Impaired HA-specific T follicular helper cell and antibody responses to influenza vaccination are linked to inflammation in humans

The inflammaging microenvironment induces dysfunctional rewiring of Tfh cell differentiation

Humoral immunity is orchestrated by follicular helper T (Tfh) cells, which promote cognate B cells to produce high-affinity, protective antibodies. In aged individuals, humoral immunity after vaccination is diminished despite the presence of Tfh cells, suggesting defects after initial Tfh cell formation. In this study, we utilized both murine and human systems to investigate how aging alters Tfh cell differentiation after influenza vaccination. We found that young Tfh cells underwent progressive differentiation after influenza vaccination, culminating in clonal expansion of effector-like cells in both draining lymph nodes and blood. In aging, early stages of Tfh cell development occurred normally. However, aging rewired the later stages of development in Tfh cells, resulting in a transcriptional program reflective of cellular senescence, sustained pro-inflammatory cytokine production, and metabolic reprogramming. We investigated the extent to which this rewiring of aged Tfh cells is due to the age-associated inflammatory ("inflammaging") microenvironment and found that this setting was sufficient to both block the transition of Tfh cells to a post-effector resting state and skew Tfh cells toward the age-rewired state. Together, these data suggest that aging dampens humoral immunity by cytokine-mediated rewiring of late effector Tfh cell differentiation into an activated, yet less functional, cellular state.

Role of T Follicular Helper Cells in Viral Infections and Vaccine Design

T follicular helper (Tfh) cells are a specialized subset of CD4+ T lymphocytes that are essential for the development of long-lasting humoral immunity. Tfh cells facilitate B lymphocyte maturation, promote germinal center formation, and drive high-affinity antibody production. Our current knowledge of Tfh interactions with the humoral immune system effectors suggests that they have a critical role in supporting the immune response against viral infections. This review discusses the mechanisms through which Tfh cells influence anti-viral immunity, highlighting their interactions with B cells and their impact on antibody quality and quantity. We explore the role of Tfh cells in viral infections and examine how vaccine design can be improved to enhance Tfh cell responses. Innovative vaccine platforms, such as mRNA vaccines and self-assembling protein nanoplatforms (SAPNs), are promising strategies to enhance Tfh cell activation. Their integration and synergistic combination could further enhance immunity and Tfh responses (SAPN-RNA vaccines). In summary, we provide a comprehensive overview of the current insights into Tfh cells' role during viral infections, emphasizing their potential as strategic targets for innovative vaccine development.

The cellular factors that impair the germinal center in advanced age

Long-lasting immunological memory is a core feature of the adaptive immune system that allows an organism to have a potent recall response to foreign agents that have been previously encountered. Persistent humoral immunity is afforded by long-lived memory B cells and plasma cells, which can mature in germinal centers (GCs) in secondary lymphoid organs. The development of new GC-derived immunity diminishes with age, thereby impairing our immune system's response to both natural infections and vaccinations. This review will describe the current knowledge of how aging affects the cells and microenvironment of the GC. A greater understanding of how the GC changes with age, and how to circumvent these changes, will be critical for tailoring vaccines for older people. This area of research is critical given the twenty-first century will witness a doubling of the aging population and an increased frequency of pandemics.

Immunometabolic regulation of germinal centers and its implications for aging

Aging, metabolism, and immunity have long been considered distinct domains. Aging is primarily associated with the gradual decline of physiological functions, metabolism regulates energy production and maintains cellular processes, and the immune system manages innate and adaptive responses against pathogens and vaccines. However, recent studies have revealed that these three systems are intricately interconnected, collectively influencing an individual's response to stress and disease. This review explores the interplay between immunometabolism, T follicular helper cells, B cells, and aging, focusing on how these interactions impact immune function in the elderly.

