BACKGROUND: Flow cytometry is not routinely performed in clinical laboratories for the diagnosis of classic Hodgkin lymphoma (CHL).
METHODS: Fourteen cases of CHL and 132 cases of the control group were studied by 10-color flow cytometry, with markers including CD3, CD4, CD7, CD8, and CD26, as well as calculated parameters such as the CD4:CD8 ratio, percent CD3+CD4+CD26- T-cells of CD3+CD4+ T-cells, percent CD3+CD4+CD26- T-cells of total events, CD7 coefficient of variation among CD3+CD4+CD26- T-cells, and CD7 median fluorescence intensity of CD3+CD4+CD26- T-cells relative to CD3+CD8+ T-cells.
RESULTS: CHL cases showed a median percent CD3+CD4+CD26- of CD3+CD4+ T-cells of 72.3% with range from 41.1% to 94.4%, median percent CD3+CD4+CD26- T-cells of total events of 17.4% with range from 4.6% to 52.5%, CD7 coefficient of variation among CD3+CD4+CD26- T-cells less than 100%, and CD7 median fluorescence intensity of CD3+CD4+CD26- T-cells relative to CD3+CD8+ T-cells of 1.7 with range from 0.4 to 3.5. In the control group, every entity showed some degree of overlap with CHL in terms of these parameters. A \"Hodgkin score\" was thus constructed to enhance separation of CHL from other entities. A threshold Hodgkin score of 15.35 achieved a sensitivity of 78.6% and specificity of 96.2% in the diagnosis of CHL. Incorporating the Hodgkin score into a simple algorithm raises the specificity to 100%.
CONCLUSIONS: In this study, we used flow cytometry to demonstrate increased CD3+CD4+CD26- T-cells in CHL, and derived a Hodgkin score for the diagnosis of CHL.

Background/Objectives: Colorectal cancer (CRC) is still accompanied by significant mortality, which poses the necessity of novel markers to predict treatment success and patient survival. This study aims to evaluate the prognostic and survival impact of flowytometry (FC) in CRC patients. Methods: In this prospective study, 106 surgically resectable CRC patients were included. Tissue specimens from tumor and normal mucosa were collected and analyzed by FC. DNA and tumor index were calculated. In a subgroup of 46 patients, the CD26 expression on tumor cells was estimated. These parameters were compared with patients\' tumor characteristics as stage, histology data, responsiveness to treatment, metastasis/recurrence, and, finally, patients\' survival to identify possible new biomarkers. Results: The overall survival and the disease-specific survival in our study group was 76% and 72%, respectively, during the 7-year follow up period. Diploid tumors had better median survival than the aneuploid ones. The DNA index had significant correlation to the tumor index and response to neoadjuvant treatment. Similarly, the tumor index was also significantly related to the response to neoadjuvant treatment. Patients with a higher tumor index had worst survival rates. Surprisingly, CD26 levels were not associated with any of the parameters examined and were negatively related to tumor stage and differentiation. Conclusions: FC is a rapid and reliable method of cell analysis. In CRC, it has been used for prognostic and diagnostic purposes. In this study, we have shown that DNA and tumor index could become predictive biomarkers of tumor response to neoadjuvant treatment and survival of resectable CRC patients.

Immune cell function is impaired in hyperglycemic patients with diabetes but thought to improve with normalization of blood glucose levels. In this study, we hypothesized that this improvement might involve changes in T cell function. We compared the peripheral T cell markers between the people with and without type 2 diabetes (T2D) admitted to our hospital for glycemic control, and then in patients with T2D before and after the improvement of hyperglycemia by inpatient treatment. Expression of programmed death 1 (PD-1) and T-cell immunoglobulin and mucin domain 3 (TIM-3), co-suppressive molecules, CD26 and CD28 on CD4-positive and/or CD8-positive T cells, the Th1/Th2 ratio, and the number of regulatory T cells (Tregs) were not significantly different between the people with and without T2D. Although an average of 10.6 days of inpatient treatment with improved hyperglycemia did not affect expression of PD-1 and TIM-3 in T cells, the Th1/Th2 ratio, or Tregs, it significantly reduced expression of CD26 and CD28 on CD4-positive T cells. CD26 and CD28 on CD4-positive T cells may be associated with the altered immune function after rapid improvement of hyperglycemia but that the other T-cell markers investigated here may not be.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s13340-024-00697-7.

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.

Improving cancer immunotherapy efficacy hinges on identifying key T-cell populations critical for tumor control and response to Immune Checkpoint Blockade (ICB). We have recently reported that while the co-expression of PD-1 and CD28 is associated with impaired functionality in peripheral blood, it significantly enhances T-cell fitness in the tumor site of non-small cell lung cancer (NSCLC) patients. To uncover the underlying mechanisms, we explored the role of CD26, a key player in T-cell activation through its interaction with adenosine deaminase (ADA), a crucial intra/extracellular enzyme able to neutralize local adenosine (ADO). We found that an autocrine ADA/CD26 axis enhances CD8+PD-1+CD28+ T-cell function, particularly within an immunosuppressive environment marked by CD39 expression. Then, we interrogated the TCGA and OAK datasets to gain insight into the prognostic/predictive potential of our findings. We identified a signature predicting overall survival (OS) in LUAD patients and response to atezolizumab in advanced LUAD cases. These findings suggest promising avenues for therapeutic intervention targeting the ADA/CD26 axis.

