Recombinant subunits of SARS-CoV-2 spike protein as vaccine candidates to elicit neutralizing antibodies

The spike protein has been reported as one of the most critical targets for vaccine design strategies against the SARS-COV-2 infection. Hence, we have designed, produced, and evaluated the potential use of recombinant proteins derived from spike protein as vaccine candidates capable of neutralizing SARS-COV-2 virus. In silico tools were used to design spike-based subunit recombinant proteins (P1, P2, and P3). These proteins were checked for their ability to be identified by the anti-SARS-COV-2 antibodies by exposing them to Covid-19 serum samples. The proteins were then injected into mice and rabbits and the antibody titers were measured for 170 days. The virus neutralization test (VNT) was performed to analyze the obtained antibodies for their neutralization efficiency. The antibodies that existed in the serum of COVID-19 patients have identified the designed proteins. The anti-spike antibody titer was increased in the animals injected with recombinant proteins. The VNT results revealed that the produced antibodies could neutralize the cultured live virus. The long-lasting antibody titers (130 and 170 days for rabbit and mouse groups) indicated the elicitation of a strong immune response by the recombinant proteins. Subunit vaccines could also be considered as robust tools for effective vaccination against COVID-19. Using a combination of in silico, in vitro, and in vivo experiments, it was shown that the injection of spike-based recombinant proteins could stimulate long-lasting and neutralizing antibody responses. Further evaluation of the recombinant proteins examined in our studies in higher primates and human would elucidate their true potentials.