The weakened immune systems of older people could be rejuvenated using mRNA technology, scientists believe.
They discovered that immune cells lost naturally during ageing could be temporarily replicated, describing this as a “fountain of youth”.
In a study in mice, older animals were able to develop robust immune responses and fight tumours.
Published in the journal Nature, researchers from the German Cancer Research Centre, the Hi-Stem institute and the Broad Institute explained that with age, the immune system loses power: the body's defence against infection weakens, tumour cells run rampant and vaccinations become less effective.
The underlying cause is the shrinking of the thymus gland, a small organ above the heart, which is responsible for the maturing of crucial white blood cells, known as T cells, in young people.
As the thymus diminishes, in turn the number of T cells decreases, the range of markers for illness they can recognise shrinks and immune responses become weaker.
“Much has already been attempted to halt or reverse the age-related involution of the thymus,” said the study's first author Mirco Friedrich. “Unfortunately, without much success so far.”
The researchers identified three particular signals that are crucial for the function of immune cells that weaken as the thymus shrinks.
Using mRNA molecules, or DNA templates, packaged in tiny fat droplets introduced to the liver cells of mice, they found a way to artificially substitute the signals.
It meant older mice were able to produce more T cells and ward off illness. They were also able to better respond to vaccinations and fight tumours.
The researchers deliberately designed the effect of mRNA therapy to be temporary. The mRNA is converted into proteins in the liver for only a short time and the signalling factors produced disappear again after a while. This allows the effect to be finely dosed and minimises the risk of unintended long-term changes.
The team said the results open up great potential for mRNA therapy using the liver as it naturally releases large amounts of proteins into the bloodstream.
“The immune system ages but it does not irreversibly lose its abilities,” said Mr Friedrich. "If we provide it with the missing signals again, it can once more perform amazing feats."
He said the study highlights the potential of modern mRNA technology far beyond known applications in vaccines such as the ones used to tackle Covid.
