Controlled human infection with RSV: The opportunities of experimental challenge

Vaccines for the Elderly and Vaccination Programs in Europe and the United States

The share of the elderly population is growing worldwide as life expectancy increases. Immunosenescence and comorbidities increase infectious diseases' morbidity and mortality in older adults. Here, we aimed to summarize the latest findings on vaccines for the elderly against herpes zoster, influenza, respiratory syncytial virus (RSV), COVID-19, and pneumococcal disease and to examine vaccine recommendation differences for this age group in Europe and the United States. PubMed was searched using the keywords "elders" and "vaccine" alongside the disease/pathogen in question and paraphrased or synonymous terms. Vaccine recommendations were also sought in the European and US Centers for Disease Control and Prevention databases. Improved vaccines, tailored for the elderly, mainly by using novel adjuvants or by increasing antigen concentration, are now available. Significant differences exist between immunization policies, especially between European countries, in terms of the recipient's age, number of doses, vaccination schedule, and implementation (mandatory or recommended). Understanding the factors that influence the immune response to vaccination in the elderly may help to design vaccines that offer long-term protection for this vulnerable age group. A consensus-based strategy in Europe could help to fill the gaps in immunization policy in the elderly, particularly regarding vaccination against RSV and pneumococcus.

Sequence-Optimized mRNA Vaccines Against Infectious Disease

Developing effective mRNA vaccines poses certain challenges concerning mRNA stability and ability to induce sufficient immune stimulation and requires a specific panel of techniques for production and testing. Here, we describe the production of stabilized mRNA vaccines (RNActive® technology) with enhanced immunogenicity, generated using conventional nucleotides only, by introducing changes to the mRNA sequence and by formulation into lipid nanoparticles. Methods described here include the synthesis, purification, and formulation of mRNA vaccines as well as a comprehensive panel of in vitro and in vivo methods for evaluation of vaccine quality and immunogenicity.

Human T cells efficiently control RSV infection

Respiratory syncytial virus (RSV) infection causes significant morbidity and mortality in infants, immunocompromised individuals, and older individuals. There is an urgent need for effective antivirals and vaccines for high-risk individuals. We used 2 complementary in vivo models to analyze RSV-associated human lung pathology and human immune correlates of protection. RSV infection resulted in widespread human lung epithelial damage, a proinflammatory innate immune response, and elicited a natural adaptive human immune response that conferred protective immunity. We demonstrated a key role for human T cells in controlling RSV infection. Specifically, primed human CD8+ T cells or CD4+ T cells effectively and independently control RSV replication in human lung tissue in the absence of an RSV-specific antibody response. These preclinical data support the development of RSV vaccines, which also elicit effective T cell responses to improve RSV vaccine efficacy.

Combination Ad26.RSV.preF/preF protein vaccine induces superior protective immunity compared with individual vaccine components in preclinical models

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory disease for which no licensed vaccine is available. We have previously shown that a prefusion (preF) conformation-stabilized RSV F protein antigen and an adenoviral vector encoding RSV preF protein (Ad26.RSV.preF) are immunogenic and protective in animals when administered as single components. Here, we evaluated a combination of the 2 components, administered as a single injection. Strong induction of both humoral and cellular responses was shown in RSV-naïve and pre-exposed mice and pre-exposed African green monkeys (AGMs). Both components of the combination vaccine contributed to humoral immune responses, while the Ad26.RSV.preF component was the main contributor to cellular immune responses in both mice and AGMs. Immunization with the combination elicited superior protection against RSV A2 challenge in cotton rats. These results demonstrate the advantage of a combination vaccine and support further clinical development.

Antibodies face the challenge against human respiratory syncytial virus

In the December 22 issue of Cell, Bartsch et al. describe functional profiling of the antibody response to respiratory syncytial virus in human adults vaccinated with an experimental adenovirus-based prefusion-stabilized HRSV-F vaccine and subsequently intranasally challenged with HRSV. The authors identified various antibody effector functions as humoral correlates of protection.

