Adoptively transferred HyTK-modified T cells. (A-C) Persistence of adoptively transferred HyTK-modified T cells in vivo. PBMCs from each of the 3 patients were obtained at various time points before and after infusion of HyTK-positive T cells and evaluated for the presence of HyTK-transduced cells by quantitative PCR as described in “Patients, materials, and methods.” (D-F) Rapid induction of a HyTK-specific CTL response after adoptive transfer of HyTK-modified T cells. PBMCs from each of the 3 patients were obtained prior to and at various times after infusion and stimulated in vitro with γ-irradiated HyTK-positive donor T cells. Aliquots of these cultures were then evaluated in a chromium release assay for recognition of HyTK-positive target cells (▪) or unmodified controls (□). The killing of HyTK-positive LCLs is shown at an effector-target ratio of 10:1. The arrows indicate the day of the HyTK-positive T-cell infusion.