A dose-dependent plasma signature of the safety and immunogenicity of the rVSV-Ebola vaccine in Europe and Africa

Innate and Cellular Immune Response to the Ebola Vaccine Ad26.ZEBOV, MVA-BN-Filo: An Ancillary Study of the EBL2001 Phase 2 Trial

BACKGROUND

The EBL2001 phase 2 trial tested the 2-dose Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine in Europe. Safety and humoral immunogenicity assessments led to European Union market authorization in 2020. Complementary analyses of immune responses are warranted to better characterize vaccine effects.

METHODS

We conducted an ancillary study to analyze changes in the serum and cellular responses. Serum biomarkers of activation/inflammation were evaluated using a Luminex assay. Vaccine-elicited T-cell responses and functions were evaluated by assessing their phenotype, cytokine production, proliferation, and cytotoxic potential. Integrated data analysis was performed through correlation and principal component analysis of serum biomarkers and cellular immune responses.

RESULTS

Forty-eight volunteers were included. The Ad26.ZEBOV, MVA-BN-Filo vaccine elicited (1) serum increase of inflammatory/activation markers mainly at 1 day after the Ad26.ZEBOV vaccine; and (2) durable EBOV-specific T-cell proliferation and CD8+ T cells exhibiting a cytotoxic phenotype after Ad26.ZEBOV prime, after MVA-BN-Filo boost, and 6 months postvaccination. Integrated analysis revealed correlations between (1) EBOV-specific CD8+ T-cell proliferation and cytotoxic phenotype; and (2) high EBOV-specific CD8+ T-cell cytotoxic phenotype and low inflammatory marker IL-8 at day 1 postvaccination.

DISCUSSION

This study provides unique insights into the in vivo contribution of proliferation/cytotoxic CD8+ T cells and inflammation to the Ad26.ZEBOV, MVA-BN-Filo vaccine-induced potency. Clinical Trials Registration. NCT02416453.

rVSV-ZEBOV vaccination in people with pre-existing immunity to Ebolavirus: an open-label safety and immunogenicity study in Guinean communities affected by Ebola virus disease (l'essai proches)

BACKGROUND

Zaire Ebolavirus disease (EVD) outbreaks can be controlled using rVSV-ZEBOV vaccination and other public health measures. People in high-risk areas may have pre-existing antibodies from asymptomatic Ebolavirus exposure that might affect response to rVSV-ZEBOV. Therefore, we assessed the impact pre-existing immunity had on post-vaccination IgG titre, virus neutralisation, and reactogenicity following vaccination.

METHODS

In this prospective cohort study, 2115 consenting close contacts ("proches") of EVD survivors were recruited. Proches were vaccinated with rVSV-ZEBOV and followed up for 28 days for safety and immunogenicity. Anti-GP IgG titre at baseline and day 28 was assessed by ELISA. Samples from a representative subset were evaluated using live virus neutralisation.

RESULTS

Ten percent were seropositive at baseline. At day 28, IgG in baseline seronegative (GMT 0.106 IU/ml, 95% CI: 0.100 to 0.113) and seropositive (GMT 0.237 IU/ml, 0.210 to 0.267) participants significantly increased from baseline (both p < 0.0001). There was strong correlation between antibody titres and virus neutralisation in day 28 samples (Spearman's rho 0.75). Vaccinees with baseline IgG antibodies against Zaire Ebolavirus had similar safety profiles to those without detectable antibodies (63.6% vs 66.1% adults experienced any adverse event; 49.1% vs 60.9% in children), with almost all adverse events graded as mild. No serious adverse events were attributed to vaccination. No EVD survivors tested positive for Ebolavirus by RT-PCR.

CONCLUSIONS

These data add further evidence of rVSV-ZEBOV safety and immunogenicity, including in people with pre-existing antibodies from suspected natural ZEBOV infection whose state does not blunt rVSV-ZEBOV immune response. Pre-vaccination serological screening is not required.

A causal multiomics study discriminates the early immune features of Ad5-vectored Ebola vaccine recipients

The vaccine-induced innate immune response is essential for the generation of an antibody response. To date, how Ad5-vectored vaccines are influenced by preexisting anti-Ad5 antibodies during activation of the early immune response remains unclear. Here, we investigated the specific alterations in GP1,2-specific IgG-related elements of the early immune response at the genetic, molecular, and cellular levels on days 0, 1, 3, and 7 after Ad5-EBOV vaccination. In a causal multiomics analysis, distinct early immune responses associated with GP1,2-specific IgG were observed in Ad5-EBOV recipients with a low level of preexisting anti-Ad5 antibodies. This study revealed the correlates of the Ad5-EBOV-induced IgG response and provided mechanistic evidence for overcoming preexisting Ad5 immunity during the administration of Ad5-vectored vaccines.

Refined innate plasma signature after rVSVΔG-ZEBOV-GP immunization is shared among adult cohorts in Europe and North America

Background

During the last decade Ebola virus has caused several outbreaks in Africa. The recombinant vesicular stomatitis virus-vectored Zaire Ebola (rVSVΔG-ZEBOV-GP) vaccine has proved safe and immunogenic but is reactogenic. We previously identified the first innate plasma signature response after vaccination in Geneva as composed of five monocyte-related biomarkers peaking at day 1 post-immunization that correlates with adverse events, biological outcomes (haematological changes and viremia) and antibody titers. In this follow-up study, we sought to identify additional biomarkers in the same Geneva cohort and validate those identified markers in a US cohort.

Methods

Additional biomarkers were identified using multiplexed protein biomarker platform O-link and confirmed by Luminex. Principal component analysis (PCA) evaluated if these markers could explain a higher variability of the vaccine response (and thereby refined the initial signature). Multivariable and linear regression models evaluated the correlations of the main components with adverse events, biological outcomes, and antibody titers. External validation of the refined signature was conducted in a second cohort of US vaccinees (n=142).

Results

Eleven additional biomarkers peaked at day 1 post-immunization: MCP2, MCP3, MCP4, CXCL10, OSM, CX3CL1, MCSF, CXCL11, TRAIL, RANKL and IL15. PCA analysis retained three principal components (PC) that accounted for 79% of the vaccine response variability. PC1 and PC2 were very robust and had different biomarkers that contributed to their variability. PC1 better discriminated different doses, better defined the risk of fever and myalgia, while PC2 better defined the risk of headache. We also found new biomarkers that correlated with reactogenicity, including transient arthritis (MCP-2, CXCL10, CXCL11, CX3CL1, MCSF, IL-15, OSM). Several innate biomarkers are associated with antibody levels one and six months after vaccination. Refined PC1 correlated strongly in both data sets (Geneva: r = 0.97, P < 0.001; US: r = 0.99, P< 0.001).

Conclusion

Eleven additional biomarkers refined the previously found 5-biomarker Geneva signature. The refined signature better discriminated between different doses, was strongly associated with the risk of adverse events and with antibody responses and was validated in a separate cohort.

Baseline gene signatures of reactogenicity to Ebola vaccination: a machine learning approach across multiple cohorts

Introduction

The rVSVDG-ZEBOV-GP (Ervebo®) vaccine is both immunogenic and protective against Ebola. However, the vaccine can cause a broad range of transient adverse reactions, from headache to arthritis. Identifying baseline reactogenicity signatures can advance personalized vaccinology and increase our understanding of the molecular factors associated with such adverse events.

Methods

In this study, we developed a machine learning approach to integrate prevaccination gene expression data with adverse events that occurred within 14 days post-vaccination.

Results and Discussion

We analyzed the expression of 144 genes across 343 blood samples collected from participants of 4 phase I clinical trial cohorts: Switzerland, USA, Gabon, and Kenya. Our machine learning approach revealed 22 key genes associated with adverse events such as local reactions, fatigue, headache, myalgia, fever, chills, arthralgia, nausea, and arthritis, providing insights into potential biological mechanisms linked to vaccine reactogenicity.

