Subunit vaccine H56/CAF01 induces a population of circulating CD4 T cells that traffic into the Mycobacterium tuberculosis-infected lung

A mucosal vaccine formulation against tuberculosis by exploiting the adjuvant activity of S100A4-A damage-associated molecular pattern molecule

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), remains one of the top three causes of death. Currently, the only licensed vaccine against TB is the bacillus Calmette-Guerin (BCG), which lacks efficacy in preventing and controlling pulmonary TB in adults. We aimed to evaluate a nasal TB vaccine formulation composed of the Mtb-specific vaccine antigen ESAT-6, an Mtb-associated protein that can trigger protective immune responses, and S100A4, a recently characterized novel mucosal adjuvant. Mice were intranasally given recombinant ESAT-6 in the presence or absence of S100A4 as an adjuvant. We have provided experimental evidence demonstrating that S100A4 admixed to ESAT-6 could induce Mtb-specific adaptive immune responses after intranasal immunization. S100A4 remarkably augmented the levels of anti-ESAT-6 IgG in serum and IgA in mucosal sites, including lung exudates, bronchoalveolar lavage fluid (BALF) and nasal lavage. Furthermore, in both lung and spleen tissues, S100A4 strongly promoted ESAT-6-specific expansion of CD4 T cells. Both CD4 and CD8 T cells from these tissues expressed increased levels of IFN-γ, TNF-α, and IL-17, cytokines critical for antimicrobial activity. Antigen-reencounter-induced T cell proliferative responses, a key vaccine performance indicator, were augmented in the spleen of S100A4-adjuvanted mice. Furthermore, CD8 T cells from the spleen and lung tissues of these mice expressed higher levels of granzyme B upon antigen re-stimulation. S100A4-adjuvanted immunization may predict good mucosal protection against TB.

Immune correlates of protection as a game changer in tuberculosis vaccine development

The absence of validated correlates of protection (CoPs) hampers the rational design and clinical development of new tuberculosis vaccines. In this review, we provide an overview of the potential CoPs in tuberculosis vaccine research. Major hindrances and potential opportunities are then discussed. Based on recent progress, it is reasonable to anticipate that success in the ongoing efforts to identify CoPs would be a game-changer in tuberculosis vaccine development.

MINCLE and TLR9 agonists synergize to induce Th1/Th17 vaccine memory and mucosal recall in mice and non-human primates

Development of new vaccines tailored for difficult-to-target diseases is hampered by a lack of diverse adjuvants for human use, and none of the currently available adjuvants induce Th17 cells. Here, we develop a liposomal adjuvant, CAF®10b, that incorporates Mincle and Toll-like receptor 9 agonists. In parallel mouse and non-human primate studies comparing to CAF® adjuvants already in clinical trials, we report species-specific effects of adjuvant composition on the quality and magnitude of the responses. When combined with antigen, CAF®10b induces Th1 and Th17 responses and protection against a pulmonary infection with Mycobacterium tuberculosis in mice. In non-human primates, CAF®10b induces higher Th1 responses and robust Th17 responses detectable after six months, and systemic and pulmonary Th1 and Th17 recall responses, in a sterile model of local recall. Overall, CAF®10b drives robust memory antibody, Th1 and Th17 vaccine-responses via a non-mucosal immunization route across both rodent and primate species.

Promotion of Th17 Polarized Immunity via Co-Delivery of Mincle Agonist and Tuberculosis Antigen Using Silica Nanoparticles

Adjuvants and immunomodulators that effectively drive a Th17-skewed immune response are not part of the standard vaccine toolkit. Vaccine adjuvants and delivery technologies that can induce Th17 or Th1/17 immunity and protection against bacterial pathogens, such as tuberculosis (TB), are urgently needed. Th17-polarized immune response can be induced using agonists that bind and activate C-type lectin receptors (CLRs) such as macrophage inducible C-type lectin (Mincle). A simple but effective strategy was developed for codelivering Mincle agonists with the recombinant Mycobacterium tuberculosis fusion antigen, M72, using tunable silica nanoparticles (SNP). Anionic bare SNP, hydrophobic phenyl-functionalized SNP (P-SNP), and cationic amine-functionalized SNP (A-SNP) of different sizes were coated with three synthetic Mincle agonists, UM-1024, UM-1052, and UM-1098, and evaluated for adjuvant activity in vitro and in vivo. The antigen and adjuvant were coadsorbed onto SNP via electrostatic and hydrophobic interactions, facilitating multivalent display and delivery to antigen presenting cells. The cationic A-SNP showed the highest coloading efficiency for the antigen and adjuvant. In addition, the UM-1098-adsorbed A-SNP formulation demonstrated slow-release kinetics in vitro, excellent stability over 12 months of storage, and strong IL-6 induction from human peripheral blood mononuclear cells. Co-adsorption of UM-1098 and M72 on A-SNP significantly improved antigen-specific humoral and Th17-polarized immune responses in vivo in BALB/c mice relative to the controls. Taken together, A-SNP is a promising platform for codelivery and proper presentation of adjuvants and antigens and provides the basis for their further development as a vaccine delivery platform for immunization against TB or other diseases for which Th17 immunity contributes to protection.

Vaccination with Mincle agonist UM-1098 and mycobacterial antigens induces protective Th1 and Th17 responses

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of the top infectious killers in the world. The only licensed vaccine against TB, Bacille Calmette-Guérin (BCG), provides variable protection against pulmonary TB, especially in adults. Hence, novel TB vaccine approaches are urgently needed. Both Th1 and Th17 responses are necessary for protection against TB, yet effective adjuvants and vaccine delivery systems for inducing robust Th1 and Th17 immunity are lacking. Herein we describe a synthetic Mincle agonist, UM-1098, and a silica nanoparticle delivery system that drives Th1/Th17 responses to Mtb antigens. Stimulation of human peripheral blood mononuclear cells (hPBMCs) with UM-1098 induced high levels of Th17 polarizing cytokines IL-6, IL-1β, IL-23 as well as IL-12p70, IL-4 and TNF-α in vitro. PBMCs from both C57BL/6 and BALB/c mice responded with a similar cytokine pattern in vitro and in vivo. Importantly, intramuscular (I.M.) vaccination with UM-1098-adjuvanted TB antigen M72 resulted in significantly higher antigen-specific IFN-γ and IL-17A levels in C57BL/6 wt mice than Mincle KO mice. Vaccination of C57BL/6 wt mice with immunodominant Mtb antigens ESAT6/Ag85B or M72 resulted in predominantly Th1 and Th17 responses and induced antigen-specific serum antibodies. Notably, in a virulent Mtb challenge model, vaccination with UM-1098 adjuvanted ESAT6/Ag85B or M72 significantly reduced lung bacterial burden when compared with unvaccinated mice and protection occurred in the absence of pulmonary inflammation. These data demonstrate that the synthetic Mincle agonist UM-1098 induces strong Th1 and Th17 immunity after vaccination with Mtb antigens and provides protection against Mtb infection in mice.

Live attenuated Mycobacterium bovis strains combined with the encapsulated H65 antigen as a vaccine strategy against bovine tuberculosis in a mouse model

Mycobacterium bovis is an etiological agent of bovine tuberculosis (bTB) that also infects other mammals, including humans. The lack of an effective vaccine for the control of bTB highlights the need for developing new vaccines. In this study, we developed and evaluated an M. bovis strain deleted in the virulence genes phoP, esxA and esxB as a vaccine candidate against bTB in BALBc mice. The evaluated strains were the new live vaccine and BCG, alone or in combination with ncH65vD. The immunogen ncH65vD is a fusion protein H65, encapsulated together with vitamin D3, within the oily body of a nanocapsule composed of an antigen-loading polymeric shell. All vaccines conferred protection against the M. bovis challenge. However, no significant differences were detected among the vaccinated groups regarding bacterial loads in lungs and spleen. Mice vaccinated with the mutant strain plus ncH65vD showed negative Ziehl Neelsen staining of mycobacteria in their lungs, which suggests better control of bacteria replication according to this protection parameter. Consistently, this vaccination scheme showed the highest proportion of CD4 + T cells expressing the protection markers PD-1 and CXCR3 among the vaccinated groups. Correlation studies showed that PD-1 and CXCR3 expression levels in lung-resident CD4 T cells negatively correlated with the number of colony forming units of M. bovis in the lungs of mice. Therefore, the results suggest a link between the presence of PD-1 + and CXCR3 + cells at the site of the immune response against mycobacteria and the level of mycobacterial loads.

