Cytomegalovirus Seropositivity Predicts a Decline in the T Cell But Not the Antibody Response to Influenza in Vaccinated Older Adults Independent of Type 2 Diabetes Status

Association of Cytomegalovirus Serostatus With Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine Responsiveness in Nursing Home Residents and Healthcare Workers

Background

Latent cytomegalovirus (CMV) infection is immunomodulatory and could affect mRNA vaccine responsiveness. We sought to determine the association of CMV serostatus and prior severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection with antibody (Ab) titers after primary and booster BNT162b2 mRNA vaccinations in healthcare workers (HCWs) and nursing home (NH) residents.

Methods

Nursing home residents (N = 143) and HCWs (N = 107) were vaccinated and serological responses monitored by serum neutralization activity against Wuhan and Omicron (BA.1) strain spike proteins, and by bead-multiplex immunoglobulin G immunoassay to Wuhan spike protein and its receptor-binding domain (RBD). Cytomegalovirus serology and levels of inflammatory biomarkers were also measured.

Results

Severe acute respiratory syndrome coronavirus 2-naive CMV seropositive (CMV+) HCWs had significantly reduced Wuhan-neutralizing Ab (P = .013), anti-spike (P = .017), and anti-RBD (P = .011) responses 2 weeks after primary vaccination series compared with responses among CMV seronegative (CMV-) HCWs, adjusting for age, sex, and race. Among NH residents without prior SARS-CoV-2 infection, Wuhan-neutralizing Ab titers were similar 2 weeks after primary series but were reduced 6 months later (P = .012) between CMV+ and CMV- subjects. Wuhan-neutralizing Ab titers from CMV+ NH residents who had prior SARS-CoV-2 infection consistently trended lower than titers from SARS-CoV-2 experienced CMV- donors. These impaired Ab responses in CMV+ versus CMV- individuals were not observed after booster vaccination or with prior SARS-CoV-2 infection.

Conclusions

Latent CMV infection adversely affects vaccine-induced responsiveness to SARS-CoV-2 spike protein, a neoantigen not previously encountered, in both HCWs and NH residents. Multiple antigenic challenges may be required for optimal mRNA vaccine immunogenicity in CMV+ adults.

Granzyme B: a double-edged sword in the response to influenza infection in vaccinated older adults

Background

Influenza-specific cytolytic T lymphocytes (CTL) have a critical role in clearing the virus from the lungs, but are poorly stimulated by current inactivated influenza vaccines. Our previous work suggests that granzyme B (GrB) activity predicts protection against laboratory-confirmed influenza infection (LCII) in older adults. However, basal GrB (bGrB) activity increases with age and the frequency of GrB+ CTL that do not co-express perforin increases following influenza infection, thereby acting as a potential contributor to immune pathology.

Objectives

Using data from a 4-year randomized trial of standard- versus high-dose influenza vaccination, we sought to determine whether measurements of GrB activity alone indicate a protective vs. pathologic response to influenza infection. We compared LCII to No-LCII subsets according to: pre-vaccination bGrB activity; and induced GrB activity in ex vivo influenza-challenged peripheral blood mononuclear cells (PBMC) at 4- and 20-weeks post-vaccination.

Results

Over four influenza seasons (2014-2018), 27 of 608 adult participants aged 65 years and older developed influenza A/H3N2-LCII (n=18) or B-LCII (n=9). Pre-vaccination, there was a significant correlation between bGrB and ex vivo GrB activity in each of the H3N2-LCII, B-LCII, and No-LCII subsets. Although pre-vaccination ex vivo GrB activity was significantly higher in B-LCII vs. No-LCII with a trend for H3N2-LCII vs. No-LCII, there was no difference in the response to vaccination. In contrast, there was a trend toward increased pre-vaccination bGrB activity and LCII: Odds Ratio (OR) (95% confidence intervals) OR = 1.46 (0.94, 2.33). By 20-weeks post-vaccination, there were significant fold-increases in ex vivo GrB activity specific for the infecting subtype in H3N2-LCII: OR = 1.63 (1.35, 2.00) and B-LCII: OR = 1.73 (1.34, 2.23).

Conclusions

Our results suggest that the poor GrB responses to influenza vaccination that led to development of LCII can be attributed to inactivated formulations rather than the aging immune system since LCII cases generated robust ex vivo GrB responses following natural infection. Further, we identified bGrB as a biomarker of those who remain at risk for LCII following vaccination. Future studies will focus on understanding the mechanisms responsible for the shift in GrB-mediated protection vs. potential immune pathology caused by GrB release.

B Cell Immunosenescence

Innate and adaptive immune responses decline with age, leading to greater susceptibility to infectious diseases and reduced responses to vaccines. Diseases are more severe in old than in young individuals and have a greater impact on health outcomes such as morbidity, disability, and mortality. Aging is characterized by increased low-grade chronic inflammation, so-called inflammaging, that represents a link between changes in immune cells and a number of diseases and syndromes typical of old age. In this review we summarize current knowledge on age-associated changes in immune cells with special emphasis on B cells, which are more inflammatory and less responsive to infections and vaccines in the elderly. We highlight recent findings on factors and pathways contributing to inflammaging and how these lead to dysfunctional immune responses. We summarize recent published studies showing that adipose tissue, which increases in size with aging, contributes to inflammaging and dysregulated B cell function.

