For decades, researchers in Irv Weissman’s group at Stanford University in California have painstakingly tracked the fate of blood stem cells. These replenish the body’s stores of red blood cells (which carry oxygen from the lungs to all parts of the body) and white blood cells (which are key components of the immune system).

In older mice, however, this balance becomes skewed towards the pro-inflammatory innate immune cells. Similar changes have been reported in the blood stem cells of older humans.

If that were the case, then restoring balance to the populations of blood stem cells could also rejuvenate the immune system.

The team tested this by generating antibodies that bind to the blood stem cells that predominantly generate innate immune cells. They then infused these antibodies into older mice, hoping that the immune system would destroy the stem cells bound by the antibodies.

The antibody treatment rejuvenated the immune systems of the treated mice.

They had a stronger reaction to vaccination, and were better able to fend off viral infection, than older mice who had not received the treatment. The treated mice also produced lower levels of proteins associated with inflammation than did old, untreated mice.