Production of a Highly Immunogenic Antigen from SARS-CoV-2 by Covalent Coupling of the Receptor Binding Domain of Spike Protein to a Multimeric Carrier

ARGENTINIAN ANTICOVID CONSORTIUM; CECILIA D ALESSIO; DIEGO G. NOSEDA; JAVIER SANTOS; LUCAS RUBERTO; ALEJANDRO NADRA

BioRxiv

Cold Spring Harbor Laboratory

Año: 2021

2692-8205

Since the discovery of SARS-CoV-2, several antigens have been proposed to be part ofCOVID-19 vaccines. The receptor binding domain (RBD) of Spike protein is one of the promisingcandidates to develop effective vaccines since it can induce potent neutralizing antibodies. Wepreviously reported the production of RBD in Pichia pastoris and showed it is structurallyidentical to the protein produced in mammalian HEK-293T cells. In this work we designed anRBD multimer construct with the purpose of increasing RBD immunogenicity. We producedmultimeric particles by a transpeptidation reaction between the RBD expressed in P. pastoris andLumazine Synthase from Brucella abortus (BLS), which is a highly immunogenic and verystable decameric protein of 170 kDa. We vaccinated mice with two doses 30 days apart, and thenwe measured humoral immune response. When the number of RBD copies coupled to BLS washigh (6-7 RBD molecules per BLS decamer, in average), the immune response was significantlybetter than that elicited by RBD alone or even by RBD-BLS comprising low number of RBDcopies (1-2 RBD molecules per BLS decamer). Remarkably, the construct with high number ofRBD copies induced high IgG titers with high neutralizing capacity. Furthermore, a superiorimmune response was observed when Al(OH)3 adjuvant was added to this formulation,exhibiting a higher titer of neutralizing antibodies. Altogether our results suggest that RBDcovalent coupled to BLS forming a multimer-particle shows an advantageous architecture to theantigen-presentation to the immune system which enhances immune responses. This new antigenshould be considered a potent candidate for a protein-based vaccine.