Recombinant BCG Expressing Mycobacterium ulcerans Ag85A Imparts Enhanced Protection against Experimental Buruli ulcer

PLoS Negl Trop Dis. 2015 Sep 22;9(9):e0004046. doi: 10.1371/journal.pntd.0004046. eCollection 2015 Sep.

Abstract

Buruli ulcer, an emerging tropical disease caused by Mycobacterium ulcerans (MU), is characterized by disfiguring skin necrosis and high morbidity. Relatively little is understood about the mode of transmission, pathogenesis, or host immune responses to MU infection. Due to significant reduction in quality of life for patients with extensive tissue scarring, and that a disproportionately high percentage of those affected are disadvantaged children, a Buruli ulcer vaccine would be greatly beneficial to the worldwide community. Previous studies have shown that mice inoculated with either M. bovis bacille Calmette-Guérin (BCG) or a DNA vaccine encoding the M. ulcerans mycolyl transferase, Ag85A (MU-Ag85A), are transiently protected against pathology caused by intradermal challenge with MU. Building upon this principle, we have generated quality-controlled, live-recombinant strains of BCG and M. smegmatis which express the immunodominant MU Ag85A. Priming with rBCG MU-Ag85A followed by an M. smegmatis MU-Ag85A boost strongly induced murine antigen-specific CD4+ T cells and elicited functional IFNγ-producing splenocytes which recognized MU-Ag85A peptide and whole M. ulcerans better than a BCG prime-boost vaccination. Strikingly, mice vaccinated with a single subcutaneous dose of BCG MU-Ag85A or prime-boost displayed significantly enhanced survival, reduced tissue pathology, and lower bacterial load compared to mice vaccinated with BCG. Importantly, this level of superior protection against experimental Buruli ulcer compared to BCG has not previously been achieved. These results suggest that use of BCG as a recombinant vehicle expressing MU antigens represents an effective Buruli ulcer vaccine strategy and warrants further antigen discovery to improve vaccine efficacy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, Bacterial / genetics
  • Antigens, Bacterial / immunology*
  • Bacterial Vaccines / administration & dosage
  • Bacterial Vaccines / genetics
  • Bacterial Vaccines / immunology*
  • Buruli Ulcer / immunology*
  • Buruli Ulcer / prevention & control*
  • CD4-Positive T-Lymphocytes / immunology
  • Disease Models, Animal
  • Female
  • Interferon-gamma / metabolism
  • Mice, Inbred C57BL
  • Mycobacterium bovis / genetics
  • Mycobacterium bovis / immunology*
  • Mycobacterium smegmatis / genetics
  • Mycobacterium smegmatis / immunology
  • Mycobacterium ulcerans / genetics
  • Mycobacterium ulcerans / immunology*
  • Survival Analysis
  • Treatment Outcome
  • Vaccination / methods
  • Vaccines, Attenuated / administration & dosage
  • Vaccines, Attenuated / genetics
  • Vaccines, Attenuated / immunology
  • Vaccines, Synthetic / administration & dosage
  • Vaccines, Synthetic / genetics
  • Vaccines, Synthetic / immunology

Substances

  • Antigens, Bacterial
  • Bacterial Vaccines
  • Vaccines, Attenuated
  • Vaccines, Synthetic
  • Interferon-gamma

Grants and funding

Funding was provided by the Duke Human Vaccine Institute (http://dhvi.duke.edu/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.