Closing in on a Zika virus vaccine

Scientific and technological contributions of Latin America and Caribbean countries to the Zika virus outbreak

Background

The recent Zika virus (ZIKAV) epidemics disclosed a major public health threat and a scientific and technological (S&T) challenge. The lessons learned from the S&T response of Latin America and the Caribbean (LAC) countries are critical to inform further research and guide scientific investments. The present study aimed to assess how new S&T knowledge produced and disseminated regionally can contribute to address global health challenges.

Methods

Scientometric and social network analysis methods were used to assess the LAC scientific contribution and potential technological development on ZIKAV up to December 2017. ZIKAV-related publications were retrieved from the Web of Science, Scopus, and PubMed databases. Regionally published articles were obtained from SciELO (Scientific Electronic Library Online) and LILACS (Literature in the Health Sciences in Latin America and the Caribbean) databases. Patent registries were retrieved using Orbit Intelligence and Derwent Innovation. Records from each database were individually downloaded, integrated, standardized and analyzed.

Results

We retrieved 5421 ZIKAV-related publications, revealing a sharp increase from 2015 onwards. LAC countries accounted for 20% of all publications and Brazil was among the top three most central countries in the global network for ZIKAV research. A total of 274 patent families backed up by experimental evidence were retrieved. Only 5% were filed by LAC assignees, all of them based in Brazil. The largest contribution of LAC research was on the clinical manifestations of the ZIKAV infection, along with vector control, which was also the main focus of patents.

Conclusions

Our analysis offered a comprehensive overview of ZIKAV’s research and development and showed that (i) LAC countries had a key role in generating and disseminating scientific knowledge on ZIKAV; (ii) LAC countries have expressively contributed to research on ZIKAV clinical manifestations; (iii) the Brazilian scientific community was potentially very effective in knowledge sharing and diffusion in the ZIKAV research network; (iv) Brazil was the single LAC country filing patents, mostly represented by independent inventors and low-tech patents. The paper advocates the need for a continued interdisciplinary approach to improve LAC countries ability to prevent, prepare for and control future outbreaks.

Electronic supplementary material

The online version of this article (10.1186/s12889-019-6842-x) contains supplementary material, which is available to authorized users.

A yellow fever-Zika chimeric virus vaccine candidate protects against Zika infection and congenital malformations in mice

The recent Zika virus (ZIKV) epidemic in the Americas led to an intense search for therapeutics and vaccines. Here we report the engineering of a chimeric virus vaccine candidate (YF-ZIKprM/E) by replacing the antigenic surface glycoproteins and the capsid anchor of YFV-17D with those of a prototypic Asian lineage ZIKV isolate. By intracellular passaging, a variant with adaptive mutations in the E protein was obtained. Unlike YFV-17D, YF-ZIKprM/E replicates poorly in mosquito cells. Also, YF-ZIKprM/E does not cause disease nor mortality in interferon α/β, and γ receptor KO AG129 mice nor following intracranial inoculation of BALB/c pups. A single dose as low as 1 × 10² PFU results, as early as 7 days post vaccination, in seroconversion to neutralizing antibodies and confers full protection in AG129 mice against stringent challenge with a lethal inoculum (10⁵ LD₅₀) of either homologous or heterologous ZIKV strains. Induction of multi-functional CD4⁺ and CD8⁺ T cell responses against ZIKV structural and YFV-17D non-structural proteins indicates that cellular immunity may also contribute to protection. Vaccine immunogenicity and protection was confirmed in other mouse strains, including after temporal blockade of interferon-receptors in wild-type mice to facilitate ZIKV replication. Vaccination of wild-type NMRI dams with YF-ZIKprM/E results in complete protection of foetuses against brain infections and malformations following a stringent intraplacental challenge with an epidemic ZIKV strain. The particular characteristic of YF-ZIKprM/E in terms of efficacy and its marked attenuation in mice warrants further exploration as a vaccine candidate.

