Enhanced CD25 expression and IL-2/STAT5 signaling characterize β-galactosidase+ senescent and aged CD4+ T cells 2257543

Introduction Alterations to the IL-2 signaling axis contribute to age-related immune decline, with increased IL-2RA (CD25) expression linked to impaired T cell function. However, the contribution of age-associated T cell senescence to this phenomenon is unknown. Using a biochemical senescence-associated β-galactosidase (SA β-Gal) assay, we examined IL-2-STAT5 signaling in total and senescent CD4+ T cells during aging. Methods PBMCs from 65 older (≥60 years) and 54 young (18-40 years) adults from an ongoing R01 study (NCT04487041) were analyzed by flow cytometry for T cell phenotype and SA β-Gal expression. IL-2-induced STAT5 phosphorylation was assessed by phosphoflow in FoxP3- CD4+ T cells and quantified as the fold-change (FC) in median fluorescence intensity (MFI) after IL-2 stimulation. Bulk RNA-seq was performed on anti-CD3/anti-CD28-stimulated SA β-Gal+ and SA β-Gal- CD4+ T cells FACS-sorted from 3 older donors. Flow data were analyzed in OMIQ with Welch’s or paired t-tests. RNA-seq analysis was performed with DESeq2 and EnrichR in R. Results Older adults had higher frequencies of CD25 + (7.1% vs. 6.1%, p = 0.03) and SA β-Gal + (8.1% vs. 5.6%, p = 0.005) CD4+ T cells and elevated IL-2-induced STAT5 (2.9 vs. 1.4, p < 0.0001). CD25 expression was ∼3-fold higher in SA β-Gal+ vs. SA β-Gal- T cells (p < 0.0001). We identified 2,130 DEGs in SA β-Gal+ vs. SA β-Gal- T cells, with upregulation of senescence genes CDKN1A (p21) and CDKN2A (p16), and Th1 transcription factor TBX21 (T-bet), and downregulation of follicular helper (Tfh) differentiation genes TCF7, LEF1, SELL, and CCR7. FoxP3 expression was not increased in SA β-Gal+ cells. IL-2-STAT5 signaling was the second most enriched MSigDB term in SA β-Gal+ T cells. Conclusion CD25+ and senescent CD4+ T cells accumulate with age and exhibit enhanced IL-2-STAT-5 signaling and Th1 polarization, and reduced Tfh-associated gene expression, providing a potential mechanism through which CD4+ T cell senescence contributes to age-related immune dysfunction. Funding Source National Institute on Aging (NIA) - National Institutes of Health (NIH)