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. 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.” 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.