DLL4 and neoplasm: To determine the relative contributions of blocking stromal (mouse) Dll4 vs. Dll4 expressed by tumor cells (human) to the overall anti-tumor activity, we treated RP-R-01 tumor-bearing SCID mice with the human Dll4-specific monoclonal antibody REGN421 (enoticumab), the mouse Dll4-specific antibody REGN1035, or the combination.