Biomedical subjects

Rita B Effros

Publications and source records attributed to Rita B Effros.

At least 19 recordsLinked to original sources

PubMed2006

Telomerase induction in T cells: a cure for aging and disease?

Cells of the immune system are unique among normal somatic cells in that they have the capacity to upregulate the telomere-extending enzyme, telomerase, albeit in a precisely controlled fashion. Kinetic analysis of telomerase activity in long-term T cell cultures has documented that the high level of telomerase induced in concert with activation reaches a peak at 3-5 days, then declines by 3 weeks. The process is recapitulated during secondary antigenic stimulation, but by the third, and all subsequent stimulations in vitro, CD8 T cells are unable to upregulate telomerase. Cell division in the absence of telomerase activity results in progressive telomere shortening, and ultimately, the DNA damage/cell cycle arrest that is signaled by critically short telomeres. Cultures of senescent CD8 T cells show altered cytokine patterns, resistance to apoptosis, and absence of expression of the CD28 costimulatory receptor. CD8 T cells with these and other features of replicative senescence accumulate progressively with age, and at an accelerated rate, during chronic infection with HIV-1. 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.

Aging↗

PubMed2006

Role of T lymphocyte replicative senescence in vaccine efficacy.

Immunological changes associated with aging play a major role in both the blunted responses to infections as well as to vaccines intended to prevent many of these infections. Several independent studies on immune correlates of poor vaccine responsiveness have identified a novel immune biomarker of reduced antibody response to vaccination, namely high proportions of memory CD8 T lymphocytes lacking expression of the CD28 costimulatory molecule. Research on this population of CD8(+)CD28(-) T lymphocytes has documented characteristics suggestive of replicative senescence, including inability to proliferate, reduced telomere length, and altered cytokine profiles. CD8(+)CD28(-) T lymphocytes have also been associated with suppressor functions and with early mortality in the elderly. This article discusses some of the challenges involved in custom-designing vaccines for the elderly, and suggests several immunomodulatory strategies that may enhance vaccine responsiveness in this age group.

Aging↗

PubMed2005

Roy Walford and the immunologic theory of aging.

Roy Walford died on April 27, 2004, at the age of 79. His contributions to gerontological research in such diverse areas as caloric restriction, genetics of lifespan, immunosenescence, DNA repair and replicative senescence were truly remarkable in their depth and innovation. Significantly, most of the areas that he pioneered during his illustrious research career remain the "hot" areas of current gerontological research. In this sense, he has achieved the most important type of immortality. His death was a major personal and professional loss to numerous scientists within the gerontological community. In launching this new journal on Immunity and Ageing, it is highly fitting, therefore, to remember him on the anniversary of his death by briefly reviewing the contributions of Roy Walford to this important facet of gerontology. Indeed, it was Roy who actually first coined the commonly used term "immunosenescence".

Journal Article↗

PubMed2005

Decreased perforin and granzyme B expression in senescent HIV-1-specific cytotoxic T lymphocytes.

Cytotoxic T lymphocyte (CTL) senescence may be an important mechanism of immune failure in HIV-1 infection. We find that senescence of HIV-1-specific CTL clones causes loss of killing activity, preventable by transduction with telomerase. Furthermore, senescence is associated with reduced expression of the effector molecules granzyme and perforin, suggesting CTL "exhaustion" can result in hypofunction. These results agree with other studies showing that HIV-1-specific CTL exhibit abnormal phenotypes in vivo, and suggest the possibility that chronic turnover is an important mechanism of antiviral failure in HIV-1 infection.

Aging↗

PubMed2005

The role of CD8+ T-cell replicative senescence in human aging.

The strict limit in proliferative potential of normal human somatic cells - a process known as replicative senescence - is highly relevant to the immune system, because clonal expansion is fundamental to adaptive immunity. CD8(+) T cells that undergo extensive rounds of antigen-driven proliferation in cell culture invariably reach the end stage of replicative senescence, characterized by irreversible cell-cycle arrest and a critically short telomere length. Cultures of senescent CD8(+) T cells also show resistance to apoptosis, permanent loss of CD28 expression, altered cytokine profiles, reduced ability to respond to stress, and various functional changes. Cells with similar characteristics accumulate during normal aging as well as in younger persons infected with human immunodeficiency virus, suggesting that the process of replicative senescence is not an artifact of cell culture but is also occurring in vivo. Interestingly, in elderly persons, the presence of high proportions of CD8(+) T cells with characteristics of replicative senescence is correlated with reduced antibody responses to vaccines as well as with osteoporotic fractures. CD8(+)CD28(-) T cells also accumulate in patients with certain types of cancer. The emerging picture is that senescent CD8(+) T cells may modulate both immune and non-immune functions, contributing not only to reduced anti-viral immunity but also to diverse age-related pathologies.

