Molecular and phenotypic analysis of a working seed lot of yellow fever virus 17DD vaccine strain produced from the secondary seed lot 102/84 with an additional passage in chicken embryos

Establishment of certified reference material for the potency assay in yellow fever vaccine quality control, in accordance with International Standards Organization guidance

The attenuated yellow fever vaccine (YFV) is offered free of charge to the Brazilian population through the National Immunization Program (NIP). One of the specifications for quality control analyses of the vaccine is the potency determination. This test determines the number of plaque forming units (PFU) in Vero cells. In order to validate the results, the reference material (RM) is analysed in parallel with an established reference vaccine. The aim of this study was to establish certified RM for use as an internal control in the potency assay for the production chain of YFV. The candidate RM homogeneity and stability were determined, and characterized by a collaborative study for further certification. The RM was considered sufficiently homogeneous with average 4.68 log₁₀ IU/HD and stable at (-20 ± 10) ºC and (22.5 ± 2.5) ºC for 715 and 183 days, respectively. When reconstituted and stored in aliquots of 0.6 mL, it was stable at (-20 ± 10) ºC for eight days. But it was not stable at (5 ± 3) ºC for three days. In a collaborative study, two independents' laboratories gave an averaged value of 4.56 ± 0.030 log₁₀ IU/HD. After determining the expanded uncertainty of homogeneity, stability, and characterization, the certified RM lot: 195VFA020Z presented a property value of 4.56 ± 0.22 log₁₀ IU/HD. It was concluded that the new certified RM can be used in routine analysis of a YFV producer, since it has its property value established and it is stable. The possibility of using it in aliquots after reconstitution will also allow the RM to have a much longer shelf life.

Evaluation of hydrogen peroxide virucidal efficacy against yellow fever virus 17DD vaccine strain for application in a vaccine manufacturing industry

The aim of this study was to evaluate the inactivation performance of hydrogen peroxide to the yellow fever virus 17DD vaccine strain, used for the production of attenuated yellow fever vaccine, in two matrixes: formulated yellow fever vaccine (FYV) and yellow fever viral suspension - active pharmaceutical ingredient (API). The samples were dried on stainless steel and exposed to hydrogen peroxide liquid (HPL) at concentrations of 30, 10, 3 and 1% for 20 and 60 min; and to hydrogen peroxide vapour (HPV) in an isolator. The exposure to HPL 30 and 10 %, within 20 min, reduced the virus titre at least 3.85 log₁₀ PFU/mL (74.8 %). During 60 min of exposure, the HPL 30, 10 and 3% reduced the virus titre by at least 3.18 log₁₀ PFU/mL (62.6 %). HPV exposure resulted in complete virus inactivation in FYV (≥ 4.42 log₁₀ PFU/mL reduction) and for API samples 3.17 log₁₀ PFU/mL (64.3 %) reduction. Hydrogen peroxide showed to be a promising disinfectant for elimination of yellow fever virus. However, the optimum concentration and contact time will vary depending on the type of application, and as such may complement individual risk assessments of biological production processes.

Testing the genomic stability of the Brazilian yellow fever vaccine strain using next-generation sequencing data

The live attenuated yellow fever (YF) vaccine was developed in the 1930s. Currently, the 17D and 17DD attenuated substrains are used for vaccine production. The 17D strain is used for vaccine production by several countries, while the 17DD strain is used exclusively in Brazil. The cell passages carried out through the seed-lot system of vaccine production influence the presence of quasispecies causing changes in the stability and immunogenicity of attenuated genotypes by increasing attenuation or virulence. Using next-generation sequencing, we carried out genomic characterization and genetic diversity analysis between vaccine lots of the Brazilian YF vaccine, produced by BioManguinhos–Fiocruz, and used during 11 years of vaccination in Brazil. We present 20 assembled and annotated genomes from the Brazilian 17DD vaccine strain, eight single nucleotide polymorphisms and the quasispecies spectrum reconstruction for the 17DD vaccine, through a pipeline here introduced. The V2IDA pipeline provided a relationship between low genetic diversity, maintained through the seed lot system, and the confirmation of genetic stability of lots of the Brazilian vaccine against YF. Our study sets precedents for use of V2IDA in genetic diversity analysis and in silico stability investigation of attenuated viral vaccines, facilitating genetic surveillance during the vaccine production process.

