Abstract
Chikungunya virus (CHIKV) is becoming a global concern due to the increasing number of outbreaks throughout the world and the absence of any CHIKV-specific vaccine or treatment. Virus-like particles (VLPs) are multistructured proteins that mimic the organization and conformation of native viruses but lack the viral genome. They are noninfectious and potentially safer vaccine candidates. Recent studies demonstrated that the yield of CHIKV VLPs varies depending on the strains, despite the 95% amino acid similarity of the strains. This might be due to the codon usage, since protein expression is differently controlled by different organisms. We optimized the region encoding CHIKV structural proteins, C-E3-E2-6k-E1, inserted it into a mammalian expression vector, and used the resulting construct to transfect 293 cells. We detected 50-kDa proteins corresponding to E1 and/or E2 in the cell lysate and the supernatant. Transmission electron microscopy revealed spherical particles with a 50- to 60-nm diameter in the supernatant that resembled the native CHIKV virions. The buoyant density of the VLPs was 1.23 g/mL, and the yield was 20 µg purified VLPs per 108 cells. The VLPs aggregated when mixed with convalescent sera from chikungunya patients, indicating that their antigenicity is similar to that of native CHIKV. Antibodies elicited with the VLPs were capable of detecting native CHIKV, demonstrating that the VLPs retain immunogenicity similar to that of the native virion. These results indicated that CHIKV VLPs are morphologically, antigenically, and immunologically similar to the native CHIKV, suggesting that they have potential for use in chikungunya vaccines.
Highlights
Chikungunya fever is a mosquito-borne disease in Africa, South Asia, and Southeast Asia that usually starts 2–4 days after chikungunya virus (CHIKV) infection
Immunoreactive protein bands with molecular masses of approx. 47 kDa were detected in the supernatants from the cells transfected with both optimized and natural codon-based plasmids. This size corresponds to the predicted molecular mass of the envelope glycoprotein E2 and/ or E1, whereas no immunoreactive band was detected when pooled serum obtained from healthy individuals was used. These results indicated that the structural proteins were produced and released into the supernatant
It is noteworthy that the expression of the proteins with the optimized codons was much higher than that obtained with the natural codons
Summary
Chikungunya fever is a mosquito-borne disease in Africa, South Asia, and Southeast Asia that usually starts 2–4 days after chikungunya virus (CHIKV) infection. Aedes albopictus, is present in habitats across Europe, North America, and East Asia, CHIKV infections have become a serious public health concern [2,3,4,5,6]. CHIKV was first isolated in Tanzania in 1953 and the recent epidemics have continued to underscore the need for therapeutic and preventive measures, there are still no treatment agents or vaccines for this infection [10]. The genome of CHIKV is composed of a positivesense single-stranded RNA genome of 11.7 kb encoding four nonstructural and five structural proteins. The structural proteins are translated from a subgenomic 26S mRNA as a single polyprotein, which is processed cotranslationally into five structural proteins: capsid, E3, E2, 6K and E1 [11]
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