Monoclonal antibodies are laboratory-made molecules that can mimic the human immune system’s antibodies. They can be used to target cancer cells, or other undesirable cells such as those that have been infected with viruses. They have been used successfully to treat a wide ranger of diseases, from cancer to rheumatoid arthritis.

They work by supplementing a person’s own immune system with antibodies targeted against a specific invader. In the case of COVID-19, that would be antibodies targeted against specific regions of the coronavirus.

From the earliest days on the pandemic, researchers have focused on monoclonal antibodies as a potential treatment. There are dozens of groups working on making versions of monoclonal antibodies. The first to begin studies in humans is one developed by the Canadian biotech company AbCellera and the pharmaceutical company Eli Lilly.

A second drug based on monoclonal antibodies begins trials in humans today. The drug is actually a cocktail of two monoclonal antibodies. It’s made by the pharmaceutical company Regeneron.