Tumor immune evasion, a hallmark of cancer, allows malignant cells to escape immune surveillance and elimination. While immune checkpoint inhibitors, such as anti-PD-1, anti-CTLA-4, and anti-PD-L1 antibodies, have revolutionized cancer therapy by enhancing T-cell responses, their efficacy is often limited by additional immunosuppressive mechanisms within the tumor microenvironment (TME). Elevated adenosine (Ado) levels, generated by the ectoenzymes CD39 and CD73, significantly contribute to immunosuppression by activating adenosine receptors (ARs) on immune cells. Although targeting the CD39-CD73-AR axis shows therapeutic promise, limited clinical success underscores the need for a deeper understanding of Ado metabolism complexity within the heterogeneous TME.

This thesis investigates cell-type-specific Ado metabolic pathways, focusing on human vascular endothelial cells, cancer cells, and T cells. I identify a complex network of purine-converting ectoenzymes, including CD39 and CD73, as well as ENPP1, NDPK, AK, and ADA, with distinct cell-specific distributions. While endothelial cells rely on the “classical” ATP-inactivating/Ado-producing pathway involving CD39 and CD73, breast and prostate cancer cells utilize an alternative pathway, incorporating ENPP1 and CD73 while lacking CD39. In T cells, CD73 is primarily expressed on naïve T cells, whereas CD39 is prevalent on activated T cells. Hypoxia further modulates Ado metabolic pathways in a cell-specific manner, increasing CD39 activity in endothelial cells and upregulating CD73 in cancer cells.

Beyond the “canonical” Ado signaling pathways, I uncover the underexplored role of intracellular Ado metabolism in cancer progression and immunomodulation. My research shows that extracellular Ado, taken up by cancer cells and T cells via the equilibrative nucleoside transporter ENT1, reduces cancer cell tumorigenic potential in vivo and exerts potent immunosuppressive effects on T cells by inhibiting their proliferation, cytokine production, and conventional ATP-generating pathways.

Taken together, this study emphasizes the importance of accounting for the complexity of the TME when developing effective therapies targeting Ado pathways. My findings also highlight intracellular Ado metabolism as a promising therapeutic target that merits further investigation.