Canadian researchers are planning clinical trials for a potential treatment for COVID-19 which would use transfusions of blood plasma from people who have recovered from the disease.
Blood plasma from recovered patients — called “convalescent plasma,” is expected to be rich in virus-fighting immune molecules called antibodies, produced by the body in response to infection.
Dr. Dana Devine, the Chief Scientist with Canadian Blood Services told Quirks & Quarks host Bob McDonald that there is probably a key moment in the illness when this is likely to be most useful.
“We think it’s most likely to be effective is when you have a patient who is clearly sick with the virus but whose own immune system hasn’t had a chance to make antibodies yet.”
Fighting plagues with the blood of the recovered
The use of convalescent plasma in medicine dates back before the discovery of antibiotics. It was used to fight the Spanish Flu epidemic in 1918 and has been used sporadically since, perhaps most recently when the World Health Organization provided guidelines for its use in Ebola epidemics.
In the current pandemic, blood plasma has been used in a small number of critical cases, said Devine, but these were done in less than ideal circumstances.
“China, South Korea, and Singapore, have actually used convalescent plasma to treat patients but they’ve not done a comparison between using convalescent plasma and not so we can’t be completely sure that the therapy worked.”
Devine and her colleagues at Canadian Blood Services are currently working with researchers at several locations across the country to develop protocols for the clinical trial to submit to Health Canada.
Canadian Blood Service will handle collection of the plasma from donors, said Devine. An important step will be screening the donors who have recovered from COVID-19.
“We’re going to check before we collect that plasma to make sure that there’s enough of the right kind of antibody in there and then we will be collecting plasma and providing it for the clinical trial which is operating at multiple sites across Canada.
How antibodies are produced to fight the virus
Antibodies are small molecules produced by immune cells. They can recognize and stick to parts of the virus — usually parts of its protein coat. Often the antibodies bind to precisely those parts of the virus that the virus itself uses to bind to the cells it is going to infect.
This allows the antibodies to perform several functions. They can simply block viruses from being able to bind to and infect cells. They can also attract white blood cells from the immune system to destroy the virus. “They are the way the immune system marks things for destruction,” said Devine.
Once an individual has cleared an infection, antibodies remain in the bloodstream. It is these that researchers hope to harvest in blood plasma, and use to treat those whose immune systems have not yet mounted a strong defence.
Donations of plasma will be critical
For the trial Canadian Blood Service will handle collection of the plasma from donors, said Devine. An important step will be screening the donors who have recovered from COVID-19. “We’re going to check before we collect that plasma to make sure that there’s enough of the right kind of antibody in there and then we will be collecting plasma and providing it for the clinical trial which is operating at multiple sites across Canada.”
Donors will have to be matched by blood type, as for any blood transfusion. For the clinical trial only a small number of donors will be necessary. However if the trial is successful, a much larger pool of donors will have to be recruited.
Apart from efficacy, a key issue in this trial is going to be safety. Devine said investigators will be watching for a phenomenon called “antibody dependent enhancement” which can trigger an dangerous immune overreaction in patients who are already very sick.
“When you give those patients someone else’s plasma you sometimes can actually make the disease worse.”
The next step in antibody therapy
“We hope that we are actually up and running within the next four weeks or so and then it’ll probably take about four months total to run the study,” said Devine. “We hope we know sometime this summer what the answer is.”
But plasma therapy is probably not the end-point in this kind of antibody treatment.
“We anticipate that there’s an immediate need for this convalescent plasma but that eventually it will start to be replaced by other therapies — things like growing up antibodies in the laboratory,” said Devine.
Indeed a Vancouver based company called AbCellara has received funding to do exactly that. They’ll be working to isolate the antibodies that COVID-19 patients are using to fight the virus. These could then be incorporated into a drug to treat coronavirus infections.
Produced by Sonya Buyting and Jim Lebans. Written by Jim Lebans
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