B Cells from Aged Mice Do Not Have Intrinsic Defects in Affinity Maturation in Response to Immunization

Affinity maturation, the progressive increase in serum Ab affinity after vaccination, is an essential process that contributes to an effective humoral response against vaccines and infections. Germinal centers are key for affinity maturation, because they are where B cells undergo somatic hypermutation of their Ig genes in the dark zone before going through positive selection in the light zone via interactions with T follicular helper cells and follicular dendritic cells. In aged mice, affinity maturation has been shown to be impaired after immunization, but whether B cell-intrinsic factors contribute to this defect remains unclear. In this study, we show that B cells from aged BCR transgenic mice are able to become germinal center B cells, which are capable of receiving positive selection signals to a similar extent as B cells from young adult mice. Consistent with this, aging also does not impact the ability of B cells to undergo somatic hypermutation and acquire affinity-enhancing mutations. By contrast, transfer of B cells from young adult BCR mice into aged recipients resulted in the impaired acquisition of affinity-enhancing mutations, demonstrating that the aged microenvironment causes altered affinity maturation.

Accumulation of immune-suppressive CD4 + T cells in aging - tempering inflammaging at the expense of immunity

The 'immune risk profile' has been shown to predict mortality in the elderly, highlighting the need to better understand age-related immune dysfunction. While aging leads to many defects affecting all arms of the immune system, this review is focused on the accrual of immuno-suppressive CD4 + T cell populations, including FoxP3 + regulatory T cells, and subsets of IL-10-producing T follicular helper cells. New data suggest that such accumulations constitute feedback mechanisms to temper the ongoing progressive low-grade inflammation that develops with age, the so-called "inflammaging", and by doing so, how they have the potential to promote healthier aging. However, they also impair effector immune responses, notably to infections, or vaccines. These studies also reinforce the idea that the aged immune system should not be considered as a poorly functional version of the young one, but more as a dynamic system in which CD4 + T cells, and other immune/non-immune subsets, differentiate, interact with their milieu and function differently than in young hosts. A better understanding of these unique interactions is thus needed to improve effector immune responses in the elderly, while keeping inflammaging under control.

Humoral and Cellular Immunity Induced by Adjuvanted and Standard Trivalent Influenza Vaccine in Older Nursing Home Residents

BACKGROUND

Despite wide use of adjuvanted influenza vaccine in nursing home residents (NHR), little immunogenicity data exist for this population.

METHODS

We collected blood from NHR (n = 85) living in nursing homes participating in a cluster randomized clinical trial comparing MF59-adjuvanted trivalent inactivated influenza vaccine (aTIV) with nonadjuvanted vaccine (TIV) (parent trial, NCT02882100). NHR received either vaccine during the 2016-2017 influenza season. We assessed cellular and humoral immunity using flow cytometry and hemagglutinin inhibition, antineuraminidase (enzyme-linked lectin assay), and microneutralization assays.

RESULTS

Both vaccines were similarly immunogenic and induced antigen-specific antibodies and T cells, but aTIV specifically induced significantly larger 28 days after vaccination (D28) titers against A/H3N2 neuraminidase than TIV.

CONCLUSIONS

NHRs respond immunologically to TIV and aTIV. From these data, the larger aTIV-induced antineuraminidase response at D28 may help explain the increased clinical protection observed in the parent clinical trial for aTIV over TIV in NHR during the A/H3N2-dominant 2016-2017 influenza season. Additionally, a decline back to prevaccination titers at 6 months after vaccination emphasizes the importance of annual vaccination against influenza.

CLINICAL TRIALS REGISTRATION

NCT02882100.

Antigen-specific CD4+ T cells exhibit distinct transcriptional phenotypes in the lymph node and blood following vaccination in humans

SARS-CoV-2 infection and mRNA vaccination induce robust CD4+ T cell responses that are critical for the development of protective immunity. Here, we evaluated spike-specific CD4+ T cells in the blood and draining lymph node (dLN) of human subjects following BNT162b2 mRNA vaccination using single-cell transcriptomics. We analyze multiple spike-specific CD4+ T cell clonotypes, including novel clonotypes we define here using Trex, a new deep learning-based reverse epitope mapping method integrating single-cell T cell receptor (TCR) sequencing and transcriptomics to predict antigen-specificity. Human dLN spike-specific T follicular helper cells (TFH) exhibited distinct phenotypes, including germinal center (GC)-TFH and IL-10+ TFH, that varied over time during the GC response. Paired TCR clonotype analysis revealed tissue-specific segregation of circulating and dLN clonotypes, despite numerous spike-specific clonotypes in each compartment. Analysis of a separate SARS-CoV-2 infection cohort revealed circulating spike-specific CD4+ T cell profiles distinct from those found following BNT162b2 vaccination. Our findings provide an atlas of human antigen-specific CD4+ T cell transcriptional phenotypes in the dLN and blood following vaccination or infection.

