Monoclonal antibody SP-21 defines a sialosyl-Tn antigen expressed on carcinomas and K562 erythroleukemia cells.

Monoclonal antibody (mab) SP-21 resembles the well established mab B72.3 by high affinity binding to peptide linked sialosyl-Tn disaccharide, NeuAc alpha 2-6 GalNAc alpha, and non-reactivity to the related trisaccharide NeuAc alpha 2-6 (Gal beta 1-3)GalNAc alpha. Although mab SP-21 may be classified, accordingly, into the family of mabs defining the sialosyl-Tn antigen, its fine specificity is distinct from the reference antibody B72.3 by binding of mab SP-21 to fetal mucins from human meconium or amniotic fluid. The distinct immunoreactivity of this mab is also documented by its specific cell staining of the erythroleukemia cell line K562, where it binds to a 105 KDa glycoprotein. Moreover a subpopulation of normal lymphocytes stains to this mab SP-21.