Patients who recovered from COVID-19 harbour SARS-CoV-2-specific T cells as shown in a Singapore study. This, the scientists suggest, bodes well for the development of long-term protective immunity against the coronavirus.

T cells, along with antibodies, target and kill infected cells, but their importance in fighting SARS-CoV-2, the virus that causes COVID-19, remains unclear.

Interestingly, the Singapore study found that even people who had SARS infection 17 years ago, and over 50 percent of healthy individuals who had not been infected with SARS or SARS-CoV-2, have these cellular defences. The researchers said these were likely because of  cross-reactive immunity obtained from previous exposure to common cold viruses or some unknown animal coronaviruses. [Nature 2020;]

“This suggests that  infection and exposure to coronaviruses induce long-lasting memory T cells … and a level of pre-existing SARS-CoV-2 immunity may have been present in the general population,” said corresponding author Professor Antonio Bertoletti from the Duke-NUS Emerging Infectious Diseases programme. However, this does not mean that people who have recovered from COVID-19 are protected from re-infection.

First-of-a-kind rapid COVID-19 test

Singapore scientists have developed a first-of-a-kind rapid SARS-CoV-2 surrogate virus neutralisation test (sVNT) that could aid COVID-19 investigations in the heat of the pandemic.

sVNT could help determine infection rate, herd immunity, predicted humoral protection, and vaccine efficacy during clinical trials.

The test has been validated in two cohorts of COVID-19 patients in Singapore (n=375) and China (n=250), showing 99–100 percent specificity and 95–100 percent sensitivity. sVNT can detect the functional neutralising antibodies (NAbs) that block coronavirus spike protein binding to the ACE2 host receptor, which mimics the virus-host interaction. [Nat Biotechnol 2020;]

Infection or immunity to the virus is diagnosed by the presence of NAbs in a patient’s blood sample, justifying the need for a robust serological test that could detect NAbs during COVID-19 investigations.

Current platforms for detecting NAbs require live viruses and cells and take longer to return results. In contrast,  the sVNT kit can detect functional NAbs in an hour, said Professor Wang Linfa, Director of Duke-NUS Emerging Infectious Diseases programme, who developed the test with his team. “It can differentiate [NAbs] with binding antibodies [Babs], without the need for live virus or a biocontainment facility … it can also detect total receptor binding domain (RBD)-targeting neutralising antibodies in patient samples, in contrast to most SARS-CoV-2 antibody tests published or marketed, which are isotype-specific. This makes the sVNT accessible to the broader community for both research and clinical applications.”

The sVNT kit is commercialised by GenScript under the brand cPass™ and is currently for research use alone. An Emergency Use Authorisation has been filed by its maker with the US FDA.