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

High dose of vesicular stomatitis virus-vectored Ebola virus vaccine causes vesicular disease in swine without horizontal transmission

ABSTRACTThe recent impact of Ebola virus disease (EVD) on public health in Africa clearly demonstrates the need for a safe and efficacious vaccine to control outbreaks and mitigate its threat to global health. ERVEBO® is an effective recombinant Vesicular Stomatitis Virus (VSV)-vectored Ebola virus vaccine (VSV-EBOV) that was approved by the FDA and EMA in late 2019 for use in prevention of EVD. Since the parental virus VSV, which was used to construct VSV-EBOV, is pathogenic for livestock and the vaccine virus may be shed at low levels by vaccinated humans, widespread deployment of the vaccine requires investigation into its infectivity and transmissibility in VSV-susceptible livestock species. We therefore performed a comprehensive clinical analysis of the VSV-EBOV vaccine virus in swine to determine its infectivity and potential for transmission. A high dose of VSV-EBOV resulted in VSV-like clinical signs in swine, with a proportion of pigs developing ulcerative vesicular lesions at the nasal injection site and feet. Uninoculated contact control pigs co-mingled with VSV-EBOV-inoculated pigs did not become infected or display any clinical signs of disease, indicating the vaccine is not readily transmissible to naïve pigs during prolonged close contact. In contrast, virulent wild-type VSV Indiana had a shorter incubation period and was transmitted to contact control pigs. These results indicate that the VSV-EBOV vaccine causes vesicular illness in swine when administered at a high dose. Moreover, the study demonstrates the VSV-EBOV vaccine is not readily transmitted to uninfected pigs, encouraging its safe use as an effective human vaccine.

Mucosal Delivery of Recombinant Vesicular Stomatitis Virus Vectors Expressing Envelope Proteins of Respiratory Syncytial Virus Induces Protective Immunity in Cotton Rats

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract (LRT) infections, with increased severity in high-risk human populations, such as infants, the immunocompromised, and the elderly. Although the virus was identified more than 60 years ago, there is still no licensed vaccine available. Over the years, several vaccine delivery strategies have been evaluated. In this study, we developed two recombinant vesicular stomatitis virus (rVSV) vector-based vaccine candidates expressing the RSV-G (attachment) protein (rVSV-G) or F (fusion) protein (rVSV-F). All vectors were evaluated in the cotton rat animal model for their in vivo immunogenicity and protective efficacy against an RSV-A2 virus challenge. Intranasal (i.n.) delivery of rVSV-G and rVSV-F together completely protected the lower respiratory tract (lungs) at doses as low as 10³ PFU. In contrast, doses greater than 10⁶ PFU were required to protect the upper respiratory tract (URT) completely. Reimmunization of RSV-immune cotton rats was most effective with rVSV-F. In immunized animals, overall antibody responses were sufficient for protection, whereas CD4 and CD8 T cells were not necessary. A prime-boost immunization regimen increased both protection and neutralizing antibody titers. Overall, mucosally delivered rVSV-vector-based RSV vaccine candidates induce protective immunity and therefore represent a promising immunization regimen against RSV infection.IMPORTANCE Even after decades of intensive research efforts, a safe and efficacious RSV vaccine remains elusive. Expression of heterologous antigens from rVSV vectors has demonstrated several practical and safety advantages over other virus vector systems and live attenuated vaccines. In this study, we developed safe and efficacious vaccine candidates by expressing the two major immunogenic RSV surface proteins in rVSV vectors and delivering them mucosally in a prime-boost regimen. The main immune parameter responsible for protection was the antibody response. These vaccine candidates induced complete protection of both the upper and lower respiratory tracts.

Ebolavirus: Comparison of Survivor Immunology and Animal Models in the Search for a Correlate of Protection

Ebola viruses are enveloped, single-stranded RNA viruses belonging to the Filoviridae family and can cause Ebola virus disease (EVD), a serious haemorrhagic illness with up to 90% mortality. The disease was first detected in Zaire (currently the Democratic Republic of Congo) in 1976. Since its discovery, Ebola virus has caused sporadic outbreaks in Africa and was responsible for the largest 2013-2016 EVD epidemic in West Africa, which resulted in more than 28,600 cases and over 11,300 deaths. This epidemic strengthened international scientific efforts to contain the virus and develop therapeutics and vaccines. Immunology studies in animal models and survivors, as well as clinical trials have been crucial to understand Ebola virus pathogenesis and host immune responses, which has supported vaccine development. This review discusses the major findings that have emerged from animal models, studies in survivors and vaccine clinical trials and explains how these investigations have helped in the search for a correlate of protection.

Vaccine formulations in clinical development for the prevention of severe acute respiratory syndrome coronavirus 2 infection

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an unprecedented effort toward the development of an effective and safe vaccine. Aided by extensive research efforts into characterizing and developing countermeasures towards prior coronavirus epidemics, as well as recent developments of diverse vaccine platform technologies, hundreds of vaccine candidates using dozens of delivery vehicles and routes have been proposed and evaluated preclinically. A high demand coupled with massive effort from researchers has led to the advancement of at least 31 candidate vaccines in clinical trials, many using platforms that have never before been approved for use in humans. This review will address the approach and requirements for a successful vaccine against SARS-CoV-2, the background of the myriad of vaccine platforms currently in clinical trials for COVID-19 prevention, and a summary of the present results of those trials. It concludes with a perspective on formulation problems which remain to be addressed in COVID-19 vaccine development and antigens or adjuvants which may be worth further investigation.

Development of leading first-generation vaccines against SARS-CoV-2

SARS-CoV-2 has infected more than 167 million individuals globally. Highly effective and safe vaccines are required to accelerate the development of herd immunity to end the pandemic. This review focuses on vaccines that are being developed at unprecedented speed globally and are completing late phase clinical trials to meet this urgent need.