Zika virus (ZIKV) infection generally results in mild symptoms but can cause serious developmental abnormalities in infants born to ZIKV infected mothers. Kai Dallmeier and colleagues at the KU Leuven in Belgium, engineered a chimeric live-attenuated vaccine (YF-ZIKprM/E) by swapping the glycoprotein from the Yellow Fever vaccine YFV-17D with that of a pre-epidemic ZIKV strain. YF-ZIKprM/E is very well tolerated with no adverse effects even following high dose intracranial infection. Mice highly susceptible to ZIKV infection—including AG129 and type I interferon receptor deficient strains—vaccinated with a single dose of YF-ZIKprM/E are fully protected from lethal ZIKV challenge. Protection can be achieved within 7 days and by low doses of YF-ZIKprM/E, is durable and generally results in sterilizing immunity. YF-ZIKprM/E elicits both neutralizing antibodies and robust cellular immunity. Finally, YF-ZIKprM/E can also prevent vertical transmission of ZIKV and achieve efficient protection of pups from neurological defects following intraplacental challenge.

The Multifaceted Roles of Autophagy in Flavivirus-Host Interactions

Autophagy is an evolutionarily conserved cellular process in which intracellular components are eliminated via lysosomal degradation to supply nutrients for organelle biogenesis and metabolic homeostasis. Flavivirus infections underlie multiple human diseases and thus exert an immense burden on public health worldwide. Mounting evidence indicates that host autophagy is subverted to modulate the life cycles of flaviviruses, such as hepatitis C virus, dengue virus, Japanese encephalitis virus, West Nile virus and Zika virus. The diverse interplay between autophagy and flavivirus infection not only regulates viral growth in host cells but also counteracts host stress responses induced by viral infection. In this review, we summarize the current knowledge on the role of autophagy in the flavivirus life cycle. We also discuss the impacts of virus-induced autophagy on the pathogeneses of flavivirus-associated diseases and the potential use of autophagy as a therapeutic target for curing flavivirus infections and related human diseases.

Inflammatory-dependent Sting activation induces antiviral autophagy to limit zika virus in the Drosophila brain

Incidences of congenital syndrome associated with maternal zika virus (ZIKV) infection during pregnancy are well documented; however, the cellular and molecular mechanisms by which ZIKV infection causes these devastating fetal pathologies are still under active investigation. ZIKV is a member of the flavivirus family and is mainly transmitted to human hosts through Aedes mosquito vectors. However, in vivo models for the neurological tropism of the virus and the arthropod vector have been lacking. A recent study published in Cell Host & Microbe from Dr. Sara Cherry's lab investigates both of these key aspects of the ZIKV infectious life cycle. Liu et al. demonstrate how inflammatory activated Sting/dSTING-dependent antiviral macroautophagy/autophagy is sufficient to restrict ZIKV infection in the Drosophila melanogaster brain. Additionally, this study provides further evidence for the ancestral function of autophagy in protecting host cells from viral invaders. Abbreviations: AGO2: Argonaute 2; ATG: autophagy-related; Dcr-2: Dicer-2; DptA/Dipt: Diptericin A; Drs: Drosomycin; DCV: Drosophila C virus; IMD: immune-deficiency; qRT-PCR: quantitative real-time PCR; Rel/NF-κB: Relish; RNAi: RNA interference; ZIKV: zika virus.

Process intensification of EB66® cell cultivations leads to high-yield yellow fever and Zika virus production

A live-attenuated, human vaccine against mosquito-borne yellow fever virus has been available since the 1930s. The vaccine provides long-lasting immunity and consistent mass vaccination campaigns counter viral spread. However, traditional egg-based vaccine manufacturing requires about 12 months and vaccine supplies are chronically close to shortages. In particular, for urban outbreaks, vaccine demand can be covered rarely by global stockpiling. Thus, there is an urgent need for an improved vaccine production platform, ideally transferable to other flaviviruses including Zika virus. Here, we present a proof-of-concept study regarding cell culture-based yellow fever virus 17D (YFV) and wild-type Zika virus (ZIKV) production using duck embryo-derived EB66® cells. Based on comprehensive studies in shake flasks, 1-L bioreactor systems were operated with scalable hollow fiber-based tangential flow filtration (TFF) and alternating tangential flow filtration (ATF) perfusion systems for process intensification. EB66® cells grew in chemically defined medium to cell concentrations of 1.6 × 10⁸ cells/mL. Infection studies with EB66®-adapted virus led to maximum YFV titers of 7.3 × 10⁸ PFU/mL, which corresponds to about 10 million vaccine doses for the bioreactor harvest. For ZIKV, titers of 1.0 × 10¹⁰ PFU/mL were achieved. Processes were automated successfully using a capacitance probe to control perfusion rates based on on-line measured cell concentrations. The use of cryo-bags for direct inoculation of production bioreactors facilitates pre-culture preparation contributing to improved process robustness. In conclusion, this platform is a powerful option for next generation cell culture-based flavivirus vaccine manufacturing.

