AID activity in B cells strongly correlates with polyclonal antibody affinity maturation in-vivo following pandemic 2009-H1N1 vaccination in humans

High-Affinity H7 Head and Stalk Domain-Specific Antibody Responses to an Inactivated Influenza H7N7 Vaccine After Priming With Live Attenuated Influenza Vaccine

Recent studies have shown that live attenuated influenza vaccines (LAIVs) expressing avian influenza virus hemagglutinins (HAs) prime for strong protective antibody responses to an inactivated influenza vaccine (IIV) containing the HA. To better understand this priming effect, we compared H7 HA head and stalk domain-specific B-cell responses in H7N7 LAIV-primed subjects and non-H7-primed controls after a single dose of H7N7 IIV. As previously reported, H7N7 LAIV-primed subjects but not control subjects generated strong hemagglutination-inhibiting and neutralizing antibody responses to the H7N7 IIV. Here, we found that the quantity, epitope diversity, and affinity of H7 head-specific antibodies increased rapidly in only H7N7 LAIV-primed subjects after receipt of the IIV. However, all cohorts generated a vigorous, high-affinity, stalk-specific antibody response. Consistent increases in circulating memory B-cell frequencies after receipt of the IIV reflected the specificity of high-affinity antibody production. Our findings emphasize the value of LAIVs as a vehicle for prepandemic vaccination.

Waning and aging of cellular immunity to Bordetella pertussis

While it is clear that the maintenance of Bordetella pertussis-specific immunity evoked both after vaccination and infection is insufficient, it is unknown at which pace waning occurs and which threshold levels of sustained functional memory B and T cells are required to provide long-term protection. Longevity of human cellular immunity to B. pertussis has been studied less extensively than serology, but is suggested to be key for the observed differences between the duration of protection induced by acellular vaccination and whole cell vaccination or infection. The induction and maintenance of levels of protective memory B and T cells may alter with age, associated with changes of the immune system throughout life and with accumulating exposures to circulating B. pertussis or vaccine doses. This is relevant since pertussis affects all age groups. This review summarizes current knowledge on the waning patterns of human cellular immune responses to B. pertussis as addressed in diverse vaccination and infection settings and in various age groups. Knowledge on the effectiveness and flaws in human B. pertussis-specific cellular immunity ultimately will advance the improvement of pertussis vaccination strategies.

MicroRNAs miR-155 and miR-16 Decrease AID and E47 in B Cells from Elderly Individuals

Our research in the past few years has identified B cell-specific biomarkers able to predict optimal Ab responses in both young and elderly individuals. These biomarkers are activation-induced cytidine deaminase (AID), the enzyme of class switch recombination and somatic hypermutation; the transcription factor E47, crucial for AID expression; and the ability to generate optimal memory B cells. Moreover, we have found that the increased proinflammatory status of the elderly, both in sera and intrinsic to B cells, negatively impacts B cell function. We have now investigated whether particular inflammatory microRNAs (miRs) contribute to decreased E47 and AID in aged B cells. Our data indicate that E47 and AID mRNA stability is lower in stimulated B cells from elderly individuals. We measured the expression of two miRs crucial for class switch recombination, miR-155 and miR-16, in human unstimulated B cells from young and elderly individuals with the rationale that increases in these before stimulation would decrease E47/AID upon cell activation. We found these miRs and B cell-intrinsic inflammation upregulated in aged unstimulated B cells and negatively associated with AID in the same B cells after stimulation with CpG. We propose that the downregulation of AID in aged human B cells may occur through binding of miR-155 to the 3'-untranslated regions of AID mRNA and/or binding of miR-16 to the 3'-untranslated regions of E47 mRNA, as well as at the transcriptional level of less E47 for AID. Our results indicate novel molecular pathways leading to reduced B cell function with aging.

Seeking help: B cells adapting to flu variability

The study of influenza vaccines has revealed potential interactions between preexisting immunological memory and antigenic context and/or adjuvantation. In the face of antigenic diversity, the process of generating B cell adaptability is driven by cross-reactive CD4 memory cells, such as T follicular helper cells from previous infections or vaccinations. Although such "helped" B cells are capable of adapting to variant antigens, lack of CD4 help could lead to a suboptimal antibody response. Collectively, this indicates an interplay between CD4 T cells, adjuvant, and B cell adaptability.

