Intratracheal administration of third-generation lentivirus vector encoding MPT51 from Mycobacterium tuberculosis induces specific CD8+ T-cell responses in the lung

Inhaled aerosol viral-vectored vaccines against tuberculosis

Bacille Calmette-Guérin (BCG) remains the sole licensed vaccine against tuberculosis (TB), despite its variable efficacy in protecting against pulmonary TB. The development of effective TB vaccines faces significant challenges, marked by the absence of validated correlates of protection and predictive animal models. Strategic approaches to enhance TB vaccines and augment BCG efficacy include utilising prime-boost strategies with viral-vectored vaccines and exploring innovative delivery techniques, such as mucosal vaccine administration. Viral vectors offer numerous advantages, including the capacity to accommodate genes encoding extensive antigenic fragments and the induction of robust immune responses. Aerosol delivery aligns with the route of Mycobacterium tuberculosis infection and holds the potential to enhance protective mucosal immunity. Aerosolised viral-vectored vaccines overcome anti-vector immunity, facilitating repeated aerosol deliveries.

Research Advances for Virus-vectored Tuberculosis Vaccines and Latest Findings on Tuberculosis Vaccine Development

Tuberculosis (TB), caused by respiratory infection with Mycobacterium tuberculosis, remains a major global health threat. The only licensed TB vaccine, the one-hundred-year-old Bacille Calmette-Guérin has variable efficacy and often provides poor protection against adult pulmonary TB, the transmissible form of the disease. Thus, the lack of an optimal TB vaccine is one of the key barriers to TB control. Recently, the development of highly efficacious COVID-19 vaccines within one year accelerated the vaccine development process in human use, with the notable example of mRNA vaccines and adenovirus-vectored vaccines, and increased the public acceptance of the concept of the controlled human challenge model. In the TB vaccine field, recent progress also facilitated the deployment of an effective TB vaccine. In this review, we provide an update on the current virus-vectored TB vaccine pipeline and summarize the latest findings that might facilitate TB vaccine development. In detail, on the one hand, we provide a systematic literature review of the virus-vectored TB vaccines are in clinical trials, and other promising candidate vaccines at an earlier stage of development are being evaluated in preclinical animal models. These research sharply increase the likelihood of finding a more effective TB vaccine in the near future. On the other hand, we provide an update on the latest tools and concept that facilitating TB vaccine research development. We propose that a pre-requisite for successful development may be a better understanding of both the lung-resident memory T cell-mediated mucosal immunity and the trained immunity of phagocytic cells. Such knowledge could reveal novel targets and result in the innovative vaccine designs that may be needed for a quantum leap forward in vaccine efficacy. We also summarized the research on controlled human infection and ultra-low-dose aerosol infection murine models, which may provide more realistic assessments of vaccine utility at earlier stages. In addition, we believe that the success in the ongoing efforts to identify correlates of protection would be a game-changer for streamlining the triage of multiple next-generation TB vaccine candidates. Thus, with more advanced knowledge of TB vaccine research, we remain hopeful that a more effective TB vaccine will eventually be developed in the near future.

PPE57 induces activation of macrophages and drives Th1-type immune responses through TLR2

Proline-glutamic acid (PE) and proline-proline-glutamic acid (PPE) are related proteins exclusive to Mycobacteria that play diverse roles in modulating critical innate immune pathways. In this study, we observed that the PPE57 protein is associated with the cell wall and is exposed on the cell surface. PPE57 enhances Mycobacterium spp. entering into macrophages and plays a role in macrophage phagocytosis. To explore the underlying mechanism, we demonstrated that PPE57 is able to recognise Toll-like receptor 2 (TLR2) and further induce macrophage activation by augmenting the expression of several cell surface molecules (CD40, CD80, CD86 and MHC class II) and pro-inflammatory cytokines (TNF-α, IL-6 and IL-12p40) within macrophages. These molecules are involved in the mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) signalling pathways. We demonstrated that PPE57 effectively polarises T cells to secrete interferon (IFN)-γ and IL-2 and to up-regulate CXCR3 expression in vivo and in vitro, suggesting that this protein may contribute to Th1 polarisation during the immune response. Moreover, recombinant Bacillus Calmette-Guérin (BCG) over-expressing PPE57 could provide better protective efficacy against Mycobacterium tuberculosis challenge compared with BCG. Taken together, our data provides several pieces of evidence that PPE57 may regulate innate and adaptive immunity by interacting with TLR2. These findings indicate that PPE57 protein is a potential antigen for the rational design of an efficient vaccine against M. tuberculosis.

