Bone marrow cells participate in tumor vessel formation that supports the growth of Ewing's sarcoma in the lung

An MHC-mismatch bone marrow (BM) transplant Ewing's sarcoma mouse model was used to investigate whether BM cells participate in the vessel formation that support Ewing's sarcoma lung metastasis. BM cells from H-2K^b/d donor mice were transplanted into suble-thally irradiated H-2K^d recipient mice. Donor BM cells were identified using the H-2K^b marker. Engraftment was confirmed by identifying the H-2K^b IL-1β-type specific polymorphism. After engraftment highly lung metastatic TC71-PM4 cells were injected intravenously. Mice were sacrificed 10 weeks after tumor cell injection. Hematoxy-lin-and-eosin staining was performed to identify lung metastatic foci. These tumors were then evaluated using immunohistochemical analysis. H-2K^b-positive cells were found in lung metastases but not in normal lung, liver or spleen tissues. Injection of CM-Dil-labeled BM cells into tumor bearing and control mice showed that nonspecific organ migration occurred at 24 h, but that these cells were absent 1 week later in control mice. These data suggest that the migration of the H-2K^b BM cells to lung nodules was specific because these cells were observed 14 weeks after transplantation. Co-localization of H-2K^b and CD31 or VE-Cadherin demonstrated that some endothelial cells were BM-derived. Co-localization of H-2K^b and Desmin, smooth muscle actin (α-SMA) or PDGFR-β indicated that a fraction of pericytes was also BM-derived. These results suggest that BM cells participate in the vascular formation that supports the growth of Ewing's sarcoma lung metas-tases. BM cells migrated to the metastatic tumor and differentiated into endothelial cells and pericytes. These data indicated that targeting this process may have therapeutic potential.