New research conducted by investigators at Massachusetts General Hospital (MGH) and published in the New England Journal of Medicine challenges the conventional view of the thymus gland as nonfunctional in adults. The thymus is a crucial organ that produces immune T cells before birth and during childhood. However, it is often removed during cardiac surgery to gain better access to the heart and major blood vessels.
The new study reveals that the thymus plays a critical role in adult health, particularly in preventing cancer and autoimmune diseases. To assess the health benefits provided by the thymus in adults, the research team examined the risk of death, cancer, and autoimmune disease among 1,146 adults who had their thymus removed during surgery and a demographically matched control group of 1,146 patients who underwent similar cardiothoracic surgery without thymectomy. They also measured T cell production and levels of immune-related molecules in a subgroup of patients.Â
The findings were striking. Five years after surgery, the thymectomy group had a mortality rate of 8.1% compared to 2.8% in the control group, representing a 2.9 times higher risk of death for those who had their thymus removed. Additionally, 7.4% of the thymectomy group developed cancer during that period, while only 3.7% of the control group did, resulting in a 2.0 times higher risk of cancer in the thymectomy group.Â
Senior author Dr. David T. Scadden, director of the Center for Regenerative Medicine at MGH and co-director of the Harvard Stem Cell Institute, emphasizes the significance of the findings: “By studying people who had their thymus removed, we discovered that the thymus is absolutely required for health. If it isn’t there, people’s risk of dying and risk of cancer is at least double. This indicates that the consequences of thymus removal should be carefully considered when contemplating thymectomy.”Â
A further analysis was conducted on all patients in the thymectomy group with more than five years of follow-up, revealing a higher overall mortality rate (9.0% vs. 5.2%) and a higher mortality rate due to cancer (2.3% vs. 1.5%) compared to the general U.S. population.Â
Although the risk of autoimmune disease did not show significant differences between the thymectomy and control groups in the overall analysis, the researchers observed a discrepancy when they excluded patients with infection, cancer, or autoimmune disease before surgery. In this subgroup, 12.3% of the thymectomy group developed autoimmune disease compared to 7.9% in the control group, resulting in a 1.5 times higher risk. The study also examined the production of new T cells and immune-related molecules in a subgroup of patients.
Those who had undergone thymectomy showed consistently lower production of new T cells compared to controls, along with higher levels of pro-inflammatory molecules in their blood. Looking ahead, Dr. Scadden and his team plan to further investigate how various levels of thymus function in adults impact their overall health. “We can test the relative Vigor of the thymus and define whether the level of thymus activity, rather than just whether it is present, is associated with better health,” he explains.Â
The study’s results shed new light on the importance of the thymus in adult health and challenge the perception that it is nonfunctional in later life. Understanding the role of the thymus in preventing cancer and autoimmune diseases could lead to a re-evaluation of surgical decisions that involve thymus removal. The research also opens avenues for future investigations into the relationship between thymus activity and overall health, potentially paving the way for new therapeutic strategies in the prevention and treatment of diseases related to immune function.Â
