title: Genomic analysis of chimeric human cytomegalovirus vaccine candidates derived from strains Towne and Toledo.
abstract: Human cytomegalovirus (HCMV) is an important opportunistic pathogen in immunocompromised patients and a major cause of congenital birth defects when acquired in utero. In the 1990s, four chimeric viruses were constructed by replacing genome segments of the high passage Towne strain with segments of the low passage Toledo strain, with the goal of obtaining live attenuated vaccine candidates that remained safe but were more immunogenic than the overly attenuated Towne vaccine. The chimeras were found to be safe when administered to HCMV-seronegative human volunteers, but to differ significantly in their ability to induce seroconversion. This suggests that chimera-specific genetic differences impacted the ability to replicate or persist in vivo and the consequent ability to induce an antibody response. To identify specific genomic breakpoints between Towne and Toledo sequences and establish whether spontaneous mutations or rearrangements had occurred during construction of the chimeras, complete genome sequences were determined. No major deletions or rearrangements were observed, although a number of unanticipated mutations were identified. However, no clear association emerged between the genetic content of the chimeras and the reported levels of vaccine-induced HCMV-specific humoral or cellular immune responses, suggesting that multiple genetic determinants are likely to impact immunogenicity. In addition to revealing the genome organization of the four vaccine candidates, this study provided an opportunity to probe the genetics of HCMV attenuation in humans. The results may be valuable in the future design of safe live or replication-defective vaccines that optimize immunogenicity and efficacy.
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, UK.
authors.forename: Nicolás M
authors.initials: NM
authors.lastname: Suárez
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, UK.
authors.forename: Betty
authors.initials: B
authors.lastname: Lau
authors.affiliation: 3-V Biosciences, Inc., Menlo Park, CA, USA.
authors.forename: George M
authors.initials: GM
authors.lastname: Kemble
authors.affiliation: Department of Pediatrics, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Ronzo
authors.initials: R
authors.lastname: Lee
authors.affiliation: Department of Microbiology and Immunology, Emory Vaccine Center, Emory University, Atlanta, GA, USA.
authors.forename: Edward S
authors.initials: ES
authors.lastname: Mocarski
authors.affiliation: Division of Infection and Immunity, School of Medicine, Cardiff University, Cardiff, UK.
authors.forename: Gavin W G
authors.initials: GWG
authors.lastname: Wilkinson
authors.affiliation: CMV Research Foundation, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Stuart P
authors.initials: SP
authors.lastname: Adler
authors.affiliation: Department of Pediatrics, Virginia Commonwealth University, Richmond, VA, USA. michael.mcvoy@vcuhealth.org.
authors.forename: Michael A
authors.initials: MA
authors.lastname: McVoy
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Davison
mesh_terms: D000914:Antibodies, Viral / Q000276:immunology; D003587:Cytomegalovirus / Q000145:classification / Q000235:genetics* / Q000276:immunology* / Q000302:isolation & purification; D003586:Cytomegalovirus Infections / Q000276:immunology / Q000517:prevention & control / Q000821:virology*; D022482:Cytomegalovirus Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D016679:Genome, Viral; D023281:Genomics; D006801:Humans; D007114:Immunization; D011995:Recombination, Genetic
chemical_list: D000914:Antibodies, Viral; D022482:Cytomegalovirus Vaccines
keywords: Attenuation; Cytomegalovirus; Recombinant; Vaccine; Virulence