Heterologous vaccine effects

Associations of infections and vaccines with Alzheimer's disease point to a role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been associated with Alzheimer's disease (AD) and related traits in various studies. This suggests that compromised immunity, rather than specific microbes, may play a role in AD by increasing an individual's vulnerability to various infections, which could contribute to neurodegeneration. If true, then vaccines that have heterologous effects on immunity, extending beyond protection against the targeted disease, may hold a potential for AD prevention.

METHODS

We evaluated the associations of common adult infections (herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses), and vaccinations against shingles and pneumonia, with the risks of AD and other dementias in a pseudorandomized sample of the Health and Retirement Study (HRS).

RESULTS

Shingles, pneumonia and mycoses, diagnosed between ages 65 and 75, were all associated with significantly increased risk of AD later in life, by 16 %-42 %. Pneumococcal and shingles vaccines administered between ages 65-75 were both associated with a significantly lower risk of AD, by 15 %-21 %. These effects became less pronounced when AD was combined with other dementias.

DISCUSSION

Our findings suggest that both the pneumococcal polysaccharide vaccine and the live attenuated zoster vaccine can offer significant protection against AD. It remains to be determined if non-live shingles vaccine has a similar beneficial effect on AD. This study also found significant associations of various infections with the risk of AD, but not with the risks of other dementias. This indicates that vulnerability to infections may play a more significant role in AD than in other types of dementia, which warrants further investigation.

DNA Vaccines: Their Formulations, Engineering and Delivery

The concept of DNA vaccination was introduced in the early 1990s. Since then, advancements in the augmentation of the immunogenicity of DNA vaccines have brought this technology to the market, especially in veterinary medicine, to prevent many diseases. Along with the successful COVID mRNA vaccines, the first DNA vaccine for human use, the Indian ZyCovD vaccine against SARS-CoV-2, was approved in 2021. In the current review, we first give an overview of the DNA vaccine focusing on the science, including adjuvants and delivery methods. We then cover some of the emerging science in the field of DNA vaccines, notably efforts to optimize delivery systems, better engineer delivery apparatuses, identify optimal delivery sites, personalize cancer immunotherapy through DNA vaccination, enhance adjuvant science through gene adjuvants, enhance off-target and heritable immunity through epigenetic modification, and predict epitopes with bioinformatic approaches. We also discuss the major limitations of DNA vaccines and we aim to address many theoretical concerns.

Associations of infections and vaccines with Alzheimer's disease point to a major role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been linked to Alzheimer's disease (AD) indicating a possibility that the culprit may be compromised immunity rather than particular microbe. If true, then vaccines with broad beneficial effects on immunity might be protective against AD.

METHODS

We estimated associations of common adult infections, including herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses, as well as vaccinations against shingles and pneumonia, with the risk of AD in a pseudorandomized sample of the Health and Retirement Study.

RESULTS

Shingles, pneumonia, and mycoses diagnosed between ages 65-75, were all associated with higher risk of AD later in life, by 16%-42%. Pneumococcal and shingles vaccines received between ages 65-75 both lowered the risk of AD, by 15%-21%.

DISCUSSION

Our results support the idea that the connection between AD and infections involves compromised immunity rather than specific pathogen. We discuss mechanisms by which the declining immune surveillance may promote AD, and the role of biological aging in it. Repurposing of vaccines with broad beneficial effects on immunity could be a reasonable approach to AD prevention. Pneumococcal and zoster vaccines are promising candidates for such repurposing.

Bystander activation of Bordetella pertussis-induced nasal tissue-resident memory CD4 T cells confers heterologous immunity to Klebsiella pneumoniae

Tissue-resident memory CD4 T (T_RM ) cells induced by infection with Bordetella pertussis persist in respiratory tissues and confer long-term protective immunity against reinfection. However, it is not clear how they are maintained in respiratory tissues. Here, we demonstrate that B. pertussis-specific CD4 T_RM cells produce IL-17A in response to in vitro stimulation with LPS or heat-killed Klebsiella pneumoniae (HKKP) in the presence of dendritic cells. Furthermore, IL-17A-secreting CD4 T_RM cells expand in the lung and nasal tissue of B. pertussis convalescent mice following in vivo administration of LPS or HKKP. Bystander activation of CD4 T_RM cells was suppressed by anti-IL-12p40 but not by anti-MHCII antibodies. Furthermore, purified respiratory tissue-resident, but not circulating, CD4 T cells from convalescent mice produced IL-17A following direct stimulation with IL-23 and IL-1β or IL-18. Intranasal immunization of mice with a whole-cell pertussis vaccine induced respiratory CD4 T_RM cells that were reactivated following stimulation with K. pneumoniae. Furthermore, the nasal pertussis vaccine conferred protective immunity against B. pertussis but also attenuated infection with K. pneumoniae. Our findings demonstrate that CD4 T_RM cells induced by respiratory infection or vaccination can undergo bystander activation and confer heterologous immunity to an unrelated respiratory pathogen.

