Reconstitution of anti-CMV protective immunity by TK⁺ DLI. (A) Patient 12 experienced a CMV reactivation syndrome with high titers of viremia, as detected by quantitative PCR (shaded area). TK⁺ DLI was followed by a rapid expansion of gene-modified cells, as measured by FACS analysis for ΔLNGFR expression, which peaked at 115 cells/μL after 20 days. At this time point nearly all circulating CD3⁺ cells (●) were TK⁺ (▴). Concomitantly, CMV viremia dropped and all clinical signs of CMV disease disappeared. (B) At a time corresponding to the peak of TK⁺ cells in the circulation, PBMCs were harvested (■) and stimulated with irradiated autologous PBMCs pulsed with the CMV-immunodominant pp65_495-503 peptide. For comparison, a sample of preinfusion TK⁺ cells (□) was also stimulated and tested. After 7 days, specific lysis of the 2 effector populations was measured against HLA-A0201⁺ T2 cells pulsed with the pp65_495-503 peptide in a chromium-release assay. No lysis of unpulsed T2 cells was observed.