A Virus-Like Particle Vaccine Elicits Broad Neutralizing Antibody Responses in Humans to All Chikungunya Virus Genotypes

Abstract

Chikungunya virus (CHIKV) is an alphavirus that has emerged as a global health burden. There are 3 CHIKV genotypes: Asian, West African, and Eastern/Central/South African. No licensed CHIKV vaccine is available, and whether the antibody response elicited by one genotype can neutralize heterologous genotypes is unclear. We assessed neutralizing antibody (NAb) responses of volunteers in a phase 1 study of a CHIKV vaccine against 9 viral strains representing all 3 genotypes. Minimal differences in vaccine-elicited NAb responses were observed among genotypes, suggesting that vaccination with a single CHIKV strain can elicit cross-protective NAbs against all 3 genotypes.

Keywords: chikungunya virus; neutralizing antibodies; virus-like particle vaccine.

Figure 1.

Production of infectious Semliki Forest virus (SFV)–green fluorescent protein (GFP)–chikungunya virus (CHIKV) chimeric viruses. A, Genomic organization of alphaviruses (top). A modified SFV replicon (pSFV-GFP-BB) consisting of a truncated SFV genome under the transcriptional control of the cytomegalovirus promoter (bottom). The hepatitis delta virus ribozyme and polyadenylation sequence of SV40 were introduced to create the 3′ terminus of the genome. BamHI and AscI endonuclease recognition sites were introduced downstream of the 26S subgenomic promoter to allow introduction of structural gene fragments from multiple CHIKV strains. A GFP reporter gene was introduced under a second 26S subgenomic promoter to allow infection to be scored by GFP expression. B, Crystal structure of the CHIKV heterotrimer of E3 (gray ribbon), E2 (cyan ribbon), and E1 (green ribbon) proteins (PDB 3N44). Blue and black spheres highlight variation at amino acid residues found in 1 or >1 of the 9 CHIKV strains tested, respectively. C, SFV-GFP-CHIKV viruses collected 72 hours after transfection of HEK-293T cells with pSFV-GFP-BB only or with pSFV-GFP-BB containing CHIKV structural genes from 1 of 9 different strains were serially diluted and used to infect Vero cells to determine infectivity, as measured by the percentage of GFP-positive cells. Error bars indicate the range of infectivity from duplicate wells. Data are representative of 5 independent experiments performed with independent virus preparations. D, Growth kinetics of SFV-GFP-CHIKV viruses. Vero cells were infected with SFV-GFP-CHIKV at a multiplicity of infection of 0.05. Virus-containing supernatant collected at the indicated times was serially diluted and used to infect Vero cells to determine virus titer. Shown are average titers, reported as infectious units/milliliter, obtained from 2 independent experiments performed in duplicate with independent virus stocks. Errors bars represent the range of infection. Abbreviation: UTR, untranslated region.

Figure 2.

Neutralization sensitivity of Semliki Forest virus (SFV)–green fluorescent protein (GFP)–chikungunya virus (CHIKV) chimeric viruses. Representative neutralization curves of chimeric viruses expressing the structural genes of 9 CHIKV strains against (A) monoclonal antibody (mAb) CHK-166 and (B) serum obtained from a recipient of the CHIKV virus-like particle (VLP) vaccine are shown. Error bars indicate the range of infectivity from duplicate wells. Data are representative of 3 independent experiments performed with independent virus stocks. C, Average 50% neutralization titers (NT₅₀) of sera from 12 vaccine recipients against 9 CHIKV strains obtained from 3 independent experiments. Each dotted line connects the NT₅₀ of a vaccine recipient against the 9 strains. Error bars indicate the standard error of the mean. D, Comparison of the sensitivity of CHIKV strains to neutralization by vaccine sera, using 1-way analysis of variance, followed by Dunnett multiple comparisons test. We calculated the fold change in average NT₅₀ of each CHIKV strain against 12 serum samples relative to strain LR_OPY-1 2006, which was assigned a value of 1. Error bars indicate the standard error of the mean. *P < .0001.