Key Determinants of Cell-Mediated Immune Responses: A Randomized Trial of High Dose Vs. Standard Dose Split-Virus Influenza Vaccine in Older Adults

Background: Efforts to improve influenza vaccine effectiveness in older adults have resulted in some successes, such as the introduction of high-dose split-virus influenza vaccine (HD-SVV), yet studies of cell-mediated immune responses to these vaccines remain limited. We have shown that granzyme B (GrB) activity in influenza A/H3N2 challenged peripheral blood mononuclear cells (PBMC) correlates with protection against influenza following standard dose vaccination (SD-SVV) in older adults. Further, the interferon-γ (IFNγ) to interleukin-10 (IL-10) ratio can be a correlate of protection.

Methods: In a double-blind trial (ClinicalTrials.gov NCT02297542) older adults (≥65 years, n = 582) were randomized to receive SD-SVV or HD-SVV (Fluzone®) from 2014/15 to 2017/18. Young adults (20–40 years, n = 79) received SD-SVV. At 0, 4, 10, and 20 weeks post-vaccination, serum antibody titers, IFNγ, IL-10, and inducible GrB (iGrB) were measured in ex vivo influenza-challenged PBMC. iGrB is defined as the fold change in GrB activity from baseline levels (bGrB) in circulating T cells. Responses of older adults were compared to younger controls, and in older adults, we analyzed effects of age, sex, cytomegalovirus (CMV) serostatus, frailty, and vaccine dose.

Results: Prior to vaccination, younger compared to older adults produced significantly higher IFNγ, IL-10, and iGrB levels. Relative to SD-SVV recipients, older HD-SVV recipients exhibited significantly lower IFNγ:IL-10 ratios at 4 weeks post-vaccination. In contrast, IFNγ and iGrB levels were higher in younger SD vs. older SD or HD recipients; only the HD group showed a significant IFNγ response to vaccination compared to the SD groups; all three groups showed a significant iGrB response to vaccination. In a regression analysis, frailty was associated with lower IFNγ levels, whereas female sex and HD-SVV with higher IL-10 levels. Age and SD-SVV were associated with lower iGrB levels. The effect of prior season influenza vaccination was decreased iGrB levels, and increased IFNγ and IL-10 levels, which correlated with influenza A/H3N2 hemagglutination inhibition antibody titers.

Conclusion: Overall, HD-SVV amplified the IL-10 response consistent with enhanced antibody responses, with little effect on the iGrB response relative to SD-SVV in either younger or older adults. These results suggest that enhanced protection with HD-SVV is largely antibody-mediated.

Clinical Trial Registration: ClinicalTrials.gov (NCT02297542).

Non-autoimmune diabetes mellitus and the risk of virus infections: a systematic review and meta-analysis of case-control and cohort studies

A significant number of studies invoked diabetes as a risk factor for virus infections, but the issue remains controversial. We aimed to examine whether non-autoimmune diabetes mellitus enhances the risk of virus infections compared with the risk in healthy individuals without non-autoimmune diabetes mellitus. In this systematic review and meta-analysis, we assessed case-control and cohort studies on the association between non-autoimmune diabetes and viruses. We searched PubMed, Embase, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, and Web of Science with no language restriction, to identify articles published until February 15, 2021. The main outcome assessment was the risk of virus infection in individuals with non-autoimmune diabetes. We used a random-effects model to pool individual studies and assessed heterogeneity (I2) using the χ2 test on Cochrane's Q statistic. This study is registered with PROSPERO, number CRD42019134142. Out of 3136 articles identified, we included 68 articles (90 studies, as the number of virus and or diabetes phenotype varied between included articles). The summary OR between non-autoimmune diabetes and virus infections risk were, 10.8(95% CI: 10.3-11.4; 1-study) for SARS-CoV-2; 3.6(95%CI: 2.7-4.9, I2 = 91.7%; 43-studies) for HCV; 2.7(95% CI: 1.3-5.4, I2 = 89.9%, 8-studies;) for HHV8; 2.1(95% CI: 1.7-2.5; 1-study) for H1N1 virus; 1.6(95% CI: 1.2-2.13, I2 = 98.3%, 27-studies) for HBV; 1.5(95% CI: 1.1-2.0; 1-study) for HSV1; 3.5(95% CI: 0.6-18.3 , I2 = 83.9%, 5-studies) for CMV; 2.9(95% CI: 1-8.7, 1-study) for TTV; 2.6(95% CI: 0.7-9.1, 1-study) for Parvovirus B19; 0.7(95% CI: 0.3-1.5 , 1-study) for coxsackie B virus; and 0.2(95% CI: 0-6.2; 1-study) for HGV. Our findings suggest that, non-autoimmune diabetes is associated with increased susceptibility to viruses especially SARS-CoV-2, HCV, HHV8, H1N1 virus, HBV and HSV1. Thus, these viruses deserve more attention from diabetes health-care providers, researchers, policy makers, and stakeholders for improved detection, overall proper management, and efficient control of viruses in people with non-autoimmune diabetes.

