No abstract

Mutations in both the viral phosphotransferase gene, UL97, and the DNA polymerase gene, UL54, have been shown to confer ganciclovir resistance to cytomegalovirus (CMV). Moreover, UL54 alterations have been associated with in vitro cross-resistance of CMV to cidofovir. To investigate the relative significance of UL97 versus UL54 alterations in conferring antiviral resistance, phenotypic and genotypic characterization of 28 ganciclovir-resistant clinical CMV isolates was undertaken. Isolates were either low-level ganciclovir-resistant, which have ganciclovir ID50 values > or =8 microM and <30 microM and sensitivity to cidofovir, or high-level ganciclovir-resistant, which have ganciclovir ID50 values > or =30 microM and cross-resistance to cidofovir. Low-level ganciclovir-resistant isolates were associated with UL97 alterations and short periods of ganciclovir treatment, while high-level ganciclovir-resistant isolates were associated with both UL97 and polymerase alterations and were cultured after extended ganciclovir therapy.

Specific mutations in the UL97 region of human cytomegalovirus (HCMV) have been found to confer resistance to laboratory-adapted strains subjected to ganciclovir selection. In this study, mutations in the UL97 region of HCMV isolates obtained from patients receiving ganciclovir therapy were examined to determine whether they would confer ganciclovir resistance, and if these mutations could be detected directly in the plasma of AIDS patients with progressive HCMV disease despite ganciclovir treatment. A single nucleotide change within a conserved region of UL97 was found in five resistant isolates, resulting in an amino acid substitution in residue 595: from leucine to phenylalanine in one, and from leucine to serine in four resistant isolates. A sixth resistant isolate demonstrated a single nucleotide change, leading to a threonine to isoleucine substitution in residue 659. The role of the 595 amino acid substitution in conferring ganciclovir resistance was confirmed by marker transfer experiments. In further studies, direct sequencing of HCMV DNA present in plasma obtained from persons with resistant viruses revealed the identical amino acid substitutions in plasma as those present in the cultured viruses. These findings indicate that clinical resistance to ganciclovir can result from specific point mutations in the UL97 gene, and that the emergence of the resistant genotype can be detected directly in patient plasma. (J. Clin. Invest. 1995. 95:257-263.)

To determine the incidence of clinical resistance to intraocular cidofovir injection for treatment of acquired immunodeficiency syndrome (AIDS)related cytomegalovirus (CMV) retinitis, and to identify virologic features associated with cidofovir treatment failure.Patients and Methods: Clinical resistance to intravitreal cidofovir was examined in 64 patients with CMV retinitis who received at least 1 injection of 20 µg of cidofovir. Histopathologic examination, culture, and polymerase chain reaction were used to detect CMV in ocular specimens. Antiviral resistance was assessed by plaque reduction assay and DNA sequencing.Results: Clinical resistance to intravitreal cidofovir injections was identified in 3 patients (5%) and was asso-ciated with prior oral ganciclovir or intravenous cidofovir use. Ganciclovir-and cidofovir-resistant CMV isolates were cultured from 2 patients and harbored resistanceassociated mutations in the UL97 and polymerase genes. Resistance mutations were also detected by direct analysis of vitreous. In 1 patient, different resistance mutations were identified in ocular vs extraocular CMV strains.

Inflammatory IRU can be differentiated from active CMV retinitis by the presence of IL-12, less IL-6, and absence of detectable CMV replication.