Replicative history of CD4⁺ T-cell populations defined by the expression of CD45RA, CCR7, and CD25. CD4⁺ T cells were separated into conventional CD4⁺CD25^– (1), CD4⁺CD25^low (2), and regulatory CD4⁺CD25^highT cells (3) defined by their expression of CD25. These subsets were further sorted according to their CD45RA and CCR7 expression in 3 subsets each, namely T_naive (CD45RA⁺CCR7⁺), T_CM (CD45RA^–CCR7⁺), and T_EM cells (CD45RA^–CCR7^–). These CD4⁺ T-cell subsets were then assessed for TREC content. Genomic DNA of sorted subsets was isolated, and the number of TRECs was determined by quantitative real-time PCR. Data are shown as the mean values obtained for 2 independent donors and 2 MM patients. Error bars represent SD. (A) Conventional CD4⁺CD25^–, (B) CD4⁺CD25^low, and (C) CD4⁺CD25^highT cells from 2 healthy individuals. (D) Conventional CD4⁺CD25^–, (E) CD4⁺CD25^low, and (F) CD4⁺CD25^highT cells from 2 MM patients.