Role of T lymphocyte replicative senescence in vaccine efficacy

Hepatitis B vaccine antibody response and the risk of clinical AIDS or death

BACKGROUND

Whether seroresponse to a vaccine such as hepatitis B virus (HBV) vaccine can provide a measure of the functional immune status of HIV-infected persons is unknown.This study evaluated the relationship between HBV vaccine seroresponses and progression to clinical AIDS or death.

METHODS AND FINDINGS

From a large HIV cohort, we evaluated those who received HBV vaccine only after HIV diagnosis and had anti-HBs determination 1-12 months after the last vaccine dose. Non-response and positive response were defined as anti-HBs <10 and ≥ 10 IU/L, respectively. Participants were followed from date of last vaccination to clinical AIDS, death, or last visit. Univariate and multivariable risk of progression to clinical AIDS or death were evaluated with Cox regression models. A total of 795 participants vaccinated from 1986-2010 were included, of which 41% were responders. During 3,872 person-years of observation, 122 AIDS or death events occurred (53% after 1995). Twenty-two percent of non-responders experienced clinical AIDS or death compared with 5% of responders (p<0.001). Non-response to HBV vaccine was associated with a greater than 2-fold increased risk of clinical AIDS or death (HR 2.47; 95% CI, 1.38-4.43) compared with a positive response, after adjusting for CD4 count, HIV viral load, HAART use, and delayed type hypersensitivity skin test responses (an in vivo marker of cell-mediated immunity). This association remained evident among those with CD4 count ≥ 500 cells/mm³ (HR 3.40; 95% CI, 1.39-8.32).

CONCLUSIONS

HBV vaccine responses may have utility in assessing functional immune status and risk stratificating HIV-infected individuals, including those with CD4 count ≥ 500 cells/mm³.

Influenza vaccination in the face of immune exhaustion: is herd immunity effective for protecting the elderly?

At the start of the 21st century, seasonal influenza virus infection is still a major public health concern across the world. The recent body of evidence confirms that trivalent inactivated influenza vaccines (TIVs) are not optimal within the population who account for approximately 90% of all influenza-related death: elderly and chronically ill individuals regardless of age. With the ever increasing aging of the world population and the recent fears of any pandemic influenza rife, great efforts and resources have been dedicated to developing more immunogenic vaccines and strategies for enhancing protection in these higher-risk groups. This paper describes the mechanisms that shape immune response at the extreme ages of life and how they have been taken into account to design more effective immunization strategies for these vulnerable populations. Furthermore, consideration will be given to how herd immunity may provide an effective strategy in preventing the burden of seasonal influenza infection within the aged population.

The unmet need in the elderly: how immunosenescence, CMV infection, co-morbidities and frailty are a challenge for the development of more effective influenza vaccines

Influenza remains the single most important cause of excess disability and mortality during the winter months. In spite of widespread influenza vaccination programs leading to demonstrated cost-savings in the over 65 population, hospitalization and death rates for acute respiratory illnesses continue to rise. As a person ages, increased serum levels of inflammatory cytokines are commonly recorded (TNF-α, IL-1, IL-6). Termed "inflammaging", this has been linked to persistent cytomegalovirus (CMV) infection and immune senescence, while increased anti-inflammatory cytokines (IL-10, TGF-β) are possibly associated with more healthy aging. Paradoxically, a shift with aging toward an anti-inflammatory (IL-10) response and decline in the IFN-γ:IL-10 ratio in influenza-challenged peripheral blood mononuclear cells is associated with a decline in the cytolytic capacity of CD8+ T cells responsible for clearing influenza virus from infected lung tissue. Thus, it is seemingly counter intuitive that the immune phenotype of healthy aging predicts a poor cell-mediated immune response and more serious outcomes of influenza. Herein we postulate a mechanistic link between the accumulation of late-stage, potentially terminally differentiated T cells, many or most of which result from CMV infection, and the immunopathogenesis of influenza infection, mediated by granzyme B in older adults. Further, adjuvanted influenza vaccines that stimulate inflammatory cytokines and suppress the IL-10 response to influenza challenge, would be expected to enhance protection in the 65+ population.

Evaluation of hepatitis B vaccine immunogenicity among older adults during an outbreak response in assisted living facilities

BACKGROUND

During the past decade, in the United States, an increasing number of hepatitis B outbreaks have been reported in assisted living facilities (ALFs) as a result of breaches in infection control practices. We evaluated the seroprotection rates conferred by hepatitis B vaccine among older adults during a response to an outbreak that occurred in multiple ALFs and assessed the influence of demographic and clinical factors on vaccine response.

METHODS

Residents were screened for hepatitis B and C infection prior to vaccination and susceptible residents were vaccinated against hepatitis B with one dose of 20 μg Engerix-B™ (GSK) given at 0, 1, and 4 months. Blood samples were collected 80-90 days after the third vaccine dose to test for anti-HBs levels.

RESULTS

Of the 48 residents who had post-vaccination blood specimens collected after the third vaccine dose, 16 (33.3%) achieved anti-HBs concentration ≥10 mIU/mL. Age was a significant determinant of seroprotection with rates decreasing from 88% among persons aged ≤60 years to 12% among persons aged ≥90 years (p=0.001). Geometric mean concentrations were higher among non-diabetic than diabetic residents, however, the difference was not statistically significant (5.1 vs. 3.8 mIU/mL, p=0.7).

CONCLUSIONS

These findings highlight that hepatitis B vaccination is of limited effectiveness when administered to older adults. Improvements in infection control and vaccination at earlier ages might be necessary to prevent spread of infection in ALFs.

An age-specific CD8+ T cell pathway that impairs the effectiveness of strategies to prolong allograft survival

Age-related decline in immunity can impair cell-mediated responses during an infection, malignancy, and acute allograft rejection. Although much research has been allocated to understand the immune responses that impact the former two conditions, the cellular mechanisms by which aging impacts the immune acceptance of organ allografts are not completely clear. In this study, we examined how recipient age impacts the efficacy of therapies that modulate immune recognition of allografts using an immunogenic murine skin transplant model. We found that costimulatory blockade-based treatment failed to extend allograft survival in older recipients to the same extent as that observed in younger recipients. CD8(+) T cells were critical for the inability of aged recipients to achieve maximal allograft survival. Although aged mice displayed a larger number of effector memory T cells prior to transplantation, these cells did not exhibit enhanced alloreactivity compared with young memory T cells. In contrast, naive aged CD8(+) T cells exhibited enhanced IFN-γ production to allostimulation compared with young naive T cells. Our results provide evidence that aging enhances CD8(+) T cell alloreactivity. This could impair the ability of costimulatory blockade-based therapies to prolong allograft survival. Thus, targeting CD8(+) T cells in humans may be a way to improve outcomes in older patients requiring immune modulatory therapy.

