Dipeptidyl peptidase IV: serum activity and expression on lymphocytes in different hematological malignancies

Soluble CD26: From Suggested Biomarker for Cancer Diagnosis to Plausible Marker for Dynamic Monitoring of Immunotherapy

Soluble CD26 (sCD26), a glycoprotein with dipeptidyl peptidase (DPP4) enzymatic activity, can contribute to early diagnosis of colorectal cancer and advanced adenomas and has been studied, including for prognostic purposes, across various other types of cancer and disease. The latest research in this field has confirmed that most, though not all, serum/plasma sCD26 is related to inflammation. The shedding and/or secretion of sCD26 from different immune cells are being investigated, and blood DPP4 activity levels do not correlate very strongly with protein titers. Some of the main substrates of this enzyme are key chemokines involved in immune cell migration, and both soluble and cell-surface CD26 can bind adenosine deaminase (ADA), an enzyme involved in the metabolism of immunosuppressor extracellular adenosine. Of note, there are T cells enriched in CD26 expression and, in mice tumor models, tumor infiltrating lymphocytes exhibited heightened percentages of CD26+ correlating with tumor regression. We employed sCD26 as a biomarker in the follow-up after curative resection of colorectal cancer for the early detection of tumor recurrence. Changes after treatment with different biological disease-modifying antirheumatic drugs, including Ig-CTLA4, were also observed in rheumatoid arthritis. Serum soluble CD26/DPP4 titer variation has recently been proposed as a potential prognostic biomarker after a phase I trial in cancer immunotherapy with a humanized anti-CD26 antibody. We propose that dynamic monitoring of sCD26/DPP4 changes, in addition to well-known inflammatory biomarkers such as CRP already in use as informative for immune checkpoint immunotherapy, may indicate resistance or response during the successive steps of the treatment. As tumor cells expressing CD26 can also produce sCD26, the possibility of sorting immune- from non-immune-system-originated sCD26 is discussed.

CD26/DPP4 - a potential biomarker and target for cancer therapy

CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4. In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed. A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

Activity and expression of dipeptidyl peptidase IV on peripheral blood mononuclear cells in patients with early steroid and disease modifying antirheumatic drugs naïve rheumatoid arthritis

BACKGROUND

Dipeptidyl peptidase IV (DPPIV/CD26) plays an important role in T cell activation and immune regulation, however the role of this enzyme in early rheumatoid arthritis (eRA) has not been clearly defined. The aim of this study was to determine the serum activity of DPPIV, its expression on peripheral blood mononuclear cells (PBMC) and to examine possible correlations with disease activity (DAS28) in untreated patients with eRA.

METHODS

The study included 50 patients newly diagnosed with RA, who had not received any corticosteroid or disease modifying antirheumatic drugs (DMARD) therapy and whose conventional radiographs of hands and feet showed no structural damage. The control group consisted of 40 healthy volunteers. Also, 30 patients with chronic RA (cRA) were examined. The serum activity of DPPIV was determined by the direct photometric method, while expression of CD26 on PBMC was determined using flow cytometry.

RESULTS

Decreased DPPIV serum activity was detected in patients with eRA and cRA compared to the control group (p=0.024, p<0.0001, respectively). Although, the percentage of overall CD26+ white blood cells (WBC) was significantly decreased in eRA patients (p<0.001), the percentage of CD26+ lymphocytes and monocytes and mean fluorescence intensity of CD26 on these cells in eRA patients showed no significant difference compared to healthy volunteers. DAS28 showed no significant correlation with CD26 expression or DPPIV serum activity, but a significant inverse correlation between the duration of symptoms and DPPIV serum activity was observed.

CONCLUSIONS

Our results show that a decrease in DPPIV serum activity, but not CD26 expression, is present in an early stage of rheumatoid arthritis.