Prophylactic and therapeutic insights into trained immunity: A renewed concept of innate immune memory

Trained immunity is a renewed concept of innate immune memory that facilitates the innate immune system to have the capacity to remember and train cells via metabolic and transcriptional events to enable them to provide nonspecific defense against the subsequent encounters with a range of pathogens and acquire a quicker and more robust immune response, but different from the adaptive immune memory. Reversing the epigenetic changes or targeting the immunological pathways may be considered potential therapeutic approaches to counteract the hyper-responsive or hypo-responsive state of trained immunity. The efficient regulation of immune homeostasis and promotion or inhibition of immune responses is required for a balanced response. Trained immunity-based vaccines can serve as potent immune stimuli and help in the clearance of pathogens in the body through multiple or heterologous effects and confer protection against nonspecific and specific pathogens. This review highlights various features of trained immunity and its applications in developing novel therapeutics and vaccines, along with certain detrimental effects, challenges as well as future perspectives.

The BCG Moreau Vaccine Upregulates In Vitro the Expression of TLR4, B7-1, Dectin-1 and EP2 on Human Monocytes

Background: Tuberculosis (TB) is currently the second greatest killer worldwide and is caused by a single infectious agent. Since Bacillus Calmette−Guérin (BCG) is the only vaccine currently in use against TB, studies addressing the protective role of BCG in the context of inducible surface biomarkers are urgently required for TB control. Methods: In this study, groups of HIV-negative adult healthy donors (HD; n = 22) and neonate samples (UCB; n = 48) were voluntarily enrolled. The BCG Moreau strain was used for the in vitro mononuclear cell infections. Subsequently, phenotyping tools were used for surface biomarker detection. Monocytes were assayed for TLR4, B7-1, Dectin-1, EP2, and TIM-3 expression levels. Results: At 48 h, the BCG Moreau induced the highest TLR4, B7-1, and Dectin-1 levels in the HD group only (p-value < 0.05). TIM-3 expression failed to be modulated after BCG infection. At 72 h, BCG Moreau equally induced the highest EP2 levels in the HD group (p-value < 0.005), and higher levels were also found in HD when compared with the UCB group (p-value < 0.05). Conclusions: This study uncovers critical roles for biomarkers after the instruction of host monocyte activation patterns. Understanding the regulation of human innate immune responses is critical for vaccine development and for treating infectious diseases.

Neonatal Bacillus Calmette-Guérin Vaccination to Prevent Early-Life Eczema: A Systematic Review and Meta-analysis

ABSTRACT

Increasing evidence suggests that early-life bacillus Calmette-Guérin (BCG) vaccine could prevent atopic eczema through its beneficial off-target effects. In this meta-analysis, 3 randomized control trials with similar methods were included and enabled robust estimations with low heterogeneity, involving a total of 5655 children randomized to early-life BCG Denmark (n = 2832) or no BCG (n = 2823). Meta-analyses suggest a beneficial effect of BCG to prevent eczema (risk ratio [RR], 0.89; 95% confidence interval [CI], 0.82-0.98). In subgroup analyses, BCG was more beneficial in boys (RR, 0.84; 95% CI, 0.74-0.95) and in children born to 2 atopic parents (RR, 0.81; 95% CI, 0.68-0.97). The NNT to prevent one case of eczema among children of 1 or 2 atopic parent was 20 (95% CI, 12-50). Bacillus Calmette-Guérin Denmark leads to an 11% reduction in the risk of eczema in early life. A greater effect was observed with increasing predisposition. Given its well-established safety profile, neonatal BCG vaccination should be considered for children of atopic parents.

BCG Vaccination: A potential tool against COVID-19 and COVID-19-like Black Swan incidents

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the coronavirus disease 2019 (COVID-19), and its variants have brought unprecedented impacts to the global public health system, politics, economy, and other fields. Although more than ten COVID-19 specific vaccines have been approved for emergency use, COVID-19 prevention and control still face many challenges. Bacille Calmette–Guérin (BCG) is the only authorized vaccine used to fight against tuberculosis (TB), it has been hypothesized that BCG may prevent and control COVID-19 based on BCG-induced nonspecific immune responses. Herein, we summarized: 1) The nonspecific protection effects of BCG, such as prophylactic protection effects of BCG on nonmycobacterial infections, immunotherapy effects of BCG vaccine, and enhancement effect of BCG vaccine on unrelated vaccines; 2) Recent evidence of BCG's efficacy against SARS-COV-2 infection from ecological studies, analytical analyses, clinical trials, and animal studies; 3) Three possible mechanisms of BCG vaccine and their effects on COVID-19 control including heterologous immunity, trained immunity, and anti-inflammatory effect. We hope that this review will encourage more scientists to investigate further BCG induced non-specific immune responses and explore their mechanisms, which could be a potential tool for addressing the COVID-19 pandemic and COVID-19-like “Black Swan” events to reduce the impacts of infectious disease outbreaks on public health, politics, and economy.

