Engineering, production and characterization of Spike and Nucleocapsid structural proteins of SARS-CoV-2 in Nicotiana benthamiana as vaccine candidates against COVID-19

The COVID-19 pandemic, which is caused by SARS-CoV-2 has rapidly spread to more than 216 countries and has put global public health at high risk. The world urgently needs a cost-effective and safe SARS-CoV-2 coronavirus vaccine, antiviral and therapeutic drugs to control the COVID-19 pandemic. In this study, we engineered the Nucleocapsid (N) and Spike protein (S) variants (Receptor binding domain, RBD and S1 domain) of SARS-CoV-2 genes and produced in Nicotiana benthamiana plant. The purification yields were at least 20 mg of pure protein/kg of plant biomass for each target protein. The S protein variants of SARS-CoV-2 showed specific binding to angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 receptor. The purified plant produced N and S variants were recognized by N and S protein specific monoclonal and polyclonal antibodies demonstrating specific reactivity of mAb to plant produced N and S protein variants. In addition, IgG responses of plant produced N and S antigens elicited significantly high titers of antibody in mice. This is the first report demonstrating production of functional active S1 domain and Nucleocapsid protein of SARC-CoV-2 in plants. In addition, in this study, for the first time, we report the co-expression of RBD with N protein to produce a cocktail antigen of SARS-CoV-2, which elicited high-titer antibodies compared to RBD or N proteins. Thus, obtained data support that plant produced N and S antigens, developed in this study, are promising vaccine candidates against COVID-19.