The Secret to Living Past 110? An Army of Cancer-Killing Immune Cells

Posted on 25 August, 2026 by Mehrdad Fathi

What if the key to extreme longevity isn’t slowing down ageing, but an immune system that keeps adapting? A study published in Cell Reports reveals that supercentenarians — people aged 110 and older — carry unusually large populations of a rare type of cancer-killing immune cell, offering a striking new perspective on how some individuals reach extraordinary ages while fending off heart disease, dementia and cancer.

Rethinking Immune Ageing

For decades, research on the ageing immune system has told a story of decline: weaker responses to infection, slower recovery, reduced surveillance against malignant cells. The new study, led by researchers at the University of Osaka in Japan, challenges that narrative.

“Most of immune ageing research has focused on decline,” says co-author Kosuke Hashimoto. “Our study suggests that even at extreme old age, the immune system may still selectively adapt.”

The cells at the centre of this story are CD4 cytotoxic T lymphocytes (CD4 CTLs) — killer T cells that typically make up less than 5% of the body’s total T cell population. Although less studied than other T cell types, they are commonly detected during viral infections, and growing evidence shows they can kill cancer cells, including lung cancer and melanoma cells.

A Rare Study of Rare Individuals

Supercentenarians are exceptionally difficult to study for a simple reason: very few people live that long. In Japan, only about 150 people are aged 110 or older. The team enrolled 28 participants across three groups: eight individuals aged 70–90, ten centenarians (aged 100–109) and ten supercentenarians.

The results showed a clear age-related pattern. CD4 CTLs made up a normal 4% of total T cells in the youngest group — but around 10% in centenarians and around 18% in supercentenarians. This suggests the immune adaptation begins at around age 100 and intensifies with extreme age.

Cloned Armies Responding to a Persistent Trigger

The most intriguing finding lies in how these cells multiply. Every T cell carries a unique receptor that recognises a specific antigen; when a killer T cell encounters its target, it clones itself into an identical army. In the centenarians and supercentenarians, single clonal lines dominated the CD4 CTL population — in one centenarian, 53.8% of these cells were identical to each other. Their immune systems were clearly mobilising against something specific and persistent.

What that something is remains an open question. Because the cells were sampled from blood, the researchers could not observe which tissues they enter or what they do there. But when the team compared the receptor sequences of the most common cell lines against a database of CD4 receptors, around 30 sequences matched those from people with cancer — most frequently lung cancer — even though none of the study participants had ever experienced cancer in their lives.

A Barrier to Tumour Growth — or Something Else?

The findings have prompted cautious excitement among immunologists. Ana Caetano Faria of the Federal University of Minas Gerais in Brazil, who is co-leading a parallel study of Brazilian centenarians, suggests these cells might proliferate later in life as an adaptive response to ageing, potentially acting as “a barrier to tumour growth in centenarians.”

Others urge restraint. Shawn Demehri of Massachusetts General Hospital notes that the clonal expansion demonstrates a response to a specific antigen — not necessarily to cancer cells — and that detection bias may be at play, since CD4 CTL receptors have mostly been studied in cancer contexts. Alejandro López-Soto of the University of Oviedo in Spain captures the field’s consensus: the cancer-protection hypothesis is “biologically plausible and exciting, but remains speculative until their antigens are identified and direct tumour killing is demonstrated.”

Why This Matters

If these cells are confirmed to suppress tumours, the implications extend well beyond a small group of remarkable individuals. Understanding how the immune system selectively strengthens its anti-cancer defences at extreme ages could inform immunotherapy design, cancer prevention strategies and healthy-ageing interventions for the broader population. Hashimoto’s team is now analysing single-cell data sets to trace where these cells travel in the body — the next step toward understanding what they actually do.

The immune systems of the world’s longest-lived people may be quietly teaching us how to help everyone stay healthier, longer.

Source: Adapted from Nature news, doi: https://doi.org/10.1038/d41586-026-02587-1

References:

1. Hashimoto, K. et al. Cell Rep. https://doi.org/10.1016/j.celrep.2026.117728 (2026).

2. Hashimoto, K. et al. Proc. Natl Acad. Sci. USA 116, 24242–24251 (2019).