Cytomegalovirus (CMV) seropositivity decreases B cell responses to the influenza vaccine

Cytomegalovirus (CMV)-seropositivity has been shown to have a negative effect on influenza vaccine-specific antibody responses. In this paper, we confirm and extend these results showing for the first time, a negative association between CMV-seropositivity and B cell predictive biomarkers of optimal vaccine responses. These biomarkers are switched memory B cells and AID in CpG-stimulated B cell cultures measured before vaccination which positively correlate with the serum response to the influenza vaccine. We also found that CMV-seropositivity is associated with increased levels of B cell-intrinsic inflammation and these both correlate with lower B cell function. Finally, CMV-seropositivity is associated with decreased percentages of individuals responding to the vaccine in both young and elderly individuals.

Oral priming with replicating adenovirus serotype 4 followed by subunit H5N1 vaccine boost promotes antibody affinity maturation and expands H5N1 cross-clade neutralization

A Phase I trial conducted in 2009-2010 demonstrated that oral vaccination with a replication competent Ad4-H5 (A/Vietnam) vector with dosages ranging from 107-1011 viral particles was well tolerated. HA-specific T-cell responses were efficiently induced, but very limited hemagglutination-inhibiting (HI) humoral responses were measured. However, a single boost of Ad4-H5-Vtn vaccinated individuals with a unadjuvanted licensed H5N1 (A/Vietnam) subunit vaccine resulted in superior HI titers compared with unprimed subjects. In the current study, the impact of Ad4-H5 priming on the quality of the polyclonal humoral immune response was evaluated using a real-time kinetics assay by surface plasmon resonance (SPR). Total binding of serum polyclonal antibodies from the Ad4-H5-Vtn primed groups against both homologous H5N1-A/Vietnam/1194/2004 (clade 1) and heterologous A/Indonesia-5/2005 (clade 2.1) HA1 head domain was significantly higher compared with sera from individuals that received subunit H5N1 vaccination alone. SPR measurements also demonstrated that the antigen-antibody complex dissociation rates (a surrogate for antibody affinity) of serum antibodies against the HA1 of H5N1-A/Vietnam were significantly higher in the Ad4-H5 primed groups compared with those from the unprimed group. Furthermore, strong correlations were observed between the antibody affinities for HA1 (but not HA2) and the virus neutralization titers against the homologous strain and a panel of heterologous clade 2 H5N1 strains. These findings support the concept of oral prime-boost vaccine approaches against pandemic influenza to elicit long-term memory B cells with high affinity capable of rapid response to variant pandemic viruses likely to emerge and adapt to human transmissions.

Activation-Induced Cytidine Deaminase and Switched Memory B Cells as Predictors of Effective In Vivo Responses to the Influenza Vaccine

Aging impairs humoral immune responses, leading to increased frequency and severity of infectious diseases and reduced protective effects of vaccination. We have identified B-cell biomarkers that are reduced by aging and that can be used as predictive markers of the response of an individual to vaccination. The identification of these biomarkers will have an impact on the development of effective vaccines to protect the elderly from infections and other debilitating diseases.

CD25(+) Bcl6(low) T follicular helper cells provide help to maturing B cells in germinal centers of human tonsil

The majority of CXCR5(+) PD1(+) CD4(+) T follicular helper (Tfh) cells (>90%) are CD25(-) Bcl6(hi) , while a small subpopulation (<10%) are CD25(+) Bcl6(low) but do not express FoxP3 and are not T regulatory cells. We purified T:B-cell conjugates from tonsils and found they were enriched for the CD25(+) Bcl6(low) Tfh-cell subpopulation. In response to IL-2, these CD25(+) Tfh cells increased expression of costimulatory molecules ICOS or OX40, upregulated transcription factor cMaf, produced cytokines IL-21, IL-17, and IL-10, and raised the levels of antiapoptotic protein Bcl2. Conjugates formed with CD25(+) BCl6(low) Tfh cells included B cells expressing higher levels of activation-induced cytidine deaminase (AID), memory marker CD45RO, surface IgG or IgA, and MHC class II compared to B-cell conjugates including CD25(-) Bcl6(hi) Tfh cells. While IL-2 suppresses early Tfh-cell differentiation, Tfh-cell recognition of antigen-presenting B cells and signaling through the T-cell receptor likely triggers expression of the high-affinity IL-2 receptor and responses to IL-2 including downregulation of Bcl6. CD25 expression on Tfh cells and local production of IL-2 in tonsil or lymph node may support B helper T-cell function during later stages of B-cell maturation and the development of immune memory.

