Receptor binding domain proteins of SARS‐CoV‐2 variants produced in Nicotiana benthamiana elicit neutralizing antibodies against variants of concern

Abstract

The constantly emerging severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) variants of concerns (VOCs) with mutations in the receptor-binding domain (RBD) spread rapidly and has become a severe public health problem worldwide.Effective vaccines and optimized booster vaccination strategies are thus highly required. Here, the gene encoding six different RBD (Alpha, Beta, Gamma, Kappa, Delta, and Epsilon variants) along with the Fc fragment of human IgG1 (RBD-Fc) was cloned into plant expression vector and produced in Nicotiana benthamiana by transient expression. Further, the immunogenicity of plant-produced variant RBD-Fc fusion proteins were tested in cynomolgus monkeys. Each group of cynomolgus monkeys was immunized three times intramuscularly with variant RBD-Fc vaccines at Day 0, 21, 42, and neutralizing antibody responses were evaluated against ancestral (Wuhan), Alpha, Beta, Gamma, and Delta variants. The results showed that three doses of the RBD-Fc vaccine significantly enhanced the immune response against all tested SARS-CoV-2 variants. In particular, the vaccines based on Delta and Epsilon mutant RBD elicit broadly neutralizing antibodies against ancestral (Wuhan), Alpha, and Delta SARS-CoV-2 variants whereas Beta and Gamma RBD-Fc vaccines elicit neutralizing antibodies against their respective SARS-CoV-2 strains.The Delta and Epsilon RBD-Fc based vaccines displayed cross-reactive immunogenicity and might be applied as a booster vaccine to induce broadly neutralizing antibodies. These proof-of-concept results will be helpful for the development of plant-derived RBD-Fc-based vaccines against SARS-CoV-2 and its variants.

A Gamma-adapted recombinant subunit vaccine induces broadly neutralizing antibodies against SARS-CoV-2 variants and protects mice from infection

“…Interestingly, the Beta variant originated in South Africa, while the Gamma variant originated in Brazil a few months later. Until now, there are few studies using a Gamma variant adapted vaccine [17][18][19] .…”

A randomized, placebo-controlled trial of a nasal spray solution containing broadly potent neutralizing antibodies against SARS-CoV-2 variants in healthy volunteers

“…Pseudovirus microneutralization assays were performed as previously described 13,14 to assess the neutralization potency of COVITRAP™ against various SARS-CoV-2 pseudoviruses, i.e., Ancestral, Alpha, Delta, Omicron BA.1, Omicron BA.2, Omicron BA.4/5, and Omicron BA.2.75. The results revealed that COVITRAP™ potently neutralized all mentioned pseudoviruses with 50% pseudovirus neutralization titers (PVNT 50 ) ranging from 0.0035 to 3.1997 μg/ml (Table 1).…”

Preclinical evaluation of immunogenicity, efficacy and safety of a recombinant plant-based SARS-CoV-2 RBD vaccine formulated with 3M-052-Alum adjuvant

“…The neutralizing activity of sera isolated from SARS-CoV-2-immunized monkeys against pseudoviruses using the firefly luciferase reporter displaying full length spike protein of various SARS-CoV-2 variants including Alpha, Beta, Gamma, Delta and Omicron was determined in a spike-pseudovirus neutralization assay using methods as described previously [25] . This test was performed at the Virology and Cell Technology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Thailand.…”