Stimulation with APCs that express CD83 enhances proliferation and inhibits apoptosis, permitting continued expansion of MART1-specific T cells beyond 6 weeks. (A) Following 5 rounds of stimulation with MART1 peptide-pulsed APC/A2/CD80, T-cell lines noted to cease expansion were split and subsequently stimulated with either peptide-pulsed APC/A2/CD80 (▪) or peptide-pulsed APC/A2/CD80/CD83 (○). Between the stimulations, IL-2 and IL-15 were added to the culture. Those T cells stimulated by peptide-pulsed APC/A2/CD80/CD83 demonstrated significant antigen-specific expansion, while those stimulated by peptide-pulsed APC/A2/CD80 did not (P = .006). (B) An increase in MART1-specific T-cell proliferation was determined by tetramer staining and BrdU incorporation. This was consistently observed in both donors tested at weeks 7 and 8. (C) Apoptosis was inhibited as determined by Annexin V staining. This was consistently observed in both donors tested at weeks 7 and 8. The proliferating (B) and apoptotic fractions (C) are shown as a percentage of MART1 tetramer-positive cells. Two experiments with different donors were performed.