title: Safety mechanism assisted by the repressor of tetracycline (SMART) vaccinia virus vectors for vaccines and therapeutics.
abstract: Replication-competent viruses, such as Vaccinia virus (VACV), are powerful tools for the development of oncolytic viral therapies and elicit superior immune responses when used as vaccine and immunotherapeutic vectors. However, severe complications from uncontrolled viral replication can occur, particularly in immunocompromised individuals or in those with other predisposing conditions. VACVs constitutively expressing interferon-γ (IFN-γ) replicate in cell culture indistinguishably from control viruses; however, they replicate in vivo to low or undetectable levels, and are rapidly cleared even in immunodeficient animals. In an effort to develop safe and highly effective replication-competent VACV vectors, we established a system to inducibly express IFN-γ. Our SMART (safety mechanism assisted by the repressor of tetracycline) vectors are designed to express the tetracycline repressor under a constitutive VACV promoter and IFN-γ under engineered tetracycline-inducible promoters. Immunodeficient SCID mice inoculated with VACVs not expressing IFN-γ demonstrated severe weight loss, whereas those given VACVs expressing IFN-γ under constitutive VACV promoters showed no signs of infection. Most importantly, mice inoculated with a VACV expressing the IFN-γ gene under an inducible promoter remained healthy in the presence of doxycycline, but exhibited severe weight loss in the absence of doxycycline. In this study, we developed a safety mechanism for VACV based on the conditional expression of IFN-γ under a tightly controlled tetracycline-inducible VACV promoter for use in vaccines and oncolytic cancer therapies.
authors.affiliation: International Laboratory of Molecular Biology for Tropical Disease Agents, School of Veterinary Medicine, University of California, Davis, CA 95616.
authors.forename: Patricia
authors.initials: P
authors.lastname: Grigg
authors.forename: Allison
authors.initials: A
authors.lastname: Titong
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Jones
authors.forename: Tilahun D
authors.initials: TD
authors.lastname: Yilma
authors.forename: Paulo H
authors.initials: PH
authors.lastname: Verardi
mesh_terms: D000818:Animals; D002460:Cell Line; D004337:Drug Carriers / Q000592:standards; D004797:Enzyme-Linked Immunosorbent Assay; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D005822:Genetic Vectors; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D051379:Mice; D016513:Mice, SCID; D008856:Microscopy, Fluorescence; D061214:Patient Safety / Q000592:standards*; D011401:Promoter Regions, Genetic / Q000187:drug effects* / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology*; D014612:Vaccines / Q000592:standards; D014616:Vaccinia virus
chemical_list: D004337:Drug Carriers; D014612:Vaccines; D007371:Interferon-gamma; D013752:Tetracycline