Does this disappearing organ hold the secret of longevity? Scientists are increasingly focused on the thymus, an immune gland that naturally becomes less active with age. Nestled beneath the sternum in the upper chest is a soft, overlooked organ that quietly shrinks with age.

This organ, the thymus, was named by the Greeks, who believed it was home to the soul. The word itself means soul in Greek. Long seen as an organ that outlived its usefulness after childhood, the thymus is now attracting renewed interest.

Scientists increasingly believe it could hold clues to one of humanity’s constant hopes — increasing longevity. Here is more about the thymus, its function and the latest research about it. What is the thymus?

The thymus is a gland located beneath the breastbone, in front of the heart. It is relatively large in newborns and is already well developed before birth, but it gradually shrinks and becomes less active with age. The thymus is where T lymphocytes or T cells mature.

Immature T cells first arise from stem cells in the bone marrow and then travel to the thymus. There, they develop into functional T cells, a type of white blood cell that can hunt down infected or cancerous cells and help coordinate the body’s immune response. “The thymus begins to shrink surprisingly early in life, with the process starting during childhood and accelerating around puberty.

It continues to decrease in size throughout adulthood,” Paola Bonfanti, a professor of epithelial cell biology and regenerative medicine at the University College of London’s Institute of Immunity and Transplantation, told Al Jazeera. “As the thymus shrinks, its ability to produce new T cells, an essential part of the immune system, gradually declines. This loss of function can be measured by assessing the output of newly produced T cells in the blood.” What have recent studies revealed?

Since the 1990s, researchers have been exploring whether halting its decline might strengthen the immune system and improve health in later life. Now, new studies have added significant momentum to this approach, suggesting that the thymus may be critical for longevity and cancer immunotherapy response. In March, a team led by Harvard Medical School scientists published research in the journal Nature, where they used AI to analyse thousands of CT scans.

They found that adults with a healthy-appearing thymus lived longer and had lower rates of cardiovascular disease and cancer than those with an unhealthy thymus. In the same edition of Nature, a separate study analysing CT scans revealed that in patients with cancer, thymic health may influence response to immunotherapy, which is a treatment contingent on the strength of a patient’s immune system. Earlier, in 2023, a study revealed that people who had their thymus removed were three times more likely to die and twice as likely to develop cancer five years after its removal, compared with people who did not have their thymus removed.

“However, these findings are correlational and do not establish cause and effect,” Bonfanti cautioned. “It is equally plausible that healthier individuals are simply better able to preserve thymic tissue as they age, rather than a larger thymus being the reason they are healthier.” She added that studies are still needed to determine whether preserving or restoring thymic function can directly improve health or extend lifespan.