Professor Ray Owens, of Oxford University,who leads the nanobodies programme at the Franklin, said the researchers hope they can push the breakthrough on into pre-clinical trials.

Professor David Stuart, of Diamond Light Source and Oxford University, said: “The electron microscopy structures showed us that the three nanobodies can bind to the virus spike, essentially covering up the portions that the virus uses to enter human cells.”

Researchers started from a lab-based library of llama antibodies and are now screening antibodies from Fifi, one of the “Franklin llamas”based at the University of Reading, taken after she was immunised with harmless purified virus proteins.

The team is looking at preliminary results which show that Fifi’s immune system has produced different antibodies from those already identified, which will enable cocktails of nanobodies to be tested against the virus.

In a separate study, published in Nature Medicine, scientists say they have uncovered how a crucial component of the immune system responds to the spike protein of Sars-CoV-2.

Coronavirus particles have a corona (crown) of proteins that resemble spikes, which enable the virus to attach and enter cells in humans. The spike protein is crucial in inducing neutralising antibodies to protect from reinfection. Neutralising antibodies not only bind to the viral spike protein, but prevent it from being able to attach to and enter human cells.

Researchers from the Peter Doherty Institute for Infection and Immunity in Australia investigated how the immune system, particularly B and T-cells, responds to the spike.

B-cells are responsible for producing the antibodies that recognise Sars-CoV-2, while T-cells play an important role in supporting the development of the B-cell response.

Dr Jennifer Juno, of the University of Melbourne and a postdoctoral researcher at the Doherty Institute, said researchers looked at people who had recovered from Covid-19 and had mostly experienced mild or no symptoms.

She said: “We found that those who showed strong neutralising antibody activity had a robust B-cell response, but most surprisingly, we also found that a particular subset of T-cells, called T-follicular helper cells, was a great predictor of an effective immune response.

“Now we know how the immune system responds to the spike protein, and we have these biomarkers, or predictors of what elicits a good or poor immune response to Covid-19, we can look at the vaccine candidates and see what will offer the best protection.”

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