Animals↗

PubMed2004

Genetic manipulation of telomerase in HIV-specific CD8+ T cells: enhanced antiviral functions accompany the increased proliferative potential and telomere length stabilization.

A large proportion of the CD8(+) T cell pool in persons chronically infected with HIV consists of cells that show features of replicative senescence, an end stage characterized by irreversible cell cycle arrest, multiple genetic and functional changes, and shortened telomeres. The objective of our research was to determine whether constitutive expression of the gene for the human telomerase (hTERT) can prevent senescence-induced impairments in human virus-specific CD8(+) T cells, particularly in the context of HIV-1 disease. Our results indicate that hTERT-expressing HIV-specific CD8(+) lymphocytes show both an enhanced and sustained capacity to inhibit HIV-1 replication in in vitro coculture experiments, as well as prolonged ability to produce IFN-gamma and TNF-alpha in response to stimulation with HIV-1-derived peptides, as compared with vector-transduced controls. Loss of CD28 expression, the signature change of replicative senescence in cell culture, was retarded in those CD8(+) T cell cultures that had high levels of CD28 at the time of hTERT transduction. These findings suggest that telomere shortening may be the primary driving force behind several aspects of CD8(+) T cell dysfunction associated with replicative senescence. We also demonstrate reduced accumulation of the p16(INK4a) and p21(WAF1) cell cycle inhibitors in hTERT-transduced lymphocytes, providing a possible mechanism by which stable hTERT expression is able to circumvent the senescence barrier in CD8(+) T cells. Given the key role of CD8(+) T cell function in controlling a variety of acute and latent viral infections, approaches to retard the functional decrements associated with replicative senescence may lead to novel types of immunotherapy.

Adjuvants, Immunologic↗

PubMed2004

Replicative senescence of CD8 T cells: potential effects on cancer immune surveillance and immunotherapy.

The process of replicative senescence, which stringently limits the proliferative potential of normal T cells, constitutes a potential problem for cancer immunotherapy. The ability of CD8 T cells to recognize and destroy tumor cells has been well-established, but the requirement for massive, prolonged proliferative T-cell expansion and maintenance of functional integrity poses a significant obstacle to the success of cancer immunotherapy. Cancer immune surveillance may also be compromised by the long-term exposure of T cells to tumor antigens, particularly those of latent viruses, which could drive certain T cells to replicative senescence. This review summarizes the major characteristics of T-cell replicative senescence and raises the possibility that this process has the potential to affect both cancer development and treatment. Experimental strategies aimed at preventing T-cell replicative senescence are discussed in the context of cancer immunotherapy and vaccines.

Antigens, Neoplasm↗

PubMed2004

Replicative senescence of CD8 T cells: effect on human ageing.

Elderly persons have been exposed to a myriad of pathogens over their lifespan. This life-long immunological history leads, in some cases, to the generation of expanded populations of memory CD8 T cells that have reached the end stage of replicative senescence. In cell culture, CD8 T cells that are subjected to repeated rounds of antigen-driven proliferation eventually show irreversible cell cycle arrest, permanent and complete loss of CD28 gene expression, apoptosis resistance, reduced gene transcription of the major stress protein in response to heat shock, and shortened telomeres compared to their CD28-expressing progenitors. Clinical studies have documented that high proportions of CD8 T cells that lack CD28 are correlated with reduced antibody response to influenza vaccination and are also an immune marker of increased risk of mortality in persons greater than 80 years of age. In addition, CD8 T cells lacking CD28 expression have been documented to have suppressive influences on immune function. Thus, senescent CD8 T cells may affect immune function both directly and indirectly by modulating other immune cell types. The potential role of senescent T cells in bone homeostasis is suggested as a potentially fruitful area for future investigation. The patterns of cytokine changes observed during the progression to senescence in cell culture are consistent with this possibility, and T cells producing these same cytokines have, in fact, been identified within the bone marrow in murine models of osteoporosis. Interestingly, CD8 T cells with markers of replicative senescence are correlated with increased osteoporotic fractures in the elderly. Thus, senescent CD8 T cells are associated with a variety of deleterious health-related outcomes, suggesting that these cells may exert pleiotropic negative effects on both immune and non-immune organ systems during ageing.