Leveraging Beneficial Off-Target Effects of Live-Attenuated Rotavirus Vaccines

Following the introduction of live-attenuated rotavirus vaccines in many countries, a notable reduction in deaths and hospitalisations associated with diarrhoea in children <5 years of age has been reported. There is growing evidence to suggest that live-attenuated vaccines also provide protection against other infections beyond the vaccine-targeted pathogens. These so called off-target effects of vaccination have been associated with the tuberculosis vaccine Bacille Calmette Guérin (BCG), measles, oral polio and recently salmonella vaccines, and are thought to be mediated by modified innate and possibly adaptive immunity. Indeed, rotavirus vaccines have been reported to provide greater than expected reductions in acute gastroenteritis caused by other enteropathogens, that have mostly been attributed to herd protection and prior underestimation of rotavirus disease. Whether rotavirus vaccines also alter the immune system to reduce non targeted gastrointestinal infections has not been studied directly. Here we review the current understanding of the mechanisms underlying off-target effects of vaccines and propose a mechanism by which the live-attenuated neonatal rotavirus vaccine, RV3-BB, could promote protection beyond the targeted pathogen. Finally, we consider how vaccine developers may leverage these properties to improve health outcomes in children, particularly those in low-income countries where disease burden and mortality is disproportionately high relative to developed countries.

Vaccine-Induced Cellular Immunity against Bordetella pertussis: Harnessing Lessons from Animal and Human Studies to Improve Design and Testing of Novel Pertussis Vaccines

Pertussis ('whooping cough') is a severe respiratory tract infection that primarily affects young children and unimmunised infants. Despite widespread vaccine coverage, it remains one of the least well-controlled vaccine-preventable diseases, with a recent resurgence even in highly vaccinated populations. Although the exact underlying reasons are still not clear, emerging evidence suggests that a key factor is the replacement of the whole-cell (wP) by the acellular pertussis (aP) vaccine, which is less reactogenic but may induce suboptimal and waning immunity. Differences between vaccines are hypothesised to be cell-mediated, with polarisation of Th1/Th2/Th17 responses determined by the composition of the pertussis vaccine given in infancy. Moreover, aP vaccines elicit strong antibody responses but fail to protect against nasal colonisation and/or transmission, in animal models, thereby potentially leading to inadequate herd immunity. Our review summarises current knowledge on vaccine-induced cellular immune responses, based on mucosal and systemic data collected within experimental animal and human vaccine studies. In addition, we describe key factors that may influence cell-mediated immunity and how antigen-specific responses are measured quantitatively and qualitatively, at both cellular and molecular levels. Finally, we discuss how we can harness this emerging knowledge and novel tools to inform the design and testing of the next generation of improved infant pertussis vaccines.

Repurposing of the childhood vaccines: could we train the immune system against the SARS-CoV-2

INTRODUCTION

The COVID-19 pandemic is a globalized health concern caused by a beta-coronavirus named Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Since December 2019, when this outbreak flared in Wuhan, China, COVID-19 cases have been continuously rising all over the world. Due to the emergence of SARS-CoV-2 mutants, subsequent waves are flowing in a faster manner as compared to the primary wave, which is more contagious and causing higher mortality. Recently, India has emerged as the new epicenter of the second wave by mutants of SARS-CoV-2. After almost eighteen months of this outbreak, some COVID-19 dedicated therapeutics and vaccines are available, and a few are under trial, but the situation is still uncontrolled.

AREA COVERED

This perspective article covers the repurposing of childhood vaccines like Bacille Calmette-Guerin (BCG), Measles, Mumps, Rubella (MMR), and Oral Polio Vaccine (OPV), which are live attenuated vaccines and have been shown the protective effect through 'trained immunity and 'crossreactivity.'

EXPERT OPINION

This perspective article has suggested that combinatorial use of these childhood vaccines might exert a better protective effect along with the available COVID-19 therapeutic and vaccines which could be considered as a preventive option against SARS-CoV-2 infection as well as its subsequent waves.

