Dr Kang Lan Tee's new paper 'Purification of recombinant SARS-CoV-2 spike, its receptor binding domain, and CR3022 mAb for serological assay' published in bioRxiv is addressing serological testing for COVID-19.
Why is this paper important?
Diagnostics play a crucial role in our COVID-19 pandemic response. The serological test for instance is a blood-based test with relatively short diagnosis time that can be used to detect both active and past infection when timely applied. This helps us to map the extent of the outbreak, identify the links of transmission and test effectiveness of vaccines.
Antigens are essential components in serological tests and the SARS-CoV-2 spike (S) protein is a primary viral antigen used in this test. Good quality antigens improve the sensitivity and specificity of the test, and hence its reliability. As a final stage in the antigen manufacturing process, protein purification of the SARS-CoV-2 spike (S) and its receptor binding domain (RBD) protein is an important checkpoint for controlling protein quality. This important process is however often omitted from or briefly described in research publications.
The purification scheme we have developed enables the production of high purity antigen for reliable serological testing and can be scaled to address our current need."
Dr Kang Lan Tee
Department of Chemical and Biological Engineering
How did you do this?
We set out to develop a protein purification scheme that is simple, has high capacity and produces high quality protein. Typically, increasing the number of steps in a purification scheme will increase protein purity. We have however intentionally minimised the number of purification steps to strike a balance between protein purity that suffices a serological test, and processing time and capacity for desired protein productivity. This was achieved using a combination of chromatography techniques and the ÄKTA protein purification system. Specifically, we used affinity chromatography and a desalting step to produce relatively pure trimeric S protein and its RBD domain that were recombinantly expressed in CHO and HEK293 cells. These purified proteins can be stored frozen and later thawed for used in serological tests.
What is the potential impact of the study?
As we devise and adjust our COVID-19 response and recovery plan, serological testing and data will prove increasingly important to understand the pandemics' trend over time, identify the links between infection cases, support the vaccine trials and predict its future development. The purification scheme we have developed enables the production of high purity antigen for reliable serological testing and can be scaled to address our current needs. This is an important contribution to the arsenal for our collaborative fight against COVID-19.