Reconstituted dry powder formulations of ZnO-adjuvanted ovalbumin induce equivalent antigen specific antibodies but lower T cell responses than ovalbumin adjuvanted with Alhydrogel® or cationic adjuvant formulation 01 (CAF®01)

Most licensed human vaccines are based on liquid dosage forms but have poor storage stability and require continuous and expensive cold-chain storage. In contrast, the use of solid vaccine dosage forms produced by for example spray drying, extends shelf life and eliminates the need for a cold chain. Zinc oxide (ZnO)-based nanoparticles display immunomodulatory properties, but their adjuvant effect as a dry powder formulation is unknown. Here, we show that reconstituted dry powder formulations of ZnO particles containing the model antigen ovalbumin (OVA) induce antigen-specific CD8+ T-cell and humoral responses. By systematically varying the ratio between ZnO and mannitol during spray drying, we manufactured dry powder formulations of OVA-containing ZnO particles that displayed: (i) a spherical or wrinkled surface morphology, (ii) an aerodynamic diameter and particle size distribution optimal for deep lung deposition, and (iii) aerosolization properties suitable for lung delivery. Reconstituted dry powder formulations of ZnO particles were well-tolerated by Calu-3 lung epithelial cells. Furthermore, almost equivalent OVA-specific serum antibody responses were stimulated by reconstituted ZnO particles, OVA adjuvanted with Alhydrogel®, and OVA adjuvanted with the cationic adjuvant formulation 01 (CAF®01). However, reconstituted dry powder ZnO particles and OVA adjuvanted with Alhydrogel® induced significantly lower OVA-specific CD8+CD44+ T-cell responses in the spleen than OVA adjuvanted with CAF®01. Similarly, reconstituted dry powder ZnO particles activated significantly lower percentages of follicular helper T cells and germinal center B cells in the draining lymph nodes than OVA adjuvanted with CAF®01. Overall, our results show that reconstituted dry powder formulations of ZnO nanoparticles can induce antigen-specific antibodies and can be used in vaccines to enhance antigen-specific humoral immune responses against subunit protein antigens.

CXCR3 Provides a Competitive Advantage for Retention of Mycobacterium tuberculosis-Specific Tissue-Resident Memory T Cells Following a Mucosal Tuberculosis Vaccine

Mycobacterium tuberculosis is a major human pathogen, and new vaccines are needed to prevent transmission. Mucosal vaccination may confer protection against M. tuberculosis by stimulating tissue-resident memory (TRM) CD4+ T cells in the lungs. The chemokine receptor CXCR3 promotes lung recruitment of T cells, but its role in TRM development is unknown. This study demonstrates the recombinant influenza A virus vaccine PR8.p25, expressing the immunodominant M. tuberculosis T cell epitope p25, induces CXCR3 expression on p25-specific CD4+ T cells in the lungs so that the majority of vaccine-induced CD4+ TRM expresses CXCR3 at 6 weeks. However, CXCR3-/- mice developed equivalent antigen-specific CD4+ T cell responses to wild-type (WT) mice following PR8.p25, and surprisingly retained more p25-specific CD4+ TRM in the lungs than WT mice at 6 weeks. The adoptive transfer of CXCR3-/- and WT P25 T cells into WT mice revealed that the initial recruitment of vaccine-induced CD4+ T cells into the lungs was independent of CXCR3, but by 6 weeks, CXCR3-deficient P25 T cells, and especially CXCR3-/- TRM, were significantly reduced compared to CXCR3-sufficient P25 T cells. Therefore, although CXCR3 was not essential for CD4+ TRM recruitment or retention, it provided a competitive advantage for the induction of M. tuberculosis-specific CD4+ TRM in the lungs following pulmonary immunization.

Memory T Cells in the Immunoprevention of Cancer: A Switch from Therapeutic to Prophylactic Approaches

Cancer immunoprevention, the engagement of the immune system to prevent cancer, is largely overshadowed by therapeutic approaches to treating cancer after detection. Vaccines or, alternatively, the utilization of genetically engineered memory T cells could be methods of engaging and creating cancer-specific T cells with superb memory, lenient activation requirements, potent antitumor cytotoxicity, tumor surveillance, and resilience against immunosuppressive factors in the tumor microenvironment. In this review we analyze memory T cell subtypes based on their potential utility in cancer immunoprevention with regard to longevity, localization, activation requirements, and efficacy in fighting cancers. A particular focus is on how both tissue-resident memory T cells and stem memory T cells could be promising subtypes for engaging in immunoprevention.

CD30 co-stimulation drives differentiation of protective T cells during Mycobacterium tuberculosis infection

Control of Mycobacterium tuberculosis (Mtb) infection requires generation of T cells that migrate to granulomas, complex immune structures surrounding sites of bacterial replication. Here we compared the gene expression profiles of T cells in pulmonary granulomas, bronchoalveolar lavage, and blood of Mtb-infected rhesus macaques to identify granuloma-enriched T cell genes. TNFRSF8/CD30 was among the top genes upregulated in both CD4 and CD8 T cells from granulomas. In mice, CD30 expression on CD4 T cells is required for survival of Mtb infection, and there is no major role for CD30 in protection by other cell types. Transcriptomic comparison of WT and CD30-/- CD4 T cells from the lungs of Mtb-infected mixed bone marrow chimeric mice showed that CD30 directly promotes CD4 T cell differentiation and the expression of multiple effector molecules. These results demonstrate that the CD30 co-stimulatory axis is highly upregulated on granuloma T cells and is critical for protective T cell responses against Mtb infection.

Method of manufacturing CAF®09 liposomes affects immune responses induced by adjuvanted subunit proteins

The ability to induce antigen-specific CD4+ and CD8+T-cell responses is one of the fundamental requirements when developing new efficacious vaccines against challenging infectious diseases and cancer. However, no adjuvants are currently approved for human subunit vaccines that induce T-cell immunity. Here, we incorporated a Toll-like receptor 4 agonist, i.e., the ionizable lipidoid L5N12, in the liposomal cationic adjuvant formulation 09 (CAF®09), and found that modified CAF®09 liposomes possess preserved adjuvant function as compared to unmodified CAF®09. CAF®09 consists of the cationic lipid dimethyldioctadecylammonium (DDA), monomycoloyl glycerol analogue 1 (MMG-1), and polyinosinic:polycytidylic acid [poly(I:C)]. By using the microfluidic mixing technology for liposome preparation, we gradually replaced DDA with L5N12, while keeping the molar ratios of MMG-1 and poly(I:C) constant. We found that this type of modification resulted in colloidally stable liposomes, which were significantly smaller and displayed reduced surface charge as compared to unmodified CAF®09, prepared by using the conventional thin film method. We showed that incorporation of L5N12 decreases the membrane rigidity of CAF®09 liposomes. Furthermore, vaccination with antigen adjuvanted with L5N12-modified CAF®09 or antigen adjuvanted with unmodified CAF®09, respectively, induced comparable antigen-specific serum antibody titers. We found that antigen adjuvanted with L5N12-modified CAF®09 induced antigen-specific effector and memory CD4+ and CD8+T-cell responses in the spleen comparable to those induced when unmodified CAF®09 was used as adjuvant. However, incorporating L5N12 did not have a synergistic immunopotentiating effect on the antibody and T-cell responses induced by CAF®09. Moreover, vaccination with antigen adjuvanted with unmodified CAF®09, which was manufactured by using microfluidic mixing, induced significantly lower antigen-specific CD4+ and CD8+T-cell responses than vaccination with antigen adjuvanted with unmodified CAF®09, which was prepared by using the thin film method. These results show that the method of manufacturing affects CAF®09 liposome adjuvanted antigen-specific immune responses, which should be taken into consideration when evaluating immunogenicity of subunit protein vaccines.

