SummaryAging is associated with immune dysfunction, especially T‐cell defects, which result in increased susceptibility to various diseases. Previous studies showed that T cells from aged mice express multiple inhibitory receptors, providing evidence of the relationship between T‐cell exhaustion and T‐cell senescence. In this study, we showed that T‐cell immunoglobulin and immunoreceptor tyrosine‐based inhibitory motif (ITIM) domain (TIGIT), a novel co‐inhibitory receptor, was upregulated in CD8+ T cells of elderly adults. Aged TIGIT
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CD8+ T cells expressed high levels of other inhibitory receptors including PD‐1 and exhibited features of exhaustion such as downregulation of the key costimulatory receptor CD28, representative intrinsic transcriptional regulation, low production of cytokines, and high susceptibility to apoptosis. Importantly, their functional defects associated with aging were reversed by TIGIT knockdown. CD226 downregulation on aged TIGIT
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CD8+ T cells is likely involved in TIGIT‐mediated negative immune suppression. Collectively, our findings indicated that TIGIT acts as a critical immune regulator during aging, providing a strong rationale for targeting TIGIT to improve dysfunction related to immune system aging.
Spontaneous mutations introduce uncertainty into COVID-19 control procedures and vaccine development. Here, we perform spatio-temporal analysis on intra-host single-nucleotide variations (iSNVs) in 402 clinical samples from 170 patients, which reveals an increase in genetic diversity over time post-symptoms onset within individual patients. Nonsynonymous mutations are over-represented in the pool of iSNVs, but underrepresent at the single nucleotide polymorphism (SNP) level, suggesting a two-step fitness selection process: a large number of nonsynonymous substitutions are generated within the host (positive selection), and these substitutions tend to be unfixed as SNPs in population (negative selection). Dynamic iSNVs changes in subpopulations of different gender, age, illness severity and viral shedding time displayed a varied fitness selection process among populations. Taken together, our study highlights iSNVs provide a mutational pool shaping the virus rapid global evolution.
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