B cell function and influenza vaccine responses in healthy aging and disease

Influenza vaccination is less effective in elderly as compared to young individuals. Several studies have addressed the identification of immune biomarkers able to monitor or predict a protective humoral immune response to the vaccine. In this review, we summarize these data, with emphasis on the effects of aging on influenza vaccine-specific B cell responses in healthy individuals and patients with Type-2 Diabetes, HIV and cardiovascular diseases.

Age effects on mouse and human B cells

Our laboratory has contributed to the areas of B cell receptor (BCR) and pre-BCR gene identification and transcription and has focused on the problem of the aged immune system in mice and humans for the last 15 years. We have found biomarkers for the decrease in B cell function in aged mice and humans. These include decreases in immunoglobulin (Ig) class switch (e.g., IgM to IgG), decreases in the enzyme AID (activation-induced cytidine deaminase) and decreases in the transcription factor E47. The E47 mRNA stability is decreased in old B cells due to decreased phospho-MAPKinase and phospho-TTP (tristetraprolin). Inflammation, e.g., TNF-α, which increases with age, impacts B cells directly by increasing their TNF-α and NF-κB and leads to the above decreased pathway. Both class switch and affinity maturation are decreased in elderly responses to the influenza vaccine and biomarkers we have found (numbers and percentages of switched memory B cells and AID in stimulated B cells in culture) can predict a beneficial or decreased immune response to the vaccine. Current and future avenues to improve the humoral immune response in the elderly are discussed.

Early highly active antiretroviral therapy enhances B-cell longevity: a 5 year follow up

BACKGROUND

We have previously reported that an early initiation of highly active antiretroviral therapy (HAART) in HIV-1 vertically infected children enhanced the function of memory B-cells gained during childhood routine vaccinations. On the other hand, a significant waning of immunity was observed for patients with a late treatment. In this follow-up study, we report data from a sample of patients in our cohort including late-treated patients being revaccinated with routine childhood vaccines.

METHODS

The levels of serum antibodies and cellular immunity were measured by antigen-specific enzyme-linked immunosorbent assay and B-cell ELISpot. Moreover, flow cytometry on the frequencies of mature-activated (CD10-CD21-) and double-negative (CD27-IgD-) B-cells as hallmarks of immune activation and immune senescence, respectively, was performed for all patients.

RESULTS

Reduced protective humoral immunity and cellular immunity to routine childhood vaccines was observed in late-treated patients. Moreover, we found that timing of HAART related with the frequencies of mature activated and double negative.

CONCLUSIONS

Altogether the data presented in this follow-up study reenforce the importance for an early start of HAART in HIV-1 vertically infected individuals and suggest that timing of HAART is a fundamental factor to take into account for vaccination design in this population.

Heterologous prime-boost vaccination with MF59-adjuvanted H5 vaccines promotes antibody affinity maturation towards the hemagglutinin HA1 domain and broad H5N1 cross-clade neutralization

In an open label clinical study (2007), MF59-adjuvanted hemagglutinin (HA) vaccine from H5N1-A/Vietnam/1194/2004 (clade 1) was administered to subjects previously vaccinated (primed) with clade 0 H5N3 (A/duck/Singapore/97) vaccine at least 6 years earlier (in 1999 or 2001). The primed individuals responded rapidly and generated high neutralizing antibody titers against the H5N1-Vietnam strain within 7 days of a single booster vaccination. Furthermore, significant cross-neutralization titers were measured against H5N1 clade 0, 1, and 2 viruses. In the current study, the impact of MF59 adjuvant during heterologous priming on the quality of humoral polyclonal immune response in different vaccine arms were further evaluated using real time kinetics assay by surface plasmon resonance (SPR). Total anti-H5N1 HA1 polyclonal sera antibody binding from the heterologous prime-boost groups after a single MF59-H5N1 boost was significantly higher compared with sera from unprimed individuals that received two MF59-H5N1 vaccinations. The antigen-antibody complex dissociation rates (surrogate for antibody affinity) of the polyclonal sera against HA1 of H5N1-A/Vietnam/1194/2004 from the MF59-H5N3 primed groups were significantly higher compared to sera from unadjuvanted primed groups or unprimed individuals that received two MF59-H5N1 vaccines. Furthermore, strong inverse correlations were observed between the antibody dissociation off-rates of the immune sera against HA1 (but not HA2) and the virus neutralization titers against H5 vaccine strains and heterologous H5N1 strains. These findings supports the use of oil-in-water-adjuvanted pandemic influenza vaccines to elicit long term memory B cells with high affinity BCR capable of responding to potential variant pandemic viruses likely to emerge and adapt to human transmissions.