KEY MESSAGES

PPE57 is located on the cell surface and enhances mycobacterium entry into macrophage. PPE57 interacts directly with TLR2 on macrophages. PPE57 plays a key role in the activation of macrophages in a TLR2-dependent manner. PPE57 induces a Th1 immune response via TLR2-mediated macrophage functions. Recombinant BCG over-expressing PPE57 could improve protective efficacy against M. tuberculosis.

Prime-boost bacillus Calmette-Guérin vaccination with lentivirus-vectored and DNA-based vaccines expressing antigens Ag85B and Rv3425 improves protective efficacy against Mycobacterium tuberculosis in mice

To prevent the global spread of tuberculosis (TB), more effective vaccines and vaccination strategies are urgently needed. As a result of the success of bacillus Calmette-Guérin (BCG) in protecting children against miliary and meningeal TB, the majority of individuals will have been vaccinated with BCG; hence, boosting BCG-primed immunity will probably be a key component of future vaccine strategies. In this study, we compared the ability of DNA-, protein- and lentiviral vector-based vaccines that express the antigens Ag85B and Rv3425 to boost the effects of BCG in the context of immunity and protection against Mycobacterium tuberculosis in C57BL/6 mice. Our results demonstrated that prime-boost BCG vaccination with a lentiviral vector expressing the antigens Ag85B and Rv3425 significantly enhanced immune responses, including T helper type 1 and CD8(+) cytotoxic T lymphocyte responses, compared with DNA- and protein-based vaccines. However, lentivirus-vectored and DNA-based vaccines greatly improved the protective efficacy of BCG against M. tuberculosis, as indicated by a lack of weight loss and significantly reduced bacterial loads and histological damage in the lung. Our study suggests that the use of lentiviral or DNA vaccines containing the antigens Ag85B and Rv3425 to boost BCG is a good choice for the rational design of an efficient vaccination strategy against TB.

Analysis of the secretome and identification of novel constituents from culture filtrate of bacillus Calmette-Guerin using high-resolution mass spectrometry

Tuberculosis (TB) is an infectious bacterial disease that causes morbidity and mortality, especially in developing countries. Although its efficacy against TB has displayed a high degree of variability (0%-80%) in different trials, Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been recognized as an important weapon for preventing TB worldwide for over 80 years. Because secreted proteins often play vital roles in the interaction between bacteria and host cells, the secretome of mycobacteria is considered to be an attractive reservoir of potential candidate antigens for the development of novel vaccines and diagnostic reagents. In this study, we performed a proteomic analysis of BCG culture filtrate proteins using SDS-PAGE and high-resolution Fourier transform mass spectrometry. In total, 239 proteins (1555 unique peptides) were identified, including 185 secreted proteins or lipoproteins. Furthermore, 17 novel protein products not annotated in the BCG database were detected and validated by means of RT-PCR at the transcriptional level. Additionally, the translational start sites of 52 proteins were confirmed, and 22 proteins were validated through extension of the translational start sites based on N-terminus-derived peptides. There are 103 secreted proteins that have not been reported in previous studies on BCG [corrected] secretome and are unique to our study. The physicochemical characteristics of the secreted proteins were determined. Major components from the culture supernatant, including low-molecular-weight antigens, lipoproteins, Pro-Glu and Pro-Pro-Glu family proteins, and Mce family proteins, are discussed; some components represent potential predominant antigens in the humoral and cellular immune responses.

Roles of Mucosal Immunity against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is one of the world's leading infectious causes of morbidity and mortality. As a mucosal-transmitted pathogen, Mtb infects humans and animals mainly through the mucosal tissue of the respiratory tract. Apart from providing a physical barrier against the invasion of pathogen, the major function of the respiratory mucosa may be to serve as the inductive sites to initiate mucosal immune responses and sequentially provide the first line of defense for the host to defend against this pathogen. A large body of studies in the animals and humans have demonstrated that the mucosal immune system, rather than the systemic immune system, plays fundamental roles in the host's defense against Mtb infection. Therefore, the development of new vaccines and novel delivery routes capable of directly inducing respiratory mucosal immunity is emphasized for achieving enhanced protection from Mtb infection. In this paper, we outline the current state of knowledge regarding the mucosal immunity against Mtb infection, including the development of TB vaccines, and respiratory delivery routes to enhance mucosal immunity are discussed.