Polysaccharides and glycolipids of Mycobacterium tuberculosis and their induced immune responses

Tuberculosis (TB) is a chronic infectious disease mainly caused by Mycobacterium tuberculosis (M. tuberculosis). The structures of polysaccharides and glycolipids at M. tuberculosis cell wall vary among different strains, which affect the physiology and pathogenesis of mycobacteria by activating or inhibiting innate and acquired immunity. Among them, some components such as lipomannan (LM) and lipoarabinomannan (LAM) activate innate immunity by recognizing some kinds of pattern recognition receptors (PRRs) like Toll-like receptors, while other components like mannose-capped lipoarabinomannan (ManLAM) could prevent innate immune responses by inhibiting the secretion of pro-inflammatory cytokines and maturation of phagosomes. In addition, many glycolipids can activate natural killer T (NKT) cells and CD1-restricted T cells to produce interferon-γ (IFN-γ). Furthermore, humoral immunity against cell wall components, such as antibodies against LAM, plays a role in immunity against M. tuberculosis infection. Cell wall polysaccharides and glycolipids of M. tuberculosis have potential applications as antigens and adjuvants for novel TB subunit vaccines.

Towards the development of subunit vaccines against tuberculosis: The key role of adjuvant

According to the World Health Organization (WHO), tuberculosis (TB) is the leading cause of death triggered by a single infectious agent, worldwide. Bacillus Calmette-Guerin (BCG) is the only currently licensed anti-TB vaccine. However, other strategies, including modification of recombinant BCG vaccine, attenuated Mycobacterium tuberculosis (Mtb) mutant constructs, DNA and protein subunit vaccines, are under extensive investigation. As whole pathogen vaccines can trigger serious adverse reactions, most current strategies are focused on the development of safe anti-TB subunit vaccines; this is especially important given the rising TB infection rate in immunocompromised HIV patients. The whole Mtb genome has been mapped and major antigens have been identified; however, optimal vaccine delivery mode is still to be established. Isolated protein antigens are typically poorly immunogenic so adjuvants are required to induce strong and long-lasting immune responses. This article aims to review the developmental status of anti-TB subunit vaccine adjuvants.

Pulmonary Administration of the Liposome-Based Adjuvant CAF01: Effect of Surface Charge on Mucosal Adjuvant Function

Mucosal surfaces of the lungs represent a major site of entry for airborne pathogens, and pulmonary administration of vaccines is an attractive strategy to induce protective mucosal immunity in the airways. Recently, we demonstrated the potential of pulmonary vaccination with the tuberculosis subunit antigen H56 adjuvanted with the cationic liposomal adjuvant formulation CAF01, which consists of the cationic lipid dimethyldioctadecylammonium (DDA) bromide and the synthetic cord factor trehalose-6,6'-dibehenate. However, the cationic charge of DDA represents a major safety challenge. Hence, replacing DDA with a safer zwitterionic or anionic phospholipid is an attractive approach to improve vaccine safety, but the effect of liposomal surface charge on the induction of mucosal immunity after airway immunization is poorly understood. Here, we investigated the effect of surface charge by replacing the cationic DDA component of CAF01 with zwitterionic dipalmitoylphosphatidylcholine (DPPC) or anionic dipalmitoylphosphatidylglycerol (DPPG), and we show that charge modification enhances antigen-specific pulmonary T-cell responses against co-formulated H56. We systematically replaced DDA with either DPPC or DPPG and found that these modifications resulted in colloidally stable liposomes that have similar size and morphology to unmodified CAF01. DPPC- or DPPG-modified CAF01 displayed surface charge-dependent protein adsorption and induced slightly higher follicular helper T cells and germinal center B cells in the lung-draining lymph nodes than unmodified CAF01. In addition, modified CAF01 induced significantly higher levels of H56-specific Th17 cells and polyfunctional CD4⁺ T cells in the lungs, as compared to unmodified CAF01. However, the strong H56-specific humoral responses induced by CAF01 in the lungs and spleen were not influenced by surface charge. Hence, these results provide insights into the importance of surface charge for liposomal adjuvant function and can also guide the design of safe pulmonary subunit vaccines against other mucosal pathogens.

IL-10 Overexpression After BCG Vaccination Does Not Impair Control of Mycobacterium tuberculosis Infection

Control of tuberculosis depends on the rapid expression of protective CD4+ T-cell responses in the Mycobacterium tuberculosis (Mtb)-infected lungs. We have recently shown that the immunomodulatory cytokine IL-10 acts intrinsically in CD4+ T cells and impairs their parenchymal migratory capacity, thereby preventing control of Mtb infection. Herein, we show that IL-10 overexpression does not impact the protection conferred by the established memory CD4+ T-cell response, as BCG-vaccinated mice overexpressing IL-10 only during Mtb infection display an accelerated, BCG-induced, Ag85b-specific CD4+ T-cell response and control Mtb infection. However, IL-10 inhibits the migration of recently activated ESAT-6-specific CD4+ T cells into the lung parenchyma and impairs the development of ectopic lymphoid structures associated with reduced expression of the chemokine receptors CXCR5 and CCR7. Together, our data support a role for BCG vaccination in preventing the immunosuppressive effects of IL-10 in the fast progression of Mtb infection and may provide valuable insights on the mechanisms contributing to the variable efficacy of BCG vaccination.

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.

All trans retinoic acid as a host-directed immunotherapy for tuberculosis

Tuberculosis (TB) is the top bacterial infectious disease killer and one of the top ten causes of death worldwide. The emergence of strains of multiple drug-resistant tuberculosis (MDR-TB) has pushed our available stock of anti-TB agents to the limit of effectiveness. This has increased the urgent need to develop novel treatment strategies using currently available resources. An adjunctive, host-directed therapy (HDT) designed to act on the host, instead of the bacteria, by boosting the host immune response through activation of intracellular pathways could be the answer. The integration of multidisciplinary approaches of repurposing currently FDA-approved drugs, with a targeted drug-delivery platform is a very promising option to reduce the long timeline associated with the approval of new drugs - time that cannot be afforded given the current levels of morbidity and mortality associated with TB infection. The deficiency of vitamin A has been reported to be highly associated with the increased susceptibility of TB. All trans retinoic acid (ATRA), the active metabolite of vitamin A, has proven to be very efficacious against TB both in vitro and in vivo. In this review, we discuss and summarise the importance of vitamin A metabolites in the fight against TB and what is known regarding the molecular mechanisms of ATRA as a host-directed therapy for TB including its effect on macrophages cytokine profile and cellular pathways. Furthermore, we focus on the issues behind why previous clinical trials with vitamin A supplementation have failed, and how these issues might be overcome.

Photochemically-Mediated Inflammation and Cross-Presentation of Mycobacterium bovis BCG Proteins Stimulates Strong CD4 and CD8 T-Cell Responses in Mice

Conventional vaccines are very efficient in the prevention of bacterial infections caused by extracellular pathogens due to effective stimulation of pathogen-specific antibodies. In contrast, considering that intracellular surveillance by antibodies is not possible, they are typically less effective in preventing or treating infections caused by intracellular pathogens such as Mycobacterium tuberculosis. The objective of the current study was to use so-called photochemical internalization (PCI) to deliver a live bacterial vaccine to the cytosol of antigen-presenting cells (APCs) for the purpose of stimulating major histocompatibility complex (MHC) I-restricted CD8 T-cell responses. For this purpose, Mycobacterium bovis BCG (BCG) was combined with the photosensitiser tetraphenyl chlorine disulfonate (TPCS2a) and injected intradermally into mice. TPCS2a was then activated by illumination of the injection site with light of defined energy. Antigen-specific CD4 and CD8 T-cell responses were monitored in blood, spleen, and lymph nodes at different time points thereafter using flow cytometry, ELISA and ELISPOT. Finally, APCs were infected and PCI-treated in vitro for analysis of their activation of T cells in vitro or in vivo after autologous vaccination of mice. Combination of BCG with PCI induced stronger BCG-specific CD4 and CD8 T-cell responses than treatment with BCG only or with BCG and TPCS2a without light. The overall T-cell responses were multifunctional as characterized by the production of IFN-γ, TNF-α, IL-2 and IL-17. Importantly, PCI induced cross-presentation of BCG proteins for stimulation of antigen-specific CD8 T-cells that were particularly producing IFN-γ and TNF-α. PCI further facilitated antigen presentation by causing up-regulation of MHC and co-stimulatory proteins on the surface of APCs as well as their production of TNF-α and IL-1β in vivo. Furthermore, PCI-based vaccination also caused local inflammation at the site of vaccination, showing strong infiltration of immune cells, which could contribute to the stimulation of antigen-specific immune responses. This study is the first to demonstrate that a live microbial vaccine can be combined with a photochemical compound and light for cross presentation of antigens to CD8 T cells. Moreover, the results revealed that PCI treatment strongly improved the immunogenicity of M. bovis BCG.

