Stimulation of immune response in mice using the plant-produced SARS-CoV-2 S1 subunit protein linked to the fc region

Abstract

Coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 made a devastating impact worldwide, and virus management is challenging owing to a lack of specific therapies or affordable vaccines, especially in low-and middle-income countries. Hence a low-cost and efficient vaccine is necessary. In the present study, the immunogenicity of the plant-produced S1 subunit protein of SARS-CoV-2 was investigated in order to utilize it as a subunit vaccine. The SARS-CoV-2 S1 subunit protein was fused with the Fc region of human immunoglobulin (IgG1) and expressed in tobacco plants in species of Nicotiana benthamiana plants by agroinfiltration. The SARS-CoV-2 S1-Fc protein was generated within 4 days of infiltration with 30 µg/gram of fresh-weight leaves. Afterward, plant-produced S1-Fc protein from the crude extract was purified using protein A chromatography. The S1-Fc fusion protein was observed in an expected band at 100-150 kDa under reducing conditions and 250 kDa under non-reducing conditions by analysis of SDS-PAGE gel and western blot. The S1-Fc fusion protein was formulated with alum as an adjuvant. The S1-Fc protein from plants induced a significant immune response in mice and an interferon-gamma (IFN-g) enzyme-linked immunospot test revealed that the S1-Fc protein vaccine enhanced antigen-specific T-lymphocyte responses. Hence the plant-derived SARS-CoV-2 S1-Fc may provide a candidate strategy for the development of a COVID-19 vaccine.