Assessing Vaccine Protection for Older Adults with Diabetes: A Systematic Review

Immunosenescence and comorbidities increase the susceptibility of older adults with diabetes mellitus (DM) to vaccine-preventable diseases, hospitalization, disability, or death. This systematic review synthesizes research on protecting older adults with DM during pandemics, exploring vaccine safety, tolerance, and vaccination uptake by older adults in anticipation of seasonal influenza outbreaks during the current COVID-19 threat. Addressed were: (a) age-related factors influencing the effectiveness of vaccines against infectious disease in older adults; (b) vaccine safety, tolerance, effectiveness for older persons with DM; and (c) issues affecting older adults accepting immunization recommendations. Medline and CINAHL databases yielded 214 studies with 43 meeting inclusion criteria (32 descriptive and 11 controlled trials). Findings show altered glycemic control stimulates proinflammatory mediators, increasing infection risk, vaccines, and annual revaccinations safely reduce hospitalization rates, mortality outcomes, without affecting glycemic control. However, vaccines fail to evoke optimal antibody responses in older adults. Unawareness, fear of side effects, tend to lower vaccination participation.

The burden of influenza in older adults: meeting the challenge

Influenza is an acute respiratory infection for which vaccination is our best prevention strategy. Small seasonal changes in circulating influenza viruses (antigenic drift) result in the need for annual influenza vaccination, in which the vaccine formulation is updated to better match the predominant circulating influenza viruses that have undergone important antigenic changes. Although the burden of influenza infection and its complications is the highest in older adults, vaccine effectiveness is the lowest in this vulnerable population. This is largely due to waning of the immune response with age known as "immune senescence", and presents an important, unmet challenge. Possible strategies to tackle this include adjuvant and high-dose vaccines, and herd immunity induced by greater vaccine uptake.

The impact of immuno-aging on SARS-CoV-2 vaccine development

The SARS-CoV-2 pandemic has almost 56 million confirmed cases resulting in over 1.3 million deaths as of November 2020. This infection has proved more deadly to older adults (those >65 years of age) and those with immunocompromising conditions. The worldwide population aged 65 years and older is increasing, and the total number of aged individuals will outnumber those younger than 65 years by the year 2050. Aging is associated with a decline in immune function and chronic activation of inflammation that contributes to enhanced viral susceptibility and reduced responses to vaccination. Here we briefly review the pathogenicity of the virus, epidemiology and clinical response, and the underlying mechanisms of human aging in improving vaccination. We review current methods to improve vaccination in the older adults using novel vaccine platforms and adjuvant systems. We conclude by summarizing the existing clinical trials for a SARS-CoV-2 vaccine and discussing how to address the unique challenges for vaccine development presented with an aging immune system.

Antibody and Cell-Mediated Immune Responses Are Correlates of Protection against Influenza Infection in Vaccinated Older Adults

Despite efforts to design better vaccines for older adults, the risk for serious complications of influenza remains disproportionately high. Identifying correlates of vaccine effectiveness and understanding the heterogeneity of health outcomes in older adults are key to the vaccine development pipeline. We sought correlates of protection against laboratory-confirmed influenza illness (LCII) in a 4-year randomized trial of standard versus high-dose influenza vaccination of adults 65 years and older. To this end, we quantified serum hemagglutination-inhibition (HAI) titers and interferon-gamma (IFNγ) and interleukin-10 (IL-10) secretion by virus-challenged peripheral blood mononuclear cells. Of the 608 participants included, 26 developed either A/H3N2-(n = 17) or B-LCII (n = 9) at 10-20 weeks post-vaccination. Antibody titres for A/H3N2 at 4-weeks post-vaccination were significantly associated with protection against LCII, where every 1-standard deviation increase reduced the odds of A/H3N2-LCII by 53%. Although B-titres did not correlate with protection against B-LCII, the fold-increase in IFNγ:IL-10 ratios from pre- to 4-weeks post-vaccination was significantly associated with protection against B-LCII, where every 1-standard deviation increase reduced the odds by 71%. Our results suggest that both antibody and cell-mediated immune measures are valuable and potentially complementary correlates of protection against LCII in vaccinated older adults, although this may depend on the viral type causing infection.

