gms | German Medical Science

Objective: Glioblastoma multiforme (GBM) remains one of the most malignant brain tumors with a mean survival time of solely a few months despite of extensive research. One feature of this tumor is the high angiogenic activity. In the present study, we investigate the contribution of immune cells originated from the myeloid lineage (CD11b+) to tumor vascularization and their relationship to the grade of malignancy.

Method: Brain tissue samples from 65 patients (35 female, 30 male) with astrocytomas (WHO°III and °IV) or epilepsy (control group) were obtained during therapeutic surgical treatment. Tissue was enzymatically homogenized and the CD11b+ cell fraction was analyzed by FACS concerning activation markers. Furthermore, CD11b+ cells of brain samples were isolated by MACS technology, subsequently RNA isolation and qRT-PCRs regarding pro-angiogenic factors were performed. In addition, fixed and cut tissue was used for immunofluorescence stainings.

Results: We defined different subgroups of myeloid cells within brain tissues by FACS. In controls and astrocytomas °III only one myeloid cell fraction was observed. These cells displayed CD11b and low levels of CD45. In glioblastomas an additional population with CD11b+CD45high expression was detected. Both cell populations were positive for Iba-1 indicating their affiliation to the microglia/macrophage lineage. Furthermore, approx. halve of the GBM specimens showed high amounts of a third cell fraction characterized by CD11bhighCD45intermediate and identified as granulocytes. For all GBM samples we found increased levels of several pro-angiogenic factors (e.g. VEGF, CXCL8, CXCL2) within the CD11b+ isolated cells in comparison to epilepsy and astrocytoma °III, whereby upregulation was strongest in the GBM group that exhibit the three mentioned cell fractions. Moreover, determination of MHCI, MHCII and CD86 on myeloid cells revealed an altered activation phenotype between different grades of astrocytoma. Finally, immunofluorescence stainings elucidated a remarkable association of CD11b+ cells with tumor blood vessels especially in GBM tissues.

Conclusions: Our data indicate, that cells of the myeloid lineage are capable of supporting vascularization in human GBM by secretion of pro-angiogenic factors and therefore contribute to tumor progression. Regarding the insufficient treatment options in glioblastomas, myeloid cells may represent a new therapeutic target to improve the median survival of GBM patients.