Monoclonal antibodies and HEK293

I was recently asked (informally) to look into the two monoclonal antibody options on the market and any connection with HEK293 (sometimes known as 293T and 293F, among other names), which is an aborted fetal cell strain from a kidney cell from the 1970s. 

I am by no means an expert on this, but I spent some time reading and wanted to pass along so others do not reinvent the wheel. Any corrections appreciated. I also understand that not all referenced articles mean a direct connection to HEK. However, I tried hard to identify articles that were critical to the studying in vitro action of the antibodies by these two companies themselves and used to support preclinical evidence of effectiveness. 

There are two currently available monoclonal antibody options in the US: Regen-CoV by Regeneron and Sotrovimab by GSK-Vir. 

Regeneron

Regeneron isolated something like 30 antibodies to Sars-CoV-2, and then worked on identifying the most effective at the in-vitro cellular level. They decided to pair two antibodies together rather than just use one type of monoclonal antibody. Therefore, Regen-Cov has two antibodies: casirivimab (REGN10933) and imdevimab (REGN10987). These do have connections in development with HEK293 in preclinical (which is cellular or in-vitro) studies. HEK was used to help them explore the action of these antibodies.

Regeneron's EUA approval fact sheet does not describe HEK directly, but they do prominently link the FDA  approval to both a Cell article and Science article, below. 

1. The Cell article looks at the two antibody responses, especially out of concern for variants and antibody resistance. They pair two antibodies together trying to reduce the potential to create resistant variants by natural selection. In their methods, it appears they created a SARS-Cov-2 pseudovirus (using VSV and HEK293 to create a VSV-SARS-CoV-2-Spike), and subsequently tested this with antibodies on Vero. This article also cites several key studies on this antibody cocktail, including Hansen et al, which uses HEK293 in one area of research, although not the predominant area of research. Baum et al also uses HEK293 but you have to download the supplementary materials and methods (linked at the bottom of the article) to see it. These are the two most cited sources that back up the in-vitro studies on Regen-CoV. Both Hansen and Baum appear to be employed by Regeneneron (listed in their footnotes). 

2. The Science article by Baum et al does not directly cite HEK293 but it is there in a number of their key supporting references that they systematically address and summarize in the results, including references 6, 9, 11. I didn't go through all the references, but I suspect that more of the 19 referenced articles do use HEK293.  

Another Regeneron press release from June highlights their Science article by Hansen and Baum (et al) where they were trying to study various potent antibody options (including REGN10933 and REGN10987) in humanized mice and convalescent humans. There is also an inclusion of HEK293 in the methods. 

Sotrovimab: 

For clinical trials, Sotrovimab was named VIR-7831 by GlaxoSmithKline-Vir Biotechnology (a joint company effort). Here is some background: 

• Sotrovimab: This monoclonal antibody was originally identified in 2003 from a SARS-CoV survivor. It targets an epitope in the RBD of the spike protein that is conserved between SARS-CoV and SARS-CoV-2.
• Sotrovimab was initially named S309 (so it’s basically a repurposed antibody from SARS itself, since SARS is very similar to SARS-COV-2). The original research of isolating and understanding this antibody did involve HEK and this research is clearly referenced in the current research on Sotrovimab (reference 21 on the biorxiv article):
• https://www.nature.com/articles/s41586-020-2349-y 

Here is the list of trials and information from GSK. While several more Phase 2 and 3 trials are coming, COMET-ICE Trial is the current Clinical Phase 3 Trial (in vivo) supporting Sotrovimab by GlaxoKline and appears to be what was used to support FDA EUA approval. It is still preprint. https://www.medrxiv.org/content/10.1101/2021.05.27.21257096v1  

This preprint cites other articles describing the preclinical testing (in vitro) of VIR-7831 by the Vir Biotech company, most notably the preprint article below. This article is clearly testing Sotrovimab with HEK, which is called Lenti-X 293T cells (or Takara). 

https://www.biorxiv.org/content/10.1101/2021.03.09.434607v6.full

The results section on the Biorvix article also relies heavily on reference 21 and reference 30 which uses 293: 

• 21: https://www.nature.com/articles/s41586-020-2349-y  (with S309, the original sotrovimab)
• 30: https://www.nature.com/articles/s41591-021-01294-w

I didn't check all the other references because it was already clear that HEK was used to understand the structure and function of this antibody in particular and its original action with SARS. Other lines were used too (hamster, vero) for antibody testing at the in-vitro level. As far as I can tell, these two preprint articles are what is used for FDA EUA approval, since this is the primary in-vitro research.

So, in my assessment, both options on the market were developed using testing with HEK in order to identify and study the best antibodies, explore in-vitro actions when infected with virus or pseudovirus, and identify if these antibodies are effective at reducing infection at the cellular level, and also to review the risk of variants and resistance. Both options also used other cell lines, like hamster and vero. 

Feel free to cross-check and let me know about corrections!