Peculiarities of Zika Immunity and Vaccine Development: Lessons from Dengue and the Contribution from Controlled Human Infection Model

Addition of nucleotide adjuvants enhances the immunogenicity of a recombinant subunit vaccine against the Zika virus in BALB/c mice

Zika virus (ZIKV) infection remains a global public health problem. After the "Public Health Emergencies of International Concern" declared in February 2016, the incidence of new infections by this pathogen has been decreasing in many areas. However, there is still a likely risk that ZIKV will spread to more countries. To date, there is no vaccine or antiviral drug available to prevent or treat Zika virus infection. In the Zika vaccine development, those based on protein subunits are attractive as a non-replicable platform due to their potentially enhanced safety profile to be used in all populations. However, these vaccines frequently require multiple doses and adjuvants to achieve protective immunity. In this study we show the immunological evaluation of new formulations of the recombinant protein ZEC, which combines regions of domain III of the envelope and the capsid from ZIKV. Two nucleotide-based adjuvants were used to enhance the immunity elicited by the vaccine candidate ZEC. ODN 39M or c-di-AMP was incorporated as immunomodulator into the formulations combined with aluminum hydroxide. Following immunizations in immunocompetent BALB/c mice, the formulations stimulated high IgG antibodies. Although the IgG subtypes suggested a predominantly Th1-biased immune response by the formulation including the ODN 39M, cellular immune responses measured by IFNγ secretion from spleen cells after in vitro stimulations were induced by both immunomodulators. These results demonstrate the capacity of both immunomodulators to enhance the immunogenicity of the recombinant subunit ZEC as a vaccine candidate against ZIKV.

A randomized, placebo-controlled, blinded phase 1 study investigating a novel inactivated, Vero cell-culture derived Zika virus vaccine

BACKGROUND

Zika virus (ZIKV) is an emerging public health threat, rendering development of a safe and effective vaccine against the virus a high priority to face this unmet medical need. Our vaccine candidate has been developed on the same platform used for the licensed vaccine IXIARO®, a vaccine against Japanese Encephalitis virus, another closely related member of the Flaviviridae family.

METHODS

Between 24 February 2018 and 16 November 2018, we conducted a randomized, observer-blinded, placebo controlled, single center phase 1 study to assess the safety and immunogenicity of an adjuvanted, inactivated, purified whole-virus Zika vaccine candidate in the USA. A total of 67 healthy flavivirus-naïve adults aged 18-49 years were randomly assigned to one of five study arms to receive two immunizations of either high dose or low dose (6 antigen units or 3 antigen units) with both dose levels applied in two different immunization regimens or placebo as control.

RESULTS

Our vaccine candidate showed an excellent safety profile independent of dose and vaccination regimen with predominantly mild adverse events (AEs). No serious AE has been reported. The ZIKV vaccine induced neutralizing antibodies in all tested doses and regimens with seroconversion rates up to 85.7% (high dose), which remained up to 40% (high dose) at 6 months follow-up. Of note, the rapid regimen triggered a substantial immune response within days.

CONCLUSIONS

The rapid development and production of a ZIKV vaccine candidate building on a commercial Vero-cell manufacturing platform resulted in a safe and immunogenic vaccine suitable for further clinical development. To optimize antibody persistence, higher doses and a booster administration might be considered.

Reverse Genetics of Zika Virus Using a Bacterial Artificial Chromosome

Zika virus (ZIKV) is a mosquito-borne member of the Flaviviridae family that has become a global threat to human health. Although ZIKV has been known to circulate for decades causing mild febrile illness, the more recent ZIKV outbreaks in the Americas and the Caribbean have been associated with severe neurological disorders and congenital abnormalities. The development of ZIKV reverse genetics approaches have allowed researchers to address key questions on the biology of ZIKV by genetically engineering infectious recombinant (r)ZIKV. This has resulted in a better understanding of the biology of ZIKV infections, including viral pathogenesis, molecular mechanisms of viral replication and transcription, or the interaction of viral and host factors, among others aspects. In addition, reverse genetics systems have facilitated the identification of anti-ZIKV compounds and the development of new prophylactic approaches to combat ZIKV infections. Different reverse genetics strategies have been implemented for the recovery of rZIKV. All these reverse genetics systems have faced and overcome multiple challenges, including the viral genome size, the toxicity of viral sequences in bacteria, etc. In this chapter we describe the generation of a ZIKV full-length complementary (c)DNA infectious clone based on the use of a bacterial artificial chromosome (BAC) and the experimental procedures for the successful recovery of rZIKV. Importantly, the protocol described in this chapter provides a powerful method for the generation of infectious clones of other flaviviruses with genomes that have stability problems during bacterial propagation.

Insight into the Natural Biomolecules (BMs): Promising Candidates as Zika Virus Inhibitors

Zika virus (ZIKV) is among the relatively new infectious disease threats that include SARS-CoV-2, coronavirus, monkeypox (Mpox) virus, etc. ZIKV has been reported to cause severe health risks to the fetus. To date, satisfactory treatment is still not available for the treatment of ZIKV infection. This review examines the last five years of work using natural biomolecules (BMs) to counteract the ZIKV through virtual screening and in vitro investigations. Virtual screening has identified doramectin, pinocembrin, hesperidins, epigallocatechin gallate, pedalitin, and quercetin as potentially active versus ZIKV infection. In vitro, testing has shown that nordihydroguaiaretic acid, mefloquine, isoquercitrin, glycyrrhetinic acid, patentiflorin-A, rottlerin, and harringtonine can reduce ZIKV infections in cell lines. However, in vivo, testing is limited, fortunately, emetine, rottlerin, patentiflorin-A, and lycorine have shown in vivo anti- ZIKV potential. This review focuses on natural biomolecules that show a particularly high selective index (>10). There is limited in vivo and clinical trial data for natural BMs, which needs to be an active area of investigation. This review aims to compile the known reference data and discuss the barriers associated with discovering and using natural BM agents to control ZIKV infection.

A Prototype-Pathogen Approach for the Development of Flavivirus Countermeasures

Flaviviruses are a genus within the Flaviviridae family of positive-strand RNA viruses and are transmitted principally through mosquito and tick vectors. These viruses are responsible for hundreds of millions of human infections worldwide per year that result in a range of illnesses from self-limiting febrile syndromes to severe neurotropic and viscerotropic diseases and, in some cases, death. A vaccine against the prototype flavivirus, yellow fever virus, has been deployed for 85 years and is highly effective. While vaccines against some medically important flaviviruses are available, others have proven challenging to develop. The emergence and spread of flaviviruses, including dengue virus and Zika virus, demonstrate their pandemic potential. This review highlights the gaps in knowledge that need to be addressed to allow for the rapid development of vaccines against emerging flaviviruses in the future.

Recent updates on correlates of vaccine-induced protection

Correlates of protection are key for vaccine development against any pathogen. In this paper we summarize recent information about correlates for vaccines against dengue, Ebola, influenza, pneumococcal, respiratory syncytial virus, rotavirus, shigella, tuberculosis and Zika virus.