First-in-human study to evaluate safety, tolerability, and immunogenicity of heterologous regimens using the multivalent filovirus vaccines Ad26.Filo and MVA-BN-Filo administered in different sequences and schedules: A randomized, controlled study

[Vaccinations for emerging and re-emerging viral diseases]

BACKGROUND

Emerging or re-emerging viral diseases have a pandemic potential and threaten global health. Vaccination is of crucial importance in the prevention of emerging and re-emerging viral diseases.

OBJECTIVE

Description of the current status of vaccine development against Filoviridae, highly pathogenic coronaviruses, smallpox viruses, influenza viruses and arboviruses.

MATERIAL AND METHODS

Focused literature search.

RESULTS

The World Health Organization (WHO) regularly publishes a list of infectious diseases that are expected to pose a major threat to humanity as they are could potentially trigger new pandemics; however, in addition to these human-to-human transmissible diseases, some arboviruses also have pandemic potential. In recent years numerous new vaccines, some of which are highly effective, have been licensed against new and re-emerging viral diseases and other promising vaccine candidates are currently in development.

CONCLUSION

There are still gaps in the development of vaccines in the area of Filoviridae and highly pathogenic coronaviruses. Vaccinations against smallpox viruses have been available for a long time. Developing influenza vaccines against novel strains in a timely manner is a challenge and universal influenza vaccines could be a possible solution. Modern vaccines are available against the arboviruses dengue and Chikungunya fever.

Filovirus vaccines as a response paradigm for emerging infectious diseases

Nowadays, filovirus vaccine development may be seen as a paradigm for our response capabilities to emerging and re-emerging infectious diseases. Specifically, the West African Ebola virus disease (EVD) epidemic accelerated countermeasure licensure for several vaccine and therapeutic products. Those products have been successfully used to control EVD outbreaks in Central Africa over the past years. This positive development, however, has not yet reached beyond EVD. Therefore, it is pertinent to increase our efforts in the development of countermeasures for other human pathogenic members of the family Filoviridae as they continue to threaten public health in Sub-Saharan Africa. This review article summarizes the current filovirus vaccines in preclinical macaque studies and human clinical trials and discusses the most promising recent advancements.

An update on nonhuman primate usage for drug and vaccine evaluation against filoviruses

INTRODUCTION

Due to their faithful recapitulation of human disease, nonhuman primates (NHPs) are considered the gold standard for evaluating drugs against Ebolavirus and other filoviruses. The long-term goal is to reduce the reliance on NHPs with more ethical alternatives. In silico simulations and organoid models have the potential to revolutionize drug testing by providing accurate, human-based systems that mimic disease processes and drug responses without the ethical concerns associated with animal testing. However, as these emerging technologies are still in their developmental infancy, NHP models are presently needed for late-stage evaluation of filovirus vaccines and drugs, as they provide critical insights into the efficacy and safety of new medical countermeasures.

AREAS COVERED

In this review, the authors introduce available NHP models and examine the existing literature on drug discovery for all medically significant filoviruses in corresponding models.

EXPERT OPINION

A deliberate shift toward animal-free models is desired to align with the 3Rs of animal research. In the short term, the use of NHP models can be refined and reduced by enhancing replicability and publishing negative data. Replacement involves a gradual transition, beginning with the selection and optimization of better small animal models; advancing organoid systems, and using in silico models to accurately predict immunological outcomes.

MVA-based vaccines are protective against lethal eastern equine encephalitis virus aerosol challenge in cynomolgus macaques

MVA-based monovalent eastern equine encephalitis virus (MVA-BN-EEEV) and multivalent western, eastern, and Venezuelan equine encephalitis virus (MVA-BN-WEV) vaccines were evaluated in the cynomolgus macaque aerosol model of EEEV infection. Macaques vaccinated with two doses of 5 × 108 infectious units of the MVA-BN-EEEV or MVA-BN-WEV vaccine by the intramuscular route rapidly developed robust levels of neutralizing antibodies to EEEV that persisted at high levels until challenge at day 84 via small particle aerosol delivery with a target inhaled dose of 107 PFU of EEEV FL93-939. Robust protection was observed, with 7/8 animals receiving MVA-BN-EEEV and 100% (8/8) animals receiving MVA-BN-WEV surviving while only 2/8 mock vaccinated controls survived lethal challenge. Complete protection from viremia was afforded by both vaccines, with near complete protection from vRNA loads in tissues and any pathologic evidence of central nervous system damage. Overall, the results indicate both vaccines are effective in eliciting an immune response that is consistent with protection from aerosolized EEEV-induced disease.

