This text is taken from our newsletter “Le Courrier du coronavirus” of May 9, 2022. To subscribe, click here.
We all know a household in which COVID-19 has invited itself, but where a person, to everyone’s surprise, has been spared by the little beast after days of intensive exposure. How is it possible ?
The question seems simple, but two and a half years after the appearance of SARS-CoV-2, it is still tormenting the scientific community.
“I would like to give you an answer, but we don’t have one yet,” observes Donald Vinh, professor and researcher in microbiology and immunology at the McGill University Health Centre. Despite his modesty, this specialist nevertheless has several possible explanations.
In vaccinated people, first, it is mainly the response to vaccination that makes some people avoid an infection, while others give in to it. Two people who received the same doses of vaccine at the same time will not necessarily have developed the same protection.
However, where the question becomes really interesting is in the “immunologically naïve” population – people who have never been vaccinated, never infected – where there are a few individuals who seem completely resistant to COVID-19.
We are not talking here about asymptomatic patients, but about people who, even after prolonged exposure, do not feel any symptoms and repeatedly obtain negative PCR test results.
The phenomenon is not new in the history of medicine: some people are resistant to gastroenteritis thanks to a genetic variation which influences the surface of their cells. Variations in the human genome also confer resistance to tuberculosis to more than 90% of the population.
And what about COVID? An international group of researchers, of which Dr. Vinh is a member, is currently carrying out a research project to find these resistant people, sequence their genome and pinpoint the secret of their infallible defense.
Their immunity could derive from a host of molecules in the human body: some forming part of the immune system as it is currently understood, others being on the surface of the epithelial cells that line the respiratory tract, and still others being on the inside the cells themselves, etc.
The Covid Human Genetic Effort group thus strives to consider all the possibilities that could explain the resistance. “We keep an open mind,” explains Dr. Vinh.
Results within a few months
So far, the team has found around 700 people across the globe — from Canada to Australia, Brazil, Kenya and Italy — who appear to be COVID-resistant. -19. Within three months, the researchers should have completed the genome sequencing of these people.
Of the batch, the atypical genetic profiles will be the subject of laboratory tests. Researchers will generate molecules associated with unusual genes in vitro to see how they behave in the presence of the coronavirus. The possible biological mechanisms responsible for resistance will be understood.
The stakes are immense: these biological mechanisms could reveal the position of a crucial “therapeutic target” for the development of drugs.
Genetics is not the only possible explanation for resistance to COVID-19: epigenetics (the mechanisms that modify gene expression) and the human microbiome (the microorganisms living inside us) are other possible factors. Nevertheless, the genetic approach is particularly promising, because “if you don’t have genes, you don’t exist”, recalls Dr Vinh.
Already, the recruitment of resistant people is causing surprises. Of the approximately 700 individuals recruited in the 278 participating medical centers around the world, approximately 80 come from Canada, especially Quebec.
“Most of the people we found [au Québec] for the resistance project are elderly people in CHSLDs, explains Dr. Vinh. And 98% of these people are native Quebecers, French-speaking. »
“It is possible that there is an enrichment [une surreprésentation de certaines variations génétiques] in this population, he continues. It is possible that there is something unique. But it’s as possible as not. »
A story to follow in five to six months, when the international team will have completed its analysis.