Modeling pre-existing immunity to adenovirus in rodents: immunological requirements for successful development of a recombinant adenovirus serotype 5-based ebola vaccine

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.

Immunogenicity of adenovirus-vector vaccine targeting hepatitis B virus: non-clinical safety assessment in non-human primates

Background

A new promising therapeutic approach has emerged for patients chronically infected by the hepatitis B virus (HBV) with the development of a non-replicative adenovirus vector vaccine candidate (Ad-HBV). The vaccine encodes a fusion protein composed of a truncated HBV core protein, mutated polymerase protein, and two envelope domains. In this study, we assessed the immunogenicity of Ad-HBV administered to cynomolgus monkeys during a non-clinical safety assessment.

Methods

The virus was subcutaneously administered at 1.0 × 10⁹ viral particles (VP)/animal (low-dose group), 1.0 × 10¹⁰ VP/animal (mid-dose group), and 1.0 × 10¹¹ VP/animal (high-dose group); the control groups were administered an Ad5-null virus (1.0 × 10¹¹ VP/animal) and saline only.

Results

Except for inflammatory cell infiltration under the skin at the injection sites and transient elevation of body temperature and serum albumin, no Ad-HBV-related toxic effects were noted in any treatment group. Moreover, interferon (IFN)-γ enzyme-linked immunospot assays showed that Ad-HBV induced the targeting of T cells to a broad spectrum of HBV-specific epitopes spanning all three of the selected HBV immunogens (core, polymerase, and envelope domains) in a dose-dependent manner. Although anti-Ad antibody was produced in all groups (except for the saline control), the antibody titers were significantly lower in the high-dose Ad-HBV group than in the group that received the same dose of the Ad-null empty vector. In addition, the IFN-γ and IL-2 expression levels in the liver were significantly improved for the mid-dose, high-dose, and Ad-null control group (p < 0.05), but not for the low-dose group.

Conclusions

Taken together, this safety assessment indicates that the Ad-HBV candidate vaccine is a potent specific immunotherapeutic agent, supporting its further clinical development as an anti-HBV infection vaccine.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1026-3) contains supplementary material, which is available to authorized users.

Decreased Vector Gene Expression from E2b Gene-Deleted Adenovirus Serotype 5 Vaccines Intensifies Proinflammatory Immune Responses

Recombinant adenovirus serotype 5 (Ad5) vectors are promising vaccine candidates due to their intrinsic immunogenicity and potent transgene expression; however, widespread preexisting Ad5 immunity has been considered a developmental impediment to the use of traditional, or conventional, E1 and E3 gene-deleted Ad5 (Ad5[E1-]) vaccines. Even in the presence of anti-Ad5 immunity, recent murine and human studies have confirmed E2b gene-deleted Ad5 (Ad5[E1-,E2b-]) vaccines to be highly efficacious inducers of transgene-specific memory responses and significantly less toxic options than Ad5[E1-] vaccines. While these findings have been substantially confirmed, the molecular mechanisms underlying the different reactions to these vaccine platforms are unknown. Using cultures of human peripheral blood mononuclear cells (hPBMCs) derived from multiple human donors, we found that Ad5[E1-,E2b-] vaccines trigger higher levels of hPBMC proinflammatory cytokine secretion than Ad5[E1-] vaccines. Interestingly, these responses were generated regardless of the donors' preexisting anti-Ad5 humoral and cell-mediated immune response status. In vitro hPBMC infection with the Ad5[E1-,E2b-] vaccine also provoked greater Th1-dominant gene responses yet smaller amounts of Ad-derived gene expression than Ad5[E1-] vaccines. These results suggest that Ad5[E1-,E2b-] vaccines, in contrast to Ad5[E1-] vaccines, do not promote activities that suppress innate immune signaling, thereby allowing for improved vaccine efficacy and a superior safety profile independently of previous Ad5 immunity.

Safety and immunogenicity of a recombinant adenovirus type-5 vector-based Ebola vaccine in healthy adults in Sierra Leone: a single-centre, randomised, double-blind, placebo-controlled, phase 2 trial

BACKGROUND

A recombinant adenovirus type-5 vector-based vaccine expressing the glycoprotein of Ebola Zaire Makona variant showed good safety and immunogenicity in a phase 1 trial of healthy Chinese adults. We aimed to assess the safety and immunogenicity of this vaccine in healthy adults in Sierra Leone and to determine the optimal dose.