Identification of early gene expression profiles associated with long-lasting antibody responses to the Ebola vaccine Ad26.ZEBOV/MVA-BN-Filo

Ebola virus disease is a severe hemorrhagic fever with a high fatality rate. We investigate transcriptome profiles at 3 h, 1 day, and 7 days after vaccination with Ad26.ZEBOV and MVA-BN-Filo. 3 h after Ad26.ZEBOV injection, we observe an increase in genes related to antigen presentation, sensing, and T and B cell receptors. The highest response occurs 1 day after Ad26.ZEBOV injection, with an increase of the gene expression of interferon-induced antiviral molecules, monocyte activation, and sensing receptors. This response is regulated by the HESX1, ATF3, ANKRD22, and ETV7 transcription factors. A plasma cell signature is observed on day 7 post-Ad26.ZEBOV vaccination, with an increase of CD138, MZB1, CD38, CD79A, and immunoglobulin genes. We have identified early expressed genes correlated with the magnitude of the antibody response 21 days after the MVA-BN-Filo and 364 days after Ad26.ZEBOV vaccinations. Our results provide early gene signatures that correlate with vaccine-induced Ebola virus glycoprotein-specific antibodies.

Immunological correlates of protection afforded by PHV02 live, attenuated recombinant vesicular stomatitis virus vector vaccine against Nipah virus disease

Introduction

Immune correlates of protection afforded by PHV02, a recombinant vesicular stomatitis (rVSV) vector vaccine against Nipah virus (NiV) disease, were investigated in the African green monkey (AGM) model. Neutralizing antibody to NiV has been proposed as the principal mediator of protection against future NiV infection.

Methods

Two approaches were used to determine the correlation between neutralizing antibody levels and outcomes following a severe (1,000 median lethal doses) intranasal/intratracheal (IN/IT) challenge with NiV (Bangladesh): (1) reduction in vaccine dose given 28 days before challenge and (2) challenge during the early phase of the antibody response to the vaccine.

Results

Reduction in vaccine dose to very low levels led to primary vaccine failure rather than a sub-protective level of antibody. All AGMs vaccinated with the nominal clinical dose (2 × 107 pfu) at 21, 14, or 7 days before challenge survived. AGMs vaccinated at 21 days before challenge had neutralizing antibodies (geometric mean titer, 71.3). AGMs vaccinated at 7 or 14 days before challenge had either undetectable or low neutralizing antibody titers pre-challenge but had a rapid rise in titers after challenge that abrogated the NiV infection. A simple logistic regression model of the combined studies was used, in which the sole explanatory variable was pre-challenge neutralizing antibody titers. For a pre-challenge titer of 1:5, the predicted survival probability is 100%. The majority of animals with pre-challenge neutralizing titer of ≥1:20 were protected against pulmonary infiltrates on thoracic radiograms, and a majority of those with titers ≥1:40 were protected against clinical signs of illness and against a ≥fourfold antibody increase following challenge (indicating sterile immunity). Controls receiving rVSV-Ebola vaccine rapidly succumbed to NiV challenge, eliminating the innate immunity stimulated by the rVSV vector as a contributor to survival in monkeys challenged as early as 7 days after vaccination.

Discussion and conclusion

It was concluded that PHV02 vaccine elicited a rapid onset of protection and that any detectable level of neutralizing antibody was a functional immune correlate of survival.

A review of criteria strictness in "Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials"

To assess safety in vaccine development, stricter grading scales, such as the "Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in Preventive Vaccine Clinical Trials" issued by the U.S. Food and Drug Administration (FDA grading scale), are required. However, concern exists that their strictness may lead to an overestimation of some adverse events (AEs). We analyzed the details of AEs in a phase I clinical trial of a preventive vaccine for infectious diseases. In this trial, we observed the high occurrence of Grade 1 or greater AEs in hemoglobin changes from baseline value, and hypernatremia, and hypokalemia by FDA grading scale. The range considered as non-AE according to the FDA grading scale shifted or became narrower when compared to reference intervals, especially for a Japanese cohort. For sodium grading, the criterion for hypernatremia was around 2 to mEq/L lower than the upper limit of most standards in several countries. Also, the criterion for hypokalemia was around 0.2 mEq/L higher than the lower limit of most standards. Regarding a decrease in hemoglobin from baseline, the criterion of "any decrease" used for a Grade 1 AE was too strict and we suggest this be omitted. Upper and lower limits of AE criteria for sodium and potassium should be equal to, or 10-20% above, the reference interval consistent with other toxicities determined by laboratory tests. Consideration should be given to the issues surrounding the criteria that determine AEs before conducting clinical trials.

Viral vectored vaccines: design, development, preventive and therapeutic applications in human diseases

Human diseases, particularly infectious diseases and cancers, pose unprecedented challenges to public health security and the global economy. The development and distribution of novel prophylactic and therapeutic vaccines are the prioritized countermeasures of human disease. Among all vaccine platforms, viral vector vaccines offer distinguished advantages and represent prominent choices for pathogens that have hampered control efforts based on conventional vaccine approaches. Currently, viral vector vaccines remain one of the best strategies for induction of robust humoral and cellular immunity against human diseases. Numerous viruses of different families and origins, including vesicular stomatitis virus, rabies virus, parainfluenza virus, measles virus, Newcastle disease virus, influenza virus, adenovirus and poxvirus, are deemed to be prominent viral vectors that differ in structural characteristics, design strategy, antigen presentation capability, immunogenicity and protective efficacy. This review summarized the overall profile of the design strategies, progress in advance and steps taken to address barriers to the deployment of these viral vector vaccines, simultaneously highlighting their potential for mucosal delivery, therapeutic application in cancer as well as other key aspects concerning the rational application of these viral vector vaccines. Appropriate and accurate technological advances in viral vector vaccines would consolidate their position as a leading approach to accelerate breakthroughs in novel vaccines and facilitate a rapid response to public health emergencies.

The Evolution of Medical Countermeasures for Ebola Virus Disease: Lessons Learned and Next Steps

The Ebola virus disease outbreak that occurred in Western Africa from 2013-2016, and subsequent smaller but increasingly frequent outbreaks of Ebola virus disease in recent years, spurred an unprecedented effort to develop and deploy effective vaccines, therapeutics, and diagnostics. This effort led to the U.S. regulatory approval of a diagnostic test, two vaccines, and two therapeutics for Ebola virus disease indications. Moreover, the establishment of fieldable diagnostic tests improved the speed with which patients can be diagnosed and public health resources mobilized. The United States government has played and continues to play a key role in funding and coordinating these medical countermeasure efforts. Here, we describe the coordinated U.S. government response to develop medical countermeasures for Ebola virus disease and we identify lessons learned that may improve future efforts to develop and deploy effective countermeasures against other filoviruses, such as Sudan virus and Marburg virus.

Transcriptomic signatures induced by the Ebola virus vaccine rVSVΔG-ZEBOV-GP in adult cohorts in Europe, Africa, and North America: a molecular biomarker study

BACKGROUND

A recombinant vesicular stomatitis virus vector expressing the Zaire Ebola virus glycoprotein (rVSVΔG-ZEBOV-GP) vaccine has been reported as safe, immunogenic, and highly protective in a ring vaccination trial. We aimed to identify transcriptomic immune response biomarker signatures induced by vaccination and associated signatures with its immunogenicity and reactogenicity to better understand the potential mechanisms of action of the vaccine.

METHODS

354 healthy adult volunteers were vaccinated in randomised, double-blind, placebo-controlled trials in Europe (Geneva, Switzerland [November, 2014, to January, 2015]) and North America (USA [Dec 5, 2014, to June 23, 2015]), and dose-escalation trials in Africa (Lambaréné, Gabon [November, 2014, to January, 2015], and Kilifi, Kenya [December, 2014, to January, 2015]) using different doses of the recombinant vesicular stomatitis virus vector expressing the Zaire Ebola virus glycoprotein (rVSVΔG-ZEBOV-GP; 3 × 10⁵ to 1 × 10⁸ plaque-forming units [pfu]). Longitudinal transcriptomic responses (days 0, 1, 2, 3, 7, 14, and 28) were measured in whole blood using a targeted gene expression profiling platform (dual-colour reverse-transcriptase multiplex ligation-dependent probe amplification) focusing on 144 immune-related genes. The effect of time and dose on transcriptomic response was also assessed. Logistic regression with lasso regularisation was applied to identify host signatures with optimal discriminatory capability of vaccination at day 1 or day 7 versus baseline, whereas random-effects models and recursive feature elimination combined with regularised logistic regression were used to associate signatures with immunogenicity and reactogenicity.