COVID-19 mRNA vaccine immunogenicity decay and breakthrough illness in adolescents and young adults with childhood-onset rheumatic diseases

OBJECTIVES

To evaluate the humoral immunogenicity for 6 months after the two-dose coronavirus disease 2019 (COVID-19) mRNA vaccination in adolescents and young adults (AYAs) with childhood-onset rheumatic diseases (cRDs).

METHODS

This monocentric observational study was conducted between August 2020 and March 2022. Humoral immunogenicity was assessed at 2-3 weeks after first vaccine dose and 1, 3 and 6 months after the second dose by the cPass™ severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralization antibody (nAb) assay. An inhibition signal of ≥30% defined the seroconversion threshold and the readings were calibrated against the World Health Organization International Standard for SARS-CoV-2 antibodies.

RESULTS. ONE HUNDRED AND SIXTY-NINE

AYAs with cRDs were recruited [median age 16.8 years (interquartile range, IQR 14.7-19.5), 52% female, 72% Chinese]. JIA (58%) and SLE (18%) comprised the major diagnoses. After second vaccine dose, 99% seroconverted with a median nAb titre of 1779.8 IU/ml (IQR 882.8-2541.9), declining to 935.6 IU/ml (IQR 261.0-1514.9) and 683.2 IU/ml (IQR 163.5-1400.5) at the 3- and 6-month timepoints, respectively. The diagnosis of JIA [odds ratio (OR) 10.1, 95% CI 1.8-58.4, P = 0.010] and treatment with anti-TNF-α (aTNF) (OR 10.1, 95% CI 1.5-70.0, P = 0.019) were independently associated with a >50% drop of nAb titres at 6 months. Withholding MTX or MMF did not affect the vaccine response or decay rate. The COVID-19 breakthrough infection was estimated at 18.2 cases/1000 patient-months with no clinical risk factors identified.

CONCLUSION

Over half of AYAs with cRDs had a significant drop in SARS-CoV-2 nAb at 6-month despite an initial robust humoral response. JIA and aTNF usage are predictors of a faster decay rate.

Age-dependent changes in T follicular helper cells shape the humoral immune response to vaccination

Vaccination is an excellent strategy to limit the morbidity and mortality associated with infectious disease. Vaccination creates protective, long-lived antibody-mediated immunity by inducing the germinal centre response, an intricate immune reaction that produces memory B cells and long-lived antibody-secreting plasma cells that provide protection against (re)infection. The magnitude and quality of the germinal centre response declines with age, contributing to poor vaccine-induced immunity in older individuals. T follicular helper cells are essential for the formation and function of the germinal centre response. This review will discuss how age-dependent changes in T follicular helper cells influence the germinal centre response, and the evidence that age-dependent changes need not be a barrier to successful vaccination in the later years of life.

Atypical B cells and impaired SARS-CoV-2 neutralization following heterologous vaccination in the elderly

Suboptimal responses to a primary vaccination course have been reported in the elderly, but there is little information regarding the impact of age on responses to booster third doses. Here, we show that individuals 70 years or older (median age 73, range 70-75) who received a primary two-dose schedule with AZD1222 and booster third dose with mRNA vaccine achieve significantly lower neutralizing antibody responses against SARS-CoV-2 spike pseudotyped virus compared with those younger than 70 (median age 66, range 54-69) at 1 month post booster. Impaired neutralization potency and breadth post third dose in the elderly is associated with circulating "atypical" spike-specific B cells expressing CD11c and FCRL5. However, when considering individuals who received three doses of mRNA vaccine, we did not observe differences in neutralization or enrichment in atypical B cells. This work highlights the finding that AdV and mRNA COVID-19 vaccine formats differentially instruct the memory B cell response.

