title: Characterization of Francisella tularensis Schu S4 defined mutants as live-attenuated vaccine candidates.
abstract: Francisella tularensis (Ft), the etiological agent of tularemia and a Tier 1 select agent, has been previously weaponized and remains a high priority for vaccine development. Ft tularensis (type A) and Ft holarctica (type B) cause most human disease. We selected six attenuating genes from the live vaccine strain (LVS; type B), F. novicida and other intracellular bacteria: FTT0507, FTT0584, FTT0742, FTT1019c (guaA), FTT1043 (mip) and FTT1317c (guaB) and created unmarked deletion mutants of each in the highly human virulent Ft strain Schu S4 (Type A) background. FTT0507, FTT0584, FTT0742 and FTT1043 Schu S4 mutants were not attenuated for virulence in vitro or in vivo. In contrast, Schu S4 gua mutants were unable to replicate in murine macrophages and were attenuated in vivo, with an i.n. LD50 > 10(5) CFU in C57BL/6 mice. However, the gua mutants failed to protect mice against lethal challenge with WT Schu S4, despite demonstrating partial protection in rabbits in a previous study. These results contrast with the highly protective capacity of LVS gua mutants against a lethal LVS challenge in mice, and underscore differences between these strains and the animal models in which they are evaluated, and therefore have important implications for vaccine development.
authors.affiliation: Departments of Pediatrics, University of Virginia Children's Hospital, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Araceli E
authors.initials: AE
authors.lastname: Santiago
authors.affiliation: Department of Medicine, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Mann
authors.affiliation: Department of Medicine, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Aiping
authors.initials: A
authors.lastname: Qin
authors.affiliation: Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Aimee L
authors.initials: AL
authors.lastname: Cunningham
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Leah E
authors.initials: LE
authors.lastname: Cole
authors.affiliation: Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Christen
authors.initials: C
authors.lastname: Grassel
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Stefanie N
authors.initials: SN
authors.lastname: Vogel
authors.affiliation: Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Myron M
authors.initials: MM
authors.lastname: Levine
authors.affiliation: Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA ebarry@medicine.umaryland.edu.
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Barry
mesh_terms: D000818:Animals; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D004195:Disease Models, Animal; D005604:Francisella tularensis / Q000235:genetics* / Q000254:growth & development / Q000276:immunology* / Q000502:physiology; D017353:Gene Deletion; D005798:Genes, Bacterial; D007928:Lethal Dose 50; D008264:Macrophages / Q000382:microbiology; D008810:Mice, Inbred C57BL; D050296:Microbial Viability; D016019:Survival Analysis; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology; D014774:Virulence
chemical_list: D001428:Bacterial Vaccines; D014613:Vaccines, Attenuated
keywords: Francisella tularensis; Schu S4; live attenuated; mutants; tularemia; vaccines