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Aging is associated with functional deficits in the naive T cell compartment, which compromise the generation of de novo immune responses against previously unencountered Ags. The mechanisms that underlie this phenomenon have nonetheless remained unclear. We found that naive CD8 + T cells in elderly humans were prone to apoptosis and proliferated suboptimally in response to stimulation via the TCR. These abnormalities were associated with dysregulated lipid metabolism under homeostatic conditions and enhanced levels of basal activation. Importantly, reversal of the bioenergetic anomalies with lipid-altering drugs, such as rosiglitazone, almost completely restored the Ag responsiveness of naive CD8 + T cells. Interventions that favor lipid catabolism may therefore find utility as adjunctive therapies in the elderly to promote vaccine-induced immunity against targetable cancers and emerging pathogens, such as seasonal influenza viruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)., (Copyright © 2022 by The American Association of Immunologists, Inc.)

αβ CD8 + , γδ, and NK lymphocytes are fundamental effector cells against viruses and tumors. These cells can be divided into multiple subsets according to their phenotype. Based on progressive telomere attrition from naive to late effector memory cells, human CD8 + T cell subsets have been positioned along a pathway of differentiation, which is also considered as a process of lymphocyte aging or senescence. A similar categorization has not been clearly established for γδ and NK cell populations. Moreover, the distinction between the aging of these populations due to cellular differentiation or due to the chronological age of the donor has not been formally considered. In this study, we performed systematic measurements of telomere length and telomerase activity in human αβ CD8 + , γδ, and NK lymphocytes based on subset division and across age to address these points and better understand the dichotomy between differentiation and temporal aging. This approach enables us to position phenotypically distinct γδ or NK subsets along a putative pathway of differentiation, such as for CD8 + T cells. Moreover, our data show that both cellular differentiation and donor aging have profound but independent effects on telomere length and telomerase activity of lymphocyte subpopulations, implying distinct mechanisms and consequences on the immune system., (Copyright © 2019 by The American Association of Immunologists, Inc.)

Aging is associated with impaired vaccine efficacy and increased susceptibility to infectious and malignant diseases. CD8(+) T-cells are key players in the immune response against pathogens and tumors. In aged mice, the dwindling naïve CD8(+) T-cell compartment is thought to compromise the induction of de novo immune responses, but no experimental evidence is yet available in humans. Here, we used an original in vitro assay based on an accelerated dendritic cell coculture system in unfractioned peripheral blood mononuclear cells to examine CD8(+) T-cell priming efficacy in human volunteers. Using this approach, we report that old individuals consistently mount quantitatively and qualitatively impaired de novo CD8(+) T-cell responses specific for a model antigen. Reduced CD8(+) T-cell priming capacity in vitro was further associated with poor primary immune responsiveness in vivo. This immune deficit likely arises as a consequence of intrinsic cellular defects and a reduction in the size of the naïve CD8(+) T-cell pool. Collectively, these findings provide new insights into the cellular immune insufficiencies that accompany human aging., (© 2015 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

A recent consensus has emerged regarding the association between chronic immune activation and poor outcome in HIV-1 infection. However, its basis remains unclear. Accumulating evidence suggests that the cells of the immune system may have a limited replicative lifespan in vivo. In this context, persistent activation during chronic HIV infection may lead to an exhaustion of immune resources. This may occur at two levels: Clonal and Global. Some HIV-1-specific CD8+ T-cells start expressing the senescence marker CD57 soon after primary infection. Persistently activated HIV-1-specific T-cell clones may eventually reach stages of replicative senescence and disappear, resulting in the specific loss of CD8+ T-cell populations important to control viral replication. In addition, HIV-1 infected individuals are characterized by the accumulation of highly differentiated CD8+ and CD4+ T-cells overtime. Together with the decline of T-cell renewal capacities, this may reflect a general ageing of the lymphocyte population. Similar observations have been done in HIV non-infected elderly individuals, which suggests that premature immunosenescence occurs in HIV-1 infection, as a result of persistent immune activation.

Progress in the fight against the HIV/AIDS epidemic is hindered by our failure to elucidate the precise reasons for the onset of immunodeficiency in HIV-1 infection. Increasing evidence suggests that elevated immune activation is associated with poor outcome in HIV-1 pathogenesis. However, the basis of this association remains unclear. Through ex vivo analysis of virus-specific CD8(+) T-cells and the use of an in vitro model of naïve CD8(+) T-cell priming, we show that the activation level and the differentiation state of T-cells are closely related. Acute HIV-1 infection induces massive activation of CD8(+) T-cells, affecting many cell populations, not only those specific for HIV-1, which results in further differentiation of these cells. HIV disease progression correlates with increased proportions of highly differentiated CD8(+) T-cells, which exhibit characteristics of replicative senescence and probably indicate a decline in T-cell competence of the infected person. The differentiation of CD8(+) and CD4(+) T-cells towards a state of replicative senescence is a natural process. It can be driven by excessive levels of immune stimulation. This may be part of the mechanism through which HIV-1-mediated immune activation exhausts the capacity of the immune system., Competing Interests: The authors have declared that no conflicts of interest exist.