08/10/2025
This year’s medicine laureate Shimon Sakaguchi discovered a new class of T cells.
At the start of the 1980s Sakaguchi isolated T cells that had matured in genetically identical mice and injected them into the mice without a thymus. This had an interesting effect: there appeared to be T cells that could protect the mice from autoimmune diseases.
This and other similar results convinced Sakaguchi that the immune system must have some form of security guard, one that calms down other T cells and keeps them in check. But what type of cell was this?
When researchers differentiate between T cells, they use proteins located on the cells’ surface. Helper T cells can be recognised thanks to a protein called CD4, while killer T cells are distinguished by CD8.
In the experiment in which Sakaguchi protected the mice from autoimmune diseases, he used cells with CD4 on their surface – helper T cells. Ordinarily, these cells wake up the immune system and set it to work, but in Sakaguchi’s experiment the immune system was held back. His conclusion was that there must be different forms of T cells that carry CD4.
To test his hypothesis, Sakaguchi needed to find a way of differentiating between the various types of T cell. This took him over a decade, but in 1995 he presented an entirely new class of T cells to the world. In ‘The Journal of Immunology’ he demonstrated that these T cells – which calm the immune system – are characterised not only by carrying CD4 on their surface, but also a protein called CD25.
This newly identified T cell class was named regulatory T cells.
Read more about the story behind this year’s medicine prize: https://bit.ly/46NpqbG
