Expression and Characterization of Yeast Derived Chikungunya Virus Like Particles (CHIK-VLPs) and Its Evaluation as a Potential Vaccine Candidate

Chikungunya virus (CHIKV) has emerged as a global health concern due to its recent spread in both old and new world. So far, no CHIKV specific drug or vaccine is licensed for human use. In this study, we report production of Chikungunya virus like particles (CHIK-VLPs) using novel yeast expression system (Pichia pastoris) and its evaluation as vaccine candidate. The gene encoding structural polyprotein of CHIKV from a recent epidemic strain was cloned into yeast expression system. The multicopy integrants were processed for expression of CHIK-VLPs. The VLPs were purified and confirmed through electron microscopic analysis for their morphological identity with CHIKV. The in vitro and in vivo evaluation of CHIK-VLPs as vaccine candidate was determined in Balb/c mice. Induction of both humoral and cellular immune response was observed with different doses of CHIK-VLPs. The humoral immune response was studied through different techniques like enzyme linked immunosorbent assay, IgG Isotyping and plaque reduction neutralization test. CHIK-VLPs were found to elicit high titer of antibodies that are able to recognize native CHIKV. Higher level of IgG2a and IgG1 subtypes was identified suggestive of balanced Th1/Th2 response. Both in vitro and in vivo neutralization activity of CHIK-VLPs antibodies was observed even with low concentration, which shows its high specificity and neutralizing activity against two different CHIKV strains. Neonatal mice receiving anti-CHIK-VLPs antibodies were protected from CHIKV challenge. Induction of cellular immune response was confirmed through higher level of TNF-α, IL-10 and substantial level of IL-2, IL-4 and IFN-γ indicating a balanced response. This is the first report, where CHIK-VLPs has been expressed by Pichia pastoris and evaluated for neutralizing activity against CHIKV. These promising results indicate the utility of CHIK-VLPs as a promising vaccine candidate against emerging CHIKV.
Author Summary Chikungunya virus (CHIKV) has emerged in many parts of tropics in last decade. The absence of an approved vaccine or antiviral drug for CHIKV makes it one of the important public health challenges. Though attempt to develop a CHIKV vaccine was initiated in 1980s, however it has not succeeded so far. The Virus like particles (VLPs) are now explored as promising vaccine candidate against many viruses viz. HBV, HPV etc. In this study, we report the production of CHIK-VLPs using novel yeast expression system (Pichia pastoris) and its evaluation as vaccine candidate. These CHIK-VLPs share morphological identity to native CHIKV. The results indicate that CHIK-VLPs induced both cell mediated as well as humoral response in a balanced manner, which fulfils its criteria as a potent immunogen. Further, antibodies generated against CHIK-VLPs demonstrated efficient in vitro and in vivo neutralization activity, as evaluated through plaque reduction in Vero cells and protection in CHIKV infected neonatal mice respectively using two different CHIKV strains, which makes it a promising vaccine candidate. The yeast expressed CHIK-VLPs has high potential for development of an effective vaccine candidate against CHIKV during epidemic situations.