Mucosal administration of a live attenuated recombinant COVID-19 vaccine protects nonhuman primates from SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the COVID-19 global pandemic. SARS-CoV-2 is an enveloped RNA virus that relies on its trimeric surface glycoprotein spike for entry into host cells. Here we describe the COVID-19 vaccine candidate MV-014-212, a live, attenuated, recombinant human respiratory syncytial virus expressing a chimeric SARS-CoV-2 spike as the only viral envelope protein. MV-014-212 was attenuated and immunogenic in African green monkeys (AGMs). One mucosal administration of MV-014-212 in AGMs protected against SARS-CoV-2 challenge, reducing by more than 200-fold the peak shedding of SARS-CoV-2 in the nose. MV-014-212 elicited mucosal immunoglobulin A in the nose and neutralizing antibodies in serum that exhibited cross-neutralization against virus variants of concern Alpha, Beta, and Delta. Intranasally delivered, live attenuated vaccines such as MV-014-212 entail low-cost manufacturing suitable for global deployment. MV-014-212 is currently in Phase 1 clinical trials as an intranasal COVID-19 vaccine.

Wearable sensor-based detection of influenza in presymptomatic and asymptomatic individuals

BACKGROUND

The COVID-19 pandemic highlighted the need for early detection of viral infections in symptomatic and asymptomatic individuals to allow for timely clinical management and public health interventions.

METHODS

Twenty healthy adults were challenged with an influenza A (H3N2) virus and prospectively monitored from 7 days before through 10 days after inoculation, using wearable electrocardiogram and physical activity sensors (Clinical Trial: NCT04204493; https://clinicaltrials.gov/ct2/show/NCT04204993). This framework allowed for responses to be accurately referenced to the infection event. For each participant, we trained a semi-supervised multivariable anomaly detection model on data acquired before inoculation and used it to classify the post-inoculation dataset.

RESULTS

Inoculation with this challenge virus was well-tolerated with an infection rate of 85%. With the model classification threshold set so that no alarms were recorded in the 170 healthy days recorded, the algorithm correctly identified 16 of 17 (94%) positive presymptomatic and asymptomatic individuals, on average 58 hours post inoculation and 23 hrs before the symptom onset.

CONCLUSION

The data processing and modeling methodology show promise for the early detection of respiratory illness. The detection algorithm is compatible with data collected from smartwatches using optical techniques but needs to be validated in large heterogeneous cohorts in normal living conditions.

Controlled Human Infection Challenge Studies with RSV

Despite considerable momentum in the development of RSV vaccines and therapeutics, there remain substantial barriers to the development and licensing of effective agents, particularly in high-risk populations. The unique immunobiology of RSV and lack of clear protective immunological correlates has held back RSV vaccine development, which, therefore, depends on large and costly clinical trials to demonstrate efficacy. Studies involving the deliberate infection of human volunteers offer an intermediate step between pre-clinical and large-scale studies of natural infection. Human challenge has been used to demonstrate the potential efficacy of vaccines and antivirals while improving our understanding of the protective immunity against RSV infection. Early RSV human infection challenge studies determined the role of routes of administration and size of inoculum on the disease. However, inherent limitations, the use of highly attenuated/laboratory-adapted RSV strains and the continued evolutionary adaptation of RSV limits extrapolation of results to present-day vaccine testing. With advances in technology, it is now possible to perform more detailed investigations of human mucosal immunity against RSV in experimentally infected adults and, more recently, older adults to optimise the design of vaccines and novel therapies. These studies identified defects in RSV-induced humoral and CD8+ T cell immunity that may partly explain susceptibility to recurrent RSV infection. We discuss the insights from human infection challenge models, ethical and logistical considerations, potential benefits, and role in streamlining and accelerating novel antivirals and vaccines against RSV. Finally, we consider how human challenges might be extended to include relevant at-risk populations.

Divergent age-related humoral correlates of protection against respiratory syncytial virus infection in older and young adults: a pilot, controlled, human infection challenge model

BACKGROUND

Respiratory viral infections are typically more severe in older adults. Older adults are more vulnerable to infection and do not respond effectively to vaccines due to a combination of immunosenescence, so-called inflamm-ageing, and accumulation of comorbidities. Although age-related changes in immune responses have been described, the causes of this enhanced respiratory disease in older adults remain poorly understood. We therefore performed volunteer challenge with respiratory syncytial virus (RSV) in groups of younger and older adult volunteers. The aim of this study was to establish the safety and tolerability of this model and define age-related clinical, virological, and immunological outcomes.

