Identification of CD133+ cells in pituitary adenomas

Stem-like cells in tumors are capable of self-renewal and pluri-differentiation; they are thought to play important roles in tumor initiation and maintenance. Stem-like cells in malignant glioma express CD133. We examined samples from human pituitary adenoma, a generally benign neoplasm, for CD133 expression using routine immunohistochemical and biochemical methods. Our study of 70 pituitary adenomas (clinically nonfunctioning adenomas and growth hormone-, prolactin-, adrenocorticotropic hormone-, and thyroid-stimulating hormone-producing adenomas) showed that 18 (25.7%) expressed CD133. This rate was higher in clinically nonfunctioning (33.3%) than functioning adenomas (12.0%) (p = 0.085). Real-time PCR assay revealed the expression of CD133 mRNA in samples immunohistochemically positive for CD133. Neither the patient age and gender, nor the tumor size or postoperative recurrence rate correlated with CD133 positivity. CD133+ cells ubiquitously coexpressed CD34, nestin, and VEGFR2 (KDL1). S-100 and GFAP were not coexpressed with CD133. Chromogranin A, Pit-1, SF-1, and NeuroD1 were immune-negative, indicating that CD133+ cells did not have the potential to differentiate into functional endocrine cells. Our data suggest that the expression of CD133 in pituitary adenomas is related to immature endothelial progenitor cells that may play a role in the neovascularization of pituitary adenomas. Further studies are needed to elucidate the significance of CD133+ cells with respect to neovascularization and their sustainable growth in pituitary adenomas.