A promising antibody therapy rejuvenates the immune system of older mice, enhancing their ability to combat infections and reduce inflammation. This treatment could potentially reverse age-related declines in human immunity, addressing susceptibility to disease in older adults. Age-related immune decline is linked to changes in blood stem cells, which become skewed towards producing certain immune cells over others with age. This imbalance weakens immune function and promotes chronic inflammation, contributing to accelerated aging and increased risk of age-related diseases such as heart disease, cancer, and type 2 diabetes.