They develop a new treatment for COVID-19 and its dangerous variants

During the coronavirus pandemic, new viral variants that quickly became dominant. These tend to be more infectious than the strain that first appeared in Wuhan, China. Its mutated spike protein can also “escape” neutralization by certain effective antibodies originally coming from infected, cured or vaccinated people. This makes it more difficult, even for a trained immune system, to eliminate the virus. This problem also affects previously developed therapeutic antibodies and nanobodies.

Now, Researchers in Göttingen, Germany, have developed mini-antibodies that effectively block the SARS-CoV-2 coronavirus and its dangerous new variants. These so-called nanobodies bind and neutralize the virus up to 1000 times better than mini-antibodies developed previously. Additionally, scientists have optimized their mini-antibodies for stability and resistance to extreme heat. This unique combination makes them promising agents for the treatment of COVID-19. Since nanobodies can be produced inexpensively in large quantities, could meet the global demand for COVID-19 therapies. They are currently in preparation for clinical trials.

Antibodies help our immune system defend itself against pathogens. For example, molecules stick to viruses and neutralize them so that they can no longer infect cells.. Antibodies can also be produced industrially and administered to critically ill patients. They then act as drugs, relieving symptoms and shortening recovery from the disease. This is an established practice for the treatment of hepatitis B and rabies. The antibodies are also used to treat patients with COVID-19. However, producing these molecules on an industrial scale is too complex and expensive to meet global demand. Nanobodies could solve this problem.

Scientists from the Max Planck Institute (MPI) for Biophysical Chemistry in Göttingen (Germany) and the University Medical Center in Göttingen (UMG) they were responsible for the discovery published in a scientific journal. “For the first time, they combine extreme stability and exceptional efficacy against the virus and its mutants Alpha, Beta, Gamma and Delta”, underlines Dirk Görlich, director of the MPI for Biophysical Chemistry.

At first glance, the new nanobodies do not differ much from the anti-SARS-CoV-2 nanobodies developed by other laboratories. All of them are directed against a crucial part of the coronavirus peaks, the receptor binding domain that the virus displays to invade host cells. Nanobodies block this binding domain and thus prevent the virus from infecting cells. “Our nanobodies can withstand temperatures of up to 95 ° C without losing their function or forming aggregates”, explains Dr Matthias Dobbelstein, professor and director of the Institute for Molecular Oncology at UMG. “On the one hand, it tells us that they can stay active in the body long enough to be effective. On the other hand, heat resistant nanobodies are easier to produce, process and store.”.

Single, double and triple nanobodies

The simplest mini-antibodies developed by the Göttingen team already bind up to 1000 times more strongly to the spike protein than those previously reported. They also bind very well to mutated receptor binding domains of Alpha, Beta, Gamma and Delta strains. “Our individual nanobodies are potentially suitable for inhalation and therefore for the direct neutralization of the virus in the respiratory tract”, explains Dobbelstein. “Plus, because they’re so small, they could easily penetrate tissue and prevent the virus from spreading. more at the site of infection ”.

A “nanobody triad” further improves binding: The researchers grouped three identical nanobodies based on the symmetry of the spike protein, which is made up of three identical building blocks with three binding domains. “With this triad, we are literally joining forces: in an ideal scenario, each of the three nanobodies adheres to one of the three binding domains,” reports Thomas Güttler, scientist in the Görlich team. “This creates an almost irreversible bond. The triple will not allow the spike protein to be released and neutralizes the virus even up to 30,000 times better than individual nanobodies”. Another advantage: the larger size of the triad of nanobodies will delay renal excretion. This keeps them in the body longer and promises a longer lasting therapeutic effect.

As a third design, scientists have produced tandems. These combine two nanobodies that target different parts of the receptor binding domain and together they can bind to the spike protein.. “These tandems are extremely resistant to viral mutations and the resulting ‘immune escape’ because they bind so tightly to the viral peak,” explains Metin Aksu, researcher in Görlich’s team. For all variants of nanobodies (monomers, doubles and triples), the researchers found that very small amounts are enough to stop the pathogen. If used as a medicine, it would allow a low dose and therefore less side effects and lower production costs.

Origin of alpacas

“Our nanobodies come from alpacas and are smaller and simpler than conventional antibodies», Says Görlich. To generate the nanobodies against SARS-CoV-2, the researchers immunized three alpacas (Britta, Nora and Xenia from the MPI for Biophysical Chemistry herd) with parts of the coronavirus spike protein. The mares then produced antibodies and the scientists took a small blood sample from the animals.. For alpacas, the mission was over, as all the extra steps were done using enzymes, bacteria, bacteriophages and yeasts. “The overall burden on our animals is very low, comparable to vaccination and blood tests in humans,” Görlich explains.

Görlich’s team extracted around a billion blueprints of nanobodies from the blood of alpacas. What followed was a fine-tuned laboratory routine for many years: Biochemists used bacteriophages to select the best nanobodies from the initial large pool of candidates. They were then tested for their effectiveness against SARS-CoV-2 and further improved in successive optimization cycles.

Not all antibodies are “neutralizing”. Therefore, researchers in Dobbelstein’s group determined whether nanobodies prevent viruses from replicating in cells grown in the laboratory, and to what extent they prevent. “By testing a wide range of dilutions of nanobodies, we found out how much is sufficient to achieve this effect,” explains Antje Dickmanns of the Dobbelstein team. His colleague Kim Stegmann adds: “Some of the nanobodies were really impressive. Less than a millionth of a gram per liter of medium was sufficient to completely prevent infection. In the case of the nanobody triads, even another twenty-fold dilution was sufficient. “

As the experts concluded, “these nanobodies can allow simplified vaccine production and adaptation to viral escape mutations.”

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