The murine epitope sequence recognized by antibody E4B9 shares 100% homology with human VE-cadherin, so this antibody was examined to determine if it cross-reacts with human VIE-cadherin. Western-blot analysis of several VE-cadherin expressing human and murine ceH indicated that E4B9 indeed cross-reacts with human VE-cadherin (FIG. 6). This finding facilitates development of a "humanized" E4B9 antibody and its success in the prectinical development since its anti-tumor activity can be tested extensively in several mouse models.