Study sheds light on how virus-fighting cells develop during long COVID

A new long-term study into long COVID has investigated how a certain population of white blood cells, called memory T cells, are established and develop as part of the body's defense to fight off the disease.

The study, led by researchers from the Peter Doherty Institute for Infection and Immunity (Doherty Institute) and published in PNAS , found that despite the long COVID diagnosis, memory T cells that recognize SARS-CoV-2, the virus that causes COVID-19, can be established and maintain their ability to fight subsequent infections after two years.

T cells fight off viral infections by killing cells that are infected with the virus. They play a special role in the body's immune defense system, in that they can remember their encounters with the virus and become long-term memory T cells for protection against subsequent infections, even when the virus mutates.

Dr. Louise Rowntree, a first author on the paper and Senior Research Fellow at the Doherty Institute, said the study included 31 people from Australia and Hong Kong with long COVID.

"In this study, we looked at memory T cells that can recognize SARS-CoV-2 in people with long COVID over a period of two years following SARS-CoV-2 infection and subsequent COVID-19 vaccination," she said.

"We found that these SARS-CoV-2 memory T cells can be established and maintain key features over that period. Our findings are novel, as long-term T cell immunity in people with long COVID is understudied."

The symptoms of long COVID are varied, and can include weakness, fatigue, impaired concentration and chest pain , and can last between 12 weeks to two years.

Dr. Oanh Nguyen, Senior Research Fellow at the Doherty Institute, who co-led the study, said the recall of T cell memory is necessary for a more rapid recovery from COVID, and the establishment of these robust T cell responses is important for protection against subsequent infections of newer strains.

"We know that long COVID is a rare disease following a COVID-19 infection, but it can hugely impact a person's daily life, as well as substantially impacting the health care system," she said.

"While research into underlying mechanisms is evolving, immunity is an area that remains understudied, and this is an important step in understanding how the body responds."

Laureate Professor Peter Doherty, an author on the study, said this manuscript represents important research.

"Applying the lessons learned and technologies developed to study the cellular immune response in human influenza has allowed us to move fast on analyzing this aspect of our immune response in COVID-19," said Professor Doherty.

"That opens an important portal for understanding where we need to go with future therapies and vaccines."