The coronavirus disease 2019 (COVID-19) pandemic has severely impacted the health and wellbeing of the global population. With case numbers still skyrocketing in many parts of the world, the scientific community has rushed rapidly to develop treatments and vaccines to help mitigate disease severity and curtail viral transmission.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – the causative pathogen of COVID-19 – has mirrored other recent viral outbreaks such as the H1N1 Influenza (2009), Ebola Virus (2014) and Zika Virus (2015), and the response to these viruses included lessons for public health to strategize an accelerated response for COVID-19. While there have been major developments in the realm of vaccines, treatments for the disease itself have proven to be quite difficult. This has given rise to a major research concentration into novel therapeutics.
New research undertaken by researchers in the USA describes two parallel but distinct in vivo approaches for the accelerated discovery of antibodies targeting SARS-CoV-2 spike protein.
A pre-print version of the paper is available on the bioRxiv* server, while the article undergoes peer review.
Antibodies for therapeutics
Antibodies can aid in next-generation vaccine designs through their targeting of viral epitopes. The most valuable and useful antiviral antibodies exhibit cross-reactivity to related viruses and are unaffected by variants.
These antibodies can have properties such as basic receptor-blocking activity and can either work alone or in conjunction with oligoclonal mixtures of non-competing antibodies. When aggregated, high-resolution screening strategies may be required in order to be able to identify which type of antibodies work the best.
The study undertaken by the researchers highlights various techniques and antibody discovery workflows that aid the discovery and characterization of antibody panels targeting the SARS-CoV-2 spike protein.
The team used two separate mouse strains that were immunized with the spike protein’s S1 subunit, containing the receptor-binding domain (RBD), including a humanized strain and an engineered mouse strain. The humanized strain was used to facilitate the discovery of fully human antibodies, while the engineered mouse strain was designed to create greater epitopic diversity and increase the overall immune response.
The researchers then used two upstream discovery methods, such as a hybridoma discovery platform for high-content screening and efficiency, as well as a high-throughput single B-cell screening platform. The final characterization and analysis were performed with Carterra LSATM.
The single B-cell discovery workflow can interact with antibodies secreted by the plasma cells for binding specificity and angiotensin-converting enzyme 2 (ACE2) receptor blocking activity.
To infect a cell, SARS-CoV-2 would have to interact with the cell surface protein ACE2 through its spike protein. Within the spike protein, the RBD interfaces with ACE2, enabling the virus to bind to the host cell surface and instigate membrane fusion. Because this is the interaction that facilitates SARS-CoV-2 infiltration of host cells, it has gained most attention from scientists for novel therapeutic research.
Are antibodies a viable option?
Using this novel screening method, the study identified a range of antibody candidates spanning multiple epitopes with high affinity as well as both receptor-blocking and non-blocking activity. The humanized strain indicated non-blocking activity, which may be due to the epitope immunodominance seen as a common occurrence in COVID-19. However, with extended immunization, the antibodies within this strain did have high affinity for epitopes.
The traditional methods of in vivo antibody drug discovery can have disadvantages which can include the timeline associated with immunization as well as with humanization and downstream lead optimization. This can be overcome with novel technology that can accelerate the upstream drug discovery process, making in vivo antibody discovery a more viable method.
This is due to this approach’s ability to observe the responses in a more accelerated fashion for novel viral threats as well as for further research into therapeutics for COVID-19. Humanized mouse strains can be used synergistically with genetically engineered mice designed to increase epitopic diversity.
Utilizing this approach can provide lead and backup antibody drug candidates when novel therapies are being researched and can help determine the efficacy of new therapeutic candidates.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Mullen, T., Abdullah, R., Boucher, J., Brousseau, A., Dasuri, N., Ditto, N., Doucette, A., Emery, C., Gabriel, J., Greamo, B., Patil, K., Rothenberger, K., Stolte, J. and Souders, C., 2021. Accelerated Antibody Discovery Targeting the SARS-CoV-2 Spike Protein for COVID-19 Therapeutic Potential. doi: https://doi.org/10.1101/2021.05.31.446421, https://www.biorxiv.org/content/10.1101/2021.05.31.446421v1