METHODS

We did a single-centre, randomised, double-blind, placebo-controlled, phase 2 clinical trial at Sierra Leone-China Friendship Hospital, Freetown, Sierra Leone. We recruited healthy adults aged 18-50 years who were HIV negative, had no history of Ebola virus infection, and had no previous immunisation with other Ebola vaccine candidates. Participants were sequentially enrolled and randomly assigned (2:1:1), by computer-generated block randomisation (block size of eight), to receive the high-dose vaccine (1·6 × 10¹¹ viral particles), low-dose vaccine (8·0 × 10¹⁰ viral particles), or placebo (containing only vaccine excipients, with no viral particles). Participants, investigators, and study staff (except two study pharmacists) were masked from treatment allocation. The primary safety outcome was occurrence of solicited adverse reactions within 7 days of vaccination, analysed by intention to treat. The primary immunogenicity outcome was glycoprotein-specific antibody responses at days 14, 28, and 168 after vaccination, analysed in all vaccinated participants who had blood samples drawn for antibody tests. The trial is registered with the Pan African Clinical Trials Registry, number PACTR201509001259869, and is completed.

FINDINGS

During Oct 10-28, 2015, 500 participants were enrolled and randomly assigned to receive the high-dose vaccine (n=250), low-dose vaccine (n=125), or placebo (n=125). 132 (53%) participants in the high-dose group, 60 (48%) in the low-dose group, and 54 (43%) in the placebo group reported at least one solicited adverse reaction within 7 days of vaccination. Most adverse reactions were mild and self-limiting. Solicited injection-site adverse reactions were significantly more frequent in vaccine recipients (65 [26%] in high-dose group and 31 [25%] in low-dose group) than in those receiving placebo (17 [14%]; p=0·0169). Glycoprotein-specific antibody responses were detected from day 14 onwards (geometric mean titre 1251·0 [95% CI 976·6-1602·5] in low-dose group and 1728·4 [1459·4-2047·0] in high-dose group) and peaked at day 28 (1471·8 [1151·0-1881·8] and 2043·1 [1762·4-2368·4]), but declined quickly in the following months (223·3 [148·2-336·4] and 254·2 [185·0-349·5] at day 168). Geometric mean titres in the placebo group remained around 6·0-6·8 throughout the study period. Three serious adverse events (malaria, gastroenteritis, and one fatal asthma episode) were reported in the high-dose vaccine group, but none was deemed related to the vaccine.

INTERPRETATION

The recombinant adenovirus type-5 vector-based Ebola vaccine was safe and highly immunogenic in healthy Sierra Leonean adults, and 8·0 × 10¹⁰ viral particles was the optimal dose.

FUNDING

Chinese Ministry of Science and Technology and the National Health and Family Planning Commission, Beijing Institute of Biotechnology, and Tianjin CanSino Biotechnology.

Novel chimpanzee adenovirus-vectored respiratory mucosal tuberculosis vaccine: overcoming local anti-human adenovirus immunity for potent TB protection

Pulmonary tuberculosis (TB) remains to be a major global health problem despite many decades of parenteral use of Bacillus Calmette-Guérin (BCG) vaccine. Developing safe and effective respiratory mucosal TB vaccines represents a unique challenge. Over the past decade or so, the human serotype 5 adenovirus (AdHu5)-based TB vaccine has emerged as one of the most promising candidates based on a plethora of preclinical and early clinical studies. However, anti-AdHu5 immunity widely present in the lung of humans poses a serious gap and limitation to its real-world applications. In this study we have developed a novel chimpanzee adenovirus 68 (AdCh68)-vectored TB vaccine amenable to the respiratory route of vaccination. We have evaluated AdCh68-based TB vaccine for its safety, T-cell immunogenicity, and protective efficacy in relevant animal models of human pulmonary TB with or without parenteral BCG priming. We have also compared AdCh68-based TB vaccine with its AdHu5 counterpart in both naive animals and those with preexisting anti-AdHu5 immunity in the lung. We provide compelling evidence that AdCh68-based TB vaccine is not only safe when delivered to the respiratory tract but, importantly, is also superior to its AdHu5 counterpart in induction of T-cell responses and immune protection, and limiting lung immunopathology in the presence of preexisting anti-AdHu5 immunity in the lung. Our findings thus suggest AdCh68-based TB vaccine to be an ideal candidate for respiratory mucosal immunization, endorsing its further clinical development in humans.

Immunology and evolvement of the adenovirus prime, MVA boost Ebola virus vaccine

The 2014 Ebola virus outbreak caused an order of magnitude more deaths in a single outbreak than all previous known outbreaks combined, affecting both local and international public health, and threatening the security and economic stability of the countries in West Africa directly confronting the outbreak. The severity of the epidemic lead to a global response to assist with patient care, outbreak control, and deployment of vaccines. The latter was possible due to the long history of basic and clinical research aimed at identifying a safe and effective vaccine to protect against Ebola virus infection. This review highlights the immunology, development, and progress of vaccines based on replication-defective adenovirus vectors, culminating in the successful launch of the first Phase III trial of an Ebola virus vaccine.

