SARS-CoV-2 D614G variant enhances infectivity, replication and transmission

Researchers in the United States and Japan have conducted studies showing common mutations in Spike protein Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)-a drug that causes coronavirus disease 2019 (COVD-19)-promotes virus infectivity, replication, and early infection.

A study by a team of SARS-CoV-2 designed to contain the D614G mutation found that this strain replicates more efficiently in primary human proximal airway epithelial cells than wild-type virus.

In a hamster infection model, the D614G strain also showed much faster transmission of respiratory droplets than the wild-type virus immediately after infection.

Ralph Barrick (University of North Carolina at Chapel Hill) and colleagues at the University of Wisconsin-University of Tokyo and the National Institute of Infectious Diseases support the need for regular reviews of SARS-CoV-2 modern isolates. It states that it is. Identify new mutants that may have increased infectivity and etiology.

Preprinted paper is available on the server bioRxiv*, While the article is undergoing peer review.

D614G substitution does not alter SARS-CoV-2 virion morphology and S protein cleavage patterns, but susceptibility to the virus Neutralizing antibody.. A. Transmission electron micrographs of WT and D614G virions on the surface of airway epithelial cells, scale bar: 200 nm. B. Scanning electron micrographs of WT and D614G virions on the surface of airway epithelial cells, scale bar: 100 nm.

Importance of spike proteins

Since the first case of SARS-CoV-2 infection was confirmed in Wuhan, China at the end of last year, the virus has continued to dominate the world, now infecting more than 33.8 million people and killing more than 1 million people. There is.

Most infected people develop only mild or asymptomatic illnesses, but some develop serious complications such as heart problems, coagulopathy, stroke, and acute respiratory distress syndrome.

To gain invasion into host cells, SARS-CoV-2 uses a surface structure called spikes. Glycoprotein It binds to the human cell receptor angiotensin converting enzyme 2 (ACE2).

Therefore, this spike protein has become a central concern in research aimed at developing vaccines and therapies.

During the epidemic of a pandemic in a naive population, the virus may select mutations that alter its pathogenicity, etiology, or infectivity.

Studies have recently confirmed that the D614G substitution of spiked glycoprotein is the most common strain of SARS-CoV-2 circulating worldwide.

However, the effect of this mutant on SARS-CoV-2 function, etiology, and infectivity remains unclear.

What did the researchers do?

To investigate the function of D614G substitution in SARS-CoV-2 replication and infectivity, researchers have included a mutant containing the D614G mutation in the spike protein and a second gene containing the bioluminescent reporter nanoLuciferease (nLuc). I designed a mutant.

The team compared the growth of wild-type SARS-CoV-2 and D614G mutants in the primary human nasal epithelium (HNE), large (proximal) airway epithelium (LAE), and distal lung small airway epithelium (SAE). did.

HNE and LAE cultures infected with D614G showed significantly higher viral titers than cultures infected with wild-type, not SAE cultures.

Competitive co-infection assays performed on LAE cultures infected with both viruses simultaneously, regardless of whether the wild-type virus was originally present in a 1: 1 or 10: 1 ratio to the D614G mutant. We have shown that the D614G mutant predominates in culture.

“These data suggest that D614G substitution enhances SARS-CoV-2 replication compatibility of primary epithelial cells and has significant benefits for upper airway epithelial cells of the nasal and large (proximal) airway epithelia. “Baric et al. Said.

The team then performed scans and transmission electron microscopy to visualize the virions present on the surface of primary human airway cell cultures. No significant difference was observed in the morphology of virions or the number of spiked proteins between the two viruses.

Further analysis reveals more differences between the viruses

Researchers used nLuc-expressing recombinant SARS-CoV-2, which encodes either wild-type or D614G spikes, to neutralize serum samples from serum samples taken from mice vaccinated with D614 (wild-type) spikes. The activity was measured.

This revealed that half of the maximum inhibitory dilution of the sample against D614G virus was 0.8-5.1 times higher than that against wild-type virus, making SARS-CoV-2 more sensitive to neutralizing antibodies. Indicates to do.

Assessment of the infectivity of respiratory droplets

To assess the role of the D614G mutant in the transmission of SARS-CoV-2 respiratory droplets, researchers set up eight sets of hamsters, each containing a naive hamster, with the infected animal one day after infection. Did.

Both the wild-type virus and the D614G virus efficiently infected naive hamsters. Four and six days after infection, infected and exposed hamsters showed similar viral titers, regardless of the infected virus.

However, 5 of the 8 hamsters exposed to the D614G-infected group showed infection and had detectable viral shedding on day 2, whereas hamsters exposed to the wild-type infected group were infected or shedding. Did not show. This suggests that the D614G mutant is transmitted much more quickly between hamsters via droplets and aerosols than the wild-type virus.

“Our study has shown that SARS-CoV2 D614G substitution enhances infectivity, replication compatibility, and early infection,” the researchers conclude.

“Our data regularly review SARS-CoV-2 modern isolates worldwide and increase transmission and etiology and / or antigens, especially as levels of human herd immunity and intervention alter selectivity. It supports the crucial need to identify the emergence of new mutants with sexual changes. The power to act on the genome, “the team advises.

*Important Notices

bioRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.