglec-7 has never been measured.