The active variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have become of growing concern around the world due to their rapid transmission and ability to cause serious infection. New research by Ronit Rosenfeld of the Israel Institute for Biological Research confirms evidence that specific monoclonal antibodies can bind to the receptor binding domain of B.1.1.7 and B.1.351 variants and effectively neutralize them.
The study “The neutralizing power of therapeutic anti-SARS-CoV-2 human monoclonal antibodies is conserved against new viral variants” is available as a pre-print on the bioRxiv* server, while the article is subject to peer review.
The research team previously reported that certain monoclonal antibodies specific for receptor binding and N-terminal domain such as MD65 successfully neutralized SARS-CoV-2 in vitro and in vivo studies.
The current study builds on these results by measuring the binding capacity of four SARS-CoV-2 neutralizing monoclonal antibodies – MD65, MD62, MD29 and BL6 – to four distinct epitopes of the spike receptor binding domains. The receptor binding domains contained six mutations commonly associated with variants of concern, including N501Y, S477N, P.1, and E484K.
They also evaluated the neutralizing power of two monoclonal antibodies specific for the N-terminal domain of B.1.1.7 and of the B.1351 variant. Biolayer interferometry analysis was used to assess binding ability.
Binding profile among monoclonal antibodies
Researchers found about 5-22% of the binding lost due to five or six substitutions in the SARS-CoV-2 receptor binding domain.
A significant reduction in binding of 74% was observed with the K417N mutation by the monoclonal antibody MD62. There was also a 17% reduction in binding upon pairing with the MD65 antibody.
Of the 4 monoclonal antibodies specific for the receptor binding domain, MD65 was the most effective in both neutralizing and providing long-term immunity at low doses.
Comparison of epitope recognition with competitor MD65
The LY-CoV555 monoclonal antibody potentially competes with the MD65 monoclonal antibody by binding to hACE2. Although the researchers note that the two monoclonal antibodies do not have similar sequences, and their recognition patterns may differ despite targeting closely related epitopes.
To test this theory, the researchers assessed the binding of LY-CoV555 against the SARS-CoV-2 spike protein and compared with the binding profile of MD65.
In the presence of the monoclonal antibody MD65, the LY-CoV555 antibody could not bind to the rRBD protein, suggesting that the two antibodies share epitope targets.
Against SARS-CoV-2 mutations, LY-CoV555 has been recognized and successfully linked to N439K, Y453Y, S477N and N501Y.
However, the presence of the E484K substitution blocked the binding of LY-CoV555 to the epitopes. “This observation is consistent with recently reported studies suggesting that the E484K substitution is responsible for the abolition of the neutralization of natural variants of SARS-CoV-2, carriers of this mutation, by LY-CoV555 mAb”, wrote the researchers.
Binding capacity against several mutations in SARS-CoV-2
The researchers used recombinant mutated spike S1 subunit proteins that were a mixture of mutations found with the B.1.1.7 and B.1.351 variants. It contains the N501Y, K417N and E484K mutations.
The monoclonal antibodies MD65, MD29, BL6 and LY-CoV555 successfully bind to the recombinant spike protein B.1.1.7. However, the binding capacity of MD62 decreased by approximately 45%. This suggests that structural changes in the spike protein B.1.1.7 may have affected the binding of MD62.
The reduction in LY-CoV555 binding and an 18% decrease in BL6 binding in the recombinant spike protein B.1.351 was probably due to the E484K substitution. The MD62 monoclonal antibody was unable to recognize and bind to the epitope, and there was a 65% reduction in binding from MD65. The researchers suggest that the decrease in binding capacity is likely due to the presence of the K417N substitution.
Potential for immune leakage of the worrisome variants
The researchers evaluated the ability of six monoclonal antibodies and LY-CoV555 to neutralize the worrisome variants that have been associated with escaping the immune system. More precisely, they evaluated their towards the N-terminal domain for the living variants B.1.1.7 and B.1.351.
MD65, MD62, MD29, BL6 and LY-CoV555 were the most effective in neutralizing variant B.1.1.7. The researchers observed that MD65, MD29 and BL6 exhibited superior neutralization.
The B.1.351 variant showed a more robust immune escape potential than the B.1.1.7 variant. Similar to what was observed with the recombinant spike protein B.1.351, MD62 and LY-CoV555 showed complete loss of binding.
Fortunately, MD65, MD29, and BL6 effectively neutralized the B.1.351 variant.
* bioRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behaviors, or be treated as established information.