Most COVID-19 convalescent individuals have long-lasting memory T cell responses

Antigen-specific T-cell and B-cell responses play critical roles in the pathology of most viral infections. The establishment of T- and B-cell memory after recovery from the viral infection is crucial for protection against disease during re-exposure to the same virus.

The unprecedented global health and socioeconomic crisis resulting from the current coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has forced the scientific community worldwide to focus on mapping the determinants of immunity against SARS-CoV-2.

Do people recovering from COVID-19 have immunity against SARS-CoV-2?

A key question that is still not addressed enough during the current pandemic is how long immunity lasts in people who recover from a COVID-19 infection. Increasing evidence from studies suggests that T cells may play a significant role in the clearance of SARS-CoV-2.

However, all currently available data on T cell memory was mainly generated from COVID-19 convalescent individuals during a short follow-up period less than 60 days post disease onset. It is unclear whether natural SARS-CoV-2 infections elicit long-lasting memory T cell responses and how these responses change in the long term.

A comprehensive analyses of memory T cell responses against SARS-CoV-2 post-recovery

Recently, researchers from the Huazhong University of Science and Technology, China, and the University of Duisburg-Essen, Germany, conducted a comprehensive analysis of memory T cell responses against SARS-CoV-2 in individuals who have recovered from COVID-19. Their study is published on the preprint server bioRxiv*.

Their analysis detected robust responses for up to 9 months after disease onset in most convalescent people. Loss of memory CD4 T cell responses were observed in only 16.13% and loss of memory CD8 T cell responses in 25.81% of convalescent individuals. This shows that the overall magnitude of memory CD4 and CD8 T cell responses were stable and correlated with the time from disease onset.

Natural SARS-CoV-2 infection could prevent recurrent disease

The researchers performed longitudinal analyses and found that the kinetics of SARS-CoV-2 memory CD4 and CD8 T cell responses were highly heterogeneous among patients. The only considerable decrease in the T cell response was found in memory CD4 cells in the first 6 months after the onset of COVID-19. Loss of CD4 T cell responses was seen more in asymptomatic cases than in symptomatic COVID-19 cases.

“Longitudinal analyses revealed that the kinetics of SARS-CoV-2 memory CD4 and CD8 T cell responses were quite heterogenous between patients.”

The few convalescent individuals in whom SARS-CoV-2-specific IgG responses disappeared had more lasting CD4 T cell responses than recovered individuals who stayed IgG-positive for months. This observation is crucial because it suggests that natural infection with SARS-CoV-2 could prevent recurring bouts of severe COVID-19.

Majority of convalescent individuals had strong memory T cell responses 9 months after disease onset

The extent to which immunity lasts in patients recovering from COVID-19 is one of the most challenging questions facing us today. According to previous studies, the persistence of immunity against different human coronaviruses varies significantly. The durability of immunity against seasonal coronaviruses is short-lived, while immunity against SARS and Middle East respiratory syndrome coronavirus (MERS) is known to last longer.

Some studies report that although SARS-CoV-2 infection may weaken long-lived antibody responses, immune memory may still be possible through virus-specific memory T cell responses. These responses have been detected in recently recovered individuals, both asymptomatic cases and those who had undetectable antibody responses.

This study characterizes long-term memory T cell responses in a group of individuals recovering from COVID-19 for up to 9 months following SARS-CoV-2 infection. They show that the magnitude and breadth of long-lasting memory T cell responses against SARS-CoV-2 are heterogeneous. While most of these individuals demonstrate strong memory T cell responses for up to 9 months after the onset of disease, some lost their T cell responses within 6 months.

Overall, this might be the first detailed characterization of the long-term memory T-cell response in COVID-19 convalescent individuals, and it suggests that most people recovering from COVID-19 have long-lasting SARS-CoV-2-specific T cell immunity.

“Collectively, we provide the first comprehensive characterization of the long-term memory T cell response in CIs, suggesting that SARS-CoV-2-specific T cell immunity is long-lasting in the majority
of individuals.”

*Important Notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Susha Cheriyedath

Written by

Susha Cheriyedath

Susha has a Bachelor of Science (B.Sc.) degree in Chemistry and Master of Science (M.Sc) degree in Biochemistry from the University of Calicut, India. She always had a keen interest in medical and health science. As part of her masters degree, she specialized in Biochemistry, with an emphasis on Microbiology, Physiology, Biotechnology, and Nutrition. In her spare time, she loves to cook up a storm in the kitchen with her super-messy baking experiments.

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