FINDINGS

Our results indicated that perturbation of gene expression peaked on day 1 and returned to baseline levels between day 7 and day 28. The magnitude of the response was dose-dependent, with vaccinees receiving a high dose (≥9 × 10⁶ pfu) of rVSVΔG-ZEBOV-GP exhibiting the largest amplitude. The most differentially expressed genes that were significantly upregulated following vaccination consisted of type I and II interferon-related genes and myeloid cell-associated markers, whereas T cell, natural killer cell, and cytotoxicity-associated genes were downregulated. A gene signature associated with immunogenicity (common to all four cohorts) was identified correlating gene expression profiles with ZEBOV-GP antibody titres and a gene signatures associated with reactogenicity (Geneva cohort) was identified correlating gene expression profiles with an adverse event (ie, arthritis).

INTERPRETATION

Collectively, our results identify and cross-validate immune-related transcriptomic signatures induced by rVSVΔG-ZEBOV-GP vaccination in four cohorts of adult participants from different genetic and geographical backgrounds. These signatures will aid in the rational development, testing, and evaluation of novel vaccines and will allow evaluation of the effect of host factors such as age, co-infection, and comorbidity on responses to vaccines.

FUNDING

Innovative Medicines Initiative 2 Joint Undertaking.

The next major emergent infectious disease: reflections on vaccine emergency development strategies

INTRODUCTION

Major emergent infectious diseases (MEID) pose the most serious threat to human health. The research proposes targeted response strategies for the prevention and control of potential MEID.

AREAS COVERED

Based on the analysis of infectious diseases, this research analyzes pandemics that have a high probability of occurrence and aims to synthesize the past experience and lessons learned of controlling infectious diseases such as coronavirus, influenza, Ebola, etc. In addition, by integrating major infectious disease response guidelines developed by WHO, the European Union, the United States, and the United Kingdom, we intend to bring forward national vaccine R&D development strategies for emergency use.

EXPERT OPINION

We advise to establish and improve existing laws, regulations, and also prevention and control systems for the emergent R&D and application of vaccines in response to potential infectious diseases. The strategies would not only help increase the various abilities in response to the research, development, evaluation, production, and supervision of emergency vaccines, but also establish surrogate endpoint of immunogenicity protection in early clinical studies to enable a rapid evaluation of the efficacy of emergency vaccines.

Therapeutic vaccination strategies against EBOV by rVSV-EBOV-GP: the role of innate immunity

Zaire Ebola virus (EBOV) is a member of the Filoviridae family. Infection with EBOV causes Ebola virus disease (EVD) characterized by excessive inflammation, lymphocyte death, coagulopathy, and multi-organ failure. In 2019, the FDA-approved the first anti-EBOV vaccine, rVSV-EBOV-GP (Ervebo® by Merck). This live-recombinant vaccine confers both prophylactic and therapeutic protection to nonhuman primates and humans. While mechanisms conferring prophylactic protection are well-investigated, those underlying protection conferred shortly before and after exposure to EBOV remain poorly understood. In this review, we review data from in vitro and in vivo studies analyzing early immune responses to rVSV-EBOV-GP and discuss the role of innate immune activation in therapeutic protection.

Risk factors for treatment failure in women with uncomplicated lower urinary tract infection

Given rising antibiotic resistance and increasing use of delayed prescription for uncomplicated lower urinary tract infections (UTI), patients at risk for treatment failure should be identified early. We assessed risk factors for clinical and microbiological failure in women with lower UTI. This case-control study nested within a randomized clinical trial included all women in the per-protocol population (PPP), those in the PPP with microbiologically confirmed UTI, and those in the PPP with UTI due to Escherichia coli. Cases were women who experienced clinical and/or microbiologic failure; controls were those who did not. Risk factors for failure were assessed using multivariate logistic regression. In the PPP, there were 152 clinical cases for 307 controls. Among 340 women with microbiologically confirmed UTI, 126 and 102 cases with clinical and microbiological failure were considered with, respectively, 214 and 220 controls. Age ≥52 years was independently associated with clinical (adjusted OR 3.01; 95%CI 1.84-4.98) and microbiologic failure (aOR 2.55; 95%CI 1.54-4.25); treatment with fosfomycin was associated with clinical failure (aOR 2.35; 95%CI 1.47-3.80). The association with age persisted among all women, and women with E. coli-related UTI. Diabetes was not an independent risk factor, nor were other comorbidities. Postmenopausal age emerged as an independent risk factor for both clinical and microbiological treatment failure in women with lower UTI and should be considered to define women at-risk for non-spontaneous remission, and thus for delayed antibiotic therapy; diabetes mellitus was not associated with failure.

Association of Transcriptomic Signatures of Inflammatory Response with Viral Control after Dendritic Cell-Based Therapeutic Vaccination in HIV-1 Infected Individuals

Systems vaccinology has seldomly been used in therapeutic HIV-1 vaccine research. Our aim was to identify early gene ‘signatures’ that predicted virus load control after analytical therapy interruption (ATI) in participants of a dendritic cell-based HIV-1 vaccine trial (DCV2). mRNA and miRNA were extracted from frozen post-vaccination PBMC samples; gene expression was determined by microarray method. In gene set enrichment analysis, responders showed an up-regulation of 14 gene sets (TNF-alpha/NFkB pathway, inflammatory response, the complement system, Il6 and Il2 JAK-STAT signaling, among others) and a down-regulation of 7 gene sets (such as E2F targets or interferon alpha response). The expression of genes regulated by three (miR-223-3p, miR-1183 and miR-8063) of the 9 differentially expressed miRNAs was significantly down-regulated in responders. The deregulation of certain gene sets related to inflammatory processes seems fundamental for viral control, and certain miRNAs may be important in fine-tuning these processes.

Predictive Markers of Immunogenicity and Efficacy for Human Vaccines

Vaccines represent one of the major advances of modern medicine. Despite the many successes of vaccination, continuous efforts to design new vaccines are needed to fight "old" pandemics, such as tuberculosis and malaria, as well as emerging pathogens, such as Zika virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Vaccination aims at reaching sterilizing immunity, however assessing vaccine efficacy is still challenging and underscores the need for a better understanding of immune protective responses. Identifying reliable predictive markers of immunogenicity can help to select and develop promising vaccine candidates during early preclinical studies and can lead to improved, personalized, vaccination strategies. A systems biology approach is increasingly being adopted to address these major challenges using multiple high-dimensional technologies combined with in silico models. Although the goal is to develop predictive models of vaccine efficacy in humans, applying this approach to animal models empowers basic and translational vaccine research. In this review, we provide an overview of vaccine immune signatures in preclinical models, as well as in target human populations. We also discuss high-throughput technologies used to probe vaccine-induced responses, along with data analysis and computational methodologies applied to the predictive modeling of vaccine efficacy.

Immunization and Drug Metabolizing Enzymes: Focus on Hepatic Cytochrome P450 3A

OBJECTIVE

Infectious disease emergencies like the 2013-2016 Ebola epidemic and the 2009 influenza and current SARS-CoV-2 pandemics illustrate that vaccines are now given to diverse populations with preexisting pathologies requiring pharmacological management. Many natural biomolecules (steroid hormones, fatty acids, vitamins) and ~60% of prescribed medications are processed by hepatic cytochrome P450 (CYP) 3A4. The objective of this work was to determine the impact of infection and vaccines on drug metabolism.

METHODS

The impact of an adenovirus-based vaccine expressing Ebola glycoprotein (AdEBO) and H1N1 and H3N2 influenza viruses on hepatic CYP 3A4 and associated nuclear receptors was evaluated in human hepatocytes (HC-04 cells) and in mice.

RESULTS

CYP3A activity was suppressed by 55% in mice 24 h after administration of mouse-adapted H1N1, while ˂10% activity remained in HC-04 cells after infection with H1N1 and H3N2 due to global suppression of cellular translation capacity, indicated by reduction (70%, H1N1, 56%, H3N2) of phosphorylated eukaryotic translation initiation factor 4e (eIF4E). AdEBO suppressed CYP3A activity in vivo (44%) and in vitro (26%) 24 hours after infection.