Transgene expression knock-down in recombinant Modified Vaccinia virus Ankara vectors improves genetic stability and sustained transgene maintenance across multiple passages

Modified vaccinia virus Ankara is a versatile vaccine vector, well suited for transgene delivery, with an excellent safety profile. However, certain transgenes render recombinant MVA (rMVA) genetically unstable, leading to the accumulation of mutated rMVA with impaired transgene expression. This represents a major challenge for upscaling and manufacturing of rMVA vaccines. To prevent transgene-mediated negative selection, the continuous avian cell line AGE1.CR pIX (CR pIX) was modified to suppress transgene expression during rMVA generation and amplification. This was achieved by constitutively expressing a tetracycline repressor (TetR) together with a rat-derived shRNA in engineered CR pIX PRO suppressor cells targeting an operator element (tetO) and 3' untranslated sequence motif on a chimeric poxviral promoter and the transgene mRNA, respectively. This cell line was instrumental in generating two rMVA (isolate CR19) expressing a Macaca fascicularis papillomavirus type 3 (MfPV3) E1E2E6E7 artificially-fused polyprotein following recombination-mediated integration of the coding sequences into the DelIII (CR19 M-DelIII) or TK locus (CR19 M-TK), respectively. Characterization of rMVA on parental CR pIX or engineered CR pIX PRO suppressor cells revealed enhanced replication kinetics, higher virus titers and a focus morphology equaling wild-type MVA, when transgene expression was suppressed. Serially passaging both rMVA ten times on parental CR pIX cells and tracking E1E2E6E7 expression by flow cytometry revealed a rapid loss of transgene product after only few passages. PCR analysis and next-generation sequencing demonstrated that rMVA accumulated mutations within the E1E2E6E7 open reading frame (CR19 M-TK) or deletions of the whole transgene cassette (CR19 M-DelIII). In contrast, CR pIX PRO suppressor cells preserved robust transgene expression for up to 10 passages, however, rMVAs were more stable when E1E2E6E7 was integrated into the TK as compared to the DelIII locus. In conclusion, sustained knock-down of transgene expression in CR pIX PRO suppressor cells facilitates the generation, propagation and large-scale manufacturing of rMVA with transgenes hampering viral replication.

Prevention and post-exposure management of occupational exposure to Ebola virus

There have been significant advances in the prevention and management of Ebola virus disease (EVD) caused by Zaire Ebola virus (ZEBOV), including the development of two effective vaccines, rVSV-ZEBOV and Ad26.ZEBOV/MVA-BN-Filo. In addition, ZEBOV monoclonal antibodies have become first-line therapy for EVD. However, the 2022-23 outbreak of Sudan Ebola virus (SUDV) in Uganda has highlighted the gap in current therapies and vaccines, whose efficacy is uncertain against non-ZEBOV species. Health-care and laboratory staff working in EVD treatment centres or Ebola virus diagnostic and research laboratories face unique risks relating to potential occupational exposure to Ebola viruses. Given the substantial morbidity and mortality associated with EVD, facilities should have strategies in place to manage occupational exposures, including consideration of post-exposure therapies. In this Review, we discuss currently available evidence for prevention and post-exposure prophylaxis of EVD, including therapies currently under evaluation for SUDV.

Protective MVA-ST Vaccination Robustly Activates T Cells and Antibodies in an Aged-Hamster Model for COVID-19

Aging is associated with a decline in immune system functionality. So-called immunosenescence may impair the successful vaccination of elderly people. Thus, improved vaccination strategies also suitable for an aged immune system are required. Modified Vaccinia virus Ankara (MVA) is a highly attenuated and replication-deficient vaccinia virus that has been established as a multipurpose viral vector for vaccine development against various infections. We characterized a recombinant MVA expressing a prefusion-stabilized version of SARS-CoV-2 S protein (MVA-ST) in an aged-hamster model for COVID-19. Intramuscular MVA-ST immunization resulted in protection from disease and severe lung pathology. Importantly, this protection was correlated with a potent activation of SARS-CoV-2 specific T-cells and neutralizing antibodies. Our results suggest that MVA vector vaccines merit further evaluation in preclinical models to contribute to future clinical development as candidate vaccines in elderly people to overcome the limitations of age-dependent immunosenescence.

Immunogenicity and safety of ebolavirus vaccines in healthy adults: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

This review aimed to systematically evaluate the immunogenicity and safety of the candidate Ebola virus vaccine (EVV).

