Development of novel monoclonal antibodies with specific binding affinity for denatured human CD26 in formalin-fixed paraffin-embedded and decalcified specimens

A 110-kDa type II transmembrane glycoprotein with dipeptidyl peptidase IV (DPPIV) activity in its extracellular region, CD26 has a multitude of biological functions and plays an important role in the regulation of inflammatory responses and tumor biology. Our work has focused on CD26 as a novel therapeutic target for various tumors and immune disorders, and we have recently developed a humanized anti-CD26 monoclonal antibody (mAb), YS110, which has promising safety profile and clinical activity in patients with malignant pleural mesothelioma. The development of an anti-human CD26 mAb that can clearly and reliably detect the denatured CD26 molecule in formalin-fixed paraffin-embedded (FFPE) tissues in the clinical setting is therefore of the utmost importance. To develop novel anti-CD26 mAbs capable of binding to denatured CD26, we immunized mice with urea-treated CD26 protein. Hybridoma supernatants were screened for specific reactivity with human CD26 by immunostaining through the use of a set of FFPE human CD26-positive or negative tumor cell lines. This screening method enables us to develop novel anti-human CD26 mAbs suitable for immunohistochemical staining of CD26 in FFPE non-tumor and tumor tissue sections with reliable clarity and intensity. Specifically, these mAbs display strong binding affinity to denatured human CD26 rather than undenatured human CD26, and are capable of detecting denatured human CD26 in decalcified specimens. These novel anti-CD26 mAbs are potentially useful for the analysis of CD26 expression in cancer patients with bony metastasis, and may help decide the appropriateness of YS110 therapy for future cancer patients.