To fight against the COVID-19, the scientists have identified a small neutralising antibody, a so-called nanobody, which has the capacity to block SARS-CoV-2 from entering human cells.
The study, published in the journal Nature Communications, suggests that this nanobody has the potential to be developed as an antiviral treatment against COVID-19.
“We hope our findings can contribute to the amelioration of the COVID-19 pandemic by encouraging further examination of this nanobody as a therapeutic candidate against this viral infection,” said study co-author Gerald McInerney from the Karolinska Institute in Sweden.
The search for effective nanobodies–which are fragments of antibodies that occur naturally in camelids and can be adapted for humans–began in February when an alpaca (animal) was injected with the new coronavirus’ spike protein, which is used to enter our cells.
After 60 days, blood samples from the alpaca showed a strong immune response against the spike protein.
Next, the researchers cloned, enriched and analysed nanobody sequences from the alpaca’s B cells, a type of white blood cell, to determine which nanobodies were best suited for further evaluation.
They identified one, Ty1 (named after the alpaca Tyson), that efficiently neutralizes the virus by attaching itself to the part of the spike protein that binds to the receptor ACE2, which is used by SARS-CoV-2 to infect cells.
This blocks the virus from slipping into the cells and thus prevents infection.
“Using cryo-electron microscopy, we were able to see how the nanobody binds to the viral spike at an epitope which overlaps with the cellular receptor ACE2-binding site, providing a structural understanding for the potent neutralisation activity,” said study researcher Leo Hanke.
According to the researchers, nanobodies offer several advantages over conventional antibodies as candidates for specific therapies.
They span less than one-tenth the size of conventional antibodies and are typically easier to produce cost-effectively at scale.
Critically, they can be adapted for humans with current protocols and have a proven record of inhibiting viral respiratory infections.
“Our results show that Ty1 can bind potently to the SARS-CoV-2 spike protein and neutralize the virus, with no detectable off-target activity,” the study authors wrote.
“We are now embarking on preclinical animal studies to investigate the neutralizing activity and therapeutic potential of Ty1 in vivo,” they noted.