Live attenuated Bordetella pertussis vaccine candidate BPZE1 transiently protects against lethal pneumococcal disease in mice

BPZE1 is a live attenuated vaccine against infection by Bordetella pertussis, the causative agent of whooping cough. It was previously shown that BPZE1 provides heterologous protection in mouse models of disease caused by unrelated pathogens, such as influenza virus and respiratory syncytial virus. Protection was also observed in mouse models of asthma and contact dermatitis. In this study, we demonstrate that BPZE1 also displays protection against an unrelated bacterial pathogen in a mouse model of invasive pneumococcal disease mediated by Streptococcus pneumoniae. While a single administration of BPZE1 provided no protection, two doses of 10⁶ colony-forming units of BPZE1 given in a three-week interval protected against mortality, lung colonization and dissemination in both BALB/c and C57BL/6 mice. Unlike for the previously reported influenza challenge model, protection was short-lived, and waned within days after booster vaccination. Formaldehyde-killed BPZE1 protected only when administered following a live prime, indicating that priming requires live BPZE1 for protection. Protection against mortality was directly linked to substantially decreased bacterial dissemination in the blood and was lost in MyD88 knock-out mice, demonstrating the role of the innate immune system in the mechanism of protection. This is the first report on a heterologous protective effect of the live BPZE1 vaccine candidate against an unrelated bacterial infection.

Economic Evaluation of Vaccines: Belgian Reflections on the Need for a Broader Perspective

OBJECTIVES

The standard framework of economic evaluation of health programs, which is increasingly used for policy funding decisions, is insufficiently equipped to reflect the full range of health and economic benefits conferred by vaccines and thus undervalues vaccination.

METHODS

In 2019, a group of Belgian health economic and clinical experts, supported by 2 senior international vaccination experts (1 American, 1 Belgian), convened 4 roundtable meetings to highlight which particular value elements of vaccination remain neglected in economic evaluations.

RESULTS

They concluded that the standard economic evaluation framework fails to reflect the full value of vaccination with respect to prevention of complications linked to some vaccine-preventable diseases, health gains for caregivers, herd effects, changes in exposure to and distribution of serotypes, the effect on antimicrobial resistance, productivity gains for caregivers and patients, and the distributive implications of vaccination programs.

CONCLUSIONS

Here, suggestions are made regarding how these shortcomings can be addressed in future economic evaluations of vaccines and how a more level playing field between vaccines and other health programs can be created.

Cross-Reactive Effects of Vaccines: Heterologous Immunity between Tetanus and Chlamydia

Vaccines can have heterologous effects on the immune system, i.e., effects other than triggering an immune response against the disease targeted by the vaccine. We investigated whether monoclonal antibodies (mAbs) specific for tetanus could cross-react with Chlamydia and confer heterologous protection against chlamydial infection. The capability of two tetanus-specific mAbs, namely mAb26 and mAb51, to prevent chlamydial infection has been assessed: (i) in vitro, by performing a neutralization assay using human conjunctival epithelial (HCjE) cells infected with Chlamydia trachomatis serovar B, and (ii) in vivo, by using a guinea pig model of Chlamydiacaviae-induced inclusion conjunctivitis. The mAb26 has been superior in comparison with mAb51 in the prevention of chlamydial infection in HCjE cells. The mAb26 has conferred ≈40% inhibition of the infection, compared to less than 5% inhibition in the presence of the mAb51. In vivo, mAb26 significantly diminished ocular pathology intensity in guinea pigs infected with C. caviae compared to either the mAb51-treated or sham-treated guinea pigs. Our data provide insights that tetanus immunization generates antibodies which induce heterologous chlamydial immunity and promote protection beyond the intended target pathogen.

Suppression of a SARS-CoV-2 outbreak in the Italian municipality of Vo'

On 21 February 2020, a resident of the municipality of Vo', a small town near Padua (Italy), died of pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection¹. This was the first coronavirus disease 19 (COVID-19)-related death detected in Italy since the detection of SARS-CoV-2 in the Chinese city of Wuhan, Hubei province². In response, the regional authorities imposed the lockdown of the whole municipality for 14 days³. Here we collected information on the demography, clinical presentation, hospitalization, contact network and the presence of SARS-CoV-2 infection in nasopharyngeal swabs for 85.9% and 71.5% of the population of Vo' at two consecutive time points. From the first survey, which was conducted around the time the town lockdown started, we found a prevalence of infection of 2.6% (95% confidence interval (CI): 2.1-3.3%). From the second survey, which was conducted at the end of the lockdown, we found a prevalence of 1.2% (95% CI: 0.8-1.8%). Notably, 42.5% (95% CI: 31.5-54.6%) of the confirmed SARS-CoV-2 infections detected across the two surveys were asymptomatic (that is, did not have symptoms at the time of swab testing and did not develop symptoms afterwards). The mean serial interval was 7.2 days (95% CI: 5.9-9.6). We found no statistically significant difference in the viral load of symptomatic versus asymptomatic infections (P = 0.62 and 0.74 for E and RdRp genes, respectively, exact Wilcoxon-Mann-Whitney test). This study sheds light on the frequency of asymptomatic SARS-CoV-2 infection, their infectivity (as measured by the viral load) and provides insights into its transmission dynamics and the efficacy of the implemented control measures.

