A coronavirus toolset

Dr Yuning Chen reveals how a life sciences expert has responded to the current Covid-19 pandemic by developing a series of active reagents (virus proteins, antibodies and pseudoviruses) to facilitate serologic tests and anti-viral drug developments

The basis for recombinant protein expression is to over-produce a foreign protein in a host cell by harnessing the power of its cellular protein generation machinery. The foreign protein is usually carried in a vector (e.g. a plasmid) and introduced into the host cell via non-invasive methods. It is a well-established technology with a history of about five decades and it is the basis of modern biotechnology and biopharmaceutics. A selection of expression hosts, including E. coli, yeast, insect cells, HEK293, and CHO have been established to generate various recombinant proteins and antibodies.

The spike protein is the attachment point of the SARS-CoV-2 to the host cell and it is the gateway for virus invasion. The full-length spike protein as well as its segments, e.g. S1, receptor-binding domain (RBD), N-terminal domain (NTD), and S2, has been produced in HEK293 cells based on the reference sequences and validated for their interactions against human ACE2. Sino Biological is also monitoring the mutations occurring within the spike protein, especially in RBD, constantly and has been adding high-abundance mutations into the inventory continuously. So far, a library of >40 RBD mutants has been constructed, covering all major RBD mutations. This library is useful for screening of broad-spectrum neutralising antibodies against spike-ACE2 interactions. Besides the array of RBD mutants, an S1 version bearing the dominant D614G mutation has also been made with confirmed ACE2 binding activity.

Lastly, under a non-exclusive license, Sino Biological is eligible for the manufacturing of Hexapro, an engineered spike protein with a stable pre-fusion state that is an excellent candidate for SARS-CoV-2 antibody assay development. Hexapro has been produced in HEK293 with enhanced yield, stability, and well-defined conformational status. It is also worth noting that E.coli cultures are also extensively used in producing active SARS-CoV-2 enzymes as well as nuclepcapsid protein with a correct oligomer status.

Antibodies against covid-19

Antibodies (immunoglobulin) are bio-macromolecules generated by the immune system of vertebrates to “flag’ exogenous agents, which are subsequently neutralised by various immune cells. To generate antibodies against a certain entity, it requires unique pieces of that entity to be recognised by the immune system as foreign objects. For SARS-CoV-2, its surface glycoprotein (spike) and nucleocapsid protein are good candidates for this purpose. To ensure the speedy generation of anti-CoV-2 antibodies, the company used both antibody library screening and antibody discovery methods. During antibody library screening, its team investigated the pre-existing antibody library against SARS-CoV and identified several antibodies with high sensitivities against SARS-CoV-2 spike and nucleocapsid proteins of. While during the antibody discovery campaigns, immunogens such as S1 and RBD of the spike protein and nucleocapsid protein of SARS-CoV-2 were used to immunise mice and rabbits. Via techniques such as hybridoma and phage display, the company has identified SARS-CoV-2 specific antibodies with no cross-reactivates against other coronaviruses and several neutralising antibodies that blocked the interaction of SARS-CoV-2 pseudovirus in an ACE2 over-expressing HEK293 cells.

All antibodies, including 9 against the nucleocapsid protein and 12 against the spike protein, are available as reagents for SARS-CoV-2 research and serologic assay ingredients. In the meantime, a CoV2 spike-displaying pseudovirus system using the HIV backbone has also been developed, which would be extremely useful for quick screening of SARS-CoV-2 neutralising antibodies or other inhibitory molecules that block the interaction between CoV2 spike protein and ACE2.

Sino Biological has a special focus on viruses and other forms of infectious diseases. With the establishment of the ProVir viral antigen bank and a large selection of anti-viral antibodies, ELISA kits and cell lysates, the company is dedicated to contributing to the research of these disease areas. Besides catalogue products, most sections of its recombinant protein/antibody expression and antibody discovery platforms are available for contracted research projects as well.

Dr Yuning Chen is with Sino Biological

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