Purified Inactivated Zika Vaccine Candidates Afford Protection against Lethal Challenge in Mice

In response to the 2016 global public health emergency of international concern announced by the World Health Organization surrounding Zika virus (ZIKV) outbreaks, we developed a purified inactivated Zika virus vaccine (PIZV) candidate from ZIKV strain PRVABC59, isolated during the outbreak in 2015. The virus isolate was plaque purified, creating six sub-isolated virus stocks, two of which were selected to generate PIZV candidates for preclinical immunogenicity and efficacy evaluation in mice. The alum-adjuvanted PIZV candidates were highly immunogenic in both CD-1 and AG129 mice after a 2-dose immunization. Further, AG129 mice receiving 2 doses of PIZV formulated with alum were fully protected against lethal ZIKV challenge and mouse immune sera elicited by the PIZV candidates were capable of neutralizing ZIKVs of both African and Asian genetic lineages in vitro. Additionally, passive immunization of naïve mice with ZIKV-immune serum showed strong positive correlation between neutralizing ZIKV antibody (NAb) titers and protection against lethal challenge. This study supported advancement of the PIZV candidate toward clinical development.

Genetic and phenotypic characterization of manufacturing seeds for a tetravalent dengue vaccine (DENVax)

Background

We have developed a manufacturing strategy that can improve the safety and genetic stability of recombinant live-attenuated chimeric dengue vaccine (DENVax) viruses. These viruses, containing the pre-membrane (prM) and envelope (E) genes of dengue serotypes 1–4 in the replicative background of the attenuated dengue-2 PDK-53 vaccine virus candidate, were manufactured under cGMP.

Methodology/Principal Findings

After deriving vaccine viruses from RNA-transfected Vero cells, six plaque-purified viruses for each serotype were produced. The plaque-purified strains were then analyzed to select one stock for generation of the master seed. Full genetic and phenotypic characterizations of the master virus seeds were conducted to ensure these viruses retained the previously identified attenuating determinants and phenotypes of the vaccine viruses. We also assessed vector competence of the vaccine viruses in sympatric (Thai) Aedes aegypti mosquito vectors.

Conclusion/Significance

All four serotypes of master vaccine seeds retained the previously defined safety features, including all three major genetic loci of attenuation, small plaques, temperature sensitivity in mammalian cells, reduced replication in mosquito cell cultures, and reduced neurovirulence in new-born mice. In addition, the candidate vaccine viruses demonstrated greatly reduced infection and dissemination in Aedes aegypti mosquitoes, and are not likely to be transmissible by these mosquitoes. This manufacturing strategy has successfully been used to produce the candidate tetravalent vaccine, which is currently being tested in human clinical trials in the United States, Central and South America, and Asia.

Transmitted by Aedes spp. mosquitoes found worldwide, dengue is the most important mosquito-borne viral disease in the world. The incidence of dengue has increased 30-fold over the past 50 years, and is now endemic in over 100 countries. Vaccination is believed to be one of the most effective strategies in dengue prevention. However, no vaccine is currently available, and prevention strategies to control mosquitoes in endemic areas have been insufficient in controlling dengue. We have developed a recombinant live-attenuated tetravalent vaccine against all four serotypes of dengue virus. This candidate vaccine is currently under human clinical evaluation. In this report, we provide information regarding our manufacturing strategy, and present details of the genetic and biological characterization of the master seed virus for each vaccine serotype. The study described here, our previously reported and ongoing pre-clinical studies, and current clinical trials will provide critical information to evaluate the safety and efficacy of the vaccine to protect humans against dengue.

Chikungunya virus and prospects for a vaccine

In 2004, chikungunya virus (CHIKV) re-emerged from East Africa to cause devastating epidemics of debilitating and often chronic arthralgia that have affected millions of people in the Indian Ocean Basin and Asia. More limited epidemics initiated by travelers subsequently occurred in Italy and France, as well as human cases exported to most regions of the world, including the Americas where CHIKV could become endemic. Because CHIKV circulates during epidemics in an urban mosquito-human cycle, control of transmission relies on mosquito abatement, which is rarely effective. Furthermore, there is no antiviral treatment for CHIKV infection and no licensed vaccine to prevent disease. Here, we discuss the challenges to the development of a safe, effective and affordable chikungunya vaccine and recent progress toward this goal.

