Heterologous expression of Chimeric hepatitis B core virus like particles harboring SARS-CoV2 epitope and evaluation of its immunization potential in mice

Abstract

Background: Due to the potential of virus-like particle (VLP)-based vaccines for effective elicitation of immune response and controlling disease, this investigation was projected to explore the feasibility of HBc-VLP-based vaccine regarding SARS-CoV-2 infection, which has not yet been studied. We used the HBc-VLP platform for expressing the SARS-CoV-2 spike antigenic epitope. Results: Insertion of the selected epitope was done into the major immunodominant region (MIR) of truncated (149 residues) hepatitis B core capsid protein. The chimeric protein was constructed in PET28a+ and expressed through the bacterial E. coli BL21 expression system. However, the protein was expressed in inclusion body forms and they were extracted following urea denaturation from the insoluble phase. Following the extraction, the vaccine protein was purified using Ni2+ iminodiacetic acid (IDA) affinity chromatography. SDS-PAGE and western blotting were used to confirm the protein expression. Regarding the denaturation step, the unavoidable refolding process was carried out, so that the chimeric VLP reassembled in native conformation. Based on the transmission electron microscopy (TEM) microscopic analysis, the HBC VLP was successfully assembled. Confirming the assembled chimeric VLP, we explored the immunogenic effectivity of the vaccine through mice immunization with two-dose vaccination with and without adjuvant. The utilization of adjuvant was suggested to assess the effect of adjuvant on improving the immune elicitation of chimeric VLP-based vaccine. Immunization analysis based on anti-spike specific IgG antibody showed a significant increase in antibody production in harvested serums from immunized mice with HBc-VLP harboring antigenic epitope compared to HBc-VLP and PBS-injected mice. Conclusions: The results approved the successful production and the effectiveness of the vaccine in terms of humoral IGG antibody production. Therefore, this platform can be considered a promising strategy for developing safe and reasonable vaccines; however, more complementary immunological evaluations are needed.