Engineering a new vaccine platform for heterologous antigen delivery in live-attenuated Mycobacterium tuberculosis

Tuberculosis vaccines and therapeutic drug: challenges and future directions

Tuberculosis (TB) remains a prominent global health challenge, with the World Health Organization documenting over 1 million annual fatalities. Despite the deployment of the Bacille Calmette-Guérin (BCG) vaccine and available therapeutic agents, the escalation of drug-resistant Mycobacterium tuberculosis strains underscores the pressing need for more efficacious vaccines and treatments. This review meticulously maps out the contemporary landscape of TB vaccine development, with a focus on antigen identification, clinical trial progress, and the obstacles and future trajectories in vaccine research. We spotlight innovative approaches, such as multi-antigen vaccines and mRNA technology platforms. Furthermore, the review delves into current TB therapeutics, particularly for multidrug-resistant tuberculosis (MDR-TB), exploring promising agents like bedaquiline (BDQ) and delamanid (DLM), as well as the potential of host-directed therapies. The hurdles in TB vaccine and therapeutic development encompass overcoming antigen diversity, enhancing vaccine effectiveness across diverse populations, and advancing novel vaccine platforms. Future initiatives emphasize combinatorial strategies, the development of anti-TB compounds targeting novel pathways, and personalized medicine for TB treatment and prevention. Despite notable advances, persistent challenges such as diagnostic failures and protracted treatment regimens continue to impede progress. This work aims to steer future research endeavors toward groundbreaking TB vaccines and therapeutic agents, providing crucial insights for enhancing TB prevention and treatment strategies.

MTBVAC induces superior antibody titers and IgG avidity compared to BCG vaccination in non-human primates

The only currently licensed vaccine against tuberculosis (TB), Bacille Calmette Guérin (BCG), is insufficient to control the epidemic. MTBVAC is a live attenuated strain of Mycobacterium tuberculosis (M.tb) and is one the most advanced TB vaccine candidates in the pipeline. It is more efficacious than BCG in preclinical models including non-human primates (NHPs), and has demonstrated safety and immunogenicity in human populations. To better understand the immune mechanisms underlying the superior efficacy conferred by MTBVAC, we characterized M.tb-specific antibody responses in NHPs vaccinated with either BCG or MTBVAC. MTBVAC vaccination induced higher titers of IgG, IgM and IgA, and higher avidity IgG compared with BCG vaccination. IgG avidity correlated with protection following M.tb challenge in the same animals, validating the association previously reported between this measure and protection in the context of intravenous BCG vaccination, suggesting that IgG avidity may represent a relevant marker or correlate of protection from TB.

Challenges and Strategies for Developing Recombinant Vaccines against Leptospirosis: Role of Expression Platforms and Adjuvants in Achieving Protective Efficacy

The first leptospiral recombinant vaccine was developed in the late 1990s. Since then, progress in the fields of reverse vaccinology (RV) and structural vaccinology (SV) has significantly improved the identification of novel surface-exposed and conserved vaccine targets. However, developing recombinant vaccines for leptospirosis faces various challenges, including selecting the ideal expression platform or delivery system, assessing immunogenicity, selecting adjuvants, establishing vaccine formulation, demonstrating protective efficacy against lethal disease in homologous challenge, achieving full renal clearance using experimental models, and reproducibility of protective efficacy against heterologous challenge. In this review, we highlight the role of the expression/delivery system employed in studies based on the well-known LipL32 and leptospiral immunoglobulin-like (Lig) proteins, as well as the choice of adjuvants, as key factors to achieving the best vaccine performance in terms of protective efficacy against lethal infection and induction of sterile immunity.

Proteome Profile Changes Induced by Heterologous Overexpression of Mycobacterium tuberculosis-Derived Antigens PstS-1 (Rv0934) and Ag85B (Rv1886c) in Mycobacterium microti

The development of new tuberculosis vaccines remains a global priority, and recombinant vaccines are a frequently investigated option. These vaccines follow a molecular strategy that may enhance protective efficacy. However, their functional differences, particularly with respect to glycosylation, remain unknown. Recent studies have shown that glycosylation plays a key role in the host-pathogen interactions during immune recognition. The aim of this study was to determine the differences in the glycosylation profiles of two recombinant strains of Mycobacterium microti, overexpressing Ag85B (Rv1886c) and PstS-1 (Rv0934) antigens of M. tuberculosis. For each strain, the glycosylation profile was determined by Western blotting with lectins. The results showed the presence of mannosylated proteins and evidence of linked sialic acid proteins. Interestingly, different proteome and glycoproteome profiles were observed between the two recombinant strains and the wild-type strain. We have shown here that the construction of the recombinant strains of M. microti has altered the proteome and glycosylation profiles of these strains, leading us to ask what impact these changes might have on the immune response.

Codon usage divergence of important functional genes in Mycobacterium tuberculosis

Sequence characteristics are usually used to explain the adaptive ability to hosts, metabolism, genetic diversity, drug resistance, and infectivity of Mycobacterium tuberculosis. Exploring the codon usage pattern of coding sequences in Mycobacterium tuberculosis is of great significance. In the present study, two hundred random complete genomes of Mycobacterium tuberculosis were downloaded from the National Center for Biotechnology Information database. The important codon usage pattern, such as the codon bias index, the effective number of codons, the relative synonymous codon usage as well as the base component, of twenty one specific functional genes were counted or calculated. The differences of the relative synonymous codon usage values among those functional genes, and the summation of the standard deviations of codon usage parameters were used to evaluate the divergence degree of the concerned genes. The results show that among the concerned genes, 1) all genes are high GC sequences, the codon usage frequency corresponding to each amino acid of these functional genes had a significant bias; 2) the genes of those with high effective number of codons, such as the coding sequences of Myco-bacterial membrane protein large family, usually have higher divergences; and 3) genes with lower divergences, such as the ag85A and the sigH, are usually highly conserved and are often used as drug target genes. The findings of the present work would improve new understandings on the evolution of Mycobacterium tuberculosis and on the measures to prevent and control tuberculosis from the gene engineering.

A Mycobacteriophage-Based Vaccine Platform: SARS-CoV-2 Antigen Expression and Display

The explosion of SARS-CoV-2 infections in 2020 prompted a flurry of activity in vaccine development and exploration of various vaccine platforms, some well-established and some new. Phage-based vaccines were described previously, and we explored the possibility of using mycobacteriophages as a platform for displaying antigens of SARS-CoV-2 or other infectious agents. The potential advantages of using mycobacteriophages are that a large and diverse variety of them have been described and genomically characterized, engineering tools are available, and there is the capacity to display up to 700 antigen copies on a single particle approximately 100 nm in size. The phage body may itself be a good adjuvant, and the phages can be propagated easily, cheaply, and to high purity. Furthermore, the recent use of these phages therapeutically, including by intravenous administration, suggests an excellent safety profile, although efficacy can be restricted by neutralizing antibodies. We describe here the potent immunogenicity of mycobacteriophage Bxb1, and Bxb1 recombinants displaying SARS-CoV-2 Spike protein antigens.