IL-21–treated cultures enrich for a population of CD28^hi Ag-specific memory CTLs. Cells were collected 7 days after second stimulation with MART-1 peptide–pulsed autologous DCs and stained for MART-1 tetramer and simultaneously with CD28, CCR7, or CD45RA under the conditions described: PBMCs (untreated control culture), PBMCs + IL-21 (addition of IL-21 at 30 ng/mL during the first stimulation), CD25depl (CD25-depleted PBMCs used as a source of T cells), and CD25depl + IL-21 (combined CD25 depletion and IL-21 treatment). These results are representative of cultures from 3 donors.