This program has a number of objectives involving characterization and genetic manipulation of endothelial stem cells and differentiated endothelium using retro- and adenoviral gene delivery systems. We are also evaluating anti-angiogenesis therapy in human tumor models.
Endothelial Stem Cells: The existence of a circulating bone marrow-derived endothelial stem cell (angioblasts) was first suggested in collaborative studies with the Hope Hart Institute. In these studies, dogs that had been transplanted with allogeneic marrow were grafted with dacron artificial arteries which rapidly became lined with endothelium that was of the marrow donor genotype. We have identified a rare cell, comprising <1% of the total CD34+ population of human marrow, mobilized blood or umbilical cord blood, that expresses the vascular endothelial growth factor (VEGF) Receptor-2 (KDR), as well as CD34 and the hematopoietic stem cell antigen AC133. We believe these cells are committed endothelial stem cells (angioblasts) since they differentiate to functional endothelium capable of capillary formation in the presence of VEGF and we have been unable to induce their hematopoietic differentiation. In collaboration with the Laboratory of Dr R. Kolesnick, we have developed a panel of lentivectors expressing marker genes under the control of various endothelial specific enhancer/promoter elements and are transducing human and murine bone marrow endothelial progenitors and evaluating their contribution to the vasculature in various in vivo models of angiogenesis.
Endothelial Support For Hematopoiesis: We have shown that normal bone marrow sinusoidal endothelium, umbilical cord endothelium and hTERT-immortalized endothelial cell lines can support long-term proliferation and differentiation of human stem cells. We have transduced these cells with adenovectors expressing various hematopoietic growth factors (thrombopoietin, erythropoietin, GM-CSF, c-kit Ligand, flt3/flk-2 ligand) and have shown lineage appropriated expansion of mature hematopoietic cells (red cells, megakaryocytes, neutrophils), as well as prolonged expansion of pluripotent stem cells. We are developing these transduced endothelial cells for support of stem cell expansion on a clinical scale in a bioreactor system.
Anti-Angiogenesis Studies: We are evaluating antibodies to human VEGFR1, VEGFR-2 and VEGFR3 as anti-angiogenic agents in NOD-SCID mouse xenograft models of human tumors, including leukemias.