The plasma of convalescents to neutralize the coronavirus

Le plasma de convalescents pour neutraliser le coronavirus

Several studies are currently examining whether the transfusion of antibodies produced by survivors of the COVID-19 could help to cure patients affected by the disease.

This is not a new concept. During the 1890s, the German physician, Emil Behring and his japanese colleague Kitasato Shibasaburō have discovered that the blood of people or animals that had survived an infection contained an ” antitoxin “, that is to say, an active principle able to neutralize the agent responsible for the disease.

More importantly, this antitoxin possessed a healing power : they have observed that it was possible to cure patients with diphtheria, an infectious disease prevalent at this time, simply by injecting the sick, the liquid fraction of blood (plasma) from animals that had been infected by the bacteria responsible for this disease.

This first form of immunotherapy was a discovery quite revolutionary, rewarded with the first Nobel prize in physiology and medicine in 1901.

Passive immunity

We now know that this “antitoxin” was, in fact, the amount of antibodies developed by animals convalescents against the infectious agent.

This plasma convalescent offers what is called a passive immunity : rather than produce our own antibodies capable of neutralizing the infection, the sick borrow rather those that have been successfully developed by another person who is able to overcome the disease.

The protection offered is obviously of a short duration and is not equivalent to that of a vaccine, where a person develops his own antibodies against a virus or bacteria and is protected for several years.

By contrast, in the presence of an infectious agent against which there is no vaccine (as is currently the case for the coronavirus SARS-CoV-2), these antibodies borrowed can prove to be very useful to compensate for the absence of an effective immune response and allow patients to reduce the infection and possibly lead to a cure.

Actions antiviral

This approach of passive immunity has been used several times in the course of the Twentieth century to treat patients affected by several viral infections, including measles, mumps, polio, and influenza.

For example, during the Spanish flu pandemic of 1918, it was observed that the mortality rate could be reduced by half in patients injected with plasma convalescent, especially when the transfusion was carried out at the beginning of the disease.

The method of plasma-convalescent has also been used during outbreaks of SARS (2002), SEAS (2012) and Ebola (2015).

Still today, the best treatment for Ebola remains the use of antibodies isolated from plasma convalescent and products by the following large-scale laboratory(1).

Clinical trials

Several clinical trials are currently underway in the United States, France and Canada to determine if the approach of the plasma convalescent could be used for the treatment of patients with the COVID-19.

The results of a pilot study conducted among 10 critically ill patients, recently published in the proceedings of the american Academy of sciences (PNAS), are very encouraging : after you have injected the patients with a single dose of 200 ml of plasma convalescent containing high amounts of antibodies against the SARS-CoV-2, the researchers observed three days later a marked improvement of the main clinical symptoms of the disease such as fever, cough, difficulty breathing and chest pain(2).

The white blood cell count and liver function were also improved and the viral load was completely undetectable in seven of 10 patients. After seven days, the analysis by computed tomography (CT-scan) revealed a decrease in lung lesions, without major side-effects detected.

Even if these preliminary results must be confirmed by randomized clinical studies on a larger scale, this approach seems to be promising and could save many lives in the meantime the development of an effective vaccine.

(1) Corti D et al. Protective monotherapy against lethal Ebola virus infection by a potently neutralizing antibody. Science 2016 ; 351 : 1339-42.

(2) Duan K, et al. Effectiveness of convalescent plasma therapy in severe COVID-19 patients. Proc. Natl Acad. Sci USA, published online 6 April 2020.

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