A well-functioning immune system is essential for protection against infections. However, with increasing age, the functioning of the immune system diminishes, which is also due to age-related damage in hematopoietic (blood) stem cells. Researchers at the Leibniz Institute on Aging – Fritz Lipmann Institute (FLI) in Jena, Germany, have now discovered how the co-activator of the Hippo signaling pathway, the TAZ protein, can protect hematopoietic stem cells from aging and thus prevent them from loss of function. Moreover, hematopoietic stem cells age very heterogeneously. In addition to old cells, one can also find “youthful” cells when the protective mechanism has worked effectively.