To investigate whether FOXP3 can be expressed by any T cell subset or if expression is restricted to a distinct lineage, FOXP3 mRNA expression was analyzed in freshly isolated T cells such as CD25-depleted CD4+ cells, CD45RA+ naive or CD45RO+ memory T cells (Figure 1A), as well as T cells driven in vitro toward Th1, Th2, or iTreg phenotypes (Figure 1B; phenotype on Figure S1).