Development and Testing of a Spray-Dried Tuberculosis Vaccine Candidate in a Mouse Model

Converting a vaccine into a thermostable dry powder is advantageous as it reduces the resource burden linked with the cold chain and provides flexibility in dosage and administration through different routes. Such a dry powder presentation may be especially useful in the development of a vaccine towards the respiratory infectious disease tuberculosis (TB). This study assesses the immunogenicity and protective efficacy of spray-dried ID93+GLA-SE, a promising TB vaccine candidate, against Mycobacterium tuberculosis (Mtb) in a murine model when administered via different routes. Four administration routes for the spray-dried ID93+GLA-SE were evaluated along with relevant controls—1) reconstitution and intramuscular injection, 2) reconstitution and intranasal delivery, 3) nasal dry powder delivery via inhalation, and 4) pulmonary dry powder delivery via inhalation. Dry powder intranasal and pulmonary delivery was achieved using a custom nose-only inhalation device, and optimization using representative vaccine-free powder demonstrated that approximately 10 and 44% of the maximum possible delivered dose would be delivered for intranasal delivery and pulmonary delivery, respectively. Spray-dried powder was engineered according to the different administration routes including maintaining approximately equivalent delivered doses of ID93 and GLA. Vaccine properties of the different spray-dried lots were assessed for quality control in terms of nanoemulsion droplet diameter, polydispersity index, adjuvant content, and antigen content. Our results using the Mtb mouse challenge model show that both intranasal reconstituted vaccine delivery as well as pulmonary dry powder vaccine delivery resulted in Mtb control in infected mice comparable to traditional intramuscular delivery. Improved protection in these two vaccinated groups over their respective control groups coincided with the presence of cytokine-producing T cell responses. In summary, our results provide novel vaccine formulations and delivery routes that can be harnessed to provide protection against Mtb infection.

Synthetic Vaccines Targeting Mincle Through Conjugation of Trehalose Dibehenate

The covalent fusion of immunostimulatory adjuvants to immunogenic antigens is a promising strategy for the development of effective synthetic vaccines for infectious diseases. Herein, we describe the conjugation of a...

Immunological Assessment of Chitosan or Trimethyl Chitosan-Coated PLGA Nanospheres Containing Fusion Antigen as the Novel Vaccine Candidates Against Tuberculosis

The crucial challenge in tuberculosis (TB) as a chronic infectious disease is to present a novel vaccine candidate that improves current vaccination and provides efficient protection in individuals. The present study aimed to evaluate the immune efficacy of multi-subunit vaccines containing chitosan (CHT)- or trimethyl chitosan (TMC)-coated PLGA nanospheres to stimulate cell-mediated and mucosal responses against Mycobacterium Tuberculosis (Mtb) in an animal model. The surface-modified PLGA nanoparticles (NPs) containing tri-fusion protein from three Mtb antigens were produced by the double emulsion technique. The subcutaneously or nasally administered PLGA vaccines in the absence or presence of BCG were assessed to compare the levels of mucosal IgA, IgG1, and IgG2a production as well as secretion of IFN-γ, IL-17, IL-4, and TGF-β cytokines. According to the release profile, the tri-fusion encapsulated in modified PLGA NPs demonstrated a biphasic release profile including initial burst release on the first day and sustained release within 18 days. All designed PLGA vaccines induced a shift of Th1/Th2 balance toward Th1-dominant response. Although immunized mice through subcutaneous injection elicited higher cell-mediated responses relative to the nasal vaccination, the intranasally administered groups stimulated robust mucosal IgA immunity. The modified PLGA NPs using TMC cationic polymer were more efficient to elevate Th1 and mucosal responses in comparison with the CHT-coated PLGA nanospheres. Our findings highlighted that the tri-fusion loaded in TMC-PLGA NPs may represent an efficient prophylactic vaccine and can be considered as a novel candidate against TB.

Lung Epithelial Signaling Mediates Early Vaccine-Induced CD4+ T Cell Activation and Mycobacterium tuberculosis Control

Tuberculosis (TB) is one of the leading causes of death due to a single infectious agent. The development of a TB vaccine that induces durable and effective immunity to Mycobacterium tuberculosis (Mtb) infection is urgently needed. Early and superior Mtb control can be induced in M. bovis Bacillus Calmette-Guérin (BCG)-vaccinated hosts when the innate immune response is targeted to generate effective vaccine-induced immunity. In the present study, we show that innate activation of DCs is critical for mucosal localization of clonally activated vaccine-induced CD4⁺ T cells in the lung and superior early Mtb control. In addition, our study reveals that Th1/Th17 cytokine axis play an important role in superior vaccine-induced immunity. Our studies also show that activation of the nuclear factor kappa-light-chain enhancer of activated B cell (NF-κβ) pathway in lung epithelial cells is critical for the mucosal localization of activated vaccine-induced CD4⁺ T cells for rapid Mtb control. Thus, our study provides novel insights into the immune mechanisms that can overcome TB vaccine bottlenecks and provide early rapid Mtb control.

In Vivo Antigen Expression Regulates CD4 T Cell Differentiation and Vaccine Efficacy against Mycobacterium tuberculosis Infection

Tuberculosis, caused by Mtb, constitutes a global health crisis of massive proportions, and the impact of the current coronavirus disease 2019 (COVID-19) pandemic is expected to cause a rise in tuberculosis-related deaths. Improved vaccines are therefore needed more than ever, but a lack of knowledge on protective immunity hampers their development.

New vaccines are urgently needed against Mycobacterium tuberculosis (Mtb), which kills more than 1.4 million people each year. CD4 T cell differentiation is a key determinant of protective immunity against Mtb, but it is not fully understood how host-pathogen interactions shape individual antigen-specific T cell populations and their protective capacity. Here, we investigated the immunodominant Mtb antigen, MPT70, which is upregulated in response to gamma interferon (IFN-γ) or nutrient/oxygen deprivation of in vitro-infected macrophages. Using a murine aerosol infection model, we compared the in vivo expression kinetics of MPT70 to a constitutively expressed antigen, ESAT-6, and analyzed their corresponding CD4 T cell phenotype and vaccine protection. For wild-type Mtb, we found that in vivo expression of MPT70 was delayed compared to ESAT-6. This delayed expression was associated with induction of less differentiated MPT70-specific CD4 T cells but, compared to ESAT-6, also reduced protection after vaccination. In contrast, infection with an MPT70-overexpressing Mtb strain promoted highly differentiated KLRG1⁺CX3CR1⁺ CD4 T cells with limited lung-homing capacity. Importantly, this differentiated phenotype could be prevented by vaccination, and against the overexpressing strain, vaccination with MPT70 conferred protection similar to vaccination with ESAT-6. Together, our data indicate that high in vivo antigen expression drives T cells toward terminal differentiation and that targeted vaccination with adjuvanted protein can counteract this phenomenon by maintaining T cells in a protective less differentiated state. These observations shed new light on host-pathogen interactions and provide guidance on how future Mtb vaccines can be designed to tip the immune balance in favor of the host.

