title: Modification of the Tet-On regulatory system prevents the conditional-live HIV-1 variant from losing doxycycline-control.
abstract: BACKGROUND
  We have previously constructed a doxycycline (dox)-dependent HIV-1 variant by incorporating the Tet-On gene regulatory system into the viral genome. Replication of this HIV-rtTA virus is driven by the dox-inducible transactivator protein rtTA, and can be switched on and off at will. We proposed this conditional-live virus as a novel vaccine approach against HIV-1. Upon vaccination, replication of HIV-rtTA can be temporarily activated by transient dox administration and controlled to the extent needed for optimal induction of the immune system. However, subsequent dox-withdrawal may impose a selection for virus variants with reduced dox-dependence.
  
  
  RESULTS
  We simulated this on/off switching of virus replication in multiple, independent cultures and could indeed select for HIV-rtTA variants that replicated without dox. Nearly all evolved variants had acquired a typical amino acid substitution at position 56 in the rtTA protein. We developed a novel rtTA variant that blocks this undesired evolutionary route and thus prevents HIV-rtTA from losing dox-control.
  
  
  CONCLUSIONS
  The loss of dox-control observed upon evolution of the dox-dependent HIV-1 variant was effectively blocked by modification of the Tet-On regulatory system.
authors.affiliation: Laboratory of Experimental Virology, Department of Medical Microbiology, Center for Infection and Immunity Amsterdam (CINIMA), Academic Medical Center of the University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands. x.zhou@amc.uva.nl
authors.forename: Xue
authors.initials: X
authors.lastname: Zhou
authors.forename: Monique
authors.initials: M
authors.lastname: Vink
authors.forename: Ben
authors.initials: B
authors.lastname: Berkhout
authors.forename: Atze T
authors.initials: AT
authors.lastname: Das
mesh_terms: D001665:Binding Sites; D004318:Doxycycline / Q000494:pharmacology*; D019143:Evolution, Molecular; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D015696:Gene Products, tat / Q000235:genetics*; D005798:Genes, Bacterial; D005818:Genetic Engineering; D015497:HIV-1 / Q000235:genetics* / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009875:Operator Regions, Genetic; D010641:Phenotype; D014779:Virus Replication / Q000187:drug effects*; D054322:tat Gene Products, Human Immunodeficiency Virus
chemical_list: D015696:Gene Products, tat; D054322:tat Gene Products, Human Immunodeficiency Virus; D004318:Doxycycline