COVID-19: Antibody fragment could prevent infection

Research suggests that an antibody fragment, or “nanobody,” can neutralize SARS-CoV-2. The authors also say that it is possible to produce the nanobody cheaply and at scale, making it a promising candidate for the widespread prevention of COVID-19.

As cases of COVID-19 continue to rise, the search for an effective vaccine against the disease continues.

A recent report provides encouraging results for a vaccine candidate under development in Russia, but there are still no data showing that any vaccine can prevent COVID-19.

It could be months, if not years, before a vaccine reaches the general population.

In the meantime, however, scientists are busy looking for an effective treatment to mitigate symptoms or, even better, to prevent infection from occurring in the first place.

Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

In a new study in the journal Nature Communications, a group of researchers from Karolinska Institutet in Sweden describe one such treatment.

They outline the production of an antibody fragment that binds strongly to the SARS-CoV-2 spike protein to neutralize the virus.

They also say that it is possible to produce the fragment cheaply and at scale, and that it has good potential as an antiviral agent against the new coronavirus.

Alpaca antibodies

A nanobody, which is a fragment of an antibody, is less than one-tenth of the size of a normal antibody. Although much smaller, nanobodies are just as specific and effective as regular antibodies.

Camelids — the family of animals including camels, llamas, and alpacas — naturally produce nanobodies. In this study, the nanobody came from an alpaca.

To obtain the nanobody, the scientists injected the alpaca with the spike protein of the new coronavirus back in February. The virus uses the spike protein to enter cells, but by itself, it is harmless.

After 60 days, the researchers took blood samples from the alpaca. The blood samples revealed that its immune system had responded to the spike protein by generating several nanobodies.

The researchers then analyzed the sequences of these nanobodies to see if any had the potential to become a treatment option.

How it works

They found one nanobody in particular, called Ty1, that binds strongly to the part of the spike protein that usually binds to its receptor, ACE2.

Cells in the body express ACE2, and the virus uses it to access and infect cells. Stopping the interaction between the spike protein and the ACE2 receptor, as this nanobody does, can effectively prevent infection.

“Using cryo-electron microscopy, we were able to see how the nanobody binds to the viral spike at an epitope [that] overlaps with the cellular receptor ACE2-binding site, providing a structural understanding for the potent neutralization activity,” explains first study author Dr. Leo Hanke.

The scientists suggest that, if further development is successful, it may be possible to use the nanobody to prevent infection in those with the highest risk of COVID-19.

It could also be usable on a bigger scale to allow larger sections of the population to safely return to work, school, and other currently restricted activities.

Mass production

The authors claim that such widespread use of the nanobody is viable because manufacturers can produce it cheaply and on a large scale.

This is because nanobodies are smaller and easier to manufacture than regular antibodies and because bacteria can express them in large quantities.

Scientists can also make the nanobodies safe for use in humans by using existing methods. Indeed, previous research has suggested that they can help prevent respiratory infections.

The team is currently exploring strategies to improve the potency of the nanobody and planning preclinical studies in animals to assess whether or not the treatment can help prevent COVID-19.

The researchers have also made the nanobody sequence freely available online to facilitate collaborative research efforts and enable rapid production.

“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.”

– Senior study author Prof. Gerald McInerney

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