Use of Soluble Extracellular Regions of MmpL (SERoM) as Vaccines for Tuberculosis.

The current vaccine for tuberculosis (TB) is a live attenuated strain of Mycobacterium bovis (BCG) and while effective at reducing the potential for disseminated TB in young children its disease protection rates in adults is highly variable while it confers little protection against latent TB. With these limitations a new vaccine is desperately needed. We investigated the efficacy of three members of the mycobacterial membrane protein Large (MmpL) family as potential subunit vaccines for TB. MmpLs are large, multifunctional integral membrane proteins, and as such are recalcitrant to purification. Here, we describe a strategy of producing synthetic antigens comprised of the soluble, extracellular regions of MmpL (SERoM)-1, MmpL8 and MmpL10 (SERoM-8 and 10 respectively) as potential vaccine candidates. SERoM-1 and SERoM-8 were determined to be highly immunogenic by IFN-γ ELISpot assays, with 0.1% of all splenocytes from SERoM-1 vaccinated mice producing IFN-γ when re-stimulated with MmpL1. A combined SERoM-1, -8 and -10 vaccine demonstrated significant protection against M. tuberculosis challenge in a murine model of TB, resulting in approximately 10-fold reduction in bacterial numbers following challenge in both the lungs and spleens compared to adjuvant only vaccinated mice. These protective effects were comparable to that achieved with BCG.