Sheila Govind

CMV and Immunosenescence: from basics to clinics

Alone among herpesviruses, persistent Cytomegalovirus (CMV) markedly alters the numbers and proportions of peripheral immune cells in infected-vs-uninfected people. Because the rate of CMV infection increases with age in most countries, it has been suggested that it drives or at least exacerbates “immunosenescence”. This contention remains controversial and was the primary subject of the Third International Workshop on CMV & Immunosenescence which was held in Cordoba, Spain, 15-16th March, 2012. Discussions focused on several main themes including the effects of CMV on adaptive immunity and immunosenescence, characterization of CMV-specific T cells, impact of CMV infection and ageing on innate immunity, and finally, most important, the clinical implications of immunosenescence and CMV infection. Here we summarize the major findings of this workshop.

Effectiveness of influenza vaccine in aging and older adults: comprehensive analysis of the evidence

Foremost amongst the diseases preventable by vaccination is influenza. Worldwide, influenza virus infection is associated with serious adverse events leading to hospitalization, debilitating complications, and death in elderly individuals. Immunization is considered to be the cornerstone for preventing these adverse health outcomes, and vaccination programs are timed to optimize protection during the annual influenza season. Trivalent inactivated influenza virus vaccines are believed to be both effective and cost-saving; however, in spite of widespread influenza vaccination programs, rates of hospitalization for acute respiratory illness and cardiovascular diseases have been increasing in this population during recent annual influenza seasons. From meta-analyses summarizing estimates of influenza vaccine effectiveness from available observational clinical studies, this review aims to examine how effective current influenza vaccine strategies are in the aging and older adult population and to analyze which are the most important biases that interfere with measurements of influenza vaccine effectiveness. Furthermore, consideration is given to strategies that should be adopted in order to optimize influenza vaccine effectiveness in the face of immune exhaustion.

Immunosenescence: Implications for vaccination programmes in adults

Vaccination is crucially important in preventing infection and protecting vulnerable population from infectious diseases. However, a multitude of changes in the immune system occurring with advancing age, termed immunosenescence, lead to limit the protective effects of vaccination in older adults. While it is widely believed that the current immunization strategies saves many lives, vaccine preventable infectious diseases (VPDs) still place a considerable burden, not only on older individuals, but also on the adult population and healthcare systems of developed countries. This review will first examine the evidence linking the contribution of immunosenescence to a less than optimal vaccine response in aged individuals in order to demonstrate that strategy of promoting vaccination in these populations is not sufficient to reduce the burden associated with VPDs. Furthermore, based upon the side effects of the herd immunity when vaccine-policies are mainly childhood-centered, considerations will be given on the imperative necessity to frame shift our thinking and efforts away from a nearly complete childhood-centered vaccine programme toward a life-span immunization programmes.

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.

Immune Senescence and Vaccination in the Elderly

Vaccines are powerful public health tools that have been of tremendous benefit in protecting vulnerable populations worldwide from many pathogens. However, vaccine- preventable diseases still remain a considerable burden and this is particularly true among aging and aged populations in industrialized countries. The predicted demographic shift in the population landscape towards an ever-increasing aging population and the evidence suggesting that older individuals mount less-than optimal immune response to vaccination have raised the question of improving vaccine responses in older individuals. This review presents recent progress in the understanding at the cellular and molecular levels of age related immune decline and strategies to translate current knowledge into the development of immunization strategies to promote healthy aging, keeping older members of our society autonomous and independent.

Real time-PCR assay estimating the naive T-cell pool in whole blood and dried blood spot samples: Pilot study in young adults

Because of their central role orchestrating the immune response, the decrease in repertoire number and diversity of naïve T-cells is a significant feature of immnosenescence. Reflecting the effective naive T-cell pool, quantifying the sj-TREC ratio (number of signal joint T-cell receptor excision circles/10(5) T-cells) in blood samples suffers however from constraints. The most limiting one is the absolute requirement of the flow cytometry analysis of peripheral blood samples for the T-cell numeration. In order to make this ratio more accessible for clinical and epidemiological studies addressing how changes in responsiveness of the immune system lead to an increased susceptibility to various diseases and poorer response to vaccination, we have developed a rapid and simple method for the quantification of the sj-TREC ratio in whole blood and in dried blood spot (DBS) samples. This novel method is a QPCR analysis using fluorescently labelled sequence-specific probes both for quantifying sj-TREC and T-cell count and therefore eliminating the absolute necessity of the flow cytometer analysis. In this pilot study, we have compared the sj-TREC ratio we obtained with this novel method in whole blood and in DBS samples of 10 healthy volunteers with those obtained with the technique of reference and found that they are comparable.