Engineering Vaccines for Tissue-Resident Memory T Cells

In recent years, tissue-resident memory T cells (TRM) have attracted significant attention in the field of vaccine development. Distinct from central and effector memory T cells, TRM cells take up residence in home tissues such as the lung or urogenital tract and are ideally positioned to respond quickly to pathogen encounter. TRM have been found to play a role in the immune response against many globally important infectious diseases for which new or improved vaccines are needed, including influenza and tuberculosis. It is also increasingly clear that TRM play a pivotal role in cancer immunity. Thus, vaccines that can generate this memory T cell population are highly desirable. The field of immunoengineering-that is, the application of engineering principles to study the immune system and design new and improved therapies that harness or modulate immune responses-is ideally poised to provide solutions to this need for next-generation TRM vaccines. This review covers recent developments in vaccine technologies for generating TRM and protecting against infection and cancer, including viral vectors, virus-like particles, and synthetic and natural biomaterials. In addition, it offers critical insights on the future of engineering vaccines for tissue-resident memory T cells.

In vivo antigen expression regulates CD4 T cell differentiation and vaccine efficacy against Mycobacterium tuberculosis infection

New vaccines are urgently needed against Mycobacterium tuberculosis (Mtb), which kills more than 1.4 million people each year. CD4 T cell differentiation is a key determinant of protective immunity against Mtb, but it is not fully understood how host-pathogen interactions shape individual antigen-specific T cell populations and their protective capacity. Here, we investigated the immunodominant Mtb antigen, MPT70, which is upregulated in response to IFN-γ or nutrient/oxygen deprivation of in vitro infected macrophages. Using a murine aerosol infection model, we compared the in vivo expression kinetics of MPT70 to a constitutively expressed antigen, ESAT-6, and analysed their corresponding CD4 T cell phenotype and vaccine-protection. For wild-type Mtb, we found that in vivo expression of MPT70 was delayed compared to ESAT-6. This delayed expression was associated with induction of less differentiated MPT70-specific CD4 T cells but, compared to ESAT-6, also reduced protection after vaccination. In contrast, infection with an MPT70-overexpressing Mtb strain promoted highly differentiated KLRG1+CX3CR1+ CD4 T cells with limited lung-homing capacity. Importantly, this differentiated phenotype could be prevented by vaccination and, against the overexpressing strain, vaccination with MPT70 conferred similar protection as ESAT-6. Together our data indicate that high in vivo antigen expression drives T cells towards terminal differentiation and that targeted vaccination with adjuvanted protein can counteract this phenomenon by maintaining T cells in a protective less-differentiated state. These observations shed new light on host-pathogen interactions and provide guidance on how future Mtb vaccines can be designed to tip the immune-balance in favor of the host.

Using an effective TB vaccination regimen to identify immune responses associated with protection in the murine model

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Boosting BCG with ChAdOx1.85A and MVA85A (B-C-M) improves its protective efficacy.

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B-C-M induces pulmonary and systemic Ag85A-specific cytokine and antibody responses.

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B-C-M enhances resident memory CD4⁺ and CD8⁺ T cells in the lung parenchyma.

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Protection associated with lung parenchymal Ag85A-specific CD4⁺ CXCR3⁺ KLRG1^- T cells.

A vaccine against tuberculosis (TB), a disease resulting from infection with Mycobacterium tuberculosis (M.tb), is urgently needed to prevent more than a million deaths per year. Bacillus Calmette–Guérin (BCG) is the only available vaccine against TB but its efficacy varies throughout the world. Subunit vaccine candidates, based on recombinant viral vectors expressing mycobacterial antigens, are one of the strategies being developed to boost BCG-primed host immune responses and efficacy. A promising vaccination regimen composed of intradermal (i.d.) BCG prime, followed by intranasally (i.n.) administered chimpanzee adenoviral vector (ChAdOx1) and i.n. or i.d. modified vaccinia Ankara virus (MVA), both expressing Ag85A, has been previously reported to significantly improve BCG efficacy in mice. Effector and memory immune responses induced by BCG-ChAdOx1.85A-MVA85A (B-C-M), were evaluated to identify immune correlates of protection in mice. This protective regime induced strong Ag85A-specific cytokine responses in CD4⁺ and CD8⁺ T cells, both in the systemic and pulmonary compartments. Lung parenchymal CXCR3⁺ KLRG1^- Ag85A-specific memory CD4⁺ T cells were significantly increased in B-C-M compared to BCG immunised mice at 4, 8 and 20 weeks post vaccination, but the number of these cells decreased at the latter time point. This cell population was associated with the protective efficacy of this regime and may have an important protective role against M.tb infection.

Synthetic protein conjugate vaccines provide protection against Mycobacterium tuberculosis in mice

The global incidence of tuberculosis remains unacceptably high, with new preventative strategies needed to reduce the burden of disease. We describe here a method for the generation of synthetic self-adjuvanted protein vaccines and demonstrate application in vaccination against Mycobacterium tuberculosis Two vaccine constructs were designed, consisting of full-length ESAT6 protein fused to the TLR2-targeting adjuvants Pam₂Cys-SK₄ or Pam₃Cys-SK₄ These were produced by chemical synthesis using a peptide ligation strategy. The synthetic self-adjuvanting vaccines generated powerful local CD4⁺ T cell responses against ESAT6 and provided significant protection in the lungs from virulent M. tuberculosis aerosol challenge when administered to the pulmonary mucosa of mice. The flexible synthetic platform we describe, which allows incorporation of adjuvants to multiantigenic vaccines, represents a general approach that can be applied to rapidly assess vaccination strategies in preclinical models for a range of diseases, including against novel pandemic pathogens such as SARS-CoV-2.

Developing New Anti-Tuberculosis Vaccines: Focus on Adjuvants

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb) that sits in the top 10 leading causes of death in the world today and is the current leading cause of death among infectious diseases. Although there is a licensed vaccine against TB, the Mycobacterium bovis bacilli Calmette–Guérin (BCG) vaccine, it has several limitations, namely its high variability of efficacy in the population and low protection against pulmonary tuberculosis. New vaccines for TB are needed. The World Health Organization (WHO) considers the development and implementation of new TB vaccines to be a priority. Subunit vaccines are promising candidates since they can overcome safety concerns and optimize antigen targeting. Nevertheless, these vaccines need adjuvants in their formulation in order to increase immunogenicity, decrease the needed antigen dose, ensure a targeted delivery and optimize the antigens delivery and interaction with the immune cells. This review aims to focus on adjuvants being used in new formulations of TB vaccines, namely candidates already in clinical trials and others in preclinical development. Although no correlates of protection are defined, most research lines in the field of TB vaccination focus on T-helper 1 (Th1) type of response, namely polyfunctional CD4+ cells expressing simultaneously IFN-γ, TNF-α, and IL-2 cytokines, and also Th17 responses. Accordingly, most of the adjuvants reviewed here are able to promote such responses. In the future, it might be advantageous to consider a wider array of immune parameters to better understand the role of adjuvants in TB immunity and establish correlates of protection.

The Impact of Nanoparticles on Innate Immune Activation by Live Bacteria

The innate immune system evolved to detect and react against potential dangers such as bacteria, viruses, and environmental particles. The advent of modern technology has exposed innate immune cells, such as monocytes, macrophages, and dendritic cells, to a relatively novel type of particulate matter, i.e., engineered nanoparticles. Nanoparticles are not inherently pathogenic, and yet cases have been described in which specific nanoparticle types can either induce innate/inflammatory responses or modulate the activity of activated innate cells. Many of these studies rely upon activation by agonists of toll-like receptors, such as lipopolysaccharide or peptidoglycan, instead of the more realistic stimulation by whole live organisms. In this review we examine and discuss the effects of nanoparticles on innate immune cells activated by live bacteria. We focus in particular on how nanoparticles may interfere with bacterial processes in the context of innate activation, and confine our scope to the effects due to particles themselves, rather than to molecules adsorbed on the particle surface. Finally, we examine the long-lasting consequences of coexposure to nanoparticles and bacteria, in terms of potential microbiome alterations and innate immune memory, and address nanoparticle-based vaccine strategies against bacterial infection.

