Disruption of the SapM locus in Mycobacterium bovis BCG improves its protective efficacy as a vaccine against M. tuberculosis

Nele Festjens,Peter Brouckaert,Peggy Jacques,Monique A Willart,Evelyn Plets,Eef Parthoens,Dirk Elewaut,Anjana Batni,Erica Houthuys,Bram Laukens,Pieter Bogaert,Kris Huygen,Bart N Lambrecht,Nico Callewaert,Dieter Vanderschaeghe,Bob Asselbergh,Riet De Rycke

doi:10.1002/emmm.201000125

Abstract

Mycobacterium bovis bacille Calmette-Guerin (BCG) provides only limited protection against pulmonary tuberculosis. We tested the hypothesis that BCG might have retained immunomodulatory properties from its pathogenic parent that limit its protective immunogenicity. Mutation of the molecules involved in immunomodulation might then improve its vaccine potential. We studied the vaccine potential of BCG mutants deficient in the secreted acid phosphatase, SapM, or in the capping of the immunomodulatory ManLAM cell wall component with α-1,2-oligomannoside. Both systemic and intratracheal challenge of mice with Mycobacterium tuberculosis following vaccination showed that the SapM mutant, compared to the parental BCG vaccine, provided better protection: it led to longer-term survival. Persistence of the SapM-mutated BCG in vivo resembled that of the parental BCG indicating that this mutation will likely not compromise the safety of the BCG vaccine. The SapM mutant BCG vaccine was more effective than the parental vaccine in inducing recruitment and activation of CD11c+MHC-IIintCD40int dendritic cells (DCs) to the draining lymph nodes. Thus, SapM acts by inhibiting recruitment of DCs and their activation at the site of vaccination.

Highlights

One-third of the world’s population is infected with Mycobacterium tuberculosis (M. tb), the cause of tuberculosis (TB)
Both systemic and intratracheal challenge of mice with Mycobacterium tuberculosis following vaccination showed that the survival as compared to non-vaccinated mice (SapM) mutant, compared to the parental bacille Calmette-Guerin (BCG) vaccine, provided better protection: it led to longer-term survival
The SapM mutant is more protective than M. bovis BCG wild-type (WT) as well as the Mb2203 and Mb1661c mutants in BALB/c mice BALB/c mice were vaccinated subcutaneously with 105 CFU of the parental or mutant M. bovis BCG strains

Summary

INTRODUCTION

One-third of the world’s population is infected with Mycobacterium tuberculosis (M. tb), the cause of tuberculosis (TB). If a M. bovis BCG strain that is more protective than the licensed strain could be developed by targeted inactivation of endogenous genes rather than by expression of heterologous virulence genes, safety concerns could likely be further assuaged and the stability of the genetic manipulation could be assured in a more straightforward way In this regard it is important to note that, as in attenuated M. tb (Hinchey et al, 2007), the secA2 mutation in BCG in combination with anti-oxidant gene mutations (such as SodA) enhances the BCG vaccine’s efficacy in mice (Sadagopal et al, 2009), through a mechanism that involves increased induction of apoptosis in phagocytes. We show that the SapM mutant (but not the ManLAM mutants) is a better vaccine than the parental M. bovis BCG strain, even when assessed in the most stringent tests (long-term survival of TB-challenged animals) While analysing this improved vaccine efficiency, we found that the SapM mutation does not act by counteracting the inhibition of phagosomal maturation in APCs (and neither does ManLAM capping mutation). Boding well for potential synergism of combined-mutation vaccine design, other validated mechanisms of action of improved live-Mycobacterium vaccines were not at play: when using the SapM mutant BCG, reactive oxygen species (ROS) production in APCs was not increased (Hinchey et al, 2007; Sadagopal et al, 2009) and neither was induction of autophagy (Jagannath et al, 2009)

RESULTS

DISCUSSION

MATERIALS AND METHODS