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A map of the immune system has revealed how cells that are key to fighting off infections and certain medical conditions change with age. This could help improve vaccines and treatments for age-related diseases, such as cancer and rheumatoid arthritis.

It is well-known that our immune system declines with age, but a detailed picture of how its cells change across a person’s life is lacking, says at the Allen Institute in Seattle, Washington.

Now, Gustafson and her colleagues have analysed genetic molecules called RNAs, some of which encode proteins vital to the immune system, in more than 13 million immune cells. These were collected via blood samples from 49 people aged 25 to 35, and 47 people aged 55 to 65.

The researchers found that the number of copies of RNA molecules inside T-cells – immune cells that target pathogens and cancer – changed the most with age out of all the cells studied, differing substantially between the younger and older participants.

To explore these changes across a wider age span, the researchers also analysed RNAs in T-cells collected from a separate group of 234 people, aged 40 to 90. This revealed that a subset of more than 100 RNAs increased gradually from age 40 to 65, before plateauing.

But from age 65 to 90, the number of a different group of RNAs rapidly decreased, marking a distinct phase of immune system ageing.

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These changes probably influence how effectively T-cells can kill rogue cells and avoid harming healthy ones, which could help explain why cancer and autoimmune conditions such as rheumatoid arthritis become more common as we age, says at the Royal Veterinary College in London.

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A better understanding of all these changes could help researchers develop vaccines that are tailored to the immune systems of people at different ages, says Palmer.

Mapping out immune ageing could also improve cancer therapies for older people who receive genetically engineered T-cells, called CAR T-cells, says Gustafson. This involves taking T-cells from the blood, engineering them to recognise and kill cancer, and then infusing them back into the body.

But all of the participants in both parts of the study were from the US and most were white. Further research is required in a more diverse group of people before these results can be applied in practice, says Palmer.