Rare Immune Cells in People Over 100 May Help Explain Their Exceptional Longevity

Scientists studying people who live to 100 and beyond have identified a rare type of immune cell that may provide important clues about how some individuals remain healthy into extreme old age. The cells, known as CD4 cytotoxic T lymphocytes, or CD4 CTLs, appear to become more prominent in some very elderly people and may help the body respond to abnormal cells, including cells associated with cancer.

The findings come from researchers at the University of Osaka in Japan, who examined blood samples from adults across different age groups. Their research, published in Cell Reports, adds to growing scientific interest in the relationship between the immune system, cancer and exceptional longevity.

The study does not establish that these immune cells are the reason some people live longer, nor does it show that they can prevent cancer. Instead, the researchers say the results point to a potentially important feature of the ageing immune system that deserves further investigation.

What are CD4 CTL immune cells?

CD4 T cells are a major component of the body's adaptive immune system. They are commonly associated with coordinating immune responses, helping other immune cells identify and respond to threats. CD4 CTLs are a less common subset that can directly attack certain target cells.

The Osaka researchers were particularly interested in these cells because previous research had suggested that they can recognise and destroy some abnormal or tumour-related cells. Their latest work looked at whether the cells might also be associated with the unusual immune profiles found in people who reach very advanced ages.

The researchers analysed blood samples from 28 individuals divided into three groups: people aged 70 to 99, those aged 100 to 109, and people aged 110 or older. The proportion of CD4 CTLs appeared to increase with age, with the researchers identifying a particularly notable presence among some centenarians and supercentenarians.

Supercentenarians are people who reach at least 110 years old. They are extremely rare, making them an important group for researchers investigating the biological characteristics associated with exceptional survival.

Immune cells may adapt as people age

One of the most interesting aspects of the research is the evidence that CD4 CTLs can undergo what scientists call clonal expansion.

When the immune system encounters a particular threat, immune cells that recognise it can multiply rapidly. This creates a larger population of cells capable of responding to the same target. The process is known as clonal expansion.

The researchers found evidence that this process may be particularly pronounced in some exceptionally old individuals. In one centenarian included in the study, a single clone accounted for more than half of that person's CD4 CTLs.

This suggests that the immune system may not simply deteriorate steadily with age. Instead, parts of it may adapt to the challenges that accumulate over a lifetime.

Ageing is accompanied by numerous biological changes. Damaged cells, senescent cells and abnormal cells become more common, while the immune system itself undergoes significant changes. The ability to maintain effective surveillance against potentially dangerous cells could therefore be an important factor in healthy ageing.

Possible connection with cancer

The researchers also investigated whether the expanded immune cell populations might recognise molecules associated with cancer.

They compared structures found on the surface of the most abundant CD4 CTL clones with information contained in a public database. Some of the molecular matches were associated with people who had lung, breast or liver cancers.

This does not mean the centenarians in the study had those cancers. None of the participants had been diagnosed with the cancers identified through the database comparison.

Instead, the findings raise the possibility that some of the immune cells had developed in response to cancer-related targets or abnormal cellular activity before a detectable cancer had emerged.

This is one of the most significant implications of the research. The immune system is constantly monitoring the body for signs of infection and abnormal cellular behaviour. If certain immune cells are particularly effective at identifying and eliminating potentially dangerous cells, they could theoretically help reduce the likelihood that small abnormalities develop into established disease.

However, that remains a hypothesis rather than a demonstrated explanation for exceptional longevity.

The findings need to be treated cautiously

Although the study offers an intriguing insight into the biology of ageing, it is relatively small. Only 28 people were included, and the participants cannot necessarily be considered representative of everyone who reaches old age.

The research also cannot establish cause and effect. It is possible that the unusual CD4 CTL profiles contribute to healthy ageing. It is also possible that living to an exceptionally advanced age creates biological conditions that encourage the expansion of these cells.

Another important point is that the relationship between the immune system and cancer is extremely complex. Cancer can develop through many different biological pathways, and immune surveillance is only one part of the picture.

The researchers themselves caution against interpreting the findings as proof that having more CD4 CTLs prevents cancer or directly causes people to live longer.

Interestingly, the highest proportion of these cells was not found exclusively in the oldest group. One participant under the age of 100 had the greatest proportion of CD4 CTLs in the study. This indicates that the phenomenon may not be unique to centenarians or supercentenarians.

What the research could mean for healthy ageing

The study nevertheless contributes to a wider scientific effort to understand why some people remain comparatively healthy despite reaching very advanced ages.

Rather than viewing ageing solely as a process of immune decline, researchers are increasingly examining how the immune system changes and adapts over time. Certain immune functions may weaken, while others could become more specialised or expand in response to repeated exposure to infections, abnormal cells and other biological stresses.

Understanding these changes could eventually help scientists identify biological markers associated with healthy ageing. It could also potentially inform future research into treatments designed to strengthen immune surveillance.

Any medical applications are still a long way off. Researchers would first need to establish precisely what the CD4 CTLs recognise, why particular clones expand, whether their activity genuinely protects against cancer and whether similar immune patterns occur in larger populations.

Future studies involving more participants and longer periods of observation could help answer these questions. Researchers may also investigate whether the same immune characteristics are found in people who remain cancer-free into their 90s and 100s.

A possible clue, not a longevity cure

The Osaka study provides another piece of evidence that exceptional ageing may be linked to unusual patterns of immune function. The discovery of expanded CD4 CTL populations in some centenarians is particularly interesting because these cells appear capable of responding to abnormal targets.

But the research should not be interpreted as evidence that a particular immune cell can guarantee a longer life or prevent cancer.

Longevity is influenced by a combination of genetics, environment, lifestyle, disease history and chance. The immune system is one part of that complicated picture.

For now, the most important finding is that the immune systems of people who live beyond 100 may retain, and in some respects strengthen, specialised responses to biological threats. Further research could reveal whether these cells are merely a marker of exceptional ageing or whether they actively contribute to the ability of some people to remain healthy for so long.

Source

The Independent, August 20, 2026 and research from scientists at the University of Osaka published in the journal Cell Reports.

Disclaimer

This article is for informational purposes only and does not constitute medical advice. The research discussed is preliminary and does not prove that CD4 CTLs prevent cancer, cause exceptional longevity or provide a treatment for cancer. Anyone seeking advice about cancer prevention, immune health or ageing should consult a qualified healthcare professional.