Spatial dysregulation of T follicular helper cells impairs vaccine responses in aging

The magnitude and quality of the germinal center (GC) response decline with age, resulting in poor vaccine-induced immunity in older individuals. A functional GC requires the co-ordination of multiple cell types across time and space, in particular across its two functionally distinct compartments: the light and dark zones. In aged mice, there is CXCR4-mediated mislocalization of T follicular helper (TFH) cells to the dark zone and a compressed network of follicular dendritic cells (FDCs) in the light zone. Here we show that TFH cell localization is critical for the quality of the antibody response and for the expansion of the FDC network upon immunization. The smaller GC and compressed FDC network in aged mice were corrected by provision of TFH cells that colocalize with FDCs using CXCR5. This demonstrates that the age-dependent defects in the GC response are reversible and shows that TFH cells support stromal cell responses to vaccines.

Severe respiratory viral infections: T-cell functions diverging from immunity to inflammation

Respiratory viral infections such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus (IAV) trigger distinct clinical outcomes defined by immunity-based viral clearance or disease associated with exaggerated and prolonged inflammation. The important role of T cells in shaping both antiviral immunity and inflammation has revived interest in understanding the host-pathogen interactions that lead to the diverse functions of T cells in respiratory viral infections. Inborn deficiencies and acquired insufficiency in immunity can prolong infection and shift the immune response towards exacerbated inflammation, which results from persistent innate immune activation and bystander T-cell activation that is nonspecific to the pathogen but is often driven by cytokines. This review discusses how virus variants, exposure doses, routes of infection, host genetics, and immune history can modulate the activation and function of T cells, thus influencing clinical outcomes. Knowledge of virus-host interaction can inform strategies to prevent immune dysfunction in respiratory viral infection and help in the treatment of associated diseases.

Targeting the hallmarks of aging to improve influenza vaccine responses in older adults

Age-related declines in immune response pose a challenge in combating diseases later in life. Influenza (flu) infection remains a significant burden on older populations and often results in catastrophic disability in those who survive infection. Despite having vaccines designed specifically for older adults, the burden of flu remains high and overall flu vaccine efficacy remains inadequate in this population. Recent geroscience research has highlighted the utility in targeting biological aging to improve multiple age-related declines. Indeed, the response to vaccination is highly coordinated, and diminished responses in older adults are likely not due to a singular deficit, but rather a multitude of age-related declines. In this review we highlight deficits in the aged vaccine responses and potential geroscience guided approaches to overcome these deficits. More specifically, we propose that alternative vaccine platforms and interventions that target the hallmarks of aging, including inflammation, cellular senescence, microbiome disturbances, and mitochondrial dysfunction, may improve vaccine responses and overall immunological resilience in older adults. Elucidating novel interventions and approaches that enhance immunological protection from vaccination is crucial to minimize the disproportionate effect of flu and other infectious diseases on older adults.

Elevated CD153 Expression on Aged T Follicular Helper Cells is Vital for B cell Responses

Our recent data showed that an aberrant IL-10-producing T follicular helper population (Tfh10) accumulates dramatically with age and is associated with age-related declines in vaccine responsiveness. Through single cell gene expression and chromatin accessibility analysis of IL-10+ and IL-10- memory CD4+ T cells from young and aged mice, we identified increased expression of CD153 on aged Tfh and Tfh10 cells. Mechanistically, we linked inflammaging (increased IL-6 levels) to elevated CD153 expression of Tfh cells through c-Maf. Surprisingly, blockade of CD153 in aged mice significantly reduced their vaccine-driven antibody response, which was associated with decreased expression of ICOS on antigen-specific Tfh cells. Combined, these data show that an IL-6/c-Maf/CD153 circuit is critical for maintaining ICOS expression. Thus, although overall Tfh-mediated B cell responses are reduced in the context of vaccines and aging, our data suggest that elevated expression of CD153 on Tfh cells potentiates the remaining Tfh function in aged mice.