Evaluation of kinase inhibitors as potential therapeutics for flavivirus infections

The recent introduction of Zika virus (ZIKV), the recurrence of dengue virus (DENV), and the lethality of yellow fever virus (YFV) have had a significant impact on Brazilian society and public health. Here, we targeted two cellular kinases implicated in cell proliferation and cancer that are also important for viral replication: mitogen-activated protein kinase kinase (MEK) and Src. We used two MEK inhibitors - trametinib and selumetinib - and two Src inhibitors - saracatinib and bosutinib - to inhibit ZIKV, DENV, and YFV replication in cell culture. The cytotoxicity of the four inhibitors was determined by the observation of abnormal morphology and quantification of adherent cells by crystal violet staining. The antiviral activity of these drugs was assessed based on the reduction of plaque-forming units in cell culture as evidence of the inhibition of the replication of the selected flaviviruses. All four inhibitors showed antiviral activity, but among them, trametinib was the safest and most efficacious against all of the viruses, inhibiting the replication of ZIKV and YFV by 1000-fold, and DENV2/3 by nearly 100-fold. This pan-antiviral effect shows that trametinib could be repurposed for the treatment of flaviviral infections.

Flavivirus-Mediating B Cell Differentiation Into Antibody-Secreting Cells in Humans Is Associated With the Activation of the Tryptophan Metabolism

Patients infected with the Dengue virus (DENV) often present with a massive generation of DENV-specific antibody-secreting cells (ASCs) in the blood. In some cases, these ASCs represent more than 50% of the circulating B cells, a higher magnitude than those induced by other infections, vaccinations, and plasma cell lymphomas. However, it remains unclear how the DENV infection elicits this colossal response. To address this issue, we utilised an in vitro strategy to induce human PBMCs of healthy individuals incubated with DENV particles (DENV4 TVP/360) to differentiate into ASCs. As controls, PBMCs were incubated with a mitogen cocktail or supernatants of uninfected C6/36 cells (mock). The ASC phenotype and function were increasingly detected in the DENV and mitogen-cultured PBMCs as compared to mock-treated cells. In contrast to the in vivo condition, secreted IgG derived from the PBMC-DENV culture was not DENV-specific. Lower ASC numbers were observed when inactivated viral particles or purified B cells were added to the cultures. The physical contact was essential between B cells and the remaining PBMCs for the DENV-mediated ASC response. Considering the evidence for the activation of the tryptophan metabolism detected in the serum of Dengue patients, we assessed its relevance in the DENV-mediated ASC differentiation. For this, tryptophan and its respective metabolites were quantified in the supernatants of cell cultures through mass spectrophotometry. Tryptophan depletion and kynurenine accumulation were found in the supernatants of PBMC-DENV cultures, which presented enhanced detection of indoleamine 2,3-dioxygenase 1 and 2 transcripts as compared to controls. In PBMC-DENV cultures, tryptophan and kynurenine levels strongly correlated to the respective ASC numbers, while the kynurenine levels were directly proportional to the secreted IgG titers. Contrastingly, PBMCs incubated with Zika or attenuated Yellow Fever viruses showed no correlation between their kynurenine concentrations and ASC numbers. Therefore, our data revealed the existence of distinct pathways for the DENV-mediated ASC differentiation and suggest the involvement of the tryptophan metabolism in this cellular process triggered by flavivirus infections.

Increasing plasmid-based DNA vaccine construct (16 kb pSVK-HBVA) production in Escherichia coli XL10-Gold through optimization of media component

At present, there are production processes to produce protein by Escherichia coli (E. coli) fermentation. Research on the design and optimization of the plasmid fermentation medium, however, is less advanced. The fermentation medium that is optimized for plasmid DNA production is different from the medium that is optimized for protein production. So, establishing a scientific and rational method to optimize the fermentation medium used for plasmid production is very important. Previously, our laboratory developed a novel therapeutic DNA vaccine (named pSVK-HBVA) for hepatitis B based on the alphavirus replicon, and found that E. coli XL10-Gold was the optimal host strain for the production of plasmid pSVK-HBVA. The aim of this study was to establish a scientific and rational method to optimize the fermentation medium used for plasmid production, and investigate the effect of growth medium composition on the production of plasmid pSVK-HBVA harboured in E. coli XL10-Gold, as well as to optimize the medium composition.

