GANCICLOVIR RESISTANCE AS A RESULT OF ORAL GANCICLOVIR IN A HEART-TRANSPLANT RECIPIENT WITH MULTIPLE HUMAN CYTOMEGALOVIRUS STRAINS IN BLOOD

Background The emergence of a ganciclovir (GCV)-resistant human cytome galovirus (HCMV) strain in a heart transplant recipient (HTR) coinfect ed by multiple HCMV strains was investigated. Methods. A HTR with prim ary HCMV infection was treated with three induction courses of intrave nous GCV followed by a 2-month maintenance treatment with oral GCV. HC MV antigenemia, viremia, and leukoDNAemia levels were monitored. GCV s usceptibility was analyzed by an immediate-early antigen plaque reduct ion assay and by a rapid screening assay performed using peripheral bl ood leukocytes (PBL) as viral inoculum. The viral population in blood was investigated by restriction analysis of multiple genome regions. U L97 and UL54 genes were sequenced in parallel in both HCMV isolates an d the relevant PBL samples. A rapid molecular assay for detection and quantitation of the GCV-resistant mutant was developed. Results. The e mergence of a GCV-resistant UL97 mutant (Cys-607 --> Tyr) was responsi ble for treatment failure during oral GCV therapy. The genetic analysi s of the HCMV population showed the sequential appearance in blood of two unrelated strains (referred to as A and B). Strain A most Likely d erived from the transplanted organ and strain B from a subsequent bloo d transfusion. The resistant variant (B-r) emerged from strain B and b ecame predominant ''in vivo'' under the GCV pressure. However, after f oscarnet administration, the resistant mutant disappeared in viral iso lates, whereas it was still present as a minor proportion in PBL sampl es, Conclusion. (a) Oral GCV may select resistant strains in transplan ted patients; (b) results of the rapid screening assay were clinically useful for shifting to an alternative treatment, thus avoiding the ap pearance of HCMV disease; (c) virus isolation may not be the most reli able approach to detection of HCMV drug-resistant strains; (d) a novel molecular assay for rapid detection of UL97 Cys-607 --> Tyr mutation directly in clinical specimens was developed, allowing earlier ''in vi vo'' detection of the resistant mutant.