Post-vaccination serum cytokines levels correlate with breakthrough influenza infections

Post-vaccination cytokine levels from 256 young adults who subsequently suffered breakthrough influenza infections were compared with matched controls. Modulation within the immune system is important for eliciting a protective response, and the optimal response differs according to vaccine formulation and delivery. For both inactivated influenza vaccine (IIV) and live attenuated influenza vaccines (LAIV) lower levels of IL-8 were observed in post-vaccination sera. Post-vaccination antibody levels were higher and IFN-γ levels were lower in IIV sera compared to LAIV sera. Subjects who suffered breakthrough infections after IIV vaccination had higher levels of sCD25 compared to the control group. There were differences in LAIV post-vaccination interleukin levels for subjects who subsequently suffered breakthrough infections, but these differences were masked in subjects who received concomitant vaccines. Wide variances, sex-based differences and confounders such as concomitant vaccines thwart the establishment of specific cytokine responses as a correlate of protection, but our results provide real world evidence that the status of the immune system following vaccination is important for successful vaccination and subsequent protection against disease.

The memory B cell response to influenza vaccination is impaired in older persons

Influenza infection imparts an age-related increase in mortality and morbidity. The most effective countermeasure is vaccination; however, vaccines offer modest protection in older adults. To investigate how aging impacts the memory B cell response, we track hemagglutinin-specific B cells by indexed flow sorting and single-cell RNA sequencing (scRNA-seq) in 20 healthy adults that were administered the trivalent influenza vaccine. We demonstrate age-related skewing in the memory B cell compartment 6 weeks after vaccination, with younger adults developing hemagglutinin-specific memory B cells with an FcRL5+ "atypical" phenotype, showing evidence of somatic hypermutation and positive selection, which happened to a lesser extent in older persons. We use publicly available scRNA-seq from paired human lymph node and blood samples to corroborate that FcRL5+ atypical memory B cells can derive from germinal center (GC) precursors. Together, this study shows that the aged human GC reaction and memory B cell response following vaccination is defective.

Identification of aging-associated immunotypes and immune stability as indicators of post-vaccination immune activation

Immunosenescence describes immune dysfunction observed in older individuals. To identify individuals at-risk for immune dysfunction, it is crucial to understand the diverse immune phenotypes and their intrinsic functional capabilities. We investigated immune cell subsets and variation in the aging population. We observed that inter-individual immune variation was associated with age and cytomegalovirus seropositivity. Based on the similarities of immune subset composition among individuals, we identified nine immunotypes that displayed different aging-associated immune signatures, which explained inter-individual variation better than age. Additionally, we correlated the immune subset composition of individuals over approximately a year as a measure of stability of immune parameters. Immune stability was significantly lower in immunotypes that contained aging-associated immune subsets and correlated with a circulating CD38 + CD4+ T follicular helper cell increase 7 days after influenza vaccination. In conclusion, immune stability is a feature of immunotypes and could be a potential indicator of post-vaccination cellular kinetics.

B cell-intrinsic changes with age do not impact antibody-secreting cell formation but delay B cell participation in the germinal centre reaction

Vaccines typically protect against (re)infections by generating pathogen-neutralising antibodies. However, as we age, antibody-secreting cell formation and vaccine-induced antibody titres are reduced. Antibody-secreting plasma cells differentiate from B cells either early post-vaccination through the extrafollicular response or from the germinal centre (GC) reaction, which generates long-lived antibody-secreting cells. As the formation of both the extrafollicular antibody response and the GC requires the interaction of multiple cell types, the impaired antibody response in ageing could be caused by B cell intrinsic or extrinsic factors, or a combination of the two. Here, we show that B cells from older people do not have intrinsic defects in their proliferation and differentiation into antibody-secreting cells in vitro compared to those from the younger donors. However, adoptive transfer of B cells from aged mice to young recipient mice showed that differentiation into extrafollicular plasma cells was favoured at the expense of B cells entering the GC during the early stages of GC formation. In contrast, by the peak of the GC response, GC B cells derived from the donor cells of aged mice had expanded to the same extent as those from the younger donors. This indicates that age-related intrinsic B cell changes delay the GC response but are not responsible for the impaired antibody-secreting response or smaller peak GC response in ageing. Collectively, this study shows that B cells from aged individuals are not intrinsically defective in responding to stimulation and becoming antibody-secreting cells, implicating B cell-extrinsic factors as the primary cause of age-associated impairment in the humoral immunity.

