| 1. |
- Conlan, J Wayne, et al.
(author)
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Differential ability of novel attenuated targeted deletion mutants of Francisella tularensis subspecies tularensis strain SCHU S4 to protect mice against aerosol challenge with virulent bacteria : effects of host background and route of immunization
- 2010
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In: Vaccine. - : Elsevier BV. - 0264-410X .- 1873-2518. ; 28:7, s. 1824-1831
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Journal article (peer-reviewed)abstract
- Francisella tularensis subspecies tularensis is a highly virulent facultative intracellular pathogen of humans and a potential biological weapon. A live vaccine strain, F. tularensis LVS, was developed more than 50 years ago by pragmatic attenuation of a strain of the less virulent holarctica subspecies. LVS was demonstrated to be highly effective in human volunteers who were exposed to intradermal challenge with fully virulent subsp. tularensis, but was less effective against aerosol exposure. LVS faces regulatory hurdles that to date have prevented its licensure for general use. Therefore, a better defined and more effective vaccine is being sought. To this end we have created gene deletion mutants in the virulent subsp. tularensis strain and tested them for their ability to elicit a protective immune response against systemic or aerosol challenge with the highly virulent wild-type subsp. tularensis strain, SCHU S4. Both oral and intradermal (ID) primary vaccination routes were assessed in BALB/c and C3H/HeN mice as was oral boosting. One SCHU S4 mutant missing the heat shock gene, clpB, was significantly more attenuated than LVS whereas a double deletion mutant missing genes FTT0918 and capB was as attenuated as LVS. In general mice immunized with SCHU S4DeltaclpB were significantly better protected against aerosol challenge than mice immunized with LVS. A single ID immunization of BALB/c mice with SCHU S4DeltaclpB was at least as effective as any other regimen examined. Mice immunized with SCHU S4Delta0918DeltacapB were generally protected to a similar degree as mice immunized with LVS. A preliminary examination of immune responses to vaccination with LVS, SCHU S4DeltaclpB, or SCHU S4Delta0918DeltacapB provided no obvious correlate to their relative efficacies.
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| 2. |
- Conlan, J. Wayne, et al.
(author)
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Modern Development and Production of a New Live Attenuated Bacterial Vaccine, SCHU S4 Delta clpB, to Prevent Tularemia
- 2021
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In: Pathogens. - : MDPI. - 2076-0817. ; 10:7
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Journal article (peer-reviewed)abstract
- Inhalation of small numbers of Francisella tularensis subspecies tularensis (Ftt) in the form of small particle aerosols causes severe morbidity and mortality in people and many animal species. For this reason, Ftt was developed into a bona fide biological weapon by the USA, by the former USSR, and their respective allies during the previous century. Although such weapons were never deployed, the 9/11 attack quickly followed by the Amerithrax attack led the U.S. government to seek novel countermeasures against a select group of pathogens, including Ftt. Between 2005-2009, we pursued a novel live vaccine against Ftt by deleting putative virulence genes from a fully virulent strain of the pathogen, SCHU S4. These mutants were screened in a mouse model, in which the vaccine candidates were first administered intradermally (ID) to determine their degree of attenuation. Subsequently, mice that survived a high dose ID inoculation were challenged by aerosol or intranasally (IN) with virulent strains of Ftt. We used the current unlicensed live vaccine strain (LVS), first discovered over 70 years ago, as a comparator in the same model. After screening 60 mutants, we found only one, SCHU S4 Delta clpB, that outperformed LVS in the mouse ID vaccination-respiratory-challenge model. Currently, SCHU S4 Delta clpB has been manufactured under current good manufacturing practice conditions, and tested for safety and efficacy in mice, rats, and macaques. The steps necessary for advancing SCHU S4 Delta clpB to this late stage of development are detailed herein. These include developing a body of data supporting the attenuation of SCHU S4 Delta clpB to a degree sufficient for removal from the U.S. Select Agent list and for human use; optimizing SCHU S4 Delta clpB vaccine production, scale up, and long-term storage; and developing appropriate quality control testing approaches.
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| 3. |
- Conlan, J Wayne, et al.
(author)
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Molecular immunology of experimental primary tularemia in mice infected by respiratory or intradermal routes with type A Francisella tularensis.
