CD8 T cells: A double-edged sword in immunity and disease-Mechanisms and therapeutic targets.

The generation of long-lived immune memory is a hallmark of adaptive immunity, ensuring rapid recall responses upon antigen re-exposure. Within the memory CD8 T cell compartment, T cells (CD45RACCR7) represent a unique, terminally differentiated population defined by potent cytotoxicity and distinct migratory properties. Historically viewed as a state of replicative senescence and dysfunction, recent evidence has shifted this paradigm, portraying T cells as hyper-functional effectors with a Senescence-Associated Secretory Phenotype (SASP). This review comprehensively synthesizes the biological complexity of CD8 T cells, dissecting the transcriptional (e.g., ZEB2, T-bet) and metabolic reprogramming (e.g., glycolytic reliance) that governs their fate. We critically examine their dichotomous roles in health and disease: while serving as indispensable sentinels in antiviral and anti-tumor immunity, their dysregulation contributes to tissue pathology in autoimmune disorders and chronic infections. Furthermore, we address the "tumor immunity paradox" by discussing the confounding role of bystander virus-specific cells and the predictive value of specific subsets (e.g., CX3CR1 T). Finally, we highlight the potential of targeting metabolic checkpoints and senescence pathways as novel therapeutic strategies to modulate T function in clinical settings.