A significant physiological problem underlying a broad spectrum of diseases is the well-recognized progressive decline in immune competence with age. One widely characterized effect of age on the immune system is thymic involution, which involves a severe architectural disruption as well as reduced T cell development (thymopoiesis) and export of naïve T cells into the periphery. The impacts of this degeneration manifest at many levels including increased opportunistic infections, incidence and burden of cancer and, somewhat paradoxically, autoimmune disease. Clinically, this decline in thymic function results in not only a markedly reduced capacity to respond to overt vaccines, but also very poor recovery from immune insults such as common cancer treatments like chemotherapy and radiotherapy. Therefore, it is clearly of major clinical and social importance to enhance the recovery of immune function as part of the armory against the increasing disease burden linked to age. One of the focuses of the immune reconstitution group is to apply our knowledge of immune boosting therapies to enhance thymic function in the aged. In particular, we are interested in improving recovery following immune-depleting therapies, as well as to enhance the response to new vaccines by rejuvenating thymic function.