Antibodies from convalescent plasma protects against COVID-19

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The researchers found passive transfer of neutralising antibodies isolated from convalescent plasma into Syrian hamsters protect the animals against the disease when exposed to the virus and also protects hamsters against heavy viral exposure.

A team of scientists led by Dennis R. Burton from the Scripps Research Institute has discovered neutralising antibodies present in the blood of COVID-19 who have recovered offers powerful protection against novel coronavirus in animals. The researchers found passive transfer of neutralising antibodies into Syrian hamsters protects the animals against the disease when exposed to the virus. The protection was found when antibodies at high dose were transferred to the animals.

The small animals that received high dose of antibodies did not lose weight and the amount of virus in the lungs was low compared with those animals that received low dose of the antibodies and the control group. “The study suggests a role for neutralising antibodies in prophylaxis, and potentially therapy, of COVID-19. The neutralising antibodies define protective epitopes to guide vaccine design,” they write in a paper published in the journal Science.

Prior to transferring and testing the ability of the antibodies to protect the animals from the virus, the researchers tested it on human cell cultures and found the antibodies to have superior ability to protect against the virus.

Two different antibodies in five different concentrations were tested on the small animals to evaluate dose-dependent protection. The highest dose tested was 2 mg/animal and the lowest dose was 8 microgram/animal. The animals were challenged with the virus 12 hours after the antibodies were transferred. Lung tissues were collected to measure viral load on day 5 post virus challenge.

In contrast to the antibody to receptor-binding domain of the virus, the less potent and incompletely neutralizing antibody showed no evidence of protection at any concentration compared to the control animals.

The authors state that the efficacy of the antibodies in Syrian hamsters is “promising” and suggest that human studies be undertaken based on animal trial results.

Incidentally, the researchers also identified one antibody that can neutralise the 2002 SARS virus.

Therapeutic, vaccine

According to the release, the antibodies can be injected into patients in the early stage of the disease to reduce the viral load and thus protect the patient from progressing to the severe form of the disease. “The antibodies also may be used to provide temporary, vaccine-like protection against SARS-CoV-2 infection for healthcare workers, elderly people and others who respond poorly to traditional vaccines or are suspected of a recent exposure to the coronavirus,” the release says.

The antibodies can then be mass-produced either as a treatment to prevent deterioration of the disease and as a preventive vaccine, as in the case of Ebola virus, the release notes.

“If further safety tests in animals and clinical trials in people go well, then conceivably the antibodies could be used in clinical settings as early as next January,” the researchers say in the release.

Choosing the best

More than 1,000 antibody-producing immune cells called the B cells were first isolated. These antibodies were isolated based on their ability to bind to the virus and prevent the it from infecting the test cells.

Each of the 1,000 immune B cell produced a distinct antibody against the virus. In order to mass-produce the antibody, the researchers obtained the gene sequence of each antibody. They then screened each antibody and 33 antibodies that could block the virus from binding to the test cells were identified. They also identified one antibody that could also protect hamsters against heavy viral exposure.

Published in the Hindu on June 20, 2020