In a recent study published in ImmunologyAnd The researchers identified a human monoclonal antibody (mAb), 87G7, with in the laboratory Neutralizing activity against several variants of concern for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), including Alpha, Beta, Gamma, Delta and Omicron.
The evolution of SARS-CoV-2 at the antigenic level continues to pose challenges to the development of clinical mAbs to prevent and treat coronavirus disease 2019 (COVID-19).
In a clinical setting, the neutralization potential of an anti-SARS-CoV-2 mAb remains the first selection criteria. However, the next important consideration is the possibility of mAb to neutralize SARS-CoV-2 variants by targeting highly conserved sites on the spike (S) protein to mitigate the risks of immune evasion by future emerging variants.
In this study, researchers explored the antibody repertoire of H2L2 transgenic mice after vaccination with the SARS-CoV-2 S ectodomain. These mice carried the chimeric immunoglobulin (IgG) genes with the human variable heavy and light chains and the murine constant region.
The team examined the neutralizing activity of the hybridoma supernatant against SARS-CoV-2 S pseudovirus carrying the S E484K mutation. It is noteworthy that the mutation in this residue differs in VOCs with the potential for immune escape.
The team evaluated the antibody’s interference with S-mediated receptor binding activity to understand the mechanism of neutralizing antibodies against SARS-CoV-2 and its VOCs. In addition, they used enzyme-linked immunosorbent assay (ELISA), bilayer interferometry (BLI), cryo-electron microscopy (cryo-EM), and site-directed mutagenesis for their experiments.
The researchers used mice and Syrian hamsters (small animals) to assess the protective efficacy mediated by antibodies against SARS-CoV-2 and VOC challenges. After euthanasia, the team identified the infectious virus in lung and nasal tissues in cultured cells. In addition, they used immunohistochemistry to study viral antigens and evaluate pathology in lung tissue and nasal conchae using histology.
mAb, 87G7, Wuhan-Hu-1 S-mediated cell entry neutralized at half maximum inhibitory concentration (IC50) 5.4 ng/ml. In addition, he blocked several pseudoviruses harboring S proteins of the Beta, Alpha, Delta and Omicron BA.1 sub-variable with IC50 Values range from 1.4 to 5.1 ng/ml.
On the contrary, REGN10987 lost the neutralizing potency against Omicron, while REGN10933 showed a 20-fold and 350-fold loss of IC50 against beta and omicron respectively. In a live virus neutralization assay, REGN10933 completely lost its neutralizing activity against the Omicron BA.1 sub-substitute. By contrast, 87G7 neutralized alpha, beta, gamma, delta, omicron and BA.1 and BA.2 VOC subvariants with IC50 Values range from 3.1 to 12.5 ng/mL. In addition, 87G7 neutralized the Lambda and Mu variants using IC50 1.2 and 4.8 ng/ml, respectively.
ELISA showed that 87G7 was bound to the S receptor-binding domain (RBD), and BLI data revealed that 87G7 displayed a bivalent binding to the S trimer. It showed strong affinity against the monomeric S1 domain and the three-dimensional S ectodomain. Similar to REGN10933, 87G7 inhibited the binding of the recombinant S trimer to angiotensin converting enzyme 2 (ACE2), confirming its neutralization potential.
Three-dimensional (3D) data classification revealed that the outer band S contained all three RBDs in the open conformation with the 87G7 Fab fragment attached to the convex end of the receptor-binding edge (RBR). Furthermore, the 87G7 loop interferes with the ACE2 binding site, preventing receptor interaction through the steric hindrance.
The results of site mutations showed that the F486A mutation prevented binding by REGN10933, whereas it did not alter the neutralizing potency of REGN10987. On the contrary, it severely reduced the binding of 87G7 and S, as observed by ELISA.
First, the researchers intraperitoneally injected K18-hACE2 transgenic mice with 87G7 (10 mg/kg body weight) or control IgG1 isotype. Next, challenge these animals to 105 PFU of SARS-CoV-2 strain D614G, Alpha, Beta, Gamma, or Delta VOCs, 16 hours later.
The 87G7 treated animals remained protected against weight loss during the SARS-CoV-2 challenge. Compared with the homozygous control-treated animals, they showed a decrease in lung antigen levels on day 5 after viral challenge. Furthermore, live virus in lung homogenates was reduced by one to three orders of magnitude compared to mice receiving the control antibody.
Intraperitoneal injection of 87G7 on the first day after nasal challenge with D614G reduced weight loss by up to 13% compared to 22% in the control group, lung antigen levels, and infectious SARS-CoV-2 titers in the lungs by two orders of magnitude relative to to IgG1 homozygous treated mice.
Overall, the study data highlighted the preventive and therapeutic efficacy of 87G7 against SARS-CoV-2 challenge and four VOCs in mice. In addition, prophylactic treatment with 87G7 significantly reduced antigen expression in the nasal cavity and lungs of Syrian hamsters.
The results of the current study could aid the development of sustainable mAb strategies against COVID-19 using combinations of large-scale neutralizing clinical mAbs that more robustly combat the diversity of SARS-CoV-2 antigens. Importantly, the study identified an 87G7 mAb of potential value for treating individuals unable to make autoantibodies in response to vaccination or infection.