CONCLUSION

As the clinical evaluation of vaccines for SARS-CoV-2 and other global pathogens rise, studies to evaluate the impact of new vaccines and emerging pathogens on CYP3A4 and other metabolic enzymes are warranted to avoid therapeutic failures that could further compromise the public health during infectious disease emergencies.

Human Transcriptomic Response to the VSV-Vectored Ebola Vaccine

Ebolavirus Disease (EVD) is a severe haemorrhagic fever that occurs in epidemic outbreaks, with a high fatality rate and no specific therapies available. rVSVΔG-ZEBOV-GP (Ervebo^®), a live-attenuated recombinant vesicular stomatitis virus vector expressing the glycoprotein G of Zaire Ebolavirus, is the first vaccine approved for prevention of EVD. Both innate and adaptive responses are deemed to be involved in vaccine-induced protection, yet the mechanisms are not fully elucidated. A global transcriptomic approach was used to profile the blood host-response in 51 healthy volunteers enrolled in a phase 1/2 clinical trial. Signatures of the host responses were investigated assessing the enrichment in differentially expressed genes (DEGs) of specific “blood transcription modules” (BTM). Comparison of gene-expression levels showed that vaccination produces a peak of 5469 DEGs at day one, representing 38.6% of the expressed genes. Out of 346 BTMs, 144 were significantly affected by vaccination. Innate immunity pathways were induced from day 1 to day 14. At days 2 and 3, neutrophil modules were downregulated and complement-related modules upregulated. T-cell and cell-cycle associated modules were upregulated at days 7 and 14, while at day 28, no modules remained activated. At day 14, a direct correlation was observed between ZEBOV glycoprotein-specific antibody titres and activation of seven BTMs, including two related to B-cell activation and B cell receptor signalling. Transcriptomic analysis identified an rVSVΔG-ZEBOV-GP-induced signature and demonstrated a direct correlation of blood transcriptomic changes with ZEBOV glycoprotein-specific antibody titres.

Development of sustainable research excellence with a global perspective on infectious diseases: Centre de Recherches Médicales de Lambaréné (CERMEL), Gabon

Medical research in sub-Saharan Africa is of high priority for societies to respond adequately to local health needs. Often enough it remains a challenge to build up capacity in infrastructure and human resources to highest international standards and to sustain this over mid-term to long-term periods due to difficulties in obtaining long-term institutional core funding, attracting highly qualified scientists for medical research and coping with ever changing structural and political environments. The Centre de Recherches Médicales de Lambaréné (CERMEL) serves as model for how to overcome such challenges and to continuously increase its impact on medical care in Central Africa and beyond. Starting off as a research annex to the Albert Schweitzer Hospital in Lambaréné, Gabon, it has since then expanded its activities to academic and regulatory clinical trials for drugs, vaccines and diagnostics in the field of malaria, tuberculosis, and a wide range of poverty related and neglected tropical infectious diseases. Advancing bioethics in medical research in Africa and steadily improving its global networks and infrastructures, CERMEL serves as a reference centre for several international consortia. In close collaboration with national authorities, CERMEL has become one of the main training hubs for medical research in Central Africa. It is hoped that CERMEL and its leitmotiv “to improve medical care for local populations” will serve as an inspiration to other institutions in sub-Saharan Africa to further increase African capacity to advance medicine.

Environmental Risk Assessment for rVSVΔG-ZEBOV-GP, a Genetically Modified Live Vaccine for Ebola Virus Disease

rVSVΔG-ZEBOV-GP is a live, attenuated, recombinant vesicular stomatitis virus (rVSV)-based vaccine for the prevention of Ebola virus disease caused by Zaire ebolavirus. As a replication-competent genetically modified organism, rVSVΔG-ZEBOV-GP underwent various environmental evaluations prior to approval, the most in-depth being the environmental risk assessment (ERA) required by the European Medicines Agency. This ERA, as well as the underlying methodology used to arrive at a sound conclusion about the environmental risks of rVSVΔG-ZEBOV-GP, are described in this review. Clinical data from vaccinated adults demonstrated only infrequent, low-level shedding and transient, low-level viremia, indicating a low person-to-person infection risk. Animal data suggest that it is highly unlikely that vaccinated individuals would infect animals with recombinant virus vaccine or that rVSVΔG-ZEBOV-GP would spread within animal populations. Preclinical studies in various hematophagous insect vectors showed that these species were unable to transmit rVSVΔG-ZEBOV-GP. Pathogenicity risk in humans and animals was found to be low, based on clinical and preclinical data. The overall risk for non-vaccinated individuals and the environment is thus negligible and can be minimized further through defined mitigation strategies. This ERA and the experience gained are relevant to developing other rVSV-based vaccines, including candidates under investigation for prevention of COVID-19.

Severe fever with thrombocytopenia syndrome virus: a highly lethal bunyavirus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel bunyavirus. Since 2007, SFTS disease has been reported in China with high fatality rate up to 30%, which drew high attention from Centre for Disease Control and Prevention and government. SFTSV is endemic in the centra l and eastern China, Korea and Japan. There also have been similar cases reported in Vietnam. The number of SFTSV infection cases has a steady growth in these years. As SFTSV could transmitted from person to person, it will expose the public to infectious risk. In 2018 annual review of the Blueprint list of priority diseases, World Health Organisation has listed SFTSV infection as prioritised diseases for research and development in emergency contexts. However, the pathogenesis of SFTSV remains largely unclear. Currently, there are no specific therapeutics or vaccines to combat infections of SFTSV. This review discusses recent findings of epidemiology, transmission pathway, pathogenesis and treatments of SFTS disease.

Immunological Assessment of Pediatric Multisystem Inflammatory Syndrome Related to Coronavirus Disease 2019

BACKGROUND

Recently, cases of multisystem inflammatory syndrome in children (MIS-C) associated with coronavirus disease 2019 (COVID-19) have been reported worldwide. Negative polymerase chain reaction (RT-PCR) testing associated with positive serology in most of the cases suggests a postinfectious syndrome. Because the pathophysiology of this syndrome is still poorly understood, extensive virological and immunological investigations are needed.

METHODS

We report a series of 4 pediatric patients admitted to Geneva University Hospitals with persistent fever and laboratory evidence of inflammation meeting the published definition of MIS-C related to COVID-19, to whom an extensive virological and immunological workup was performed.

RESULTS

RT-PCRs on multiple anatomical compartments were negative, whereas anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin A (IgA) and immunoglobulin G (IgG) were strongly positive by enzyme-linked immunosorbent assay and immunofluorescence. Both pseudoneutralization and full virus neutralization assays showed the presence of neutralizing antibodies in all children, confirming a recent infection with SARS-CoV-2. The analyses of cytokine profiles revealed an elevation in all cytokines, as reported in adults with severe COVID-19. Although differing in clinical presentation, some features of MIS-C show phenotypic overlap with hemophagocytic lymphohistiocytosis (HLH). In contrast to patients with primary HLH, our patients showed normal perforin expression and natural killer (NK) cell degranulation. The levels of soluble interleukin (IL)-2 receptor (sIL-2R) correlated with the severity of disease, reflecting recent T-cell activation.

CONCLUSION

Our findings suggest that MIS-C related to COVID-19 is caused by a postinfectious inflammatory syndrome associated with an elevation in all cytokines, and markers of recent T-cell activation (sIL-2R) occurring despite a strong and specific humoral response to SARS-CoV-2. Further functional and genetic analyses are essential to better understand the mechanisms of host-pathogen interactions.

