Dynamics of coexisting HCMV-UL97 and UL54 drug-resistance associated mutations in patients after haematopoietic cell transplantation.

Background: Resistance to antiviral drugs can be a severe problem in transplant recipients. Mutations in the HCMV phosphotransferase-gene (UL97) and the polymerase-gene (UL54) are responsible for resistance against ganciclovir (GCV), cidofovir (CDV) and foscarnet (PFA). Most frequently mutations in the UL97-gene are associated with resistance to GCV. Resistance against PFA and CDV is associated to mutations in the UL54-gene. There are only few reports about multidrug-resistance with mutations in both genes in patients after allogeneic haematopoietic cell transplantation (HCT).

Objectives: To asses retrospectively the role of UL97/UL54-mutations for clinical deterioration.

Study Design: We present here three patients after HCT developing multidrug-resistance with coexisting UL97 and UL54-mutations. Genotypical resistance screening was done with restriction-fragment-length-polymorphism (RFLP), sequencing of UL97/UL54, and LightCycler real-time PCR. Phenotyipcal testing was performed by a cell-associated plaque-reduction-assay. Plasma viral-load (VL) was determined longitudinally using Roche Cobas-Amplicor-System (Roche Diagnostics). In one case VL was also correlated to different ratios of coexisting UL97-wildtype and mutant variants.

Results: All three patients developed multidrug resistant HCMV-infections with one or more UL97 and UL54-mutation detected by RFLP, sequencing and LightCycler-analysis. Two out of three patients showed biphasic VL kinetics with manifestation of UL97 drug-resistance prior/or at peak VL. UL54-mutations emerged also in all three patients either at increasing VL levels of ≥10(5)copies/ml or at peak VL.

Conclusions: The development of coexisting HCMV UL97 and UL54-mutations conferring drug-resistance after HCT is not strictly associated with fatal outcome in one of our three patients. Manifestation of drug resistant combined UL97/UL54-mutations occurred prior to a second VL peak under (V)GCV/PFA co-treatment.