Enhanced immunogenicity of BCG vaccine by using a viral-based GM-CSF transgene adjuvant formulation

Promising Cytokine Adjuvants for Enhancing Tuberculosis Vaccine Immunity

Tuberculosis, caused by Mycobacterium tuberculosis (M. tuberculosis), remains a formidable global health challenge, affecting a substantial portion of the world's population. The current tuberculosis vaccine, bacille Calmette-Guérin (BCG), offers limited protection against pulmonary tuberculosis in adults, underscoring the critical need for innovative vaccination strategies. Cytokines are pivotal in modulating immune responses and have been explored as potential adjuvants to enhance vaccine efficacy. The strategic inclusion of cytokines as adjuvants in tuberculosis vaccines holds significant promise for augmenting vaccine-induced immune responses and strengthening protection against M. tuberculosis. This review delves into promising cytokines, such as Type I interferons (IFNs), Type II IFN, interleukins such as IL-2, IL-7, IL-15, IL-12, and IL-21, alongside the use of a granulocyte-macrophage colony-stimulating factor (GM-CSF) as an adjuvant, which has shown effectiveness in boosting immune responses and enhancing vaccine efficacy in tuberculosis models.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

Co-Administration of Anticancer Candidate MK-2206 Enhances the Efficacy of BCG Vaccine Against Mycobacterium tuberculosis in Mice and Guinea Pigs

The failure of M. bovis BCG to induce long-term protection has been endowed to its inability to escape the phagolysosome, leading to mild activation of CD8⁺ mediated T cell response. Induction of apoptosis in host cells plays an important role in potentiating dendritic cells-mediated priming of CD8⁺ T cells, a process defined as “cross-priming.” Moreover, IL-10 secretion by infected cells has been reported to hamper BCG-induced immunity against Tuberculosis (TB). Previously, we have reported that apoptosis of BCG-infected macrophages and inhibition of IL-10 secretion is FOXO3 dependent, a transcription factor negatively regulated by the pro-survival activated threonine kinase, Akt. We speculate that FOXO3-mediated induction of apoptosis and abrogation of IL-10 secretion along with M. bovis BCG immunization might enhance the protection imparted by BCG. Here, we have assessed whether co-administration of a known anti-cancer Akt inhibitor, MK-2206, enhances the protective efficacy of M. bovis BCG in mice model of infection. We observed that in vitro MK-2206 treatment resulted in FOXO3 activation, enhanced BCG-induced apoptosis of macrophages and inhibition of IL-10 secretion. Co-administration of M. bovis BCG along with MK-2206 also increased apoptosis of antigen-presenting cells in draining lymph nodes of immunized mice. Further, MK-2206 administration improved BCG-induced CD4⁺ and CD8⁺ effector T cells responses and its ability to induce both effector and central memory T cells. Finally, we show that co-administration of MK-2206 enhanced the protection imparted by M. bovis BCG against Mtb in aerosol infected mice and guinea pigs. Taken together, we provide evidence that MK-2206-mediated activation of FOXO3 potentiates BCG-induced immunity and imparts protection against Mtb through enhanced innate immune response.

T Cell Production of GM-CSF Protects the Host during Experimental Tuberculosis

Although classically associated with myelopoiesis, granulocyte-macrophage colony-stimulating factor (GM-CSF) is increasingly recognized as being important for tuberculosis (TB) resistance. GM-CSF is expressed by nonhematopoietic and hematopoietic lineages following infection with Mycobacterium tuberculosis and is necessary to restrict M. tuberculosis growth in experimental models. Until the recent study by Rothchild et al. (mBio 8:e01514-17, 2017, https://doi.org/10.1128/mBio.01514-17), it was unknown whether GM-CSF-producing T cells contribute to TB resistance. Rothchild et al. identify which conventional and nonconventional T cell subsets produce GM-CSF during experimental TB, establish their protective nature using a variety of approaches, and provide a mechanistic basis for their ability to restrict M. tuberculosis growth. This commentary discusses the significance of these findings to basic and applied TB research. As translated to human disease, these findings suggest vaccine-mediated expansion of GM-CSF-producing T cells could be an effective prophylactic or therapeutic TB strategy.

