Category — immune system

Steven Russell Fauce, Beth D. Jamieson , Allison C. Chin, Ronald T. Mitsuyasu , Stan T. Parish, Hwee L. Ng, Christina M. Ramirez Kitchen, Otto O. Yang, Calvin B. Harley , and Rita B. Effros. Department of Pathology and Laboratory Medicine and Department of Medicine, David Geffen School of Medicine, University of California-Los Angeles, Los Angeles, CA 90095; Geron, Menlo Park, CA 94025; and Department of Biostatistics, University of California-Los Angeles, School of Public Health, Los Angeles, CA 90095

Telomerase reverse transcribes telomere DNA onto the ends of linear chromosomes and retards cellular aging. In contrast to most normal somatic cells, which show little or no telomerase activity, immune cells up-regulate telomerase in concert with activation. Nevertheless, during aging and chronic HIV-1 infection, there are high proportions of dysfunctional CD8+ CTL with short telomeres, suggesting that telomerase is limiting. The present study shows that exposure of CD8+ T lymphocytes from HIV-infected human donors to a small molecule Telomerase Activator (TAT2) modestly retards telomere shortening, increases proliferative potential, and, importantly, enhances cytokine/chemokine production and antiviral activity. The enhanced antiviral effects were abrogated in the presence of a potent and specific telomerase inhibitor, suggesting that TAT2 acts primarily through telomerase activation. Our study is the first to use a pharmacological telomerase-based approach to enhance immune function, thus directly addressing the telomere loss immunopathologic facet of chronic viral infection.

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Carolina L. Montes, Andrei I. Chapoval, Jonas Nelson, Vbenosa Orhue, Xiaoyu Zhang, Dan H. Schulze, Scott E. Strome, and Brian R. Gastman

Senescent and suppressor T cells are reported to be increased in select patients with cancer and are poor prognostic indicators. Based on the association of these T cells and poor outcomes, we hypothesized that tumors induce senescence in T cells, which negatively effects antitumor immunity. In this report, we show that human T cells from healthy donors incubated with tumor for only 6 h at a low tumor to T-cell ratio undergo a senescence-like phenotype, characterized by the loss of CD27 and CD28 expression and telomere shortening. Tumor-induced senescence of T cells is induced by soluble factors and triggers increases in expression of senescence-associated molecules such as p53, p21, and p16. Importantly, these T cells are not only phenotypically altered, but also functionally altered as they can suppress the proliferation of responder T cells. This suppression requires cell-to-cell contact and is mediated by senescent CD4+ and CD8+ subpopulations, which are distinct from classically described natural T regulatory cells. Our observations support the novel concept that tumor can induce senescent T cells with suppressor function and may effect both the diagnosis and treatment of cancer. [Cancer Res 2008;68(3):870-9]

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Nan-ping Weng. Laboratory of Immunology, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD 21224, United States; Mechanisms of Aging and Development 2008

The adaptive immune response relies on the ability of lymphocytes to undergo periodic massive expansion. It is an enigma how lymphocytes are able to undergo this seemingly unlimited number of cell divisions. Telomeres and telomerase play a critical role in regulation of the replicative lifespan of cells, providing a potential mechanism which lymphocytes may employ. Here I will review the recent progress of the role of telomeres and telomerase in lymphocyte differentiation, function, and aging.

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Rita Effros Presentation Summary for SENS (Aubrey de Grey) Conference 6 Sept 2007

R.B. Effros David Geffen School of Medicine at UCLA, Department of Pathology and Laboratory Medicine, 10833 Le Conte Avenue, Los Angeles, CA 90095-1732, USA

