Adenosine as a metabolic checkpoint in CD8+ T cell dysfunction.

CD8+ T cell dysfunction, characterized by impaired effector function, proliferative capacity, and sustained inhibitory receptor expression, limits immune control in both cancer and chronic viral infections. Despite arising from distinct disease processes, these conditions induce a shared state of CD8+ T cell dysfunction, suggesting convergence on common regulatory pathways. Adenosine (ADO), an immunosuppressive purine metabolite generated through extracellular ATP catabolism, has emerged as a context-integrating metabolic checkpoint that regulates immune responses in response to tissue stress and inflammation. Across tumors and HIV, dysregulated ADO signaling reinforces checkpoint pathways and stabilizes dysfunctional CD8+ T cell states. In this review, we examine how the ADO-adenosine deaminase-1 axis shapes CD8+ T cell dysfunction across disease contexts and discuss its potential as a broadly applicable target for immune restoration.