The one-factor-at-a-time experiments demonstrated that Luria-Bertani (LB) was the optimal basic medium. The optimal carbon source and nitrogen source were glycerol and home-made proteose peptone, respectively. Based on the Plackett–Burman (PB) design, proteose peptone, glycerol and NH₄Cl were identified as the significant variables, which were further optimized by the steepest ascent (descent) method and central composite design. Growth medium optimization in 500-mL shake flasks by response surface methodology resulted in a maximum volumetric yield of 13.61 mg/L, which was approximately 2.5 times higher than that obtained from the basic medium (LB).

17DD yellow fever vaccine: a double blind, randomized clinical trial of immunogenicity and safety on a dose-response study

OBJECTIVE

To verify if the Bio-Manguinhos 17DD yellow fever vaccine (17DD-YFV) used in lower doses is as immunogenic and safe as the current formulation.

RESULTS

Doses from 27,476 IU to 587 IU induced similar seroconversion rates and neutralizing antibodies geometric mean titers (GMTs). Immunity of those who seroconverted to YF was maintained for 10 mo. Reactogenicity was low for all groups.

METHODS

Young and healthy adult males (n = 900) were recruited and randomized into 6 groups, to receive de-escalating doses of 17DD-YFV, from 27,476 IU to 31 IU. Blood samples were collected before vaccination (for neutralization tests to yellow fever, serology for dengue and clinical chemistry), 3 to 7 d after vaccination (for viremia and clinical chemistry) and 30 d after vaccination (for new yellow fever serology and clinical chemistry). Adverse events diaries were filled out by volunteers during 10 d after vaccination. Volunteers were retested for yellow fever and dengue antibodies 10 mo later. Seropositivity for dengue was found in 87.6% of volunteers before vaccination, but this had no significant influence on conclusions.

CONCLUSION

In young healthy adults Bio-Manguinhos/Fiocruz yellow fever vaccine can be used in much lower doses than usual. INTERNATIONAL REGISTER: ISRCTN 38082350.

17DD and 17D-213/77 yellow fever substrains trigger a balanced cytokine profile in primary vaccinated children

BACKGROUND

This study aimed to compare the cytokine-mediated immune response in children submitted to primary vaccination with the YF-17D-213/77 or YF-17DD yellow fever (YF) substrains.

METHODS

A non-probabilistic sample of eighty healthy primary vaccinated (PV) children was selected on the basis of their previously known humoral immune response to the YF vaccines. The selected children were categorized according to their YF-neutralizing antibody titers (PRNT) and referred to as seroconverters (PV-PRNT(+)) or nonseroconverters (PV-PRNT(-)). Following revaccination with the YF-17DD, the PV-PRNT(-) children (YF-17D-213/77 and YF-17DD groups) seroconverted and were referred as RV-PRNT(+). The cytokine-mediated immune response was investigated after short-term in vitro cultures of whole blood samples. The results are expressed as frequency of high cytokine producers, taking the global median of the cytokine index (YF-Ag/control) as the cut-off.

RESULTS

The YF-17D-213/77 and the YF-17DD substrains triggered a balanced overall inflammatory/regulatory cytokine pattern in PV-PRNT(+), with a slight predominance of IL-12 in YF-17DD vaccinees and a modest prevalence of IL-10 in YF-17D-213/77. Prominent frequency of neutrophil-derived TNF-α and neutrophils and monocyte-producing IL-12 were the major features of PV-PRNT(+) in the YF-17DD, whereas relevant inflammatory response, mediated by IL-12(+)CD8(+) T cells, was the hallmark of the YF-17D-213/77 vaccinees. Both substrains were able to elicit particular but relevant inflammatory events, regardless of the anti-YF PRNT antibody levels. PV-PRNT(-) children belonging to the YF-17DD arm presented gaps in the inflammatory cytokine signature, especially in terms of the innate immunity, whereas in the YF-17D-213/77 arm the most relevant gap was the deficiency of IL-12-producing CD8(+)T cells. Revaccination with YF-17DD prompted a balanced cytokine profile in YF-17DD nonresponders and a robust inflammatory profile in YF-17D-213/77 nonresponders.