The impact of aging on cancer vaccination

Cancer vaccination is less effective at old than at young age, due to T cell unresponsiveness, caused by various age-related changes of the immune system. This includes lack of naïve T cells, defects in activation pathways of T cells and antigen-presenting cells (APC), and age-related changes in the tumor microenvironment. Although evidence exists that also natural killer (NK) and natural killer T (NKT) cells of the innate immune system change with age, comparison of various studies involving adaptive and innate immune responses in elderly and cancer patients, as well as cancer vaccination at young and old age in this review, indicates that also innate immune responses should be tested as a potential candidate to improve immunotherapy against cancer at older age.

[Immunosenescence. Current status and molecular mechanisms]

One of the most important biological changes occurring during human aging is termed 'immunosenescence' characterized by a functional decline in immunity leading to a progressive immunodeficiency. Regulatory mechanisms also are diminished, leading to an inefficient and poorly controlled pro-inflammatory activation of the immune response. This increases the risk for disorders such as infectious, autoimmune, neoplastic, cardiovascular and neurodegenerative disease. Many of these entities are quite relevant for dermatology. Hence, immunosenescence constitutes a pathologic process contributing to morbidity and mortality of important clinical relevance in an aging population. Investigation of the underlying pathomechanisms and the application of modern mechanism-directed therapy offer many opportunities for a targeted modulation and "rejuvenation", thus indicating possible targets for the reduction of age-associated morbidity and mortality. Some promising targeted 'molecular' therapies are already currently being used in the context of other diseases, also in the field of dermatology.

Vaccine effectiveness in older individuals: what has been learned from the influenza-vaccine experience

Vaccination policies in most high-income countries attempt to reduce the adverse impact of influenza targeting people aged at least 60 years. However, while it is widely believed that the current immunization strategy saves many lives, influenza infection still remains a severe burden in aged individuals leading to a wide debate on the exact magnitude of the benefit of vaccination in this population. The first aim of the present review is to examine how effective current influenza-vaccine strategies are in aged adults, by analysing which are the most important factors modulating the interpretation of study results in this population. Furthermore, consideration will be given to how immune factors influence the measurement of vaccine efficacy/effectiveness, where advancing age leads to deleterious changes in the adaptive immune system, resulting in less than optimal responses to infectious agents and vaccination. Finally this review concludes with possible strategies to improve the ability of the senescent immune system to respond to vaccination.

Influenza vaccine responses in older adults

The most profound consequences of immune senescence with respect to public health are the increased susceptibility to influenza and loss of efficacy of the current split-virus influenza vaccines in older adults, which are otherwise very effective in younger populations. Influenza infection is associated with high rates of complicated illness including pneumonia, heart attacks and strokes in the 65+ population. Changes in both innate and adaptive immune function not only converge in the reduced response to vaccination and protection against influenza, but present significant challenges to new vaccine development. In older adults, the goal of vaccination is more realistically targeted to providing clinical protection against disease rather sterilizing immunity. Correlates of clinical protection may not be measured using standard techniques such as antibody titres to predict vaccine efficacy. Further, antibody responses to vaccination as a correlate of protection may fail to detect important changes in cellular immunity and enhanced vaccine-mediated protection against influenza illness in older people. This article will discuss the impact of influenza in older adults, immunologic targets for improved efficacy of the vaccines, and alternative correlates of clinical protection against influenza that are needed for more effective translation of novel vaccination strategies to improved protection against influenza in older adults.

Interleukin-7 inhibits tumor-induced CD27-CD28- suppressor T cells: implications for cancer immunotherapy

PURPOSE

We have previously reported that many types of tumors can induce changes in human T cells that lead to the acquisition of suppressive function and phenotypic alterations resembling those found in senescent T cells. In the present study, we find a role for interleukin 7 (IL-7) in protecting T cells from these changes and further define involved signaling pathways.

EXPERIMENTAL DESIGN

We evaluated the ability of IL-7 treatment to prevent the gain of suppressive function and phenotypic alterations in human T cells after a short coculture with tumor cells in vitro. We then used inhibitors of components of the phosphoinositide 3-kinase (PI3K)/AKT pathway and short interfering RNA knockdown of Mcl-1 and Bim to evaluate the role of these signaling pathways in IL-7 protection.

RESULTS

We found that IL-7 inhibits CD27/CD28 loss and maintains proliferative capacity, IL-2 production, and reduced suppressive function. The protective ability of IL-7 depended on activation of the PI3K/AKT pathway, which inhibited activation of glycogen synthase kinase 3β, which, in turn, prevented the phosphorylation and loss of Mcl-1. We further showed a key role for Mcl-1 in that its knockdown or inhibition abrogated the effects of IL-7. In addition, knockdown of the Mcl-1 binding partner and proapoptotic protein Bim protected T cells from these dysfunctional alterations.

CONCLUSION

These observations confirm the role for Bcl-2 family members in cytokine signaling and suggest that IL-7 treatment in combination with other immunotherapies could lead to new clinical strategies to maintain normal T-cell function and reduce tumor-induced generation of dysfunctional and suppressor T cells.

Age-related changes in memory and effector T cells responding to influenza A/H3N2 and pandemic A/H1N1 strains in humans

Age-dependent changes in the cellular immune response have been mainly described in CD8+ T cells, with relative sparing of CD4+ T cells. We show that in older compared to young adults, effector memory and effector CD8+ T-cell subsets responding to influenza A/H3N2 challenge have diminished cytolytic activity. In contrast, effector CD4+ T-cell subsets in older adults share similar phenotypic and functional characteristics with those from young adults. Further, we observed a diminished cytolytic T-cell response to both seasonal influenza A/H3N2 and pandemic H1N1 (pH1N1) strains in older compared to young adults who had received seasonal influenza vaccine. These results are consistent with the observed rates of serious complications from seasonal and pandemic influenza infections in different age groups, and suggest that CD4+ T cells may provide a compensatory response to influenza infection when CD8+ T cells become compromised during the aging process.