A Reverse Genetics System for Zika Virus Based on a Simple Molecular Cloning Strategy

The Zika virus (ZIKV) has recently attracted major research interest as infection was unexpectedly associated with neurological manifestations in developing foetuses and with Guillain-Barré syndrome in infected adults. Understanding the underlying molecular mechanisms requires reverse genetic systems, which allow manipulation of infectious cDNA clones at will. In the case of flaviviruses, to which ZIKV belongs, several reports have indicated that the construction of full-length cDNA clones is difficult due to toxicity during plasmid amplification in Escherichia coli. Toxicity of flaviviral cDNAs has been linked to the activity of cryptic prokaryotic promoters within the region encoding the structural proteins leading to spurious transcription and expression of toxic viral proteins. Here, we employ an approach based on in silico prediction and mutational silencing of putative promoters to generate full-length cDNA clones of the historical MR766 strain and the contemporary French Polynesian strain H/PF/2013 of ZIKV. While for both strains construction of full-length cDNA clones has failed in the past, we show that our approach generates cDNA clones that are stable on single bacterial plasmids and give rise to infectious viruses with properties similar to those generated by other more complex assembly strategies. Further, we generate luciferase and fluorescent reporter viruses as well as sub-genomic replicons that are fully functional and suitable for various research and drug screening applications. Taken together, this study confirms that in silico prediction and silencing of cryptic prokaryotic promoters is an efficient strategy to generate full-length cDNA clones of flaviviruses and reports novel tools that will facilitate research on ZIKV biology and development of antiviral strategies.

Rational Zika vaccine design via the modulation of antigen membrane anchors in chimpanzee adenoviral vectors

Zika virus (ZIKV) emerged on a global scale and no licensed vaccine ensures long-lasting anti-ZIKV immunity. Here we report the design and comparative evaluation of four replication-deficient chimpanzee adenoviral (ChAdOx1) ZIKV vaccine candidates comprising the addition or deletion of precursor membrane (prM) and envelope, with or without its transmembrane domain (TM). A single, non-adjuvanted vaccination of ChAdOx1 ZIKV vaccines elicits suitable levels of protective responses in mice challenged with ZIKV. ChAdOx1 prME ∆TM encoding prM and envelope without TM provides 100% protection, as well as long-lasting anti-envelope immune responses and no evidence of in vitro antibody-dependent enhancement to dengue virus. Deletion of prM and addition of TM reduces protective efficacy and yields lower anti-envelope responses. Our finding that immunity against ZIKV can be enhanced by modulating antigen membrane anchoring highlights important parameters in the design of viral vectored ZIKV vaccines to support further clinical assessments.

The immunology of Zika Virus

Zika virus (ZIKV) was initially thought to cause only mild, self-limiting symptoms. However, recent outbreaks have been associated with the autoimmune disease Guillain-Barré syndrome and causally linked to a congenital malformation known as microcephaly. This has led to an urgent need for a safe and effective vaccine. A comprehensive understanding of the immunology of ZIKV infection is required to aid in the design of such a vaccine. Whilst details of both innate and adaptive immune responses to ZIKV are emerging, further research is needed. As immunopathogenesis has been implicated in poor outcomes following infection with the related dengue virus, identification of cross-reactive immune responses between flaviviruses and the impact they may have on disease progression is also of high importance.