METHODS

In this human infection challenge pilot study, adults aged 18-55 years and 60-75 years were assessed for enrolment using protocol-defined inclusion and exclusion criteria. Symptoms were documented by self-completed diaries and viral load determined by quantitative PCR of nasal lavage. Peripheral blood B cell frequencies were measured by enzyme-linked immunospot and antibodies against pre-fusion and post-fusion, NP, and G proteins in the blood and upper respiratory tract were measured. The study was registered with ClinicalTrials.gov, NCT03728413.

FINDINGS

381 adults aged 60-75 years (older cohort) and 19 adults aged 18-55 years (young cohort) were assessed for enrolment using protocol-defined inclusion and exclusion criteria between Nov 12, 2018, and Feb 26, 2020. 12 healthy volunteers aged 60-75 years and 21 aged 18-55 years were inoculated intranasally with RSV Memphis-37. Nine (67%) of the 12 older volunteers became infected, developing mild-to-moderate upper respiratory tract symptoms that resolved without serious adverse events or sequelae. Viral load peaked on day 6 post-inoculation and symptoms peaked between days 6 and 8. Increases in circulating IgG-positive and IgA-positive antigen-specific plasmablasts, serum neutralising antibodies, and pre-F specific IgG were similar younger and older adults. However, in contrast to young participants, secretory IgA titres in older volunteers failed to increase during infection and, unlike serum IgG, did not correlate with protection.

INTERPRETATION

Better understanding of age-related differences in clinical outcomes and immune correlates of protection can overcome reduction in vaccine efficacy with advancing age. We identify correlates of protection in older adults, revealing previously unrecognised factors which might have implications for targeted vaccine discovery and drug development in this vulnerable group.

FUNDING

Medical Research Council and GlaxoSmithKline EMINENT Consortium.

Diagnostic accuracy of Xpert Xpress Flu/RSV for detection of Influenza and Respiratory syncytial virus

Xpert Xpress Flu/RSV is a fast and automated real-time nucleic acid amplification tool for detecting influenza virus and respiratory syncytial virus (RSV). The aim of this study was to verify the accuracy of Xpert Xpress Flu/RSV in detecting influenza virus and RSV. PubMed, EMBASE, Cochrane Library, and Web of Science were searched up to October 2020. The quality of original research was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 guidelines. Meta-DiSc 1.4 software was used to analyze the sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and Summary receiver operating characteristic curve. Deek's funnel plot asymmetry test was used to evaluate the publication bias by Stata 12.0. Ten studies with 25 fourfold tables were included in this analysis. The sensitivity of Xpert Xpress Flu/RSV in detecting influenza A, influenza B, and RSV was 0.97, 0.98, 0.96, respectively, and the specificity was 0.97, 1.00, 1.00, respectively. Compared with other common clinical real-time reverse transcriptase PCR (RT-PCR), Xpert Xpress Flu/RSV is a valuable tool for diagnosing influenza virus and RSV with high sensitivity and specificity.

Conserved T-cell epitopes of respiratory syncytial virus (RSV) delivered by recombinant live attenuated influenza vaccine viruses efficiently induce RSV-specific lung-localized memory T cells and augment influenza-specific resident memory T-cell responses

Respiratory syncytial virus (RSV) can cause recurrent infection in people because it does not stimulate a long-lived immunological memory. There is an urgent need to develop a safe and efficacious vaccine against RSV that would induce immunological memory without causing immunopathology following natural RSV infection. We have previously generated two recombinant live attenuated influenza vaccine (LAIV) viruses that encode immunodominant T-cell epitopes of RSV M2 protein in the neuraminidase or NS1 genes. These chimeric vaccines afforded protection against influenza and RSV infection in mice, without causing pulmonary eosinophilia or inflammatory RSV disease. The current study assessed the formation of influenza-specific and RSV-specific CD4 and CD8 T-cell responses in the lungs of mice, with special attention to the lung tissue-resident memory T cell subsets (T_RM). The RSV epitopes did not affect influenza-specific CD4 effector memory T cell (Tem) levels in the lungs. The majority of these cells formed by LAIV or LAIV-RSV viruses had CD69⁺CD103^- phenotype. Both LAIV+NA/RSV and LAIV+NS/RSV recombinant viruses induced significant levels of RSV M2₈₂ epitope-specific lung-localized CD8 Tem cells expressing both CD69 and CD103 T_RM markers. Surprisingly, the CD69⁺CD103⁺ influenza-specific CD8 Tem responses were augmented by the addition of RSV epitopes, possibly as a result of the local microenvironment formed by the RSV-specific memory T cells differentiating to T_RM in the lungs of mice immunized with LAIV-RSV chimeric viruses. This study provides evidence that LAIV vector-based vaccination can induce robust lung-localized T-cell immunity to the inserted T-cell epitope of a foreign pathogen, without altering the immunogenicity of the viral vector itself.

