The COVID-19 is a global pandemic seriously damaging public health and social economy, and effective control methods are urgently needed. Antibodies have a good application precedent in the prevention and treatment of sudden severe infectious diseases. Hundreds of SARS-CoV-2 antibody R&D projects around the world are carrying outusing different strategies, some of which have entered the clinic stages.
As the name implies, neutralizing antibodies are a type of antibodies that can perform a reaction similar to "acid-base neutralization". When pathogenic microorganisms invade the human body, B lymphocytes produce a variety of antibodies including neutralizing antibodies, but only some of them can quickly recognize pathogenic microorganisms and bind to antigens on their surface, to prevent the pathogenic microorganisms from binding to the receptors on the surface of target cells to invade cells, and thereby protecting the body.
The most common MOA of the SARS-COV-2 neutralizing antibodies is binding the RBD of the S1 subunit and thereby blocking the binding of RBD to the ACE2 receptor on the host cell surface, which means that the affinity of the therapeutic drug should be stronger than that of ACE2 binding to the RBD domain to achieve an exclusive barrier effect.
Relevant researches are carried out on small-molecule antiviral drugs, plasma therapy, vaccines, and neutralizing antibodies. Researchers successfully treated 49 SARS-CoV-2 infected patients with the plasma from recovered patients, indicating that antibodies with neutralizing activity in the plasma of recovered patients are powerful treatment. The use of recovered plasma for treatment is a quick and effective emergency measure to deal with complex and sudden infectious diseases. However, due to the limited source of plasma, it is difficult to apply to the clinic on a large scale. Monoclonal antibodies with neutralizing activity have high specificity and high purity, and are applicable for large-scale preparation, which area powerful measurement for the prevention and control of infectious diseases. Currently, a variety of monoclonal antibodies have been applied. For example, in a phase II/III clinical trial of an anti-Ebola antibody, the experimental group (mAb114) and the control group (REGN-EB3 and ZMapp) showed good preventive and therapeutic effects. The mAb114 antibody has been granted Breakthrough Therapy Designation (BTD) by the FDA. Since the outbreak of COVID-19, hundreds of neutralizing antibody projects are actively developed.
Major targets
The S protein on the surface of SARS-CoV-2 contains two subunits, S1 and S2. The S1 subunit is divided into N-terminal domain (NTD) and the C-terminal region containing the receptor binding domain (RBD).The S2 subunit contains the fusion peptide, two 7-peptide repeats HR, and the transmembrane region, which are required for the membrane fusion process element. Similar to SARS-CoV, SARS-CoV-2 enters the cell through the processes of RBD binding with angiotensin converting enzyme 2 (ACE2) on the surface of the host cell, and membrane fusion mediated by S2 protein. Most of the currently developed SARS-CoV-2 neutralizing antibodies target S protein, including S1 protein, S2 protein, and ACE2-Ig.
SARS-CoV-2 antibody screening technology
Commonly used antibody screening technologies include murine hybridoma fusion technology, phage display technology, transgenic mouse technology, and single B cell isolation and cloning technology.
In vitro evaluation
ELISA and SPR methods can be used to determine the affinity and blocking activity of antibodies. Currently, a method of combining recombinant SARS-CoV-2 antigen-expressing cells with flow cytometry has also been developed for high-throughput analysis of antibody affinity and blocking activity.
In vivo evaluation
It is necessary to use appropriate animal models to evaluate the effects of SARS-CoV-2 neutralizing antibodies in vivo for prevention or/and treatment before entering the clinic. A suitable animal model requires genetic stability, obvious pathological characteristics after infection, and the ability to simulate the changes in physical signs under the same conditions in the human body. Currently commonly used animal models include mice/rats, ferrets, and NHPs.
The world is looking forward to vaccines and specific drugs for COVID-19. Thecandidates under clinical research are mainlyfour categories, that is, small molecule antiviral drugs, anti-inflammatory drugs, neutralizing antibodies, and vaccines. Neutralizing antibodies have high specificity, satisfactory safety, and have the dual role of prevention and treatment, and are expected to become a "seed" of COVID-19 specific drugs.