Accelerating Development of Therapeutic Tuberculosis Vaccines Using an Ex Vivo Immune Assay Platform

Drug treatment and vaccination remain the main strategies to control tuberculosis (TB), which is the leading infectious cause of death globally. Lengthy treatment is often cited as a major obstacle towards improved control of TB. It has been proposed that a combination of TB vaccination with pharmacological treatment, termed therapeutic vaccination, may provide a greater therapeutic value. Several therapeutic TB vaccine candidates have been developed and are currently progressing in the pipeline. We hypothesise that an ex-vivo mycobacterial growth inhibition assay (MGIA) can be implemented to investigate and accelerate development of therapeutic vaccination strategies for TB, in the context of both human clinical and animal murine studies. This thesis describes for the first time, the combined effect of immunoprophylaxis by routine vaccination with Bacillus Calmette–Guérin (BCG) and chemotherapy using the ex vivo immune assay platform. The first research chapter of the thesis elaborates a proofof- principle study investigating the combined effect between historical BCG vaccination and two major first-line TB drugs (isoniazid and rifampicin), which is considered essential to further expedite the development of therapeutic vaccination strategies for TB. The second part of the thesis describes a study in which immunisation of mice with RUTI, a novel therapeutic TB vaccine candidate, was shown to enhance inhibition of mycobacterial growth ex vivo by inducing a shift of monocyte phenotype. We also investigated the effects of RUTI and BCG vaccination towards ex vivo drug-mediated killing in mice. The third research part of the thesis discusses the impact of individual-level factors on ex-vivo mycobacterial growth inhibition, specifically the influence of immune cell phenotype, cytomegalovirus-specific response and sex on immunity following BCG vaccination in humans. In the absence of an immune correlate of protection following TB vaccination, implementation of the ex vivo MGIA assay could be beneficial to screen TB vaccine candidates at early phases in order to prioritise which candidates should be tested with the available funding and field sites. Collectively, our findings support the implementation of MGIA as an effort to accelerate the development of therapeutic TB vaccines.