Enhanced expression of CD13 in vessels of inflammatory and neoplastic tissues

Aminopeptidase-N (CD13) is an important target of tumor vasculature-targeting drugs. The authors investigated its expression by immunohistochemistry with three anti-CD13 monoclonal antibodies (WM15, 3D8, and BF10) in normal and pathological human tissues, including 58 normal, 32 inflammatory, and 149 tumor tissue specimens. The three antibodies stained vessels in most neoplastic tissues, interestingly with different patterns. As a matter of fact, WM15 stained almost all intratumor and peritumor capillaries and only partially large vessels, whereas BF10 and 3D8 reacted with arteries and venules and to a lesser extent with capillaries. These antibodies also stained the stroma in about half of neoplastic tissues. In inflammatory lesions, the three antibodies stained vessels and stroma, whereas in normal tissues, they stained a small percentage of blood vessels. Finally, the three antibodies failed to stain endothelial cells of normal colon, whereas they reacted with activated human umbilical vein endothelial cells and with endothelial cells of colon adenocarcinoma vessels. Overall, WM15 was the most specific antibody for angiogenic tumor vessels, suggesting that it may be a good tool for detecting the CD13 form associated with the tumor vasculature. This finding may be relevant for CD13-mediated vascular targeting therapies.