A single dose of recombinant VSV-∆G-spike vaccine provides protection against SARS-CoV-2 challenge

The COVID-19 pandemic caused by SARS-CoV-2 imposes an urgent need for rapid development of an efficient and cost-effective vaccine, suitable for mass immunization. Here, we show the development of a replication competent recombinant VSV-∆G-spike vaccine, in which the glycoprotein of VSV is replaced by the spike protein of SARS-CoV-2. In-vitro characterization of this vaccine indicates the expression and presentation of the spike protein on the viral membrane with antigenic similarity to SARS-CoV-2. A golden Syrian hamster in-vivo model for COVID-19 is implemented. We show that a single-dose vaccination results in a rapid and potent induction of SARS-CoV-2 neutralizing antibodies. Importantly, vaccination protects hamsters against SARS-CoV-2 challenge, as demonstrated by the abrogation of body weight loss, and  alleviation of the extensive tissue damage and viral loads in lungs and nasal turbinates. Taken together, we suggest the recombinant VSV-∆G-spike as a safe, efficacious and protective vaccine against SARS-CoV-2.

Here, the authors generate a replication-competent VSV based vaccine expressing SARS-CoV-2 spike protein and show protection in the hamster model with one dose. Analysis of the antibody response in mice shows induction of neutralizing antibodies and suggests a desirable Th1-biased response to the vaccine.

New viral vectors for infectious diseases and cancer

Since the discovery in 1796 by Edward Jenner of vaccinia virus as a way to prevent and finally eradicate smallpox, the concept of using a virus to fight another virus has evolved into the current approaches of viral vectored genetic vaccines. In recent years, key improvements to the vaccinia virus leading to a safer version (Modified Vaccinia Ankara, MVA) and the discovery that some viruses can be used as carriers of heterologous genes encoding for pathological antigens of other infectious agents (the concept of 'viral vectors') has spurred a new wave of clinical research potentially providing for a solution for the long sought after vaccines against major diseases such as HIV, TB, RSV and Malaria, or emerging infectious diseases including those caused by filoviruses and coronaviruses. The unique ability of some of these viral vectors to stimulate the cellular arm of the immune response and, most importantly, T lymphocytes with cell killing activity, has also reawakened the interest toward developing therapeutic vaccines against chronic infectious diseases and cancer. To this end, existing vectors such as those based on Adenoviruses have been improved in immunogenicity and efficacy. Along the same line, new vectors that exploit viruses such as Vesicular Stomatitis Virus (VSV), Measles Virus (MV), Lymphocytic choriomeningitis virus (LCMV), cytomegalovirus (CMV), and Herpes Simplex Virus (HSV), have emerged. Furthermore, technological progress toward modifying their genome to render some of these vectors incompetent for replication has increased confidence toward their use in infant and elderly populations. Lastly, their production process being the same for every product has made viral vectored vaccines the technology of choice for rapid development of vaccines against emerging diseases and for 'personalised' cancer vaccines where there is an absolute need to reduce time to the patient from months to weeks or days. Here we review the recent developments in viral vector technologies, focusing on novel vectors based on primate derived Adenoviruses and Poxviruses, Rhabdoviruses, Paramixoviruses, Arenaviruses and Herpesviruses. We describe the rationale for, immunologic mechanisms involved in, and design of viral vectored gene vaccines under development and discuss the potential utility of these novel genetic vaccine approaches in eliciting protection against infectious diseases and cancer.

New vaccine production platforms used in developing SARS-CoV-2 vaccine candidates

The threat of the current coronavirus disease pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is accelerating the development of potential vaccines. Candidate vaccines have been generated using existing technologies that have been applied for developing vaccines against other infectious diseases. Two new types of platforms, mRNA- and viral vector-based vaccines, have been gaining attention owing to the rapid advancement in their methodologies. In clinical trials, setting appropriate immunological endpoints plays a key role in evaluating the efficacy and safety of candidate vaccines. Updated information about immunological features from individuals who have or have not been exposed to SARS-CoV-2 continues to guide effective vaccine development strategies. This review highlights key strategies for generating candidate SARS-CoV-2 vaccines and considerations for vaccine development and clinical trials.

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.

A promising antiviral candidate drug for the COVID-19 pandemic: A mini-review of remdesivir

Remdesivir (GS-5734), a viral RNA-dependent RNA polymerase (RdRP) inhibitor that can be used to treat a variety of RNA virus infections, is expected to be an effective treatment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. On May 1, 2020, The U.S. Food and Drug Administration (FDA) has granted Emergency Use Authorization (EUA) for remdesivir to treat COVID-19 patients. In light of the COVID-19 pandemic, this review presents comprehensive information on remdesivir, including information regarding the milestones, intellectual properties, anti-coronavirus mechanisms, preclinical research and clinical trials, and in particular, the chemical synthesis, pharmacology, toxicology, pharmacodynamics and pharmacokinetics of remdesivir. Furthermore, perspectives regarding the use of remdesivir for the treatment of COVID-19 are also discussed.

The Propagation, Quantification, and Storage of Vesicular Stomatitis Virus

Vesicular stomatitis virus (VSV) is the prototypical member of the Rhabdoviridae family of negative-sense single-stranded RNA viruses. This virus has been used as a powerful model system for decades and is currently being used as a vaccine platform and an oncolytic agent. Here, we present methods to propagate, quantitate, and store VSV. We also review the proper safety protocol for the handling of VSV, which is classified as a Biosafety Level 2 pathogen by the United States Centers for Disease Control and Prevention. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Generation, purification, and storage of vesicular stomatitis virus stocks Basic Protocol 2: Quantification of vesicular stomatitis virus by plaque assay Support Protocol: Propagation of Vero cells.

