A pinboard by
Marissa Fahlberg

I have a love/hate relationship with flaviviruses.


The development of a Zika Virus vaccine is feasible and researchers are optimistic.

In 10 seconds? Multiple different vaccines against Zika virus (ZIKV) are effective in animal models, and researchers are optimistic about the development of a vaccine against Zika in humans.

Can we really develop a vaccine against Zika virus? There is a great chance of developing of a vaccine against ZIKV. We currently have effective vaccines against other related viruses, including those that cause Yellow Fever and Japanese Encephalitis. Research into the biology of the virus has accumulated rapidly since the epidemic in South America.

What are challenges in developing a Zika vaccine? ZIKV severely affects fetuses, and therefore immunizing pregnant women is ideal. However, trials involving pregnant women are often last to be conducted because of the risk to the mother and the fetus. In addition, microcephaly and neurological damage is relatively rare, so it will require the administration of the vaccine to thousands before we understand the true efficacy. Further, the standards for protection may be higher than that for other vaccines, considering the susceptibility of pregnant women and their fetuses to disease. There is also a possibility that an immune response developed against ZIKV could exacerbate disease after infection with dengue, a related virus.

Are there vaccines in clinical trials right now? Yes! There are three different ZIKV vaccines in Phase I clinical trials right now, and they are all different. Another three are currently in development and anticipate entering pre-clinical trial phases.

What are the phases of clinical trials that the Zika vaccine must pass? In the pre-clinical phase, vaccines must show that they are safe and effective in animal models, such as in mice or monkeys. In Phase I, the vaccine is administered to a small group of people (10-100), and the biggest concern is safety and that the vaccine elicits a measurable immune response. In Phase II, the vaccine is given to hundreds of people, and though safety remains the largest priority, more data in terms of efficacy is gathered. In Phase III, the last phase, the vaccine is given to thousands of people, is randomized, and double-blind. Safety and rare adverse events are recorded, and the efficacy becomes critical before the drug goes on to become manufactured and sold. Typically, a new vaccine takes 10-15 years to develop and manufacture. However, a Zika Virus vaccine that shows promise in the earlier stages is likely to be expedited.


The Development of Small Animal Models for Zika Virus Vaccine Efficacy Testing and Pathological Assessment.

Abstract: Zika virus (ZIKV) is a mosquito-borne flavivirus serologically grouped within the family Flaviviridae, which was initially isolated from a febrile sentinel monkey in the Zika Forest of Uganda in 1947. Subsequent genetic analyses have demonstrated the presence of two distinctive African and Asian viral genotypes. After years of being associated only with sporadic human illness, the first outbreak of ZIKV disease was reported in 2007, on the island of Yap in the Federated States of Micronesia (with 49 laboratory confirmed cases documented). In subsequent years, ZIKV was associated with outbreaks in French Polynesia and then in the South Pacific Islands of New Caledonia and Easter Island, before disease being identified in Brazil in early 2015. Although the majority of human ZIKV infections have been found to result in asymptomatic or mild illness, the recent identification of an association of ZIKV infection during pregnancy with an increase in the incidence of microcephaly in neonates, as well as the development of Guillain-Barré syndrome resulted in the World Health Organization's declaration that the ZIKV outbreak constituted a "Public Health Emergency of International Concern." The unprecedented geographic expansion of the virus, with up to 1.3 million estimated human infections as of December 2015, its sexual transmission potential, and its severe pathogenic effects in fetuses (microcephaly, ocular malformations) have emphasized the critical need for available vaccines and antiviral therapies, as well as an improved understanding of the pathological mechanisms that result in human disease after infection with this virus.

Pub.: 04 May '16, Pinned: 16 Apr '17

From ZikV Genome to Vaccine: In Silico Approach for the Epitope based peptide vaccine against Zika virus envelope glycoprotein.

