As we age our thymus shrinks and is replaced by fatty tissue, losing its essential ability to grow and develop T cells and leaving us susceptible to infections, immune disorders and cancers. Institute scientists have identified a cell that they believe is involved in the curious disappearance of our thymus; and could be the key to regenerating this vital organ. The aging thymus The thymus is a little organ that sits behind the collarbone, but it performs an important job. The thymus is where essential immune cells called T cells are made and trained to go out into the body and fight infections and cancer. A peculiar feature of the thymus is that it disappears as we get older. The thymus starts deteriorating after birth but the process speeds up after puberty and, by age 65, we are basically unable to make new T cells. As the organ shrinks, the T cell areas are replaced with fatty tissue, in a process called involution. As it is replaced by fatty tissue, the thymus can...