[Human herpesvirus-6 associated with hematopoietic stem cell transplantation]

Reactivation of human herpesvirus (HHV)-6B is a relatively common occurrence after allogeneic stem cell transplantation (SCT), and it is associated with the development of various post-transplant complications. HHV-6 encephalitis appears to be a significant, life-threatening complication caused by HHV-6B reactivation. HHV-6 encephalitis typically develops 2-6 weeks after SCT, and the symptoms are characterized by memory loss, seizures, and consciousness loss. Magnetic resonance imaging typically shows limbic encephalitis. Recent large-scale studies and a prospective study showed a similar incidence of HHV-6 encephalitis development, with 7.9-9.9% in cord blood transplant recipients and 0.5-1.2% in bone marrow or peripheral blood stem cell transplant recipients. Epidemiological studies suggest that post-transplant immune reactions such as GVHD, pre-engraftment immune reaction, or engraftment syndrome play important roles in the development of HHV-6 encephalitis. The mortality rate remains high, and even among survivors, many patients are left with serious neurological impairments, such as memory disturbance and seizures. Elucidation of the pathophysiology and establishment of appropriate prophylactic measures are necessary to overcome this serious complication. Besides encephalitis, associations between HHV-6 and various post-transplant complications have been reported, including pneumonitis, gastroenterocolitis, hepatitis, bone marrow suppression, and GVHD. Further investigations are needed to determine the role of HHV-6 in these complications.