Dengue Virus and Vaccines: How Can DNA Immunization Contribute to This Challenge?

Dengue infections still have a tremendous impact on public health systems in most countries in tropical and subtropical regions. The disease is systemic and dynamic with broad range of manifestations, varying from mild symptoms to severe dengue (Dengue Hemorrhagic Fever and Dengue Shock Syndrome). The only licensed tetravalent dengue vaccine, Dengvaxia, is a chimeric yellow fever virus with prM and E genes from the different dengue serotypes. However, recent results indicated that seronegative individuals became more susceptible to develop severe dengue when infected after vaccination, and now WHO recommends vaccination only to dengue seropositive people. One possibility to explain these data is the lack of robust T-cell responses and antibody-dependent enhancement of virus replication in vaccinated people. On the other hand, DNA vaccines are excellent inducers of T-cell responses in experimental animals and it can also elicit antibody production. Clinical trials with DNA vaccines have improved and shown promising results regarding the use of this approach for human vaccination. Therefore, in this paper we review preclinical and clinical tests with DNA vaccines against the dengue virus. Most of the studies are based on the E protein since this antigen is the main target for neutralizing antibody production. Yet, there are other reports with DNA vaccines based on non-structural dengue proteins with protective results, as well. Combining structural and non-structural genes may be a solution for inducing immune responses aging in different infection moments. Furthermore, DNA immunizations are also a very good approach in combining strategies for vaccines against dengue, in heterologous prime/boost regimen or even administering different vaccines at the same time, in order to induce efficient humoral and cellular immune responses.

Polyclonal antibodies against properly folded Dengue virus NS1 protein expressed in E. coli enable sensitive and early dengue diagnosis.

The non-structural 1 (NS1) protein plays an important role in dengue diagnosis because it has been detected as a soluble serum antigen in both primary and secondary infections. The NS1 protein was expressed in Escherichia coli cells, and the efficiency of four different refolding protocols was tested. All of the protocols generated dimeric NS1 in a conformation similar to that of the protein expressed by eukaryotic cells. A polyclonal antibody produced from the properly folded E. coli recombinant NS1 (rNS1) protein proved to be a useful tool for the diagnosis of Dengue virus because it detected 100% of the Dengue virus 2 (DENV2) in infected patients' sera and 60% of the DENV IgM-positive sera not detected by commercial NS1-based diagnostic kits. These data suggest a high-efficiency method for correctly folding rNS1 that maintains its structural and immunogenic properties. In addition, a detection method using the polyclonal antibody against correctly folded rNS1 seemed to be more sensitive and efficient for NS1 detection in serum, highlighting its usefulness for developing a high-sensitivity diagnostic kit.

Refolded dengue virus type 2 NS1 protein expressed in Escherichia coli preserves structural and immunological properties of the native protein.

The dengue virus NS1 protein has been shown to be a protective antigen under different experimental conditions but the recombinant protein produced in bacterial expression systems is usually not soluble and loses structural and immunological features of the native viral protein. In the present study, experimental conditions leading to purification and refolding of the recombinant dengue virus type 2 (DENV-2) NS1 protein expressed in Escherichia coli are described. The refolded recombinant protein was recovered as heat-stable soluble dimers with preserved structural features, as demonstrated by spectroscopic methods. In addition, antibodies against epitopes of the NS1 protein expressed in eukaryotic cells recognized the refolded protein expressed in E. coli but not the denatured form or the same protein submitted to a different refolding condition. Collectively, the results demonstrate that the recombinant NS1 protein preserved important conformation and antigenic determinants of the native virus protein and represents a valuable reagent either for the development of vaccines or for diagnostic methods.

Vacinas de DNA contra o vírus da dengue utilizando como antígenos as proteínas NS1 e NS3 / DNA vaccines against dengue virus using as antigens the NS1 and NS3 proteins

O vírus da dengue (DENV) consiste de quatro sorotipos antigenicamente relacionados: DENV-1, DENV-2, DENV-3 e DENV-4. Apesar dos diversos esforços para o desenvolvimento de uma vacina contra dengue, ainda não há nenhuma comercialmente disponível. As proteínas não estruturais 1 e 3 (NS1 e NS3) são indicadas como antígenos promissores para o desenvolvimento de uma vacina contra DENV. Segundo alguns estudos, a proteína NS1 é capaz de induzir uma resposta protetora de anticorpos com atividade de fixação do complemento. A proteína NS3, que realiza reações enzimáticas essenciais para a replicação viral, parece ser imunogênica, contendo um predomínio de epítopos para linfócitos T CD4+ e CD8+. No presente trabalho nós avaliamos o potencial de vacinas de DNA baseadas nas proteínas NS1 e NS3 de DENV-2. Foram construídos cinco plasmídeos, pcTPANS3, pcTPANS3H, pcTPANS3P, pcTPANS3N e pcTPANS3C, contendo a seqüência que codifica o peptídeo sinal do ativador de plasminogênio de tecido humano (t-PA) fusionado ao gene NS3 inteiro ou partes destes. Todos estes plasmídeos mediaram a expressão das proteínas recombinantes in vitro em células eucarióticasCamundongos foram inoculados com estes plasmídeos e desafiados com DENV-2 por via intracerebral (i.c.). Nenhuma destas construções induziu níveis satisfatórios de proteção. Além dos plasmídeos com NS3, foram construídas quatro vacinas de DNA baseadas no gene NS1: 1 - pcENS1, que codifica a região C-terminal da proteína E fusionada à NS1, 2 - pcENS1ANC, similar ao pcENS1 com a adição da porção N-terminal da NS2A (ANC), 3 - pcTPANS1, que codifica o peptídeo sinal t-PA fusionado à NS1 e 4 - pcTPANS1ANC, semelhante ao pcTPANS1 com a adição da seqüência ANC. A proteína NS1 recombinante foi detectada nos extratos celulares e sobrenadante das culturas de células BHK transfectadas com pcTPANS1, pcENS1 e pcENS1ANC. Tais resultados indicam que as seqüências sinais t-PA e E direcionaram a NS1 para secreção...