Following HCMV D⁺/R⁺, EBV D^-/R⁺ alloSCT, an immunodominant HCMV-specific donor CD8⁺ T-cell clone expanded and persisted in recipient 02, and a primary EBV-specific CD8⁺ T-cell response developed within 5 months. (A) Clonotypic probing was used to quantify the donor CD8⁺ T-cell clone specific for HCMV pp65_417-426 (clone 2.1) in sequential peripheral blood samples taken from recipient 02 before and after alloSCT. The clone was not detected in recipient 02 prior to transplantation but was detectable at all time points tested following alloSCT. All blood tests for HCMV DNAemia (performed weekly until 5 months after alloSCT) were negative. Because of renal dysfunction cyclosporin was discontinued at 3 months. (B) In the same EBV-seropositive recipient 02, an EBV EBNA3C_880-891 CD8⁺ T-cell clone (clone 2.3) was not present in the donor but following alloSCT was detected in the recipient from 5 months onward.