The DTLacO-1 cells stably expressing LacI-HP1 were selected to identify mAbs against three cell surface antigens of therapeutic interest: the receptor tyrosine kinases, VEGFR2 and TIE2, which play essential roles in physiologic and pathologic angiogenesis, most notably in cancer [18], [19]; and the glycoprotein, TROP2, which is overexpressed in numerous epithelial cancers [20]. The gene discussed is KDR; the disease is cancer.