Structure based design of effective HtpG-derived vaccine antigens against M. tuberculosis

Novel fusion protein REA induces robust prime protection against tuberculosis in mice

While many novel candidates for tuberculosis vaccines are presently undergoing pre-clinical or clinical trials, none of them have been able to eliminate infection entirely. In this study, we engineered a potent chimeric protein vaccine candidate, Rv2299cD2D3-ESAT-6-Ag85B (REA), which induced Th1 and Th17 responses via dendritic cell maturation. REA-activated macrophages operated the killing mechanisms of Mycobacterium tuberculosis (MTB), such as phagosomal maturation and phagolysosome fusion, through the (PI3K)-p38 MAPK-Ca2+-NADPH oxidase pathway. Dendritic cells and macrophages activated by REA elicited synergistic anti-mycobacterial responses. Notably, REA-immunized mice suppressed MTB growth to undetectable levels at 16 weeks post-infection, which was supported by gross and pathologic findings and acid-fast staining of the lung tissues, and maintained antigen-specific multifunctional IFN-γ+IL-2+TNF-α CD4+ T and long-lasting T cells producing cytokines in the tissues. Our findings suggest that REA is an outstanding prime prophylactic vaccine candidate against tuberculosis.

HtpG-A Major Virulence Factor and a Promising Vaccine Antigen against Mycobacterium tuberculosis

Tuberculosis (TB) is the leading global cause of death f rom an infectious bacterial agent. Therefore, limiting its epidemic spread is a pressing global health priority. The chaperone-like protein HtpG of M. tuberculosis (Mtb) is a large dimeric and multi-domain protein with a key role in Mtb pathogenesis and promising antigenic properties. This dual role, likely associated with the ability of Heat Shock proteins to act both intra- and extra-cellularly, makes HtpG highly exploitable both for drug and vaccine development. This review aims to gather the latest updates in HtpG structure and biological function, with HtpG operating in conjunction with a large number of chaperone molecules of Mtb. Altogether, these molecules help Mtb recovery after exposure to host-like stress by assisting the whole path of protein folding rescue, from the solubilisation of aggregated proteins to their refolding. Also, we highlight the role of structural biology in the development of safer and more effective subunit antigens. The larger availability of structural information on Mtb antigens and a better understanding of the host immune response to TB infection will aid the acceleration of TB vaccine development.

Virulence Factors in Mycobacterium tuberculosis Infection: Structural and Functional Studies

Tuberculosis (TB) remains one of the main causes of death by infection, especially in immunocompromised patients [...].

ESAT-6 a Major Virulence Factor of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis (TB), is one of the most successfully adapted human pathogens. Human-to-human transmission occurs at high rates through aerosols containing bacteria, but the pathogen evolved prior to the establishment of crowded populations. Mtb has developed a particular strategy to ensure persistence in the host until an opportunity for transmission arises. It has refined its lifestyle to obviate the need for virulence factors such as capsules, flagella, pili, or toxins to circumvent mucosal barriers. Instead, the pathogen uses host macrophages, where it establishes intracellular niches for its migration into the lung parenchyma and other tissues and for the induction of long-lived latency in granulomas. Finally, at the end of the infection cycle, Mtb induces necrotic cell death in macrophages to escape to the extracellular milieu and instructs a strong inflammatory response that is required for the progression from latency to disease and transmission. Common to all these events is ESAT-6, one of the major virulence factors secreted by the pathogen. This narrative review highlights the recent advances in understanding the role of ESAT-6 in hijacking macrophage function to establish successful infection and transmission and its use as a target for the development of diagnostic tools and vaccines.

A Structural View at Vaccine Development against M. tuberculosis

Tuberculosis (TB) is still the leading global cause of death from an infectious bacterial agent. Limiting tuberculosis epidemic spread is therefore an urgent global public health priority. As stated by the WHO, to stop the spread of the disease we need a new vaccine, with better coverage than the current Mycobacterium bovis BCG vaccine. This vaccine was first used in 1921 and, since then, there are still no new licensed tuberculosis vaccines. However, there is extremely active research in the field, with a steep acceleration in the past decades, due to the advance of technologies and more rational vaccine design strategies. This review aims to gather latest updates in vaccine development in the various clinical phases and to underline the contribution of Structural Vaccinology (SV) to the development of safer and effective antigens. In particular, SV and the development of vaccine adjuvants is making the use of subunit vaccines, which are the safest albeit the less antigenic ones, an achievable goal. Indeed, subunit vaccines overcome safety concerns but need to be rationally re-engineered to enhance their immunostimulating effects. The larger availability of antigen structural information as well as a better understanding of the complex host immune response to TB infection is a strong premise for a further acceleration of TB vaccine development.