COVID-19 is a respiratory viral disease caused by a new coronavirus called SARS-CoV-2. This disease has spread rapidly worldwide with a high rate of morbidity and mortality. The receptor-binding domain (RBD) of protein spike (S) mediates the attachment of the virus to the host’s cellular receptor. The RBD domain constitutes a very attractive target for subunit vaccine development due to its ability to induce a neutralizing antibody response against the virus. With the aim of boosting the immunogenicity of RBD, it was fused to the extracellular domain of CD154, an immune system modulator molecule. To obtain the chimeric protein, stable transduction of HEK-293 was carried out with recombinant lentivirus and polyclonal populations and cell clones were obtained. RBD-CD was purified from culture supernatant and further characterized by several techniques. RBD-CD immunogenicity evaluated in mice and non-human primates (NHP) indicated that recombinant protein was able to induce a specific and high IgG response after two doses. NHP sera also neutralize SARS-CoV-2 infection of Vero E6 cells. RBD-CD could improve the current vaccines against COVID-19, based in the enhancement of the host humoral and cellular response. Further experiments are necessary to confirm the utility of RBD-CD as a prophylactic vaccine and/or booster purpose.
Background
The COVID-19 pandemic caused by the SARS-CoV-2 coronavirus has currently affected millions of people around the world. To combat the rapid spread of COVID-19 there is an urgent need to implement technological platforms for the production of vaccines, drugs and diagnostic systems by the scientific community and pharmaceutical companies. The SARS-CoV-2 virus enters the cells by the interaction between the receptor-binding domain (RBD) present in the viral surface spike protein and its human receptor ACE2. The RBD protein is therefore considered as the target for potential subunit-based vaccines.
Methods and results
We evaluate the use of
Nicotiana benthamiana
plants as the host to transiently-producing recombinant RBD (RBDr) protein. The identity of the plant-produced RBDr was confirmed by immune assays and mass spectrometry. Immunogenicity was confirmed through the specific antibodies generated in all of the immunized mice compared to the PBS treated group.
Conclusions
In conclusions, the immunogenicity of the RBDr produced in
N. benthamiana
was confirmed. These findings support the use of plants as an antigen expression system for the rapid development of vaccine candidates.
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