Recombinant phenotyping of cytomegalovirus sequence variants detected after 200 or 100 days of valganciclovir prophylaxis.

BACKGROUND: In a phase III controlled trial IMproved Protection Against Cytomegalovirus in Transplantation (IMPACT) comparing 200 with 100 days of valganciclovir prophylaxis in 318 cytomegalovirus D+/R- kidney transplant recipients, an equal number of patients (n=3 per arm) had known ganciclovir resistance mutations detected during viral breakthrough. In addition, many other viral sequence variants were observed that were of unknown significance for ganciclovir resistance. Recombinant phenotyping was performed to determine whether the previously uncharacterized genotypic changes affected ganciclovir susceptibility, especially in those receiving the longer duration of prophylaxis. METHODS: Sequences encoding individual amino acid substitutions in the UL97 kinase or UL54 DNA polymerase gene were transferred by recombination into a cloned cytomegalovirus laboratory strain, followed by reporter-based yield reduction phenotypic assay of the resulting virus for ganciclovir susceptibility. RESULTS: Twenty-six uncharacterized amino acid substitutions were detected, 2 in UL97 and 24 in UL54. All 10 substitutions in the 200-day arm and 9 of 17 substitutions in the 100-day arm (prioritized based on location and conservation) were selected for phenotyping; one substitution was detected in both subsets. Results were generated for nine of ten 200-day and eight of nine 100-day substitutions, with no substitution demonstrating a significant reduction in ganciclovir susceptibility. The two remaining amino acid substitutions, both in UL54, were not evaluated because of poor viral viability. CONCLUSION: Phenotypic evaluation of previously uncharacterized viral genotypes in the 200-day valganciclovir prophylaxis group showed no evidence of an increased incidence of genotypic ganciclovir resistance when compared with those in the 100-day prophylaxis group.

Extended valganciclovir prophylaxis in D+/R- kidney transplant recipients is associated with long-term reduction in cytomegalovirus disease: two-year results of the IMPACT study.

BACKGROUND: Whether the early reduction in cytomegalovirus (CMV) disease seen at 1 year with prolongation of antiviral prophylaxis (up to 200 days) persists in the long term is unknown. METHODS: This international, randomized, prospective, double-blind study, compared 318 CMV D+/R- kidney transplant recipients receiving valganciclovir (900 mg) once daily for up to 200 days vs. 100 days. Long-term outcomes including CMV disease, acute rejection, graft loss, patient survival, and seroconversion were assessed. RESULTS: At 2 years posttransplant, CMV disease occurred in significantly less patients in the 200- vs. the 100-day group: 21.3% vs. 38.7%, respectively (P<0.001). Between year 1 and 2, there were only 10 new cases of CMV disease; 7 in the 200-day group and 3 in the 100-day group. Patient survival was 100% in the 200-day group and 97% in the 100-day group (p=not significant). Biopsy-proven acute rejection and graft loss rates were comparable in both groups (11.6% vs. 17.2%, P=0.16, and 1.9% vs. 4.3%, P=0.22, in the 200-day vs. 100-day groups, respectively). Seroconversion was delayed in the 200-day group but was similar to the 100-day group by 2 years posttransplant (IgM or IgG seroconversion; 55.5% in the 200-day group vs. 62.0% in the 100-day group at 2-years; P=0.26). Assessment of seroconversion at the end of prophylaxis was of limited utility for predicting late-onset CMV disease. CONCLUSION: Extending valganciclovir prophylaxis from 100 to 200 days is associated with a sustained reduction in CMV disease up to 2 years posttransplant.