Mutation in region III of the DNA polymerase gene conferring foscarnet resistance in cytomegalovirus isolates from 3 subjects receiving prolonged antiviral therapy.

Three human immunodeficiency virus-infected subjects with progressive cytomegalovirus (CMV) retinitis despite prolonged antiviral therapy had buffy coat CMV isolates that were resistant to both ganciclovir and foscarnet. Genetic analysis of the resistant isolates showed that each contained a well-known ganciclovir resistance mutation in the viral UL97 phosphotransferase sequence, as well as a mutation (Ala to Val at codon 809, V809) in conserved region III of the DNA polymerase (Pol) sequence. A segment of the Pol sequence from one of the clinical isolates was transferred to CMV laboratory strain AD169 by homologous recombination. The recombinant virus containing V809 showed 6.3-fold increased foscarnet resistance and 2.6-fold increased ganciclovir resistance. Occurrence of the V809 mutation in 3 unrelated cases suggests that it is a clinically significant viral genetic marker for foscarnet resistance and decreased susceptibility to ganciclovir.

Evolution of mutations conferring multidrug resistance during prophylaxis and therapy for cytomegalovirus disease.

In a human immunodeficiency virus-infected subject, cytomegalovirus (CMV) isolated 9 months after the patient began oral ganciclovir prophylaxis was resistant to ganciclovir and cidofovir and contained mutations in both UL97 and Pol coding regions. At 1 year, retinitis developed, which progressed despite intravenous ganciclovir followed by foscarnet and then cidofovir. A subsequent buffy coat virus isolate was resistant to all three drugs and contained new mutations in UL97 and Pol. By individually transferring the observed mutations to laboratory strain AD169, it was shown that a mutation at codon 603 of UL97 conferred resistance to ganciclovir, a mutation at codon 412 of Pol conferred resistance to both ganciclovir and cidofovir, and a mutation at codon 802 of Pol conferred resistance to ganciclovir and foscarnet. This case illustrates the development of multidrug resistance during prolonged exposure to antiviral therapy for CMV and cross-resistance arising from point mutations in the CMV Pol gene.

Analysis of interstrain variation in a putative immediate-early region of human herpesvirus 6 DNA and definition of variant-specific sequences.

Sequences of a 2.6- to 2.9-kb open reading frame in a putative immediate-early region of the human herpesvirus 6 (HHV6) genome were determined and compared in three reference and six local isolates of HHV6. The sequences segregated into two variant groups (A and B) having only 75% nucleotide homology and 62% peptide homology, in part because of deletions in the variant A strains. Among the variant B isolates, further sequence grouping was evident; two clinical isolates segregated with reference strain Z29 into a cluster that had 96.6% nucleotide homology and 92.6% peptide homology when compared to a second variant B cluster of four isolates. Within each cluster of variant B isolates, nucleotide homology was 99.4% or more. Two pairs of isolates had identical sequences. The marked divergence of variants A and B permitted the design of variant-specific oligonucleotide primers that could detect in a single polymerase chain reaction the presence of either or both variant A and B HHV6 DNA. Variation in this gene region of HHV6 is more extensive than in the envelope glycoprotein (gB and gH) coding regions and could be related to known biological differences between variant groups.

Homology of the envelope glycoprotein B of human herpesvirus-6 and cytomegalovirus.

The envelope glycoprotein B (gB) coding sequences of two strains of human herpesvirus-6 (HHV6 GS and Z29) were determined by sequencing a 2.5-kb open reading frame adjacent to the DNA polymerase sequence. The deduced primary translation product is 830 amino acids in length and is 96% conserved between the two divergent strains with no localized hypervariability noted. It contains the expected signal and transmembrane sequence motifs as well as a putative site of protease cleavage. There was 39% amino acid identity with the gB of human cytomegalovirus (CMV, strain AD169). HHV6-CMV gB peptide homology was evident through the entire sequence, but was especially strong in the amino-terminal portion of CMV gp55, which contains linear and conformational epitopes recognized by CMV-neutralizing antibodies. All 10 cysteine residues of HHV6 gB match corresponding residues of CMV gB. Sequence data suggest strong structural similarity and possible immunologic cross-reactivity of gB from the two viruses.