Targeting Inflammation and Immunosenescence to Improve Vaccine Responses in the Elderly

One of the most appreciated consequences of immunosenescence is an impaired response to vaccines with advanced age. While most studies report impaired antibody responses in older adults as a correlate of vaccine efficacy, it is now widely appreciated that this may fail to identify important changes occurring in the immune system with age that may affect vaccine efficacy. The impact of immunosenescence on vaccination goes beyond the defects on antibody responses as T cell-mediated responses are reshaped during aging and certainly affect vaccination. Likewise, age-related changes in the innate immune system may have important consequences on antigen presentation and priming of adaptive immune responses. Importantly, a low-level chronic inflammatory status known as inflammaging has been shown to inhibit immune responses to vaccination and pharmacological strategies aiming at blocking baseline inflammation can be potentially used to boost vaccine responses. Yet current strategies aiming at improving immunogenicity in the elderly have mainly focused on the use of adjuvants to promote local inflammation. More research is needed to understand the role of inflammation in vaccine responses and to reconcile these seemingly paradoxical observations. Alternative approaches to improve vaccine responses in the elderly include the use of higher vaccine doses or alternative routes of vaccination showing only limited benefits. This review will explore novel targets and potential new strategies for enhancing vaccine responses in older adults, including the use of anti-inflammatory drugs and immunomodulators.

Recent advances in influenza vaccines

Seasonal influenza remains a major public health problem, responsible for hundreds of thousands of deaths every year, mostly of elderly people. Despite the wide availability of vaccines, there are multiple problems decreasing the effectiveness of vaccination programs. These include viral variability and hence the requirement to match strains by estimating which will become prevalent each season, problems associated with vaccine and adjuvant production, and the route of administration as well as the perceived lower vaccine efficiency in older adults. Clinical protection is still suboptimal for all of these reasons, and vaccine uptake remains too low in most countries. Efforts to improve the effectiveness of influenza vaccines include developing universal vaccines independent of the circulating strains in any particular season and stimulating cellular as well as humoral responses, especially in the elderly. This commentary assesses progress over the last 3 years towards achieving these aims. Since the beginning of 2020, an unprecedented international academic and industrial effort to develop effective vaccines against the new coronavirus SARS-CoV-2 has diverted attention away from influenza, but many of the lessons learned for the one will synergize with the other to mutual advantage. And, unlike the SARS-1 epidemic and, we hope, the SARS-CoV-2 pandemic, influenza will not be eliminated and thus efforts to improve influenza vaccines will remain of crucial importance.

Reliable reference genes for the quantification of mRNA in human T-cells and PBMCs stimulated with live influenza virus

Background

Quantitative PCR (qPCR) is a powerful tool that is particularly well-suited to measure mRNA levels in clinical samples, especially those with relatively low cell counts. However, a caveat of this approach is that reliable, stably expressed reference (housekeeping) genes are vital in order to ensure reproducibility and appropriate biological inference. In this study, we evaluated the expression stability of six reference genes in peripheral blood mononuclear cells (PBMCs) and isolated CD3⁺ T-cells from young and old adults (n = 10), following ex vivo stimulation with mock (unstimulated) or live influenza virus. Our genes included: β-actin (ACTB), glyercaldehyde-3-phostphate dehydrogenase (GAPDH), ribosomal protein L13a (RPL13a), ribosomal protein S18 (RPS18), succinate dehydrogenase complex flavoprotein subunit A (SDHA), and ubiquitin-conjugating enzyme E2D2 (UBE2D2).

Results

Reference gene expression varied significantly depending on cell type and stimulation conditions, but not age. Using the comparative ΔCt method, and the previously published software BestKeeper, NormFinder, and geNorm, we show that in PBMCs and T-cells, UBE2D2 and RPS18 were the most stable reference genes, followed by ACTB; however, the expression of UBE2D2 and RPS18 was found to increase with viral stimulation in isolated T-cells, while ACTB expression did not change significantly. No age-related differences in stability were observed for any gene

Conclusions

This study suggests the use of a combination of UBE2D2, RPS18, and ACTB for the study of influenza responses in PBMCs and T-cells, although ACTB alone may be the most optimal choice if choosing to compare target gene expression before and after viral stimulation. Both GAPDH and RPL13a were found to be poor reference genes and should be avoided for studies of this nature.

Effect of latent cytomegalovirus infection on the antibody response to influenza vaccination: a systematic review and meta-analysis

Latent infection with cytomegalovirus (CMV) is thought to accelerate aging of the immune system. With age, influenza vaccine responses are impaired. Although several studies investigated the effect of CMV infection on antibody responses to influenza vaccination, this led to contradicting conclusions. Therefore, we investigated the relation between CMV infection and the antibody response to influenza vaccination by performing a systematic review and meta-analysis. All studies on the antibody response to influenza vaccination in association with CMV infection were included (n = 17). The following outcome variables were extracted: (a) the geometric mean titer pre-/post-vaccination ratio (GMR) per CMV serostatus group, and in addition (b) the percentage of subjects with a response per CMV serostatus group and (c) the association between influenza- and CMV-specific antibody titers. The influenza-specific GMR revealed no clear evidence for an effect of CMV seropositivity on the influenza vaccine response in young or old individuals. Meta-analysis of the response rate to influenza vaccination showed a non-significant trend towards a negative effect of CMV seropositivity. However, funnel plot analysis suggests that this is a consequence of publication bias. A weak negative association between CMV antibody titers and influenza antibody titers was reported in several studies, but associations could not be analyzed systematically due to the variety of outcome variables. In conclusion, by systematically integrating the available studies, we show that there is no unequivocal evidence that latent CMV infection affects the influenza antibody response to vaccination. Further studies, including the level of CMV antibodies, are required to settle on the potential influence of latent CMV infection on the influenza vaccine response.

