Antigen identification strategies and preclinical evaluation models for advancing tuberculosis vaccine development.

In its myriad devastating forms, Tuberculosis (TB) has existed for centuries, and humanity is still affected by it. Mycobacterium tuberculosis (M. tuberculosis), the causative agent of TB, was the foremost killer among infectious agents until the COVID-19 pandemic. One of the key healthcare strategies available to reduce the risk of TB is immunization with bacilli Calmette-Guerin (BCG). Although BCG has been widely used to protect against TB, reports show that BCG confers highly variable efficacy (0-80%) against adult pulmonary TB. Unwavering efforts have been made over the past 20 years to develop and evaluate new TB vaccine candidates. The failure of conventional preclinical animal models to fully recapitulate human response to TB, as also seen for the failure of MVA85A in clinical trials, signifies the need to develop better preclinical models for TB vaccine evaluation. In the present review article, we outline various approaches used to identify protective mycobacterial antigens and recent advancements in preclinical models for assessing the efficacy of candidate TB vaccines.

Identification of Mycobacterium tuberculosis BioA inhibitors by using structure-based virtual screening.

BACKGROUND: 7,8-Diaminopelargonic acid synthase (BioA), an enzyme of biotin biosynthesis pathway, is a well-known promising target for anti-tubercular drug development. METHODS: In this study, structure-based virtual screening was employed against the active site of BioA to identify new chemical entities for BioA inhibition and top ranking compounds were evaluated for their ability to inhibit BioA enzymatic activity. RESULTS: Seven compounds inhibited BioA enzymatic activity by greater than 60% at 100 µg/mL with most potent compounds being A36, A35 and A65, displaying IC50 values of 10.48 µg/mL (28.94 µM), 33.36 µg/mL (88.16 µM) and 39.17 µg/mL (114.42 µM), respectively. Compounds A65 and A35 inhibited Mycobacterium tuberculosis (M. tuberculosis) growth with MIC90 of 20 µg/mL and 80 µg/mL, respectively, whereas compound A36 exhibited relatively weak inhibition of M. tuberculosis growth (83% inhibition at 200 µg/mL). Compound A65 emerged as the most potent compound identified in our study that inhibited BioA enzymatic activity and growth of the pathogen and possessed drug-like properties. CONCLUSION: Our study has identified a few hit molecules against M. tuberculosis BioA that can act as potential candidates for further development of potent anti-tubercular therapeutic agents.

An attenuated quadruple gene mutant of Mycobacterium tuberculosis imparts protection against tuberculosis in guinea pigs.

Previously we had developed a triple gene mutant of Mycobacterium tuberculosis (MtbΔmms) harboring disruption in three genes, namely mptpA, mptpB and sapM Though vaccination with MtbΔmms strain induced protection in the lungs of guinea pigs, the mutant strain failed to control the hematogenous spread of the challenge strain to the spleen. Additionally, inoculation with MtbΔmms resulted in some pathological damage to the spleens in the early phase of infection. In order to generate a strain that overcomes the pathology caused by MtbΔmms in spleen of guinea pigs and controls dissemination of the challenge strain, MtbΔmms was genetically modified by disrupting bioA gene to generate MtbΔmmsb strain. Further, in vivo attenuation of MtbΔmmsb was evaluated and its protective efficacy was assessed against virulent M. tuberculosis challenge in guinea pigs. MtbΔmmsb mutant strain was highly attenuated for growth and virulence in guinea pigs. Vaccination with MtbΔmmsb mutant generated significant protection in comparison to sham-immunized animals at 4 and 12 weeks post-infection in lungs and spleen of infected animals. However, the protection imparted by MtbΔmmsb was significantly less in comparison to BCG immunized animals. This study indicates the importance of attenuated multiple gene deletion mutants of M. tuberculosis for generating protection against tuberculosis.

Boosting with recombinant MVA expressing M. tuberculosis α-crystallin antigen augments the protection imparted by BCG against tuberculosis in guinea pigs.

Tuberculosis (TB) is one of the major causes of mortality all over the globe. BCG, the only vaccine available against this disease has been successful in preventing the severe forms of childhood TB. However, the unsatisfactory performance of BCG in controlling the adult pulmonary tuberculosis has made the development of an effective vaccine against M. tuberculosis a prime objective of the TB research. In this study, a genetically stable, marker-free recombinant MVA expressing α-crystallin of M. tuberculosis (rMVA.acr) was generated which was further evaluated for its ability to impart protection as a booster vaccine against tuberculosis in a heterologous prime boost approach. Our results demonstrated that intradermal delivery of rMVA.acr was able to efficiently boost the BCG induced protection against M. tuberculosis infection in guinea pigs by significantly reducing the pulmonary bacillary load (1.27 log10 fewer bacilli) in comparison to BCG vaccination alone. In addition, boosting BCG vaccinated animals with intramuscular delivery of rMVA.acr resulted in significantly superior protective efficacy in both lungs and spleen with 0.83 log10 and 0.74 log10 CFU fewer bacilli, respectively, when compared to animals vaccinated with BCG only. These findings establish the promise of this prime-boost strategy involving rMVA.acr in enhancing the efficacy of BCG.