Mesothelioma, a highly aggressive
cancer with poor prognosis and refractory to currently available
therapies show increasing trends of its incidence in Japan and other developing countries. Although surgery is a gold standard for patients with early
mesothelioma, most patients with advanced disease are not suitable for surgical resection and have option of palliative
chemotherapy alone. One of the new treatment strategies for
mesothelioma, the humanized anti-CD26
monoclonal antibody therapy is under development. CD26, a 110-kDa transmembrane
glycoprotein with known
dipeptidyl peptidase IV activity, plays a role in
tumor development and its expression was reported in various human
malignancies. This study determined the preliminary selection criteria for humanized monoclonal anti-CD26 antibody
therapy. Eighty-one epithelioid (49 differentiated and 32 less differentiated), 34 sarcomatoid, 19 biphasic
mesothelioma and 8
mesothelioma cell lines were immunohistochemically examined using 8 different commercially available anti-CD26
antibodies for membranous and cytoplasmic expression. The cytoplasmic expression of CD26 was observed in all histological types of
mesothelioma, while the membranous expression of CD26 was found in 88% of differentiated and 69% of less differentiated epithelioid
mesothelioma, and none of sarcomatoid
mesothelioma with anti-CD26
antibodies with rabbit polyclonal anti-DPP4 antibody and similar results were also obtained with goat polyclonal anti-DPP4/CD26 antibody. These
antibodies absorbed with soluble human CD26
proteins do not show CD26 expression in
mesothelioma tissue, suggesting these two
antibodies localize true CD26
protein. Seven
mesothelioma cell lines, including sarcomatoid types, also showed membranous expression of CD26 in cellblock preparation. CD26 vector transfection to CD26-negative MSTO-211H cells showed membranous expression of CD26 by flow cytometry, but not in
tumor developed in NOD/SCID mice with inoculation of CD26 vector transfected MSTO-211H cells. We found that both rabbit and goat polyclonal
antibodies are suitable for immunohistochemical evaluation of membranous expression of CD26 in
mesothelioma.