DPP4 and malignant mesothelioma: To investigate the nuclear localization of CD26 in cancer cells, four malignant mesothelioma cell lines that differed in CD26 expression status were first examined: one that expressed CD26 endogenously (JMN); one CD26-negative cell line (MSTO); and two cell lines that expressed CD26 exogenously (MSTO/clone8, MSTO/clone12).