A long-lasting, single-dose nasal vaccine for Ebola: a practical armament for an outbreak with significant global impact

In response to the severity and scale of the 2014 Ebola outbreak, several experimental vaccines were granted fast-track status for clinical testing. Although they may provide long-lasting protection from Ebola, they are, in their current states, far from optimal for populations that need them the most. In this context, nasal immunization addresses the: immune response required at the mucosa where Ebola initiates infection; needs of a population in terms of cost and compliance; and potency of each platform as they contain viruses that naturally infect the respiratory tract. Understanding the attributes of nasal immunization and its application will lead to potent vaccines that can effectively end Ebola and other emerging infectious diseases in developing and industrialized countries.

Bolstering Components of the Immune Response Compromised by Prior Exposure to Adenovirus: Guided Formulation Development for a Nasal Ebola Vaccine

The severity and longevity of the current Ebola outbreak highlight the need for a fast-acting yet long-lasting vaccine for at-risk populations (medical personnel and rural villagers) where repeated prime-boost regimens are not feasible. While recombinant adenovirus (rAd)-based vaccines have conferred full protection against multiple strains of Ebola after a single immunization, their efficacy is impaired by pre-existing immunity (PEI) to adenovirus. To address this important issue, a panel of formulations was evaluated by an in vitro assay for their ability to protect rAd from neutralization. An amphiphilic polymer (F16, FW ∼39,000) significantly improved transgene expression in the presence of anti-Ad neutralizing antibodies (NAB) at concentrations of 5 times the 50% neutralizing dose (ND₅₀). In vivo performance of rAd in F16 was compared with unformulated virus, virus modified with poly(ethylene) glycol (PEG), and virus incorporated into poly(lactic-co-glycolic) acid (PLGA) polymeric beads. Histochemical analysis of lung tissue revealed that F16 promoted strong levels of transgene expression in naive mice and those that were exposed to adenovirus in the nasal cavity 28 days prior to immunization. Multiparameter flow cytometry revealed that F16 induced significantly more polyfunctional antigen-specific CD8⁺ T cells simultaneously producing IFN-γ, IL-2, and TNF-α than other test formulations. These effects were not compromised by PEI. Data from formulations that provided partial protection from challenge consistently identified specific immunological requirements necessary for protection. This approach may be useful for development of formulations for other vaccine platforms that also employ ubiquitous pathogens as carriers like the influenza virus.

A Single Dose Respiratory Recombinant Adenovirus-Based Vaccine Provides Long-Term Protection for Non-Human Primates from Lethal Ebola Infection

As the Ebola outbreak in West Africa continues and cases appear in the United States and other countries, the need for long-lasting vaccines to preserve global health is imminent. Here, we evaluate the long-term efficacy of a respiratory and sublingual (SL) adenovirus-based vaccine in non-human primates in two phases. In the first, a single respiratory dose of 1.4 × 10⁹ infectious virus particles (ivp)/kg of Ad-CAGoptZGP induced strong Ebola glycoprotein (GP) specific CD8⁺ and CD4⁺ T cell responses and Ebola GP-specific antibodies in systemic and mucosal compartments and was partially (67%) protective from challenge 62 days after immunization. The same dose given by the SL route induced Ebola GP-specific CD8⁺ T cell responses similar to that of intramuscular (IM) injection, however, the Ebola GP-specific antibody response was low. All primates succumbed to infection. Three primates were then given the vaccine in a formulation that improved the immune response to Ebola in rodents. Three primates were immunized with 2.0 × 10¹⁰ ivp/kg of vaccine by the SL route. Diverse populations of polyfunctional Ebola GP-specific CD4⁺ and CD8⁺ T cells and significant anti-Ebola GP antibodies were present in samples collected 150 days after respiratory immunization. The formulated vaccine was fully protective against challenge 21 weeks after immunization. While diverse populations of Ebola GP-specific CD4⁺ T cells were produced after SL immunization, antibodies were not neutralizing and the vaccine was unprotective. To our knowledge, this is the first time that durable protection from a single dose respiratory adenovirus-based Ebola vaccine has been demonstrated in primates.

Challenges, progress, and opportunities: proceedings of the filovirus medical countermeasures workshop

On August 22–23, 2013, agencies within the United States Department of Defense (DoD) and the Department of Health and Human Services (HHS) sponsored the Filovirus Medical Countermeasures (MCMs) Workshop as an extension of the activities of the Filovirus Animal Non-clinical Group (FANG). The FANG is a federally-recognized multi-Agency group established in 2011 to coordinate and facilitate U.S. government (USG) efforts to develop filovirus MCMs. The workshop brought together government, academic and industry experts to consider the needs for filovirus MCMs and evaluate the status of the product development pipeline. This report summarizes speaker presentations and highlights progress and challenges remaining in the field.