CD133 Immunohistochemisty in Glioblastoma – Identification of Tumor Stem Cells or a Matter of Coincidence?

The putative stem cell marker CD133 is the marker of choice for identifying brain tumor stem cells in gliomas, but the use of different antibody clones recognizing different epitopes with different glycosylation status, confuses the field. In this study, we sat out to highlight if current discordant CD133 observations could be a result of using different CD133 antibodies for immunohistochemical identification of CD133. Paraffin embedded sections of glioblastoma were stained with four different CD133 antibody clones and subsequently analyzed using stereology. Results revealed presence of CD133+ niches in glioblastomas, often in close relation to blood vessels, using all four antibody clones. The distribution of identified niches did, however, rarely correspond among each antibody clone. Staining of glioblastoma single and niche cells was predominantly cytoplasmatic, although membranous staining was also observed in niches. Quantitative stereology revealed vast dissimilarities regarding fractions of CD133+ niches and single cells among the CD133 antibody clones. Generally, the fraction of CD133 positivity identified by clone W6B3C1 was significantly higher than CD133 fractions identified by clones AC133, ab19898 and C24B9. Furthermore, clone W6B3C1 was the only clone to stain tumor blood vessels. In conclusion, we report that the use of different CD133 antibodies for immunohistochemical identification of CD133+ cells on paraffin sections will most likely cause different results. We therefore suggest that CD133 immunohistochemical studies take this in to consideration by using different CD133 antibody clones together with other stem cell markers and e.g. PCR techniques before too firm conclusions are drawn.