Analysis of Mural Cell Recruitment to Tumor Vessels

Background— Tumor blood vessels are both structurally and functionally abnormal compared with normal vessels. A limited support of mural cells may contribute to these abnormalities. Here, we characterized mural cell recruitment in 2 mouse tumor models and addressed the question of why tumor vessels fail to recruit a proper coat of mural cells. Methods and Results— We studied mural cell recruitment to the vasculature of 2 transplantable mouse tumor models, T241 fibrosarcoma and KRIB osteosarcoma. We found that both tumors formed a vessel network with heterogeneous and highly abnormal organization of mural cells. Transplantation of tumors to mice expressing lacZ in mural cells demonstrated that these cells were host-derived. Although tumor vessel endothelium expressed PDGF-B, an embryonic mitogen for mural cells, only very few PDGFRβ-positive cells were found to be associated with the developing tumor vasculature, suggesting a limited pool of recruitable mural cells. We tested whether exogenous mural cells ...