Development and evaluation of an inactivated Chikungunya virus vaccine

Abstract

Background: Chikungunya (CHIK) is a debilitating viral disease that can result in high levels of morbidity and, sometimes, even mortality.
It is caused by the chikungunya virus (CHIKV), which belongs to the Togaviridae family. Chikungunya disease is characterized by a triad
of symptoms: fever, rash, and joint pain. It is generally treated with painkillers and non-steroidal anti-inflammatory drugs (NSAIDs).
Chikungunya is a vaccine-preventable disease and various vaccine platforms are being used, including recombinant protein subunit,
live-attenuated, inactivated, viral vector, virus-like particles (VLPs), and nucleic acids (DNA and RNA). Objective: The inactivated (killed)
virus platform is one of the safest, as there is no chance of reversion to the wild-type virus. Since this uses a traditional vaccine platform,
its efficacy and safety are time-tested. Therefore, the study was aimed at developing an inactivated vaccine against CHIKV. Methods:
Chikungunya virus was isolated from 53 sera samples. These were then purified, cloned, and sequenced. The 53 isolates were narrowed
down to five CHIKV isolates cultured in African green monkey kidney (Vero) cells. The fastest growing isolate was used as the candidate
vaccine. It was inactivated using three chemicals – β-propiolactone (BPL), formaldehyde, and binary ethyleneimine (BEI). These were
formulated with and without Mycobacterium w (Mw) and used for immunization of Balb/c mice to evaluate the immunogenicity of
these formulations. The neutralizing antibody titers were estimated using the plaque reduction neutralization test with a 50% end-point
(PRNT50). Results: Purification, cloning and sequencing of the samples confirmed that these were indeed CHIKV isolates. Cell culture of
the isolates revealed that five isolates grew better than the rest. The isolate AHD4 grew the fastest and was chosen as the candidate
vaccine. It was formulated with BPL, formaldehyde, and BEI, with and without Mw. The six formulations were tested for immunogenicity
in eight Balb/c mice in each group. The BEI-inactivated CHIKV formulated with Mw elicited the highest neutralizing antibody response.
Conclusion: The BEI-inactivated CHIKV formulated with Mw is the best candidate vaccine that could be taken forward for further
evaluation in rhesus monkeys