Development of CMV-specific T effector cells is detected in patients with or without detectable CMV viremia. Total PBLs were collected at the indicated time points after transplantation and were assessed for the presence of IFN-γ–producing effectors in response to CMV, as described in “IFN-γ ELISpot assay.” Cultures incubated with CMV lysates were scored as positive if the number of resulting spots was 3 standard deviations above the control. (A) Representative patient with detectable CMV effectors and CMV viremia. (B) Representative patient with detectable CMV effectors without detectable viremia.