USC Researchers Link Thymulin Hormone to Inflammation and Cancer Immunity

Deep beneath the breastbone and just in front of the heart lies an organ that humans have spent centuries overlooking, misunderstanding, or surgically discarding. The thymus, an upper chest gland named by ancient Greeks who believed it housed the human soul, shrinks steadily as people age. Long dismissed as a disposable relic of childhood, the organ is now driving a wave of biotechnology investment and clinical research aimed at extending human healthspan.

Recent scientific breakthroughs have linked the health of this disappearing organ to everything from cancer immunotherapy response to overall mortality risk. Yet researchers are still untangling whether a shrinking thymus simply marks the passage of time or actively drives the bodily decay associated with growing old.

How Thymulin Regulates Inflammation and Cancer Immunity

Scientists at the Keck School of Medicine of USC have identified a previously unknown biological mechanism connecting the thymus to chronic low-level inflammation known as inflammaging. As the body ages, levels of a hormone called thymulin, which is produced by the thymus, naturally decline. That drop correlates directly with rising systemic inflammation.

To test whether restoring the hormone could reverse age-related damage, researchers paired older mice with younger mice to share a blood supply. This experimental pairing lowered inflammation in the older animals. When investigators artificially increased thymulin levels in older mice with cancer, the treatment enhanced immune responses against tumors and improved survival rates.

The hormone treatment also improved the effectiveness of anti-PD-1/PD-L1 therapy, a form of immunotherapy that helps immune cells recognize and attack tumors. Lead author Dr. Fumito Ito noted that the work offers the first evidence that a substance naturally produced by the thymus declines with age and can reverse age-related inflammation. However, experts emphasize that these findings remain confined to preclinical animal models and do not prove that thymulin prevents or treats cancer in humans.

Investment Surge Follows Startling Clinical Data on Thymus Health

The renewed scientific interest stems from a string of stark epidemiological discoveries. A 2023 study revealed that individuals who underwent surgical removal of the thymus were nearly three times more likely to die and twice as likely to develop cancer within five years compared to people who did not have their thymus removed. Jennifer Cowan, an immunologist at University College London, called the data very striking enough to make patients reconsider elective removal of the organ.

Additional momentum arrived in March, when Harvard Medical School researchers published a study in Nature utilizing artificial intelligence to analyze thousands of computed tomography scans. They discovered that adults possessing a healthy-appearing thymus lived longer and experienced lower rates of cardiovascular disease and cancer. A separate study published in the same journal edition indicated that thymic health may influence how cancer patients respond to immunotherapy.

Venture capitalists and pharmaceutical companies are taking notice of the data. In January, a Basel, Switzerland-based biotech firm called TECregen raised 10 million Swiss francs (US$12.4 million) to develop therapies aimed at regenerating the thymus to slow aging and prevent cancer. Last October, a Cambridge, Massachusetts-based startup named Zag Bio launched with $80 million in funding dedicated to thymus research.

Separating Biological Correlation from Direct Causation

Despite the commercial rush and striking statistical correlations, leading biologists urge caution against treating the thymus as a simple fountain of youth. The organ undergoes a natural lifelong shrinking process known as involution, during which functional tissue is gradually replaced by fat and connective tissue. By age 40, the thymus produces roughly one-quarter of the T cells it generated at age 8. By age 65, that output drops to just 10 percent.

Paola Bonfanti, a professor of epithelial cell biology and regenerative medicine at University College London’s Institute of Immunity and Transplantation, notes that the causal relationship remains unproven.

Bonfanti points out that healthier individuals may simply possess a greater natural capacity to preserve thymic tissue as they age, rather than a larger thymus being the direct cause of their superior health. Marcel van den Brink, chief physician and president of City of Hope in Duarte, California, who has studied the thymus since 1996, recalls when peers viewed his research focus as a waste of time. Today, prominent medical centers and biotech ventures are actively launching programs to harness the organ’s regenerative potential.

While researchers continue investigating whether restoring thymulin or regenerating thymic tissue can safely extend human lifespan, scientists emphasize that immune aging is driven by multiple factors, including bone marrow degradation and lymph node wear. Preserving thymic function offers a promising avenue for healthier immune aging, but researchers agree it remains far from a guaranteed path to longevity.