Memory T cells were resistant to TGFβ induction of FOXP3 expression. (A) Flow cytometric analyses of FOXP3 with 259D on postsorted and day 5-activated CD45RA⁺ or CD45RA⁻ cells treated with and without exogenous TGFβ1. Numbers in each quadrant as in Figure 1. (B) The average percentage and range of FOXP3 induction on day 5-activated CD45RA⁺ cells from 30 different healthy adult donors and CD45RA⁻ cells from 15 of these donors treated with and without exogenous TGFβ1.