Genotypic and Phenotypic Study of Antiviral Resistance Mutations in Refractory Cytomegalovirus Infection

Background This study describes the genotypic and phenotypic characterization of novel human cytomegalovirus (HCMV) genetic variants of a cohort of 94 clinically resistant HCMV patients. Methods and results Antiviral-resistant mutations were detected in the UL97, UL54, and UL56 target genes of 25 of 94 (26.6%) patients. The genotype-phenotype correlation study resolved the status of 5 uncharacterized UL54 deoxyribonucleic acid polymerase (G441S, A543V, F460S, R512C, A928T) and 2 UL56 terminase (F345L, P800L) mutations found in clinical isolates. A928T conferred high, triple resistance to ganciclovir, foscarnet, and cidofovir, and A543V had 10-fold reduced susceptibility to cidofovir. Viral growth assays showed G441S, A543V, F345L, and P800L impaired viral growth capacities compared with wild-type AD169 HCMV. Three-dimensional modeling predicted A543V and A928T phenotypes but not R512C, reinforcing the need for individual characterization of mutations by recombinant phenotyping. Conclusions Extending mutation databases is crucial to optimize treatments and to improve the assessment of patients with resistant/refractory HCMV infection. Genotype-phenotype correlation study resolved the status of UL54 A928T high triple-resistant mutation to ganciclovir, foscarnet, and cidofovir and UL54 A543V-resistant mutation to cidofovir found in clinical isolates. Moreover, UL54 G441S, A543V and UL56 F345L, P800L impaired viral growth capacities.