Aging↗

PubMed2004

Age related microsatellite instability in T cells from healthy individuals.

Many immune functions decline with age and may jeopardize the elderly, as illustrated, for example by the significantly higher mortality rate from influenza in old age. Although innate and humoral immunity are affected by aging, it is the T cell compartment, which manifests most alterations. The mechanisms behind these alterations are still unclear, and several explanations have been offered including thymic involution and Telomere attrition leading to cell senescence. Age related accumulation of mutations has been documented and could serve as an additional mechanism of T cell dysfunction. One effective repair mechanism capable of rectifying errors in DNA replications is the mismatch repair (MMR) system. We previously reported a comparative examination of individual DNA samples from blood cells obtained at 10 year intervals from young and old subjects. We showed significantly higher rates of microsatellite instability (MSI), an indicator of MMR dysfunction in older subjects, compared to young. In the present study we confirm this result, using direct automated sequencing and in addition, we demonstrate that as CD8 lymphocytes from aged individuals, undergo repeated population doublings (PDs) in culture, they develop MSI. CD4 clones that also undergo repeated PDs in culture develop significant MSI as well. Elucidation of this previously unexplored facet of lymphocyte dynamics in relation to aging may help identify novel mechanisms of immunosenescence and pathways that could serve as targets for interventions to restore immune function.

Adult↗

PubMed2004

From Hayflick to Walford: the role of T cell replicative senescence in human aging.

The immunologic theory of aging, proposed more than 40 years ago by Roy Walford, suggests that the normal process of aging in man and in animals is pathogenetically related to faulty immunological processes. Since that time, research on immunological aging has undergone extraordinary expansion, leading to new information in areas spanning from molecular biology and cell signaling to large-scale clinical studies. Investigation in this area has also provided unexpected insights into HIV disease, many aspects of which represent accelerated immunological aging. This article describes the initial insights and vision of Roy Walford into one particular facet of human immunological aging, namely, the potential relevance of the well-studied human fibroblast replicative senescence model, initially developed by Leonard Hayflick, to cells of the immune system. Extensive research on T cell senescence in cell culture has now documented changes in vitro that closely mirror alterations occurring during in vivo aging in humans, underscoring the biological significance of T cell replicative senescence. Moreover, the inclusion of high proportions of putatively senescent T cells in the 'immune risk phenotype' that is associated with early mortality in octogenarians provides initial clinical confirmation of both the immunologic theory of aging and the role of the T cell Hayflick Limit in human aging, two areas of gerontological research pioneered by Roy Walford.

Aged↗

PubMed2004

Impact of the Hayflick Limit on T cell responses to infection: lessons from aging and HIV disease.

Aging and HIV disease show certain immunological similarities. In both situations, control over viral infection is diminished, and there is an increase in certain types of cancer. The immune cell type responsible for controlling viral infections and cancer is the so-called CD8 or cytotoxic T cell. In elderly persons and individuals chronically infected with HIV, there are high proportions of CD8 T cells that resemble cells that reach the end stage of replicative senescence in cell culture after repeated rounds of antigen-driven proliferation. Senescent cultures are characterized by irreversible cell cycle arrest, shortened telomeres, inability to upregulate telomerase, loss of CD28 expression, and apoptosis resistance. Strategies that retard replicative senescence may, therefore, provide novel approaches to enhancing immune function during aging and HIV disease.

Cell Division↗

PubMed2004

T cell replicative senescence: pleiotropic effects on human aging.

Long-term culture studies using CD8 T cells, the immune cells responsible for control of viral infection, have identified the major features of replicative senescence. Aging is associated with increased proportions of CD8 T cells with similar characteristics, such as absence of expression of the CD28 costimulatory molecule and reduced antiviral effector functions. Proinflammatory cytokines produced by senescent CD8 T cells also may exert pleiotropic suppressive effects on overall immune function and bone homeostasis. Thus, modulation of T cell replicative senescence may provide a comprehensive therapeutic strategy to prevent multiple age-associated pathologies.

