MUTATIONS IN HUMAN CYTOMEGALOVIRUS UL97 GENE CONFER CLINICAL RESISTANCE TO GANCICLOVIR AND CAN BE DETECTED DIRECTLY IN PATIENT PLASMA

Specific mutations in the UL97 region of human cytomegalovirus (HCMV) have been found to confer resistance to laboratory-adapted strains sub jected to ganciclovir selection. In this study, mutations in the UL97 region of HCMV isolates obtained from patients receiving ganciclovir t herapy were examined to determine whether they would confer ganciclovi r resistance, and if these mutations could be detected directly in the plasma of AIDS patients with progressive HCMV disease despite gancicl ovir treatment. A single nucleotide change within a conserved region o f UL97 was found in five resistant isolates, resulting in an amino aci d substitution in residue 595: from leucine to phenylalanine in one, a nd from leucine to serine in four resistant isolates. A sixth resistan t isolate demonstrated a single nucleotide change, leading to a threon ine to isoleucine substitution in residue 659. The role of the 595 ami no acid substitution in conferring ganciclovir resistance was confirme d by marker transfer experiments. In further studies, direct sequencin g of HCMV DNA present in plasma obtained from persons with resistant v iruses revealed the identical amino acid substitutions in plasma as th ose present in the cultured viruses. These findings indicate that clin ical resistance to ganciclovir can result from specific point mutation s in the UL97 gene, and that the emergence of the resistant genotype c an be detected directly in patient plasma.