A Surrogate Animal Model for Screening of Ebola and Marburg Glycoprotein-Targeting Drugs Using Pseudotyped Vesicular Stomatitis Viruses

Filoviruses, including Ebola virus (EBOV) and Marburg virus (MARV), cause severe hemorrhagic fever in humans and nonhuman primates with high mortality rates. There is no approved therapy against these deadly viruses. Antiviral drug development has been hampered by the requirement of a biosafety level (BSL)-4 facility to handle infectious EBOV and MARV because of their high pathogenicity to humans. In this study, we aimed to establish a surrogate animal model that can be used for anti-EBOV and -MARV drug screening under BSL-2 conditions by focusing on the replication-competent recombinant vesicular stomatitis virus (rVSV) pseudotyped with the envelope glycoprotein (GP) of EBOV (rVSV/EBOV) and MARV (rVSV/MARV), which has been investigated as vaccine candidates and thus widely used in BSL-2 laboratories. We first inoculated mice, rats, and hamsters intraperitoneally with rVSV/EBOV and found that only hamsters showed disease signs and succumbed within 4 days post-infection. Infection with rVSV/MARV also caused lethal infection in hamsters. Both rVSV/EBOV and rVSV/MARV were detected at high titers in multiple organs including the liver, spleen, kidney, and lungs of infected hamsters, indicating acute and systemic infection resulting in fatal outcomes. Therapeutic effects of passive immunization with an anti-EBOV neutralizing antibody were specifically observed in rVSV/EBOV-infected hamsters. Thus, this animal model is expected to be a useful tool to facilitate in vivo screening of anti-filovirus drugs targeting the GP molecule.

Oncolytic Virus with Attributes of Vesicular Stomatitis Virus and Measles Virus in Hepatobiliary and Pancreatic Cancers

Recombinant vesicular stomatitis virus (VSV)-fusion and hemagglutinin (FH) was developed by substituting the promiscuous VSV-G glycoprotein (G) gene in the backbone of VSV with genes encoding for the measles virus envelope proteins F and H. Hybrid VSV-FH exhibited a multifaceted mechanism of cancer-cell killing and improved neurotolerability over parental VSV in preclinical studies. In this study, we evaluated VSV-FH in vitro and in vivo in models of hepatobiliary and pancreatic cancers. Our results indicate that high intrahepatic doses of VSV-FH did not result in any significant toxicity and were well tolerated by transgenic mice expressing the measles virus receptor CD46. Furthermore, a single intratumoral treatment with VSV-FH yielded improved survival and complete tumor regressions in a proportion of mice in the Hep3B hepatocellular carcinoma model but not in mice xenografted with BxPC-3 pancreatic cancer cells. Our preliminary findings indicate that VSV-FH can induce potent oncolysis in hepatocellular and pancreatic cancer cell lines with concordant results in vivo in hepatocellular cancer and discordant in pancreatic cancer without the VSV-mediated toxic effects previously observed in laboratory animals. Further study of VSV-FH as an oncolytic virotherapy is warranted in hepatocellular carcinoma and pancreatic cancer to understand broader applicability and mechanisms of sensitivity and resistance.

Vesicular Stomatitis Virus and DNA Vaccines Expressing Zika Virus Nonstructural Protein 1 Induce Substantial but Not Sterilizing Protection against Zika Virus Infection

The nonstructural protein 1 (NS1) of several flaviviruses, including West Nile, dengue, and yellow fever viruses, is capable of inducing variable degrees of protection against flavivirus infection in animal models. However, the immunogenicity of NS1 protein of Zika virus (ZIKV) is less understood. Here, we determined the efficacy of ZIKV NS1-based vaccine candidates using two delivery platforms, methyltransferase-defective recombinant vesicular stomatitis virus (mtdVSV) and a DNA vaccine. We first show that expression of ZIKV NS1 could be significantly enhanced by optimizing the signal peptide. A single dose of mtdVSV-NS1-based vaccine or two doses of DNA vaccine induced high levels of NS1-specfic antibody and T cell immune responses but provided only partial protection against ZIKV viremia in BALB/c mice. In Ifnar1^-/- mice, neither NS1-based vaccine provided protection against a lethal high dose (10⁵ PFU) ZIKV challenge, but mtdVSV-NS1-based vaccine prevented deaths from a low dose (10³ PFU) challenge, though they experienced viremia and body weight loss. We conclude that ZIKV NS1 alone conferred substantial, but not complete, protection against ZIKV infection. Nevertheless, these results highlight the value of ZIKV NS1 for vaccine development.IMPORTANCE Most Zika virus (ZIKV) vaccine research has focused on the E or prM-E proteins and the induction of high levels of neutralizing antibodies. However, these ZIKV neutralizing antibodies cross-react with other flaviviruses, which may aggravate the disease via an antibody-dependent enhancement (ADE) mechanism. ZIKV NS1 protein may be an alternative antigen for vaccine development, since antibodies to NS1 do not bind to the virion, thereby eliminating the risk of ADE. Here, we show that recombinant VSV and DNA vaccines expressing NS1, alone, confer partial protection against ZIKV infection in both immunocompetent and immunodeficient mice, highlighting the value of NS1 as a potential vaccine candidate.

A tool with many applications: vesicular stomatitis virus in research and medicine

INTRODUCTION

Vesicular stomatitis virus (VSV) has long been a useful research tool in virology and recently become an essential part of medicinal products. Vesiculovirus research is growing quickly following its adaptation to clinical gene and cell therapy and oncolytic virotherapy.

AREAS COVERED

This article reviews the versatility of VSV as a research tool and biological reagent, its use as a viral and vaccine vector delivering therapeutic and immunogenic transgenes and an oncolytic virus aiding cancer treatment. Challenges such as the immune response against such advanced therapeutic medicinal products and manufacturing constraints are also discussed.

EXPERT OPINION

The field of in vivo gene and cell therapy is advancing rapidly with VSV used in many ways. Comparison of VSV's use as a versatile therapeutic reagent unveils further prospects and problems for each application. Overcoming immunological challenges to aid repeated administration of viral vectors and minimizing harmful host-vector interactions remains one of the major challenges. In the future, exploitation of reverse genetic tools may assist the creation of recombinant viral variants that have improved onco-selectivity and more efficient vaccine vector activity. This will add to the preferential features of VSV as an excellent advanced therapy medicinal product (ATMP) platform.

