Endothelial Progenitor Cells in Tumor Angiogenesis: Another Brick in the Wall

Table 1

Main characteristics distinguishing endothelial outgrowth cells and angiogenic cells.

Characteristic	Endothelial outgrowth cells	Angiogenic cells
Time for culture growth	7–21 days	3–5 days
Morphology	Confluent cobblestone monolayer	Round to spindle-shaped
Surface antigens	CD34^+ VEGFR-2^+ CD45^− CD14^− CD133^−	CD34^low VEGFR-2^low CD45^+ CD14^+
Nitric oxide production	High	Low
Cytokine secretion	Low	High
Vascular tube formation	Generate vascular tubes in Matrigel	Do not generate vascular tubes in Matrigel
Neovascularization capacity	Improve neovascularization	Improve neovascularization
Cell properties	Bind UEA-I lectin and take up LDL	Bind UEA-I lectin and take up LDL

VEGFR: vascular endothelial growth factor receptor; UEA-I: Ulex europaeus agglutinin I; LDL: low-density lipoprotein.