Abstract
The COVID-19 pandemic has put global public health at high risk, rapidly spreading around the world. Although several COVID-19 vaccines are available for mass immunization, the world still urgently needs highly effective, reliable, cost-effective, and safe SARS-CoV-2 coronavirus vaccines, as well as antiviral and therapeutic drugs, to control the COVID-19 pandemic given the emerging variant strains of the virus. Recently, we successfully produced receptor-binding domain (RBD) variants in the Nicotiana benthamiana plant as promising vaccine candidates against COVID-19 and demonstrated that mice immunized with these antigens elicited a high titer of RBD-specific antibodies with potent neutralizing activity against SARS-CoV-2. In this study, we engineered the nucleocapsid (N) protein and co-expressed it with RBD of SARS-CoV-2 in Nicotiana benthamiana plant to produce an antigen cocktail. The purification yields were about 22 or 24 mg of pure protein/kg of plant biomass for N or N+RBD antigens, respectively. The purified plant produced N protein was recognized by N protein-specific monoclonal and polyclonal antibodies demonstrating specific reactivity of mAb to plant-produced N protein. 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 with potent neutralizing activity against SARS-CoV-2. Thus, obtained data support that a plant-produced antigen cocktail, developed in this study, is a promising vaccine candidate against COVID-19.
Highlights
The global public health risk associated with the novel and highly pathogenic coronavirus, currently designated as SARS-CoV-2, continues to grow
On SDS-PAGE and Western blotting, the plant-produced N protein molecule appeared as a doublet protein with an MM
Both molecular forms of plant-produced N proteins were recognized by anti-FLAG antibody (Figure 1B) and by N protein-specific mAb (Figure 1C), demonstrating specific reactivity of mAb to the two forms; it confirmed that epitopes for mAb are still present in the ~24 kDa fragment
Summary
The global public health risk associated with the novel and highly pathogenic coronavirus, currently designated as SARS-CoV-2, continues to grow. The world urgently needs more effective COVID-19 vaccines with a stable immune response and long-term immunity against possible emerging mutated variants of SARS-CoV-2 viruses. Since the S protein of SARS-CoV, MERS-CoV, and SARS-CoV-2 contains neutralizing epitopes, it has been shown to be a leading candidate for vaccine developments. In this regard, a number of studies demonstrated that the S protein induced potent humoral and cellular immune responses in tested animal models [1,2,3,4,5].
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