Two groups of human herpesvirus 6 identified by sequence analyses of laboratory strains and variants from Hodgkin's lymphoma and bone marrow transplant patients.

Fifteen human herpesvirus 6 (HHV-6) strain variants were analysed by PCR amplifications, restriction enzyme site polymorphism and sequence analyses. Three DNA regions were chosen for study: a fragment of a variable glycoprotein gene (210 bp), the conserved glycoprotein H (gH) gene complete with intergenic sequences (2381 bp) and the 5' intergenic region with the N-terminal coding sequence of gH up to a polymorphic BamHI site (427 bp). Infected cell DNA from five laboratory reference strains including GS, U1102, AJ, Z29 and KF were examined together with DNA from peripheral blood lymphocytes infected with HHV-6 reactivated from blood and/or marrow from five bone marrow transplant (BMT) patients. Separate blood and marrow isolates were obtained from four BMT patients. In addition, HHV-6 sequences were examined directly from one of six Hodgkin's lymphomas and six B cell proliferations which contained HHV-6 DNA as detected by PCR amplification. The results show two groups of very closely related but heterogeneous strains which correlate with previous groupings by antigenic and restriction site differences. These are variant A strains (including laboratory strains GS, U1102 and AJ) and variant B strains (including laboratory strains Z29 and KF, the Hodgkin's lymphoma strain, and the nine BMT patient isolates). Variations between the groups were 4 to 6% in nucleotide sequence and 5 to 8.5% in amino acid sequence. Within each group maximum heterogeneity was observed in different genes. Variant A strains differed by 2.0% in the variable glycoprotein gene sequence whereas variant B strains were identical in this region; conversely, variant B strains differed by 2 to 3% in the gH N-terminal and intergenic sequences whereas variant A strains differed there by less than 0.2%. There was evidence for sequence drift independent of selection: relationships between the groups were shown by analyses of amino acid sequence, coding nucleotide sequence as well as intergenic sequence, and the B variant-specific BamHI site in the gH gene was due to a non-coding nucleotide substitution. There was little evidence for in vivo or in vitro variation: the gH nucleotide sequence from the uncultured lymphoma strain (first variant B gH gene identified) was almost identical to the gH sequence from four BMT isolates, and matched BMT isolates from blood and marrow were identical or with a single nucleotide substitution.(ABSTRACT TRUNCATED AT 400 WORDS)