In the bone marrow, as in a barracks, there is a constant roll call. Rookie T cells wait for their first assignment, and for a while they all look alike. But with age, soldiers with a special mark on their uniform start to appear among them: the protein annexin A1. This mark is not a decoration but a brake shoe that keeps the cell from charging into battle.

Researchers peered into the bone marrow of 15 healthy donors aged 3 to 91 and watched how the makeup of this barracks changes. The main age-related shift is a shrinking share of naive CD8+ T cells, those very rookies. But among those that remain, more and more carry ANXA1. These cells keep their naive appearance, yet inside they are no longer fighters: their senescence markers are elevated, their activation and proliferation are reduced, and instead of a battle cry they release pro-inflammatory signals that poison those around them.

To understand how this brake shoe works, the scientists turned to mice. In mice with a knockout of the Anxa1 gene, T cells activated more strongly, produced more interferon-gamma and destroyed melanoma cells more effectively. And when old mice received monthly transplants of CD8+ naive T cells without ANXA1, those cells selectively eliminated senescent cells throughout the body. The result: better physical performance, a rejuvenated immune profile in the bone marrow, and a median lifespan extended by more than 30 weeks.

The story comes full circle: the roll call in the barracks can become stricter if you strip the brake shoes off the uniforms. T cells without ANXA1 are not just young cells, but cells that have been given back the ability to restore order. Perhaps in the future, instead of cell transplants, drugs that block ANXA1 will appear, and then the body's own immune system will be able to clear out senescent cells on its own.

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