OBJECTIVE: Glioma, such as anaplastic astrocytoma and glioblastoma multiforme, belong to the most aggressive neoplasms in humans. Microglia and peripheral macrophages are attracted towards glioma and their abundance positively correlates with malignancy, invasiveness and tumor grade. Gliomaexhibit an immunosuppressive milieu, and glioma-associated microglia/ macrophages are polarized towards an M2-like anti- inflammatory phenotype and actively support tumor growth, e.g. via the release of immune-suppressive cytokines, and factors that stimulate angiogenesis and tumor invasion. Here we seek to identify new glioma-regulated genes to further elucidate the pathways of glioma-microglia interaction. METHODS:In order to achieve this,wecompared the gene expression profiles of glioma-associated microglia/macrophages isolated from experimental allogeneic GL261 tumors and human gliomas with microglia and peritoneal macrophages isolated from control animals and humans. RESULTS: The microarray experiment we performed with RNA samples from CD11b+ MACS-sorted cells from GL261 tumors and naïve brains revealed highly altered gene expression patterns in tumor-associated microglia/macrophages. More than 600 genes were more than 5-fold up- or downregulated in tumor-associated cells when compared to control cells. The qPCRvalidation we performed with FACS-sorted samples confirmed the regulation of our target genes and revealed that genes are either strongly upregulated in tumour-associated microglia or macrophages, but not in both cell types at the same time. This demonstrates that intrinsic microglia and invading macrophages fulfill different tasks in the tumor. We are currently collecting samples fromtheRCAStumor model to validate the expression of our target genes in an independent mouse tumor model. CONCLUSIONS: In future experiments we will confirm the expression of our target genes on protein level, using FACS, IHC and western blot. Furthermore we will test the expression of our target genes in RNA samples we are currently collecting from CD11b+ MACS sorted cells from human glioblastoma and normal brain samples.