Efficacy of a tetravalent chimeric dengue vaccine (DENVax) in Cynomolgus macaques

Three tetravalent formulations of chimeric dengue (DENVax) viruses containing the pre-membrane and envelope genes of serotypes 1-4 expressed by the attenuated DENV-2 PDK-53 genome were tested for safety, immunogenicity, and efficacy in cynomolgus macaques (Macaca fascicularis). Subcutaneous injection of the DENVax formulations was well-tolerated. Low levels of viremia of only one of the four vaccine viruses were detected yet virus neutralizing antibody titers were induced against all four dengue virus serotypes after one or two administrations of vaccine. All animals immunized with the high-dose formulation were protected from viremia, and all immunized animals were completely protected from DENV-3 and DENV-4 challenge. A lower dose of DENVax formulation partially protected animals from DENV-1 or DENV-2 challenge. In contrast, all control animals developed high levels of viremia for multiple days after challenge with DENV 1-4. This study highlights the immunogenicity and efficacy of the tetravalent DENVax formulations in nonhuman primates.

Novel formulations enhance the thermal stability of live-attenuated flavivirus vaccines

Thermal stability is important for the manufacture, distribution and administration of vaccines, especially in tropical developing countries, where particularly adverse field conditions exist. Current live-attenuated flavivirus vaccines exhibit relatively poor liquid stability in clinical settings, and clinicians are instructed to discard the yellow fever vaccine 1h after reconstitution. We have identified novel combinations of excipients that greatly enhance the thermal stability of live-attenuated DEN-2 PDK-53-based flavivirus vaccine candidates. Liquid formulations comprising a sugar, albumin and a pluronic polymer minimized the loss of flavivirus infectious titer to less than 0.5 log(10)pfu after storage for at least 8h at 37°C, 7 days at room temperature or at least 11 weeks at 4°C. Additionally, these formulations prevented reduction of viral infectivity after two freeze-thaw cycles of virus. Formulated candidate vaccines were readily lyophilized and reconstituted with minimal loss of viral titers. In mice, the formulations were safe and did not hinder the ability of the vaccine virus to generate a potent, protective immune response. These formulations provided significantly greater liquid-phase stability than has been reported previously for other flavivirus vaccine formulations. The enhanced thermal stability provided by the formulations described here will facilitate the effective distribution of flavivirus vaccines worldwide.

Invasion of human neuronal and glial cells by an infectious strain of Borrelia burgdorferi

Human infection by Borrelia burgdorferi, the etiological agent for Lyme disease, can result in serious acute and late-term disorders including neuroborreliosis, a degenerative condition of the peripheral and central nervous systems. To examine the mechanisms involved in the cellular pathogenesis of neuroborreliosis, we investigated the ability of B. burgdorferi to attach to and/or invade a panel of human neuroglial and cortical neuronal cells. In all neural cells tested, we observed B. burgdorferi in association with the cell by confocal microscopy. Further analysis by differential immunofluorescent staining of external and internal organisms, and a gentamicin protection assay demonstrated an intracellular localization of B. burgdorferi. A non-infectious strain of B. burgdorferi was attenuated in its ability to associate with these neural cells, suggesting that a specific borrelial factor related to cellular infectivity was responsible for the association. Cytopathic effects were not observed following infection of these cell lines with B. burgdorferi, and internalized spirochetes were found to be viable. Invasion of neural cells by B. burgdorferi provides a putative mechanism for the organism to avoid the host's immune response while potentially causing functional damage to neural cells during infection of the CNS.

