Background & objective: Some studies indicate that endothelial progenitor cells (EPCs) originated from the bone marrow participate in neoplastic angiogenesis, and that bone marrow origin of inflammatory cells potentially contribute to neoplastic invasion, angiogenesis and metastasis. This study was to observe the origin of neovascular endothelial cells and infiltration of bone marrow-originated inflammatory cells in a murine tumor model.
Methods: Healthy C57BL/6 mice were irradiated with 60Co at 8 Gy. Bone marrow cells of green fluorescent protein (GFP) transgenic C57BL/6 mice (donators) were transplanted intravenously into C57BL/6 mice (recipients) via the tail vein 24 h after irradiation. Lewis lung tumor cells were inoculated subcutaneously into recipient mice 2 weeks after transplantation. The xenograft tumors were removed until their diameters reached approximately 1- 2 cm. Subsequently, tumor vessels and inflammatory cells were observed under fluorescent microscopy and detected using immunohistochemistry (IHC).
Results: Unsuccessive green fluorescence emitted by neoplastic vascular endothelial cells and inflammatory cells was observed, most of which appeared positive IHC staining. A large number of macrophages were observed inside or adjacent to the necrotic areas of the tumor. A few lymphatic cells were mainly dispersed inside tumor stroma and tumor cells.
Conclusions: Partial endothelial cells of neoplastic neovessels originate from the bone marrow. The murine tumor model could be used as a specific and direct approach to observe bone marrow-originated cells in neoplasms.