Development of SARS-CoV-2 neutralizing antibody detection assay by using recombinant plant-produced proteins

Detecting immunity against SARS-CoV-2 is vital for evaluating vaccine response and natural infection, but conventional virus neutralization test (cVNT) requires BSL3 and live viruses, and pseudo-virus neutralization test (pVNT) needs specialized equipment and trained professionals. The surrogate virus neutralization test (sVNT) was developed to overcome these limitations. This study explored the use of angiotensin converting enzyme 2 (ACE2) produced from Nicotiana benthamiana for the development of an affordable neutralizing antibodies detection assay. The results showed that the plant-produced ACE2 can bind to the receptor binding domain (RBD) of the SARS-CoV-2, and was used to develop sVNT with plant-produced RBD protein. The sVNT developed using plant-produced proteins showed high sensitivity and specificity when validated with a group of 30 RBD vaccinated mice sera and the results were correlated with cVNT titer. This preliminary finding suggests that the plants could offer a cost-effective platform for producing diagnostic reagents.