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.

Combination therapy with oncolytic viruses and immune checkpoint inhibitors

Introduction: Immune checkpoint inhibitors (ICI) have dramatically improved the outcome for cancer patients across multiple tumor types. However the response rates to ICI monotherapy remain relatively low, in part due to some tumors cultivating an inherently 'cold' immune microenvironment. Oncolytic viruses (OV) have the capability to promote a 'hotter' immune microenvironment which can improve the efficacy of ICI.Areas covered: In this article we conducted a literature search through Pubmed/Medline to identify relevant articles in both the pre-clinical and clinical settings for combining OVs with ICIs and discuss the impact of this approach on treatment as well as changes within the tumor microenvironment. We also explore the future directions of this novel combination strategy.Expert opinion: The imminent results of the Phase 3 study combining pembrolizumab with or without T-Vec injection are eagerly awaited. OV/ICI combinations remain one of the most promising avenues to explore in the success of cancer immunotherapy.

Pseudovirus rVSVΔG-ZEBOV-GP Infects Neurons in Retina and CNS, Causing Apoptosis and Neurodegeneration in Neonatal Mice

Zaire Ebola virus (ZEBOV) survivors experience visual and CNS sequelae that suggests the ZEBOV glycoprotein can mediate neurotropism. Replication-competent rVSVΔG-ZEBOV-GP vaccine candidate is generally well tolerated; however, its potential neurotropism requires careful study. Here, we show that a single inoculation of rVSVΔG-ZEBOV-GP virus in neonatal C57BL/6 mice results in transient viremia, neurological symptoms, high viral titers in eyes and brains, and death. rVSVΔG-ZEBOV-GP infects the inner layers of the retina, causing severe retinitis. In the cerebellum, rVSVΔG-ZEBOV-GP infects neurons in the granular and Purkinje layers, resulting in progressive foci of apoptosis and neurodegeneration. The susceptibility to infection is not due to impaired type I IFN responses, although MDA5^-/-, IFNβ^-/-, and IFNAR1^-/- mice have accelerated mortality. However, boosting interferon levels by co-administering poly(I:C) reduces viral titers in CNS and improves survival. Although these data should not be directly extrapolated to humans, they challenge the hypothesis that VSV-based vaccines are non-neurotropic.

Usp18 Expression in CD169+ Macrophages is Important for Strong Immune Response after Vaccination with VSV-EBOV

Ebola virus epidemics can be effectively limited by the VSV-EBOV vaccine (Ervebo) due to its rapid protection abilities; however, side effects prevent the broad use of VSV-EBOV as vaccine. Mechanisms explaining the efficient immune activation after single injection with the VSV-EBOV vaccine remain mainly unknown. Here, using the clinically available VSV-EBOV vaccine (Ervebo), we show that the cell-intrinsic expression of the interferon-inhibitor Usp18 in CD169⁺ macrophages is one important factor modulating the anti-Ebola virus immune response. The absence of Usp18 in CD169⁺ macrophages led to the reduced local replication of VSV-EBOV followed by a diminished innate as well as adaptive immune response. In line, CD169-Cre^+/ki x Usp18^fl/fl mice showed reduced innate and adaptive immune responses against the VSV wildtype strain and died quickly after infection, suggesting that a lack of Usp18 makes mice more susceptible to the side effects of the VSV vector. In conclusion, our study shows that Usp18 expression in CD169⁺ macrophages is one important surrogate marker for effective vaccination against VSV-EBOV, and probably other VSV-based vaccines also.

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.

A single dose of a vesicular stomatitis virus-based influenza vaccine confers rapid protection against H5 viruses from different clades

The avian influenza virus outbreak in 1997 highlighted the potential of the highly pathogenic H5N1 virus to cause severe disease in humans. Therefore, effective vaccines against H5N1 viruses are needed to counter the potential threat of a global pandemic. We have previously developed a fast-acting and efficacious vaccine against Ebola virus (EBOV) using the vesicular stomatitis virus (VSV) platform. In this study, we generated recombinant VSV-based H5N1 influenza virus vectors to demonstrate the feasibility of this platform for a fast-acting pan-H5 influenza virus vaccine. We chose multiple approaches regarding antigen design and genome location to define a more optimized vaccine approach. After the VSV-based H5N1 influenza virus constructs were recovered and characterized in vitro, mice were vaccinated by a single dose or prime/boost regimen followed by challenge with a lethal dose of the homologous H5 clade 1 virus. We found that a single dose of VSV vectors expressing full-length hemagglutinin (HAfl) were sufficient to provide 100% protection. The vaccine vectors were fast-acting as demonstrated by uniform protection when administered 3 days prior to lethal challenge. Moreover, single vaccination induced cross-protective H5-specific antibodies and protected mice against lethal challenge with various H5 clade 2 viruses, highlighting the potential of the VSV-based HAfl as a pan-H5 influenza virus emergency vaccine.