Differential effects of age, cytomegalovirus-seropositivity and end-stage renal disease (ESRD) on circulating T lymphocyte subsets

The age- and cytomegalovirus (CMV)-seropositivity-related changes in subsets and differentiation of circulating T cells were investigated in end-stage renal disease (ESRD) patients (n = 139) and age-matched healthy individuals. The results show that CMV-seropositivity is associated with expansion of both CD4⁺ and CD8⁺ memory T cells which is already observed in young healthy individuals. In addition, CMV-seropositive healthy individuals have a more differentiated memory T cell profile. Only CMV-seropositive healthy individuals showed an age-dependent decrease in CD4⁺ naïve T cells. The age-related decrease in the number of CD8⁺ naïve T cells was CMV-independent. In contrast, all ESRD patients showed a profound naïve T-cell lymphopenia at every decade. CMV-seropositivity aggravated the contraction of CD4⁺ naïve T cells and increased the number of differentiated CD4⁺ and CD8⁺ memory T cells. In conclusion, CMV-seropositivity markedly alters the homeostasis of circulating T cells in healthy individuals and aggravates the T cell dysregulation observed in ESRD patients.

Predicting cytotoxic T-cell age from multivariate analysis of static and dynamic biomarkers

Adoptive T-cell transfer therapy relies upon in vitro expansion of autologous cytotoxic T cells that are capable of tumor recognition. The success of this cell-based therapy depends on the specificity and responsiveness of the T cell clones before transfer. During ex vivo expansion, CD8+ T cells present signs of replicative senescence and loss of function. The transfer of nonresponsive senescent T cells is a major bottleneck for the success of adoptive T-cell transfer therapy. Quantitative methods for assessing cellular age and responsiveness will facilitate the development of appropriate cell expansion and selection protocols. Although several biomarkers of lymphocyte senescence have been identified, these proteins in isolation are not sufficient to determine the age-dependent responsiveness of T cells. We have developed a multivariate model capable of extracting combinations of markers that are the most informative to predict cellular age. To acquire signaling information with high temporal resolution, we designed a microfluidic chip enabling parallel lysis and fixation of stimulated cell samples on-chip. The acquisition of 25 static biomarkers and 48 dynamic signaling measurements at different days in culture, integrating single-cell and population based information, allowed the multivariate regression model to accurately predict CD8+ T-cell age. From surface marker expression and early phosphorylation events following T-cell receptor stimulation, the model successfully predicts days in culture and number of population doublings with R2=0.91 and 0.98, respectively. Furthermore, we found that impairment of early signaling events following T cell receptor stimulation because of long term culture allows prediction of costimulatory molecules CD28 and CD27 expression levels and the number of population divisions in culture from a limited subset of signaling proteins. The multivariate analysis highlights the information content of both averaged biomarker values and heterogeneity metrics for prediction of cellular age within a T cell population.

Successful vaccination strategies that protect aged mice from lethal challenge from influenza virus and heterologous severe acute respiratory syndrome coronavirus

Newly emerging viruses often circulate as a heterogeneous swarm in wild animal reservoirs prior to their emergence in humans, and their antigenic identities are often unknown until an outbreak situation. The newly emerging severe acute respiratory syndrome coronavirus (SARS-CoV) and reemerging influenza virus cause disproportionate disease in the aged, who are also notoriously difficult to successfully vaccinate, likely due to immunosenescence. To protect against future emerging strains, vaccine platforms should induce broad cross-reactive immunity that is sufficient to protect from homologous and heterologous challenge in all ages. From initial studies, we hypothesized that attenuated Venezuelan equine encephalitis virus (VEE) replicon particle (VRP) vaccine glycoproteins mediated vaccine failure in the aged. We then compared the efficacies of vaccines bearing attenuated (VRP(3014)) or wild-type VEE glycoproteins (VRP(3000)) in young and aged mice within novel models of severe SARS-CoV pathogenesis. Aged animals receiving VRP(3000)-based vaccines were protected from SARS-CoV disease, while animals receiving the VRP(3014)-based vaccines were not. The superior protection for the aged observed with VRP(3000)-based vaccines was confirmed in a lethal influenza virus challenge model. While the VRP(3000) vaccine's immune responses in the aged were sufficient to protect against lethal homologous and heterologous challenge, our data suggest that innate defects within the VRP(3014) platform mediate vaccine failure. Exploration into the mechanism(s) of successful vaccination in the immunosenescent should aid in the development of successful vaccine strategies for other viral diseases disproportionately affecting the elderly, like West Nile virus, influenza virus, norovirus, or other emerging viruses of the future.

Partial restoration of T-cell function in aged mice by in vitro blockade of the PD-1/ PD-L1 pathway

Programmed cell death-1 (PD-1) is a newly characterized negative regulator of immune responses. The interaction of PD-1 with its ligands (PD-L1 and PD-L2) inhibits T-cell proliferation and cytokine production in young mice. Increased PD-1 expression has been described during chronic infections, inducing chronic activation of the immune system to control it. As aging is associated with chronic immune activation, PD-1 may contribute to age-associated T-cell dysfunction. Our data showed the following results in aged mice: (i) the number of PD-1-expressing T cells and the level of expression of PD-Ls was increased on dendritic cell subsets and T cells; (ii) PD-1(+) T cells were exhausted effector memory T cells, as shown by their lower level of CD127, CD25 and CD28, as well as their limited proliferative and cytokine-producing capacity; (iii) the expression of PD-1 was up-regulated after T-cell receptor-mediated activation of CD8(+) T cells, but not of CD4(+) T cells; (iv) blockade of the PD-1/PD-L1 pathway moderately improved the cytokine production of T cells from old mice but did not restore their proliferation; and (v) blockade of the PD-1/PD-L1 pathway did not restore function of PD-1(+) T cells; its effect appeared to be exclusively mediated by increased functionality of the PD-1(-) T cells. Our data thus suggest that blockade of the PD-1/PD-L1 is not likely to be efficient at restoring exhausted T-cell responses in aged hosts, although improving the responses of PD-1(-) T cells may prove to be a helpful strategy in enhancing primary responses.