Enhancement of protective immunity against intracellular bacteria using type-1 polarized dendritic cell (DC) vaccine

The development of effective vaccine strategies for intracellular bacteria, including tuberculosis, is one of the major frontiers of medical research. Our previous studies showed that dendritic cell (DC) vaccine is a promising approach for eliciting protective immunity against intracellular bacteria. However, it has been reported that standard fully mature DCs show reduced ability to produce IL-12p70 upon subsequent interaction with antigen (Ag)-specific T cells, limiting their in vivo performance for vaccines. Recently, we found that such "DC exhaustion" could be prevented by the presence of IL-4 and IFN-γ during the maturation of mouse DCs (type-1 polarization), resulting in improved induction of anti-tumor immunity in cancer. Here we show that such type-1 polarized DCs promote dramatic enhancement of protective immunity against an intracellular bacterium, Listeria monocytogenes. Murine bone marrow-derived DCs were cultured and matured with LPS, IL-4 and IFN-γ (type-1 polarized DCs), and with LPS alone (non-polarized DCs). DCs were loaded with listeriolysin O (LLO) 91-99, H2-K(d)-restricted epitope of L. monocytogenes, and were injected into naïve BALB/c mice intravenously. Type-1 polarized DCs produced significantly higher levels of IL-12p70 than non-polarized DCs in vitro, and this vaccine strongly enhanced LLO 91-99-specific CD8(+) T cells exhibiting epitope-specific cytotoxic activity and IFN-γ production, leading to significant induction of protective immunity against L. monocytogenes. Type-1 polarized DCs are potential candidates for enhancing protective immunity in the design of effective vaccination strategies against intracellular bacteria.

Integrase-defective lentiviral-vector-based vaccine: a new vector for induction of T cell immunity

INTRODUCTION

The development of new strategies for the induction of potent and broad immune responses is of high priority in the vaccine field. In this setting, integrase-defective lentiviral vectors (IDLV) represent a new and promising delivery system for immunization purposes.

AREAS COVERED

In this review we describe the development and application of IDLV for vaccination. IDLV are turning out to be a new class of vectors endowed with peculiar characteristics, setting them apart from the parental integration-competent lentiviral vectors. Recent data suggest that IDLV are able to induce strong antigen-specific immune responses in terms of quantity, persistence and quality of CD8(+) T cell response following a single immunization in mice.

EXPERT OPINION

IDLV are a recent acquisition in the field of genetic immunization, thus allowing for the opportunity of further upgrading, including increasing antigen expression and potency of immune response. Based on recent reports showing the potential of IDLV for immunization in mouse models, further development and validation of IDLV, including comparison with other vaccine protocols and use in non-human primate models, are warranted.

Beta4-galactosyltransferase-5 is a lactosylceramide synthase essential for mouse extra-embryonic development

Glycosphingolipids (GSLs) are important for various biological functions in the nervous system, the immune system, embryogenesis and in other tissues and processes. Lactosylceramide (LacCer), which is synthesized from glucosylceramide (GlcCer) by LacCer synthase, is a core structure of GSLs, including gangliosides. LacCer synthase was reported to be synthesized by the beta4-galactosyltransferase-6 (beta4GalT-6) gene in the rat brain. However, the existence of another LacCer synthase gene was shown in cultured cells lacking beta4GalT-6. Here, we report that LacCer synthase is mainly synthesized by the beta4GalT-5 gene during early mouse embryogenesis, and its disruption is embryonic lethal. beta4GalT-5-deficient embryos showed developmental retardation from E7.5 and died by E10.5 as reported previously. LacCer synthase activity was significantly reduced in beta4GalT-5-deficient embryos and extra-embryonic endoderm (XEN) cells derived from blastocysts, and it was recovered when beta4GalT-5 cDNA was introduced into beta4GalT-5-deficient XEN cells. The amounts of LacCer and GM3 ganglioside were drastically reduced, while GlcCer accumulated in the beta4GalT-5-deficient XEN cells. Hematoma and ectopically accumulated trophoblast giant cells were observed in the anti-mesometrial pole of the extra-embryonic tissues, although all three embryonic layers formed. beta4GalT-5-deficient embryos developed until E12.5 as chimeras with wild-type tetraploid cells, which formed the extra-embryonic membranes, indicating that extra-embryonic defects caused the early embryonic lethality. Our results suggest that beta4GalT-5 is essential for extra-embryonic development during early mouse embryogenesis.

