Nobel Prize Medicine 2025: The first Nobel Prize of this year, the prize for Physiology or Medicine, has been announced. Mary E Brunkow, Fred Ramsdell, and Shimon Sakaguchi have been honoured for their work on the human immune system.The Nobel Prizes generally follow the same schedule every year, with the Medicine prize coming first, followed by Physics, Chemistry, Literature, Peace, and Economics.Among this year’s Medicine winners, Brunkow and Ramsdell are from the USA, while Sakaguchi is from Japan. The research by the two Americans proved to be the second chapter of something Sakaguchi had worked on separately some years ago. After Brunkow and Ramsdell’s findings, Sakaguchi and other scientists managed to stitch their work together.Story continues below this adWhat exactly have the scientists done, what diseases does their work help treat, and how? We explain.What have the three winners done?The human body has a powerful and complex immune system, which not just fights off various bacteria and viruses, but also knows what cells should not be attacked.According to the Nobel Prize’s official press release, “Mary Brunkow, Fred Ramsdell and Shimon Sakaguchi are awarded the Nobel Prize in Physiology or Medicine 2025 for their fundamental discoveries relating to peripheral immune tolerance. The laureates identified the immune system’s security guards, regulatory T cells, which prevent immune cells from attacking our own body.”First, the basics of the immune systemThe human body’s immune system fights off thousands of microbes attempting to invade our bodies every day. Microbes vary wildly, and many even have ‘camouflages’ that mirror human cells. Thus the immune system must distinguish what to attack and what to tolerate.Story continues below this adIt should also be able to identify our own healthy cells, so that our body does not turn upon itself. When this identification does not happen properly, people develop auto-immune diseases.Also, in case of organ or stem cell (or bone marrow) transplants, there is always the danger of the immune system attacking the newly transplanted cells. Thus, an understanding of how the immune system works — how the signal to attack or not attack is given and executed — is very important.The immune system’s work is done by T cells. While helper T cells patrol the body and raise an alert when they detect an attack, the killer T cells attack the invader (virus or any other pathogen).For a long time, it was believed that the thymus, an organ just behind our sternum, played a central role in how the immune system worked. The thymus is specially active in babies and children. The T cells travel to the thymus. If they are found attacking our own cells — basically can’t tell apart invader from the body’s constituents — the thymus does not release them into the blood stream. Thus, it was understood that passing through the thymus was a kind of exam T cells had to clear to enter the blood stream and do the job of protecting.Story continues below this adThe three Nobel laureates proved that the picture is more complicated than that, and there is a third category of T cells.“The Nobel Prize laureates identified the immune system’s security guards, regulatory T cells, thus laying the foundation for a new field of research,” the press release says.Shimon Sakaguchi’s key insightIn the mid-1990s, Shimon Sakaguchi challenged conventional belief by postulating that some specialised T cells act as “security guards” of the immune system, suppressing overly aggressive responses.In a series of experiments, he examined mice whose thymus had been removed and matured T cells injected into their bodies later. He identified a class of T cells that basically ask other T cells, which might be attacking the body’s own tissues, to calm down. These are called regulatory T cells.Story continues below this adHowever, because some related findings had not been found promising, his finding did not get much attention then.Brunkow, Ramsdell, and the FOXP3 geneFar away from Sakaguchi, Brunkow and Ramsdell were examining sick male mice, and through painstaking elimination and identification of genes, had managed to find that the particular mutation making these mice sick was related to a rare autoimmune disease among humans, called IPEX. Both the diseases were caused by mutations in the FOXP3 gene.Finally, in another few years, it was established that FOXP3 gene controls the development of regulatory T cells, whose existence Sakaguchi had earlier established. It is this composite work done over decades that has won the Nobel.What is the impact of the discoveries on medical treatment?Story continues below this adThe discoveries of regulatory T cells and the FOXP3 gene have launched a new field of immune‐regulation research, with significant implications for human health.In cancer, tumours are often surrounded by many regulatory T cells, which protect them from immune attack. Researchers are investigating how to dismantle this “protective wall” so that the immune system can better reach and destroy cancerous cells.Conversely, in autoimmune diseases, strategies aim to boost regulatory T cells, so that they can stop the attacking cells from destroying the body.Better understanding of the immune system can also help in making sure the body does not reject transplanted organs.Where do the three scientists work?Story continues below this adMary Brunkow, born in 1961, works at the Institute for Systems Biology, Seattle, USA.Frederick Ramsdell, born in 1960, works at Sonoma Biotherapeutics, San Francisco, USA.Shimon Sakaguchi, born in 1951, works at Osaka University, Japan.