METHODS

We searched five databases for randomized controlled trials (RCTs) evaluating the effects of EVV on healthy adults. The primary outcomes were relative risk (RR) of sero-conversion or sero-response of EVV in healthy adults between the groups that received EVV and the controls.

RESULTS

Twenty-nine RCTs (n = 23573) were included. There was a significant difference in RR of sero-conversion of EVV (RR 13.18; 95% CI 11.28-15.41; I2 = 33%; P < 0.01) between the two groups. There was a significant difference in RR of adverse events (AEs) of EVV (RR 1.49; 95% CI 1.27-1.74; I2 = 88%; P < 0.01), although no difference in RR of serious AE (SAE) between the two groups. Subgroup analysis showed that there was no significant difference in RR of AEs for DNAEBO, EBOV-GP, MVA, and rVSVN4CT1 vaccines, compared with controls.

CONCLUSIONS

The DNAEBO, EBOV-GP, MVA, and rVSVN4CT1 vaccines are likely to be safe and immunogenic, tending to support the vaccination against Ebola disease. These findings should provide much-needed evidence for public health policy makers to develop preventive measures based on disease prevalence features and socio-economic conditions.

Safety, tolerability, and immunogenicity of the Ebola Sudan chimpanzee adenovirus vector vaccine (cAd3-EBO S) in healthy Ugandan adults: a phase 1, open-label, dose-escalation clinical trial

BACKGROUND

Sudan Ebola virus can cause severe viral disease, with an average case fatality rate of 54%. A recent outbreak of Sudan Ebola virus in Uganda caused 55 deaths among 164 confirmed cases in the second half of 2022. Although vaccines and therapeutics specific for Zaire Ebola virus have been approved for use during outbreak situations, Sudan Ebola virus is an antigenically distinct virus with no approved vaccines available.

METHODS

In this phase 1, open-label, dose-escalation trial we evaluated the safety, tolerability, and immunogenicity of a monovalent chimpanzee adenovirus 3 vaccine against Sudan Ebola virus (cAd3-EBO S) at Makerere University Walter Reed Project in Kampala, Uganda. Study participants were recruited from the Kampala metropolitan area using International Review Board-approved written and electronic media explaining the trial intervention. Healthy adults without previous receipt of Ebola, Marburg, or cAd3 vectored-vaccines were enrolled to receive cAd3-EBO S at either 1 × 1010 or 1 × 1011 particle units (PU) in a single intramuscular vaccination and were followed up for 48 weeks. Primary safety and tolerability endpoints were assessed in all vaccine recipients by reactogenicity for the first 7 days, adverse events for the first 28 days, and serious adverse events throughout the study. Secondary immunogenicity endpoints included evaluation of binding antibody and T-cell responses against the Sudan Ebola virus glycoprotein, and neutralising antibody responses against the cAd3 vector at 4 weeks after vaccination. This study is registered with ClinicalTrials.gov, NCT04041570, and is completed.

FINDINGS

40 healthy adults were enrolled between July 22 and Oct 1, 2019, with 20 receiving 1 × 1010 PU and 20 receiving 1 × 1011 PU of cAd3-EBO S. 38 (95%) participants completed all follow-up visits. The cAd3-EBO S vaccine was well tolerated with no severe adverse events. The most common reactogenicity symptoms were pain or tenderness at the injection site (34 [85%] of 40), fatigue (29 [73%] of 40), and headache (26 [65%] of 40), and were mild to moderate in severity. Positive responses for glycoprotein-specific binding antibodies were induced by 2 weeks in 31 (78%) participants, increased to 34 (85%) participants by 4 weeks, and persisted to 48 weeks in 31 (82%) participants. Most participants developed glycoprotein-specific T-cell responses (20 [59%, 95% CI 41-75] of 34; six participants were removed from the T cell analysis after failing quality control parameters) by 4 weeks after vaccination, and neutralising titres against the cAd3 vector were also increased from baseline (90% inhibitory concentration of 47, 95% CI 30-73) to 4 weeks after vaccination (196, 125-308).

INTERPRETATION

The cAd3-EBO S vaccine was safe at both doses, rapidly inducing immune responses in most participants after a single injection. The rapid onset and durability of the vaccine-induced antibodies make this vaccine a strong candidate for emergency deployment in Sudan Ebola virus outbreaks.

FUNDING

National Institutes of Health via interagency agreement with Walter Reed Army Institute of Research.

