Contribution of human herpesvirus 6 (HHV-6) viral load in whole blood and serum to investigate integrated HHV-6 transmission after haematopoietic stem cell transplantation

BackgroundHuman herpesvirus 6 (HHV-6) is susceptible to latency and recurrence. A less-frequent form of HHV-6 persistence is the integration of viral DNA into host chromosomes.ObjectivesTo investigate HHV-6 viral load after haematopoietic stem cell transplantation (HSCT) in whole blood (WB) and serum with regard to integrated HHV-6 transmission diagnosis.Study designHHV-6 DNA quantitation in serum and WB was performed using quantitative polymerase chain reaction for the follow-up of a 16-year-old girl after HSCT. In whole blood, results were expressed as HHV-6 genomic equivalent copies (gec) per milliliter of WB or per million cells.ResultsHHV-6 viral load (undetectable before HSCT) increased up to 3.05 × 107 gec/106 cells. HHV-6 viral load in the donor sample (3.44 × 106 gec/106 cells) was in favor of viral transmission through HSCT. The correlation between viral load in WB and serum was significant (p = 0.0005). Viral load results expressed as gec/106 cells in WB was more reliable than results expressed as gec/ml of whole blood.ConclusionThese findings indicate that HHV-6 may be transmitted during HSCT as integrated virus contained in the graft. This reiterates that in the setting of HSCT, HHV-6 viral load must be correctly interpreted. Using HHV-6 viral load expressed as gec/106 cells may be more suitable for the follow-up of patients with integrated HHV-6.