Hong, Priscilla Christine (2005-08). Utilization of the persistent nature of Brucella in the development of live vaccines. Doctoral Dissertation. Thesis uri icon

abstract

  • The roles of genes responsible for the survival and persistence of Brucella in the host and the relationship between these genes and the disease were investigated via signature-tagged transposon mutagenesis. As much as 8% of the Brucella genome is important for survival of this organism in the host. This is an unusually high number and may help to explain the chronic or persistent nature of Brucella infections. Mutants attenuated in the mouse model were divided into two groups. The early mutants failed to establish infection or colonize the host. The late mutants colonized the host but failed to maintain infection. The vaccine potential of two mutants (virB10 and gcvH) that were unable to sustain infection was compared to that of a vaccine strain, S19. Survival of strain S19 in vivo was up to 12 weeks while virB10 and gcvH mutants were cleared from spleen at 8, and 24 weeks post-inoculation, respectively. Mice were vaccinated with individual mutants and then challenged with virulent S2308 at 8, 16, and 24 weeks postvaccination. As a result, protective immunity correlated with persistence of the mutant strain [gcvH>virB10]. These results suggest that survival is one of several factors that may influence protective immunity making it difficult to compare strains. For example, examination of host immune response revealed a similar pattern of host immune function (TH1 over TH2) in all mice except those vaccinated with virB10 mutant. Since gcvH mutant provided the best immunity, experiments were designed to explore its contribution of persistence to protection. In an effort to reduce non-specific activation induced by prolonged survival of gcvH mutant, protection was monitored after different periods of vaccination exposure followed with doxycycline treatment. In these studies, persistence of gcvH mutant enhanced protection against challenge. Overall, defined mutations in genes affecting survival may render mutants as vaccine candidates capable of stimulating protective immunity equal to or better than fortuitously isolated attenuated strains. Future studies should focus on characterization of these and other genes responsible for the persistence of Brucella to improve the safety and efficacy of live vaccines.
  • The roles of genes responsible for the survival and persistence of Brucella in the
    host and the relationship between these genes and the disease were investigated via
    signature-tagged transposon mutagenesis. As much as 8% of the Brucella genome is
    important for survival of this organism in the host. This is an unusually high number
    and may help to explain the chronic or persistent nature of Brucella infections. Mutants
    attenuated in the mouse model were divided into two groups. The early mutants failed
    to establish infection or colonize the host. The late mutants colonized the host but failed
    to maintain infection. The vaccine potential of two mutants (virB10 and gcvH) that were
    unable to sustain infection was compared to that of a vaccine strain, S19. Survival of
    strain S19 in vivo was up to 12 weeks while virB10 and gcvH mutants were cleared from
    spleen at 8, and 24 weeks post-inoculation, respectively. Mice were vaccinated with
    individual mutants and then challenged with virulent S2308 at 8, 16, and 24 weeks postvaccination.
    As a result, protective immunity correlated with persistence of the mutant
    strain [gcvH>virB10]. These results suggest that survival is one of several factors that may influence
    protective immunity making it difficult to compare strains. For example, examination of
    host immune response revealed a similar pattern of host immune function (TH1 over
    TH2) in all mice except those vaccinated with virB10 mutant. Since gcvH mutant
    provided the best immunity, experiments were designed to explore its contribution of
    persistence to protection. In an effort to reduce non-specific activation induced by
    prolonged survival of gcvH mutant, protection was monitored after different periods of
    vaccination exposure followed with doxycycline treatment. In these studies, persistence
    of gcvH mutant enhanced protection against challenge. Overall, defined mutations in
    genes affecting survival may render mutants as vaccine candidates capable of
    stimulating protective immunity equal to or better than fortuitously isolated attenuated
    strains. Future studies should focus on characterization of these and other genes
    responsible for the persistence of Brucella to improve the safety and efficacy of live
    vaccines.

publication date

  • August 2005