HHV-6 reactivation and associated sequelae after hematopoietic cell transplantation.

Human herpesvirus 6 (HHV-6) reactivation has been associated with acute graft-versus-host-disease (aGVHD), cytomegalovirus reactivation, and mortality after allogeneic hematopoietic cell transplantation (HCT), but previous studies have yielded inconsistent results. We performed a large prospective study of allogeneic HCT recipients in order to more definitively define the relationships between HHV-6 and these important outcomes. Plasma specimens were collected prospectively from 315 allogeneic HCT recipients and tested for HHV-6 DNA at baseline and twice weekly for 12 weeks. Cox proportional hazards models were used to evaluate the time-dependent associations between HHV-6 reactivation and the targeted outcomes. HHV-6 was detected in 111 of 315 patients (35%) at a median of 20 days after HCT. HHV-6 reactivation was associated with subsequent cytomegalovirus reactivation (adjusted hazard ratio [aHR], 1.9; 95% confidence interval [CI], 1.3-2.8; P = .002). High-level HHV-6 (>1,000 HHV-6 DNA copies/mL) was associated with subsequent grades II to IV aGVHD (aHR, 2.4; 95% CI, 1.60-3.6; P < .001). High-level HHV-6 reactivation was also associated with nonrelapse mortality (aHR, 2.7; 95% CI, 1.2-6.3; P = .02). HHV-6 reactivation was independently and quantitatively associated with increased risk of subsequent cytomegalovirus reactivation, aGVHD, and mortality after HCT. A randomized antiviral trial is warranted to establish causality between HHV-6 and these endpoints and to determine if reducing HHV-6 reactivation will improve outcome after HCT.