CONCLUSION

Our findings demonstrated that, just like the YF-17DD reference vaccine, the YF-17D-213/77 seed lot induced a mixed pattern of inflammatory and regulatory cytokines, supporting its universal use for immunization.

Description of a prospective 17DD yellow fever vaccine cohort in Recife, Brazil

From September 2005 to March 2007, 238 individuals being vaccinated for the first time with the yellow fever (YF) -17DD vaccine were enrolled in a cohort established in Recife, Brazil. A prospective study indicated that, after immunization, anti-YF immunoglobulin M (IgM) and anti-YF IgG were present in 70.6% (IgM) and 98.3% (IgG) of the vaccinated subjects. All vaccinees developed protective immunity, which was detected by the plaque reduction neutralization test (PRNT) with a geometric mean titer of 892. Of the 238 individuals, 86.6% had IgG antibodies to dengue virus; however, the presence of anti-dengue IgG did not interfere significantly with the development of anti-YF neutralizing antibodies. In a separate retrospective study of individuals immunized with the 17DD vaccine, the PRNT values at 5 and 10 years post-vaccination remained positive but showed a significant decrease in neutralization titer (25% with PRNT titers < 100 after 5 years and 35% after 10 years).

Biological and immunological characterization of recombinant Yellow Fever 17D viruses expressing a Trypanosoma cruzi Amastigote Surface Protein-2 CD8+ T cell epitope at two distinct regions of the genome

BACKGROUND

The attenuated Yellow fever (YF) 17D vaccine virus is one of the safest and most effective viral vaccines administered to humans, in which it elicits a polyvalent immune response. Herein, we used the YF 17D backbone to express a Trypanosoma cruzi CD8+ T cell epitope from the Amastigote Surface Protein 2 (ASP-2) to provide further evidence for the potential of this virus to express foreign epitopes. The TEWETGQI CD8+ T cell epitope was cloned and expressed based on two different genomic insertion sites: in the fg loop of the viral Envelope protein and the protease cleavage site between the NS2B and NS3. We investigated whether the site of expression had any influence on immunogenicity of this model epitope.

RESULTS

Recombinant viruses replicated similarly to vaccine virus YF 17D in cell culture and remained genetically stable after several serial passages in Vero cells. Immunogenicity studies revealed that both recombinant viruses elicited neutralizing antibodies to the YF virus as well as generated an antigen-specific gamma interferon mediated T-cell response in immunized mice. The recombinant viruses displayed a more attenuated phenotype than the YF 17DD vaccine counterpart in mice. Vaccination of a mouse lineage highly susceptible to infection by T. cruzi with a homologous prime-boost regimen of recombinant YF viruses elicited TEWETGQI specific CD8+ T cells which might be correlated with a delay in mouse mortality after a challenge with a lethal dose of T. cruzi.

CONCLUSIONS

We conclude that the YF 17D platform is useful to express T. cruzi (Protozoan) antigens at different functional regions of its genome with minimal reduction of vector fitness. In addition, the model T. cruzi epitope expressed at different regions of the YF 17D genome elicited a similar T cell-based immune response, suggesting that both expression sites are useful. However, the epitope as such is not protective and it remains to be seen whether expression of larger domains of ASP-2, which include the TEWETGQI epitope, will elicit better T-CD8+ responses to the latter. It is likely that additional antigens and recombinant virus formulations will be necessary to generate a protective response.

WHO Working Group on Technical Specifications for Manufacture and Evaluation of Yellow Fever Vaccines, Geneva, Switzerland, 13-14 May 2009

In May 2009, WHO convened a meeting of Working Group on Technical Specifications for Manufacturing and Evaluating Yellow Fever (YF) Vaccines, Geneva, Switzerland to initiate revision of the WHO Recommendations (formerly, Requirements) for YF vaccine published in WHO Technical Report Series number 872 (1998). The Working Group, consisting of experts from academia, industry, national regulatory authorities and national control laboratories, reviewed the latest issues of safety, efficacy and quality of YF vaccines and agreed that (i) the revision should focus on live attenuated YF vaccine virus 17D lineage; and that (ii) nonclinical and clinical guidelines for new vaccines prepared from 17D lineage be developed.

