When coronavirus disease 2019 (COVID-19) first arose, it spread across the world very rapidly, and many countries were forced to enact costly and restrictive measures in order to reduce the transmission rate. These included mandatory face masks, social distancing and even full lockdowns/stay-at-home orders.

Most countries were worried that high numbers of cases could overwhelm hospitals, and waves of preventable deaths could follow. Part of this stemmed from the lack of effective treatments against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the organism that causes Coronavirus Disease 2019 (COVID-19).

Study: A synthetic bispecific antibody capable of neutralizing SARS-CoV-2 Delta and Omicron. Image Credit: Take Photo/Shutterstock

Healthcare workers were forced to treat the symptoms with invasive mechanical ventilation or supplementary oxygen rather than treating the disease, and many of the initial monoclonal antibodies that researchers investigated were found to be largely ineffective. While vaccines have reduced the need for such treatments, both the Omicron and Delta variants have shown the ability to breakthrough vaccine protection. Researchers from Twist Bioscience have created a synthetic antibody able to bind and neutralize both variants.

The researcher’s study can be found on the bioRxiv* preprint server.

The Study

The researchers conducted surface plasmon resonance experiments using commercially sourced SARS-CoV-2 protein reagents. Flow binding assays were conducted using EBY100 cells stained with anti-FLAG, and viral cultures were created using TMPRSS2-VeroE6 cells. Virus neutralization assays were performed on serial dilutions , fixed with formaldehyde and stained with crystal violet. Analyses were done using GraphPad Prism.

The researchers constructed RBT-0813, the synthetic antibody capable of binding and neutralizing both Delta and Omicron variants, from lead VHH antibodies that were discovered in biopanning (an affinity selection technique that selects for proteins that bind to a specific target) campaigns against the ancestral (TB202-03) and Beta (TB339-031) spike proteins. They combined leads TB202-03 and TB339-031 into one bispecific construct, and performed screening using surface plasmon resonance (SPR) to reveal picomolar apparent binding affinities between RBT-0813 and the stable spike protein trimers (i.e. prefusion) of many different variants, including Alpha, Beta, Delta, Gamma, Kappa and the Omicron variants. SPR traces that were obtained with TB202-03 and TB339-031 revealed which contributed to the RBT-0813 binding to each spike protein trimer. TB202-03 bound to Alpha, Beta, Gamma and Kappa with the same affinity as the ancestral spike protein trimer but showed reduced affinities for both the Delta and Kappa variants. TB339-031 bound every variant with low affinities except for the Omicron variant. SPR experiments using variant monomers of the S1 subunit showed the same patterns. Most previous data agrees, showing reduced activity of TB202-03 against spike proteins that carry L452R (Delta and Epsilon).

Most monoclonal antibodies that have been developed or are being developed to help fight against SARS-CoV-2 fail to neutralize Omicron, even those that are proven effective against Delta. Monoclonal antibody cocktails are shown to be little better. To examine the neutralization potential of RBT-083, the scientists used authentic viruses isolated from nasopharyngeal specimens that were taken from patients suffering from the disease. These viruses were used in plaque reduction neutralization assays in order to explore if RBT-083 can successfully neutralize the wild-type disease, Omicron and Delta variants. It was found to successfully neutralize all three at half maximal effective concentrations of 521.1ng/mL for Delta and 713.6ng/mL for Omicron.

As expected, RBT-0813 neutralises both variants through the TB339-031 and TB202-03 VHH antibodies. The values obtained are very similar to the values seen using sotrovimab, one of the only monoclonal antibodies that has been shown to be effective against both variants, although studies clash on its effectiveness against Omicron. RBT-0813 was shown to neutralize wild-type SARS-CoV-2 at a half maximal effective concentration of 104.4ng/mL, much more effectively than against either Delta or Omicron, as both of the constituent parts can successfully bind to the spike protein.


The authors highlight that there are very few monoclonal antibodies that can successfully target both variants, and point out that despite the recent media domination of the Omicron variant, Delta remains a significant threat, and also appears to cause more severe disease. While the mechanism by which RBT-0813 neutralizes Omicron is not yet known, they suggest it is likely due to the TB202-02 arm, which binds at a different site compared to most other monoclonal antibodies. This could explain why it retains neutralization ability against the new variant.

This new antibody could be a powerful new tool against SARS-CoV-2, and as countries begin to re-enact the restrictive policies required to prevent the spread of the disease, it comes at a very welcome time.

Important notice:

bioRxiv publishes preprint papers that have not yet undergone peer review. The information contained within should not be taken as fact, or used to guide clinical or research practices.


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