mRNA, a cousin of DNA, encodes instructions for building proteins. Scientists have pinpointed three mRNA molecules that could help counter immune aging. (Image credit: KATERYNA KON/SCIENCE PHOTO LIBRARY via Getty Images)

A new mRNA treatment rejuvenates key immune cells in the body, which could help them fight off infections and cancer, a mouse study suggests.

T cells help train other immune cells to fight off disease. But as the body ages, the activity of these T cells declines, and they become less responsive to threats. Additionally, the thymus gland — where T cells mature — begins to shrink with age. These impacts of aging may explain why vaccines and immune-boosting cancer therapies don't work as well in older adults as they do in younger adults, Nature News reported.

Among other roles, mRNA relays instructions from DNA to cells' protein-building organelles, serving as a template from which new proteins are made. The team behind the new study studied T cells in aging mice, pinpointing three proteins that seemed to decline with age, contributing to the aging process. They then generated mRNA for those three proteins, encased them in tiny bubbles of fat, and injected them into middle-aged mice, which were around 16 months old.

These mRNA-filled bubbles traveled through the bloodstream to the liver, where they accumulated. Most T cells are in the bloodstream, and because the liver filters blood, T cells were likely cycled through the liver, where they were exposed to this waiting supply of mRNA.

Mice treated with the mRNA made more T cells than mice that were left untreated. The treated mice's T cells also responded better to vaccination and to cancer immunotherapy, the experiments suggested.

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The benefits of the treatment, which was given to the mice twice a week, disappeared quickly when the scientists paused the injections. That's not necessarily surprising, given that mRNA molecules degrade very quickly in the body, whether they were originally made by cells or produced in a lab.

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"The transient nature of mRNA delivery necessitates repeated administrations to sustain therapeutic effects," the study authors wrote in the paper. That said, "the long-term consequences of continuous exposure to these factors, especially in aged individuals should be analysed through extensive long-term safety studies."