Since we have previously shown that dexamethasone (Dex) enhances the proportion of murine Treg cells, we tested the effect of IL-7, a promoter of T cell survival, together with Dex on human CD4CD25 Treg cells in an in vitro setting. The results showed that IL-7 in concert with Dex markedly augmented the generation of CD4CD25 T cells. To discern the origin of the induced CD4CD25 T cells, MACS-purified CD4CD25, and CD4CD25 cells were cultured in the presence of Dex and/or IL-7 for 4 days. Although two thirds of CD4CD25 T cells became CD4 CD25 T cells, they had no suppressive activity. In contrast, the original CD4CD25 T cells maintained suppressive activity after Dex/IL-7 treatment, however, there was not a significant expansion in their cell number. Dex and IL-7 did not induce additional Treg cells, but additively induced the expression of the activation marker CD25 by CD4CD25 T cells. This combination may provide a novel means of priming CD4 T cells to respond to IL-2 and may prove useful in up-regulation of normal immune responses in immune deficient diseases. © 2005 Elsevier Inc. All rights reserved.