In a time when the use of personal protective equipment (PPE) has become a global and mainstream necessity, no longer limited to scientists and health care professionals, innovation by a team at the University of San Francisco is paving the way for a new era in respiratory viral prophylaxis." AeroNabs", a term coined by Dr. Peter Walter's team, UCSF Professor of Biochemistry and Biophysics and Howard Hughes Investigator, refers to aerosolized bioengineered nanobodies targeting the SARS-CoV-2 Spike protein, which may be administered as an inhalable antibody drug.
Nanobody Based Strategies to Target SARS-CoV-2
Earlier during the COVID-19 pandemic, a team from Belgium and USA had recognized the potential of nanobodies as therapeutics tools for neutralizing SARS-CoV-2 infection. In their study, however, the identified nanobody did not efficiently neutralize SARS-CoV-2 pseudoviruses. Investigators were then prompted to engineer a bivalent nanobody, VHH-Fc construct, which more effectively neutralized SARS-CoV-2 S pseudoviruses. Currently, the Belgian company ExeVir Bio has plans for clinical trials to test this new bivalent VHH-Fc lead in patients with mild to moderate COVID symptoms. The team at UCSF led by Dr. Walter ( biorxiv.preprint) took this strategy even farther by developing a trivalent nanobody. This new nanobody bound to the trimer of Spike proteins, retaining the molecules in an inactive state, by interacting with the ACE2 receptor binding domain (RBD) epitopes. Investigators found that trivalency significantly increased SARS-CoV-2 pseudovirus neutralization by ~2000 fold above the activity of the monovalent nanobody.
Adapted from “Schematic of Spike-Receptor Binding Mechanism of SARS-CoV-2”, by BioRender.com (2020).
Retrieved from https://app.biorender.com/biorender-templates
The trivalent nanobody demonstrated high efficacy in neutralizing live SARS-CoV-2. However, affinity maturation strategies allowed them to identify an even more potent nanobody. In fact, it is one of the most potent anti-SARS-CoV-2 reagents developed to date. However, questions remained regarding its potential for therapeutic use.
“GenScript’s precision mutant libraries are highly suitable for affinity maturation of an antibody or nanobody for therapeutic and diagnostic
applications”-Maung Win, PhD, Sr. Field Application Scientist, GenScript.
AeroNabs: From Nanobody to Therapy
Stability is a coveted nanobody characteristic, and one that provides great advantage in therapeutic applications. The Walter’s group went on to show that the new trivalent nanobody remained stable under conditions of high temperature, following lyophilization, and could be aerosolized without aggregation. Therefore, this potent trivalent nanobody may prove effective in preventing SARS-CoV-2 infection by administration as an inhalable antibody drug, a concept that will be tested clinically in the near future.
What are Nanobodies?
Nanobodies may prove to be an effective tool in the quest for therapeutic options to curve the COVID-19 pandemic. Nanobodies are single domain antibodies, initially developed from simpler antibody forms uniquely found in camelids and sharks. In addition to the familiar “Y” shaped antibody molecules, consisting of heavy and light immunoglobulin chain pairs, camelids such as llama and camels also produce heavy-chain-only antibodies.
Single variable domain (VHH) antibodies or nanobodies, were first bioengineered from camelids over 20 years ago by a Belgian team at Vlaams Interuniversitair Instituut voor Biotechnologie. Since then, VHHs have been highly sought-after tools for various diagnostic and therapeutic applications including treatment of inflammation, cancer, and infectious diseases. Interest has been propelled by several advantageous properties of nanobodies which set them apart from conventional antibodies, such as their ease of production, solubility, and stability. Additionally, their small size (~15 kDa) and preference for binding to concave antigen surfaces, makes them ideal reagents to probe and detect protein regions otherwise inaccessible to larger conventional antibodies (~150 kDa).