Comparison of manual and automated DNA purification for measuring TREC in dried blood spot (DBS) samples with qPCR.

Automated nucleic acid extractions from dried blood spot (DBS) samples promises standardized sample treatment, low error rates, avoidance of contamination and requirement of less hands-on time. In the present study, non-automated and automated column based extraction processes using the QIAamp Investigator procedure were compared for the extraction of DNA from DBS samples. The concentration and the purity of DNA generated were determined by optical density readings. Furthermore qPCR downstream applications using the nucleic acids extracted with the two processes and albumin and T-cell receptor excision circles (TREC) copy numbers were measured and compared. The influence of the time of storage was also investigated by analyzing samples freshly dried and stored up to 11weeks at -20°C from the same individual. Finally, we provide arguments of preferentially choosing the automated procedure for extracting DNAs from DBS samples when downstream qPCR applications are required.

Protection versus pathology in aviremic and high viral load HIV-2 infection-the pivotal role of immune activation and T-cell kinetics.

Background. Many human immunodeficiency virus (HIV)–2-infected individuals remain aviremic and behave as long-term non-progressors but some progress to AIDS. We hypothesized that immune activation and T-cell turnover would be critical determinants of non-progressor/progressor status. Methods. We studied 37 subjects in The Gambia, West Africa: 10 HIV-negative controls, 10 HIV-2-infected subjects with low viral loads (HIV-2-LV), 7 HIV-2-infected subjects with high viral loads (HIV-2-HV), and 10 with HIV-1 infection. We measured in vivo T-cell turnover using deuterium-glucose labeling, and correlated results with T-cell phenotype (by flow cytometry) and T-cell receptor excision circle (TREC) abundance. Results. Immune activation (HLA-DR/CD38 coexpression) differed between groups with a significant trend: controls <HIV-2-LV <HIV-1 <HIV-2-HV (P < .01 for all cell types). A similar trend was observed in the pattern of in vivo turnover of memory CD4+ and CD8+ T-cells and TREC depletion in naive CD4+ T-cells, although naive T-cell turnover was relatively unaffected by either infection. T-cell turnover, immune activation, and progressor status were closely associated. Conclusions. HIV-2 non-progressors have low rates of T-cell turnover (both CD4+ and CD8+) and minimal immune activation; high viral load HIV-2 progressors had high values, similar to or exceeding those in HIV-1 infection.

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.

Measuring the TREC ratio in dried blood spot samples: Intra- and inter-filter paper cards reproducibility

The level of T-cell receptor excision circles (TREC), which decline with advancing age in normal individuals, has recently gained interest as a reference marker for studies on premature or early immunosenescence under particular health conditions. In order to facilitate translational studies at population and clinical levels, essential for the understanding of how changes in TREC levels are associated with responsiveness of the immune system, we have developed and optimized a real-time polymerase chain reaction (qPCR) assay which quantifies the TREC ratio from dried blood spot (DBS) samples. The present study considers a fully automated procedure to purify DNA and amplify sequences of interests by means of qPCR from DBS samples collected in healthy adults. Both TREC:PBMC (peripheral blood mononuclear cell) and TREC:T-cell ratios were compared for intra- and inter individual reproducibility. Furthermore, the impact of the length of storage on the quality of the DNA generated was also analyzed. In conclusion we describe a fully automated procedure for extracting DNA and qPCR set up, which offers a high-precision, robust qPCR assay for the quantification of both TREC:T-cell ratio and TREC:PBMC from DBS samples.