Abstract: Recently, Zika virus has emerged as a potential threat to human health worldwide. Zika is the member of Flaviviridae, is transmitted to humans by mosquitoes. It is related to other pathogenic vector borne flaviviruses including dengue, West-Nile and Japanese encephalitis viruses, but produces a comparatively mild disease in humans. Despite of its epidemic outbreak and lack of potential medication, there is a need for improved vaccine /drugs. The use of computational technique will bring some facts into the research limelight. In this study, to begin with comparative analysis of ZikV genomes that can lead to the identification of the core characteristics that define a virus family, as well as the unique properties. Phylogenetic analysis shows the evolutionary relationship and gave the clue about protein's ancestry image. Envelope glycoprotein of ZikV was obtained from a protein database and determines the most immunogenic epitope for T_cell and B_cell which involved in cell-mediated immunity, whereas B_cells are primarily responsible for humoral immunity. We mainly focused on MHC class-I potential peptides. YRIMLSVHG, VLIFLSTAV and MMLELDPPF, GLDFSDLYY are the most potent peptides predicted as epitopes for CD4(+) and CD8(+) T_cell respectively, where as MMLELDPPF and GLDFSDLYY had found highest I-pMHC immunogenicity score and these are further tested for interaction against the HLA molecules, using in-silico docking techniques to verify the binding cleft epitope. However, this is an introductory approach to design an epitope based peptide vaccine against Zika virus; we hope that this model will be very helpful in designing and predicting novel vaccine candidate. This article is protected by copyright. All rights reserved.

Pub.: 04 Aug '16, Pinned: 16 Apr '17

A Full-Length Infectious cDNA Clone of Zika Virus from the 2015 Epidemic in Brazil as a Genetic Platform for Studies of Virus-Host Interactions and Vaccine Development.

Abstract: An arthropod-borne virus, Zika virus (ZIKV), has recently emerged as a major human pathogen. Associated with complications during perinatal development and Guillain-Barré syndrome in adults, ZIKV raises new challenges for understanding the molecular determinants of flavivirus pathogenesis. This underscores the necessity for the development of a reverse genetic system based on an epidemic ZIKV strain. Here, we describe the generation and characterization in cell cultures of an infectious cDNA clone of ZIKV isolated from the 2015 epidemic in Brazil. The cDNA-derived ZIKV replicated efficiently in a variety of cell lines, including those of both neuronal and placental origin. We observed that the growth of cDNA-derived virus was attenuated compared to the growth of the parental isolate in most cell lines, which correlates with substantial differences in sequence heterogeneity between these viruses that were determined by deep-sequencing analysis. Our findings support the role of genetic diversity in maintaining the replicative fitness of viral populations under changing conditions. Moreover, these results indicate that caution should be exercised when interpreting the results of reverse-genetics experiments in attempts to accurately predict the biology of natural viruses. Finally, a Vero cell-adapted cDNA clone of ZIKV was generated that can be used as a convenient platform for studies aimed at the development of ZIKV vaccines and therapeutics.The availability of genetic tools and laboratory models determines the progress in understanding mechanisms of virus emergence and pathogenesis. Recent large-scale outbreaks of Zika virus (ZIKV) that were linked to complications during perinatal development and Guillain-Barré syndrome in adults emphasize the urgency for the development of a reverse-genetics system based on an epidemic ZIKV strain. Here, we report a stable infectious cDNA clone for ZIKV isolated during the 2015 epidemic in Brazil, as well as a Vero cell-adapted version of it, which will be used for virus-host interaction studies and vaccine development.