[Vaccines to prevent Ebola virus disease: current challenges and perspectives]

RELEVANCE

Ebola virus disease (EVD) is an acute infectious disease with an extremely high case fatality rate reaching up to 90%. EVD has become widely known since 2014-2016, when outbreak in West Africa occurred and led to epidemic, which caused travel-related cases on the territory of other continents. There are two vaccines against EVD, prequalified by WHO for emergency use, as well as a number of vaccines, approved by local regulators in certain countries. However, even with the availability of effective vaccines, the lack of data on immune correlates of protection and duration of protective immune response in humans and primates is limiting factor for effectively preventing the spread of EVD outbreaks.

AIMS

This review highlights experience of use of EVD vaccines during outbreaks in endemic areas, summarizes data on vaccine immunogenicity in clinical trials, and discusses perspectives for further development and use of effective EVD vaccines.

[Ebola and Marburg virus disease]

Viral hemorrhagic fevers (VHF) are serious, often fatal diseases that affect humans and non-human primates. The nomenclature of these diseases has changed in that they are now referred to as viral diseases because the previously named symptoms of fever or hemorrhages are not obligatory. In this article, the focus will be on the VHFs Ebola and Marburg viral disease with the potential for human-to-human transmission; these diseases are so-called high-consequence infectious diseases (HCID), some with considerable potential for epidemic spread and the risk of nosocomial transmission.

Persistence of immunological memory as a potential correlate of long-term, vaccine-induced protection against Ebola virus disease in humans

Introduction

In the absence of clinical efficacy data, vaccine protective effect can be extrapolated from animals to humans, using an immunological biomarker in humans that correlates with protection in animals, in a statistical approach called immunobridging. Such an immunobridging approach was previously used to infer the likely protective effect of the heterologous two-dose Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine regimen. However, this immunobridging model does not provide information on how the persistence of the vaccine-induced immune response relates to durability of protection in humans.

Methods and results

In both humans and non-human primates, vaccine-induced circulating antibody levels appear to be very stable after an initial phase of contraction and are maintained for at least 3.8 years in humans (and at least 1.3 years in non-human primates). Immunological memory was also maintained over this period, as shown by the kinetics and magnitude of the anamnestic response following re-exposure to the Ebola virus glycoprotein antigen via booster vaccination with Ad26.ZEBOV in humans. In non-human primates, immunological memory was also formed as shown by an anamnestic response after high-dose, intramuscular injection with Ebola virus, but was not sufficient for protection against Ebola virus disease at later timepoints due to a decline in circulating antibodies and the fast kinetics of disease in the non-human primates model. Booster vaccination within three days of subsequent Ebola virus challenge in non-human primates resulted in protection from Ebola virus disease, i.e. before the anamnestic response was fully developed.

Discussion

Humans infected with Ebola virus may benefit from the anamnestic response to prevent disease progression, as the incubation time is longer and progression of Ebola virus disease is slower as compared to non-human primates. Therefore, the persistence of vaccine-induced immune memory could be considered as a potential correlate of long-term protection against Ebola virus disease in humans, without the need for a booster.

Highly attenuated poxvirus-based vaccines against emerging viral diseases

Although one member of the poxvirus family, variola virus, has caused one of the most devastating human infections worldwide, smallpox, the knowledge gained over the last 30 years on the molecular, virological and immunological mechanisms of these viruses has allowed the use of members of this family as vectors for the generation of recombinant vaccines against numerous pathogens. In this review, we cover different aspects of the history and biology of poxviruses with emphasis on their application as vaccines, from first- to fourth-generation, against smallpox, monkeypox, emerging viral diseases highlighted by the World Health Organization (COVID-19, Crimean-Congo haemorrhagic fever, Ebola and Marburg virus diseases, Lassa fever, Middle East respiratory syndrome and severe acute respiratory syndrome, Nipah and other henipaviral diseases, Rift Valley fever and Zika), as well as against one of the most concerning prevalent virus, the Human Immunodeficiency Virus, the causative agent of AcquiredImmunodeficiency Syndrome. We discuss the implications in human health of the 2022 monkeypox epidemic affecting many countries, and the rapid prophylactic and therapeutic measures adopted to control virus dissemination within the human population. We also describe the preclinical and clinical evaluation of the Modified Vaccinia virus Ankara and New York vaccinia virus poxviral strains expressing heterologous antigens from the viral diseases listed above. Finally, we report different approaches to improve the immunogenicity and efficacy of poxvirus-based vaccine candidates, such as deletion of immunomodulatory genes, insertion of host-range genes and enhanced transcription of foreign genes through modified viral promoters. Some future prospects are also highlighted.