*This research has now been peer reviewed and published in the journal Cell.
A recent *preprint study published in bioRxiv, suggests that many people who contract SARS-CoV-2 but have mild or no clinical signs still develop so-called T-cell-mediated immunity to the virus, even in the absence of a positive antibody test. The researchers conclude that this is likely to mean that public immunity is probably higher than antibody testing has so far suggested.
The multi-centered team based at the Karolinska Institutet and Karolinska University Hospital performed immunological analyses on over 200 people, including unexposed individuals as well as exposed family members and individuals with acute or convalescent COVID-19. From this they mapped the functional and phenotypic landscape of SARS-CoV-2-specific T-cell responses.
T cells are an important subset of our immune cells, pivotal in the immune system’s ability to recognize and destroy virus-infected cells in our bodies and mount an immune response on re-exposure to a previously encountered infection. Cytotoxic T cells are essential in destroying virus-infected cells, whilst a phenotypically distinct group of T cells, sometimes called memory T cells, are important in the development of long-term immunity.
In a University press release, Marcus Buggert, Assistant Professor at the Center for Infectious Medicine, Karolinska Institutet, and one of the paper’s main authors commented, “Advanced analyses have now enabled us to map in detail the T-cell response during and after a COVID-19 infection. Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in.”
The team showed that even in the absence of a detectable antibody response, a robust memory T cell response could be measured in many individuals, akin to the response seen following vaccination against other viral infections.
Professor Danny Altmann, British Society for Immunology spokesperson and Professor of Immunology at Imperial College London, said, “Among the many studies of cellular (T cell) immunity to SARS-CoV-2 that have appeared in the past few months, this is one of the most robust, impressive and thorough in the approaches used. It adds to the growing body of evidence that many people who were antibody-negative actually have a specific immune response as measured in T-cell assays, confirming that antibody testing alone under-estimates immunity.”
Whilst this could be good news for public health, T-cell testing is less straight-forward than antibody detection, and so may be less accessible for mass testing endeavors.
Altmann continued, “The big unknown for the moment is which parameters of immunity offer the most faithful indicator of true, protective immunity from future infection. So far, there is a sense from some studies that functional, virus-neutralizing antibody is one such correlate of protection. We urgently need experimental studies to help confirm whether T-cell immunity alone can give protection.” This sentiment was echoed by Buggert. “Larger and more longitudinal studies must now be done on both T cells and antibodies to understand how long-lasting the immunity is and how these different components of COVID-19 immunity are related”.
Updated on August 19 2020.