MEDI0639 (21H3RK) is a human monoclonal antibody (mAb) targeting DLL4. It inhibits the interaction between Notch1 and Dll4 and reverses Notch1-mediated inhibition of in vitro human umbilical vein endothelial cell growth. Additionally, MEDI0639 enhances human angiogenesis and reduces the number of smooth muscle actin-positive mural cell-covered vessels. This compound can be used in research on small cell lung cancer and solid tumors.