Youth-specific considerations in the development of preexposure prophylaxis, microbicide, and vaccine research trials

Preventing HIV infection in adolescents and young adults will require a multimodal targeted approach, including individual-directed behavioral risk reduction, community-level structural change, and biomedical interventions to prevent sexual transmission. Trials testing biomedical interventions to prevent HIV transmission will require special attention in this population due to the unique psychosocial and physiologic characteristics that differentiate them from older populations. For example, microbicide research will need to consider acceptability, dosing requirements, and coinfection rates that are unique to this population. Preexposure prophylaxis studies also will need to consider potential unique psychosocial issues such as sexual disinhibition and acceptability as well as unique pharmacokinetic parameters of antiretroviral agents. Vaccine trials also face unique issues with this population, including attitudes toward vaccines, risks related to false-positive HIV tests related to vaccine, and different immune responses based on more robust immunity. In this article, we will discuss issues around implementing each of these biomedical prevention modalities in trials among adolescents and young adults to help to guide future successful research targeting this population.

Caloric restriction: from soup to nuts

Caloric restriction (CR), reduced protein, methionine, or tryptophan diets; and reduced insulin and/or IGFI intracellular signaling can extend mean and/or maximum lifespan and delay deleterious age-related physiological changes in animals. Mice and flies can shift readily between the control and CR physiological states, even at older ages. Many health benefits are induced by even brief periods of CR in flies, rodents, monkeys, and humans. In humans and nonhuman primates, CR produces most of the physiologic, hematologic, hormonal, and biochemical changes it produces in other animals. In primates, CR provides protection from type 2 diabetes, cardiovascular and cerebral vascular diseases, immunological decline, malignancy, hepatotoxicity, liver fibrosis and failure, sarcopenia, inflammation, and DNA damage. It also enhances muscle mitochondrial biogenesis, affords neuroprotection; and extends mean and maximum lifespan. CR rapidly induces antineoplastic effects in mice. Most claims of lifespan extension in rodents by drugs or nutrients are confounded by CR effects. Transcription factors and co-activators involved in the regulation of mitochondrial biogenesis and energy metabolism, including SirT1, PGC-1alpha, AMPK and TOR may be involved in the lifespan effects of CR. Paradoxically, low body weight in middle aged and elderly humans is associated with increased mortality. Thus, enhancement of human longevity may require pharmaceutical interventions.

Factors that may impact on immunosenescence: an appraisal

The increasing ratio of ageing population poses new challenges to healthcare systems. The elderly frequently suffer from severe infections. Vaccination could protect them against several infectious diseases, but it can be effective only if cells that are capable of responding are still present in the repertoire. Recent vaccination strategies in the elderly might achieve low effectiveness due to age-related immune impairment. Immunosenescence affects both the innate and adaptive immunity.Beside individual variations of genetic predisposition, epigenetic changes over the full course of human life exert immunomodulating effects. Disturbances in macrophage-derived cytokine release and reduction of the natural killer cell mediated cytotoxicity lead to increased frequency of infections. Ageing dampens the ability of B cells to produce antibodies against novel antigens. Exhausted memory B lymphocyte subsets replace naïve cells. Decline of cell-mediated immunity is the consequence of multiple changes, including thymic atrophy, reduced output of new T lymphocytes, accumulation of anergic memory cells, and deficiencies in cytokines production. Persistent viral and parasitic infections contribute to the loss of immunosurveillance and premature exhaustion of T cells. Reduced telomerase activity and Toll-like receptor expression can be improved by chemotherapy. Reversion of thymic atrophy could be achieved by thymus transplantation, depletion of accumulated dysfunctional naive T cells and herpesvirus-specific exhausted memory cells. Administration of interleukin (IL)-2, IL-7, IL-10, keratinocyte growth factor, thymic stromal lymphopoietin, as well as leptin and growth hormone boost thymopoiesis. In animals, several strategies have been explored to produce superior vaccines. Among them, virosomal vaccines containing polypeptide antigens or DNA plasmids as well as new adjuvanted vaccine formulations elicit higher dendritic cell activity and more effective serologic than conventional vaccines responses in the elderly. Hopefully, at least some of these approaches can be translated to human medicine in a not too far future.

Cytolytic T-cell response against Epstein-Barr virus in lung cancer patients and healthy subjects

Background

This study aimed to examine whether EBV seropositive patients with lung cancer have an altered virus-specific CTL response, as compared to age-matched healthy controls and whether any variation in this response could be attributed to senescence.

Methods

Peripheral blood mononuclear cells from lung cancer patients, age-matched and younger healthy individuals were used to measure EBV-specific CTLs after in vitro amplification with the GLCTLVAML and RYSIFFDYM peptides followed by HLA-multimer staining.

Results

Lung cancer patients and aged-matched controls had significantly lesser EBV-specific CTL than younger healthy individuals. Multimer positive populations from either group did not differ with respect to the percentage of multimer positive CTLs and the intensity of multimer binding.

Conclusions

This study provides evidence that patients with lung cancer exhibit an EBV-specific CTL response equivalent to that of age-matched healthy counterparts. These data warrant the examination of whether young individuals have a more robust anti-tumor response, as is the case with the anti-EBV response.

Rapamycin: could it enhance vaccine efficacy?

EVALUATION OF: Araki K, Turner AP, Shaffer VO et al. mTOR regulates memory CD8 T-cell differentiation. Nature 460(7251), 108-112 (2009). The prime goal of vaccination is to induce an effective memory T-cell response, because memory T cells have a pivotal role in adaptive immunity. When a specific pathogen is encountered after vaccination, memory immune cells induce an adaptive immune response against that pathogen, which is faster and stronger than a primary immune response. Therefore, the development of a successful vaccine requires a T-cell response of adequate magnitude. Although many vaccines effectively induce protective immune responses against specific pathogens, some vaccines require boosting due to inadequate generation of memory immune cells. It was reported recently that rapamycin, which is used as an immunosuppressive drug for organ transplantation, stimulates the production of memory CD8 T cells. This means that rapamycin or related drugs could be used to enhance the efficacy of many types of vaccines.