Self-reported diabetes and herpes zoster are associated with a weak humoral response to the seasonal influenza A H1N1 vaccine antigen among the elderly

Background

The immune response to seasonal influenza vaccines decreases with advancing age. Therefore, an adjuvanted inactivated trivalent influenza vaccine (Fluad®) exists for elderly individuals. Fluad® is more immunogenic and efficacious than conventional influenza vaccines. However, the immune response varies and may still result in high frequencies of poor responders. Therefore, we aimed to a) examine the prevalence of a weak response to Fluad® and b) identify potential risk factors.

Methods

A prospective population-based study among individuals 65–80 years old was conducted in 2015/2016 in Hannover, Germany (n = 200). Hemagglutination-inhibition titers 21 days after vaccination with Fluad® served as indicator of vaccine responsiveness.

Results

The percentage of vaccinees with an inadequate vaccine response varied depending on the influenza strain: it was lowest for H3N2 (13.5%; 95% CI, 9.4–18.9%), intermediate for B strain (37.0%; 30.6–43.9%), and highest for H1N1 (49.0%; 42.2–55.9%). The risk of a weak response to the influenza A H1N1 strain was independently associated with self-reported diabetes (AOR, 4.64; 95% CI, 1.16–18.54), a history of herpes zoster (2.27; 1.01–5.10) and, to a much lesser extent, increasing age (change per year, 1.08; 0.99–1.16). In addition, herpes zoster was the only risk factor for a weak response to the H3N2 antigen (AOR, 3.12; 1.18–8.23). We found no significant association between sex, Body Mass Index, cancer, hypertension, heart attack and CMV seropositivity and a weak response to these two influenza A antigens. Despite its occurence in over one third of vaccinees, none of the variables examined proved to be risk factors for a weak response to the B antigen.

Conclusions

A considerable proportion of elderly individuals displayed a weak vaccine response to this adjuvanted seasonal influenza vaccine and further efforts are thus needed to improve immune responses to influenza vaccination among the elderly. Diabetes and herpes zoster were identified as potentially modifiable risk factors for a poor vaccine response against influenza A antigens, but the results also reveal the need for broader investigations to identify risk factors for inadequate responses to influenza B antigens.

Trial registration

No. NCT02362919 (ClinicalTrials.gov, date of registration: 09.02.2015).

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4214-x) contains supplementary material, which is available to authorized users.

The impact of oxidative stress, inflammation, and senescence on the maintenance of immunological memory in the bone marrow in old age

The bone marrow (BM) provides a preferential survival environment for the long-term maintenance of antigen-experienced adaptive immune cells. After the contact with antigens, effector/memory T cells and plasma cell precursors migrate to the BM, in which they can survive within survival niches in an antigen-independent manner. Despite this, the phenotype of adaptive immune cells changes with aging, and BM niches themselves are affected, leading to impaired long-term maintenance of immunological memory in the elderly as a result. Oxidative stress, age-related inflammation (inflammaging), and cellular senescence appear to play a major role in this process. This review will summarize the age-related changes in T and B cell phenotype, and in the BM niches, discussing the possibility that the accumulation of highly differentiated, senescent-like T cells in the BM during aging may cause inflammation in the BM and promote oxidative stress and senescence. In addition, senescent-like T cells may compete for space with other immune cells within the marrow, partially excluding effector/memory T cells and long-lived plasma cells from the niches.

'From immunosenescence to immune modulation': a re-appraisal of the role of cytomegalovirus as major regulator of human immune function

In the year 2000, cytomegalovirus was identified as a risk factor for mortality in a seminal study of octogenarian residents in Sweden. This finding triggered a wave of additional epidemiological investigations, some of which supported this association whilst others observed no such effect. In addition, this increased risk of death in CMV-seropositive people was correlated with observed changes within the T-cell repertoire such that accelerated 'immunosenescence' became a de facto explanation, without strong evidence to this effect. Recent years have seen a re-appraisal of these findings. Interestingly, many studies show that cytomegalovirus acts to improve immune function, most clearly in younger donors. In addition, the excess mortality in older people that is observed in CMV-seropositive cohorts appears to be related primarily to an excess of vascular disease rather than impairment of immune function. CMV is an important member of the natural 'virome' of Homo sapiens and has an important, and generally positive, modulatory influence on human immune function throughout most of life. However, within certain populations, this influence can become negative and age, co-morbidity and environment all act as determinants of this effect. As such, it is important that new interventions are developed that can mitigate the damaging influence of CMV on human health in populations at risk.

