Nanobodies Have the Potential To Eliminate COVID–19

2020-07-23 Hits(54)

2019 novel coronavirus(2019-nCoV) infection has attracted worldwide attention since the end of 2019. The epidemic situation in many countries such as American has shown a rapid growth trend. The pathogenic Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV-1) and COVID-19 coronavirus (SARS-CoV-2) have all emerged into the human population with devastating consequences. They are a member of the Coronaviridae family, so named for their “crown-like” appearance.

These viruses make use of a large envelope protein called spike (S) to engage host cell receptors and catalyze membrane fusion. Because of the vital role that these S proteins play, they represent a vulnerable target for the development of therapeutics to combat these highly pathogenic coronaviruses.

Recently, a new research describe the isolation and characterization of single-domain antibodies (VHHs) from a llama immunized with prefusion-stabilized coronavirus spikes. These VHHs are capable of potently neutralizing MERS-CoV or SARS-CoV-1 S pseudotyped viruses.

In the study, they immunized the alpaca, using the S protein from SARS virus and MERS virus. Then, they used phage display methods to find Nanobodies against these two types of S proteins. Using multiple sequence alignments and evolutionary tree analysis, the researchers found 5 Nanobodies against the S protein of SARS virus and 7 Nanobodies against the S protein of MERS virus. Among them, about half each has a high affinity for the corresponding S protein.

In order to test their neutralizing ability, the scientists used pseudotyped lentiviruses of the MERS and SARS viruses. The Study have shown that these Nanobodies show good neutralization ability. For the MERS pseudovirus, the IC50 values of several antibodies are 0.014-2.9 μg/mL. For SARS pseudovirus, the corresponding value of antibody is 0.14-5.5 μg/mL.

 

Subsequently, they used cryo-electron microscopy technology to obtain high-definition three-dimensional structures when some nanobodies were combined with viral RBD. Interestingly, the binding mechanism behind Nanobodies against MERS virus and SARS virus is different-after the former binds to the S protein, it will be inserted at the site where the DPP4 receptor binds to RBD, which directly prevents the DPP4 receptor MERS virus binding; the latter binding site does not directly affect the binding of ACE2 receptor to SARS virus.

The crystal structures of these VHHs bound to their respective viral targets reveal two distinct epitopes, but both VHHs block receptor binding. The research also show cross-reactivity between the SARS-CoV-1 S-directed VHH and SARS-CoV-2 S, and demonstrate that this cross-reactive VHH is capable of neutralizing SARS-CoV-2 S pseudotyped viruses as a bivalent human IgG Fc-fusion. These data provide a molecular basis for the neutralization of pathogenic betacoronaviruses by VHHs and suggest that these molecules may serve as useful therapeutics during coronavirus outbreaks.

Due to the inherent thermal and chemical stability of VHH, they have been studied as a class of potential therapeutic drugs to combat various diseases. Several VHHs targeting HIV and influenza viruses have been reported before, and several VHHs targeting RSV have been evaluated. The possibility of delivering these molecules by nebulizing spray is particularly attractive in the case of respiratory pathogens, because VHH can theoretically be directly inhaled into the infection site to maximize their bioavailability and function. Given the current lack of treatment for MERS, SARS, and COVID-19, as well as the devastating effects associated with the Corona Virus outbreak, there is an urgent need for preventive and therapeutic interventions. These researchers hope that MERS VHH-55, SARS VHH-72, and VHH-72-Fc will have good biophysical properties and strong neutralizing ability, and can be used as useful reagents and potential therapeutic candidates for scientists.