SARS Coronavirus Pathogenesis and Therapeutic Treatment Design

Emerging pathogens are either new or newly recognized or those that are increasing in incidence and spread. Since the identity of emerging pathogens from animal reservoirs is difficult to predict, the development for pathogen-specific therapeutics and vaccines is problematic. The highly pathogenic SARS coronavirus (SARS-CoV) emerged from zoonotic pools in 2002 to cause a global epidemic of severe acute respiratory syndrome (SARS). Many patients with SARS-CoV experienced an exacerbated form of disease called acute respiratory distress syndrome (ARDS) requiring mechanical ventilation and supplemental oxygen and half of these patients died. Similar to other viral pathogens like influenza and West Nile Virus, the severity of SARS-CoV disease increased with age. Unfortunately, successful vaccination in the most vulnerable populations is a difficult task because of immunological deficiencies associated with aging (immune senescence). Due to the rapidity of virus emergence, technologies like synthetic biology can be harnessed to facilitate rapid recombinant virus construction for studying the novel virus biology, pathogenesis and the evaluation of therapeutic interventions. Since predicting the antigenic identity of future emergence is difficult, candidate vaccines and therapeutics should have a maximal breadth of cross-protection, and panels of antigenically divergent synthetically reconstructed viruses can be used as tools for this evaluation. We discuss how synthetic reconstruction of many animal and human SARS-CoV has provided a model to study the molecular mechanisms governing emergence and pathogenesis of viral diseases. In addition, we review the evolution, epidemiology, and pathogenesis of epidemic and zoonotic SARS-CoV with focus on the development of broadly reactive therapeutics and vaccines that protect aged populations from the zoonotic pool.

Immunosenescence and vaccination of the elderly II. New strategies to restore age-related immune impairment

One of the greatest health-care challenges in the elderly is to ensure that vaccination against infections are optimally effective, but vaccination can only be effective if cells that are capable of responding are still present in the repertoire. The reversing of immunosenescence could be achieved by improving immune responses or altering vaccine formulation. Recent vaccination strategies in the elderly exert low effectiveness. Nutritional interventions and moderate exercise delay T cell senescence. Telomerase activity and expression of toll-like receptors can be improved by chemotherapy. Reversion of thymic atrophy could be achieved by thymus transplantation, depletion of accumulated dysfunctional naive T cells and herpesvirus-specific exhausted memory cells. Administration of immunostimulatory and anti-inflammatory cytokines show the best practical approach. Reduced dendritic cell activity and co-receptor expression might be increased by interleukin (IL)-2 administration. IL-7 protects both B and T lymphocytes, but IL-2, IL-10, keratinocyte growth factor, thymic stromal lymphopoietin, as well as leptin and growth hormone also have a stimulatory effect on thymopoiesis. In animals, several strategies have been explored to produce more efficacious vaccines including high dose vaccines, DNA vaccines with immunostimulatory patch, virosomal vaccines and vaccines containing new adjuvants. Hopefully, one of these approaches will be translated into human therapy in a short time.

Sex steroid ablation enhances hematopoietic recovery following cytotoxic antineoplastic therapy in aged mice

Cytotoxic antineoplastic therapy is widely used in the clinic as a treatment for malignant diseases. The treatment itself, however, leads to long-term depletion of the adaptive immune system, which is more pronounced in older patients, predominantly due to thymic atrophy. We and others have previously shown that withdrawal of sex steroids is able to regenerate the aged thymus and enhance recovery from autologous and allogeneic hematopoietic stem cell transplant. In this study we have examined the effects of sex steroid ablation (SSA) on the recovery of lymphopoiesis in the bone marrow (BM) and thymus following treatment with the chemotherapeutic agent cyclophosphamide (Cy) in middle-aged and old mice. Furthermore, we have also examined the impact of this regeneration on peripheral immunity. SSA enhanced the recovery of BM resident hematopoietic stem cells and lymphoid progenitors and promoted lymphopoiesis. Interestingly, Cy alone caused a profound increase in the recently described common lymphoid progenitor 2 (CLP-2) population in the BM. In the thymus, SSA caused a profound increase in cellularity as well as all intrathymic T-lineage progenitors including early T-lineage progenitors (ETPs) and non-canonical T cell progenitors such as the CLP-2. We also found that these transferred into numerical increases in the periphery with enhanced B and T cell numbers. Furthermore, these lymphocytes were found to have an enhanced functional capacity with no perturbation of the TCR repertoire. Taken together, these results provide the basis for the use of SSA in the clinic to enhance treatment outcomes from cytotoxic antineoplastic therapy.

Immunosenescence: what does it mean to health outcomes in older adults?

The most profound consequences of immune senescence with respect to human health are the increased susceptibility to infectious diseases and decreased vaccine efficacy. Changes in both innate and adaptive immune function converge in the reduced response to vaccination and protection against infection and related diseases. The decline in thymic output of naïve T cells diminishes responses to novel antigens, such as West Nile Virus, while clonal expansions leading to defects in the T cell repertoire are associated with blunted responses of memory T cells to conserved epitopes of the influenza virus. Recent studies on how immunologic mechanisms of protection change during aging have led to novel strategies for improving vaccine responsiveness and outcomes of infectious diseases in older adults.

Biomarkers of human immunosenescence: impact of Cytomegalovirus infection

Age-associated failing systemic immunity, loosely termed 'immunosenescence', is thought to contribute to the increased incidence and severity of infectious disease in old people. It would therefore be of great practical as well as academic interest to accurately identify which of the multitude of alterations to immune parameters thus far reported are causally related to a person's clinically unfavourable health status, in order to identify the mechanisms of immune ageing and intervene to restore appropriate immunity. This is an enormous current challenge, as it requires longitudinal studies in a very long-lived species. Circumstantial evidence and longitudinal studies limited to the very elderly have begun to reveal 'immune signatures' or biomarkers of immune ageing consisting not of a single parameter, but clusters of parameters increasingly recognized as an 'immune risk profile', or IRP. Although hinted at many years ago, a marked impact of usually asymptomatic infection with the persistent beta-herpesvirus Cytomegalovirus (CMV) on markers of immunosenescence is now becoming incontrovertible. The fascinating cohabitation of CMV with the human immune system, which commits a very significant fraction of its entire resources to CMV-immunosurveillance, may suggest an early-life benefit from infection, which becomes deleterious for the majority of the population only in later life or under pathological conditions.

