Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2016

The development of a protein-based vaccine against disease caused by Mycobacterium ulcerans (#39)

Kirstie M. Mangas 1 , Estelle Marion 2 3 , Laurent Marsollier 2 3 , Brendon Y. Chua 1 , Nicholas J. Tobias 1 , David C. Jackson 1 , Timothy P. Stinear 1
  1. Department of Microbiology and Immunology, Peter Doherty Institute, University of Melbourne, Melbourne, VIC, Australia
  2. ATOMycA, Inserm Avenir Team, CRCNA, Inserm U892, 6299 CNRS, Angers, France
  3. LUNAM, Université d’Angers, Angers, France

Background: Mycobacterium ulcerans is the causative agent of a debilitating skin disease known as Buruli ulcer (BU). Human disease is characterised by necrosis of subcutaneous tissue and dependent on the presence of mycolactone, an immunosuppressive toxin produced by the bacterium. As there is currently no vaccine against BU, the purpose of this study was to investigate the potential of two M. ulcerans proteins as protective antigens for a recombinant M. ulcerans protein-based vaccine strategy.

Methods and Results: Two highly expressed, cell–wall associated M. ulcerans proteins, MUL_3720 and Hsp18, were identified and separately formulated with a TLR2-agonist-based lipopeptide (Pam2Cys) adjuvant. Preliminary vaccination studies with both protein vaccines identified high protein-specific antibody titres in BALB/c mice accompanied by the production of cytokines involved in the Th17 response. Three strains of mice (C57BL/6, BALB/c and FVB/N) were then vaccinated with each of the protein formulations to elicit antibody responses. High antigen-specific antibody titres were induced in all vaccinated animals (with protein alone or with protein and adjuvant). However, upon challenge with M. ulcerans, all C57BL/6 and BALB/c mice developed ulcers by day 40 post-infection. No significant difference was observed in the proportion of time-to-onset of ulceration between groups vaccinated with BCG compared to protein and adjuvant vaccination.

Conclusions: Whilst recombinant MUL_3720 or Hsp18-based vaccine candidates elicit strong antibody production, this did not translate into evidence of protection against BU. Previous studies by Tanghe et al. have shown BCG is incapable of providing full protection against BU but delays the onset of symptoms compared to naïve mice and reduces bacterial burden. Our subunit vaccines whilst providing comparable protection to BCG were unsuccessful at preventing BU. This work highlights the need to explore alternative vaccine targets, such as the mycolactone synthesis pathway, which is essential to the virulence of M. ulcerans.