Pub.: 25 Aug '16, Pinned: 16 Apr '17

Vaccine protection against Zika virus from Brazil

Abstract: Zika virus (ZIKV) is a flavivirus that is responsible for the current epidemic in Brazil and the Americas1, 2. ZIKV has been causally associated with fetal microcephaly, intrauterine growth restriction, and other birth defects in both humans3, 4, 5, 6, 7, 8 and mice9, 10, 11. The rapid development of a safe and effective ZIKV vaccine is a global health priority1, 2, but very little is currently known about ZIKV immunology and mechanisms of immune protection. Here we show that a single immunization with a plasmid DNA vaccine or a purified inactivated virus vaccine provides complete protection in susceptible mice against challenge with a strain of ZIKV involved in the outbreak in northeast Brazil. This ZIKV strain has recently been shown to cross the placenta and to induce fetal microcephaly and other congenital malformations in mice11. We produced DNA vaccines expressing ZIKV pre-membrane and envelope (prM-Env), as well as a series of deletion mutants. The prM-Env DNA vaccine, but not the deletion mutants, afforded complete protection against ZIKV, as measured by absence of detectable viraemia following challenge, and protective efficacy correlated with Env-specific antibody titers. Adoptive transfer of purified IgG from vaccinated mice conferred passive protection, and depletion of CD4 and CD8 T lymphocytes in vaccinated mice did not abrogate this protection. These data demonstrate that protection against ZIKV challenge can be achieved by single-shot subunit and inactivated virus vaccines in mice and that Env-specific antibody titers represent key immunologic correlates of protection. Our findings suggest that the development of a ZIKV vaccine for humans is likely to be achievable.

Pub.: 28 Jun '16, Pinned: 16 Apr '17

Computational prediction and analysis of potential antigenic CTL epitopes in Zika virus: A first step towards vaccine development.

Abstract: The Zika virus disease is an Aedes mosquito-borne disease caused by the ZIKA virus. The unavailability of vaccines or proper chemotherapeutic treatment emphasizes the need for the development of preventive and therapeutic vaccines. T cell specific epitopes have been used as vaccine candidates to generate desired immune responses against a variety of viral pathogens. Herein, the immune-informatics approach was used for the screening of potential major histocompatibility complex class I restricted epitopes, which may be competent to generate a cell-mediated immune response in humans. A total of 63 epitopes were identified,which revealed a comprehensive binding affinity to the 42 differenthuman leukocyte antigen class I supertypes: A01, A02, A08, A23, A24, A25, A26, A29, A30, A32, A66, A68, A69, A80, B07, B08, B14, B15, B27, B35, B39, B40, B42, B45, B46, B48, B51, B53, B54, B57, B58, B83, C12, C03, C04, C05, C06, C07, C08, C12, C14, and C15, and which had no homologs in humans. By combining the human leukocyte antigen binding specificity and population coverage, nine promiscuous epitopes located in Capsid 1 Protein (MVLAILAFL(P1)), Envelop Protein (RLKGVSYSL (P2) and RLITANPVI (P3)), NS2A (AILAALTPL (P4)), NS4B (LLVAHYMYL (P5) and LVAHYMYLI (P6)) and NS5 (SLINGVVRL (P7), ALNTFTNLV (P8) and YLSTQVRYL (P9)) were shortlisted. Most of these consensus epitopes revealed 100% conservancy in all Zika virus strains and were very less conserved against the human proteome. The combination of the selected epitopes accounted for an optimal coverage in the world wide population (>99%) independent of ethnicity. Structural analysis of these selected epitopes by the PatchDock web server showed their preferential mode of presentation to the T cell receptor. All these results recommended the possibility of a combined epitope vaccine strategy and can therefore be further investigated for their immunological relevance and usefulness as vaccine candidates.

Pub.: 04 Sep '16, Pinned: 16 Apr '17

Understanding Zika Virus Stability and Developing a Chimeric Vaccine through Functional Analysis.