Psychologically adverse work conditions are associated with CD8+ T cell differentiation indicative of immunesenescence

Numerous studies have demonstrated associations between psychosocial stress and indices of poor health, and much research is now dedicated to identifying the responsible biological mechanisms. The current study examined the hypothesis that stress may impact health by promoting immunesenescence. Participants were 537 factory workers (89% male; mean age 44; range 18-65years). Blood was analyzed for two components of the aging 'immune risk phenotype': the number and proportion of late-differentiated (CD27-CD28-) CD8 T cells (CTLs) and CD4:CD8 ratio. Psychological assessment focussed on work-related stressors which have previously been found to predict morbidity and mortality. This assessment included measures of work load, effort-reward imbalance, and social support at work. High levels of job stress (low reward, high effort-reward imbalance) and low social support at work were associated with a significantly lower CD4:CD8 ratio. Also, the number of CD27-CD28- CTLs was 30% to 50% higher in employees classified in the highest tertile of each stress parameter as compared to employees in the corresponding lowest tertile (p<.01). These associations withstood adjustment for a wide range of demographic, life style, medical, and socio-economic indicators. The associations between CTL phenotype and low social support became stronger with increasing age. These results suggest that psychosocial stress may contribute to immunological aging. Prospective studies should address the long-term consequences of these associations for healthy aging.

The importance of the age factor in cancer vaccination at older age

Cancer is an age-related disease, and with the graying of the society there is an increasing need to optimize cancer management and therapy to elderly patients. Vaccine therapy for cancer is less toxic than chemotherapy or radiation and could be, therefore, especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T cell unresponsiveness, a phenomenon also observed in cancer patients per se. Therefore, research is needed to establish whether age-specific tumor-immunological variables permit optimal use of cancer vaccines and therapy in the elderly. This review summarizes the current knowledge of T cell unresponsiveness in cancer patients and elderly, and the results of cancer vaccination in preclinical models at young and old age. Finally, new directions that may lead to effective cancer vaccination at older age will be proposed.

Granzyme B: Correlates with protection and enhanced CTL response to influenza vaccination in older adults

This study compared serum antibody titers and granzyme B (GrzB) levels in virus-stimulated peripheral blood mononuclear cells following influenza vaccination. Twelve of 239 older adults who subsequently developed laboratory-diagnosed influenza illness (LDI) had significantly lower GrzB levels compared to subjects without LDI (p=0.004). Eight subjects with LDI in the previous year showed an enhanced GrzB response to vaccination (p=0.02). Serum antibody titers following vaccination did not distinguish those older adults who developed LDI from those who did not. These results suggest that GrzB levels could be combined with antibody titers to more effectively predict vaccine efficacy in older adults.

Premature aging of T cells is associated with faster HIV-1 disease progression

OBJECTIVE

To determine if untreated HIV-1 infection and progression is associated with premature aging of memory CD8 and CD4 T cells and naive CD4 T cells.

METHODS

Twenty HIV-1-infected fast progressors and 40 slow progressors were included in our study, using risk set sampling. The expression of cell surface markers reflecting the differentiation stages of lymphocytes was measured using flow cytometry analyses performed on cryopreserved peripheral blood mononuclear cells.

RESULTS

We found that HIV-1 disease progression is associated with a decreased CD28 median florescence intensity on CD4 and CD8 T cells; an increased proportion of intermediate- and late-differentiated CD8 T cells and a decreased CD31 median florescence intensity on naive CD4 T cells of recent thymic origin. A selective depletion of peripherally expanded naive CD4 T cells was found to be associated with HIV-1 infection but not with HIV-1 disease progression.

CONCLUSIONS

The overall change during HIV-1 infection and progression is associated with a shift in the T-cell population toward an aged conformation, which may be further compromised by impaired renewal of the less-differentiated CD4 T-cell population. Our results suggest that HIV-1 infection induces an accelerated aging of T lymphocytes, which is associated with the clinical progression to AIDS and death.

The ageing immune system: is it ever too old to become young again?

Ageing is accompanied by a decline in the function of the immune system, which increases susceptibility to infections and can decrease the quality of life. The ability to rejuvenate the ageing immune system would therefore be beneficial for elderly individuals and would decrease health-care costs for society. But is the immune system ever too old to become young again? We review here the promise of various approaches to rejuvenate the function of the immune system in the rapidly growing ageing population.

Immunosenescence Modulation by Vaccination

A decline in immune function is a hallmark of aging that leads to complicated illness from a variety of infectious diseases, cancer and other immune-mediated disorders, and may limit the ability to appropriately respond to vaccination. How vaccines might alter the senescent immune response and what are the immune correlates of protection will be addressed from the perspective of 1) stimulating a previously primed response as in the case of vaccines for seasonal influenza and herpes zoster, 2) priming the response to novel antigens such as pandemic influenza or other viruses, 3) vaccination against bacterial pathogens such as pneumococcus, and 4) altering the immune response to an endogenous protein as in the case of a vaccine against Alzheimer’s disease. In spite of the often limited efficacy of vaccines for older adults, influenza vaccination remains the only cost-saving medical intervention in this population. Thus, considerable opportunity exists to improve current vaccines and develop new vaccines as a preventive approach to a variety of diseases in older adults. Strategies for selecting appropriate immunologic targets for new vaccine development and evaluating how vaccines may alter the senescent immune response in terms of potential benefits and risks in the preclinical and clinical trial phases of vaccine development will be discussed.

