Study of the Safety and Immunogenicity of Bacille Calmette Guerin (BCG) Vaccine

Summary

Tuberculosis (TB) kills about three million people annually. It is estimated that one third of the world's population are latently infected with Mycobacterium tuberculosis (M.tb). Multi-drug resistant strains of M.tb, and co-infection with M.tb and HIV present major new challenges. The currently available vaccine, M. bovis BCG, is largely ineffective at protecting against adult pulmonary disease in endemic areas and it is widely agreed that a new more effective tuberculosis vaccine is a major global public health priority1. However, it may be unethical and impractical to test and deploy a vaccine strategy that does not include BCG, as BCG does confer worthwhile protection against TB meningitis and leprosy. An immunisation strategy that includes BCG is also attractive because the populations in which this vaccine candidate will need to be tested will already have been immunised with BCG. M.tb is an intracellular organism. CD4+ Th1-type cellular responses are essential for protection and there is increasing evidence from animal and human studies that CD8+ T cells also play a protective role2. However, it has generally been difficult to induce strong cellular immune responses in humans using subunit vaccines. DNA vaccines induce both CD4+ and CD8+ T cells and thus offer a potential new approach to a TB vaccine. DNA vaccines encoding various antigens from M. tuberculosis have been evaluated in the murine model, and to date no DNA vaccine alone has been shown to be superior to BCG. A heterologous prime-boost immunisation strategy involves giving two different vaccines, each encoding the same antigen, several weeks apart. Such regimes are extremely effective at inducing a cellular immune response. Using a DNA- prime/MVA-boost immunisation strategy induces high levels of CD8+ T cells in animal models of malaria and HIV5, and high levels of both CD4+ and CD8+ T cells in animal models of TB. BCG immunisation alone induces only CD4+ T cells in mice. A prime-boost strategy using BCG as the prime and a recombinant MVA encoding an antigen from M.tb that is also present in BCG (antigen 85A: 'MVA85A') as the boost, induces much higher levels of CD4+ T cells than BCG or MVA85A alone. In addition, this regime generates specific CD8+ T cells that are undetectable following immunisation with BCG alone.

Timeline

Start

2004-02

Primary completion

2005-11

Completion

2005-11

Publications

• Background McShane H, Brookes R, Gilbert SC, Hill AV. Enhanced immunogenicity of CD4(+) t-cell responses and protective efficacy of a DNA-modified vaccinia virus Ankara prime-boost vaccination regimen for murine tuberculosis. Infect Immun. 2001 Feb;69(2):681-6. doi: 10.1128/IAI.69.2.681-686.2001.
• Background McShane H, Behboudi S, Goonetilleke N, Brookes R, Hill AV. Protective immunity against Mycobacterium tuberculosis induced by dendritic cells pulsed with both CD8(+)- and CD4(+)-T-cell epitopes from antigen 85A. Infect Immun. 2002 Mar;70(3):1623-6. doi: 10.1128/IAI.70.3.1623-1626.2002.
• Whelan KT, Pathan AA, Sander CR, Fletcher HA, Poulton I, Alder NC, Hill AV, McShane H. Safety and immunogenicity of boosting BCG vaccinated subjects with BCG: comparison with boosting with a new TB vaccine, MVA85A. PLoS One. 2009 Jun 16;4(6):e5934. doi: 10.1371/journal.pone.0005934.

Drugs

Indications