RESEARKA

Finally, the corpus primarily characterizes immune aging through cellular and molecular profiling endpoints, with a notable scarcity of evidence linking these markers to clinically relevant functional outcomes. Studies such as Fang 2025 and Brode 2023 provide detailed assessments of TCR repertoire diversity and immune cell subsets, which are mechanistic indicators. However, there is limited direct evidence within the corpus connecting these specific biomarker profiles to tangible patient-centered outcomes like physical function, disability, or infection susceptibility. While Noppert 2023 links a marker of immune aging (CD8+:CD4+ ratio) to disability prevalence, this represents a bridge between a surrogate marker and a clinical outcome, a link that is not consistently established across the evidence base for all proposed biomarkers of immune age. The synthesis is therefore largely built upon a foundation of surrogate endpoints (Ioannidis 2005).

Citation Support

• source_1 Jongsma 2023
• source_2 Xie 2025
• source_3 Wallen 2024
• source_4 Hoang 2025
• source_5 Boudhabhay 2026