To B or Not to B: Mechanisms of Protection Conferred by rVSV-EBOV-GP and the Roles of Innate and Adaptive Immunity

Zaire Ebola virus (EBOV) is a member of the Filoviridae family of negative sense, single-stranded RNA viruses. EBOV infection causes Ebola virus disease (EVD), characterized by coagulopathy, lymphopenia, and multi-organ failure, which can culminate in death. In 2019, the FDA approved the first vaccine against EBOV, a recombinant live-attenuated viral vector wherein the G protein of vesicular stomatitis virus is replaced with the glycoprotein (GP) of EBOV (rVSV-EBOV-GP, Ervebo^® by Merck). This vaccine demonstrates high efficacy in nonhuman primates by providing prophylactic, rapid, and post-exposure protection. In humans, rVSV-EBOV-GP demonstrated 100% protection in several phase III clinical trials in over 10,000 individuals during the 2013–2016 West Africa epidemic. As of 2020, over 218,000 doses of rVSV-EBOV-GP have been administered to individuals with high risk of EBOV exposure. Despite licensure and robust preclinical studies, the mechanisms of rVSV-EBOV-GP-mediated protection are not fully understood. Such knowledge is crucial for understanding vaccine-mediated correlates of protection from EVD and to aid the further design and development of therapeutics against filoviruses. Here, we summarize the current literature regarding the host response to vaccination and EBOV exposure, and evidence regarding innate and adaptive immune mechanisms involved in rVSV-EBOV-GP-mediated protection, with a focus on the host transcriptional response. Current data strongly suggest a protective synergy between rapid innate and humoral immunity.

Ebola Virus: Pathogenesis and Countermeasure Development

Since its discovery in 1976, Ebola virus (EBOV) has caused numerous outbreaks of fatal hemorrhagic disease in Africa. The biggest outbreak on record is the 2013-2016 epidemic in west Africa with almost 30,000 cases and over 11,000 fatalities, devastatingly affecting Guinea, Liberia, and Sierra Leone. The epidemic highlighted the need for licensed drugs or vaccines to quickly combat the disease. While at the beginning of the epidemic no licensed countermeasures were available, several experimental drugs with preclinical efficacy were accelerated into human clinical trials and used to treat patients with Ebola virus disease (EVD) toward the end of the epidemic. In the same manner, vaccines with preclinical efficacy were administered primarily to known contacts of EVD patients on clinical trial protocols using a ring-vaccination strategy. In this review, we describe the pathogenesis of EBOV and summarize the current status of EBOV vaccine development and treatment of EVD.

Humoral and cellular immune response induced by rVSVΔG-ZEBOV-GP vaccine among frontline workers during the 2013-2016 West Africa Ebola outbreak in Guinea

BACKGROUND

As part of a Phase III trial with the Ebola vaccine rVSVΔG-ZEBOV-GP in Guinea, we invited frontline workers (FLWs) to participate in a sub-study to provide additional information on the immunogenicity of the vaccine.

METHODS

We conducted an open-label, non-randomized, single-arm immunogenicity evaluation of one dose of rVSVΔG-ZEBOV-GP among healthy FLWs in Guinea. FLWs who refused vaccination were offered to participate as a control group. We followed participants for 84 days with a subset followed-up for 180 days. The primary endpoint was immune response, as measured by ELISA for ZEBOV-glycoprotein-specific antibodies (ELISA-GP) at 28 days. We also conducted neutralization, whole virion ELISA and enzyme-linked immunospot (ELISPOT) assay for cellular response.

RESULTS

A total of 1172 participants received one dose of vaccine and were followed-up for 84 days, among them 114 participants were followed-up for 180 days. Additionally, 99 participants were included in the control group and followed up for 180 days. Overall, 86.4% (95% CI 84.1-88.4) of vaccinated participants seroresponded at 28 days post-vaccination (ELISA- GP) with 65% of these seroresponding at 14 days post-vaccination. Among those who seroresponded at 28 days, 90.7% (95% CI 82.0-95.4) were still seropositive at 180 days. The proportion of seropositivity in the unvaccinated group was 0.0% (95% CI 0.0-3.8) at 28 days and 5.4% (95% CI 2.1-13.1) at 180 days post-vaccination. We found weak correlation between ELISA-GP and neutralization at baseline but significant pairwise correlation at 28 days post-vaccination. Among samples analysed for cellular response, only 1 (2.2%) exhibited responses towards the Zaire Ebola glycoprotein (Ebola GP ≥ 10) at baseline, 10 (13.5%) at day 28 post-vaccination and 27 (48.2%) at Day 180.

CONCLUSIONS

We found one dose of rVSVΔG-ZEBOV-GP to be highly immunogenic at 28- and 180-days post vaccination among frontline workers in Guinea. We also found a cellular response that increased with time.

Rapid dose-dependent Natural Killer (NK) cell modulation and cytokine responses following human rVSV-ZEBOV Ebolavirus vaccination

The rVSV-ZEBOV Ebolavirus vaccine confers protection within days after immunization, suggesting the contribution of innate immune responses. We report modulation of rVSV-ZEBOV vaccinee blood CD56+ NK cell numbers, NKG2D or NKp30 surface receptor expression, Killer Immunoglobulin-like Receptor (KIR)+ cell percentages and NK-cell-related genes on day 1 post immunization. Inverse correlations existed between the concentration of several plasma cytokines and inhibitory KIR+ CD56dim or cytokine-responsive CD56bright NK cells. Thus, NK cells may contribute to the early protective efficacy of rVSV-ZEBOV in humans.

Safety, immunogenicity and risk-benefit analysis of rVSV-ΔG-ZEBOV-GP (V920) Ebola vaccine in Phase I-III clinical trials across regions

To evaluate the risk-benefits balance of the rVSV-ΔG-ZEBOV-GP vaccine. We performed a systematic review to summarize data on safety, immunogenicity and efficacy. About 17,600 adults and 234 children received 11 different doses of the V920 vaccine ranging from 3000 to 100 million and 20 million plaque-forming units, respectively, during Phase I-III clinical trials. Cases of severe but transient arthritis were reported in about six and 0.08% of vaccinees in high-income countries (HICs) and low-middle-income countries (LMICs), respectively. The 20 million plaque-forming units dose yielded GP-specific antibody titres which peaked at day 28 with a pooled geometric mean titres of 2557.7 (95% CI: 1665.5-3934.2) versus 1156.9 (95% CI: 832.5-1649.2) but with similar seroconversion rates at 96% (95% CI: 87-100) versus 100% (95% CI: 90-100) for HICs and LMICs, respectively. Data from stringent Phase I-II clinical trials in LMICs and HICs and from the ring efficacy trials yielded a good risk-benefit balance of the V920 vaccine in adults, but also in children and pregnant and lactating women and HIV-infected people.

Case Report: Case Series of Children With Multisystem Inflammatory Syndrome Following SARS-CoV-2 Infection in Switzerland

Since the beginning of the severe SARS-CoV-2 pandemic, an increasing number of countries reported cases of a systemic hyperinflammatory condition defined as multi-system inflammatory syndrome in children (MIS-C). The clinical features of MIS-C can be an overlap of Kawasaki Disease (KD), Toxic Shock Syndrome (TSS), Macrophage Activation Syndrome (MAS), or have often an acute abdominal presentation. Intravenous immunoglobulin (IVIG) is recommended as first line therapy in KD. Recent evidence suggests intravenous immunoglobulins (IVIG) resistance in some cases of SARS-CoV-2 related MIS-C, thereby questioning the benefit of immunomodulators such as IL-1 or IL-6 blocking agents. We report on a cohort of 6 Swiss children with SARS-CoV2 related MIS-C presenting with clinical features compatible with Incomplete KD and Toxic Shock Syndrome associated to a cytokine storm. Serum cytokine profile investigations showed increased IL1RA levels (8 to 22-fold) in 5 of the 6 patients (one patient had not been tested), whereas, IL-6 serum levels were increased only in the 3 patients of the 6 who were tested. With exception of one patient who had only benefited by Anakinra, all patients received at least one dose of IVIG. One patient has only received Anakinra with favorable evolution, and three patients had also a steroid treatment. In addition to all this anti-inflammatory medication two patients have also received one dose of anti-IL6. In conclusion, our case series reports on clinical and laboratory findings of most of Swiss cases with MIS-C and suggests the use of Anakinra as an alternative to steroids in these children, most of whom presented with high IL-1RA levels.

Methods for predicting vaccine immunogenicity and reactogenicity

Subjects receiving the same vaccine often show different levels of immune responses and some may even present adverse side effects to the vaccine. Systems vaccinology can combine omics data and machine learning techniques to obtain highly predictive signatures of vaccine immunogenicity and reactogenicity. Currently, several machine learning methods are already available to researchers with no background in bioinformatics. Here we described the four main steps to discover markers of vaccine immunogenicity and reactogenicity: (1) Preparing the data; (2) Selecting the vaccinees and relevant genes; (3) Choosing the algorithm; (4) Blind testing your model. With the increasing number of Systems Vaccinology datasets being generated, we expect that the accuracy and robustness of signatures of vaccine reactogenicity and immunogenicity will significantly improve.