- 2008
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In: Molecular Immunology. - : Elsevier BV. - 0161-5890 .- 1872-9142. ; 45:10, s. 2962-2969
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Journal article (peer-reviewed)abstract
- The type A subspecies of Francisella tularensis is a highly virulent facultative intracellular bacterial pathogen, and a potential biological weapon. Recently, there has been renewed interest in developing new vaccines and therapeutics against this bacterium. Natural cases of disease, tularemia, caused by the type A subspecies are very rare. Therefore, the United States Food and Drug Administration will rely on the so-called Animal Rule for efficacy testing of anti-Francisella medicines. This requires the human disease to be modeled in one or more animal species in which the pathogenicity of the agent is reasonably well understood. Mice are natural hosts for F. tularensis, and might be able to satisfy this requirement. Tularemia pathogenesis appears to be primarily due to the host inflammatory response which is poorly understood at the molecular level. Additionally, the extent to which this response varies depending on host and pathogen genetic background, or by pathogen challenge route or dose is unknown. Therefore, the present study examined sera and infected tissues from C57BL/6 and BALB/c mice challenged by natural intradermal (ID) and respiratory routes with one of two distinct type A strains of the pathogen for cytokine and chemokine responses that might help to explain the morbidity associated with tularemia. The results show that the molecular immune response was mostly similar regardless of the variables examined. For instance, mRNA for the proinflammatory cytokine IL-6, and chemokines KC, and IP-10 was consistently upregulated at all sites of infection. Upregulation of mRNA for several other cytokines and chemokines occurred in a more tissue restricted manner. For instance, IFN-gamma was highly upregulated in the skin of BALB/c, but not C57BL/6 mice after ID inoculation of the pathogen, whilst IL-10 mRNA upregulation was only consistently seen in the skin and lungs.
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| 4. |
- Twine, Susan M, et al.
(author)
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Roles for wbtC, wbtI, and kdtA genes in lipopolysaccharide biosynthesis, protein glycosylation, virulence, and immunogenicity in Francisella tularensis strain SCHU S4
- 2012
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In: Pathogens. - : MDPI. - 2076-0817. ; 1:1, s. 12-29
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Journal article (peer-reviewed)abstract
- Using a strategy of gene deletion mutagenesis, we have examined the roles of genes putatively involved in lipopolysaccharide biosynthesis in the virulent facultative intracellular bacterial pathogen, Francisella tularensis subspecies tularensis, strain SCHU S4 in LPS biosynthesis, protein glycosylation, virulence and immunogenicity. One mutant, ∆wbtI, did not elaborate a long chain O-polysaccharide (OPS), was completely avirulent for mice, and failed to induce a protective immune response against challenge with wild type bacteria. Another mutant, ∆wbtC, produced a long chain OPS with altered chemical and electrophoretic characteristics. This mutant showed markedly reduced glycosylation of several known glycoproteins. Additionally this mutant was highly attenuated, and elicited a protective immune response against systemic, but not respiratory challenge with wild type SCHU S4. A third mutant, ∆kdtA, produced an unconjugated long chain OPS, lacking a detectable core structure, and which was not obviously expressed at the surface. It was avirulent and elicited partial protection against systemic challenge only.
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| 5. |
- Twine, Susan M, et al.
(author)
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Virulence comparison in mice of distinct isolates of type A Francisella tularensis.
- 2006
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In: Microbial Pathogenesis. - : Elsevier BV. - 0882-4010 .- 1096-1208. ; 40:3, s. 133-8
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Journal article (peer-reviewed)abstract
- Francisella tularensis subspecies tularensis (type A F. tularensis) is considered to be one of the most virulent of all bacterial pathogens. Mice are extremely susceptible to infection with this subspecies (LD100 via various inoculation routes is <10 cfu). However, it has not been established whether overt virulence differences exist amongst type A strains of F. tularensis. To this end, the present study compared the virulence of two distinct type A strains, FSC033 and SCHU S4, for naïve mice and mice immunized with the live vaccine strain of the pathogen, F. tularensis LVS. One nominal isolate of SCHU S4 was found to be completely avirulent. Another isolate was highly virulent, but all examined cases appeared somewhat less virulent than FSC033. The implication of these findings for future infection and immunity studies is discussed.
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