Nature article on immunological memory after Covid-19
Researchers find evidence for the emergence of immunological memory in SARS-CoV-2 infection in long-lived memory CD8+ T cells.
The question whether and how exposure to SARS-CoV-2 through infection or immunisation can lead to long-term protective immunity is as yet unresolved. Onur Boyman and his research team from University Hospital Zurich and the University of Zurich, in collaboration with researchers from ETH Zurich, want to identify the factors that influence the formation of this immunological memory. They have just published their latest findings in the reputable scientific journal Nature.
Viral infections in humans, such as those caused by SARS-CoV-2, result in an immune response that fights the acute infection. At the same time, the body is prepped to better control future infections with the same virus. This phenomenon is called immunological memory and is helped by virus-specific memory cells of the immune system, including T cells and in particular CD8+ T cells. While virus-specific antibodies can be routinely measured, insight into virus-specific CD8+ T cells in humans has been limited to studies of the entire CD8+ T cell population. Hence, it has not been possible so far to determine whether the changes in CD8+ T cells linked to the transition from effector to memory phase are due to population-wide or individual CD8+ T cell clone changes.
According to the article published online in Nature (https://www.nature.com/articles/s41586-021-04280-x), Boyman and his team have now succeeded in tracing individual virus-specific CD8+ T cell clones in individuals infected with SARS-CoV-2, from acute infection to one year after recovery. The researchers distinguished two types of virus-specific CD8+ T cells: short-lived and long-lived. The long-lived ones could still be detected in the bloodstream six months after acute infection. These long-lived memory CD8+ T cells were characterised by a distinct signature that was already there during the acute infection and could therefore be distinguished from their short-lived counterparts at an early stage. The signature of the long-lived memory cells contained signals for certain cytokines, such as interferons, which are thought to be important in the control of viral infections, including SARS-CoV-2 infection.
Understanding the mechanism of how the immune system maintains memory formation may shed light on why some infections lead to robust and long-lasting immune memory while others do not. The study contributes to deciphering the complexity of these processes. The results also support further research into natural viral infections as well as the development of vaccines against viral infections and cancer immunotherapies in which the generation of long-lived memory CD8+ T cells is desired.