Tuberculosis vaccination needs to avoid 'decoy' immune reactions

Current search for a new effective vaccine against tuberculosis involves selected antigens, vectors and adjuvants. These are being evaluated usually by their booster inoculation following priming with Bacillus Calmette-Guerin. The purpose of this article is to point out, that despite being attenuated of virulence, priming with BCG may still involve immune mechanisms, which are not favourable for protection against active disease. It is postulated, that the responsible 'decoy' constituents selected during the evolution of pathogenic tubercle bacilli may be involved in the evasion from bactericidal host resistance and stimulate immune responses of a cytokine phenotype, which lead to the transition from latent closed granulomas to reactivation with infectious lung cavities. The decoy mechanisms appear as favourable for most infected subjects but leading in a minority of cases to pathology which can effectively transmit the infection. It is proposed that construction and development of new vaccine candidates could benefit from avoiding decoy-type immune mechanisms.

Mucosal delivery of a multistage subunit vaccine promotes development of lung-resident memory T cells and affords interleukin-17-dependent protection against pulmonary tuberculosis

The development of effective vaccines against bacterial lung infections requires the induction of protective, pathogen-specific immune responses without deleterious inflammation within the pulmonary environment. Here, we made use of a polysaccharide-adjuvanted vaccine approach to elicit resident pulmonary T cells to protect against aerosol Mycobacterium tuberculosis infection. Intratracheal administration of the multistage fusion protein CysVac2 and the delta-inulin adjuvant Advax™ (formulated with a TLR9 agonist) provided superior protection against aerosol M. tuberculosis infection in mice, compared to parenteral delivery. Surprisingly, removal of the TLR9 agonist did not impact vaccine protection despite a reduction in cytokine-secreting T cell subsets, particularly CD4+IFN-γ+IL-2+TNF+ multifunctional T cells. CysVac2/Advax-mediated protection was associated with the induction of lung-resident, antigen-specific memory CD4+ T cells that expressed IL-17 and RORγT, the master transcriptional regulator of Th17 differentiation. IL-17 was identified as a key mediator of vaccine efficacy, with blocking of IL-17 during M. tuberculosis challenge reducing phagocyte influx, suppressing priming of pathogen-specific CD4+ T cells in local lymph nodes and ablating vaccine-induced protection. These findings suggest that tuberculosis vaccines such as CysVac2/Advax that are capable of eliciting Th17 lung-resident memory T cells are promising candidates for progression to human trials.

Rescuing ESAT-6 Specific CD4 T Cells From Terminal Differentiation Is Critical for Long-Term Control of Murine Mtb Infection

In most cases, Mycobacterium tuberculosis (Mtb) causes life-long chronic infections, which poses unique challenges for the immune system. Most of the current tuberculosis (TB) subunit vaccines incorporate immunodominant antigens and at this point, it is poorly understood how the CD4 T cell subsets recognizing these antigens are affected during long-term infection. Very little is known about the requirements for sustainable vaccine protection against TB. To explore this, we screened 62 human-recognized Mtb antigens during chronic murine Mtb infection and identified the four most immunodominant antigens in this setting (MPT70, Rv3020c, and Rv3019c and ESAT-6). Combined into a subunit vaccine, this fusion protein induced robust protection both in a standard short-term model and in a long-term infection model where immunity from BCG waned. Importantly, replacement of ESAT-6 with another ESAT-6-family antigen, Rv1198, led to similar short-term protection but a complete loss of bacterial control during chronic infection. This observation was further underscored, as the ESAT-6 containing vaccine mediated sustainable protection in a model of post-exposure vaccination, where the ESAT-6-replacement vaccine did not. An individual comparison of the CD4 T cell responses during Mtb infection revealed that ESAT-6-specific T cells were more terminally differentiated than the other immunodominant antigens and immunization with the ESAT-6 containing vaccine led to substantially greater reduction in the overall T cell differentiation status. Our data therefore associates long-term bacterial control with the ability of a vaccine to rescue infection-driven CD4T cell differentiation and future TB antigen discovery programs should focus on identifying antigens with the highest accompanying T cell differentiation, like ESAT-6. This also highlights the importance of long-term readouts in both preclinical and clinical studies with TB vaccines.

Airway delivery of both a BCG prime and adenoviral boost drives CD4 and CD8 T cells into the lung tissue parenchyma

Heterologous BCG prime-boost regimens represent a promising strategy for an urgently required improved tuberculosis vaccine. Identifying the mechanisms which underpin the enhanced protection induced by such strategies is one key aim which would significantly accelerate rational vaccine development. Experimentally, airway vaccination induces greater efficacy than parenteral delivery; in both conventional vaccination and heterologous boosting of parenteral BCG immunisation. However, the effect of delivering both the component prime and boost immunisations via the airway is not well known. Here we investigate delivery of both the BCG prime and adenovirus boost vaccination via the airway in a murine model, and demonstrate this approach may be able to improve the protective outcome over parenteral prime/airway boost. Intravascular staining of T cells in the lung revealed that the airway prime regimen induced more antigen-specific multifunctional CD4 and CD8 T cells to the lung parenchyma prior to challenge and indicated the route of both prime and boost to be critical to the location of induced resident T cells in the lung. Further, in the absence of a defined phenotype of vaccine-induced protection to tuberculosis; the magnitude and phenotype of vaccine-specific T cells in the parenchyma of the lung may provide insights into potential correlates of immunity.

Next-Generation Pertussis Vaccines Based on the Induction of Protective T Cells in the Respiratory Tract

Immunization with current acellular pertussis (aP) vaccines protects against severe pertussis, but immunity wanes rapidly after vaccination and these vaccines do not prevent nasal colonization with Bordetella pertussis. Studies in mouse and baboon models have demonstrated that Th1 and Th17 responses are integral to protective immunity induced by previous infection with B. pertussis and immunization with whole cell pertussis (wP) vaccines. Mucosal Th17 cells, IL-17 and secretory IgA (sIgA) are particularly important in generating sustained sterilizing immunity in the nasal cavity. Current aP vaccines induce potent IgG and Th2-skewed T cell responses but are less effective at generating Th1 and Th17 responses and fail to prime respiratory tissue-resident memory T (TRM) cells, that maintain long-term immunity at mucosal sites. In contrast, a live attenuated pertussis vaccine, pertussis outer membrane vesicle (OMV) vaccines or aP vaccines formulated with novel adjuvants do induce cellular immune responses in the respiratory tract, especially when delivered by the intranasal route. An increased understanding of the mechanisms of sustained protective immunity, especially the role of respiratory TRM cells, will facilitate the development of next generation pertussis vaccines that not only protect against pertussis disease, but prevent nasal colonization and transmission of B. pertussis.

Immunization with Mycobacterium tuberculosis-Specific Antigens Bypasses T Cell Differentiation from Prior Bacillus Calmette-Guérin Vaccination and Improves Protection in Mice

Despite the fact that the majority of people in tuberculosis (TB)-endemic areas are vaccinated with the Bacillus Calmette-Guérin (BCG) vaccine, TB remains the leading infectious cause of death. Data from both animal models and humans show that BCG and subunit vaccines induce T cells of different phenotypes, and little is known about how BCG priming influences subsequent booster vaccines. To test this, we designed a novel Mycobacterium tuberculosis-specific (or "non-BCG") subunit vaccine with protective efficacy in both mice and guinea pigs and compared it to a known BCG boosting vaccine. In naive mice, this M. tuberculosis-specific vaccine induced similar protection compared with the BCG boosting vaccine. However, in BCG-primed animals, only the M. tuberculosis-specific vaccine added significantly to the BCG-induced protection. This correlated with the priming of T cells with a lower degree of differentiation and improved lung-homing capacity. These results have implications for TB vaccine design.

Moving tuberculosis vaccines from theory to practice

Tuberculosis (TB) vaccine research has reached a unique point in time. Breakthrough findings in both the basic immunology of Mycobacterium tuberculosis infection and the clinical development of TB vaccines suggest, for the first time since the discovery of the Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine more than a century ago, that a novel, efficacious TB vaccine is imminent. Here, we review recent data in the light of our current understanding of the immunology of TB infection and discuss the identification of biomarkers for vaccine efficacy and the next steps in the quest for an efficacious vaccine that can control the global TB epidemic.

