MEDICINE AND HEALTH

Adult patients with thymus removal have an increased risk of death


The thymus gland helps immune cells mature during childhood but shrinks after puberty. Image credit: Janulla/iStock

The thymus is a butterfly-like organ located between the collarbones, and to adults it seems like a useless appendage. In early childhood, the thymus gland is the main site of T cell maturation, but by puberty, the organ begins to shrink and stops producing T cells. By adulthood, the thymus was considered useless, so much so that cardiac surgeons would occasionally remove it to make it easier to access the heart.

But a study published Aug. 2 in the New England Journal of Medicine completely refutes the hypothesis that the thymus is useless: that the thymus may actually be vital to adults, and that removing the thymus can be fatal.

Marcel van den Brink, an immunologist at Memorial Sloan Kettering Cancer Center in the United States who was not involved in the study, said the new study is very welcome because there are few studies on thymus function in adults. “This new study basically confirms what many people think, but we never had sufficient evidence.”

To assess the importance of the thymus gland in adults, Harvard University hematologist David Scadden and colleagues analyzed the medical records of nearly 2,300 patients who underwent chest surgery at Massachusetts General Hospital. Half of them had a thymectomy, usually to treat thymic cancer or certain autoimmune diseases, such as myasthenia gravis.

The team found that over the next 5 years, those patients who underwent thymectomy were almost 3 times more likely to die from various causes such as infectious diseases, cancer, etc. They have twice the risk of cancer than people who preserve the thymus and develop cancer that is more aggressive. This trend persisted even though the researchers only looked at people with no history of cancer or myasthenia gravis, suggesting that thymectomy itself leads to increased mortality.

Next, the scientists studied the effects of removing the thymus gland on the immune system. Just like antibodies, each T cell attacks only one molecule, such as a virus or a protein on the surface of a bacterium. When the researchers compared the plasma of 22 thymectomy patients with that of 19 control patients, they found that the thymectomy patients had fewer biomarkers, indicating that the body was producing new, different types of T cells. This suggests that even the adult thymus can produce new mature T cells. Thymectomy patients have more inflammatory molecules in their plasma, suggesting that they may have an autoimmune disease.

Scadden said the lack of T cell diversity may make people more susceptible to infectious diseases, especially pathogens like SARS-CoV-2, which they never encountered when their thymus was most active as children. Without the thymus, the immune system would have a hard time growing T cells against new threats. He suspects that vaccines may also be less effective for these people because they do not produce an effective immune response, although this has never been directly studied.

Su Dongming, an immunologist at the University of North Texas Health Science Center who was not involved in the study, said the findings provide strong evidence that the thymus gland in adults is still functional. He also suspects that thymectomy may shorten people’s overall lifespan, although the current study didn’t follow subjects long enough.

Van den Brink added that the increased incidence of cancer in thymectomy patients also suggests that T cells from the thymus play an important role in coping with and preventing cancer. The procedure could be more harmful to adults, he said, because children’s thymus glands appear to regenerate themselves.

Other recent studies have shown that tonsil removal, which is common in children, may also damage the immune system in the long term and lead to an increased risk of infectious diseases, allergies, and respiratory diseases. Scadden said the tonsils and thymus are very different, and immune cells in other parts of the body can at least partially compensate for the loss of tonsils in the respiratory tract, but only the thymus can produce new types of mature T cells.

Su said future studies could determine whether gene or cell therapy can restore thymic function in people who have had their thymus removed. Scadden hopes the findings will re-evaluate clinical guidelines for thymectomy and raise concerns about the negative effects of thymectomy. (Source: Li Huiyu, China Science News)

Related paper information:https://doi.org/10.1056/NEJMoa2302892



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