A Chimeric Sudan Virus-Like Particle Vaccine Candidate Produced by a Recombinant Baculovirus System Induces Specific Immune Responses in Mice and Horses

Ebola virus infections lead to severe hemorrhagic fevers in humans and nonhuman primates; and human fatality rates are as high as 67%–90%. Since the Ebola virus was discovered in 1976, the only available treatments have been medical support or the emergency administration of experimental drugs. The absence of licensed vaccines and drugs against the Ebola virus impedes the prevention of viral infection. In this study, we generated recombinant baculoviruses (rBV) expressing the Sudan virus (SUDV) matrix structural protein (VP40) (rBV-VP40-VP40) or the SUDV glycoprotein (GP) (rBV-GP-GP), and SUDV virus-like particles (VLPs) were produced by co-infection of Sf9 cells with rBV-SUDV-VP40 and rBV-SUDV-GP. The expression of SUDV VP40 and GP in SUDV VLPs was demonstrated by IFA and Western blot analysis. Electron microscopy results demonstrated that SUDV VLPs had a filamentous morphology. The immunogenicity of SUDV VLPs produced in insect cells was evaluated by the immunization of mice. The analysis of antibody responses showed that mice vaccinated with SUDV VLPs and the adjuvant Montanide ISA 201 produced SUDV GP-specific IgG antibodies. Sera from SUDV VLP-immunized mice were able to block infection by SUDV GP pseudotyped HIV, indicating that a neutralizing antibody against the SUDV GP protein was produced. Furthermore, the activation of B cells in the group immunized with VLPs mixed with Montanide ISA 201 was significant one week after the primary immunization. Vaccination with the SUDV VLPs markedly increased the frequency of antigen-specific cells secreting type 1 and type 2 cytokines. To study the therapeutic effects of SUDV antibodies, horses were immunized with SUDV VLPs emulsified in Freund’s complete adjuvant or Freund’s incomplete adjuvant. The results showed that horses could produce SUDV GP-specific antibodies and neutralizing antibodies. These results showed that SUDV VLPs demonstrate excellent immunogenicity and represent a promising approach for vaccine development against SUDV infection. Further, these horse anti-SUDV purified immunoglobulins lay a foundation for SUDV therapeutic drug research.

Global Medicine, Parasites, and Tasmania

Until the 1970s, infectious disease training in most medical schools was limited to those diseases common in the area of instruction. Those wishing to explore a more globalised curriculum were encouraged to undertake specialist postgraduate training at schools or institutes of tropical medicine. However, the increase in global trade and travel from the 1970s onward led to dramatic changes in the likelihood of returning travellers and new immigrants presenting with tropical infections in temperate regions. Furthermore, population growth and the changing relationships between animals, the environment, and man in agriculture accentuated the importance of a wider understanding of emerging infectious diseases, zoonotic diseases and parasitic infections. These epidemiological facts were not adequately reflected in the medical literature or medical curriculum at the time. The orientation on tropical infections needed specialised attention, including instruction on diagnosis and treatment of such infections. We describe key global health events and how the changing field of global medicine, from the 1970s to early 2000, impacted on medical education and research. We describe the impact of global health changes in the Tasmanian context, a temperate island state of Australia. We retrospectively analysed data of patients diagnosed with parasites and present a list of endemic and non-endemic parasites reported during this period. Finally, we reflect on the new approaches to the changing needs of global health and challenges that medical programmes, learners and educators face today.

A Novel Bacterium-Like Particle-Based Vaccine Displaying the SUDV Glycoprotein Induces Potent Humoral and Cellular Immune Responses in Mice

Sudan virus (SUDV) causes severe lethal hemorrhagic fever in humans and nonhuman primates. The most effective and economical way to protect against Sudan ebolavirus disease is prophylactic vaccination. However, there are no licensed vaccines to prevent SUDV infections. In this study, a bacterium-like particle (BLP)-based vaccine displaying the extracellular domain of the SUDV glycoprotein (eGP) was developed based on a gram-positive enhancer matrix-protein anchor (GEM-PA) surface display system. Expression of the recombinant GEM-displayed eGP (eGP-PA-GEM) was verified by Western blotting and immunofluorescence assays. The SUDV BLPs (SBLPs), which were mixed with Montanide ISA 201VG plus Poly (I:C) combined adjuvant, could induce high SUDV GP-specific IgG titers of up to 1:40,960 and robust virus-neutralizing antibody titers reached 1:460. The SBLP also elicited T-helper 1 (Th1) and T-helper 2 (Th2) cell-mediated immunity. These data indicate that the SBLP subunit vaccine has the potential to be developed into a promising candidate vaccine against SUDV infections.

Maternal and Infant Death and the rVSV-ZEBOV Vaccine Through Three Recent Ebola Virus Epidemics-West Africa, DRC Équateur and DRC Kivu: 4 Years of Excluding Pregnant and Lactating Women and Their Infants from Immunization

Purpose of Review

Ebola virus infection has one of the highest overall case fatality rates of any viral disease. It has historically had an especially high case mortality rate among pregnant women and infants—greater than 90% for pregnant women in some outbreaks and close to 100 % in fetuses and newborns. The Merck recombinant vaccine against Ebola virus, termed rVSV-ZEBOV, underwent clinical trials during the 2013–2015 West Africa Ebola epidemic where it was found to be 100% efficacious. It was subsequently used during the 2018 DRC Équateur outbreak and in the 2018 DRC Kivu Ebola which is still ongoing, where its efficacy is 97.5 %. Pregnant and lactating women and their infants have previously been excluded from the design, clinical trials, and administration of many vaccines and drugs. This article critically examines the development of the rVSV-ZEBOV vaccine and its accessibility to pregnant and lactating women and infants as a life-saving form of prevention through three recent African Ebola epidemics—West Africa, DRC Équateur, and DRC Kivu.

Recent Findings

Pregnant and lactating women and their infants were excluded from participation in the clinical trials of rVSV-ZEBOV conducted during the West Africa epidemic. This policy of exclusion was continued with the occurrence of the DRC Équateur outbreak in 2018, in spite of calls from the public health and global maternal health communities to vaccinate this population. Following the onset of the DRC Kivu epidemic, the exclusion persisted. Eventually, the policy was reversed to include vaccination of pregnant and lactating women. However, it was not implemented until June 2019, 10 months after the start of the epidemic, placing hundreds of women and infants at risk for this highly fatal infection.

Summary

The historical policy of excluding pregnant and lactating women and infants from vaccine design, clinical trials, and implementation places them at risk, especially in situations of infectious disease outbreaks. In the future, all pregnant women, regardless of trimester, breastfeeding mothers, and infants, should have access to the Ebola vaccine.