The high-affinity Sp1 binding site in the HTLV-1 promoter contributes to Tax-independent basal expression

Transcriptional activation of human T-cell leukemia virus type 1 (HTLV-1) requires many cellular proteins and the virally encoded transcription factor Tax. Tax binds the three viral cAMP-response elements (CREs) with ATF/CREB (activating transcription factor/cAMP-response element-binding protein) and recruits the cellular coactivators CBP/p300. HTLV-1 also utilizes other cellular transcription factors that bind to the promoter to regulate transcription. One of these factors, Sp1, has been shown to bind to the viral promoter at two elements; one located within the third viral CRE, and the second located between the second and third viral CREs. The functional significance of Sp1 binding at each of these regions of the viral promoter is not completely understood. We set out to characterize Sp1 binding and to evaluate the functional significance of Sp1, both in the absence and presence of Tax. We found that Sp1 binds preferentially to the element located between the second and third viral CREs, and modestly activates transcription in vitro and in vivo. Sp1 was detected at the integrated HTLV-1 promoter in vivo. Surprisingly, point mutagenesis of the strong Sp1 binding site rendered the HTLV-1 reporter plasmid insensitive to Sp1 activation, and dramatically reduced basal transcription in vivo. These data indicate a role for Sp1 in basal level transcription of HTLV-1.

Paradoxical effects of DNA binding polyamides on HTLV-1 transcription

Human T-cell leukemia virus type-1 (HTLV-1) depends on the virally encoded transcription factor Tax for efficient viral replication and gene expression. In a complex with CREB, Tax contacts the minor groove of the promoter DNA at guanine and cytosine rich sequences that flank three of the off-consensus cyclic-AMP response elements (CREs). In this study, we used six Tax-directed pyrrole-imidazole polyamides specifically designed to block Tax binding to DNA at each GC sequence of the three viral CREs. We found that four of these polyamides disrupt binding of the Tax/CREB complex in vitro, and that these same molecules also inhibit Tax-mediated transcription in vitro on chromatin-assembled templates. However, of these four Tax/CREB-specific polyamides, only one polyamide appears to be uniquely Tax specific. We show that polyamides can enter the nuclei of HTLV-1 infected T-cells, and two of the four polyamides down-regulated virion production in these cells. Together, these data illustrate the importance of studying polyamide inhibition of gene expression in vitro and in vivo, as the function of the polyamides in living cells is not fully understood. Finally, our data indicates that targeted disruption of the Tax/CREB complex, or other complexes which assemble on the HTLV-1 promoter, may provide a novel approach for inhibiting viral replication in vivo.

p53 Transcriptional activity is mediated through the SRC1-interacting domain of CBP/p300

The tumor suppressor p53 recruits the cellular coactivator CBP/p300 to mediate the transcriptional activation of target genes. In this study, we identify a novel p53-interacting region in CBP/p300, which we call CR2, located near the carboxyl terminus. The 95-amino acid CR2 region (amino acids 2055--2150) is located adjacent to the C/H3 domain and corresponds precisely with the minimal steroid receptor coactivator 1 (SRC1)-interacting domain of CBP (also called IBiD). We show that the region of p53 that participates in the CR2 interaction resides within the first 107 amino acids of the protein. p53 binds strongly to the CR2 domain of both CBP and the highly homologous coactivator p300. Importantly, an in-frame deletion of CR2 within the full-length p300 protein strongly compromises p300-mediated p53 transcriptional activation from a chromatin template in vitro. The identification of the p53-interacting CR2 domain in CBP/p300 prompted us to ask if the human T-cell leukemia virus (HTLV-I) Tax protein, which also interacts with CR2, competes with p53 for binding to this domain. We show that p53 and Tax exhibit mutually exclusive binding to the CR2 region, possibly contributing to the previously reported Tax repression of p53 function. Together, these studies identify and molecularly characterize a new p53 binding site on CBP/p300 that participates in coactivator-mediated p53 transcription function. The identity of the p53.CR2 interaction indicates that at least three distinct sites on CBP/p300 may participate in mediating p53 transactivation.