HHV-6 infection after allogeneic hematopoietic stem cell transplantation: From chromosomal integration to viral co-infections and T-cell reconstitution patterns

Summary Objectives Human herpes virus 6 (HHV-6) can reactivate after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and may be associated with significant clinical manifestations. Methods Case control study of HHV-6 infections after allo-HSCT. Chromosomal integration (ciHHV-6) for viral loads ≥ 5.5-log10 copies/mL was investigated. Viral co-infections, T-cell recovery, risk factors and outcome were compared in HHV-6- and non-HHV-6-infected patients. Antiviral treatment strategies were reviewed. Results Among 366 adult allo-HSCT recipients, 75 HHV-6 infections occurred. Three (4%) recipients were ciHHV-6. HHV-6 infections were associated with CMV ( p = 0.05; sdHR 1.73, CI 0.99–3.02) and/or BKV infections ( p p = 0.34). A slower CD8+ T-cells recovery was observed until 6 months after allo-HSCT in the HHV-6-infected group ( p versus -host disease. The overall probability of survival after allo-HSCT was diminished for active HHV-6-infected patients ( p = 0.0326). Cord blood unitrecipients had a higher risk of developing HHV-6 infection compared to bone marrow recipients ( p = 0.0007; sdHR 3.82, CI 1.76–8.27). Anti-HHV-6 treatment achieved complete response in only 2/3 of the cases. Conclusions In this series of allo-HSCT recipients, 4% were ciHHV-6, active HHV-6 infection was likely associated with CMV and BKV co-reactivations, delayed CD8+ T-cell recovery and poorer outcome.