gms | German Medical Science

Objective: It has been shown that a distinct population of so-called glioma stem-like cells (GSC) mediates resistance to radiotherapy and chemotherapy and is primarily responsible for glioblastoma recurrence. Therefore, delineation of the characteristic biological attributes of GSC is a matter of high clinical relevance. GSCs are thought to possess key attributes of stemness (self-renewal, differentiation capacity, expression of certain phenotypic markers). However, the relationship between individual attributes of stemness and degree of GSCs malignancy is still unclear. The aim of our study was to investigate the relationship between morphophenotypical characteristics of cell types capable of the formation of self-renewing gliomaspheres.

Method: GSC were derived from glioma cell lines or fresh glioblastoma specimens. Neurosphere cultures were maintained in Neurobasal medium (NB) supplemented with bFGF (10 ng/ml) and EGF (20 ng/ml). Immunofluorescent staining was performed with antibodies to stem cell markers but also to CD 68 and CD11. Second generation gliomaspheres derived from xenografts after implantation of GSC and radioresistent derivatives were equally characterized.

Results: In three glioma cell lines out of the glioblastoma specimens different pattern of morphologic heterogeneity occurred NB: 1) only some of the GSC showed typical stem cell characteristics: expression of Nestin as a stem cell marker but also markers for progenitor cell lines was inhomogeneous. 2) Atypical phenotypic markers CD 68 and CD 11 were expressed in a heterogeneous manner. 3) Heterogeneity was also manifest in different sizes of the nuclei. Most of cells showed a size of the nucleus of about 10-15 µm (diameter) and Nestin-negative cells of 5-7µm (small nuclei cells, SNC). To focus on the question whether tumor-initiating potential has different phenotypes, second generation GCS derived from xenografts were analyzed. Surprisingly the proportion of SNC and Nestin negative cells was found to be increased in radioresistent derivates.

Conclusions: The results suggest that there is no universal type of GCS, but different cell types of glioma stem-like cells. A subset of GSCs may escape from identification when using basic criteria currently applied for the identification of GSCs. Therefore, the assumption that compliance with the basic criteria of stemness is sufficient to consider a particular type of GSC as the most clinically relevant type of glioma cell should be carefully reassessed.