Efficient Expression and Processing of Ebola Virus Glycoprotein Induces Morphological Changes in BmN Cells but Cannot Rescue Deficiency of Bombyx Mori Nucleopolyhedrovirus GP64

Ebola virus (EBOV) disease outbreaks have resulted in many fatalities, yet no licensed vaccines are available to prevent infection. Recombinant glycoprotein (GP) production may contribute to finding a cure for Ebola virus disease, which is the key candidate protein for vaccine preparation. To explore GP_1,2 expression in BmN cells, EBOV-GP_1,2 with its native signal peptide or the GP64 signal peptide was cloned and transferred into a normal or gp64 null Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid via transposition. The infectivity of the recombinant bacmids was investigated after transfection, expression and localization of EBOV-GP were investigated, and cell morphological changes were analyzed by TEM. The GP64 signal peptide, but not the GP_1,2 native signal peptide, caused GP_1,2 localization to the cell membrane, and the differentially localized GP_1,2 proteins were cleaved into GP₁ and GP₂ fragments in BmN cells. GP_1,2 expression resulted in dramatic morphological changes in BmN cells in the early stage of infection. However, GP_1,2 expression did not rescue GP64 deficiency in BmNPV infection. This study provides a better understanding of GP expression and processing in BmN cells, which may lay a foundation for EBOV-GP expression using the BmNPV baculovirus expression system.

Single low-dose VSV-EBOV vaccination protects cynomolgus macaques from lethal Ebola challenge

Background

Ebola virus (EBOV), variant Makona, was the causative agent of the 2013–2016 West African epidemic responsible for almost 30,000 human infections and over 11,000 fatalities. During the epidemic, the development of several experimental vaccines was accelerated through human clinical trials. One of them, the vesicular stomatitis virus (VSV)-based vaccine VSV-EBOV, showed promising efficacy in a phase 3 clinical trial in Guinea and is currently used in the ongoing EBOV outbreak in the northeastern part of the Democratic Republic of the Congo (DRC). This vaccine expresses the EBOV-Kikwit glycoprotein from the 1995 outbreak as the immunogen.

Methods

Here we generated a VSV-based vaccine expressing the contemporary EBOV-Makona glycoprotein. We characterized the vaccine in tissue culture and analyzed vaccine efficacy in the cynomolgus macaque model. Subsequently, we determined the dose-dependent protective efficacy in nonhuman primates against lethal EBOV challenge.

Findings

We observed complete protection from disease with VSV-EBOV doses ranging from 1 × 10⁷ to 1 × 10¹ plaque-forming units. Some protected animals receiving lower vaccine doses developed temporary low-level EBOV viremia. Control animals developed classical EBOV disease and reached euthanasia criteria within a week after challenge. This study demonstrates that very low doses of VSV-EBOV uniformly protect macaques against lethal EBOV challenge.

Interpretation

Our study provides missing pre-clinical data supporting the use of reduced VSV-EBOV vaccine doses without decreasing protective efficacy and at the same time increase vaccine safety and availability - two critical concerns in public health response.

Funding

Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health.

Polyclonal and convergent antibody response to Ebola virus vaccine rVSV-ZEBOV

Recombinant vesicular stomatitis virus-Zaire Ebola virus (rVSV-ZEBOV) is the most advanced Ebola virus vaccine candidate and is currently being used to combat the outbreak of Ebola virus disease (EVD) in the Democratic Republic of the Congo (DRC). Here we examine the humoral immune response in a subset of human volunteers enrolled in a phase 1 rVSV-ZEBOV vaccination trial by performing comprehensive single B cell and electron microscopy structure analyses. Four studied vaccinees show polyclonal, yet reproducible and convergent B cell responses with shared sequence characteristics. EBOV-targeting antibodies cross-react with other Ebolavirus species, and detailed epitope mapping revealed overlapping target epitopes with antibodies isolated from EVD survivors. Moreover, in all vaccinees, we detected highly potent EBOV-neutralizing antibodies with activities comparable or superior to the monoclonal antibodies currently used in clinical trials. These include antibodies combining the IGHV3-15/IGLV1-40 immunoglobulin gene segments that were identified in all investigated individuals. Our findings will help to evaluate and direct current and future vaccination strategies and offer opportunities for novel EVD therapies.

Dendritic Cells/Macrophages-Targeting Feature of Ebola Glycoprotein and its Potential as Immunological Facilitator for Antiviral Vaccine Approach

In the prevention of epidemic and pandemic viral infection, the use of the antiviral vaccine has been the most successful biotechnological and biomedical approach. In recent times, vaccine development studies have focused on recruiting and targeting immunogens to dendritic cells (DCs) and macrophages to induce innate and adaptive immune responses. Interestingly, Ebola virus (EBOV) glycoprotein (GP) has a strong binding affinity with DCs and macrophages. Shreds of evidence have also shown that the interaction between EBOV GP with DCs and macrophages leads to massive recruitment of DCs and macrophages capable of regulating innate and adaptive immune responses. Therefore, studies for the development of vaccine can utilize the affinity between EBOV GP and DCs/macrophages as a novel immunological approach to induce both innate and acquired immune responses. In this review, we will discuss the unique features of EBOV GP to target the DC, and its potential to elicit strong immune responses while targeting DCs/macrophages. This review hopes to suggest and stimulate thoughts of developing a stronger and effective DC-targeting vaccine for diverse virus infection using EBOV GP.

Tamoxifen Protects from Vesicular Stomatitis Virus Infection

BACKGROUND

Tamoxifen (TAM) is an estrogen-receptor antagonist, widely used in the adjuvant treatment of early stage estrogen-sensitive breast cancer. Several studies have revealed new biological targets of TAM that mediate the estrogen receptor independent activities of the drug. Recently, the antiviral activity of TAM on replication of human immunodeficiency virus (HIV), hepatitis C virus (HCV) and Herpes simplex virus (HSV-1) in vitro was described. In the current study, we aimed to investigate the effect of TAM on infection with vesicular stomatitis virus (VSV).

