ABSTRACT
Regulation of the host immune response serves a pivotal role in the persistence and progression of malignant glioma. To date, cytotoxic cluster of differentiation (CD)-8+ T and natural killer cells are considered the main cellular components of host tumor control. The influence of macrophages in an orthotropic C6 tumor implantation model was investigated and the aim of the present study was to characterize the effects of systemic macrophage-activation on glioma growth by using the granulocyte macrophage colony stimulating factor (rhGM-CSF). A total of 20 male Sprague-Dawley rats were orthotopically implanted with C6 glioma spheroids and treated subcutaneously with 10 µg/kg rhGM-CSF every other day; 9 animals served as controls. Serial magnetic resonance imaging was performed on days 7, 14, 21, 28, 32 and 42 post-implantation to monitor tumor volume. Histological work-up included hematoxylin and eosin, CD68/ED-1 macrophage, CD8 T-cell and Ki-67 MIB1 proliferation staining in gliomas and spleen. Experimental C6-gliomas developed in 15/20 (75%) animals. In rhGM-CSF treated rats, tumors developed significantly later and reached a smaller size (median, 134 mm3) compared with the controls (median, 262 mm3). On day 14, solid tumors presented in 11/17 (65%) rhGM-CSF-treated animals; in control animals tumor growth was detected in 3/9 animals on day 7 and in all animals on day 14. The mean survival time was 35 days in the rhGM-CSF group and significantly longer when compared with the control group (24 days). Immunohistochemistry exhibited significantly more macrophages in tumors, particularly in the perivascular zone of the rhGM-CSF group when compared with untreated animals; intratumoral CD8+ counts were equal in both groups. A systemic stimulation of macrophages by rhGM-CSF resulted in significantly reduced and delayed tumor growth in the rodent C6 glioma model. The present data suggested a significant role of macrophages in host control of experimental gliomas on the innate immune response. Until now, the role of macrophages may have been underestimated in host glioma control.
ABSTRACT
The outcome of patients suffering from glioblastoma multiforme (GBM) remains poor with a median survival of less than 15 months. To establish innovative therapeutical approaches or to analyze the effect of protein overexpression or protein knockdown by RNA interference in vivo, animal models are mandatory. Here, we describe the implantation of C6 glioma spheroids into the rats' brain and how to follow tumor growth by MRI scans. We show that C6 cells grown in Sprague-Dawley rats share several morphologic features of human glioblastoma like pleomorphic cells, areas of necrosis, vascular proliferation, and tumor cell invasion into the surrounding brain tissue. In addition, we describe a method for tumor volumetry utilizing the CISS 3D- or contrast-enhanced T1-weighted 3D sequence and freely available post-processing software.