Maternal Immunization: Nature Meets Nurture

Vaccinating women in pregnancy (i.e., maternal immunization) has emerged as a promising tool to tackle infant morbidity and mortality worldwide. This approach nurtures a 'gift of nature,' whereby antibody is transferred from mother to fetus transplacentally during pregnancy, or postnatally in breast milk, thereby providing passive, antigen-specific protection against infections in the first few months of life, a period of increased immune vulnerability for the infant. In this review, we briefly summarize the rationale for maternal immunization programs and the landscape of vaccines currently in use or in the pipeline. We then direct the focus to the underlying biological phenomena, including the main mechanisms by which maternally derived antibody is transferred efficiently to the infant, at the placental interface or in breast milk; important research models and methodological approaches to interrogate these processes, particularly in the context of recent advances in systems vaccinology; the potential biological and clinical impact of high maternal antibody titres on neonatal ontogeny and subsequent infant vaccine responses; and key vaccine- and host-related factors influencing the maternal-infant dyad across different environments. Finally, we outline important gaps in knowledge and suggest future avenues of research on this topic, proposing potential strategies to ensure optimal testing, delivery and implementation of maternal vaccination programs worldwide.

Vaccinology: time to change the paradigm?

The existing vaccine paradigm assumes that vaccines only protect against the target infection, that effective vaccines reduce mortality corresponding to the target infection's share of total mortality, and that the effects of vaccines are similar for males and females. However, epidemiological vaccine research has generated observations that contradict these assumptions and suggest that vaccines have important non-specific effects on overall health in populations. These include the observations that several live vaccines reduce the incidence of all-cause mortality in vaccinated compared with unvaccinated populations far more than can be explained by protection against the target infections, and that several non-live vaccines are associated with increased all-cause mortality in females. In this Personal View we describe current observations and contradictions and define six emerging principles that might explain them. First, that live vaccines enhance resistance towards unrelated infections. Second, non-live vaccines enhance the susceptibility of girls to unrelated infections. Third, the most recently administered vaccination has the strongest non-specific effects. Fourth, combinations of live and non-live vaccines given together have variable non-specific health effects. Fifth, vaccinating children with live vaccines in the presence of maternal immunity enhances beneficial non-specific effects and reduces mortality. Finally, vaccines might interact with other co-administered health interventions, for example vitamin A supplementation. The potential implications for child health are substantial. For example, if BCG vaccination was given to children at birth, if higher measles vaccination coverage could be obtained, if diphtheria, tetanus, and pertussis-containing vaccines were not given with or after measles vaccine, or if the BCG strain with the best non-specific effects could be used consistently, then child mortality could be considerably lower. Pursuing these emerging principles could improve our understanding and use of vaccines globally.

The immunomodulatory effects of measles-mumps-rubella vaccination on persistence of heterologous vaccine responses

It is proposed that measles-containing vaccines have immunomodulatory effects which include a reduction in all-cause childhood mortality. The antibody response to heterologous vaccines provides a means to explore these immunomodulatory effects. This is the first study to investigate the influence of measles-mumps-rubella (MMR) vaccine on the persistence of antibodies to a broad range of heterologous infant vaccinations given in the first year of life. In total, 319 children were included in the study. All infants received routine vaccinations at 6 weeks, 4 and 6 months of age. At 12 months of age, 212 children were vaccinated with MMR and Haemophilus influenzae type b-meningococcus C (Hib-MenC) vaccines while the remaining 99 children had not yet received these vaccines. In the MMR/Hib-MenC-vaccinated group, blood was taken 28 ± 14 days after receiving these vaccines. Antibodies against diphtheria, tetanus, pertussis [pertussis toxin (PT), filamentous hemagglutinin, pertactin], poliomyelitis (type 1, 2, 3) and 13 pneumococcal serotypes were measured. Seroprotection rates and geometric mean antibody concentrations were compared between MMR/MenC-Hib-vaccinated and MMR/MenC-Hib-naïve participants. In the final analysis, 311 children were included. Seroprotection rates were lower in MMR/Hib-MenC-vaccinated children against PT and pneumococcal serotype 19A. After adjustment for prespecified factors, MMR/Hib-MenC-vaccinated infants had significantly higher antibody concentrations against tetanus (likely explained by a boosting effect of the carrier protein, a tetanus toxoid), while for the other vaccine antigens there was no difference in antibody concentrations between the two groups. MMR vaccination given at 12 months of age in a developed country does not significantly influence antibody concentrations to heterologous vaccines received in the first year of life.

