- Human herpesvirus 6 (HHV-6) is a helper virus for adeno-associated virus type 2 (AAV-2) and the AAV-2 rep gene homologue in HHV-6 can mediate AAV-2 DNA replication and regulate gene expression. Thomson, B.J., Weindler, F.W., Gray, D., Schwaab, V., Heilbronn, R. Virology (1994)