Abstract: Compared with other flaviviruses, Zika virus (ZIKV) is uniquely associated with congenital diseases in pregnant women. One recent study reported that (i) ZIKV has higher thermostability than dengue virus (DENV [a flavivirus closely related to ZIKV]), which might contribute to the disease outcome; (ii) the higher thermostability of ZIKV could arise from an extended loop structure in domain III of the viral envelope (E) protein and an extra hydrogen-bond interaction between E molecules (V. A. Kostyuchenko, E. X. Y. Lim, S. Zhang, G. Fibriansah, T.-S. Ng, J. S. G. Ooi, J. Shi, and S.-M. Lok, Nature 533:425-428, 2016, https://doi.org/10.1038/nature17994). Here we report the functional analysis of the structural information in the context of complete ZIKV and DENV-2 virions. Swapping the prM-E genes between ZIKV and DENV-2 switched the thermostability of the chimeric viruses, identifying the prM-E proteins as the major determinants for virion thermostability. Shortening the extended loop of the E protein by 1 amino acid was lethal for ZIKV assembly/release. Mutations (Q350I and T351V) that abolished the extra hydrogen-bond interaction between the E proteins did not reduce ZIKV thermostability, indicating that the extra interaction does not increase the thermostability. Interestingly, mutant T351V was attenuated in A129 mice defective in type I interferon receptors, even though the virus retained the wild-type thermostability. Furthermore, we found that a chimeric ZIKV with the DENV-2 prM-E and a chimeric DENV-2 with the ZIKV prM-E were highly attenuated in A129 mice; these chimeric viruses were highly immunogenic and protective against DENV-2 and ZIKV challenge, respectively. These results indicate the potential of these chimeric viruses for vaccine development.Analysis of a recently observed high-resolution structure of ZIKV led to a hypothesis that its unusual stability may contribute to the associated, unique disease outcomes. Here we performed a functional analysis to demonstrate that viral prM-E genes are the main determinants for the high stability of ZIKV. The extra hydrogen-bond interaction (observed in the high-resolution structure) between ZIKV E proteins did not enhance virion stability, whereas the extended loop of E protein (CD loop in domain III) was essential for ZIKV assembly. More importantly, we found that a chimeric ZIKV with DENV-2 prM-E genes and a chimeric DENV-2 with ZIKV prM-E genes were highly attenuated in A129 mice. Mice immunized with these chimeric viruses generated robust neutralizing antibody responses and were fully protected from DENV-2 and ZIKV challenge, respectively, indicating that these chimeric viruses could be further developed as vaccine candidates.

Pub.: 09 Feb '17, Pinned: 16 Apr '17

A live-attenuated Zika virus vaccine candidate induces sterilizing immunity in mouse models.

Abstract: Zika virus (ZIKV) infection of pregnant women can cause a wide range of congenital abnormalities, including microcephaly, in the infant, a condition now collectively known as congenital ZIKV syndrome. A vaccine to prevent or significantly attenuate viremia in pregnant women who are residents of or travelers to epidemic or endemic regions is needed to avert congenital ZIKV syndrome, and might also help to suppress epidemic transmission. Here we report on a live-attenuated vaccine candidate that contains a 10-nucleotide deletion in the 3' untranslated region of the ZIKV genome (10-del ZIKV). The 10-del ZIKV is highly attenuated, immunogenic, and protective in type 1 interferon receptor-deficient A129 mice. Crucially, a single dose of 10-del ZIKV induced sterilizing immunity with a saturated neutralizing antibody titer, which no longer increased after challenge with an epidemic ZIKV, and completely prevented viremia. The immunized mice also developed a robust T cell response. Intracranial inoculation of 1-d-old immunocompetent CD-1 mice with 1 × 10(4) infectious focus units (IFU) of 10-del ZIKV caused no mortality, whereas infections with 10 IFU of wild-type ZIKV were lethal. Mechanistically, the attenuated virulence of 10-del ZIKV may be due to decreased viral RNA synthesis and increased sensitivity to type-1-interferon inhibition. The attenuated 10-del ZIKV was incapable of infecting mosquitoes after oral feeding of spiked-blood meals, representing an additional safety feature. Collectively, the safety and efficacy results suggest that further development of this promising, live-attenuated ZIKV vaccine candidate is warranted.

Pub.: 11 Apr '17, Pinned: 16 Apr '17