Abstract
BACKGROUND: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variants have risen to dominance, which contains far more mutations in the spike protein in comparison to previously reported variants, compromising the efficacy of most existing vaccines or therapeutic monoclonal antibodies. Nanobody screened from high-throughput naïve libraries is a potential candidate for developing preventive and therapeutic antibodies. METHODS: Four nanobodies specific to the SARS-CoV-2 wild-type receptor-binding domain (RBD) were screened from a naïve phage display library. Their affinity and neutralizing activity were evaluated by surface plasmon resonance assays, surrogate virus neutralization tests, and pseudovirus neutralization assays. Preliminary identification of the binding epitopes of nanobodies by peptide-based ELISA and competition assay. Then four multivalent nanobodies were engineered by attaching the monovalent nanobodies to an antibody-binding nanoplatform constructed based on the lumazine synthase protein cage nanoparticles isolated from the Aquifex aeolicus (AaLS). Finally, the differences in potency between the monovalent and multivalent nanobodies were compared using the same methods. RESULTS: Three of the four specific nanobodies could maintain substantial inhibitory activity against the Omicron (B.1.1.529), of them, B-B2 had the best neutralizing activity against the Omicron (B.1.1.529) pseudovirus (IC(50) = 1.658 μg/mL). The antiviral ability of multivalent nanobody LS-B-B2 was improved in the Omicron (B.1.1.529) pseudovirus assays (IC(50) = 0.653 μg/mL). The results of peptide-based ELISA indicated that LS-B-B2 might react with the linear epitopes in the SARS-CoV-2 RBD conserved regions, which would clarify the mechanisms for the maintenance of potent neutralization of Omicron (B.1.1.529) preliminary. CONCLUSION: Our study indicated that the AaLS could be used as an antibody-binding nanoplatform to present nanobodies on its surface and improve the potency of nanobodies. The multivalent nanobody LS-B-B2 may serve as a potential agent for the neutralization of SARS-CoV-2 variants.