High TNF-α levels in resting B cells negatively correlate with their response

Aging significantly decreases the influenza vaccine-specific response as we and others have previously shown. Based on our previous data in aged mice, we hypothesize that the inflammatory status of the individual and of B cells themselves would impact B cell function. We here show that the ability to generate a vaccine-specific antibody response is negatively correlated with levels of serum TNF-α. Moreover, human unstimulated B cells from elderly make higher levels of TNF-α than those from young individuals, and these positively correlate with serum TNF-α levels. These all negatively correlate with B cell function, measured by activation-induced cytidine deaminase, the enzyme of class switch recombination and somatic hypermutation. Only memory B cells (either IgM or switched), but not naïve B cells, make appreciable levels of TNF-α and more in elderly as compared to young individuals. Finally, an anti-TNF-α antibody can increase the response in cultured B cells from the elderly, suggesting that TNF-α secreted by memory B cells affects IgM memory B cells and naïve B cells in an autocrine and/or paracrine manner. Our results show an additional mechanism for reduced B cell function in the elderly and propose B cell-derived TNF-α as another predictive biomarker of in vivo and in vitro B cell responses.

Age related differences in dynamics of specific memory B cell populations after clinical pertussis infection

For a better understanding of the maintenance of immune mechanisms to Bordetella pertussis (Bp) in relation to age, we investigated the dynamic range of specific B cell responses in various age-groups at different time points after a laboratory confirmed pertussis infection. Blood samples were obtained in a Dutch cross sectional observational study from symptomatic pertussis cases. Lymphocyte subpopulations were phenotyped by flowcytometry before and after culture. Memory B (B_mem) cells were differentiated into IgG antibody secreting cells (ASC) by polyclonal stimulation and detected by an ELISPOT assay specific for pertussis antigens pertussis toxin (Ptx), filamentous haemagglutinin (FHA) and pertactin (Prn). Bp antigen specific IgG concentrations in plasma were determined using multiplex technology. The majority of subjects having experienced a clinical pertussis episode demonstrated high levels of both Bp specific IgG and B_mem cell levels within the first 6 weeks after diagnosis. Significantly lower levels were observed thereafter. Waning of cellular and humoral immunity to maintenance levels occurred within 9 months after antigen encounter. Age was found to determine the maximum but not base-line frequencies of B_mem cell populations; higher levels of B_mem cells specific for Ptx and FHA were reached in adults and (pre-) elderly compared to under-fours and schoolchildren in the first 6 weeks after Bp exposure, whereas not in later phases. This age effect was less obvious for specific IgG levels. Nonetheless, subjects' levels of specific B_mem cells and specific IgG were weakly correlated. This is the first study to show that both age and closeness to last Bp encounter impacts the size of Bp specific B_mem cell and plasma IgG levels.

Memory B cells form in aged mice despite impaired affinity maturation and germinal center kinetics

We examined whether age alters the emergence of high-affinity germinal center B (GCB) cells and switched memory B cells (swBmem) during a primary immune response to a thymus-dependent antigen, using a novel flow cytometric assay to distinguish relative BCR affinity. In young mice, high-affinity B cells predominate in the GCB pool and comprise a smaller proportion of the nascent swBmem pool two weeks after immunization. In aged mice, we observe significant reductions of high-affinity clones among GCB cells, but not nascent swBmem cells. The defect in GC affinity maturation was not overcome by providing excess carrier-specific T cells from young mice, as these cells still displayed compromised effector TFH differentiation in the aged animals. Our results suggest that B cells in aged animals have a reduced ability to prompt effector TFH differentiation, leading to a compromised GC response that results in reduced generation of high-affinity GCB and plasma cells; despite normal production of early swBmem cells.