The pre-exposure SARS-CoV-2-specific T cell repertoire determines the quality of the immune response to vaccination

SARS-CoV-2 infection and vaccination generates enormous host-response heterogeneity and an age-dependent loss of immune-response quality. How the pre-exposure T cell repertoire contributes to this heterogeneity is poorly understood. We combined analysis of SARS-CoV-2-specific CD4⁺ T cells pre- and post-vaccination with longitudinal T cell receptor tracking. We identified strong pre-exposure T cell variability that correlated with subsequent immune-response quality and age. High-quality responses, defined by strong expansion of high-avidity spike-specific T cells, high interleukin-21 production, and specific immunoglobulin G, depended on an intact naive repertoire and exclusion of pre-existing memory T cells. In the elderly, T cell expansion from both compartments was severely compromised. Our results reveal that an intrinsic defect of the CD4⁺ T cell repertoire causes the age-dependent decline of immune-response quality against SARS-CoV-2 and highlight the need for alternative strategies to induce high-quality T cell responses against newly arising pathogens in the elderly.

The dark side of Tregs during aging

In the last century, we have seen a dramatic rise in the number of older persons globally, a trend known as the grey (or silver) tsunami. People live markedly longer than their predecessors worldwide, due to remarkable changes in their lifestyle and in progresses made by modern medicine. However, the older we become, the more susceptible we are to a series of age-related pathologies, including infections, cancers, autoimmune diseases, and multi-morbidities. Therefore, a key challenge for our modern societies is how to cope with this fragile portion of the population, so that everybody could have the opportunity to live a long and healthy life. From a holistic point of view, aging results from the progressive decline of various systems. Among them, the distinctive age-dependent changes in the immune system contribute to the enhanced frailty of the elderly. One of these affects a population of lymphocytes, known as regulatory T cells (Tregs), as accumulating evidence suggest that there is a significant increase in the frequency of these cells in secondary lymphoid organs (SLOs) of aged animals. Although there are still discrepancies in the literature about modifications to their functional properties during aging, mounting evidence suggests a detrimental role for Tregs in the elderly in the context of bacterial and viral infections by suppressing immune responses against non-self-antigens. Interestingly, Tregs seem to also contribute to the reduced effectiveness of immunizations against many pathogens by limiting the production of vaccine-induced protective antibodies. In this review, we will analyze the current state of understandings about the role of Tregs in acute and chronic infections as well as in vaccination response in both humans and mice. Lastly, we provide an overview of current strategies for Treg modulation with potential future applications to improve the effectiveness of vaccines in older individuals.

Targeting TFH cells in human diseases and vaccination: rationale and practice

The identification of CD4⁺ T cells localizing to B cell follicles has revolutionized the knowledge of how humoral immunity is generated. Follicular helper T (T_FH) cells support germinal center (GC) formation and regulate clonal selection and differentiation of memory and antibody-secreting B cells, thus controlling antibody affinity maturation and memory. T_FH cells are essential in sustaining protective antibody responses necessary for pathogen clearance in infection and vaccine-mediated protection. Conversely, aberrant and excessive T_FH cell responses mediate and sustain pathogenic antibodies to autoantigens, alloantigens, and allergens, facilitate lymphomagenesis, and even harbor viral reservoirs. T_FH cell generation and function are determined by T cell antigen receptor (TCR), costimulation, and cytokine signals, together with specific metabolic and survival mechanisms. Such regulation is crucial to understanding disease pathogenesis and informing the development of emerging therapies for disease or novel approaches to boost vaccine efficacy.