Transcriptome analysis of murine thymocytes reveals age-associated changes in thymic gene expression

The decline in adaptive immunity, naïve T-cell output and a contraction in the peripheral T cell receptor (TCR) repertoire with age are largely attributable to thymic involution and the loss of critical cytokines and hormones within the thymic microenvironment. To assess the molecular changes associated with this loss of thymic function, we used cDNA microarray analyses to examine the transcriptomes of thymocytes from mice of various ages ranging from very young (1 month) to very old (24 months). Genes associated with various biological and molecular processes including oxidative phosphorylation, T- and B- cell receptor signaling and antigen presentation were observed to significantly change with thymocyte age. These include several immunoglobulin chains, chemokine and ribosomal proteins, annexin A2, vav 1 and several S100 signaling proteins. The increased expression of immunoglobulin genes in aged thymocytes could be attributed to the thymic B cells which were found to be actively producing IgG and IgM antibodies. Upon further examination, we found that purified thymic T cells derived from aged but not young thymi also exhibited IgM on their cell surface suggesting the possible presence of auto-antibodies on the surface thymocytes with advancing age. These studies provide valuable insight into the cellular and molecular mechanisms associated with thymic aging.

Influenza vaccination in the elderly: seeking new correlates of protection and improved vaccines

Influenza is foremost among all infectious diseases for an age-related increase in risk for serious complications and death. Determining the benefit of current influenza vaccines is largely limited to epidemiologic studies, since placebo-controlled trials of influenza vaccines are no longer considered ethical in the older adult population. Vaccine effectiveness is calculated from the relative reduction in influenza outcomes in individuals who elect to be vaccinated compared with those who do not, the assumptions for which are diverse and have led to considerable controversy as to the exact benefit of influenza vaccination in older adults. In spite of this controversy, there is no doubt that new influenza vaccine technologies are needed to improve protection and reverse the trend of rising hospitalization and death rates related to influenza in older adults despite widespread influenza vaccination programs. This article will review the challenges to new vaccine development, explore the potential correlates of protection against influenza, and describe how new vaccine technologies may improve protection against complicated influenza illness in the older adult population.

Understanding ageing: biomedical and bioengineering approaches, the immunologic view

During the past century, humans have gained more years of average life expectancy than in the last 10,000 years; we are now living in a rapidly ageing world. The sharp rise in life expectancy, coupled to a steady decline in birth rates in all developed countries, has led to an unprecedented demographic revolution characterized by an explosive growth in the number and proportion of older people. Ageing is a complex process that negatively impacts the development of the immune system and its ability to function. Progressive changes in the T and B cell systems over the life span have a major impact on the capacity to respond to immune challenge. These cumulative age-associated changes in immune competence are termed Immunosenescence: some immunological parameters are commonly notably reduced in the elderly and, reciprocally good function is tightly correlated to health status. Hence, a better understanding of Immunosenescence and the development of new strategies to counteract it are essential for improving the quality of life of the elderly population.

Functional regulatory T cells accumulate in aged hosts and promote chronic infectious disease reactivation

Declines in immune function are well described in the elderly and are considered to contribute significantly to the disease burden in this population. Regulatory T cells (T(regs)), a CD4(+) T cell subset usually characterized by high CD25 expression, control the intensity of immune responses both in rodents and humans. However, because CD25 expression does not define all T(regs), especially in aged hosts, we characterized T(regs) by the expression of FOXP3, a transcription factor crucial for T(reg) differentiation and function. The proportion of FOXP3(+)CD4(+) T(regs) increased in the blood of the elderly and the lymphoid tissues of aged mice. The expression of functional markers, such as CTLA-4 and GITR, was either preserved or increased on FOXP3(+) T(regs) from aged hosts, depending on the tissue analyzed. In vitro depletion of peripheral T(regs) from elderly humans improves effector T cell responses in most subjects. Importantly, T(regs) from old FoxP3-GFP knock-in mice were suppressive, exhibiting a higher level of suppression per cell than young T(regs). The increased proportion of T(regs) in aged mice was associated with the spontaneous reactivation of chronic Leishmania major infection in old mice, likely because old T(regs) efficiently suppressed the production of IFN-gamma by effector T cells. Finally, in vivo depletion of T(regs) in old mice attenuated disease severity. Accumulation of functional T(regs) in aged hosts could therefore play an important role in the frequent reactivation of chronic infections that occurs in aging. Manipulation of T(reg) numbers and/or activity may be envisioned to enhance the control of infectious diseases in this fragile population.

Cardiovascular exercise intervention improves the primary antibody response to keyhole limpet hemocyanin (KLH) in previously sedentary older adults

Based upon a prior cross-sectional study, we hypothesized that an aerobic exercise intervention in sedentary older adults would improve a primary T cell-dependent immune response. Participants were a subset of older subjects from a large, ongoing exercise intervention study who were randomly assigned to either an aerobic exercise (Cardio, n=30, 68.9+0.8 years) or flexibility/balance (Flex, n=20, 69.9+1.2 years) intervention. The intervention consisted of either three aerobic sessions for 30-60 min at 55-70% VO(2 max) or two 60 min flexibility/balance sessions weekly for 10 months. Eight months into the intervention, samples were collected before intramuscular administration of KLH (125 microg), followed by sampling at 2, 3, and 6 weeks post-KLH. Serum anti-KLH IgM, IgG1, and IgG2 was measured by ELISA. Physiological and psychosocial measures were also assessed pre- and post-intervention. While there was no difference in the anti-KLH IgG2 response between groups, Cardio displayed significantly (p<0.05) higher anti-KLH IgG1 (at weeks 2, 3, and 6 post) and IgM responses when compared to Flex. Despite cardiovascular intervention-induced improvement in physical fitness (approximately 11% vs. 1% change in VO(2 peak) in Cardio vs. Flex, respectively), we found no relationship between improved fitness and enhanced anti-KLH antibody responses. Optimism, perceived stress, and affect were all associated with enhanced immune response. We have shown for the first time that cardiovascular training in previously sedentary elderly results in significantly higher primary IgG1 and IgM antibody responses, while having no effect on IgG2 production.

The effect of age and telomere length on immune function in the horse

Telomeres, specialized structures present at the ends of linear eukaryotic chromosomes, function to maintain chromosome stability and integrity. Telomeres shorten with each cell division eventually leading to replicative senescence, a process thought to be associated with age-related decline in immune function. We hypothesized that shortened PBMC telomere length is a factor contributing to immunosenescence of the aged horse. Telomere length was assessed in 19 horses ranging in age from 1 to 25 years. Mitogen-induced 3H-thymidine incorporation, total serum IgG, and pro-inflammatory cytokine expression was also determined for each horse. Relative telomere length (RTL) was highly correlated with overall age. RTL was positively correlated with 3H-thymidine incorporation and total IgG. Expression of pro-inflammatory cytokines was negatively correlated with RTL. These measures were also correlated with age, as expected. However, RTL was not correlated with immunosenescence and inflammaging in the oldest horse.

