The immune system ages silently. It does not warn with a specific symptom, but Its wear and tear becomes evident when an infection takes longer to go away, a vaccine protects less or the cancer encounters fewer obstacles..

For years, The great desire of the science of longevity was to stop this deterioration and restore the agility of youth to the defenses.. Now, a team from MIT and the Broad Institute proposes an idea of ​​not directly rejuvenating the immune system, but teach the body to temporarily create a younger version of itself.

The study, published in Nature, focuses on the thymus, a small organ located in front of the heart that acts as a school for T lymphocytes, the key cells to recognize and eliminate threats. In that environment, lymphocytes are trained and selected to form a diverse and effective defense. The problem is that the thymus begins to shut down very early: from early adulthood it progressively shrinks and, by the age of 75, it becomes practically inactive..

“As we age the immune system begins to deteriorate”explains Mirco Friedrich, lead author of the work. The question, he says, was not how to completely reverse that process, but rather how to prolong protection longer.

The team’s response was unconventional. Instead of trying to reactivate the aging thymus or flood the blood with immunological factors—a strategy with risks and side effects—they opted for a biologically engineered solution. “Our approach is rather synthetic,” says Feng Zhang, co-author of the study.

The idea: design the body to imitate, for a time, the signals emitted by a young thymus. The organ chosen to assume this role was the liver. Capable of producing large amounts of proteins even at advanced ages and easily accessible for therapies based on messenger RNA, this organ became a temporary factory for immunological signals.

To achieve this, the researchers designed lipid nanoparticles loaded with mRNA that encodes three essential factors for the survival and maturation of T lymphocytes: DLL1, FLT-3 and IL-7. After injection, these particles accumulate in the liver, where cells begin to produce signals similar to those in the thymus.

The results in aged mice—equivalent to humans in their fifties—were striking.. After several weeks of treatment, T cell populations increased in both number and diversity. The immune system not only appeared younger, but also more flexible and able to respond to a greater variety of threats. This improvement was reflected in the response to vaccines: treated mice doubled the number of specific cytotoxic T lymphocytes after receiving an experimental vaccine, compared to animals of the same age that had not been treated.

The effect was even more evident in the fight against cancer. Combined with an immunotherapy that releases the brakes on the immune system, the strategy allowed the treated mice to live longer and show higher survival rates than those that only received the antitumor drug. None of the three factors worked alone; Only by acting together were they able to temporarily recreate an environment functionally similar to that of a young thymus.

The study does not promise eternal youth or absolute immunity, but it does suggest that some of the decline in the immune system may not be irreversible.. “If we can restore something as essential as the immune system,” Zhang concludes, “we may be able to help people stay disease-free for more of their lives.”. The key is that the effect is temporary and controllable: the messenger RNA degrades quickly, which allows the duration of treatment to be adjusted and minimize long-term risks.

Many questions remain open. The team plans to test this strategy in other animal models and study its impact on other immune cells, such as B lymphocytes. But the idea is already on the table: perhaps, instead of combating aging cell by cell, the future involves teaching the body to recreate, even for a time, the lost signals of its own immunological youth.

By María Jimena Delgado Díaz