METHODS

Vero cells were treated with different concentrations of TAM for 24 h and then infected with VSV. Additionally, C57BL/6 mice were pretreated with 4 mg TAM, one day and three days before infection with VSV. Results: Treatment of Vero cells with TAM suppressed the viral replication of VSV in vitro and in vivo. The inhibitory effect of TAM on VSV replication correlated with an enhanced interferon-I response and stimulation of macrophages. Conclusions: TAM was identified as being capable to protect from VSV infection in vitro and in vivo. Consequently, this antiviral function (as an advantageous side-effect of TAM) might give rise to new clinical applications, such as treatment of resistant virus infections, or serve as an add-on to standard antiviral therapy.

Hantavirus entry: Perspectives and recent advances

Hantaviruses are important zoonotic pathogens of public health importance that are found on all continents except Antarctica and are associated with hemorrhagic fever with renal syndrome (HFRS) in the Old World and hantavirus pulmonary syndrome (HPS) in the New World. Despite the significant disease burden they cause, no FDA-approved specific therapeutics or vaccines exist against these lethal viruses. The lack of available interventions is largely due to an incomplete understanding of hantavirus pathogenesis and molecular mechanisms of virus replication, including cellular entry. Hantavirus Gn/Gc glycoproteins are the only viral proteins exposed on the surface of virions and are necessary and sufficient to orchestrate virus attachment and entry. In vitro studies have implicated integrins (β_1-3), DAF/CD55, and gC1qR as candidate receptors that mediate viral attachment for both Old World and New World hantaviruses. Recently, protocadherin-1 (PCDH1) was demonstrated as a requirement for cellular attachment and entry of New World hantaviruses in vitro and lethal HPS in vivo, making it the first clade-specific host factor to be identified. Attachment of hantavirus particles to cellular receptors induces their internalization by clathrin-mediated, dynamin-independent, or macropinocytosis-like mechanisms, followed by particle trafficking to an endosomal compartment where the fusion of viral and endosomal membranes can occur. Following membrane fusion, which requires cholesterol and acid pH, viral nucleocapsids escape into the cytoplasm and launch genome replication. In this review, we discuss the current mechanistic understanding of hantavirus entry, highlight gaps in our existing knowledge, and suggest areas for future inquiry.

Use of Single-Injection Recombinant Vesicular Stomatitis Virus Vaccine to Protect Nonhuman Primates Against Lethal Nipah Virus Disease

Nipah virus (NiV) is a zoonotic pathogen that causes high case-fatality rates (CFRs) in humans. Two NiV strains have caused outbreaks: the Malaysia strain (NiVM), discovered in 1998-1999 in Malaysia and Singapore (≈40% CFR); and the Bangladesh strain (NiVB), discovered in Bangladesh and India in 2001 (≈80% CFR). Recently, NiVB in African green monkeys resulted in a more severe and lethal disease than NiVM. No NiV vaccines or treatments are licensed for human use. We assessed replication-restricted single-injection recombinant vesicular stomatitis vaccine NiV vaccine vectors expressing the NiV glycoproteins against NiVB challenge in African green monkeys. All vaccinated animals survived to the study endpoint without signs of NiV disease; all showed development of NiV F Ig, NiV G IgG, or both, as well as neutralizing antibody titers. These data show protective efficacy against a stringent and relevant NiVB model of human infection.

Measles-vectored vaccine approaches against viral infections: a focus on Chikungunya

INTRODUCTION

The large global burden of viral infections and especially the rapidly spreading vector-borne diseases and other emerging viral diseases show the need for new approaches in vaccine development. Several new vaccine technology platforms have been developed and are under evaluation. Areas covered: This article discusses the measles vector platform technology derived from the safe and highly efficacious measles virus vaccine. The pipeline of measles-vectored vaccine candidates against viral diseases is reviewed. Particular focus is given to the Chikungunya vaccine candidate as the first measles-vectored vaccine that demonstrated safety, immunogenicity, and functionality of the technology in humans even in the presence of pre-existing anti-measles immunity and thus achieved proof of concept for the technology. Expert commentary: Demonstrating no impact of pre-existing anti-measles immunity in humans on the response to the transgene was fundamental for the technology and indicates that the technology is suitable for large-scale immunization in measles pre-immune populations. The proof of concept in humans combined with a large preclinical track record of safety, immunogenicity, and efficacy for a variety of pathogens suggest the measles vector platform as promising plug-and-play vaccine platform technology for rapid development of effective preventive vaccines against viral and other infectious diseases.

Recombinant influenza A viruses as vaccine vectors

INTRODUCTION

Various viruses, including poxviruses, adenoviruses and vesicular stomatitis virus, have been considered as vaccine vectors for the delivery of antigens of interest in the development of vaccines against newly emerging pathogens.

AREAS COVERED

Here, we review results that have been obtained with influenza A viruses (IAV) as vaccine vectors. With the advent of reverse genetics technology, IAV-based recombinant vaccine candidates have been constructed that induce protective immunity to a variety of different pathogens of interest, including West Nile virus, Plasmodium falciparum and respiratory syncytial virus. The various cloning strategies to produce effective and attenuated, safe to use IAV-based viral vectors are discussed.

EXPERT COMMENTARY

It was concluded that IAV-based vector system has several advantages and holds promise for further development.

