Video report by ITV News Science Editor Tom Clarke
Researchers are testing two existing drugs in a bid to stop what seems to be the body's immune system overreacting to the infection.
George Gilbert, who has spent 11 days in hospital, is starting to feel better but coronavirus almost killed him.
He described having Covid-19 as a "horrible experience".
He told ITV News: "To have been so close, you appreciate life because you never know when it's going to end and I thought that would be my end."
Despite what he has been through, Mr Gilbert was one of the first patients to volunteer for a clinical trial called Tactic-R led by Dr Frances Hall.
The trial is selecting Covid-19 patients who are at risk of ending up at intensive care, where many suffer multiple suffer organ failure - not caused by the virus but by our body's response to it.
Dr Frances Hall told Science Editor Tom Clarke: "When people get sick, they seem to be getting sick not because of the direct effects of the virus replicating in their cells but because of their own immune response."
"So we need an immune response to attack the virus, so that's a good thing, but some people have an immune response that goes over-the-top and starts attacking their own cells and causing a lot of extra damage."
Some patients, who are participating in the trial, are getting their drugs in pill form while Mr Gilbert, like others, are on an anti-body medicine which is administered through a drip.
Researchers are able to see whether it's working at a lab at Cambridge University through testing blood samples.
What are the two drugs?
The first drug called Baricitinib is used to treat arthritis which calms part of the body's immune response by blocking crucial messenger chemicals called Cytokines.
The other drug, Ravulizumab, is commonly used to treat a rare blood disorder which targets proteins called Complement which often go rogue and can destroy healthy Covid patients.
What makes this trial different from others?
Researchers are using new techniques to analyse the blood down to the level of individual immune cells to see how they vary between patients receiving the different drugs.
Coronavirus: Everything you need to know: