If asked to describe where one might find the Thymus, most people would not have any idea where to begin. This walnut-sized organ is in fact located almost completely centrally in the body, between the lungs and in front of the heart. Thought to be largely inactive in adulthood, surgeons have not shied away from removing the Thymus during unrelated operations or recommending its removal for a variety of conditions. New Harvard-led research is, however, saying it plays a vital role in immune health as we age, particularly in cancer prevention, and we have been underestimating this organ at our peril for far too long.
Described as being “the fastest ageing organ”, doctors have traditionally recognised the Thymus’ role in early development calling it a bustling boot camp during early adolescence, where immature T cells are educated and fine-tuned to recognize foreign invaders while maintaining tolerance to the body’s own tissues. They have, however, also believed that somewhere around puberty it seems to atrophy into fatty tissue.
Studies in the past have revealed that the removal of the thymus in a procedure called a thymectomy can be helpful for people grappling with autoimmune disorders, particularly myasthenia gravis, in which the immune system turns traitor and attacks the neuromuscular junctions. In such cases, thymectomy can help alleviate symptoms and potentially slow down the progression of the disease. Additionally, the Thymus’ location can sometimes be directly responsible for its removal. For instance, when repairing congenital heart defects or accessing the heart’s vital chambers, surgeons may encounter the thymus along the path. While not their primary target, its presence can necessitate careful removal to access the heart.
More recently, some researchers had begun to suspect that the Thymus may be more than fatty tissue and may play a role in our health as we age, by continuing to make T-cells that contribute to the diversity of the body’s overall T-cell population, but young doctors were still being taught that in adults it was vestigial and could be removed. This contradiction intrigued study author Kameron Kooshesh 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.
Working alongside David Scadden (The Gerald and Darlene Jordan Professor of Medicine and professor in the Department of Stem Cell and Regenerative Biology, who led the study), Brody Foy (a biostatistician who helped direct the team’s statistical queries around the epidemiology of thymectomy patients), Karin Gustafsson (an expert in T-cell biology) and others, Kooshesh uncovered a staggering finding.
In looking at patients with more than five years of follow-up, the team found that those who had received a thyrectomy were almost twice as likely to have died (9% vs 5.2%) and that death by cancer was particularly notable (2.3% vs 1.5%). Those who had undergone the thymus removal also showed less new production of T-cells, both helper and cytotoxic, and had higher levels of pro-inflammatory cytokines, which are the signalling 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,” explained Kooshesh. “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.”
The study now opens up new avenues of research into the prevention and treatment of cancer, and auto-immune diseases, the causes of which have, in many cases, been a mystery.