Induction of Specific CD8 T Cells against Intracellular Bacteria by CD8 T-Cell-Oriented Immunization Approaches

For protection against intracellular bacteria such as Mycobacterium tuberculosis and Listeria monocytogenes, the cellular arm of adaptive immunity is necessary. A variety of immunization methods have been evaluated and are reported to induce specific CD8⁺ T cells against intracellular bacterial infection. Modified BCG vaccines have been examined to enhance CD8⁺ T-cell responses. Naked DNA vaccination is a promising strategy to induce CD8⁺ T cells. In addition to this strategy, live attenuated intracellular bacteria such as Shigella, Salmonella, and Listeria have been utilized as carriers of DNA vaccines in animal models. Vaccination with dendritic cells pulsed with antigenic peptides or the cells introduced antigen genes by virus vectors such as retroviruses is also a powerful strategy. Furthermore, vaccination with recombinant lentivirus has been attempted to induce specific CD8⁺ T cells. Combinations of these strategies (prime-boost immunization) have been studied for the efficient induction of intracellular bacteria-specific CD8⁺ T cells.

Amelioration of emphysema in mice through lentiviral transduction of long-lived pulmonary alveolar macrophages

Directed gene transfer into specific cell lineages in vivo is an attractive approach for both modulating gene expression and correcting inherited mutations such as emphysema caused by human alpha1 antitrypsin (hAAT) deficiency. However, somatic tissues are mainly comprised of heterogeneous, differentiated cell lineages that can be short lived and difficult to specifically transfect. Here, we describe an intratracheally instilled lentiviral system able to deliver genes selectively to as many as 70% of alveolar macrophages (AMs) in the mouse lung. Following a single in vivo lentiviral transduction, genetically tagged AMs persisted in lung alveoli and expressed transferred genes for the lifetime of the adult mouse. A prolonged macrophage lifespan, rather than precursor cell proliferation, accounted for the surprisingly sustained presence of transduced AMs. We utilized this long-lived population to achieve localized secretion of therapeutic levels of hAAT protein in lung epithelial lining fluid. In an established mouse model of emphysema, lentivirally delivered hAAT ameliorated the progression of emphysema, as evidenced by attenuation of increased lung compliance and alveolar size. After 24 weeks of sustained gene expression, no humoral or cellular immune responses to hAAT protein were detected. Our results challenge the dogma that AMs are short lived and suggest that these differentiated cells may be a possible target cell population for in vivo gene therapy applications, including the sustained correction of hAAT deficiency.

Retronectin enhances lentivirus-mediated gene delivery into hematopoietic progenitor cells

Genetic modification of hematopoietic stem cells holds great promise in the treatment of hematopoietic disorders. However, clinical application of gene delivery has been limited, in part, by low gene transfer efficiency. To overcome this problem, we investigated the effect of retronectin (RN) on lentiviral-mediated gene delivery into hematopoietic progenitor cells (HPCs) derived from bone marrow both in vitro and in vivo. RN has been shown to enhance transduction by promoting colocalization of lentivirus and target cells. We found that RN enhanced lentiviral transfer of the VENUS transgene into cultured c-Kit(+) Lin(-) HPCs. As a complementary approach, in vivo gene delivery was performed by subjecting mice to intra-bone marrow injection of lentivirus or a mixture of RN and lentivirus. We found that co-injection with RN increased the number of VENUS-expressing c-Kit(+) Lin(-) HPCs in bone marrow by 2-fold. Further analysis of VENUS expression in colony-forming cells from the bone marrow of these animals revealed that RN increased gene delivery among these cells by 4-fold. In conclusion, RN is effective in enhancing lentivirus-mediated gene delivery into HPCs.