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Protective Efficacy and Pulmonary Immune Response Following Subcutaneous and Intranasal BCG Administration in Mice

Despite global coverage of intradermal BCG vaccination, tuberculosis remains one of the most prevalent infectious diseases in the world. Preclinical data ...

University of Zaragoza

The development of a new tuberculosis vaccine is an urgent need due to the failure of the current vaccine, BCG, to protect against the respiratory form of the disease. MTBVAC is an attenuated Mycobacterium tuberculosis vaccine candidate genetically engineered to fulfil the Geneva consensus requirements to enter human clinical trials. We selected a M. tuberculosis clinical isolate to generate two independent deletions without antibiotic-resistance markers in the genes phoP, coding for a transcription factor key for the regulation of M. tuberculosis virulence, and fadD26, essential for the synthesis of the complex lipids phthiocerol dimycocerosates (DIM), one of the major mycobacterial virulence factors. The resultant strain MTBVAC exhibits safety and biodistribution profiles similar to BCG and confers superior protection in preclinical studies. These features have enabled MTBVAC to be the first live attenuated M. tuberculosis vaccine to enter clinical evaluation.

Construction, characterization and preclinical evaluation of MTBVAC, the first live-attenuated M. tuberculosis-based vaccine to enter clinical trials.

Safety of individuals at risk of immune suppression is an important concern for live vaccines. The new-generation tuberculosis vaccine candidate MTBVAC, a genetically engineered doubly attenuated Mycobacterium tuberculosis mutant with deletions in phoP and fadD26 virulence genes has demonstrated comparable safety in different relevant animal models and superior protection in mice as compared to the only currently licensed tuberculosis vaccine Mycobacterium bovis BCG. Here we describe the construction of a highly attenuated MTBVAC-based live vaccine by an additional gene inactivation generated in erp of MTBVAC. The gene product of erp is an exported repeated protein (Erp), a virulence factor described to be involved in intracellular replication of M. tuberculosis. The resultant strain, MTBVAC erp(-), was tested in severe combined immunodeficiency (SCID) mouse model showing to be severely attenuated when compared to BCG and MTBVAC. Experiments conducted in immunocompetent mice revealed that the hyper-attenuated profile observed with MTBVAC erp(-) strain did not compromise its protective efficacy profile in comparison with BCG. These results postulate MTBVAC erp(-) as a potential tuberculosis vaccine candidate for use in high-risk populations of immune suppression (e.g., due to HIV infection), where the use of BCG is not recommended.

Hyper-attenuated MTBVAC erp mutant protects against tuberculosis in mice.

Some of the most promising novel tuberculosis vaccine strategies currently under development are based on respiratory vaccination, mimicking the natural route of infection. In this work, we have compared pulmonary and subcutaneous delivery of BCG vaccine in the tuberculosis-susceptible DBA/2 mouse strain, a model in which parenterally administered BCG vaccine does not protect against tuberculosis. Our data show that intranasally but not subcutaneously administered BCG confers robust protection against pulmonary tuberculosis challenge. In addition, our results indicate that pulmonary vaccination triggers a Mycobacterium tuberculosis-specific mucosal immune response orchestrated by interleukin 17A (IL-17A). Thus, IL-17A neutralization in vivo reduces protection and abrogates M. tuberculosis-specific immunoglobulin A (IgA) secretion to respiratory airways and lung expression of polymeric immunoglobulin receptor induced following intranasal vaccination. Together, our results demonstrate that pulmonary delivery of BCG can overcome the lack of protection observed when BCG is given parenterally, suggesting that respiratory tuberculosis vaccines could have an advantage in tuberculosis-endemic countries, where intradermally administered BCG has inefficient effectiveness against pulmonary tuberculosis.

Pulmonary but Not Subcutaneous Delivery of BCG Vaccine Confers Protection to Tuberculosis-Susceptible Mice by an Interleukin 17-Dependent Mechanism.

Development of novel more efficient preventive vaccines against tuberculosis (TB) is crucial to achieve TB eradication by 2050, one of the Millennium Development Goals (MDG) for the current century. MTBVAC is the first and only live attenuated vaccine based on a human isolate of Mycobacterium tuberculosis developed as BCG-replacement strategy in newborns that has entered first-in-human adult clinical trials. In this work, we characterize the safety, immunogenicity and protective efficacy of MTBVAC in a model of newborn C57/BL6 mice. Our data clearly indicate that MTBVAC is safe for newborn mice, and does not affect animal growth or organ development. In addition, MTBVAC-vaccinated mice at birth showed enhanced immunogenicity and better protection against M. tuberculosis challenge in comparison with BCG.

MTBVAC vaccine is safe, immunogenic and confers protective efficacy against Mycobacterium tuberculosis in newborn mice.

Granzyme A, a serine protease expressed in the granules of cytotoxic T and Natural Killer cells, is involved in the generation of pro-inflammatory cytokines by macrophages. Granzyme A has been described to induce in macrophages in vitro the activation of pro-inflammatory pathways that impair intracellular mycobacterial replication. In the present study, we explored the physiological relevance of Granzyme A in the control of pulmonary Mycobacterium tuberculosis infection in vivo. Our results show that, even though Granzyme A is expressed by cytotoxic cells from mouse lungs during pulmonary infection, its deficiency in knockout mice does not have an effect in the control of M. tuberculosis infection. In addition our findings indicate that absence of Granzyme A does not affect the protection conferred by the live-attenuated M. tuberculosis vaccine MTBVAC. Altogether, our findings are in apparent contradiction with previously published in vitro results and suggest that Granzyme A does not have a crucial role in vivo in the protective response to tuberculosis.

Santiago Uranga

Department of Microbiology

University of Zaragoza

Protective Efficacy and Pulmonary Immune Response Following Subcutaneous and Intranasal BCG Administration in Mice

Santiago Uranga

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Microbiology

University of Zaragoza

Protective Efficacy and Pulmonary Immune Response Following Subcutaneous and Intranasal BCG Administration in Mice

Department of Microbiology