Non-specific Effects of Live Attenuated Pertussis Vaccine Against Heterologous Infectious and Inflammatory Diseases

Bordetella pertussis is the agent of pertussis, also referred to as whooping cough, a disease that remains an important public health issue. Vaccine-induced immunity to pertussis wanes over time. In industrialized countries, high vaccine coverage has not prevented infection and transmission of B. pertussis, leading to periodic outbreaks in people of all ages. The consequence is the formation of a large source for transmission to children, who show the highest susceptibility of developing severe whooping cough and mortality. With the aim of providing protection against both disease and infection, a live attenuated pertussis vaccine, in which three toxins have been genetically inactivated or removed, is now in clinical development. This vaccine, named BPZE1, offers strong protection in mice and non-human primates. It has completed a phase I clinical trial in which safety, transient colonization of the human airway and immunogenicity could be demonstrated. In mice, BPZE1 was also found to protect against inflammation resulting from heterologous airway infections, including those caused by other Bordetella species, influenza virus and respiratory syncytial virus. Furthermore, the heterologous protection conferred by BPZE1 was also observed for non-infectious inflammatory diseases, such as allergic asthma, as well as for inflammatory disorders outside of the respiratory tract, such as contact dermatitis. Current studies focus on the mechanisms underlying the anti-inflammatory effects associated with nasal BPZE1 administration. Given the increasing importance of inflammatory disorders, novel preventive and therapeutic approaches are urgently needed. Therefore, live vaccines, such as BPZE1, may offer attractive solutions. It is now essential to understand the cellular and molecular mechanisms of action before translating these biological findings into new healthcare solutions.

Non-specific Effects of Vaccines Illustrated Through the BCG Example: From Observations to Demonstrations

Epidemiological studies regarding many successful vaccines suggest that vaccination may lead to a reduction in child mortality and morbidity worldwide, on a grander scale than is attributable to protection against the specific target diseases of these vaccines. These non-specific effects (NSEs) of the Bacille Calmette-Guérin (BCG) vaccine, for instance, implicate adaptive and innate immune mechanisms, with recent evidence suggesting that trained immunity might be a key instrument at play. Collectively referring to the memory-like characteristics of innate immune cells, trained immunity stems from epigenetic reprogramming that these innate immune cells undergo following exposure to a primary stimulus like BCG. The epigenetic changes subsequently regulate cytokine production and cell metabolism and in turn, epigenetic changes are regulated by these effects. Novel -omics technologies, combined with in vitro models for trained immunity and other immunological techniques, identify the biological pathways within innate cells that enable training by BCG. Future research should aim to identify biomarkers for vaccine heterologous effects, such that they can be applied to epidemiological studies. Linking biological mechanisms to the reduction in all-cause mortality observed in epidemiological studies will strengthen the evidence in favor of vaccine NSEs. The universal acceptance of these NSEs would demand a re-evaluation of current vaccination policies, such as the childhood vaccination recommendations by the World Health Organization, in order to produce the maximum impact on childhood mortality.

Observational studies of non-specific effects of Diphtheria-Tetanus-Pertussis vaccines in low-income countries: Assessing the potential impact of study characteristics, bias and confounding through meta-regression

INTRODUCTION

It has been suggested that some vaccines have effects beyond protection against the diseases they target, called non-specific effects (NSEs). In 2016, a systematic review by Higgins et al., commissioned by the WHO Strategic Advisory Group of Experts (SAGE) on immunization, estimated the relative risk (RR) of all-cause mortality after whole-cell Diphtheria-Tetanus-Pertussis (DTwP) vaccination to be 1.38 (95% CI: 0.92-2.08), and described these potential NSEs as inconsistent. However, the selection of studies for meta-analysis, based on their proneness to bias and confounding, was debated.

OBJECTIVE

To identify study characteristics and postulated risks of bias and confounding that might have impacted the RR of all-cause mortality after DTwP vaccination in observational studies conducted in low-income countries.

METHODS

Based on methodological considerations on study design and analysis, we systematically assessed all 17 DTwP studies from the Higgins et al. review for risk of selection bias, exposure and outcome misclassification, confounding and differential co-interventions. We used meta-regression to assess the impact of study characteristics and the postulated risks of bias and confounding on the RR estimates, and looked for outlying and influential risk estimates. Permutation tests were performed to control for false-positive findings.

RESULTS

The overall RR of all-cause mortality after DTwP vaccination including all but one outlying and influential study was 1.32 (95% CI: 0.83-2.08). Based on uni-variable meta-regression, we found that study location (p = 0.01), studies using the landmark approach (p = 0.015) and studies at high risk of exposure misclassification (p = 0.036) were significantly associated with increased RR estimates whereas studies at high risk of selection bias (p = 0.059) showed borderline significance. The results further suggest these effect modifiers are clustered in studies conducted in West-Africa.

CONCLUSION

The increased RR of all-cause mortality after DTwP might be confined to West-African countries and/or certain postulated risks of bias might have inflated these RRs.

