Expansion of CMV-specific CD8⁺ T cells after low-dose T-cell transfer in a SCID patient. A 10-month-old boy with SCID syndrome and generalized CMV disease (patient 1) had been reconstituted with PBSCs from the father. Fourteen days after allo-HSCT, 30 000 donor-derived CMV HLA-A0201/pp65-peptide–specific CD8⁺ T cells (3750 per kg body weight) were infused. Patient-derived PBMCs were analyzed at different time points before and after adoptive transfer. (A) Visualization of CMV HLA-A0201/pp65-peptide–specific T cells using MHC multimers. The frequencies among CD3⁺ T cells are indicated. Additionally, the kinetics of endogenously selected CMV HLA-A0201/IE-1-peptide–specific CD8⁺ T cells of respective time points are illustrated (n.p., not performed). (B) Comparison of CMV-specific T-cell kinetics and CMV detection. The absolute numbers of CMV HLA-A0201/pp65-peptide–specific T cells (circles) are indicated. 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. Amplified donor and patient PCR products of an identified CDR3 region are shown (left). In control PBMCs, no product amplification was detectable. Detected PCR products (∼193 bp) were subsequently sequenced. The isolated sequences of the CDR3 region from patient and donor are shown in detail (right; blue: V segment; green: D segment; red: J segment).