Premature B-cell senescence as a consequence of chronic immune activation

Similar features between the immune system of healthy elderly people and of younger individuals subjected to conditions of chronic immune activation are progressively being observed. This is raising the hypothesis that chronic immune activation may cause the premature aging of the immune system. Here we dissect this theory by comparing changes occurring to B-cells during healthy aging to the ones occurring during chronic immune activation in younger individuals. Moreover, we discuss how these changes may affect or predict response to vaccination in immune compromised individuals.

The kinase mTOR modulates the antibody response to provide cross-protective immunity to lethal infection with influenza virus

Highly pathogenic avian influenza viruses pose a continuing global threat. Current vaccines will not protect against newly evolved pandemic viruses. The creation of 'universal' vaccines has been unsuccessful because the immunological mechanisms that promote heterosubtypic immunity are incompletely defined. We found here that rapamycin, an immunosuppressive drug that inhibits the kinase mTOR, promoted cross-strain protection against lethal infection with influenza virus of various subtypes when administered during immunization with influenza virus subtype H3N2. Rapamycin reduced the formation of germinal centers and inhibited class switching in B cells, which yielded a unique repertoire of antibodies that mediated heterosubtypic protection. Our data established a requirement for the mTORC1 complex in B cell class switching and demonstrated that rapamycin skewed the antibody response away from high-affinity variant epitopes and targeted more conserved elements of hemagglutinin. Our findings have implications for the design of a vaccine against influenza virus.

Perspectives on vaccine development for the elderly

Modern society is characterized by a steady increase in the aged population. Increasing numbers of elderly people are exposed to infectious diseases in addition to suffering from chronic non-communicable illnesses. Key differences exist between immune responses elicited against infectious agents in the elderly and in the youngest population. Responses in the aged are characterized by a physiological state of impaired immunity. Such state has forced scientist and vaccine manufacturers to re-think the way vaccines are designed and tested in the elderly. Multiple strategies have been used to overcome the consequences of immunosenescence including the use of higher antigen dose, adjuvanted vaccines, and alternative routes of immunization. However, the lack of understanding of the immune regulatory mechanisms underlying immunosenescence in the elderly represents one of the main hurdles in the pathway to produce effective vaccines for seniors. This article reviews in a succinct form the current state of the art on the development of vaccines for the elderly and critically assesses the past and current literature on this topic, while also proposing new avenues for future studies.

A comparative review of aging and B cell function in mice and humans

Immune system function declines with age. Here we review and compare age-associated changes in murine and human B cell pools and humoral immune responses. We summarize changes in B cell generation and homeostasis, as well as notable changes at the subcellular level; then discuss how these changes help to explain alterations in immune responses across the adult lifespan of the animal. In each section we compare and contrast findings in the mouse, arguably the best animal model of the aging immune system, with current understanding of B cell immunity in humans.

Age-associated cross-reactive antibody-dependent cellular cytotoxicity toward 2009 pandemic influenza A virus subtype H1N1

BACKGROUND

During the 2009 pandemic of influenza A virus subtype H1N1 (A[H1N1]pdm09) infection, older individuals were partially protected from severe disease. It is not known whether preexisting antibodies with effector functions such as antibody-dependent cellular cytotoxicity (ADCC) contributed to the immunity observed.

METHODS

We tested serum specimens obtained from 182 individuals aged 1-72 years that were collected either immediately before or after the A(H1N1)pdm09 pandemic for ADCC antibodies to the A(H1N1)pdm09 hemagglutinin (HA) protein.

RESULTS

A(H1N1)pdm09 HA-specific ADCC antibodies were detected in almost all individuals aged >45 years (28/31 subjects) before the 2009 A(H1N1) pandemic. Conversely, only approximately half of the individuals aged 1-14 years (11/31) and 15-45 years (17/31) had cross-reactive ADCC antibodies before the 2009 A(H1N1) pandemic. The A(H1N1)pdm09-specific ADCC antibodies were able to efficiently mediate the killing of influenza virus-infected respiratory epithelial cells. Further, subjects >45 years of age had higher ADCC titers to a range of seasonal H1N1 HA proteins, including from the 1918 virus, compared with younger individuals.

