1005. Phenotypes of Cytomegalovirus (CMV) DNA Polymerase (pol) Sequence Variants Detected in Transplant Recipients Treated with Ganciclovir or Valganciclovir
Session: Poster Abstract Session: CMV and Transplantation
Saturday, October 22, 2011
Room: Poster Hall B1
Background: Over 50 CMV UL54 pol sequence variants of unknown significance for drug resistance were found in blood samples obtained at days 0, 21 and 49 from 275 subjects in a published treatment trial comparing intravenous ganciclovir and oral valganciclovir in solid organ transplant recipients. No corresponding clinical CMV culture isolates were available for study.

Methods: Sequence variants were selected for resistance testing based on a change from a pretreatment sequence (S660G, I726T, E793V, Q795R, V902G, M959T), or located at a conserved pol residue or domain (A505V, F718L/S, G822D, M828V, E903G). Recombinant phenotyping was performed by transfer of specific mutations to a bacterial artificial chromosome clone of a control CMV strain, followed by standardized reporter-based yield reduction assay of the resulting live virus for ganciclovir (GCV), cidofovir (CDV) and foscarnet (FOS) concentrations that reduce viral growth by 50% (EC50), using established protocols.

Results: S660G, E793V, Q795R, V902G, E903G and M959T conferred no resistance to any drug (EC50 <1.5x of control value). A505V and I726T each conferred 1.6x to 1.9x increased EC50 for both GCV and CDV, but no change for FOS. Mutations F718L, F718S, G822D and M828V each resulted in a nonviable viral genome. Clone viability was rescued by restoring the wild type pol sequence. The 4 mutations were found in pretreatment clinical specimens as mixtures with wild type sequence (G822D and M828V in the same specimen). F718L (twice), G822D and M828V were found in subjects with no known prior antiviral therapy.

Conclusion: Despite reasonable suspicion, the previously unknown pol sequence variants tested had no detectable impact on drug susceptibility except for a borderline change conferred by A505V and I726T. Nonviable mutants at codons 718, 822 and 828 confirm the functional importance of these residues for DNA polymerization, but the clinical circumstances do not suggest a role in antiviral drug resistance. The varied phenotypes observed here support a need for individual study of pol sequence variants found in specimens from treated subjects, and consideration of technical factors that may lead to readouts of mixed wild type and variant sequences during genotypic resistance testing.


Subject Category: V. Virology including clinical and basic studies of viral infections, including hepatitis

Sunwen Chou, MD, Oregon Health & Science Univ., Portland, OR, Jane Ives, Roche Products Ltd, Welwyn Garden City, United Kingdom and Robert Elston, Ph.D., Roche Products Ltd., Welwyn Garden City, United Kingdom

Disclosures:

S. Chou, Roche Products Ltd.: Research Contractor, Research support

J. Ives, Roche Products Ltd.: Employee, Salary

R. Elston, Roche Products Ltd: Employee, Salary

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