Humanized Monoclonal Antibodies That Inhibit SARS-CoV-2 Infection

2020-07-23 Hits(75)

The 2019 new coronavirus disease (COVID-19) epidemic caused by the virus SARS-CoV-2 is the third major epidemic in the past 20 years. SARS-CoV-2 is a member of the Coronaviridae family like Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS). Since COVID-19 was first discovered in December 2019, it has shown a rapid growth trend. become a "global pandemic". Up to now, the new coronavirus is still a huge threat to public health, and new prevention and treatment strategies are urgently needed.

 

With the continuous spread of COVID-19, there are many reports on the antibodies against SARS-CoV-2 by domestic and foreign Scientists. In order to speed up the research and development of vaccines, different kinds of vaccines have successively entered clinical human trials. Neutralizing antibodies can improve the body's immunity, It provides more possibilities for the development of SARS-CoV-2 antibody drugs.

On May 13, 2020, academician Gao Fu of the Chinese Academy of Sciences, with associate researcher at the Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, and dean Liu Lei of Shenzhen Third People's Hospital published a paper in Science: A noncompeting pair of human neutralizing antibodies block COVID-19 virus binding to its receptor ACE2. The human monoclonal antibody isolated from a recovered patient was reported to effectively block the binding of the virus to the cellular receptor ACE2, showing strong neutralizing ability. The research results highlight the application prospects of antibody therapy and provide a structural basis for the rational design of SARS-CoV-2 vaccines. 

 

The researchers used the RBD protein of the new coronavirus as bait to isolate specific single memory B cells from peripheral blood mononuclear cells (PBMCs) of COVID-19 patients. The variable regions of antibody light and heavy chains were amplified from individual B cells, and then cloned into pCAGGS vectors containing constant regions and transfected into cells, producing a series of IgG1 antibodies.

The supernatant was screened using the biological layer interference method (BLI) to bind to the RBD protein. Four kinds of monoclonal antibodies (B5, B38, H2 and H4) were selected to effectively bind to SARS-CoV-2 RBD protein.

In order to study the neutralizing activity of the four monoclonal antibodies against the new coronavirus, the researchers measured the dissociation constant (Kd) of the four antibodies that bound to the new coronavirus RBD, which ranged from 107 to 109 M , IC50 value is between 0.177 μg/ml-1.375 μg/ml. At the same time, the combined use of antibodies B38 and H4 found that it can show a synergistic effect on viruses with higher titers.

The evaluation of the ability of the antibody to inhibit the binding of RBD to ACE2 also showed that the B38 and H4 antibodies competed with ACE2 for binding to the viral RBD protein, and respectively bound to different epitopes of RBD. This indicates that these two antibodies can block the binding of viral RBD to the cellular receptor ACE2 and inhibit infection.

2. The development of Humanized antibodies against SARS-CoV-2

 

Humanized antibodies provide the possibility to prevent and treat COVID-19. Compared with antiviral small molecule drugs, antibodies are highly specific, therefore may cause fewer side effects. Moreover, the engineering of antibodies can improve their stability, so that the injection of neutralizing antibodies becomes an effective way to prevent COVID-19 in the short term.

At present, many companies and research institutions around the world are carrying out the transformation and development of antibodies against SARS-CoV-2, which will help the development of the vaccine. The Utrecht University researcher in Netherland has isolated a SARS-CoV-2 neutralizing antibody 47D11. They use humanized mice that can produce antibodies to different coronavirus S proteins to create 51 cell lines, and test the collected chimeric antibodies (from humans and rats), determining whether has neutralizing antibodies. The study found that one antibody (47D11) showed neutralizing ability to both SARS-CoV and SARS-CoV-2. This chimeric antibody needs rearranged to produce fully humanized antibodies. The results showed that 47D11 is a cross-neutralizing antibody, which has the conserved common epitopes target to SARS-CoV and SARS-CoV-2. Its epitope and neutralization mechanism are worthy of further study and provide a basis for antibody therapy.