Nonexpression of CD15 by neoplastic glia: a barrier to metastasis?

Cluster of differentiation 15 (CD15) monoclonal antibodies recognise cell adhesion molecules on the surface of many cells including normal astrocytes and metastatic carcinoma cells. The CD15 epitope (fucosyl-N-acetyl-lactosamine), an adhesive oligosaccharide, functions as a ligand for the selectin family of membrane receptors. These include CD62, a cytokineinducible glycoprotein found in platelets and endothelial cells. CD15 is one of a series of putative adhesion molecules expressed in nervous tissue. Selectin-carbohydrate interactions have been implicated in the metastatic spread of cancer cells. We have immunostained a variety of cultured human brain tumours, three cell lines derived from experimental rat gliomas, two specimens of cultured human foetal astrocytes, two metastatic carcinoma cell lines and human umbilical vein endothelial cells (HUVEC) using two monoclonal antibodies which recognise CD15. While all of the animal glioma cells were positive for CD15, only two human glioma cell lines, derived from an anaplastic astrocytoma and a glioblastoma multiforme, respectively, displayed limited reactivity. Chromium radiolabel binding assays of CD15-positive and -negative cell lines including glioma and carcinoma-derived cells, using HUVEC as an attachment substrate, were carried out in the presence and absence of CD15 monoclonal antibody. The level of adhesion of neoplastic cells to HUVEC not only corresponded to CD 15 expression but application of anti-CD 15 monoclonal antibodies considerably reduced adhesion. We postulate that the absence of CD15 on human glioma cells may explain, to some extent, the general failure of intrinsic brain tumours to metastasis by precluding the adhesion of circulating neoplastic glia to 'target' organ endothelium.