Evaluating the immunogenicity of gold nanoparticles conjugated RBD with Freund's adjuvant as a potential vaccine against SARS-CoV-2

BACKGROUND: and Introduction: SARS-CoV-2 is currently considered as the most challenging issue in the field of health and medicine by causing a global pandemic. Vaccines are counted as a promising candidate to terminate this deadly pandemic. Various structural proteins in SARS-CoV-2 have recently drawn attention to be utilized as candidate vaccines to stimulate immune responses against COVID-19. MATERIALS AND METHODS: In current study, the RBD protein was cloned and expressed in E. coli host. Then, the expressed RBD protein was purified and its characterizations were evaluated through various methods. Gold nanoparticles, which were utilized as a carrier for candidate Nano-vaccine, were synthesized via oxidation-reduction reaction. While Gold NPs-conjugated RBD was injected into the second treatment group, in the first candidate vaccine, RBD was injected into the first treatment group solely. Complete and Incomplete Freud's Adjuvant were also utilized for both treatment groups to enhance the immune responses against RBD antigen. Immunizations were repeated 2 times in 14-day intervals to boost the immune system of BALB/c mice. The humoral and cell-mediated immune responses were examined through immune and cytokine assays. RESULTS: Our outcomes demonstrate that strong short-term humoral immunity (IgM) was induced in both the first and second treatment group, while long-term humoral responses (IgG) were only observed in the second treatment group. While stronger short- and long-term humoral (IgM and IgG, respectively) were observed in the second treatment group, particular cytokines production (TNF-ɑ and IFN-γ) as a marker of cell-mediated responses were significantly higher in the first treatment group. DISCUSSION AND CONCLUSION: Our study results show the high potentiality of RBD protein as an appropriate stimulating antigen in vaccine synthesis and testifies RBD-based candidate vaccines to control the COVID-19 pandemic. Our outcomes also recommend that Nano-vaccines can be more suitable candidates when stronger long-term immune responses matter.