Kameron Kooshesh, (from left), David Sykes, David Scadden, and Karin Gustafsson at work in their lab at MGH. Credit: Kris Snibbe/Harvard Staff Photographer
Key Points:
- Researchers have discovered the thymus plays an outsized role in health as humans age.
- The organ was previously thought to serve a limited purpose in adulthood.
- This study linked thymus removal to a nearly threefold higher risk of death.
Once considered expendable, doctors and researchers are now seeing wat the thymus can really do. A new Harvard-led study suggests the walnut-sized organ in the chest actually plays a vital role in immune health as humans age, particularly in cancer prevention.
The study data showed patients who had their thymus removed had a nearly threefold higher risk of death from a variety of causes, including a twofold higher risk of cancer and a more modest increase in autoimmune diseases.
Most active in churning out T-cells during early childhood, the thymus begins to atrophy into fatty tissue around puberty. That’s why, for many decades, scientists assumed it served a limited purpose in adulthood. Yet in recent years, scientists started to suspect that the thymus continues to make T-cells that contribute to the diversity of the body’s overall T-cell population.
For the study, published in the New England Journal of Medicine, researchers mined data from 1,146 adult patients who had undergone thymus removal, alongside demographically matched control patients who had undergone similar surgeries but kept their thymus. The results showed the rate of death was higher in the thymectomy group than in the general U.S. population—9 percent vs. 5.2 percent—as was death due to cancer—2.3 percent vs. 1.5 percent.
In a subgroup of patients in whom T-cell production was measured, those who had had their thymus removed had less new production of T-cells, including both helper and cytotoxic T-cells. Those patients also had higher levels of pro-inflammatory cytokines, which are small signaling proteins associated with autoimmunity and cancer, in their blood.
“The magnitude of death and cancer in patients who had undergone thymectomy was the biggest surprise for me,” said first author Kameron Kooshesh, now an internal medicine resident at Massachusetts General Hospital. “The more we dug, the more we found: The results suggested to us that the lack of a thymus appears to perturb basic aspects of immune function.”