On Aug. 18, 2020, researchers from HKU-Pasteur Research Pole at the School of Public Health, LKS Faculty of Medicine of The University of Hong Kong (HKUMed) used Luciferase Immunoprecipitation System (LIPS) assay and discovered that ORF8 and ORF3b are major targets of SARS-CoV-2 humoral immune response and can be used for more specific testing of COVID-19 infection. The study was the first among research teams worldwide to determine the most comprehensive ﾓlandscapeﾔ of antibody responses to SARS-CoV-2. The ground-breaking findings on COVID-19 serology were published in Nature Immunology.

Antibody testing is an important tool in the response to COVID-19. It allows us to define the true extent of infection in the community, may help to confirm diagnosis in suspected patients and is needed for evaluation of vaccines. To date, SARS-CoV-2 antibody testing has been focussed on two proteins of the virus – the Spike protein as it correlates with neutralising capacity of the serum, and the Nucleocapsid protein as it is abundantly made by the virus and thus more likely to elicit detectable responses. Both proteins have potential problems with false positive reactions due to cross reactivity with antibody to other human coronaviruses which are common in the population.

The research team used the Luciferase Immunoprecipitation System (LIPS) assay, an antigen discovery tool previously used for screening cancer and new pathogen antigens, and assessed the antibody responses to 15 different SARS-CoV-2 proteins in 61 COVID-19 patients. They identified that two non-structural proteins, ORF8 and ORF3b, are key SARS-CoV-2 targets that elicit early and potent antibody responses in COVID-19 patients. These proteins are unique to SARS-CoV-2, thus are able to avoid the problem of cross-reactivity with other “common cold” human coronaviruses. Such robust antibody responses against these two viral proteins could be consistently detected in the majority of COVID-19 patients (96.5% sensitivity).

Currently, ORF3b and ORF8 proteins are not mainstream targets for COVID-19 diagnosis. These findings will improve the serological tests for COVID-19 and enhance the development of second-generation diagnostic tests.