Optimizing the Boosting Schedule of Subunit Vaccines Consisting of BCG and "Non-BCG" Antigens to Induce Long-Term Immune Memory

Recombinant protein Ag85B-Rv2660c-MPT70 promotes quality of BCG-induced immune response against Mycobacterium tuberculosis H37Ra

Introduction

Bacillus Calmette-Guérin (BCG), the only licensed vaccine against Mycobacterium tuberculosis (Mtb) infection, has been extensively used worldwide for over 100 years, but the epidemic of tuberculosis (TB) remains a major challenge to human health and well-being. The quest for a more effective vaccination strategy against the Mtb infection continues. Boosting the protective immunity induced by BCG with recombinant protein is a feasible approach to improve the efficacy of BCG, due to the proven safety and effectiveness of recombinant proteins as vaccination regimes against a variety of infectious diseases. While being shown to be promising in clinical trials in preventing Mtb infection, data suggest this strategy requires further improvement.

Methods

In this study, we developed a novel fusion of proteins derived from major antigenic components of Mtb, including Ag85B, Rv2660c, and MPT70 (ARM), and assessed its antigenicity and ability to boost BCG efficacy in a murine model.

Results

The results demonstrated that the ARM immunization induced antigen-specific T and B cell responses and reduced the Mtb H37Ra burdens in the lungs and spleen. Mice that were primed with BCG and boosted with the ARM mounted a Th1-type immune response, characterized by an increased proportion of multi-functional ARM- and Mtb lysate-specific CD4+ T cells that produced IFN-γ, TNF-α, and IL-2 compared to BCG alone, and reduced the Mtb burden without the development of severe lung pathological inflammation.

Discussion

The results of our study demonstrate that the ARM boost improves the quality of the BCG-induced immune response, increases its potency of pathogen reduction, and offers an additional option for enhancing the efficacy of BCG vaccination.

Enhancing cell-mediated immunity through dendritic cell activation: the role of Tri-GalNAc-modified PLGA-PEG nanoparticles encapsulating SR717

Introduction

Vaccines against intracellular pathogens like Mycobacterium tuberculosis (M. tuberculosis) require the induction of effective cell-mediated immunity. Adjuvants primarily enhance antigen-induced adaptive immunity by promoting the activation of antigen-presenting cells (APCs).This study is to develop an adjuvant targeted to dendritic cells (DCs), one of the main APCs, so as to assist in inducing a long-term cellular immune response to M. tuberculosis protein antigens.

Methods

Polylactic-co-glycolic acid-polyethylene glycol (PLGA-PEG) nanoparticles (NPs) modified with Triantennary N-Acetylgalactosamine (Tri-GalNAc) were prepared to target DCs. Additionally, the stimulator of interferon genes (STING) agonist SR717 was encapsulated within PLGA-PEG NPs to activate DCs. Meanwhile, M. tuberculosis fusion protein (TP) was encapsulated in PLGA-PEG NPs to construct vaccine candidates: TP/Tri-GalNAc-PLGA-PEG-SR717 (TP/GPS in short) and TP/ Tri-GalNAc-PLGA-PEG (TP/GP in short). The targeting and activation effects of these NPs were assessed in vitro and in vivo, and their immunogenicity were evaluated in mice.

Results

Tri-GalNAc modification significantly enhanced the targeting of NPs to DCs, and encapsulated SR717 effectively promoted the maturation and activation of DCs. TP/GPS elicited a potent antigen-specific T cell immune response and successfully induced long-term immune memory in mice. Moreover, after the mice were infected with H37Ra via nasal instillation, TP/GPS significantly reduced the bacterial load in their lungs.

Discussion

Tri-GalNAc-modified PLGA-PEG NPs in combination with SR717 targeted and activated DCs, effectively assisting M. tuberculosis antigen in inducing long-term T cell-mediated immunity. This approach offers an innovative and effective adjuvant strategy for the development of subunit vaccine against intracellular pathogen.

The combination of Mycobacterium tuberculosis fusion proteins LT33 and LT28 induced strong protective immunity in mice

Effective subunit vaccines for tuberculosis (TB) must target antigenic components at various stages of infection. In this study, we constructed fusion proteins using secreted antigens from Mycobacterium tuberculosis (M. tuberculosis), specifically ESAT6, CFP10, MPT64, and Rv2645 from the proliferation stage, along with latency-associated antigens Rv1738 and Rv1978. The resulting fusion proteins, designated LT33 (ESAT6-CFP10-Rv1738) and LT28 (MPT6461-170-Rv19788-60-Rv264521-80), were combined with an adjuvant containing dimethyldioctadecylammonium bromide (DDA), polyriboinosinic polyribocytidylic acid (PolyI:C), and cholesterol to construct subunit vaccines. We evaluated the subunit vaccine effect in C57BL/6 mice and revealed that LT33 and LT28 exhibited strong immunogenicity and induced protective efficacy against aerosol challenge with M. tuberculosis H37Rv. Notably, the combination of LT33 and LT28 led to a significant reduction of 0.77 log10 colony-forming units (CFU) of H37Rv in the lungs compared to the adjuvant control group, highlighting their potential as promising candidates for subunit vaccine against M. tuberculosis infection.

