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How treating serious COVID-19 patients with antibodies from recovered donors could work

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Federal Health Minister announced an Australian biotechnology company is developing a potential new treatment for coronavirus, using plasma donated by people who have recovered from the disease.

This plasma is thought to contain high levels of protective antibodies that are able to fight off the virus.

CSL Behring Australian hopes to purify these antibodies and concentrate them to make a hyperimmune globulin product to give to patients with severe cases of the disease, who have not yet been ventilated.

While such antibody therapies might sound strange, they’ve been used in the past to treat diseases like Lassa fever, Ebola and swine flu.

We asked immunologist Larisa Labzin of the University of Queensland, to explain how such a treatment might work.

How treating serious COVID-19 patients with antibodies from recovered donors could work
How treating serious COVID-19 patients with antibodies from recovered donors could work

How antibodies help your immune system fight a virus

Viruses are unable to replicate without a host cell, Dr Labzin said, so getting inside our cells is their main purpose.

One of the ways our immune system fights them off is by trying to block their entry into the host cells.

“That’s what antibodies are really, really good at, so they neutralise the virus,” she said.

“It’s like they handcuff the virus, and stop them being able to unlock the door to get in the cell.”

These antibodies are produced by a type of our white blood cells known as a B cell.

These y-shaped antibodies can also act like flags on the virus and signal to other immune cells like macrophages — which are a bit like the garbage collectors of the cell — to get rid of the virus.

What you’re looking for in a treatment

Scientists are looking for signs of antibodies that neutralise the virus, which is the best indicator that someone may be immune.

“And that’s how [CSL] will expect [their treatment] to primarily work in being protective,” she said.

This response is also the main way people measure whether a vaccine works.

But it doesn’t work for all viruses.

With HIV for example, people make a lot of antibodies against it but they still get sick, so these antibodies aren’t effectively neutralising the virus.

With COVID-19, we still don’t have the full picture.

“We know that antibodies against COVID can neutralise the virus, but we don’t know yet if that means having neutralising antibodies indicates that you’re going to be immune,” Dr Labzin said.

How CSL’s approach is different

Last month, Canadian newspaper The Globe and Mail reported on the largest clinical trial in the world to date using plasma from people who have recovered from COVID-19.

Known as convalescent plasma, the technique takes whole plasma from a recovered person, and infuses it into another patient with the disease, in the hope it will reduce the duration or severity of their symptoms.

Trials with convalescent plasma will also be taking place in Australia.

But whole plasma can contain components that may be problematic, Dr Labzin said.

“We’re going to have a whole host of other factors in our plasma apart from just antibodies, and they do lots of things,” Dr Labzin said.

Of particular relevance to COVID patients are the coagulation factors in your plasma that help your blood clot, but can cause problems if that coagulation happens where it shouldn’t, for example blood clots that are causing minor strokes or potentially increasing the risk of heart attacks.

“So there’s a danger, in terms of just transferring over total patient plasma or serum, that you would accidentally be transferring over some of those components as well,” Dr Labzin said.

Instead of using whole plasma CSL plan to specifically extract antibodies from the plasma.

“With the hyperimmune [globulin product] you can take from one donor, and there could be far more patients that it can be administered to,” said CSL’s Chief Medical Officer Charmaine Gittleson in a briefing.

Dr Gittleson said it would also be easier to make a more consistent and scalable treatment with their approach, compared to convalescent plasma.

Another advantage of CSL’s approach Dr Labzin said, is that they can determine the actual dose of antibodies they’re giving to patients, and test to find out how many you need for the therapy to be protective, and also determine which antibodies are more protective than others.

“So as well as being an awesome patient therapy, it’s going to be a really useful research tool too, to develop new therapies and to let the vaccinologists know kind of what they should be aiming for in terms of a protective antibody response in a vaccine,” she said.

Lifeblood will begin collecting plasma from recovered donors who’ve had a laboratory-confirmed case of COVID-19 and have been symptom-free for a minimum of 28 days, from next Monday using their current processes and system.

What we still don’t know

“We still don’t really understand why some people are getting sick and getting really sick, while other people seem to be able to control the infection really well,” Dr Labzin said.

“We would guess it is that maybe your immune system is not mounting enough of an immune response, or maybe it’s trying to mount it too late, so the virus is already out of control.”

Scientists also want to know what the immune responses of these two groups look like.

“We don’t yet understand what about the immune response determines if someone’s going to recover or if someone’s going to get really sick, and that’s really important to understand,” Dr Labzin said.

The hope with the development of an antibody treatment like this one, is that it will be able to supplement a weak immune response.

CSL is hoping clinical trials for the treatment to determine its safety and efficacy, will begin later this year.

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