As people age, their immune function weakens. Owing to shrinkage of the thymus, where T cells normally mature and diversify, populations of these immune cells become smaller and can’t react to pathogens as quickly. But researchers at MIT and the Broad Institute have now found a way to overcome that decline by temporarily programming cells in the liver to improve T-cell function. 

To create a “factory” for the T-cell-stimulating signals that are normally produced by the thymus, the researchers identified three key factors that usually promote T cells’ maturation and encoded them into mRNA sequences that could be delivered by lipid nanoparticles. When injected into the bloodstream, these particles accumulate in the liver and the mRNA is taken up by the organ’s main cells, hepatocytes, which begin to manufacture the proteins encoded by the mRNA. 

Aged mice that received the treatment showed much larger and more diverse T-cell populations in response to vaccination, and they also responded better to cancer immunotherapy treatments.

If this type of treatment is developed for human use, says Professor Feng Zhang, the senior author of a paper on the work, “hopefully we can help people stay free of disease for a longer span of their life.”