CCR2-CCL2 signaling is involved in myeloid cell recruitment to tumors and is considered as being a crucial axis for new therapeutic strategies. In glioma, we observed that CCR2-deficient mice showed 30% less microglia/macrophage infiltration within the tumor tissue accompanied by doubling of tumor volumes. In CCR2ko mice, we detected a change in the CD11b+CD45+ cell distribution by FACS. Here, we found significantly reduced amounts of CD45high cells. Thus, we aimed to characterize the behaviour of myeloid cells regarding the CCR2-CCL2 signal and their impact on tumor progression.
We generated chimeras using lethal irradiation with head protection, afterwards bone marrow cells were injected intravenously. In order to distinguish microglia from peripheral macrophages, respective cell populations were GFP-positive or non-labeled. We established chimeras with CCR2-knock-out of either microglia (ko/wt) or macrophages (wt/ko) and with ubiquitous functional CCR2 (wt/wt) as control. After 8 weeks of reconstitution (reconstitution efficiency 65-90%), tumor cells were implanted. On day 21 of tumor growth glioma volumes were measured by MRI. FACS analysis and immunofluorescence staining followed.
Flow cytometry revealed that influx of peripheral macrophages into glioma tissue was similar in wt/wt and ko/wt chimeras (26-31%), and the percentage of CD45high cells was comparable (around 40%). In contrast, the group of wt/ko chimeras showed minor infiltration of macrophages within the CD11b+CD45+ population (approx. 2%) accompanied by reduced proportion of CD45high cells. Interestingly, the contribution of macrophages to CD45high cells differed extremely between groups. In controls, we found 55% macrophages. The CD45high fraction in wt/ko chimeras consisted of below 7% of macrophages. Indeed, we found mainly microglia on brain tumor sections. The ko/wt group showed up to 83% of macrophages within the CD45high population. Nevertheless, on brain sections, we demonstrated that both macrophages and microglia accumulate within glioma tissue. Wt/ko as well as ko/wt chimeras tended to have larger tumor volumes than the control group.
Our data implicate that recruitment of macrophages depends on the CCR2-CCL2 signaling pathway, since without functional CCR2 influx of macrophages was negligible. Taken this into account, chimeras with CCR2-deficiency show new approaches for glioma treatment as wt/ko and ko/wt tumors seem to develop larger tumors. Simultaneously, due to predominance of microglia in wt/ko chimeric mice, they offer a great tool for analyzing the specific behaviour of microglia during tumor progression.
Citation Format: Alexander D. Bungert, Susan Brandenburg, Matthäus Felsenstein, Ruth M. Urbantat, Annett Müller, Peter Vajkoczy. CCR2-CCL2 signaling is essential for macrophage recruitment to gliomas [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A103.
- ©2016 American Association for Cancer Research.