Three schedules of NK-cell infusion will be studied: Basel patients (adult and pediatric) will receive NK-DLI on days +40 and +100 (pre-emptive-late); Frankfurt patients (pediatric) will receive NK-DLI on days +3, +40, and +100 (pre-emptive early). Patients not receiving pre-emptive NK-DLI with loss in donor chimerism or with evidence of minimal residual disease will be offered "therapeutic" NK-DLI.