Neonatal Immunization: Rationale, Current State, and Future Prospects

Infections take their greatest toll in early life necessitating robust approaches to protect the very young. Here, we review the rationale, current state, and future research directions for one such approach: neonatal immunization. Challenges to neonatal immunization include natural concern about safety as well as a distinct neonatal immune system that is generally polarized against Th1 responses to many stimuli such that some vaccines that are effective in adults are not in newborns. Nevertheless, neonatal immunization could result in high-population penetration as birth is a reliable point of healthcare contact, and offers an opportunity for early protection of the young, including preterm newborns who are deficient in maternal antibodies. Despite distinct immunity and reduced responses to some vaccines, several vaccines have proven safe and effective at birth. While some vaccines such as polysaccharide vaccines have little effectiveness at birth, hepatitis B vaccine can prime at birth and requires multiple doses to achieve protection, whereas the live-attenuated Bacille Calmette-Guérin (BCG), may offer single shot protection, potentially in part via heterologous ("non-specific") beneficial effects. Additional vaccines have been studied at birth including those directed against pertussis, pneumococcus, Haemophilus influenza type B and rotavirus providing important lessons. Current areas of research in neonatal vaccinology include characterization of early life immune ontogeny, heterogeneity in and heterologous effects of BCG vaccine formulations, applying systems biology and systems serology, in vitro platforms that model age-specific human immunity and discovery and development of novel age-specific adjuvantation systems. These approaches may inform, de-risk, and accelerate development of novel vaccines for use in early life. Key stakeholders, including the general public, should be engaged in assessing the opportunities and challenges inherent to neonatal immunization.

Hypothetical endogenous SIV-like antigens in Mauritian cynomolgus macaques

Simian immunodeficiency virus (SIV) infection of Mauritian cynomolgus macaques (MCMs) is an increasingly important nonhuman primate model for HIV vaccine research. We previously reported that in MCMs anti-SIV antibodies can be naturally developed without exogenous infection or vaccination, and that a vaccine targeting SIV protease cleavage sites (PCS) can cross-induce antibodies to non-PCS SIV antigens. We speculate that this is potentially caused by the existence of endogenous SIV-like antigens. External stimuli (such as environmental factors and vaccination) may induce expression of endogenous SIV-like antigens to elicit these antibodies. Database and mass spectrometry analyses were conducted to search for such antigens. We identified endogenous SIV-like DNA sequences in cynomolgus macaque genome and non-PCS peptide homologous to SIV Env protein in PBMCs of a PCS-vaccinated monkey. Our preliminary insights suggest that endogenous SIV-like antigens may be one of the possible reasons for the natural and cross-inducible SIV antibodies in MCMs.

Herpesvirus Infection Induces both Specific and Heterologous Antiviral Antibodies in Carp

IgM antibody diversity induced by viral infection in teleost fish sera remains largely unexplored despite several studies performed on their transcript counterparts in lymphoid organs. Here, IgM binding to microarrays containing ~20,000 human proteins was used to study sera from carp (Cyprinus carpio) populations having high titers of viral neutralization in vitro after surviving an experimental infection with cyprinid herpes virus 3 (CyHV-3). The range of diversity of the induced antibodies was unexpectedly high, showing CyHV-3 infection-dependent, non-specific IgM-binding activity of a ~20-fold wider variety than that found in sera from healthy carp (natural antibodies) with no anti-CyHV-3 neutralization titers. An inverse correlation between the IgM-binding levels in healthy versus infection-survivor/healthy ratios suggests that an infection-dependent feed back-like mechanism may control such clonal expansion. Surprisingly, among the infection-expanded levels, not only specific anti-frgII_CyHV-3 and anti-CyHV-3 IgM-binding antibodies but also antibodies recognizing recombinant fragment epitopes from heterologous fish rhabdoviruses were detected in infection-survivor carp sera. Some alternative explanations for these findings in lower vertebrates are discussed.

Natural and cross-inducible anti-SIV antibodies in Mauritian cynomolgus macaques

Cynomolgus macaques are an increasingly important nonhuman primate model for HIV vaccine research. SIV-free animals without pre-existing anti-SIV immune responses are generally needed to evaluate the effect of vaccine-induced immune responses against the vaccine epitopes. Here, in order to select such animals for vaccine studies, we screened 108 naïve female Mauritian cynomolgus macaques for natural (baseline) antibodies to SIV antigens using a Bio-Plex multiplex system. The antigens included twelve 20mer peptides overlapping the twelve SIV protease cleavage sites (-10/+10), respectively (PCS peptides), and three non-PCS Gag or Env peptides. Natural antibodies to SIV antigens were detected in subsets of monkeys. The antibody reactivity to SIV was further confirmed by Western blot using purified recombinant SIV Gag and Env proteins. As expected, the immunization of monkeys with PCS antigens elicited anti-PCS antibodies. However, unexpectedly, antibodies to non-PCS peptides were also induced, as shown by both Bio-Plex and Western blot analyses, while the non-PCS peptides do not share sequence homology with PCS peptides. The presence of natural and vaccine cross-inducible SIV antibodies in Mauritian cynomolgus macaques should be considered in animal selection, experimental design and result interpretation, for their best use in HIV vaccine research.

