Molecular and epigenetic landscapes of immunosenescence in biological aging: A narrative review
Aging is increasingly recognized as a heterogeneous biological process rather than a uniform chronological phenomenon. Immunosenescence has emerged as a central hallmark of biological aging, profoundly shaping susceptibility to infection, malignancy, autoimmunity, and poor vaccine responses. This progressive decline encompasses both innate and adaptive immunity and is marked by impaired antigen presentation, thymic involution, reduced lymphopoiesis, repertoire contraction, and the establishment of chronic low-grade inflammation. Importantly, immunosenescence does not occur solely as a consequence of chronological time but is accelerated by chronic conditions such as human immunodeficiency virus (HIV) infection, autoimmune disease, metabolic syndrome, chronic kidney disease, and cancer therapy, underscoring the dissociation between chronological and biological immune age. At the molecular level, aged lymphocytes accumulate DNA damage, mitochondrial dysfunction, and metabolic stress that drive canonical senescence pathways. Classical markers, including p16 inhibitor of cyclin-dependent kinase 4a (p16INK4a), p21 cyclin-dependent kinase–interacting protein 1 (p21CIP1), gamma-H2A histone family member X (γH2AX), and senescence-associated β-galactosidase (SA-β-gal), are now complemented by novel signatures such as immune-specific DNA methylation clocks, histone modifications, noncoding RNA networks, telomeric repeat-containing RNAs, mitochondrial dysfunction metrics, and profiles of the senescence-associated secretory phenotype. These biomarkers provide quantitative measures of immune biological age that surpass chronological metrics in predicting health outcomes. This review synthesizes emerging molecular and epigenetic frameworks that redefine immunosenescence as a quantifiable and disease-modifiable dimension of biological aging rather than a passive consequence of chronological time. By integrating immune-specific epigenetic clocks, mitochondrial and telomeric stress signatures, and senescence-associated secretory phenotypes, we highlight actionable biomarkers that enable precise stratification of immune biological age. These insights provide a translational roadmap for targeting immune aging through senotherapeutics, metabolic and epigenetic interventions, and optimized vaccine strategies, advancing immunosenescence toward precision geromedicine. Future advances will arise from longitudinal studies employing single-cell multi-omics, repertoire sequencing, and artificial intelligence–driven modeling to refine predictive aging clocks. Translational strategies targeting immune aging, including senolytics, senomorphics, metabolic modulators, epigenetic reprogramming, and next-generation vaccine adjuvants, hold promise for restoring immune resilience. Integrating these insights into precision medicine frameworks may transform immunosenescence from an inevitable feature of aging into a modifiable determinant of healthspan.