Allogeneic hematopoietic stem cell transplantation (HSCT) is the only treatment option for several haematological diseases. In spite of substantial progress in this field, viral infections, mainly cytomegalovirus (CMV) and adenovirus (HAdV) in the context of delayed immunoreconstitution remain life threatening complications. Weekly screening of high-risk patients and preemptive virostatic treatment has become a current strategy. Unfortunately, treatment with virostatic drugs is associated with substantial nephro- and myelo-toxicity and of limited effectiveness. Human adenovirus (HAdV) and cytomegalvirus (CMV) disseminated infections are associated with mortality rates of up to 50%-60% despite virostatic treatment.