People who live past 110, known as supercentenarians, carry surprisingly large populations of a rare "killer" immune cell that can destroy tumor cells.
That is the finding from a study published August 19, 2026 in Cell Reports.
It suggests that in the very oldest adults, the immune system is not simply worn out but is still actively adapting.
Researchers at the University of Osaka analyzed blood from 28 Japanese adults split into three age bands.
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Eight were in their 70s to 90s, ten were centenarians aged 100 to 109, and ten were supercentenarians aged 110 or older.
They focused on a normally rare subset of T cells called CD4 cytotoxic T lymphocytes, or CD4 CTLs. Most CD4 cells act as "helpers" that coordinate the immune response.
This unusual subset behaves more like an assassin, patrolling the body to identify and destroy damaged or cancerous cells.
The proportion climbs sharply with age
In the youngest participants, CD4 CTLs made up a median of about 4 percent of all T cells.
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In centenarians the figure rose to 9.6 percent. In supercentenarians it reached 17.6 percent, more than four times the level seen in people in their 70s and 80s.
The cells were not just abundant. They also showed clear signs of clonal expansion, meaning a small number of "successful" cells had copied themselves many times over.
On average, the largest single clone made up 33 percent of a person's CD4 CTLs. In one centenarian, a single clone accounted for about half.
A possible link to cancer defense
To probe what these cells might be fighting, the team compared their T cell receptor sequences with a public database of cancer patients.
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Nearly three dozen matches were found in people with lung, breast, and liver cancers, according to The Scientist.
None of the supercentenarians in the study had been diagnosed with these cancers.
That overlap raises a possibility the researchers stress cautiously.
The expanded CD4 CTLs may be recognizing early signs of malignancy and clearing damaged cells before they can grow into disease.
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It could be one of several reasons this small group survives long past the age when cancer typically becomes a leading cause of death.
The study's limits
The findings are striking but come with real caveats.
The sample was small, just 28 people, and drawn from a single country.
The authors themselves acknowledge this limits how broadly the results can be applied.
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The research also cannot say whether the expansion of CD4 CTLs is a cause of extreme longevity or a consequence of surviving into it.
What this means for the rest of us
No proven method exists to boost CD4 CTLs specifically.
But general habits that support healthy immune aging are well documented.
Regular physical activity, for instance, has been linked to better preservation of CD4 T cell function across the lifespan in a 2026 review in the European Journal of Clinical Investigation.
Broader lifestyle patterns matter as well.
The habits associated with people who reach 100, including daily movement, a mostly plant-forward diet, strong social ties, and consistent sleep, remain the most reliable factors tied to a longer, healthier life.
If you have questions about your own risk of cancer or other diseases of aging, speak with your doctor rather than relying on findings from a small study in an extreme population.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.