Research Article: Dengue E Protein Domain III-Based DNA Immunisation Induces Strong Antibody Responses to All Four Viral Serotypes

Date Published: July 28, 2015

Publisher: Public Library of Science

Author(s): Monica Poggianella, José L. Slon Campos, Kuan Rong Chan, Hwee Cheng Tan, Marco Bestagno, Eng Eong Ooi, Oscar R. Burrone, Mauricio Martins Rodrigues.

Abstract: Dengue virus (DENV) infection is a major emerging disease widely distributed throughout the tropical and subtropical regions of the world affecting several millions of people. Despite constants efforts, no specific treatment or effective vaccine is yet available. Here we show a novel design of a DNA immunisation strategy that resulted in the induction of strong antibody responses with high neutralisation titres in mice against all four viral serotypes. The immunogenic molecule is an engineered version of the domain III (DIII) of the virus E protein fused to the dimerising CH3 domain of the IgG immunoglobulin H chain. The DIII sequences were also codon-optimised for expression in mammalian cells. While DIII alone is very poorly secreted, the codon-optimised fusion protein is rightly expressed, folded and secreted at high levels, thus inducing strong antibody responses. Mice were immunised using gene-gun technology, an efficient way of intradermal delivery of the plasmid DNA, and the vaccine was able to induce neutralising titres against all serotypes. Additionally, all sera showed reactivity to a recombinant DIII version and the recombinant E protein produced and secreted from mammalian cells in a mono-biotinylated form when tested in a conformational ELISA. Sera were also highly reactive to infective viral particles in a virus-capture ELISA and specific for each serotype as revealed by the low cross-reactive and cross-neutralising activities. The serotype specific sera did not induce antibody dependent enhancement of infection (ADE) in non-homologous virus serotypes. A tetravalent immunisation protocol in mice showed induction of neutralising antibodies against all four dengue serotypes as well.

Partial Text: Dengue is a mosquito-borne viral infection caused by dengue virus (DENV), one of the most important human pathogens worldwide [1]. The infection produces a systemic disease with a broad spectrum of outcomes, ranging from non-symptomatic/mild febrile illness (Dengue Fever, DF) to severe plasma leakage and haemorrhagic manifestations (Dengue Haemorrhagic Fever, DHF) that can further evolve into potentially fatal conditions (Dengue Shock Syndrome, DSS) [2, 3]. DENV, which is spread by Aedes spp. mosquitoes, is widely distributed throughout the tropical and subtropical regions of the world [2]. About 3 billion people, in over 100 countries, are estimated to be at risk of infection, with over 300 million infections, 500,000 episodes of DHF manifestations and 20,000 deaths reported each year [1, 4]. The remarkable spread and impact of the disease led the World Health Organization to classify it as the “most important mosquito-borne viral disease in the world” [5].

In this paper we show that immunisation with DNA plasmid constructs encoding properly engineered DIII domains of the four DENV serotypes can induce strong antibody responses in mice. In the context of the immune response against DENV E protein, the Ig-like DIII has been shown to be one of the main targets for protective neutralising antibodies. Highly neutralising epitopes have also been found in regions involving DI, DII [24, 44, 45] and, more recently, dimer-dependent epitopes at the interface between the opposing E monomers [46, 47] were described. However, antibodies reactive with DI/DII were shown to be more cross-reactive, with lower neutralisation potency and consequently implicated in enhanced severity of infection [39, 48]. Recent studies have shown that in virus infected individuals the antibody response is dominated by highly cross-reactive antibodies, while antibodies directed against the more specific DIII represent only a minor component [24]. Because of the increased risk of ADE due to the presence of such cross-reactive antibodies, several attempts for an efficient anti-dengue vaccine have focused on the use of the highly specific DIII as antigen [49].



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