Tumor Vasculogenesis Can Be Derived from the Hematopoietic Stem Cell.

Blood vessel development is essential to cancer growth and metastasis. Based on our recent findings that the hematopoietic stem cell (HSC) provides functional hemangioblast activity in repairing the ischemic retina, we questioned if the HSC also acts as a pathologic hemangioblast - contributing to tumor vasculogenesis. Using a transplant model of green fluorescent protein (GFP) marrow into wild-type C57BL/6 mice, we injected lung cancer (LLC) and allowed the tumor to grow for 14 days. All tumor specimens demonstrated tumor vessels with marrow-derived endothelial cells. Approximately 25% of tumor vessels contained marrow-derived endothelial cells as demonstrated by GFP, CD31 and vWF expression. Confocal microscopy was used to identify true marrow-derived endothelial cells lining the vascular lumen versus marrow-derived pericytes juxtaposed to endothelial cells. We further questioned whether the tumor neovasculogenesis is from a clonal, self-renewing HSC. Lung cancers grown in recipients of single cell and serially transplanted hematopoietic stem cells (n=9) demonstrate clonal, donor-derived endothelial cells in 5% of tumor vasculature, matching hematopoietic engraftment. Our results indicate that the self-renewing, clonal adult hematopoietic stem cell exhibits pathologic hemangioblast activity, capable of producing both blood and blood vessels within tumors. Given that the HSC and its EPC progeny can contribute to tumor vasculogenesis, we further hypothesized that factors that affect leukocyte trafficking likely affect the pathologic hemangioblast activity of HSC. Thus, we made slight modifications to our transplant and tumor inoculation model by administering GCSF and SCF to mobilize marrow derived EPC. Over the ensuing 14 days, the tumors in the cytokine treated group grew at a much faster rate and to a much larger size than tumors in the control mice. After 14 days of cytokine treatment and tumor growth, microvessel density was not different between cytokine treated mice (n=4) and control mice (n=4); however, marrow-derived tumor vasculogenesis was markedly elevated in the cytokine treated compared to controls (63% vs. 26%). In conclusion, the HSC contributes to blood vessels within lung cancer and strategies targeting HSC/EPC mobilization (such as during the recovery phase of chemotherapy) potentially represent excellent ant-neoplastic opportunities.