Chromosomally integrated human herpesvirus-6 in transplant recipients.

Human herpesvirus-6 (HHV-6) is unique among human herpesviruses because of its ability to integrate into chromosomes. This entity, termed chromosomally integrated HHV-6 (CIHHV-6), is often mistaken for active infection and treated unnecessarily. The clinical significance of CIHHV-6 in transplant recipients is not defined. Herein, the clinical characteristics of 7 liver transplant patients with CIHHV-6 from our recent study, together with 14 other published cases of CIHHV-6 were reviewed. Of the 21 cases, CIHHV-6B was reported most commonly among solid organ transplant recipients, while CIHHV-6A was mostly seen in allogeneic hematopoietic stem cell recipients. None of the 21 patients developed clinical symptoms related to HHV-6 after transplantation. However, antiviral therapy was administered to 5 asymptomatic patients mistaken to have HHV-6 infection because of their very high HHV-6 DNA levels, 3 who developed symptomatic cytomegalovirus disease, and 1 with graft-versus-host disease that was mistaken for HHV-6 infection. In patients who received antiviral therapy, there was no apparent decline in HHV-6 DNA load, although change in viral kinetics is difficult to discern in the setting of high baseline HHV-6 DNA load. Clinicians should be aware of this entity of CIHHV-6 so that antiviral therapy can be considered in the proper clinical context.