Sex and Gender Differences in the Outcomes of Vaccination over the Life Course

Both sex (i.e., biological differences) and gender (i.e., social or cultural influences) impact vaccine acceptance, responses, and outcomes. Clinical data illustrate that among children, young adults, and aged individuals, males and females differ in vaccine-induced immune responses, adverse events, and protection. Although males are more likely to receive vaccines, following vaccination, females typically develop higher antibody responses and report more adverse effects of vaccination than do males. Human, nonhuman animal, and in vitro studies reveal numerous immunological, genetic, hormonal, and environmental factors that differ between males and females and contribute to sex- and gender-specific vaccine responses and outcomes. Herein, we address the impact of sex and gender variables that should be considered in preclinical and clinical studies of vaccines.

Impact of Aging on the Frequency, Phenotype, and Function of CD161-Expressing T Cells

Immune-aging is associated with perturbed immune responses in the elderly. CD161-expressing T cells, i.e., the previously described subsets of CD161⁺ CD4⁺ T cells, CD161^high CD8⁺ T cells, and CD161^int CD8⁺ T cells, are highly functional, pro-inflammatory T cells. These CD161-expressing T cells are critical in immunity against microbes, while possibly contributing to autoimmune diseases. So far, little is known about the impact of aging on the frequency, phenotype, and function of these CD161-expressing T cells. In the current study, we investigated the impact of aging on CD161⁺ CD4⁺ T cells, CD161^high CD8⁺ T cells, and CD161^int CD8⁺ T cells in peripheral blood samples of 96 healthy subjects (age 20–84). Frequencies of CD161⁺ CD4⁺ T cells and CD161^int CD8⁺ T cells were stable with aging, whereas frequencies of CD161^high CD8⁺ T cells declined. Although CD161^high CD8⁺ T cells were mostly T cell receptor-Vα7.2⁺ mucosal-associated invariant T cells, CD161 expressing CD4⁺ and CD8⁺ T cells showed a limited expression of markers for gamma–delta T cells or invariant natural killer (NK) T cells, in both young and old subjects. In essence, CD161-expressing T cells showed a similar memory phenotype in young and old subjects. The expression of the inhibitory NK receptor KLRG1 was decreased on CD161⁺ CD4⁺ T cells of old subjects, whereas the expression of other NK receptors by CD161-expressing T cells was unaltered with age. The expression of cytotoxic effector molecules was similar in CD161^high and CD161^int CD8⁺ T cells of young and old subjects. The ability to produce pro-inflammatory cytokines was preserved in CD161^high and CD161^int CD8⁺ T cells of old subjects. However, the percentages of IFN-γ⁺ and interleukin-17⁺ cells were significantly lower in CD161⁺ CD4⁺ T cells of old individuals than those of young individuals. In addition, aging was associated with a decrease of nonclassic T helper 1 cells, as indicated by decreased percentages of CD161-expressing cells within the IFN-γ⁺ CD4⁺ T cell compartment of old subjects. Taken together, aging is associated with a numerical decline of circulating CD161^high CD8⁺ T cells, as well as a decreased production of pro-inflammatory cytokines by CD161⁺ CD4⁺ T cells. These aging-associated changes could contribute to perturbed immunity in the elderly.

Immunogenicity, safety, and effectiveness of seasonal influenza vaccination in patients with diabetes mellitus: A systematic review

Influenza is associated with an increased risk of complications, especially in diabetic mellitus patients who are more susceptible to influenza infection. Despite recommendations of the WHO and public health authorities, vaccination uptake in this population remains suboptimal. This systematic review identified 15 studies published between January 2000-March 2017 in PubMed, Embase and Cochrane Library, which provided data on immunogenicity, safety, effectiveness, and/or cost-effectiveness of seasonal influenza vaccination in diabetic patients. Immunogenicity of seasonal influenza vaccination in diabetic patients was generally comparable to that of healthy participants. One month after vaccination of diabetic patients, seroconversion rates and seroprotection ranged from 24.0-58.0% and 29.0-99.0%, respectively. Seasonal influenza vaccination reduced the risk of hospitalization and mortality in diabetic patients, particularly those aged ≥65 years. These review results demonstrate and reinforce the need and value of annual influenza vaccination in diabetic patients, particularly in alleviating severe complications such as hospitalization or death.

Negative Effect of Age, but Not of Latent Cytomegalovirus Infection on the Antibody Response to a Novel Influenza Vaccine Strain in Healthy Adults