A Measles Virus-Based Vaccine Candidate Mediates Protection against Zika Virus in an Allogeneic Mouse Pregnancy Model

The impact of the Zika virus (ZIKV) epidemic highlights the need for vaccines that reduce or prevent infection and reliably prevent teratogenic complications. The live-attenuated measles virus (MV) vaccine strains are a promising vaccine platform, since they induce robust humoral and cellular immune responses against additional antigens and have an excellent safety record. To explore its potential to protect against ZIKV, we compared a recombinant Schwarz strain MV that encodes ZIKV prM and soluble E proteins (MV-Zika-sE) with a prototypic alum-adjuvanted whole inactivated ZIKV particle vaccine. Analysis of MV-Zika-sE-infected cells confirmed antigen expression, and the virus replicated with vaccine strain characteristics. Immunized IFNAR-/--CD46Ge mice developed E protein-specific and neutralizing antibodies, and ZIKV E-specific cellular immune responses were observed by gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) and in vitro T cell proliferation assays. To analyze protective efficacy, vaccinated female mice were challenged with ZIKV after allogeneic mating. In MV-Zika-sE-vaccinated mice, weight gain was similar to that in uninfected mice, while no plasma viremia was detectable in the majority of the animals. In contrast, infected control animals gained less weight and experienced about 100-fold higher viremia over at least 3 days. Moreover, vaccination with MV-Zika-sE reduced the ZIKV load in different organs and the placentas and prevented infection of the fetus. Consequently, no fetal growth retardation, anemia, or death due to ZIKV infection was seen in MV-Zika-sE-vaccinated dams. In contrast, the inactivated ZIKV vaccine had little to no effect in our studies. Therefore, the MV-derived ZIKV vaccine is a promising candidate for further preclinical and clinical development.IMPORTANCE Zika virus (ZIKV) is a mosquito-borne flavivirus that causes a variety of neurological complications, including congenital birth defects. Despite the urgent need, no ZIKV vaccine has yet been licensed. Recombinant vaccine strain-derived measles viruses (MV) constitute a promising vector platform to induce immunity against foreign pathogens by expressing antigens from additional transcription units while at the same time possessing a remarkable safety profile. This concept has already been validated against different pathogens, including at least 3 other flaviviruses, and our data show that vaccination with MV expressing soluble ZIKV E protein significantly diminishes infection and prevents fetal loss or damage in an allogeneic mouse pregnancy model. It can thus be regarded as a promising emergency vaccine candidate with the potential for inclusion in routine vaccination settings in areas of endemicity to prevent teratogenic effects of circulating ZIKV during pregnancy, comparable to standard rubella virus vaccination.

Self-Replicating RNA Viruses for RNA Therapeutics

Self-replicating single-stranded RNA viruses such as alphaviruses, flaviviruses, measles viruses, and rhabdoviruses provide efficient delivery and high-level expression of therapeutic genes due to their high capacity of RNA replication. This has contributed to novel approaches for therapeutic applications including vaccine development and gene therapy-based immunotherapy. Numerous studies in animal tumor models have demonstrated that self-replicating RNA viral vectors can generate antibody responses against infectious agents and tumor cells. Moreover, protection against challenges with pathogenic Ebola virus was obtained in primates immunized with alphaviruses and flaviviruses. Similarly, vaccinated animals have been demonstrated to withstand challenges with lethal doses of tumor cells. Furthermore, clinical trials have been conducted for several indications with self-amplifying RNA viruses. In this context, alphaviruses have been subjected to phase I clinical trials for a cytomegalovirus vaccine generating neutralizing antibodies in healthy volunteers, and for antigen delivery to dendritic cells providing clinically relevant antibody responses in cancer patients, respectively. Likewise, rhabdovirus particles have been subjected to phase I/II clinical trials showing good safety and immunogenicity against Ebola virus. Rhabdoviruses have generated promising results in phase III trials against Ebola virus. The purpose of this review is to summarize the achievements of using self-replicating RNA viruses for RNA therapy based on preclinical animal studies and clinical trials in humans.

Recent Advances in Zika Virus Vaccines

The recent outbreaks of Zika virus (ZIKV) infections and associated microcephaly in newborns has resulted in an unprecedented effort by researchers to target this virus. Significant advances have been made in developing vaccine candidates, treatment strategies and diagnostic assays in a relatively short period of time. Being a preventable disease, the first line of defense against ZIKV would be to vaccinate the highly susceptible target population, especially pregnant women. Along those lines, several vaccine candidates including purified inactivated virus (PIV), live attenuated virus (LAV), virus like particles (VLP), DNA, modified RNA, viral vectors and subunit vaccines have been in the pipeline with several advancing to clinical trials. As the primary objective of Zika vaccination is the prevention of vertical transmission of the virus to the unborn fetus, the safety and efficacy requirements for this vaccine remain unique when compared to other diseases. This review will discuss these recent advances in the field of Zika vaccine development.

Poxvirus-based vector systems and the potential for multi-valent and multi-pathogen vaccines

INTRODUCTION

With the increasing number of vaccines and vaccine-preventable diseases, the pressure to generate multi-valent and multi-pathogen vaccines grows. Combining individual established vaccines to generate single-shot formulations represents an established path, with significant ensuing public health and cost benefits. Poxvirus-based vector systems have the capacity for large recombinant payloads and have been widely used as platforms for the development of recombinant vaccines encoding multiple antigens, with considerable clinical trials activity and a number of registered and licensed products.

AREAS COVERED

Herein we discuss design strategies, production processes, safety issues, regulatory hurdles and clinical trial activities, as well as pertinent new technologies such as systems vaccinology and needle-free delivery. Literature searches used PubMed, Google Scholar and clinical trials registries, with a focus on the recombinant vaccinia-based systems, Modified Vaccinia Ankara and the recently developed Sementis Copenhagen Vector.

EXPERT COMMENTARY

Vaccinia-based platforms show considerable promise for the development of multi-valent and multi-pathogen vaccines, especially with recent developments in vector technologies and manufacturing processes. New methodologies for defining immune correlates and human challenge models may also facilitate bringing such vaccines to market.

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.

Tip Your Cap for Ebola Virus Neutralization

Outbreaks of Ebola virus disease are caused by multiple virus species although current therapeutic monoclonal antibodies (mAb) are essentially limited to treating one species, Zaire ebolavirus. In this issue of Immunity, Gilchuk et al. (2018) identify new mAbs with potent cross-neutralizing activity against three ebolavirus species pathogenic to humans.