Nano-antimicrobials: A New Paradigm for Combating Mycobacterial Resistance

BACKGROUND

Mycobacterium group contains several pathogenic bacteria including M. tuberculosis where the emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) is alarming for human and animal health around the world. The condition has further aggravated due to the speed of discovery of the newer drugs has been outpaced by the rate of resistance developed in microorganisms, thus requiring alternative combat strategies. For this purpose, nano-antimicrobials have emerged as a potential option.

OBJECTIVE

The current review is focused on providing a detailed account of nanocarriers like liposome, micelles, dendrimers, solid lipid NPs, niosomes, polymeric nanoparticles, nano-suspensions, nano-emulsion, mesoporous silica and alginate-based drug delivery systems along with the recent updates on developments regarding nanoparticle-based therapeutics, vaccines and diagnostic methods developed or under pipeline with their potential benefits and limitations to combat mycobacterial diseases for their successful eradication from the world in future.

RESULTS

Distinct morphology and the underlying mechanism of pathogenesis and resistance development in this group of organisms urge improved and novel methods for the early and efficient diagnosis, treatment and vaccination to eradicate the disease. Recent developments in nanotechnology have the potential to meet both the aspects: nano-materials are proven components of several efficient targeted drug delivery systems and the typical physicochemical properties of several nano-formulations have shown to possess distinct bacteriocidal properties. Along with the therapeutic aspects, nano-vaccines and theranostic applications of nano-formulations have grown in popularity in recent times as an effective alternative means to combat different microbial superbugs.

CONCLUSION

Nanomedicine holds a bright prospect to perform a key role in global tuberculosis elimination program.

Toll like-receptor agonist Pam3Cys modulates the immunogenicity of liposomes containing the tuberculosis vaccine candidate H56

A major roadblock in the development of novel vaccines is the formulation and delivery of the antigen. Liposomes composed of a dimethyldioctadecylammonium (DDA) backbone and the adjuvant trehalose-6-6-dibehenate (TDB, termed "cationic adjuvant formulation (CAF01)", promote immunogenicity and protective efficacy of vaccines, most notably against infection with Mycobacterium tuberculosis. Specifically, the multicomponent antigen H56 delivered by CAF01 protects against tuberculosis in mice. Here we investigated whether the inclusion of immune-modulatory adjuvants into CAF01 modulates the immunogenicity of H56/CAF01 in vitro and in vivo. Based on our recent findings we selected the active sequence of the mycobacterial 19 kDa lipoprotein, Pam₃Cys, which interacts with Toll like receptor 2 to induce an antimicrobial pathway. H56/CAF01-Pam₃Cys liposomes were characterized for Pam₃Cys incorporation, size, toxicity and activation of primary human macrophages. Macrophages efficiently take up H56/CAF01-Pam₃Cys and trigger the release of significantly higher levels of TNF, IL-12 and IL-10 than H56/CAF01 alone. To evaluate the immunogenicity in vivo, we immunized mice with H56/CAF01-Pam₃Cys and measured the release of IFN-γ and IL-17A by lymph node cells and spleen cells. While the antigen-specific production of IFN-γ was reduced by inclusion of Pam₃Cys into H56/CAF01, the levels of IL-17A remained unchanged. In agreement with this finding, the concentration of the IFN-γ-associated IgG2a antibodies in the serum was lower than in H56/CAF01 immunized animals. These results provide proof of concept that Toll like-receptor agonist can be included into liposomes to modulate immune responses. The discordant results between the in vitro studies with human macrophages and in vivo studies in mice highlight the relevance and complexity of comparing immune responses in different species.

ortho-Substituted lipidated Brartemicin derivative shows promising Mincle-mediated adjuvant activity

Structure activity relationship studies of lipidated Brartemicin analogues have revealed the potent adjuvant activity of ortho-substituted Brartemicin analogue 5a, which was better than that of p-OC₁₈ (5c) and C18dMeBrar (4).

Investigating Prime-Pull Vaccination through a Combination of Parenteral Vaccination and Intranasal Boosting

Formulation of inhalable delivery systems containing tuberculosis (TB) antigens to target the site of infection (lungs) have been considered for the development of subunit vaccines. Inert delivery systems such as poly (lactic-co-glycolic acid) (PLGA) are an interesting approach due to its approval for human use. However, PLGA suffers hydrolytic degradation when stored in a liquid environment for prolonged time. Therefore, in this study, nano- and microparticles composed of different PLGA copolymers (50:50, 75:25 and 85:15), sucrose (10% w/v) and L-leucine (1% w/v) encapsulating H56 TB vaccine candidate were produced as dried powders. In vitro studies in three macrophage cell lines (MH-S, RAW264.7 and THP-1) showed the ability of these cells to take up the formulated PLGA:H56 particles and process the antigen. An in vivo prime-pull immunisation approach consisting of priming with CAF01:H56 (2 × subcutaneous (s.c.) injection) followed by a mucosal boost with PLGA:H56 (intranasal (i.n.) administration) demonstrated the retention of the immunogenicity of the antigen encapsulated within the lyophilised PLGA delivery system, although no enhancing effect could be observed compared to the administration of antigen alone as a boost. The work here could provide the foundations for the scale independent manufacture of polymer delivery systems encapsulating antigens for inhalation/aerolisation to the lungs.

Type I IFN signalling is required for cationic adjuvant formulation (CAF)01-induced cellular immunity and mucosal priming

Despite being in the midst of a global pandemic of infections caused by the pathogen Chlamydia trachomatis, a vaccine capable of inducing protective immunity remains elusive. Given the C. trachomatis mucosal port of entry, a formulation compatible with mucosal administration and capable of eliciting potent genital tract immunity is highly desirable. While subunit vaccines are considered safer and better tolerated, these are typically poorly immunogenic and require co-formulation with immune-potentiating adjuvants. However, of the adjuvants licensed for use in humans, very few drive robust cellular responses, a pre-requisite for protection against C. trachomatis infection. Recently, the cationic adjuvant formulations (CAF) have been shown to induce robust humoral and cellular immunity in pre-clinical models of chlamydia, malaria and tuberculosis (TB). Here, we demonstrate that CAF01 induces potent immune responses when combined with the major outer membrane protein (MOMP) of C. trachomatis following parenteral immunisation and also as part of a heterologous prime/boost regime. We show that a subcutaneous prime with CAF01-adjuvanted recombinant MOMP licenses antigen-specific immunity at distant mucosal sites which can be activated following oral antigen re-encounter in the absence of concomitant adjuvant stimulation. Finally, we shed light on the mechanism(s) through which CAF01 elicits robust antigen-specific immunity to co-formulated MOMP via type I interferon (IFN) signalling.

Dose Optimization of H56:IC31 Vaccine for Tuberculosis-Endemic Populations. A Double-Blind, Placebo-controlled, Dose-Selection Trial

RATIONALE

Global tuberculosis (TB) control requires effective vaccines in TB-endemic countries, where most adults are infected with Mycobacterium tuberculosis (M.tb).

OBJECTIVES

We sought to define optimal dose and schedule of H56:IC31, an experimental TB vaccine comprising Ag85B, ESAT-6, and Rv2660c, for M.tb-infected and M.tb-uninfected adults.

METHODS

We enrolled 98 healthy, HIV-uninfected, bacillus Calmette-Guérin-vaccinated, South African adults. M.tb infection was defined by QuantiFERON-TB (QFT) assay. QFT-negative participants received two vaccinations of different concentrations of H56 in 500 nmol of IC31 to enable dose selection for further vaccine development. Subsequently, QFT-positive and QFT-negative participants were randomized to receive two or three vaccinations to compare potential schedules. Participants were followed for safety and immunogenicity for 292 days.

