Proliferation of CMV-specific CD8⁺ T cells in a patient with haploidentical HSCT after B-ALL. A 14-year-old boy with B-ALL (patient 2) and therapy-refractory CMV reactivation after haploidentical allo-HSCT was treated with Streptamer-purified CMV-specific CD8⁺ T cells. He received 5130 cells per kg (in total 200 000 cells) stem cell donor–derived CMV HLA-A0201/pp65-peptide–specific T cells 5 months after allo-HSCT. Patient-derived PBMCs were analyzed at different time points before and after adoptive transfer. (A) CMV HLA-A0201/pp65-peptide–specific T cells were visualized with MHC multimers, and selected time points are demonstrated. The frequencies among CD3⁺ T cells are indicated. (B) Comparison of CMV-specific T-cell kinetics and CMV detection. The frequency of CMV HLA-A0201/pp65-peptide–specific cells among CD3⁺ T cells is indicated (circles). CMV load was measured in the peripheral blood via quantitative PCR (filled gray). (C) Tracking of donor-derived CMV HLA-A0201/pp65–specific CD8⁺ T cells via CDR3 sequencing. Amplified donor and patient PCR products (8 and 9 weeks) of an identified CDR3 region are shown (top). Detected PCR products were subsequently sequenced. The isolated sequences of the CDR3 region from patient and donor are shown in detail (bottom; blue: V segment; green: D segment; red: J segment).