Vaccines against Ebola virus and Marburg virus: recent advances and promising candidates

The filoviruses Ebola virus and Marburg virus are among the most dangerous pathogens in the world. Both viruses cause viral hemorrhagic fever, with case fatality rates of up to 90%. Historically, filovirus outbreaks had been relatively small, with only a few hundred cases reported. However, the recent West African Ebola virus outbreak underscored the threat that filoviruses pose. The three year-long outbreak resulted in 28,646 Ebola virus infections and 11,323 deaths. The lack of Food and Drug Administration (FDA) licensed vaccines and antiviral drugs hindered early efforts to contain the outbreak. In response, the global scientific community has spurred the advanced development of many filovirus vaccine candidates. Novel vaccine platforms, such as viral vectors and DNA vaccines, have emerged, leading to the investigation of candidate vaccines that have demonstrated protective efficacy in small animal and nonhuman primate studies. Here, we will discuss several of these vaccine platforms with a particular focus on approaches that have advanced into clinical development.

The how's and what's of vaccine reactogenicity

Reactogenicity represents the physical manifestation of the inflammatory response to vaccination, and can include injection-site pain, redness, swelling or induration at the injection site, as well as systemic symptoms, such as fever, myalgia, or headache. The experience of symptoms following vaccination can lead to needle fear, long-term negative attitudes and non-compliant behaviours, which undermine the public health impact of vaccination. This review presents current knowledge on the potential causes of reactogenicity, and how host characteristics, vaccine administration and composition factors can influence the development and perception of reactogenicity. The intent is to provide an overview of reactogenicity after vaccination to help the vaccine community, including healthcare professionals, in maintaining confidence in vaccines by promoting vaccination, setting expectations for vaccinees about what might occur after vaccination and reducing anxiety by managing the vaccination setting.

Recombinant vesicular stomatitis virus vector vaccines for WHO blueprint priority pathogens

The devastating Ebola virus (EBOV) outbreak in West Africa in 2013-2016 has flagged the need for the timely development of vaccines for high-threat pathogens. To be better prepared for new epidemics, the WHO has compiled a list of priority pathogens that are likely to cause future outbreaks and for which R&D efforts are, therefore, paramount (R&D Blueprint: https://www.who.int/blueprint/priority-diseases/en/ ). To this end, the detailed characterization of vaccine platforms is needed. The vesicular stomatitis virus (VSV) has been established as a robust vaccine vector backbone for infectious diseases for well over a decade. The recent clinical trials testing the vaccine candidate VSV-EBOV against EBOV disease now have added a substantial amount of clinical data and suggest VSV to be an ideal vaccine vector candidate for outbreak pathogens. In this review, we discuss insights gained from the clinical VSV-EBOV vaccine trials as well as from animal studies investigating vaccine candidates for Blueprint pathogens.

rVSVΔG-ZEBOV-GP (also designated V920) recombinant vesicular stomatitis virus pseudotyped with Ebola Zaire Glycoprotein: Standardized template with key considerations for a risk/benefit assessment

The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to evaluate the safety and characteristics of live, recombinant viral vector vaccines. A recent publication by the V3SWG described live, attenuated, recombinant vesicular stomatitis virus (rVSV) as a chimeric virus vaccine for HIV-1 (Clarke et al., 2016). The rVSV vector system is being explored as a platform for development of multiple vaccines. This paper reviews the molecular and biological features of the rVSV vector system, followed by a template with details on the safety and characteristics of a rVSV vaccine against Zaire ebolavirus (ZEBOV). The rVSV-ZEBOV vaccine is a live, replication competent vector in which the VSV glycoprotein (G) gene is replaced with the glycoprotein (GP) gene of ZEBOV. Multiple copies of GP are expressed and assembled into the viral envelope responsible for inducing protective immunity. The vaccine (designated V920) was originally constructed by the National Microbiology Laboratory, Public Health Agency of Canada, further developed by NewLink Genetics Corp. and Merck & Co., and is now in final stages of registration by Merck. The vaccine is attenuated by deletion of the principal virulence factor of VSV (the G protein), which also removes the primary target for anti-vector immunity. The V920 vaccine caused no toxicities after intramuscular (IM) or intracranial injection of nonhuman primates and no reproductive or developmental toxicity in a rat model. In multiple studies, cynomolgus macaques immunized IM with a wide range of virus doses rapidly developed ZEBOV-specific antibodies measured in IgG ELISA and neutralization assays and were fully protected against lethal challenge with ZEBOV virus. Over 20,000 people have received the vaccine in clinical trials; the vaccine has proven to be safe and well tolerated. During the first few days after vaccination, many vaccinees experience a mild acute-phase reaction with fever, headache, myalgia, and arthralgia of short duration; this period is associated with a low-level viremia, activation of anti-viral genes, and increased levels of chemokines and cytokines. Oligoarthritis and rash appearing in the second week occur at a low incidence, and are typically mild-moderate in severity and self-limited. V920 vaccine was used in a Phase III efficacy trial during the West African Ebola epidemic in 2015, showing 100% protection against Ebola Virus Disease, and it has subsequently been deployed for emergency control of Ebola outbreaks in central Africa. The template provided here provides a comprehensive picture of the first rVSV vector to reach the final stage of development and to provide a solution to control of an alarming human disease.

Lassa virus diversity and feasibility for universal prophylactic vaccine

Lassa virus (LASV) is a highly prevalent mammarenavirus in West Africa and is maintained in nature in a persistently infected rodent host, Mastomys natalensis, which is widely spread in sub-Saharan Africa. LASV infection of humans can cause Lassa fever (LF), a disease associated with high morbidity and significant mortality. Recent evidence indicates an LASV expansion outside its traditional endemic areas. In 2017, the World Health Organization (WHO) included LASV in top-priority pathogens and released a Target Product Profile (TPP) for vaccine development. Likewise, in 2018, the US Food and Drug Administration added LF to a priority review voucher program to encourage the development of preventive and therapeutics measures. In this article, we review recent progress in LASV vaccine research and development with a focus on the impact of LASV genetic and biological diversity on the design and development of vaccine candidates meeting the WHO's TPP for an LASV vaccine.

Single dose of a rVSV-based vaccine elicits complete protection against severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia virus (SFTSV) is an emerging tick-borne phlebovirus that causes lethal human disease, for which there are no licensed antiviral vaccines or therapies. Herein, we developed a live attenuated recombinant vesicular stomatitis virus (rVSV)-based vaccine candidate expressing the SFTSV Gn/Gc glycoproteins (rVSV-SFTSV/AH12-GP). High titers of cross-protective, broadly neutralizing antibodies were elicited by a single dose of rVSV-SFTSV/AH12-GP in both immunocompetent and immunocompromised mice against multiple strains of SFTSV and the related but distinct phlebovirus Heartland virus (HRTV). Remarkably, complete protection against lethal challenge with SFTSV was conferred in young and old immunocompromised mice irrespective of any pre-existing vector-specific immunity. Collectively, these results suggest that a rVSV vector expressing SFTSV glycoproteins is a promising candidate vaccine against two emerging phleboviruses associated with severe human diseases.

Durability of single-dose rVSV-ZEBOV vaccine responses: what do we know?

INTRODUCTION

The live-attenuated recombinant vesicular stomatitis virus vaccine expressing the glycoprotein (GP) of Zaire Ebola virus (rVSV-ZEBOV) has proven immunogenic in humans and effective in field studies. Yet long-term durability of vaccine responses is unknown.

AREAS COVERED

We survey the evidence available in the literature for the durability of human responses to rVSV-ZEBOV. We also review determinants of initial responses and of their persistence.

EXPERT COMMENTARY

Persistence of EBOV-GP-specific antibody responses is strong at 2 years - currently the longest post-vaccination interval studied - after a single injection. Vaccine dose predicts persistence of seropositivity, though the magnitude of antibody responses at later time points becomes less dose-dependent. Vaccine-related arthritis is a significant predictor of both persistence and magnitude of the antibody response.