Limited replication of yellow fever 17DD and 17D-Dengue recombinant viruses in rhesus monkeys

For the development of safe live attenuated flavivirus vaccines one of the main properties to be established is viral replication. We have used real-time reverse transcriptase-polymerase chain reaction and virus titration by plaque assay to determine the replication of yellow fever 17DD virus (YFV 17DD) and recombinant yellow fever 17D viruses expressing envelope proteins of dengue virus serotypes 2 and 4 (17D-DENV-2 and 17D-DENV-4). Serum samples from rhesus monkeys inoculated with YFV 17DD and 17D-DENV chimeras by intracerebral or subcutaneous route were used to determine and compare the viremia induced by these viruses. Viral load quantification in samples from monkeys inoculated by either route with YFV 17DD virus suggested a restricted capability of the virus to replicate reaching not more than 2.0 log10 PFU mL(-1) or 3.29 log10 copies mL(-1). Recombinant 17D-dengue viruses were shown by plaquing and real-time PCR to be as attenuated as YF 17DD virus with the highest mean peak titer of 1.97 log10 PFU mL(-1) or 3.53 log10 copies mL(-1). These data serve as a comparative basis for the characterization of other 17D-based live attenuated candidate vaccines against other diseases.

Evidence for interferon production and its correlation with YF 17DD vaccine virus yields in primary chick embryo cells

Early experiments have resulted in the establishment of an efficient methodology for the production of a yellow fever vaccine in chicken embryo fibroblasts (CEF) using the 17DD virus strain [Freire, M.S., Mann, G.F., Marchevsky, R.S., Yamamura, A.M., Almeida, L.F., Jabor, A.V., Malachias, J.M., Coutinho, E.S., Galler, R., 2005. Production of yellow fever 17DD vaccine virus in primary culture of chicken embryo fibroblasts: yields, thermo and genetic stability, attenuation and immunogenicity. Vaccine 23, 2501-2512]. To investigate the role of the interferon system in vaccine virus yields, CEF cultures seeded at high and low cell densities and infected with the yellow fever 17DD virus were used. The supernatants of these cultures were tested for the presence of interferon by an assay based on the reduction of cytopathic effect of a challenge virus (Sindbis), for the enzymatic activity of the interferon-induced 2',5'-oligoadenylate synthetase and for the expression of 2',5'-oligoadenylate synthetase mRNA. The presence of interferon and its influence in the replication of yellow fever 17DD virus in CEF cultures was clearly demonstrated.

Construction and biological properties of yellow fever 17D/dengue type 1 recombinant virus

Dengue virus, a mosquito-borne flavivirus, is one of the most formidable public health threats in tropical and subtropical regions. As yet, there is no licensed vaccine to protect against the disease. A chimeric yellow fever (YF) 17D/dengue (DEN) type 1 virus was constructed by replacing the pre-membrane and envelope genes of YF 17D virus with those from DEN 1 VeMir95 virus, a Venezuelan isolate. The chimeric YF 17D/DEN 1 VeMir95 virus was regenerated from full-length infectious clones stably propagated in Escherichia coli by transfection of Vero cells with in vitro transcribed RNA. The chimeric virus proliferated efficiently in Vero cells ( approximately 6.6 log(10) plaque-forming units/ml). The chimeric virus was not neurovirulent to 3-week-old Swiss Webster mice inoculated by the intracerebral route, in contrast to the YF 17DD vaccine strain that was lethal for 90% of the mice. The YF 17D/DEN 1 virus at Passage 6 was more attenuated for rhesus monkeys than the YF 17DD commercial vaccine after intracerebral inoculation according to the standard neurovirulence test. This virus is a potential candidate to be included in a tetravalent DEN vaccine formulation. The availability of the cloned cDNA allows further structure/function studies on the viral envelope.