MEASUREMENTS AND MAIN RESULTS

H56:IC31 showed acceptable reactogenicity profiles irrespective of dose, number of vaccinations, or M.tb infection. No vaccine-related severe or serious adverse events were observed. The three H56 concentrations tested induced equivalent frequencies and functional profiles of antigen-specific CD4 T cells. ESAT-6 was only immunogenic in QFT-negative participants who received three vaccinations.

CONCLUSIONS

Two or three H56:IC31 vaccinations at the lowest dose induced durable antigen-specific CD4 T-cell responses with acceptable safety and tolerability profiles in M.tb-infected and M.tb-uninfected adults. Additional studies should validate applicability of vaccine doses and regimens to both QFT-positive and QFT-negative individuals. Clinical trial registered with www.clinicaltrials.gov (NCT01865487).

Tuberculosis Vaccine Development: Progress in Clinical Evaluation

Tuberculosis (TB) is the leading killer among all infectious diseases worldwide despite extensive use of the Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine. A safer and more effective vaccine than BCG is urgently required. More than a dozen TB vaccine candidates are under active evaluation in clinical trials aimed to prevent infection, disease, and recurrence. After decades of extensive research, renewed promise of an effective vaccine against this ancient airborne disease has recently emerged. In two innovative phase 2b vaccine clinical trials, one for the prevention of Mycobacterium tuberculosis infection in healthy adolescents and another for the prevention of TB disease in M. tuberculosis-infected adults, efficacy signals were observed. These breakthroughs, based on the greatly expanded knowledge of the M. tuberculosis infection spectrum, immunology of TB, and vaccine platforms, have reinvigorated the TB vaccine field. Here, we review our current understanding of natural immunity to TB, limitations in BCG immunity that are guiding vaccinologists to design novel TB vaccine candidates and concepts, and the desired attributes of a modern TB vaccine. We provide an overview of the progress of TB vaccine candidates in clinical evaluation, perspectives on the challenges faced by current vaccine concepts, and potential avenues to build on recent successes and accelerate the TB vaccine research-and-development trajectory.

STING-Activating Adjuvants Elicit a Th17 Immune Response and Protect against Mycobacterium tuberculosis Infection

There are a limited number of adjuvants that elicit effective cell-based immunity required for protection against intracellular bacterial pathogens. Here, we report that STING-activating cyclic dinucleotides (CDNs) formulated in a protein subunit vaccine elicit long-lasting protective immunity to Mycobacterium tuberculosis in the mouse model. Subcutaneous administration of this vaccine provides equivalent protection to that of the live attenuated vaccine strain Bacille Calmette-Guérin (BCG). Protection is STING dependent but type I IFN independent and correlates with an increased frequency of a recently described subset of CXCR3-expressing T cells that localize to the lung parenchyma. Intranasal delivery results in superior protection compared with BCG, significantly boosts BCG-based immunity, and elicits both Th1 and Th17 immune responses, the latter of which correlates with enhanced protection. Thus, a CDN-adjuvanted protein subunit vaccine has the capability of eliciting a multi-faceted immune response that results in protection from infection by an intracellular pathogen.

Adjuvant Strategies for More Effective Tuberculosis Vaccine Immunity

Tuberculosis (TB) caused by Mycobacterium tuberculosis infection is responsible for the most deaths by a single infectious agent worldwide, with 1.6 million deaths in 2017 alone. The World Health Organization, through its "End TB" strategy, aims to reduce TB deaths by 95% by 2035. In order to reach this goal, a more effective vaccine than the Bacillus Calmette-Guerin (BCG) vaccine currently in use is needed. Subunit TB vaccines are ideal candidates, because they can be used as booster vaccinations for individuals who have already received BCG and would also be safer for use in immunocompromised individuals in whom BCG is contraindicated. However, subunit TB vaccines will almost certainly require formulation with a potent adjuvant. As the correlates of vaccine protection against TB are currently unclear, there are a variety of adjuvants currently being used in TB vaccines in preclinical and clinical development. This review describes the various adjuvants in use in TB vaccines, their effectiveness, and their proposed mechanisms of action. Notably, adjuvants with less inflammatory and reactogenic profiles that can be administered safely via mucosal routes, may have the biggest impact on future directions in TB vaccine design.

Ensilication Improves the Thermal Stability of the Tuberculosis Antigen Ag85b and an Sbi-Ag85b Vaccine Conjugate

There is an urgent need for the development of vaccine thermostabilisation methodologies as the maintenance of a continuous and reliable cold chain remains a major hurdle to the global distribution of safe and effective vaccines. Ensilication, a method that encases proteins in a resistant silica cage has been shown to physically prevent the thermal denaturation of a number of model proteins. In this study we investigate the utility of this promising approach in improving the thermal stability of antigens and vaccine conjugates highly relevant to the development of candidate tuberculosis vaccines, including antigen 85b conjugated with the Staphylococcus aureus-protein based adjuvant Sbi. Here we analyse the sensitivity of these constructs to thermal denaturation and demonstrate for the first time the benefits of ensilication in conferring these vaccine-relevant proteins with protection against temperature-induced loss of structure and function without the need for refrigeration. Our results reveal the potential of ensilication in facilitating the storage and transport of vaccines at ambient temperatures in the future and therefore in delivering life-saving vaccines globally, and in particular to remote areas of developing countries where disease rates are often highest.

Site-Specific DC Surface Signatures Influence CD4+ T Cell Co-stimulation and Lung-Homing

Dendritic cells (DCs) that drain the gut and skin are known to favor the establishment of T cell populations that home to the original site of DC-antigen (Ag) encounter by providing soluble “imprinting” signals to T cells in the lymph node (LN). To study the induction of lung T cell-trafficking, we used a protein-adjuvant murine intranasal and intramuscular immunization model to compare in vivo-activated Ag⁺ DCs in the lung and muscle-draining LNs. Higher frequencies of Ag⁺ CD11b⁺ DCs were observed in lung-draining mediastinal LNs (MedLN) compared to muscle-draining inguinal LNs (ILN). Ag⁺ CD11b⁺ MedLN DCs were qualitatively superior at priming CD4⁺ T cells, which then expressed CD49a and CXCR3, and preferentially trafficked into the lung parenchyma. CD11b⁺ DCs from the MedLN expressed higher levels of surface podoplanin, Trem4, GL7, and the known co-stimulatory molecules CD80, CD86, and CD24. Blockade of specific MedLN DC molecules or the use of sorted DC and T cell co-cultures demonstrated that DC surface phenotype influences the ability to prime T cells that then home to the lung. Thus, the density of dLN Ag⁺ DCs, and DC surface molecule signatures are factors that can influence the output and differentiation of lung-homing CD4⁺ T cells.

The Role of KLRG1 in Human CD4+ T-Cell Immunity Against Tuberculosis

Background

KLRG1 is a marker of terminally differentiated CD8+ T cells in viral infection, but its role in human Mycobacterium tuberculosis infection remains elusive.

Methods

A set of cohorts of patients with tuberculosis was designed, and the expression profiles and functions of KLRG1+CD4+ T cells were determined with and without antibody blocking.

Results

KLRG1 expression on CD4+ T cells was significantly increased in patients with active tuberculosis, compared with healthy controls and patients without tuberculosis. Upon M. tuberculosis-specific stimulation, the ability to secrete interferon γ, interleukin 2, and tumor necrosis factor α was significantly greater in KLRG1-expressing CD4+ T cells than in their KLRG-negative counterparts and was accompanied by a decreased proportion of regulatory T cells and increased Akt signaling. However, KLRG1-expressing CD4+ T cells had a shorter life-span, which was associated with a higher apoptosis rate but a similar proliferative response. Blockade of KLRG1 signaling significantly enhanced interferon γ and interleukin 2 secretion without affecting either cell apoptosis or multiplication. Addition of a specific Akt inhibitor prevented this increased cytokine response, implicating the Akt signaling pathway.

Conclusions

Our study delineated the profile of KLRG1+CD4+ T cells in patients with tuberculosis and suggests that M. tuberculosis infection drives CD4+ T cells to acquire increased effector function in a terminally differentiated state, which is restrained by KLRG1 via KLRG1/Akt signaling pathway.