Following D⁺/R⁺ alloSCT there is delayed emergence of an HCMV-specific CD8⁺ T-cell clone that was not detectable in the donor. (A) The CD8⁺ T-cell clone generated in donor 01, which was specific for HCMV pp65_495-503 (clone 1.1), was detectable in recipient 01 PBMCs at all time points tested following alloSCT. An HCMV IE72_198-207-specific CD8⁺ T-cell clone (clone 1.4) was obtained from recipient 01 at 13 months after alloSCT; this clone was not detected in the donor or in the recipient at 1 and 3 months after alloSCT but was first detected at 5 months following transplantation. In the controls, the pp65⁺and IE72⁺-labeled lanes refer to the positive control cDNA used from clones 1.1 and 1.4, respectively. Weekly blood tests for HCMV DNA performed until cessation of immunosuppression at 15 months were negative. (B) PBMC samples in the same donor-recipient pair were amplified by seminested PCR as described. Clone 1.4 was not detectable in donor PBMCs or allograft, or in recipient samples taken prior to transplantation or at 1 and 3 months after alloSCT but was detected at 5 months.