Older adults are more vulnerable to influenza virus infection and at higher risk for severe complications and influenza-related death compared to younger adults. Unfortunately, influenza vaccine responses tend to be impaired in older adults due to aging of the immune system (immunosenescence). Latent infection with cytomegalovirus (CMV) is assumed to enhance age-associated deleterious changes of the immune system. Although lower responses to influenza vaccination were reported in CMV-seropositive compared to CMV-seronegative adults and elderly, beneficial effects of CMV infection were observed as well. The lack of consensus in literature on the effect of latent CMV infection on influenza vaccination may be due to the presence of pre-existing immunity to influenza in these studies influencing the subsequent influenza vaccine response. We had the unique opportunity to evaluate the effect of age and latent CMV infection on the antibody response to the novel influenza H1N1pdm vaccine strain during the pandemic of 2009, thereby reducing the effect of pre-existing immunity on the vaccine-induced antibody response. This analysis was performed in a large study population (n = 263) in adults (18–52 years old). As a control, memory responses to the seasonal vaccination, including the same H1N1pdm and an H3N2 strain, were investigated in the subsequent season 2010–2011. With higher age, we found decreased antibody responses to the pandemic vaccination even within this age range, indicating signs of immunosenescence to this novel antigen in the study population. Using a generalized estimation equation regression model, adjusted for age, sex, and previous influenza vaccinations, we observed that CMV infection in contrast did not influence the influenza virus-specific antibody titer after H1N1pdm vaccination. Yet, we found higher residual protection rates (antibody level ≥40 hemagglutinin units (HAU)) in CMV-seropositive individuals than in CMV-seronegative individuals 6 months and 1 year after pandemic vaccination. In the subsequent season, no effect of age or CMV infection on seasonal influenza vaccine response was observed. In conclusion, we observed no evidence for CMV-induced impairment of antibody responses to a novel influenza strain vaccine in adults. If anything, our data suggest that there might be a beneficial effect of latent CMV infection on the protection rate after novel influenza vaccination.

The Contribution of Cytomegalovirus Infection to Immune Senescence Is Set by the Infectious Dose

The relationship between human cytomegalovirus (HCMV) infections and accelerated immune senescence is controversial. Whereas some studies reported a CMV-associated impaired capacity to control heterologous infections at old age, other studies could not confirm this. We hypothesized that these discrepancies might relate to the variability in the infectious dose of CMV occurring in real life. Here, we investigated the influence of persistent CMV infection on immune perturbations and specifically addressed the role of the infectious dose on the contribution of CMV to accelerated immune senescence. We show in experimental mouse models that the degree of mouse CMV (MCMV)-specific memory CD8⁺ T cell accumulation and the phenotypic T cell profile are directly influenced by the infectious dose, and data on HCMV-specific T cells indicate a similar connection. Detailed cluster analysis of the memory CD8⁺ T cell development showed that high-dose infection causes a differentiation pathway that progresses faster throughout the life span of the host, suggesting a virus–host balance that is influenced by aging and infectious dose. Importantly, short-term MCMV infection in adult mice is not disadvantageous for heterologous superinfection with lymphocytic choriomeningitis virus (LCMV). However, following long-term CMV infection the strength of the CD8⁺ T cell immunity to LCMV superinfection was affected by the initial CMV infectious dose, wherein a high infectious dose was found to be a prerequisite for impaired heterologous immunity. Altogether our results underscore the importance of stratification based on the size and differentiation of the CMV-specific memory T cell pools for the impact on immune senescence, and indicate that reduction of the latent/lytic viral load can be beneficial to diminish CMV-associated immune senescence.

Influenza vaccine-mediated protection in older adults: Impact of influenza infection, cytomegalovirus serostatus and vaccine dosage

Age-related changes in T-cell function are associated with a loss of influenza vaccine efficacy in older adults. Both antibody and cell-mediated immunity plays a prominent role in protecting older adults, particularly against the serious complications of influenza. High dose (HD) influenza vaccines induce higher antibody titers in older adults compared to standard dose (SD) vaccines, yet its impact on T-cell memory is not clear. The aim of this study was to compare the antibody and T-cell responses in older adults randomized to receive HD or SD influenza vaccine as well as determine whether cytomegalovirus (CMV) serostatus affects the response to vaccination, and identify differences in the response to vaccination in those older adults who subsequently have an influenza infection. Older adults (≥65years) were enrolled (n=106) and randomized to receive SD or HD influenza vaccine. Blood was collected pre-vaccination, followed by 4, 10 and 20weeks post-vaccination. Serum antibody titers, as well as levels of inducible granzyme B (iGrB) and cytokines were measured in PBMCs challenged ex vivo with live influenza virus. Surveillance conducted during the influenza season identified those with laboratory confirmed influenza illness or infection. HD influenza vaccination induced a high antibody titer and IL-10 response, and a short-lived increase in Th1 responses (IFN-γ and iGrB) compared to SD vaccination in PBMCs challenged ex vivo with live influenza virus. Of the older adults who became infected with influenza, a high IL-10 and iGrB response in virus-challenged cells was observed post-infection (week 10 to 20), as well as IFN-γ and TNF-α at week 20. Additionally, CMV seropositive older adults had an impaired iGrB response to influenza virus-challenge, regardless of vaccine dose. This study illustrates that HD influenza vaccines have little impact on the development of functional T-cell memory in older adults. Furthermore, poor outcomes of influenza infection in older adults may be due to a strong IL-10 response to influenza following vaccination, and persistent CMV infection.

