Abstract
Tumor cells have the capacity to create an adenosine-rich immunosuppressive environment, which can interfere with antitumor immunotherapy. Approaches are currently being developed with a view to suppressing the production of adenosine or its signals. Such approaches include the use of antibodies to inhibit CD39, CD73, and adenosine-receptor antagonists. However, the abundance of enzymatic pathways that control the ATP-adenosine balance, as well as the still poorly understood intracellular adenosine regulation, makes the hoped-for success unlikely. In the present study, the enzyme adenosine kinase (ADK) needed to convert adenosine to adenosine monophosphate, thereby regulating its levels, was investigated. To do so, peripheral blood samples from patients with colorectal cancer (CRC) (n = 31) were collected with blood samples from healthy donors (n = 17) used as controls. ADK gene expression levels and those of its long (ADK-L) and short (ADK-S) isoforms were measured. The relationship between the levels of ADK gene expression and that of CD39, CD73, and A2aR genes was analyzed. It turned out that in the group of CRC patients (stages III-IV), the level of ADK-L mRNA was lower (p 0.0011) when compared to that of the control. For the first time, an average correlation was found between the level of expression of CD39 and ADK-S (r = -0.468 at p = 0.043) and between CD73 and ADK-L (r = 0.518 at p = 0.0232) in CRC patients. Flow cytometry was used to assess the content of CD39/CD73-expressing CD8+, CD4+ and Treg lymphocytes, as well as their relationship with the level of ADK gene expression in CRC patients. But no significant correlations were found.