Targeting TLR4 during vaccination boosts MAdCAM-1+ lymphoid stromal cell activation and promotes the aged germinal center response

The failure to generate enduring humoral immunity after vaccination is a hallmark of advancing age. This can be attributed to a reduction in the germinal center (GC) response, which generates long-lived antibody-secreting cells that protect against (re)infection. Despite intensive investigation, the primary cellular defect underlying impaired GCs in aging has not been identified. Here, we used heterochronic parabiosis to demonstrate that GC formation was dictated by the age of the lymph node (LN) microenvironment rather than the age of the immune cells. Lymphoid stromal cells are a key determinant of the LN microenvironment and are also an essential component underpinning GC structure and function. Using mouse models, we demonstrated that mucosal adressin cell adhesion molecule-1 (MAdCAM-1)-expressing lymphoid stromal cells were among the first cells to respond to NP-KLH + Alum immunization, proliferating and up-regulating cell surface proteins such as podoplanin and cell adhesion molecules. This response was essentially abrogated in aged mice. By targeting TLR4 using adjuvants, we improved the MAdCAM-1+ stromal cell response to immunization. This correlated with improved GC responses in both younger adult and aged mice, suggesting a link between stromal cell responses to immunization and GC initiation. Using bone marrow chimeras, we also found that MAdCAM-1+ stromal cells could respond directly to TLR4 ligands. Thus, the age-associated defect in GC and stromal cell responses to immunization can be targeted to improve vaccines in older people.

Systems analysis shows a role of cytophilic antibodies in shaping innate tolerance to malaria

Natural immunity to malaria develops over time with repeated malaria episodes, but protection against severe malaria and immune regulation limiting immunopathology, called tolerance, develops more rapidly. Here, we comprehensively profile the blood immune system in patients, with or without prior malaria exposure, over 1 year after acute symptomatic Plasmodium falciparum malaria. Using a data-driven analysis approach to describe the immune landscape over time, we show that a dampened inflammatory response is associated with reduced γδ T cell expansion, early expansion of CD16⁺ monocytes, and parasite-specific antibodies of IgG1 and IgG3 isotypes. This also coincided with reduced parasitemia and duration of hospitalization. Our data indicate that antibody-mediated phagocytosis during the blood stage infection leads to lower parasitemia and less inflammatory response with reduced γδ T cell expansion. This enhanced control and reduced inflammation points to a potential mechanism on how tolerance is established following repeated malaria exposure.

Primary immune responses are negatively impacted by persistent herpesvirus infections in older people: results from an observational study on healthy subjects and a vaccination trial on subjects aged more than 70 years old

Background

Advanced age is accompanied by a decline of immune functions, which may play a role in increased vulnerability to emerging pathogens and low efficacy of primary vaccinations in elderly people. The capacity to mount immune responses against new antigens is particularly affected in this population. However, its precise determinants are not fully understood. We aimed here at establishing the influence of persistent viral infections on the naive T-cell compartment and primary immune responsiveness in older adults.

Methods

We assessed immunological parameters, related to CD8⁺ and CD4⁺ T-cell responsiveness, according to the serological status for common latent herpesviruses in two independent cohorts: 1) healthy individuals aged 19y to 95y (n = 150) and 2) individuals above 70y old enrolled in a primo-vaccination clinical trial (n = 137).

Findings

We demonstrate a prevalent effect of age and CMV infection on CD8⁺ and CD4⁺ naive T cells, respectively. CMV seropositivity was associated with blunted CD4⁺ T-cell and antibody responses to primary vaccination.

Interpretation

These data provide insights on the changes in adaptive immunity over time and the associated decline in vaccine efficacy with ageing. This knowledge is important for the management of emerging infectious diseases in elderly populations.

T follicular helper cells and their impact on humoral responses during pathogen and vaccine challenge

T follicular helper (Tfh) cells are essential for the establishment, maintenance and output of the germinal centre (GC) response. The transient nature of this response, and its location within secondary lymphoid tissues have hampered our understanding of this critical cell type, particularly in humans. A counterpart of GC Tfh cells in peripheral blood has enabled recent discoveries in disease and vaccination settings, while direct sampling of lymph nodes provides exciting new avenues to study GC responses directly in vivo. Tfh differentiation is shaped by the cytokine milieu during inflammation, vaccination and with age, and disease-specific patterns are emerging. An improved understanding of how to support a Tfh response remains key to enhancing vaccine immunity across the lifespan.