Cellular immune responses of older adults to four influenza vaccines: Results of a randomized, controlled comparison

Cellular immunity is important for protection against the serious complications of influenza in older adults. As it is unclear if newer influenza vaccines elicit greater cellular responses than standard vaccines, we compared responses to 2 standard and 2 newer licensed trivalent inactivated vaccines (TIVs) in a randomized trial in older adults. Non-frail adults ≥ 65 y old were randomly assigned to receive standard subunit, MF59-adjuvanted subunit, standard split-virus or intradermal split-virus TIV. Peripheral blood mononuclear cells (PBMC) harvested pre- and 3-weeks post-vaccination were stimulated with live A/H3N2 virus. PBMC supernatants were tested for interleukin 10 (IL-10) and interferon gamma (IFN-γ), and lysates for granzyme B (GrB). Flow cytometry identified CD4+ and CD8+ T- cells expressing intracellular IL-2, IL-10, IFN-γ, GrB, or perforin. Differences following immunization were assessed for paired subject samples and among vaccines. 120 seniors participated, 29-31 per group, which were well matched demographically. Virus-stimulated PBMCs were GrB-rich before and after vaccination, with minimal increases evident. Immunization did not increase secretion of IFN-γ or IL-10. However, cytolytic effector T-cells (CD8+GrB+perforin+) increased significantly in percentage post-vaccination in all groups, to similar mean values across groups. CD4+GrB+perforin+ T-cells also increased significantly after each vaccine, to similar mean values among vaccines. Vaccination did not increase the low baseline percentages of CD4+ or CD8+ T-cells expressing IFN-γ, IL-2 or IL-10 . In conclusion, participants had pre-existing cellular immunity to H3N2 virus. All 4 vaccines boosted cellular responses to a similar but limited extent, particularly cytolytic effector CD8+ T-cells associated with clinical protection against influenza.

Impact of Aging and Cytomegalovirus on Immunological Response to Influenza Vaccination and Infection

The number of people over the age of 60 is expected to double by 2050 according to the WHO. This emphasizes the need to ensure optimized resilience to health stressors in late life. In older adults, influenza is one of the leading causes of catastrophic disability (defined as the loss of independence in daily living and self-care activities). Influenza vaccination is generally perceived to be less protective in older adults, with some studies suggesting that the humoral immune response to the vaccine is further impaired in cytomegalovirus (CMV)-seropositive older people. CMV is a β-herpes virus infection that is generally asymptomatic in healthy individuals. The majority of older adults possess serum antibodies against the virus indicating latent infection. Age-related changes in T-cell-mediated immunity are augmented by CMV infection and may be associated with more serious complications of influenza infection. This review focuses on the impact of aging and CMV on immune cell function, the response to influenza infection and vaccination, and how the current understanding of aging and CMV can be used to design a more effective influenza vaccine for older adults. It is anticipated that efforts in this field will address the public health need for improved protection against influenza in older adults, particularly with regard to the serious complications leading to loss of independence.

CMV immune evasion and manipulation of the immune system with aging

Human cytomegalovirus (HCMV) encodes numerous proteins and microRNAs that function to evade the immune response and allow the virus to replicate and disseminate in the face of a competent innate and acquired immune system. The establishment of a latent infection by CMV, which if completely quiescent at the level of viral gene expression would represent an ultimate in immune evasion strategies, is not sufficient for lifelong persistence and dissemination of the virus. CMV needs to reactivate and replicate in a lytic cycle of infection in order to disseminate further, which occurs in the face of a fully primed secondary immune response. Without reactivation, latency itself would be redundant for the virus. It is also becoming clear that latency is not a totally quiescent state, but is characterized by limited viral gene expression. Therefore, the virus also needs immune evasion strategies during latency. An effective immune response to CMV is required or viral replication will cause morbidity and ultimately mortality in the host. There is clearly a complex balance between virus immune evasion and host immune recognition over a lifetime. This poses the important question of whether long-term evasion or manipulation of the immune response driven by CMV is detrimental to health. In this meeting report, three groups used the murine model of CMV (MCMV) to examine if the contribution of the virus to immune senescence is set by the (i) initial viral inoculum, (ii) inflation of T cell responses, (iii) or the balance between functionally distinct effector CD4+ T cells. The work of other groups studying the CMV response in humans is discussed. Their work asks whether the ability to make immune responses to new antigens is compromised by (i) age and HCMV carriage, (ii) long-term exposure to HCMV giving rise to an overall immunosuppressive environment and increased levels of latent virus, or (iii) adapted virus mutants (used as potential vaccines) that have the capacity to elicit conventional and unconventional T cell responses.

How does cytomegalovirus factor into diseases of aging and vaccine responses, and by what mechanisms?

Cytomegalovirus (CMV) is an important pathogen for both clinical and population settings. There is a growing body of research implicating CMV in multiple health outcomes across the life course. At the same time, there is mounting evidence that individuals living in poverty are more likely to be exposed to CMV and more likely to experience many of the chronic conditions for which CMV has been implicated. Further research on the causal role of CMV for health and well-being is needed. However, the strong evidence implicating CMV in type 2 diabetes, autoimmunity, cancer, cardiovascular disease, vaccination, and age-related alterations in immune function warrants clinical and public health action. This imperative is even higher among individuals living in socioeconomically disadvantaged settings and those exposed to high levels of chronic psychosocial stress.