DNA and RNA vaccines against tuberculosis: a scoping review of human and animal studies

Introduction

To comprehensively identify and provide an overview of in vivo or clinical studies of nucleic acids (NA)-based vaccines against TB we included human or animal studies of NA vaccines for the prevention or treatment of TB and excluded in vitro or in silico research, studies of microorganisms other than M. tuberculosis, reviews, letters, and low-yield reports.

Methods

We searched PubMed, Scopus, Embase, selected Web of Science and ProQuest databases, Google Scholar, eLIBRARY.RU, PROSPERO, OSF Registries, Cochrane CENTRAL, EU Clinical Trials Register, clinicaltrials.gov, and others through WHO International Clinical Trials Registry Platform Search Portal, AVMA and CABI databases, bioRxiv, medRxiv, and others through OSF Preprint Archive Search. We searched the same sources and Google for vaccine names (GX-70) and scanned reviews for references. Data on antigenic composition, delivery systems, adjuvants, and vaccine efficacy were charted and summarized descriptively.

Results

A total of 18,157 records were identified, of which 968 were assessed for eligibility. No clinical studies were identified. 365 reports of 345 animal studies were included in the review. 342 (99.1%) studies involved DNA vaccines, and the remaining three focused on mRNA vaccines. 285 (82.6%) studies used single-antigen vaccines, while 48 (13.9%) used multiple antigens or combinations with adjuvants. Only 12 (3.5%) studies involved multiepitope vaccines. The most frequently used antigens were immunodominant secretory antigens (Ag85A, Ag85B, ESAT6), heat shock proteins, and cell wall proteins. Most studies delivered naked plasmid DNA intramuscularly without additional adjuvants. Only 4 of 17 studies comparing NA vaccines to BCG after M. tuberculosis challenge demonstrated superior protection in terms of bacterial load reduction. Some vaccine variants showed better efficacy compared to BCG.

Systematic review registration

https://osf.io/, identifier F7P9G.

Tuberculosis Vaccines and T Cell Immune Memory

Tuberculosis (TB) remains a major infectious disease partly due to the lack of an effective vaccine. Therefore, developing new and more effective TB vaccines is crucial for controlling TB. Mycobacterium tuberculosis (M. tuberculosis) usually parasitizes in macrophages; therefore, cell-mediated immunity plays an important role. The maintenance of memory T cells following M. tuberculosis infection or vaccination is a hallmark of immune protection. This review analyzes the development of memory T cells during M. tuberculosis infection and vaccine immunization, especially on immune memory induced by BCG and subunit vaccines. Furthermore, the factors affecting the development of memory T cells are discussed in detail. The understanding of the development of memory T cells should contribute to designing more effective TB vaccines and optimizing vaccination strategies.

Immunogenicity and protective efficacy of Ag85A and truncation of PstS1 fusion protein vaccines against tuberculosis

Tuberculosis (TB) is an important public health problem, and the One Health approach is essential for controlling zoonotic tuberculosis. Therefore, a rationally designed and more effective TB vaccine is urgently needed. To enhance vaccine efficacy, it is important to design vaccine candidates that stimulate both cellular and humoral immunity against TB. In this study, we fused the secreted protein Ag85A as the T cell antigen with truncated forms of the mycobacterial cell wall protein PstS1 with B cell epitopes to generate vaccine candidates, Ag85A-tnPstS1 (AP1, AP2, and AP3), and tested their immunogenicity and protective efficacy in mice. The three vaccine candidates induced a significant increase in the levels of T cell-related cytokines such as IFN-γ and IL-17, and AP1 and AP2 can induce more balanced Th1/Th2 responses than AP3. Strong humoral immune responses were also observed in which the production of IgG antibodies including its subclasses IgG1, IgG2c, and IgG3 was tremendously stimulated. AP1 and AP2 induced early antibody responses and more IgG3 isotype antibodies than AP3. Importantly, the mice immunised with the subunit vaccine candidates, particularly AP1 and AP2, had lower bacterial burdens than the control mice. Moreover, the serum from immunised mice can enhance phagocytosis and phagosome-lysosome fusion in macrophages, which can help to eradicate intracellular bacteria. These results indicate that the subunit vaccines Ag85A-tnPstS1 can be promising vaccine candidates for tuberculosis prevention.

Bridging the gaps to overcome major hurdles in the development of next-generation tuberculosis vaccines

Although tuberculosis (TB) remains one of the leading causes of death from an infectious disease worldwide, the development of vaccines more effective than bacille Calmette-Guérin (BCG), the only licensed TB vaccine, has progressed slowly even in the context of the tremendous global impact of TB. Most vaccine candidates have been developed to strongly induce interferon-γ (IFN-γ)-producing T-helper type 1 (Th1) cell responses; however, accumulating evidence has suggested that other immune factors are required for optimal protection against Mycobacterium tuberculosis (Mtb) infection. In this review, we briefly describe the five hurdles that must be overcome to develop more effective TB vaccines, including those with various purposes and tested in recent promising clinical trials. In addition, we discuss the current knowledge gaps between preclinical experiments and clinical studies regarding peripheral versus tissue-specific immune responses, different underlying conditions of individuals, and newly emerging immune correlates of protection. Moreover, we propose how recently discovered TB risk or susceptibility factors can be better utilized as novel biomarkers for the evaluation of vaccine-induced protection to suggest more practical ways to develop advanced TB vaccines. Vaccines are the most effective tools for reducing mortality and morbidity from infectious diseases, and more advanced technologies and a greater understanding of host-pathogen interactions will provide feasibility and rationale for novel vaccine design and development.