Aging↗

PubMed2003

Genetic alterations in the ageing immune system: impact on infection and cancer.

The immune system, which is able to distinguish between self and non-self, is programmed to protect the organism from a huge spectrum of potential foreign invaders. Each T and B lymphocyte bears an antigen receptor of a single specificity, which is determined during development by a unique genetic mechanism that generates millions of different variants of the genes encoding the receptor molecules. When a particular antigen, such as a virus, is encountered, only those lymphocytes bearing the relevant receptors become activated and undergo massive clonal expansion. The expanded antigen-specific B cells produce antibodies, which neutralize free virus in the bloodstream, whereas the T cells, particularly the so-called CD8 T cells, actually kill cells that are infected with the virus. Once the infection is cleared, most of the expanded T cells undergo apoptosis, leaving a small number of memory cells to await future possible encounters with the same virus. During ageing, both latent and acute viral infections lead to increased morbidity and mortality, based, in large part, on the diminished ability of T cells to control the infection. To investigate the underlying mechanism of the T cell defects, we have analyzed the process of replicative senescence in human T cells. Our research has shown that following repeated stimulation with antigen in cell culture, the responding T cells eventually reach an irreversible state of cell cycle arrest, at which time they show loss of gene expression of a key T cell-specific signaling molecule required for proliferation, as well as reduced stress protein production, apoptosis resistance, shortened telomeres and inability to upregulate telomerase. Increased proportions of T cells with identical phenotypes are present in elderly individuals, suggesting that chronic/repeated stimulation of some T cells may lead to replicative senescence in vivo. Genetic modulation of this process may yield novel strategies to augment immune function in the elderly.

Aged↗

PubMed2003

Problems and solutions to the development of vaccines in the elderly.

Scientists involved in vaccine research and development face the challenge of protecting the ever-increasing elderly population from a broad spectrum of infectious diseases. The optimal vaccine-induced immune response to confer protection is undefined for many pathogens, and the field of vaccine research is undergoing a gradual shift from the original focus on humoral immunity to a focus that incorporates cellular and innate immune components. The age-related changes in various aspects of immune function, including an increase in a population of T cells that shows signs of replicative senescence, underscore the need to enhance research aimed at designing vaccines to meet the unique requirements of the elderly population.

Aged↗

PubMed2003

Differential impairment of lytic and cytokine functions in senescent human immunodeficiency virus type 1-specific cytotoxic T lymphocytes.

Telomere length is abnormally short in the CD8(+) T-cell compartment of human immunodeficiency virus type 1 (HIV-1)-infected persons, likely because of chronic cell turnover. Although clonal exhaustion of CD8(+) cytotoxic T lymphocytes (CTL) has been proposed as a mechanism for loss of antigen-specific responses, the functional consequences of exhaustion are poorly understood. Here we used telomerase transduction to evaluate the impact of senescence on CTL effector functions. Constitutive expression of telomerase in an HIV-1-specific CTL clone results in enhanced proliferative capacity, in agreement with prior studies of other human cell types. Whereas the CTL remain phenotypically normal in terms of antigenic specificity and requirements for proliferation, their cytolytic and antiviral capabilities are superior to those of control CTL. In contrast, their ability to produce gamma interferon and RANTES is essentially unchanged. The selective enhancement of cytolytic function in memory CTL by ectopic telomerase expression implies that loss of this function (but not cytokine production) is a specific consequence of replicative senescence. These data suggest a unifying mechanism for the in vivo observations that telomere lengths are shortened in the CD8(+) cells of HIV-1-infected persons and that HIV-1-specific CTL are deficient in perforin. Telomerase transduction could therefore be a tool with which to explore a potential therapeutic approach to an important pathophysiologic process of immune dysfunction in chronic viral infection.

Cytokines↗

PubMed2003

CD8 T cells and aging.