Ebola: Lessons on Vaccine Development

The West African Ebola virus (EBOV) epidemic has fast-tracked countermeasures for this rare, emerging zoonotic pathogen. Until 2013-2014, most EBOV vaccine candidates were stalled between the preclinical and clinical milestones on the path to licensure, because of funding problems, lack of interest from pharmaceutical companies, and competing priorities in public health. The unprecedented and devastating epidemic propelled vaccine candidates toward clinical trials that were initiated near the end of the active response to the outbreak. Those trials did not have a major impact on the epidemic but provided invaluable data on vaccine safety, immunogenicity, and, to a limited degree, even efficacy in humans. There are plenty of lessons to learn from these trials, some of which are addressed in this review. Better preparation is essential to executing an effective response to EBOV in the future; yet, the first indications of waning interest are already noticeable.

The vesicular stomatitis virus-based Ebola virus vaccine: From concept to clinical trials

The devastating Ebola virus (EBOV) epidemic in West Africa in 2013-2016 accelerated the progress of several vaccines and antivirals through clinical trials, including the replication-competent vesicular stomatitis virus-based vaccine expressing the EBOV glycoprotein (VSV-EBOV). Extensive preclinical testing in animal models demonstrated the prophylactic and post-exposure efficacy of this vaccine, identified the mechanism of protection, and suggested it was safe for human use. Based on these data, VSV-EBOV was extensively tested in phase 1-3 clinical trials in North America, Europe and Africa. Although some side effects of vaccination were observed, these clinical trials showed that the VSV-EBOV was safe and immunogenic in humans. Moreover, the data supported the use of VSV-EBOV as an emergency vaccine in individuals at risk for Ebola virus disease. In this review, we summarize the results of the extensive preclinical and clinical testing of the VSV-EBOV vaccine.

Immunogenicity of propagation-restricted vesicular stomatitis virus encoding Ebola virus glycoprotein in guinea pigs

Vesicular stomatitis virus (VSV) expressing the Ebola virus (EBOV) glycoprotein (GP) in place of the VSV glycoprotein G (VSV/EBOV-GP) is a promising EBOV vaccine candidate which has already entered clinical phase 3 studies. Although this chimeric virus was tolerated overall by volunteers, it still caused viremia and adverse effects such as fever and arthritis, suggesting that it might not be sufficiently attenuated. In this study, the VSV/EBOV-GP vector was further modified in order to achieve attenuation while maintaining immunogenicity. All recombinant VSV constructs were propagated on VSV G protein expressing helper cells and used to immunize guinea pigs via the intramuscular route. The humoral immune response was analysed by EBOV-GP-specific fluorescence-linked immunosorbent assay, plaque reduction neutralization test and in vitro virus-spreading inhibition test that employed recombinant VSV/EBOV-GP expressing either green fluorescent protein or secreted Nano luciferase. Most modified vector constructs induced lower levels of protective antibodies than the parental VSV/EBOV-GP or a recombinant modified vaccinia virus Ankara vector encoding full-length EBOV-GP. However, the VSV/EBOV-GP(F88A) mutant was at least as immunogenic as the parental vaccine virus although it was highly propagation-restricted. This finding suggests that VSV-vectored vaccines need not be propagation-competent to induce a robust humoral immune response. However, VSV/EBOV-GP(F88A) rapidly reverted to a fully propagation-competent virus indicating that a single-point mutation is not sufficient to maintain the propagation-restricted phenotype.

Determinants of antibody persistence across doses and continents after single-dose rVSV-ZEBOV vaccination for Ebola virus disease: an observational cohort study

BACKGROUND

The recombinant vesicular stomatitis virus (rVSV) vaccine expressing the Zaire Ebola virus (ZEBOV) glycoprotein is efficacious in the weeks following single-dose injection, but duration of immunity is unknown. We aimed to assess antibody persistence at 1 and 2 years in volunteers who received single-dose rVSV-ZEBOV in three previous trials.

METHODS

In this observational cohort study, we prospectively followed-up participants from the African and European phase 1 rVSV-ZEBOV trials, who were vaccinated once in 2014-15 with 300 000 (low dose) or 10-50 million (high dose) plaque-forming units (pfu) of rVSV-ZEBOV vaccine to assess ZEBOV glycoprotein (IgG) antibody persistence. The primary outcome was ZEBOV glycoprotein-specific IgG geometric mean concentrations (GMCs) measured yearly by ELISA compared with 1 month (ie, 28 days) after immunisation. We report GMCs up to 2 years (Geneva, Switzerland, including neutralising antibodies up to 6 months) and 1 year (Lambaréné, Gabon; Kilifi, Kenya) after vaccination and factors associated with higher antibody persistence beyond 6 months, according to multivariable analyses. Trials and the observational study were registered at ClinicalTrials.gov (Geneva: NCT02287480 and NCT02933931; Kilifi: NCT02296983) and the Pan-African Clinical Trials Registry (Lambaréné PACTR201411000919191).

FINDINGS

Of 217 vaccinees from the original studies (102 from the Geneva study, 75 from the Lambaréné study, and 40 from the Kilifi study), 197 returned and provided samples at 1 year (95 from the Geneva study, 63 from the Lambaréné, and 39 from the Kilifi study) and 90 at 2 years (all from the Geneva study). In the Geneva group, 44 (100%) of 44 participants who had been given a high dose (ie, 10-50 million pfu) of vaccine and who were seropositive at day 28 remained seropositive at 2 years, whereas 33 (89%) of 37 who had been given the low dose (ie, 300 000 pfu) remained seropositive for 2 years (p=0·042). In participants who had received a high dose, ZEBOV glycoprotein IgG GMCs decreased significantly between their peak (at 1-3 months) and month 6 after vaccination in Geneva (p<0·0001) and Lambaréné (p=0·0298) but not in Kilifi (p=0·5833) and subsequently remained stable at all sites apart from Geneva, where GMC in those given a high dose of vaccine increased significantly between 6 months and 1 year (p=0·0264). Antibody persistence was similar at 1 year and at 6 months in those who had received a low dose of vaccine, with lower titres among participants from the Geneva study at 2 years than at 1 year after vaccination (GMC ratio 0·61, 95% CI 0·49-0·77; p<0·0001). In multivariable analyses, predictors of increased IgG GMCs beyond 6 months included high-dose versus low-dose vaccination (Geneva p=0·0133; Lambaréné p=0·008) and vaccine-related arthritis (p=0·0176), but not sex, age, or baseline seropositivity (all p>0·05). Neutralising antibodies seem to be less durable, with seropositivity dropping from 64-71% at 28 days to 27-31% at 6 months in participants from the Geneva study.

INTERPRETATION

Antibody responses to single-dose rVSV-ZEBOV vaccination are sustained across dose ranges and settings, a key criterion in countries where booster vaccinations would be impractical.

FUNDING

The Wellcome Trust and Innovative Medicines Initiative 2 Joint Undertaking.

Immune barriers of Ebola virus infection

Since its initial emergence in 1976 in northern Democratic Republic of Congo (DRC), Ebola virus (EBOV) has been a global health concern due to its virulence in humans, the mystery surrounding the identity of its host reservoir and the unpredictable nature of Ebola virus disease (EVD) outbreaks. Early after the first clinical descriptions of a disease resembling a 'septic-shock-like syndrome', with coagulation abnormalities and multi-system organ failure, researchers began to evaluate the role of the host immune response in EVD pathophysiology. In this review, we summarize how data gathered during the last 40 years in the laboratory as well as in the field have provided insight into EBOV immunity. From molecular mechanisms involved in EBOV recognition in infected cells, to antigen processing and adaptive immune responses, we discuss current knowledge on the main immune barriers of infection as well as outstanding research questions.

Safety and immunogenicity of rVSVΔG-ZEBOV-GP Ebola vaccine in adults and children in Lambaréné, Gabon: A phase I randomised trial

BACKGROUND

The rVSVΔG-ZEBOV-GP vaccine prevented Ebola virus disease when used at 2 × 107 plaque-forming units (PFU) in a trial in Guinea. This study provides further safety and immunogenicity data.

