Splice variants of the cell surface glycoprotein CD44 associated with metastatic tumour cells are expressed in normal tissues of humans and cynomolgus monkeys

Certain isoforms of the CD44 glycoprotein family play an essential role in the metastatic spread of tumour cells. Protein expression of such CD44 isoforms has also been observed in a variety of human malignancies. In this study, we compared the expression of exon v5- and v6-containing CD44 isoforms in normal human and cynomolgus monkey (Macacca fasciculata) tissues. Cloning and sequencing of cynomolgus CD44 exons v5 and v6 revealed a homology of 97% and 95%, respectively, between man and monkey. Two monoclonal antibodies (MAbs) directed against an epitope encoded by human exon v5 (VFF8) and an epitope encoded by exon v6 (VFF18) were used to determine expression of CD44 isoforms in man and monkey. Immunohistochemical screening of a representative profile of normal human and cynomolgus tissues revealed that expression of exon v5- and v6-containing CD44 isoforms was almost identical in the two species. Exon v6 staining was observed only in a subset of epithelial tissues, whereas v5 staining was additionally detected on certain non-epithelial tissues. These data suggest that cynomolgus monkey could serve as a system to test the usefulness of antivariant CD44 MAbs with regard to antibody-based tumour therapy.