Immunologists are beginning to suspect that T cells are playing a much bigger role in immunity against Covid-19 than previously realised after a string of recent papers.
Scientists have pointed to growing evidence that T cells may be the key to how long patients stay resistant to reinfection with Covid-19 and may be producing broader immunity in the population than antibody studies may suggest.
A paper in Nature by a group of scientists in Singapore found that patients with a history of SARS infection from 2003 still had T cell responses 17 years later and also cross-reactivity with Covid-19 (SARS-Cov-2).
They also detected SARS-Cov-2 specific IFN-γ responses in 19 out of 37 people who had not been exposed to either SARS virus, suggesting some T cell immunity may be conferred by exposure to other coronaviruses.
Another paper, published as a pre-print, found SARS-2-Cov specific T cells in patients who had mild or asymptomatic Covid-19 or whose family members had been infected but they themselves were antibody negative.
Professor Danny Altmann, Professor of Immunology at Imperial College London, said the paper added to the growing body of evidence that antibody testing alone under-estimates immunity.
“However, the big unknown for the moment is which parameters of immunity offer the most faithful indicator of true, protective immunity from future infection.”
In a briefing on current thinking on T cell immunity Professor Altman added: “The simple take home message of where we stand at the moment on immunity to this virus by T cells is that it looks like it’s a virus that’s very stimulatory to T cells, that most people have very good T cell responses, they’re very activated.”
He added that T cells seemed to be recognising lots of parts of the virus not just the unique protein spike that has been the focus of some vaccine candidates as a means to generating antibodies.
“The other thing I would add is they look rather durable and seem to be getting made in virtually all exposed people and by that I mean everybody from very severely affected hospitalised people to PCR negative household contacts of cases.”
Professor Mala Manai, Professor of Viral Immunology at University College London who was also speaking at the briefing said antibody producing B cells and T cells needed to coordinate together to produce the very best immune response.