Detecting human cytomegalovirus drug resistant mutations and monitoring the emergence of resistant strains using real-time PCR.

Background: Antiviral resistance development is a serious complication of human cytomegalovirus virostatic therapy caused by mutations in UL 97 and/or UL54 genes.

Objectives: To determinate the presence of sensitive and resistant strains in patients developing antiviral resistance.

Study Design: We used three different molecular biological methods for mutation analysis-restriction fragment length polymorphism, sequencing and real-time PCR approach.

Results: We describe three allogeneic hematopoietic stem cell transplant patients developing the GCV resistant HCMV strains manifested by virostatic treatment failure. In these patients we identified UL97 mutations L595S, A594V and A594T and monitored the dynamics of coexisted sensitive/resistant strains. We confirmed the presence of mixed HCMV populations and in two patients a phenomenon of sensitive strain repopulation which occurred after 6.5 months and 1 month after removing GCV pressure.

Conclusions: Our results show changes in proportions of sensitive/resistant subpopulations over time but other studies would be required to demonstrate the beneficial impact of their monitoring on clinical outcome.