Aging of the immune system, or "immunosenescence," is associated with both a marked reduction in responsiveness as well as functional dysregulation. These changes have been implicated in the increased morbidity and mortality of the elderly population from infectious disease, and may also play a role in autoimmunity and cancer. Though marginal alterations in B lymphocytes are apparent, the dramatic decline in humoral and cell-mediated responses is predominantly the consequence of alterations in the T-cell compartment. The effect of aging on CD4 cell function has been extensively summarized elsewhere. This review, therefore, focuses on the CD8 T-cell subset. Age-related changes in thymic function and involution, cellular homeostasis and lifespan, population shifts, T-cell activation, the process of replicative senescence, and oligoclonal expansions are discussed in terms of their effect on CD8 T cells. Age-associated alterations in CD4 T cells and antigen-presenting cells are mentioned insofar as these cells affect CD8 T-cell activation and function. Distinct patterns of immunosenescence in humans and mice are also noted.

Aging↗

PubMed2003

Replicative senescence: the final stage of memory T cell differentiation?

One of the major obstacles to effective prolonged CD8 T cell control over HIV and other latent infections may be the intrinsic, genetically programmed barrier to unlimited proliferation that is characteristic of all normal human somatic cells. Replicative senescence, characterized extensively in cell culture for a variety of cell types, comprises both irreversible cell cycle arrest and striking changes in function. CD8 T cells with features similar to senescent CD8 T cell cultures (i.e., absence of CD28, inability to proliferate, telomeres in the 5-7 kb range, resistance to apoptosis) increase progressively during aging and in chronic HIV infection, suggesting that replicative senescence may be occurring in vivo, and, in fact, may constitute the final stage in the normal differentiation of human T cells. CD8 T cells with characteristics suggestive of senescence have also been implicated in modulating immune function and altering bone homeostasis. Further characterization of the underlying mechanism leading to the generation of senescent memory CD8 T cells and analysis of their functional attributes will help elucidate their role in HIV disease pathogenesis.

CD8-Positive T-Lymphocytes↗

PubMed2002

Simultaneous flow cytometric analysis of two cell surface markers, telomere length, and DNA content.

BACKGROUND: Various protocols for estimation of telomere length in individual cells by flow cytometry using fluorescence in situ hybridization of fluorescently labeled peptide nucleic acid (PNA) probes (Flow-FISH) have been described. Combined analysis of telomere length and cell phenotype, however, remains difficult because few fluorochromes with suitable emission spectra tolerate the harsh conditions needed for DNA denaturation during hybridization of the telomere-specific PNA probe. We overcame these problems and developed a method for measuring telomere length in cell subsets characterized by the expression of two surface antigens. METHODS: Alexa Fluor 488 and Alexa Fluor 546 were used for cell surface staining. Antigen-antibody complexes were covalently cross-linked onto the cell membrane before Flow-FISH. Cells were hybridized with a PNA probe conjugated to cyanine 5 (Cy5). Hoechst 33342 (HO342) was added for determination of cellular DNA content. For assay standardization, we added an aliquot of a single batch of 1,301 cells to each sample as an internal control before hybridization with the PNA probe. Samples were prepared in duplicate and analyzed on a standard three-laser BD LSR flow cytometer. For assay validation, the same samples were analyzed in parallel to correlate the percentage of telomere length of the sample versus 1,301 control cells to the mean size of terminal restriction fragments (TRFs) of DNA as determined by Southern gel analysis. RESULTS: The method permitted clear identification of lymphocyte subsets in samples hybridized for Flow-FISH, with subset frequencies comparable to those of untreated samples. At a concentration of 10 nM, the Cy5-labeled telomere-specific PNA probe produced a bright fluorescence signal well separated from background. Addition of HO342 in low concentration did not interfere with Cy5 telomere fluorescence, produced adequate DNA histograms, and permitted clear identification of cell phenotype. The probe concentration of 10 nM also proved optimal for inclusion of 1,301 control cells for assay standardization. Telomere length estimations by the current method correlated highly with TRF calculations by Southern gel hybridization (r(2)= 0.9, P = 0.0003). Application of our protocol to the analysis of human CD8CD28 lymphocyte subsets showed that CD8(+bright)CD28(-) lymphocytes generally exhibit shorter telomeres than CD8(+bright)CD28(+) cells. These data concurred with previous results of telomere shortening in CD8(+)CD28(-) T cells that were obtained by using different techniques. CONCLUSIONS: The multiparameter Flow-FISH protocol permitted rapid determination of differences in telomere length in subpopulations characterized by two surface markers without prior cell separation.

Antigens, CD↗