The evolution of the coronavirus
Scientists have determined which mutations make the coronavirus invulnerable
American scientists have tracked the evolutionary path that the SARS-CoV-2 virus has taken in the human body with weakened immunity for five months, and have established which mutations allow the coronavirus to evade immune protection. The results are published in the journal Cell (Clark et al., SARS-CoV-2 evolution in an immunocompromised host reveals shared neutralization escape mechanisms).
The vast majority of people who have had COVID-19 get rid of the SARS-CoV-2 virus after recovery, but some – for example, people with autoimmune diseases receiving immunosuppressive drugs – can become chronic carriers of the infection.
The weakened immune system of such people is not able to destroy the virus once and for all, but it continues to attack it, and the virus tries to rebuild itself in such a way as to avoid this attack. As a result, after some time, new mutations resistant to the effects of antibodies or antiviral drugs appear in the body of infected people with weakened immunity. The study of each such specific case gives biologists valuable information about the ways of evolution and adaptation of the virus.
Researchers from Harvard Medical School (HMS) together with colleagues from the National Laboratory of New Infectious Diseases Boston University and Boston University School of Medicine analyzed in detail the case of the evolution of the SARS-CoV-2 virus in a patient with weakened immunity, registered in December 2020 at Brigham and Women's Hospital in Boston.
The patient was receiving immunosuppressive treatment for an autoimmune disorder and developed a chronic infection. Genomic analysis of the patient's virus showed the presence of a cluster of eight mutations in the spike protein that the virus uses to penetrate human cells. It is this protein that modern antibody treatments and vaccines are aimed at. Specifically, mutations were grouped in a spike segment known as the receptor-binding domain (RBD).
Some of the identified changes at that time had not yet been identified in the dominant viral variants circulating in the population, but were already present in databases of publicly available viral sequences. Interestingly, similar changes were later found in new, particularly aggressive variants of SARS-CoV-2 from the UK and South Africa.
Laboratory research has shown that such a mutated virus is able to evade both natural antibodies in the plasma of those who have been ill, and artificially created monoclonal antibodies that are now used to treat COVID-19.
"Our experiments have shown that structural changes in the viral spike protein allow the virus to avoid neutralization by antibodies," the press release says. The words of the head of the study Jonathan Abraham, associate professor of microbiology at the HMS Blavatnik Institute and an infectious diseases specialist at Brigham and Women's Hospital. "The problem is that the accumulation of changes in the spike protein over time can affect the long–term effectiveness of monoclonal antibody therapy and vaccines targeting the spike protein."
At the same time, the authors note that, most likely, the new variant of the virus will be vulnerable to mRNA-based vaccines that target the entire spike protein, not just parts of it.
"The way the spike protein reacted to persistent immune pressure in one person for five months gives an idea of how the virus will mutate if it continues to spread around the globe," the scientist adds.
The authors note that the main measure that can prevent the development of the pathogen is the earliest universal vaccination. Otherwise, current vaccines and treatments may be ineffective against mutations of the next wave of coronavirus infection.
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