CONCLUSIONS

ADCC antibodies may have contributed to the protection exhibited in older individuals during the 2009 A(H1N1) pandemic. This work has significant implications for improved vaccination strategies for future influenza pandemics.

Young and elderly patients with type 2 diabetes have optimal B cell responses to the seasonal influenza vaccine

We evaluated immune response to the seasonal influenza vaccine in young and elderly patients with type 2 diabetes (T2D). Immune measures included the in vivo serum response to the vaccine by hemagglutination inhibition (HAI) and ELISA in 22 patients (14 young, 8 elderly) and 65 healthy age-matched controls (37 young, 28 elderly). B cell-specific biomarkers of optimal vaccine response were measured ex vivo by switched memory B cells and plasmablasts and in vitro by activation-induced cytidine deaminase (AID) in stimulated cells. Markers of systemic and B cell-intrinsic inflammation were also measured. Results show that in vivo responses, as well as B cell-specific markers identified above, decrease by age in healthy individuals but not in T2D patients. This occurred despite high levels of B cell-intrinsic inflammation (TNF-α) in T2D patients, which was surprising as we had previously demonstrated this negatively impacts B cell function. These results altogether suggest that valid protection against influenza can be achieved in T2D patients and proposed mechanisms are discussed.

Effects of age on H1N1-specific serum IgG1 and IgG3 levels evaluated during the 2011-2012 influenza vaccine season

BACKGROUND

We have previously reported an age-related impairment in the serum antibody response to pandemic (p)2009 H1N1, measured by hemagglutination inhibition assay and ELISA. The present study extends these observations and evaluates IgG subclass distribution in healthy individuals of different ages vaccinated during the 2011-2012 season.

RESULTS

The 2011-2012 vaccination season was characterized by a vaccine containing the pandemic (p)2009 H1N1 strain for the third consecutive year. All of our subjects were previously immunized, and therefore seroprotected at t0. Nevertheless, aging impaired the serum antibody response to H1N1, as antibody titers increased after vaccination in young and less in elderly individuals. The peak of the response was at day 7 (t7), in contrast with what is usually seen at day 21-28, suggesting a memory response characterized by the induction of an IgG subclass with a shorter half-life. We hypothesized that the IgG3 response, with its much shorter half-life, might be more represented. Antibodies were predominantly of the IgG1 subclass in both age groups, although a robust IgG3 response was also induced and accounted for a significant proportion of the overall response. IgG2 and IgG4 antibodies were at indiscernible levels. We showed a much higher percentage of IgG3 (40-50%) than previously in the literature (less than 10%). To explain if this was associated with a particular cytokine profile, we measured H1N1-induced T cell cytokines in vitro and found that IgG3 levels were positively correlated with TNF-α and IL-6. Moreover, activation-induced cytidine deaminase (AID) mRNA expression, a predictive biomarker of optimal in vivo vaccine response, was found to significantly correlate with IgG3 and also with IgG1 similar to what we have shown previously for total IgG.

CONCLUSIONS

In the 2011-2012 season, the pandemic (p)2009 H1N1 strain was present in the vaccine for the third consecutive year and therefore each individual was seroprotected at t0. The peak of the response was at t7, suggesting a memory response characterized by a robust induction of IgG3, which was associated with TNF-α and IL-6 production. Both IgG1 and IgG3 responses were decreased by age. AID was confirmed to be a predictive biomarker of optimal vaccine responses.

Understanding immunosenescence to improve responses to vaccines

In the older adult, the benefits of vaccination to prevent infectious disease are limited, mainly because of the adaptive immune system's inability to generate protective immunity. The age-dependent decrease in immunological competence, often referred to as 'immunosenescence', results from the progressive deterioration of innate and adaptive immune responses. Most insights into mechanisms of immunological aging have been derived from studies of mouse models. In this Review, we explore how well such models are applicable to understanding the aging process throughout the 80-100 years of human life and discuss recent advances in identifying and characterizing the mechanisms that underlie age-associated defective adaptive immunity in humans.