Formulation of a mmaA4 gene deletion mutant of Mycobacterium bovis BCG in cationic liposomes significantly enhances protection against tuberculosis

PLoS One. 2012;7(3):e32959. doi: 10.1371/journal.pone.0032959. Epub 2012 Mar 19.

Abstract

A new vaccination strategy is urgently needed for improved control of the global tuberculosis (TB) epidemic. Using a mouse aerosol Mycobacterium tuberculosis challenge model, we investigated the protective efficacy of a mmaA4 gene deletion mutant of Mycobacterium bovis BCG (ΔmmaA4BCG) formulated in dimethyl dioctadecyl ammonium bromide (DDA) - D(+) trehalose 6,6 dibenenate (TDB) (DDA/TDB) adjuvant. In previous studies, deletion of the mmaA4 gene was shown to reduce the suppression of IL-12 production often seen after mycobacterial infections. While the non-adjuvanted ΔmmaA4BCG strain did not protect mice substantially better than conventional BCG against a tuberculous challenge in four protection experiments, the protective responses induced by the ΔmmaA4BCG vaccine formulated in DDA/TDB adjuvant was consistently increased relative to nonadjuvanted BCG controls. Furthermore, the ΔmmaA4BCG-DDA/TDB vaccine induced significantly higher frequencies of multifunctional (MFT) CD4 T cells expressing both IFNγ and TNFα (double positive) or IFNγ, TNFα and IL-2 (triple positive) than CD4 T cells derived from mice vaccinated with BCG. These MFT cells were characterized by having higher IFNγ and TNFα median fluorescence intensity (MFI) values than monofunctional CD4 T cells. Interestingly, both BCG/adjuvant and ΔmmaA4BCG/adjuvant formulations induced significantly higher frequencies of CD4 T cells expressing TNFα and IL-2 than nonadjuvanted BCG or ΔmmaA4BCG vaccines indicating that BCG/adjuvant mixtures may be more effective at inducing central memory T cells. Importantly, when either conventional BCG or the mutant were formulated in adjuvant and administered to SCID mice or immunocompromised mice depleted of IFNγ, significantly lower vaccine-derived mycobacterial CFU were detected relative to immunodeficient mice injected with non-adjuvanted BCG. Overall, these data suggest that immunization with the ΔmmaA4BCG/adjuvant formulation may be an effective, safe, and relatively inexpensive alternative to vaccination with conventional BCG.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adjuvants, Immunologic
  • Animals
  • CD4-Positive T-Lymphocytes / immunology
  • Cytokines / immunology
  • Female
  • Gene Deletion*
  • Mice
  • Mice, SCID
  • Mixed Function Oxygenases*
  • Mycobacterium bovis / enzymology
  • Mycobacterium bovis / genetics
  • Mycobacterium bovis / immunology*
  • Tuberculosis / genetics
  • Tuberculosis / immunology
  • Tuberculosis / prevention & control*
  • Tuberculosis Vaccines / genetics
  • Tuberculosis Vaccines / immunology*
  • Vaccination
  • Vaccines, Attenuated / genetics
  • Vaccines, Attenuated / immunology

Substances

  • Adjuvants, Immunologic
  • Cytokines
  • Tuberculosis Vaccines
  • Vaccines, Attenuated
  • Mixed Function Oxygenases