Enhanced immunogenicity of COVID-19 RBD fused to mutant scorpion's phospholipase D for vaccine development

The management of the global COVID-19 pandemic relies, in part, on the rapid development of preventive vaccines at an unparalleled speed. The infection caused by the coronavirus is facilitated by the spike glycoprotein trimmer located on the surface of the virion, specifically through its receptor binding domain (RBD). The response of antibodies to this domain is a key indicator of the immunization's effectiveness and is well correlated with the neutralization of the viral agent. The failure of COVID-19 vaccines to induce complete neutralization provides an opportunity to find an alternative way. In this study, we show that recombinant RBD, Wuhan-specific; fused to mPLD1 protein, a highly effective immunogen from Hemiscorpius lepturus scorpion's venom, induce a potent immune response in mouse model. Conventional virus neutralization test (cVNT) with serum of mice immunized with mPLD1-RBD fusion protein, protects the Vero cells against the Omicron and Wuhan variants at the minimum of 1/64 and 1/32 dilution, respectively. The data strongly suggests that the subunit recombinant fusion protein could be a promising candidate for vaccine development against COVID-19. Our research showed that fusion of mPLD1, a highly effective immunogen, with RBD significantly boosts the immune response and substantially amplifies RBD antigenic properties in lab animals, setting the stage for their assessment in a comprehensive preclinical study.