To fight against Covid-19, scientists have identified a small neutralising antibody, a so-called nanobody, that 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. According to the researchers, nanobodies offer several advantages over conventional antibodies as candidates for specific therapies.

“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.