Purpose: CD26 is a 110-kDa cell surface antigen with a role in tumor development. In this report, we show that CD26 is highly expressed on the cell surface of malignant mesothelioma and that a newly developed humanized anti-CD26 monoclonal antibody (mAb) has an inhibitory effect on malignant mesothelioma cells in both in vitro and in vivo experiments. Experimental Design: Using immunohistochemistry, 12 patients' surgical specimens consisting of seven malignant mesothelioma, three reactive mesothelial cells, and two adenomatoid tumors were evaluated for expression of CD26. The effects of CD26 on malignant mesothelioma cells were assessed in the presence of transfection of CD26-expressing plasmid, humanized anti-CD26 mAb, or small interfering RNA against CD26. The in vivo growth inhibitory effect of humanized anti-CD26 mAb was assessed in human malignant mesothelioma cell mouse xenograft models. Results: In surgical specimens, CD26 is highly expressed in malignant mesothelioma but not in benign mesothelial tissues. Depletion of CD26 by small interfering RNA results in the loss of adhesive property, suggesting that CD26 is a binding protein to the extracellular matrix. Moreover, our in vitro data indicate that humanized anti-CD26 mAb induces cell lysis of malignant mesothelioma cells via antibody-dependent cell-mediated cytotoxicity in addition to its direct anti-tumor effect via p27 kip1 accumulation. In vivo experiments with mouse xenograft models involving human malignant mesothelioma cells show that humanized anti-CD26 mAb treatment drastically inhibits tumor growth in tumor-bearing mice, resulting in enhanced survival. Conclusions: Our data strongly suggest that humanized anti-CD26 mAb treatment may have potential clinical use as a novel cancer therapeutic agent in CD26-positive malignant mesothelioma.

CD26 is a widely distributed 110-kDa cell surface glycoprotein with an important role in T-cell costimulation. We demonstrated previously that CD26 binds to caveolin-1 in antigen-presenting cells, and following exogenous CD26 stimulation, Tollip and IRAK-1 disengage from caveolin-1 in antigen-presenting cells. IRAK-1 is then subsequently phosphorylated to up-regulate CD86 expression, resulting in subsequent T-cell proliferation. However, it is unclear whether caveolin-1 is a costimulatory ligand for CD26 in T-cells. Using soluble caveolin-1-Fc fusion protein, we now show that caveolin-1 is the costimulatory ligand for CD26, and that ligation of CD26 by caveolin-1 induces T-cell proliferation and NF-B activation in a T-cell receptor/ CD3-dependent manner. We also demonstrated that the cytoplasmic tail of CD26 interacts with CARMA1 in T-cells, resulting in signaling events that lead to NF-B activation. Ligation of CD26 by caveolin-1 recruits a complex consisting of CD26, CARMA1, Bcl10, and IB kinase to lipid rafts. Taken together, our findings provide novel insights into the regulation of T-cell costimulation via the CD26 molecule.

The inhibitory PAS (Per/Arnt/Sim) domain protein (IPAS), a dominant negative regulator of hypoxia-inducible transcription factors (HIFs), is potentially implicated in negative regulation of angiogenesis in such tissues as the avascular cornea of the eye. We have previously shown IPAS mRNA expression is up-regulated in hypoxic tissues, which at least in part involves hypoxiadependent alternative splicing of the transcripts from the IPAS/ HIF-3␣ locus. In the present study, we demonstrate that a hypoxia-driven transcriptional mechanism also plays a role in augmentation of IPAS gene expression. Isolation and analyses of the promoter region flanking to the first exon of IPAS gene revealed a functional hypoxia response element at position ؊834 to ؊799, whereas the sequence upstream of the HIF-3␣ first exon scarcely responded to hypoxic stimuli. A transient transfection experiment demonstrated that HIF-1␣ mediates IPAS promoter activation via the functional hypoxia response element under hypoxic conditions and that a constitutively active form of HIF-1␣ is sufficient for induction of the promoter in normoxic cells. Moreover, chromatin immunoprecipitation and electrophoretic mobility shift assays showed binding of the HIF-1 complex to the element in a hypoxia-dependent manner. Taken together, HIF-1 directly up-regulates IPAS gene expression through a mechanism distinct from RNA splicing, providing a further level of negative feedback gene regulation in adaptive responses to hypoxic/ischemic conditions.

CD26 is a 110 kDa surface glycoprotein with intrinsic dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5) activity that is expressed on numerous cell types and has a multitude of biological functions. CD26 role in immune regulation has been extensively characterized, with recent findings elucidating its linkage with signaling pathways and structures involved in T-lymphocyte activation as well as antigen presenting cell (APC)-T-cell interaction. In this paper, we will review emerging data on CD26-mediated T-cell costimulation, suggesting that CD26 may be an appropriate therapeutic target for the treatment of immune disorders. However, the identity of its putative natural ligand had not yet been clearly elucidated. Recently, using protein engineering and proteomic approach, we have recently characterized the putative costimulatory ligand for CD26 in T-cells and the proximal signaling events directly associated with the cytoplasmic region of CD26 in CD26-associated T-cell costimulation, processes that are independent of the CD28 costimulatory pathway. Our work therefore presents novel findings that contribute to the area of T-cell costimulation and signal transduction.

Background:YS110 is a humanised IgG1 monoclonal antibody with high affinity to the CD26 antigen. YS110 demonstrated preclinical anti-tumour effects without significant side effects.Methods:This FIH study was designed to determine the maximal tolerated dose (MTD) and recommended phase 2 dose (RP2D) to assess the tolerance, pharmacokinetics (PK) and pharmacodynamics profiles of YS110 and preliminary efficacy. YS110 were initially administered intravenously once every 2 weeks (Q2W) for three doses and then, based on PK data, once every week (Q1W) for five doses in patients with CD26-expressing solid tumours.Results:Thirty-three patients (22 mesothelioma) received a median of 3 (range 1–30) YS110 infusions across six dose levels (0.1–6 mg kg-1). MTD was not reached and two dose-limiting toxicities (infusion hypersensitivity reactions) led to the institution of a systemic premedication. Low-grade asthenia (30.3%), hypersensitivity (27.3%), nausea (15.2%), flushing (15.2%), chills (12.1%) and pyrexia (12.1%) were reported as ADRs. Pharmacokinetic parameters (AUC and Cmax) increased in proportion with the dose. sCD26/DPPIV assays indicated CD26 modulation. Prolonged stable diseases were observed in 13 out of 26 evaluable patients.Conclusions:YS110 is well tolerated up to 6 mg kg-1 Q1W, which has been defined as the RP2D, with encouraging prolonged disease stabilisations observed in a number of patients with advanced/refractory mesothelioma.