Rapid decline of influenza vaccine-induced antibody in the elderly: is it real, or is it relevant?

Advisory committees have cautioned that influenza vaccine-induced antibody declines more rapidly in the elderly, falling below seroprotective levels within 4 months. We conducted a literature review to assess this assertion. The articles that were included in this review reported antibody levels > or =4 months after influenza immunization in persons > or =60 years old, interpretable in the context of annual influenza vaccine-approval criteria (seroprotection/seroconversion) specified by the Committee for Proprietary Medicinal Products (CPMP) for the elderly. The final review included 14 studies; 8 of which reported seroprotection rates. Seroprotection exceeding CPMP criteria was maintained > or =4 months after influenza immunization in all 8 of the studies reporting this for the H3N2 component and in 5 of the 7 studies reporting this for the H1N1 and B components. In determining whether CPMP criteria were met at season's end, primary antibody response appeared to be more relevant than secondary antibody decline. Both studies reporting seroprotection rates that failed CPMP criteria > or =4 months after influenza immunization for each of the H1N1 and B components had also reported failed seroprotection at 1 month after immunization. If initially achieved after immunization, seroprotection rates of 70%-100% were maintained not just at 4 months (2 studies) but also at 5 months (2 studies) and even at >6 months (4 studies), for the H3N2 and H1N1 vaccine components. Seroprotection rates appeared less consistent for the B vaccine component, throughout the postimmunization period. Seroconversion appears to vary substantially and inversely with preimmunization titers but not with age. In 2 of 6 studies reporting seroconversion alone, CPMP criteria were still met at 4 months. In the other 4 studies, the main reason for failure at 4 months was primary failure at 1 month. A total of 6 studies compared antibody persistence by age, and no consistent differences were found on that basis. The historic concern that the influenza vaccine-induced antibody response in the elderly declines more rapidly and below seroprotective levels within 4 months of immunization should be reconsidered.

Telomere length and mortality: a study of leukocytes in elderly Danish twins

Leukocyte telomere length, representing the mean length of all telomeres in leukocytes, is ostensibly a bioindicator of human aging. The authors hypothesized that shorter telomeres might forecast imminent mortality in elderly people better than leukocyte telomere length. They performed mortality analysis in 548 same-sex Danish twins (274 pairs) aged 73-94 years, of whom 204 pairs experienced the death of one or both co-twins during 9-10 years of follow-up (1997-2007). From the terminal restriction fragment length (TRFL) distribution, the authors obtained the mean TRFL (mTRFL) and the mean values of the shorter 50% (mTRFL(50)) and shortest 25% (mTRFL(25)) of TRFLs in the distribution and computed the mode of TRFL (MTRFL). They analyzed the proportions of twin pairs in which the co-twin with the shorter telomeres died first. The proportions derived from the intrapair comparisons indicated that the shorter telomeres predicted the death of the first co-twin better than the mTRFL did (mTRFL: 0.56, 95% confidence interval (CI): 0.49, 0.63; mTRFL(50): 0.59, 95% CI: 0.52, 0.66; mTRFL(25): 0.59, 95% CI: 0.52, 0.66; MTRFL: 0.60, 95% CI: 0.53, 0.67). The telomere-mortality association was stronger in years 3-4 than in the rest of the follow-up period, and it grew stronger with increasing intrapair difference in all telomere parameters. Leukocyte telomere dynamics might help explain the boundaries of the human life span.

Age-associated decline in T cell repertoire diversity leads to holes in the repertoire and impaired immunity to influenza virus

A diverse T cell repertoire is essential for a vigorous immune response to new infections, and decreasing repertoire diversity has been implicated in the age-associated decline in CD8 T cell immunity. In this study, using the well-characterized mouse influenza virus model, we show that although comparable numbers of CD8 T cells are elicited in the lung and lung airways of young and aged mice after de novo infection, a majority of aged mice exhibit profound shifts in epitope immunodominance and restricted diversity in the TCR repertoire of responding cells. A preferential decline in reactivity to viral epitopes with a low naive precursor frequency was observed, in some cases leading to “holes” in the T cell repertoire. These effects were also seen in young thymectomized mice, consistent with the role of the thymus in maintaining naive repertoire diversity. Furthermore, a decline in repertoire diversity generally correlated with impaired responses to heterosubtypic challenge. This study formally demonstrates in a mouse infection model that naturally occurring contraction of the naive T cell repertoire can result in impaired CD8 T cell responses to known immunodominant epitopes and decline in heterosubtypic immunity. These observations have important implications for the design of vaccine strategies for the elderly.

Effectiveness of pneumococcal vaccination in older adults with chronic respiratory diseases: results of the EVAN-65 study

A prospective cohort study evaluating the clinical effectiveness of the 23-valent pneumococcal polysaccharide vaccine was conducted among 1298 Spanish older adults with chronic respiratory diseases (bronchitis, emphysema or asthma) who were followed between 2002 and 2005. Main outcomes were all-cause community-acquired pneumonia (CAP) and 30 days mortality from CAP. The association between vaccination and the risk of each outcome was evaluated by multivariable Cox proportional-hazard models adjusted for age and comorbidity pneumococcal vaccination did not alter significantly the risk of overall CAP (hazard ratio [HR]: 0.77; 95% confidence interval [CI]: 0.56-1.07) and 30 days mortality from CAP (HR: 0.87; 95% CI: 0.33-2.28). However, a borderline significant reduction of 30% in the risk of all-cause hospitalisation for CAP was observed among vaccinated subjects (HR: 0.70; 95% CI: 0.48-1.00; p=0.052). The effectiveness of the vaccine on the combined endpoint of pneumococcal and unknown organism infections reached 34% (HR: 0.66; 95% CI: 0.43-1.01; p=0.059). Although our findings suggest moderate benefits from the vaccination, the evidence of clinical effectiveness appears limited.