Tuberculosis (TB) is the leading cause of death for patients infected with HIV. The HIV epidemic has hastened the spread of TB and aided in the emergence of M. tuberculosis strains resistant to two or more anti-tuberculosis drugs causing multi-drug resistant TB (MDR-TB). There is an urgent need to develop novel therapies to control and prevent TB particularly in immunocompromised individuals. A major focus of the Jacobs laboratory research effort has been the development of genetic systems for generating defined mutations in M. tuberculosis and transferring these mutations amongst M. tuberculosis strains. Using these genetic systems, Dr. Jacobs has been able to begin to define the mechanisms of action of anti-TB drugs, mechanisms of resistance, and mechanisms of tuberculosis pathogenesis. This knowledge is providing novel strategies to develop new drugs, vaccines, and immunotherapeutics for TB. In addition, Jacobs laboratory has the ability to genetically manipulate existing TB vaccine strain, BCG, and engineer it into a recombinant vaccine vehicle capable of eliciting immune responses against cloned foreign antigen genes. They have significantly improved these capabilities and are expressing HIV antigens on BCG to make recombinant BCG::HIV vaccines.

The following projects are in progress in the Jacobs laboratory:

1. Identify and characterize virulence determinants of M. tuberculosis. A variety of different approaches are being used to identify the genes required for growth and persistence of M. tuberculosis in mice. Using the M. tuberculosis genomic sequence, targeted disruptions of putative virulence factors are being generated and tested for loss of virulence or persistence in mouse models. Alternatively, an efficient transposon mutagenesis system has been developed and a variety of screens including signature tag mutagenesis are being employed to identify genes responsible for growth and persistence in mice.

2. Determine the mechanisms of action of existing anti-tuberculosis drugs with the aim of developing improved chemotherapeutics. Without the availability of genetic systems for M. tuberculosis, determining the mechanisms of action of TB-specific drugs and the targets of drug action was not achievable. Using genetic approaches, they have identified the previously unknown targets of isoniazid, ethionamide, ethambutol, and pyrazinamide. A combination of biochemical and X-ray crystallographic analysis of the targets, in collaboration with Dr. Blanchard, has allowed them to unravel the mechanisms of action of the M. tuberculosis drugs. Moreover, this knowledge has provided new leads towards the development of novel chemotherapeutics to treat tuberculosis.

3. Development of recombinant BCG::HIV vaccines. Recombinant BCG expressing HIV antigens represents an exciting opportunity for the development of novel HIV vaccines that would be affordable in the Developing World. Such rBCG vaccines should be cost-effective to produce in the developing world. Moreover, since it is safe, long- lasting, and one of the only live-cell vaccines that can be administered to children at birth, recombinant BCG represents an attractive vaccine candidate for either eliciting protection or for priming the immune response to HIV antigens to be used in combination with rBCG. They will express a number of different HIV antigen genes so they are exported to the surface of BCG and optimize expression to elicit optimal immune responses.