Two nanobodies—small, stable immune cells similar to various antibodies and derived from llamas—have been found in tests to neutralize COVID-19 by blocking its interaction with the human receptor that it binds to.

The nanobodies block the attachment of the COVID-19 spike protein by targeting a region of the protein immediately adjacent to and slightly overlapping with the region of the cell where COVID-19 binds and enters. Both llama nanobodies were shown to neutralize live COVID-19, and showed particularly high potency and increased neutralization potential when combined with a human antibody. The findings were published in Nature Structural & Molecular Biology paper.

The development of immunizations for coronaviruses is a well-established process. The virus possesses a protein which binds to a receptor on the exterior of the cells of an infected individual.

Like a boat docking at a wharf, the virus needs a place to ‘dock' its spike protein, otherwise it cannot enter the cell. Therefore the first path for researchers and drug developers is to see how they can prevent the binding of the spike protein with the cell receptor.

"Although there is currently no ‘cure' or vaccine for the disease," writes James Naismith at the The Rosalind Franklin Institute, Didcot, UK, "passive immunotherapy by transfusing critically ill COVID-19 patients with serum from [recovered] COVID-19… individuals has been shown to improve clinical outcomes."

"This would suggest that neutralization of the virus, even at a relatively late stage in the disease, may be a useful COVID-19 therapy."

The two nanobodies—H11-H4 and H11-D4—can be "deployed to produce a highly neutralizing agent against an emerging viral threat in real time," to provide "passive immunization of severely ill COVID-19 patients." say the authors.

The research was funded by the Rosalind Franklin Institute, a medical research centre supported by the UK Government, which has filed a patent on the nanobodies.

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