METHODS AND FINDINGS

A randomised, open-label phase I trial in Lambaréné, Gabon, studied 5 single intramuscular vaccine doses of 3 × 103, 3 × 104, 3 × 105, 3 × 106, or 2 × 107 PFU in 115 adults and a dose of 2 × 107 PFU in 20 adolescents and 20 children. The primary objective was safety and tolerability 28 days post-injection. Immunogenicity, viraemia, and shedding post-vaccination were evaluated as secondary objectives. In adults, mild-to-moderate adverse events were frequent, but there were no serious or severe adverse events related to vaccination. Before vaccination, Zaire Ebola virus (ZEBOV)-glycoprotein (GP)-specific and ZEBOV antibodies were detected in 11% and 27% of adults, respectively. In adults, 74%-100% of individuals who received a dose 3 × 104, 3 × 105, 3 × 106, or 2 × 107 PFU had a ≥4.0-fold increase in geometric mean titres (GMTs) of ZEBOV-GP-specific antibodies at day 28, reaching GMTs of 489 (95% CI: 264-908), 556 (95% CI: 280-1,101), 1,245 (95% CI: 899-1,724), and 1,503 (95% CI: 931-2,426), respectively. Twenty-two percent of adults had a ≥4-fold increase of ZEBOV antibodies, with GMTs at day 28 of 1,015 (647-1,591), 1,887 (1,154-3,085), 1,445 (1,013-2,062), and 3,958 (2,249-6,967) for the same doses, respectively. These antibodies persisted up to day 180 for doses ≥3 × 105 PFU. Adults with antibodies before vaccination had higher GMTs throughout. Neutralising antibodies were detected in more than 50% of participants at doses ≥3 × 105 PFU. As in adults, no serious or severe adverse events related to vaccine occurred in adolescents or children. At day 2, vaccine RNA titres were higher for adolescents and children than adults. At day 7, 78% of adolescents and 35% of children had recombinant vesicular stomatitis virus RNA detectable in saliva. The vaccine induced high GMTs of ZEBOV-GP-specific antibodies at day 28 in adolescents, 1,428 (95% CI: 1,025-1,989), and children, 1,620 (95% CI: 806-3,259), and in both groups antibody titres increased up to day 180. The absence of a control group, lack of stratification for baseline antibody status, and imbalances in male/female ratio are the main limitations of this study.

CONCLUSIONS

Our data confirm the acceptable safety and immunogenicity profile of the 2 × 107 PFU dose in adults and support consideration of lower doses for paediatric populations and those who request boosting.

TRIAL REGISTRATION

Pan African Clinical Trials Registry PACTR201411000919191.

Safety and immunogenicity of the rVSV∆G-ZEBOV-GP Ebola virus vaccine candidate in healthy adults: a phase 1b randomised, multicentre, double-blind, placebo-controlled, dose-response study

BACKGROUND

The 2014 Zaire Ebola virus outbreak highlighted the need for a safe, effective vaccine with a rapid onset of protection. We report the safety and immunogenicity of the recombinant vesicular stomatitis virus-Zaire Ebola virus envelope glycoprotein vaccine (rVSV∆G-ZEBOV-GP) across a 6 log₁₀ dose range in two sequential cohorts.

METHODS

In this phase 1b double-blind, placebo-controlled, dose-response study we enrolled and randomly assigned healthy adults (aged 18-61 years) at eight study sites in the USA to receive a single injection of vaccine or placebo, administered by intramuscular injection. In cohort 1, participants were assigned to receive 3 × 10³, 3 × 10⁴, 3 × 10⁵, or 3 × 10⁶ PFU doses of rVSV∆G-ZEBOV-GP or placebo. In cohort 2, participants were assigned to receive 3 × 10⁶, 9 × 10⁶, 2 × 10⁷, or 1 × 10⁸ PFU doses of rVSV∆G-ZEBOV-GP or placebo. Participants were centrally allocated by the study statistician to vaccine groups or placebo through computer-generated randomisation lists. The primary safety outcome was incidence of adverse events within 14 days in the modified intention-to-treat population (all randomly assigned participants who received vaccine or placebo), and the primary outcome for immunogenicity was IgG ELISA antibody titres at day 28 in the per-protocol population. Surveillance was enhanced for arthritis and dermatitis through to day 56. This study is registered with ClinicalTrials.gov, number NCT02314923.

FINDINGS

Between Dec 26, 2014, and June 8, 2015, 513 participants were enrolled and randomly assigned; one was not immunised because of unsuccessful phlebotomy. In cohort 1, 256 participants received vaccine (3 × 10³ [n=64], 3 × 10⁴ [n=64], 3 × 10⁵ [n=64], or 3 × 10⁶ PFU [n=64]) and 74 received placebo. In cohort 2, 162 participants received vaccine (3 × 10⁶ [n=20], 9 × 10⁶ [n=47], 2 × 10⁷ [n=47], or 1 × 10⁸ PFU [n=48]) and 20 received placebo. Most adverse events occurred in the first day after vaccination, and were mild to moderate in intensity, of a short duration, and more frequent at high vaccine doses (9 × 10⁶ PFU and greater). At the 2 × 10⁷ PFU dose (used in phase 3 trials), the most common local adverse events versus placebo within the first 14 days were arm pain (57·4% [27 of 47] vs 7·4% [seven of 94]) and local tenderness (59·6% [28 of 47] vs 8·5% [eight of 94]). The most common systemic adverse events at the 2 × 10⁷ PFU dose versus placebo, occurring in the first 14 days, were headache (46·8% [22 of 47] vs 27·7% [26 of 94]), fatigue (38·3% [18 of 47] vs 19·1% [18 of 94]), myalgia (34·0% [16 of 47] vs 10·6% [10 of 94]), subjective fever (29·8% [14 of 47] vs 2·1% [two of 94]), shivering or chills (27·7% [13 of 47] vs 7·4% [seven of 94]), sweats (23·4% [11 of 47] vs 3·2% [three of 94]), joint aches and pain (19·1% [nine of 47] vs 7·4% [seven of 94]), objective fever (14·9% [seven of 47] vs 1·1% [one of 94]), and joint tenderness or swelling (14·9% [seven of 47] vs 2·1% [two of 94]). Self-limited, post-vaccination arthritis occurred in 4·5% (19 of 418) of vaccinees (median onset 12·0 days [IQR 10-14]; median duration 8·0 days [6-15]) versus 3·2% (three of 94) of controls (median onset 15·0 days [6-20]; median duration 47·0 days [37-339]), with no apparent dose relationship. Post-vaccination dermatitis occurred in 5·7% (24 of 418) of vaccinees (median onset 9·0 days [IQR 2-12]; median duration 7·0 days [4-9]) versus 3·2% (three of 94) of controls (median onset 5·0 days [3-53]; median duration 33·0 days [5-370]). A low-level, transient, dose-dependent viraemia occurred in concert with early reactogenicity. Antibody responses were observed in most participants by day 14. IgG and neutralising antibody titres were dose-related (p=0·0003 for IgG ELISA and p<0·0001 for the 60% plaque-reduction neutralisation test [PRNT60] by linear trend). On day 28 at the 2 × 10⁷ PFU dose, the geometric mean IgG ELISA endpoint titre was 1624 (95% CI 1146-2302) and seroconversion was 95·7% (95% CI 85·5-98·8); the geometric mean neutralising antibody titre by PRNT60 was 250 (176-355) and seroconversion was 95·7% (85·5-98·8). These robust immunological responses were sustained for 1 year.

INTERPRETATION

rVSV∆G-ZEBOV-GP was well tolerated and stimulated a rapid onset of binding and neutralising antibodies, which were maintained through to day 360. The immunogenicity results support selection of the 2 × 10⁷ PFU dose.

FUNDING

Biomedical Advanced Research and Development Authority, US Department of Health and Human Services.

Immunomonitoring of human responses to the rVSV-ZEBOV Ebola vaccine

The rVSV-ZEBOV vaccine is currently the only Ebola vaccine with demonstrated clinical efficacy in a ring-vaccination clinical trial. It has been shown to be reactogenic but immunogenic and safe in several Phase I clinical studies. However, its mechanisms of protection are unknown and available immunogenicity data are mostly limited to classical serological analysis; it is now of paramount importance to apply cutting-edge technologies, including transcriptomic and metabolomic analyses, and to perform integrative analyses with standard serology and clinical data to comprehensively profile the rVSV-ZEBOV immune signature.