IL-10 and TGF-β2 are overexpressed in tumor spheres cultured from human gliomas

Immune-associated cytokines including IL-10 and TGF-beta 2 are thought to play a crucial role in immunosuppression mediated by gliomas. We have investigated the possibility that glioma stem cells are the major source of these cytokines. Tumor spheres, clonal non-adherent cell colonies derived from a single tumor stem cell, were cultured from surgical specimens of eight glioma patients, including two glioblastoma multiformes (grade IV), one anaplastic oligodendroglioma (grade III) and five anaplastic astrocytomas (grade III). Real-time RT-PCR and immunoassay were used to compare the relative expression levels of IL-10 and TGF-beta 2 in stem-cell-derived tumor sphere cells (TSCs) and primary cultured glioma cells (PCGCs). TSCs were confirmed to express the brain tumor stem cell marker CD133, and on in vitro differentiation gave rise to cells expressing neuronal or glial markers. RT-PCR and immunoassay revealed that mRNA and protein levels of both IL-10 and TGF-beta 2 were significantly higher in TSCs than in PCGCs from the same tumor. Interestingly, the degree of overexpression in TSCs, but not in PCGS, appeared to correlate with the pathological grade of the glioma. These findings suggest that glioma stem cells are likely to be the major tumor source of immunosuppressive cytokines and thereby play a crucial role in determining glioma malignancy.