Immune reconstitution and viral infections after stem cell transplantation

Viral infections are important in SCT patients. Different viruses are challenges for the physician at different times after transplantation due to changing defects in the immune status of the patients. Infections with respiratory viruses in particular respiratory syncytial virus are important early after transplant but the knowledge about epidemiology, risk factors, and treatment is still limited. Parainfluenza and influenza viruses can also cause severe and sometimes fatal infections after SCT. During the acute GVHD phase, CMV has been the most important viral infection during the entire history of allogeneic SCT. Recent developments with antiviral prophylaxis, new techniques for early diagnosis, and the strategy of preemptive antiviral therapy has reduced its importance in matched sibling transplants. Instead CMV disease occurring late after SCT has become an increasingly important problem in patients who have undergone unrelated or mis-matched SCT due to poor development of T-cell function. Other herpesviruses such as human herpesvirus type 6 and EBV are also becoming important causes of severe complications after unrelated and mismatched SCT. For this group of patients new innovative preventive and therapeutic strategies are needed.