The Role of Cluster of Differentiation 39 (CD39) and Purinergic Signaling Pathway in Viral Infections

CD39 transforming cancer therapy by modulating tumor microenvironment

CD39 is a pivotal enzyme in cancer, regulating immune response and tumor progression via extracellular ATP and adenosine in the tumor microenvironment (TME). Beyond its established immunoregulatory function, CD39 influences cancer cell angiogenesis and metabolism, opening new frontiers for therapeutic interventions. Current research faces gaps in understanding CD39's full impact across cancer types, with ongoing debates about its potential beyond modulating immune evasion. This review distills CD39's multifaceted roles, examining its dual actions and implications for cancer prognosis and treatment. We analyze the latest therapeutic strategies, highlighting the need for an integrated approach that combines molecular insights with TME dynamics to innovate cancer care. This synthesis underscores CD39's integral role, charting a course for precision oncology that seeks to unravel controversies and harness CD39's therapeutic promise for improved cancer outcomes.

A Prospective Study Investigating Immune Checkpoint Molecule and CD39 Expression on Peripheral Blood Cells for the Prognostication of COVID-19 Severity and Mortality

In patients with COVID-19, broad panels of immune checkpoint molecules (ICPMs) and the purinergic signaling have not been studied in parallel. We aimed to perform in-depth immunophenotyping of major cell subsets present in human peripheral blood of COVID-19 patients and controls using PD1, TIM3, LAG3, TIGIT, and CD200R, as well as CD39, as markers for the purinergic signaling pathway. We studied 76 COVID-19 patients and 12 healthy controls using peripheral blood mononuclear cells on flow cytometry. Univariable and multivariable statistics were performed. All ICPMs studied were significantly overexpressed on different cell subsets of COVID-19 patients when compared with healthy controls. Elevated lactate dehydrogenase; C-reactive protein; age; and high expression of CD45+, CD39+CD45+, TIM3+CD39+CD4+CD45+, and TIM3+CD39+CD8+CD3+CD4+ cells were significantly associated with severe COVID-19. On multivariable analysis, however, only high expression of CD39+CD45+ (OR 51.4, 95% CI 1.5 to 1763) and TIM3+CD39+CD4+CD3+CD45+ (OR 22.6, 95% CI 1.8 to 277) cells was an independent predictor for severe COVID-19. In conclusion, numerous ICPMs are overexpressed in COVID-19 patients when compared with healthy controls, suggesting a pathophysiological role of these molecules in SARS-CoV-2 infection. However, only TIM3 in co-expression with CD39 remained as a significant independent prognostic ICPM on multivariable analysis. The flow cytometric evaluation of TIM3+CD39+CD4+CD3+CD45+, as well as CD39+CD45+, is a powerful tool for the prognostication of COVID-19 patients on hospital admission.

Elevated CD39+T-Regulatory Cells and Reduced Levels of Adenosine Indicate a Role for Tolerogenic Signals in the Progression from Moderate to Severe COVID-19

Viral infections trigger inflammation by controlling ATP release. CD39 ectoenzymes hydrolyze ATP/ADP to AMP, which is converted by CD73 into anti-inflammatory adenosine (ADO). ADO is an anti-inflammatory and immunosuppressant molecule which can enhance viral persistence and severity. The CD39-CD73-adenosine axis contributes to the immunosuppressive T-reg microenvironment and may affect COVID-19 disease progression. Here, we investigated the link between CD39 expression, mostly on T-regs, and levels of CD73, adenosine, and adenosine receptors with COVID-19 severity and progression. Our study included 73 hospitalized COVID-19 patients, of which 33 were moderately affected and 40 suffered from severe infection. A flow cytometric analysis was used to analyze the frequency of T-regulatory cells (T-regs), CD39+ T-regs, and CD39+CD4+ T-cells. Plasma concentrations of adenosine, IL-10, and TGF-β were quantified via an ELISA. An RT-qPCR was used to analyze the gene expression of CD73 and adenosine receptors (A1, A2A, A2B, and A3). T-reg cells were higher in COVID-19 patients compared to healthy controls (7.4 ± 0.79 vs. 2.4 ± 0.28; p < 0.0001). Patients also had a higher frequency of the CD39+ T-reg subset. In addition, patients who suffered from a severe form of the disease had higher CD39+ T-regs compared with moderately infected patients. CD39+CD4+ T cells were increased in patients compared to the control group. An analysis of serum adenosine levels showed a marked decrease in their levels in patients, particularly those suffering from severe illness. However, this was paralleled with a marked decline in the expression levels of CD73. IL-10 and TGF-β levels were higher in COVID-19; in addition, their values were also higher in the severe group. In conclusion, there are distinct immunological alterations in CD39+ lymphocyte subsets and a dysregulation in the adenosine signaling pathway in COVID-19 patients which may contribute to immune dysfunction and disease progression. Understanding these immunological alterations in the different immune cell subsets and adenosine signaling provides valuable insights into the pathogenesis of the disease and may contribute to the development of novel therapeutic approaches targeting specific immune mechanisms.

Purinergic signaling in the battlefield of viral infections

Purinergic signaling has been associated with immune defenses against pathogens such as bacteria, protozoa, fungi, and viruses, acting as a sentinel system that signals to the cells when a threat is present. This review focuses on the roles of purinergic signaling and its therapeutic potential for viral infections. In this context, the purinergic system may play potent antiviral roles by boosting interferon signaling. In other cases, though, it can contribute to a hyperinflammatory response and disease severity, resulting in poor outcomes, such as during flu and potentially COVID-19. Lastly, a third situation may occur since viruses are obligatory intracellular parasites that hijack the host cell machinery for their infection and replication. Viruses such as HIV-1 use the purinergic system to favor their infection and persistence within the host cell. Therefore, understanding the particular nuances of purinergic signaling in each viral infection may contribute to designing proper therapeutic strategies to treat viral diseases.