Analysis of cytomegalovirus DNA polymerase (UL54) mutations in solid organ transplant patients receiving valganciclovir or ganciclovir prophylaxis.

We previously reported the absence of CMV UL97 (kinase) gene resistance mutations up to 12 months post-transplant following 100 days of valganciclovir prophylaxis, and a low incidence of resistance mutations following 100 days of oral ganciclovir prophylaxis in a prospective multicenter study in solid organ transplant recipients excluding lung transplants. Herein, we report UL54 (DNA polymerase) gene sequencing results for all patients with previous UL97 PCR-positive samples (n = 99) in our study. One UL54 resistance mutation (L545S known to confer ganciclovir and cidofovir resistance) was detected in a routine day-100 sample from an asymptomatic patient who received oral ganciclovir. Notably, this CMV UL54 mutation occurred in the absence of a UL97 mutation. Additionally, new UL54 variants were observed. Thus, emergence of CMV UL54 mutations in the absence of UL97 mutations is a rare but possible event that is not necessarily associated with detrimental clinical outcome in solid organ transplant recipients.