DLL4 and neoplasm: Next, to test whether the role of Dll4-expressing BM-VPC was essential to tumor angiogenesis, we developed an in vivo approach in which we reconstituted NOD-SCID mice BM with BM-VPC obtained from Dll4+/− (heterozygous, with reduced Dll4 levels) or from WT (normal Dll4 levels) mice.