An adjuvant-modulated vaccine response in human whole blood

The restimulation of an immune memory response by in vitro culture of blood cells with a specific antigen has been used as a way to gauge immunity to vaccines for decades. In this commentary we discuss a less appreciated application to support vaccine process development. We report that human whole blood from pre-primed subjects can generate a profound adjuvant-modulated, antigen-specific response to several different vaccine formulations. The response is able to differentiate subtle changes in the quality of an immune memory response to vaccine formulations and can be used to select optimal conditions relating to a particular manufacture process step. While questions relating to closeness to in vivo vaccination remain, the approach is another big step nearer to the more relevant human response. It has special importance for new adjuvant development, complementing other preclinical in vivo and in vitro approaches to considerably de-risk progression of novel vaccines before and throughout early clinical development. Broader implications of the approach are discussed.

Counts of bovine monocyte subsets prior to calving are predictive for postpartum occurrence of mastitis and metritis

The heightened susceptibility to infectious diseases in postpartum dairy cows is often attributed to immune dysfunction associated with the transition period. However, the cell populations involved in this immune dysfunction and the dynamics between those populations are not well defined. Monocytes play a crucial role in governing initial immune response in bacterial infections. Bovine monocytes are subdivided in classical (CD14⁺/CD16⁻), intermediate (CD14⁺/CD16⁺) and non-classical monocytes (CD14⁻/CD16⁺) with distinct phenotypic and functional differences. This study investigated the relationship of monocyte subsets counts in blood at 42 and 14 days prior to expected calving date to occurrence of metritis and mastitis within 2 weeks postpartum. In the enrolled prospective cohort of 27 German Holstein cows, housed at the Institute of Animal Nutrition of the Friedrich-Loeffler-Institute Braunschweig, Germany, n = 13 developed metritis and/or mastitis postpartum. A multivariable logistic regression was used to analyze the relationship between prepartum cell counts of monocyte subsets and neutrophils with postpartum disease. Our model revealed that higher counts of the two CD14⁺ monocyte subsets were predictive of disease. In contrast, higher numbers of the CD14⁻ monocyte subset were negatively associated with disease. Interestingly, the neutrophil count, a common hallmark for inflammatory response, was not associated with the outcome variable at either time point. The results indicate that the number and composition of monocyte subsets before calving are related to the susceptibility to infectious disease within 2 weeks postpartum. Furthermore the oppositional effect of CD14⁺ and CD14⁻ subsets strengthens the hypothesis that these subsets have different functional roles in the inflammatory response in dairy cows.

Zebra Fish Lacking Adaptive Immunity Acquire an Antiviral Alert State Characterized by Upregulated Gene Expression of Apoptosis, Multigene Families, and Interferon-Related Genes

To investigate fish innate immunity, we have conducted organ and cell immune-related transcriptomic as well as immunohistologic analysis in mutant zebra fish (Danio rerio) lacking adaptive immunity (rag1^−/−) at different developmental stages (egg, larvae, and adult), before and after infection with spring viremia carp virus (SVCV). The results revealed that, compared to immunocompetent zebra fish (rag1^+/+), rag1^−/− acquired increased resistance to SVCV with age, correlating with elevated transcript levels of immune genes in skin/fins and lymphoid organs (head kidney and spleen). Gene sets corresponding to apoptotic functions, immune-related multigene families, and interferon-related genes were constitutively upregulated in uninfected adult rag1^−/− zebra fish. Overexpression of activated CASPASE-3 in different tissues before and after infection with SVCV further confirmed increased apoptotic function in rag1^−/− zebra fish. Concurrently, staining of different tissue samples with a pan-leukocyte antibody marker showed abundant leukocyte infiltrations in SVCV-infected rag1^−/− fish, coinciding with increased transcript expression of genes related to NK-cells and macrophages, suggesting that these genes played a key role in the enhanced immune response of rag1^−/− zebra fish to SVCV lethal infection. Overall, we present evidence that indicates that rag1^−/− zebra fish acquire an antiviral alert state while they reach adulthood in the absence of adaptive immunity. This antiviral state was characterized by (i) a more rapid response to viral infection, which resulted in increased survival, (ii) the involvement of NK-cell- and macrophage-mediated transcript responses rather than B- and/or T-cell dependent cells, and (iii) enhanced apoptosis, described here for the first time, as well as the similar modulation of multigene family/interferon-related genes previously associated to fish that survived lethal viral infections. From this and other studies, it might be concluded that some of the characteristics of mammalian trained immunity are present in lower vertebrates.