TB vaccine including a latency-associated protein shows pre- and post-exposure efficacy in mouse model
Richard Jefferys, TAG
In a new paper published yesterday by Nature Medicine , researchers from the Statens Serum Institut (SSI) in Denmark  describe encouraging results obtained with a new TB vaccine candidate. The design of the vaccine was informed by data showing that a particular TB protein, Rv2660c, remains strongly expressed during latent infection. This knowledge prompted the development of a multistage vaccine including Rv2660c along with two other TB antigens, Ag85B and ESAT-6. The resulting fusion protein vaccine is named H56. The goal is to create a vaccine capable of preventing active TB regardless of whether it is given before or after exposure.
In a mouse model of TB infection, the H56 vaccine was shown to be significantly superior in reducing bacterial load when compared to both the standard BCG vaccine and another candidate, H1, which contains only Ag85B and ESAT-6 antigens. The differences in efficacy took some time to become evident: 12 weeks after challenge in comparison to H1, and 24 weeks in comparison to BCG. Immune responses to the Rv2660c protein were weak early on but grew in magnitude over the period of follow up. In an experiment designed to evaluate the potential for post-exposure protection, H56 was found to provide a significant degree of protection against TB reactivation.
Based on these results, SSI is now initiating clinical development of H56. The current status of new TB vaccine candidates in clinical trials, including SSIs, is summarised in a recent report from the 2010 Global TB Vaccines Forum. 
Source: TAG basic science blog. (24 January 2011).
- Aagaard C et al. A multistage tuberculosis vaccine that confers efficient protection before and after exposure. Nature Medicine (2011) doi:10.1038/nm.2285. Published online 23 January 2011.
- Statens Serum Institut (SSI)
- Jefferys R et al. Tallying the TB vaccines in clinical trials.