The immune system plays a role not only in controlling infections, but also in certain age-related pathologies, such as atherosclerosis, osteoporosis, cancer and Alzheimer’s disease. In humans, ageing is associated with the accumulation of high proportions of CD8 (cytotoxic) T lymphocytes with markers of replicative senescence, including inability to proliferate, altered cytokine profiles, absence of the critical co-stimulatory receptor, CD28, reduced anti-viral function, shortened telomeres and loss of telomerase inducibility. Most of these senescent CD8 T lymphocytes are specific for latent viruses acquired early in life, and thus, reflect the constant “work” required over many decades to keep these infections from re-emerging. Since high proportions of senescent CD8 T lymphocytes are correlated with such deleterious outcomes as early mortality in the very old, reduced responses to vaccines, immune suppression, and, in persons infected with HIV, accelerated progression to AIDS, our research has focused on strategies to prevent or retard the process of replicative senescence. In earlier work, we documented that gene transduction with the human telomerase catalytic component (hTERT) leads to enhanced proliferation, telomere length stabilization, and increased anti-viral immunity. Current experiments are testing small molecule telomerase activators, which would be more suitable for clinical use, for their effects on CD8 T lymphocyte biology. Our data demonstrate that exposure to TAT2, one of these activators, significantly enhances telomerase activity, increases the ability of T lymphocytes to control viral production, enhances proliferation, increases production of anti-viral cytokines/chemokines, and retards telomere loss. The enhanced telomerase activity is associated with increased hTERT gene transcription. These studies support the notion that therapeutic manipulation of telomerase in human T lymphocytes may provide novel clinical avenues to enhancing viral immunity and retarding the immune exhaustion associated with ageing. (These studies were supported by the National Institutes of Health, TA Therapeutics, Ltd, and Geron Corporation).

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Ouyang Q, Baerlocher G, Vulto I, Lansdorp PM. Terry Fox Laboratory, BC Cancer Research Centre, 675 West 10th Avenue, Vancouver, BC, Canada, V5Z 1L3. Ann N Y Acad Sci. ;1106:240-52.

Natural killer (NK) cells are cytotoxic cells that play a critical role in the innate immune response against infections and tumors. In the elderly, the cytotoxic function of NK cells is often compromised. Telomeres progressively shorten with each cell division and with age in most somatic cells eventually leading to chromosomal instability and cellular senescence. We studied the telomere length in NK cell subsets isolated from peripheral blood using “flow FISH,” a method in which the hybridization of telomere probe in cells of interest is measured relative to internal controls in the same tube. We found that the average telomere length in human NK cells decreased with age as was previously found for human T lymphocytes. Separation of adult NK cells based on CD56 and CD16 expression revealed that the telomere length was significantly shorter in CD56(dim)CD16(+) (mature) NK cells compared to CD56(bright)CD16(-) (immature) NK cells from the same donor. Furthermore, sorting of NK cells based on expression of activation markers, such as NKG2D and LFA-1, revealed that NK cells expressing these markers have significantly shorter telomeres. Telomere fluorescence was very heterogeneous in NK cells expressing CD94, killer inhibitory receptor (KIR), NKG2A, or CD161. Our observations indicate that telomeric DNA in NK cells is lost with cell division and with age similar to what has been observed for most other hematopoietic cells. Telomere attrition in NK cells is a plausible cause for diminished NK cell function in the elderly.

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Rita B. Effros, Experimental Gerontology, Volume 42, Issue 5, 416-420.

Clinical studies have shown that high proportions of CD8 T cells with the senescent phenotype correlate with several deleterious physiologic outcomes, including poor vaccine responses, bone loss, and increased proinflammatory cytokines. CD8(+)CD28(-) T cells have also been shown to exert suppressive activity on other immune cells. Based on the central role of telomere shortening in the replicative senescence program, we are developing several telomerase-based approaches as potential immunoenhancing treatments for aging and HIV disease. Gene therapy of HIV-specific CD8 T cells with the telomerase catalytic component (hTERT) results in enhanced proliferative capacity, increased anti-viral functions, and a delay in the loss of CD28 expression, with no changes in karyotype or growth kinetics. These proof-of-principle studies have led to screening for pharmacological approaches that might mimic the gene therapy effects, in a more clinically suitable formulation.”

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Sheila A. Stewart – Departments of Cell Biology and Physiology and of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, and Robert A. Weinberg – Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142. Annu Rev Cell Dev Biol. 2006;22:531-57

The cell phenotypes of senescence and crisis operate to circumscribe the proliferative potential of mammalian cells, suggesting that both are capable of operating in vivo to suppress the formation of tumors. The key regulators of these phenotypes are the telomeres, which are located at the ends of chromosomes and operate to protect the chromosomes from end-to-end fusions. Telomere erosion below a certain length can trigger crisis. The relationship between senescence and telomere function is more complex, however: Cell-physiological stresses as well as dysfunction of the complex molecular structures at the ends of telomeric DNA can trigger senescence. Cells can escape senescence by inactivating the Rb and p53 tumor suppressor proteins and can surmount crisis by activating a telomere maintenance mechanism. The resulting cell immortalization is an essential component of the tumorigenic phenotype of human cancer cells. Here we discuss how telomeres are monitored and maintained and how loss of a functional telomere influences biological functions as diverse as aging and carcinogenesis.

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