Cancer-associated fibroblasts (CAFs) are a heterogeneous population of fibroblasts with various features in the cancer stroma and have been reported to influence cancer progression through cell-cell interactions in various types of malignancies, including lung adenocarcinoma (LUAD). Dipeptidyl peptidase 4 (DPP4) is a transmembrane protein with serine protease activity and is involved in the progression of tumors, metabolic diseases, and autoimmune diseases. In the present study, we focused on the role of DPP4-positive CAFs in LUAD. Immunohistochemistry revealed that 38 of 89 LUAD patients showed DPP4 expression in the fibrous stroma, and patients harboring DPP4-positive CAFs were more often male, had a higher Brinkman index, and had a higher Ki-67 labeling index of tumor cells than those with DPP4-negative CAFs. DPP4-positivity was associated with the expression of other CAF markers, α-SMA, periostin, and podoplanin, as well as a cellular senescence marker, p16. In the in vitro study, conditioned media collected from pulmonary fibroblast (OUS-11, HPF, and HPF-C)-induced overexpression of DPP4 significantly promoted the proliferation of LUAD cells (A549 and PC-9) and increased the expression levels of MCP-1, IL-8, IL-6, and GCSF in the media compared to those in controls. In addition, OUS-11 overexpression in DPP4 overexpression increased periostin expression. In conclusion, DPP4-positive CAFs could promote lung adenocarcinoma cell growth by producing soluble factors, and DPP4 inhibition may inhibit cancer progression.

A novel pangolin-origin MERS-like coronavirus (CoV), MjHKU4r-CoV-1, was recently identified. It is closely related to bat HKU4-CoV, and is infectious in human organs and transgenic mice. MjHKU4r-CoV-1 uses the dipeptidyl peptidase 4 (DPP4 or CD26) receptor for virus entry and has a broad host tropism. However, the molecular mechanism of its receptor binding and determinants of host range are not yet clear. Herein, we determine the structure of the MjHKU4r-CoV-1 spike (S) protein receptor-binding domain (RBD) complexed with human CD26 (hCD26) to reveal the basis for its receptor binding. Measuring binding capacity toward multiple animal receptors for MjHKU4r-CoV-1, mutagenesis analyses, and homology modeling highlight that residue sites 291, 292, 294, 295, 336, and 344 of CD26 are the crucial host range determinants for MjHKU4r-CoV-1. These results broaden our understanding of this potentially high-risk virus and will help us prepare for possible outbreaks in the future.

BACKGROUND: Leukemic stem cells (LSCs) are the transcriptionally low/silent cells which are resistant to the tyrosine kinase inhibitor. These have been found to play a pivotal role in disease relapse in chronic myeloid leukemia (CML) cases. The present study evaluated the correlation of absolute CML-LSC count in the peripheral blood (PB) at diagnosis and achievement of major molecular response (MMR) at 12 months in patients of CML-CP.
METHODS: This was a prospective, observational, non-interventional single center study including newly diagnosed adult (>18 yrs) CML-CP patients. Absolute CD26 + CML-LSC quantification was done by multiparametric flow cytometry. Patients were treated with Imatinib treatment and subsequently monitored at 3-month intervals for BCR::ABL transcript levels. MMR was defined as a BCR::ABL1 transcript level of less than 0.1% on international scale.
RESULTS: A total of 89 patients were enrolled in the study out of which 40.5% achieved MMR at 12 months. There was a significant difference in the median absolute CML-LSC count of the patients who achieved MMR at 12 months as compared to those who did not (58.5 vs 368.1 cells/μL; p value <0.001). Using a ROC analysis, a count of <165.69 CML LSC/μL was identified to have a sensitivity of 83.8% and specificity of 72.4%, in predicting the MMR at 12 months.
CONCLUSIONS: Absolute CML-LSC count at diagnosis in the PB predicts the MMR achievement at 12 months. An absolute count of less than 165 cells/μL is highly predictive of achieving MMR at 12 months.

Chimeric antigen receptor (CAR) T cell therapy is hindered in solid tumor treatment due to the immunosuppressive tumor microenvironment and suboptimal T cell persistence. Current strategies do not address nutrient competition in the microenvironment. Hence, we present a metabolic refueling approach using inosine as an alternative fuel. CAR T cells were engineered to express membrane-bound CD26 and cytoplasmic adenosine deaminase 1 (ADA1), converting adenosine to inosine. Autocrine secretion of ADA1 upon CD3/CD26 stimulation activates CAR T cells, improving migration and resistance to transforming growth factor β1 suppression. Fusion of ADA1 with anti-CD3 scFv further boosts inosine production and minimizes tumor cell feeding. In mouse models of hepatocellular carcinoma and non-small cell lung cancer, metabolically refueled CAR T cells exhibit superior tumor reduction compared to unmodified CAR T cells. Overall, our study highlights the potential of selective inosine refueling to enhance CAR T therapy efficacy against solid tumors.

Context Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasm. Recent studies have suggested that CD26-positive leukemic stem cells (LSCs) circulating in peripheral blood are specific for CML. Objective This study was undertaken to determine the proportion of CD26-positive LSCs at diagnosis and its change during tyrosine kinase inhibitor therapy. Design This prospective study was conducted on 43 cases of CML at diagnosis. For flow cytometry, peripheral blood cells were stained with CD45, CD34, CD38, CD3, and CD26. A sequential gating strategy with CD45/SSC (side scatter), CD34/SSC, and CD34/CD38 was applied to identify CD45+/34+/38- populations, from which CD26-positive stem cells were identified and compared with controls. Data analysis was done with Kaluza software. Results All patients diagnosed with CML were detected with CD26-positive LSCs. The median percentage of CD26-positive CML LSCs was 0.02 with a range of 0.001 to 1.77. None of the control samples showed CD26 positivity. The percentage and absolute count of CD26-positive CML LSCs were reduced after six months of tyrosine kinase therapy in patients with complete hematological remission. Conclusion Flow cytometric analysis of circulating CD26-positive CML LSCs is a non-invasive, rapid, and useful tool in the diagnosis and follow-up of CML.