Suspected chromosomally integrated human herpes virus 6 in hematopoietic stem cell transplantation

Background and aims: We report a case of a 27-year-old male affected by acute myeloid leukaemia MLL-PTD positive. After autologous stem cell transplantation, he was monitored based on cytomegalovirus, Epstein-Barr virus and human herpes virus 6 (HHV-6) DNA quantification in blood. Relapse occurred one year after transplantation; then the patient underwent to allogenic bone marrow transplantation using genotypically HLA-identical donor (sister). HHV-6 DNAemia was positive and persistently elevated, either after autologous either after allogenic transplant suggesting the occurrence of HHV-6 chromosomally integration. The work aim is to prove the occurrence of chromosomally integrated-HHV-6 (ci-HHV-6).
Materials and Methods: HHV-6 DNA extraction was performed by automated extractor and DNA was amplified-quantified by Real Time polymerase chain reaction. Species identification was performed by sequencing HHV6-U100 glycoprotein using automated sequencer and sequencing products were analysed using the Blast program.
Results: After autologous transplantation HHV6-DNAemia was 5.4 log copies/mL setting to 3.9 log copies/mL for a long period post allogenic transplantation. The patient’s hair follicles were tested for HHV- 6 DNA having positive results. Sequences of both strains of HHV6 extracts from blood and hair follicles resulted species B. HHV6 viral load decreased significantly after Lymphocyte Infusion by ci-HHV6 negative donor (sister), having steady viral load during the following six months of monitoring. One year later, patient is in complete haematological remission.
Conclusions: Detection of HHV-6 in hair follicles and HHV-6 DNAemia persistently elevated before allogenic transplant, confirm the occurrence of ci-HHV-6. The observed important decreasing viral load is potentially due to the successful engraftment of ci-HHV-6-negative donor marrow after allogeneic transplant.