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Two LAIV-RSV vaccine viruses induced RSV M2₈₂-specific effector memory CD8 T cells producing both IFNγ and TNFα cytokines.

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The inserted RSV epitopes did not affect influenza-specific CD4 Tem levels in the lungs of immunized mice.

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LAIV-RSV viruses induced RSV M2₈₂-specific lung-localized CD8 Tem cells expressing both CD69 and CD103 T_RM markers.

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The magnitude of RSV M2₈₂-specific CD8 Tem responses correlates with protection against RSV-induced lung pathology.

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The addition of RSV epitopes into the LAIV strain augmented CD69⁺CD103⁺ influenza-specific CD8 Tem responses in the lungs.

RSV Reprograms the CDK9•BRD4 Chromatin Remodeling Complex to Couple Innate Inflammation to Airway Remodeling

Respiratory syncytial virus infection is responsible for seasonal upper and lower respiratory tract infections worldwide, causing substantial morbidity. Self-inoculation of the virus into the nasopharynx results in epithelial replication and distal spread into the lower respiratory tract. Here, respiratory syncytial virus (RSV) activates sentinel cells important in the host inflammatory response, resulting in epithelial-derived cytokine and interferon (IFN) expression resulting in neutrophilia, whose intensity is associated with disease severity. I will synthesize key findings describing how RSV replication activates intracellular NFκB and IRF signaling cascades controlling the innate immune response (IIR). Recent studies have implicated a central role for Scg1a1⁺ expressing progenitor cells in IIR, a cell type uniquely primed to induce neutrophilic-, T helper 2 (Th2)-polarizing-, and fibrogenic cytokines that play distinct roles in disease pathogenesis. Molecular studies have linked the positive transcriptional elongation factor-b (P-TEFb), a pleiotrophic chromatin remodeling complex in immediate-early IIR gene expression. Through intrinsic kinase activity of cyclin dependent kinase (CDK) 9 and atypical histone acetyl transferase activity of bromodomain containing protein 4 (BRD4), P-TEFb mediates transcriptional elongation of IIR genes. Unbiased proteomic studies show that the CDK9•BRD4 complex is dynamically reconfigured by the innate response and targets TGFβ-dependent fibrogenic gene networks. Chronic activation of CDK9•BRD4 mediates chromatin remodeling fibrogenic gene networks that cause epithelial mesenchymal transition (EMT). Mesenchymal transitioned epithelial cells elaborate TGFβ and IL6 that function in a paracrine manner to expand the population of subepithelial myofibroblasts. These findings may account for the long-term reduction in pulmonary function in children with severe lower respiratory tract infection (LRTI). Modifying chromatin remodeling properties of the CDK9•BRD4 coactivators may provide a mechanism for reducing post-infectious airway remodeling that are a consequence of severe RSV LRTIs.

Are placebo controls necessary in controlled human infection trials for vaccines?

Controlled human infection trials, whereby a small group of healthy participants is deliberately exposed to a pathogen under controlled circumstances, can provide preliminary data for vaccine efficacy and for the selection of the most promising candidate vaccines for field trials. Because of the potential harm to participants through the deliberate exposure to a pathogen, the use of smaller groups minimises the cumulative risk. As such, a control group that receives a placebo vaccine followed by controlled exposure to a pathogen should be scientifically well justified. As these types of trials are designed to generate consistent infection rates and thus comparable outcomes across populations and trial sites, data from past studies (historical data) could be used as a valid alternative to placebo groups. In this Personal View, we review this option and highlight the considerations for choosing historical data as a suitable control. For the widespread application of this method, responsibility for the centralisation and sharing of data from controlled human infection trials lies with the scientific community.

