Chikungunya: A Potentially Emerging Epidemic?

Chikungunya virus is a mosquito-borne emerging pathogen that has a major health impact in humans and causes fever disease, headache, rash, nausea, vomiting, myalgia, and arthralgia. Indigenous to tropical Africa, recent large outbreaks have been reported in parts of South East Asia and several of its neighboring islands in 2005–07 and in Europe in 2007. Furthermore, positive cases have been confirmed in the United States in travelers returning from known outbreak areas. Currently, there is no vaccine or antiviral treatment. With the threat of an emerging global pandemic, the peculiar problems associated with the more immediate and seasonal epidemics warrant the development of an effective vaccine. In this review, we summarize the evidence supporting these concepts

A DNA Vaccine against Chikungunya Virus Is Protective in Mice and Induces Neutralizing Antibodies in Mice and Nonhuman Primates

Chikungunya virus (CHIKV) is an emerging mosquito-borne alphavirus indigenous to tropical Africa and Asia. Acute illness is characterized by fever, arthralgias, conjunctivitis, rash, and sometimes arthritis. Relatively little is known about the antigenic targets for immunity, and no licensed vaccines or therapeutics are currently available for the pathogen. While the Aedes aegypti mosquito is its primary vector, recent evidence suggests that other carriers can transmit CHIKV thus raising concerns about its spread outside of natural endemic areas to new countries including the U.S. and Europe. Considering the potential for pandemic spread, understanding the development of immunity is paramount to the development of effective counter measures against CHIKV. In this study, we isolated a new CHIKV virus from an acutely infected human patient and developed a defined viral challenge stock in mice that allowed us to study viral pathogenesis and develop a viral neutralization assay. We then constructed a synthetic DNA vaccine delivered by in vivo electroporation (EP) that expresses a component of the CHIKV envelope glycoprotein and used this model to evaluate its efficacy. Vaccination induced robust antigen-specific cellular and humoral immune responses, which individually were capable of providing protection against CHIKV challenge in mice. Furthermore, vaccine studies in rhesus macaques demonstrated induction of nAb responses, which mimicked those induced in convalescent human patient sera. These data suggest a protective role for nAb against CHIKV disease and support further study of envelope-based CHIKV DNA vaccines

Life cycle of Chikungunya virus inside infected cells.

<p>Characteristically, there are two rounds of translation: (+) sense genomic RNA (49S′ = 11.7 kb) acts directly as mRNA and is partially translated (5′ end) to produce non-structural proteins (nsp's). These proteins are responsible for replication and formation of a complementary (−) strand, the template for further (+) strand synthesis. Subgenomic mRNA (26 S = 4.1 kb) replication occurs through the synthesis of full-length (−) intermediate RNA, which is regulated by nsp4 and p123 precursor in early infection and later by mature nsp's. Translation of the newly synthesized sub-genomic RNA results in production of structural proteins such as Capsid and protein E2-6k-E1 (from 3′ end of genome). Assembly occurs at the cell surface, and the envelope is acquired as the virus buds from the cell and release and maturation almost simultaneous occurred. Replication occurs in the cytoplasm and is very rapid (∼4 h) <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000623#pntd.0000623-Edwards1" target="_blank">[28]</a>, <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000623#pntd.0000623-Strauss1" target="_blank">[29]</a>.</p

Life cycle of Chikungunya virus in Africa showing the interconnection between the sylvatic cycle on the left and the urban cycle on the right.

<p>Particularly in Africa, the virus is maintained in a sylvatic cycle comprising non-human primates and different species of forest-dwelling mosquitoes including <i>Aedene</i> mosquitoes (<i>Ae. Africanus</i>, <i>Ae. furcifer-taylori</i>, <i>Ae. dalzieli</i>, etc.,) and non <i>Aedene</i> mosquitoes (Mansonia, Culex, etc.) <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000623#pntd.0000623-Diallo1" target="_blank">[10]</a>.</p

Characterization of a small molecule modulator of inflammatory cytokine production

Abstract In the present study, the effect(s) of the immunomodulatory drug GLS-1027 on various cell types involved in inflammation were investigated. GLS-1027 reduced LPS-stimulated secretion of pro-inflammatory cytokines by macrophage or monocytic cells and cell lines. This reduction was likely due in part to decreased activation of NF-κB family transcription factors and inhibition of p38 MAPK signaling in GLS-1027-treated cells. Independent from its effects on macrophages, GLS-1027 inhibited dendritic cell maturation and differentiation of naïve CD4+ T cells into Th17 cells, reducing the production of typical pro-inflammatory cytokines associated with both processes. In vivo administration of GLS-1027 prevented the development of type 1 diabetes in NOD mice which correlated with reduced serum levels of IL17A in GLS-1027 treated animals and reduced ex vivo production of IL17A from both spleen and lymph-node cells. Overall, our data show that GLS-1027 can reduce inflammation through multiple actions, including the reduction of pro-inflammatory cytokine production by innate immune cells, the inhibition of dendritic cells maturation, and the inhibition of Th17 cells polarization

Levels of CHIKV-specific IgG in mice immunized with CHIKV vaccines.

<p>Each group of C57BL/6 mice (<i>n</i> = 5) was immunized with 12.5 µg of pVax1 control vector or CHIKV vaccine plasmids as indicated at 0 and 2 wk. Mice were bled 2 wk after each immunization, and each group's serum pool was diluted to 1∶100 and 1∶500 for reaction with specific vaccine constructs. Serum was incubated for 1 h at 37°C on 96-well plates coated with 2 mg/ml of respective CHIKV peptides, and antibody was detected using anti-mouse IgG-HRP and OD was measured at 405 nm.</p

DNA vaccinated mice are capable of producing antibodies against the antigens encoded in the DNA vaccine.

<p>Hela cells transfected with DNA plasmid vaccine encoding the CHIKV Capsid (left) and Envelope (right) genes were examined for protein expression using confocal microscopy. Serum collected from mice immunized with the DNA vaccine was used as the primary antibody for detection of CHIKV proteins. Two days post-transfection, the cells, treated with serum and then with an anti-mouse IgG conjugated with Alexa-Fluor 488, were visualized under the Ziess LSM510 META NLO Laser Scanning Confocal Microscope (×63). Expression of high levels of CHIKV proteins in these cells revealed the presence of CHIKV-specific antibodies, thereby validating the efficacy of the DNA vaccine in inducing antibodies.</p

Comparative properties of DNA vaccines over other vaccine approaches.

<p>Comparative properties of DNA vaccines over other vaccine approaches.</p