Controlled human infection for vaccination against Streptococcus pyogenes (CHIVAS): Establishing a group A Streptococcus pharyngitis human infection study

Group A Streptococcus (GAS) is a highly-adapted and human-restricted pathogen responsible for a high global burden of disease across a diverse clinical spectrum. Vaccine development has been impeded by scientific, regulatory, and commercial obstacles. Human infection studies (HIS) are increasingly contributing to drug, diagnostics, and vaccine development, reducing uncertainty at early stages, especially for pathogens with animal models that incompletely reproduce key elements of human disease. We review the small number of historical GAS HIS and present the study protocol for a dose-ranging inpatient study in healthy adults. The primary objective of the study is to establish a new GAS pharyngitis HIS with an attack rate of at least 60% as a safe and reliable platform for vaccine evaluation and pathogenesis research. According to an adaptive dose-ranging study design, emm75 GAS doses manufactured in keeping with principles of Good Manufacturing Practice will be directly applied by swab to the pharynx of carefully screened healthy adult volunteers at low risk of severe complicated GAS disease. Participants will remain as closely monitored inpatients for up to six days, observed for development of the primary outcome of acute symptomatic pharyngitis, as defined by clinical and microbiological criteria. All participants will be treated with antibiotics and followed as outpatients for six months. An intensive sampling schedule will facilitate extensive studies of host and organism dynamics during experimental pharyngitis. Ethics approval has been obtained and the study has been registered at ClinicalTrials.gov (NCT03361163).

The respiratory syncytial virus vaccine landscape: lessons from the graveyard and promising candidates

The global burden of disease caused by respiratory syncytial virus (RSV) is increasingly recognised, not only in infants, but also in older adults (aged ≥65 years). Advances in knowledge of the structural biology of the RSV surface fusion glycoprotein have revolutionised RSV vaccine development by providing a new target for preventive interventions. The RSV vaccine landscape has rapidly expanded to include 19 vaccine candidates and monoclonal antibodies (mAbs) in clinical trials, reflecting the urgency of reducing this global health problem and hence the prioritisation of RSV vaccine development. The candidates include mAbs and vaccines using four approaches: (1) particle-based, (2) live-attenuated or chimeric, (3) subunit, (4) vector-based. Late-phase RSV vaccine trial failures highlight gaps in knowledge regarding immunological protection and provide lessons for future development. In this Review, we highlight promising new approaches for RSV vaccine design and provide a comprehensive overview of RSV vaccine candidates and mAbs in clinical development to prevent one of the most common and severe infectious diseases in young children and older adults worldwide.

Experimental infection of human volunteers

Controlled human infection (CHI) trials, in which healthy volunteers are experimentally infected, can accelerate the development of novel drugs and vaccines for infectious diseases of global importance. The use of CHI models is expanding from around 60 studies in the 1970s to more than 120 publications in this decade, primarily for influenza, rhinovirus, and malaria. CHI trials have provided landmark data for several registered drugs and vaccines, and have generated unprecedented scientific insights. Because of their invasive nature, CHI studies demand critical ethical review according to established frameworks. CHI-associated serious adverse events are rarely reported. Novel CHI models need standardised safety data from comparable CHI models to facilitate evidence-based risk assessments, as well as funds to produce challenge inoculum according to regulatory requirements. Advances such as the principle of controlled colonisation, the expansion of models to endemic areas, and the use of genetically attenuated strains will further broaden the scope of CHI trials.

Siglec-1 inhibits RSV-induced interferon gamma production by adult T cells in contrast to newborn T cells

Interferon gamma (IFN‐γ) plays an important role in the antiviral immune response during respiratory syncytial virus (RSV) infections. Monocytes and T cells are recruited to the site of RSV infection, but it is unclear whether cell‐cell interactions between monocytes and T cells regulate IFN‐γ production. In this study, micro‐array data identified the upregulation of sialic acid‐binding immunoglobulin‐type lectin 1 (Siglec‐1) in human RSV‐infected infants. In vitro, RSV increased expression of Siglec‐1 on healthy newborn and adult monocytes. RSV‐induced Siglec‐1 on monocytes inhibited IFN‐γ production by adult CD4⁺ T cells. In contrast, IFN‐γ production by RSV in newborns was not affected by Siglec‐1. The ligand for Siglec‐1, CD43, is highly expressed on adult CD4⁺ T cells compared to newborns. Our data show that Siglec‐1 reduces IFN‐γ release by adult T cells possibly by binding to the highly expressed CD43. The Siglec‐1‐dependent inhibition of IFN‐γ in adults and the low expression of CD43 on newborn T cells provides a better understanding of the immune response against RSV in early life and adulthood.