Protective Immunity againstBordetella pertussisby a Recombinant DNA Vaccine and the Effect of Coinjection with a Granulocyte-Macrophage Colony Stimulating Factor Gene

A recombinant pertussis DNA vaccine was described here with its immunogenicity and the ability to induce protection against B. pertussis infection in mice. Three immunodominant antigen gene fragments of pertussis, pertussis toxin subunit 1 (pts1), fragments of pertactin (prn) and filamentous hemagglutinin (fha), were recombined as fragment pts1-prn-fha named ppf, and it was cloned to plasmid pVAX1 as pVAX1/ppf. Compared to those injected with pVAX1, the mice injected with pVAX1/ppf significantly elicited more antigen specific antibody anti-PTS1, anti-PRN, anti-FHA and cytokine IL-10, IFN-gamma. When pGM-CSF was coinjected with pVAX1/ppf, the mice showed significantly increases of the three antibodies and cytokine IL-10, IL-4, IFN-gamma and TNF-alpha compared to those injected with pVAX1 only. The mice in group pVAX1/ppf & pGM-CSF, in particular; induced much more anti-PTS1, IL-4 and TNF-alpha than those in group pVAX1/ppf. In the intracerebral mouse protection test, the mice immunized with pVAX1/ppf or pVAX1/ppf & pGM-CSF induced protection to a lethal dose of B. pertussis. The results indicate that recombinant DNA vaccine and pGM-CSF coinjection can induce protective immunity against B. pertussis, demonstrating a valuable method to prevent pertussis.

Cytokine therapy of tuberculosis at the crossroads

Drug treatment is the key strategy in TB control. However, the treatment course lasts 6-9 months because the current anti-TB drugs are poorly effective against nondividing (i.e., persistent) bacilli. As a result, completion rates are unsatisfactory, leading to emergence and spread of multidrug-resistant infection. It would, therefore, be very desirable to design a form of complementary treatment that could speed up the recovery process for people afflicted with TB and reduce the relapse rates. With the advancement of our understanding of the immunopathogenesis of TB, it has become increasingly possible to develop novel adjunctive immunotherapies for both drug-susceptible and drug-resistant TB. Notably, cytokines probably offer the most promising prospect of such a therapy being introduced in routine clinical practice. However, in many ways, the cytokine therapy of TB has reached a crossroad, since, although the initial promise failed to live up to expectations, sufficient encouraging evidence exists to warrant further exploration. There are clear arguments in favor as well as against such treatments. This review aims to provide a rationale for cytokine treatment of TB, to describe the current status of several cytokines that have been considered for that purpose and, ultimately, to make a case for the need for further clinical trials.

Immunogenicity and protective efficacy of heterologous prime-boost regimens with mycobacterial vaccines and recombinant adenovirus- and poxvirus-vectored vaccines against murine tuberculosis

OBJECTIVES

To evaluate regimens using bacillus Calmette-Guérin (BCG) or recombinant BCG (rBCG) overexpressing Ag85B for priming, followed by boosting with a modified vaccinia virus Ankara strain (MVA) and/or adenovirus vector (AD) expressing an Ag85B-ESAT6 fusion protein.

METHODS

Cellular and humoral immune responses were determined after subcutaneous vaccination, which was employed to trigger systemic immunity against intravenous infection in a mouse model of tuberculosis (TB). Bacterial loads and lung histology were evaluated.

RESULTS

The relative IgG2a and IgG1 antibody levels indicated that the viral-vectored vaccines generated a T-helper type 1 (Th1)-biased response after two doses of viral boost vaccinations. Boosting BCG-primed mice with viral vaccines induced a Th1 immune response that included both CD4 and CD8 T-cells generating antigen-specific interferon-gamma (IFN-γ) and CD8 T cytotoxic activity. Only mice vaccinated with two different viral boosters after BCG priming exhibited a significant reduction in bacterial burden in the lung after challenge. Histology examinations confirmed the attenuation of lung damage and more compact granulomas. After mycobacteria priming, boosting with AD85B-E6 followed by MVA85B-E6 afforded better protection than the reverse order of administration of the viral vectors.

CONCLUSIONS

This study demonstrates the potential of multiple heterologous viral booster vaccines, although the exact correlates of protection and optimal regimens should be further investigated for the rational design of future vaccine strategies.

Respiratory mucosal immunization with adenovirus gene transfer vector induces helper CD4 T cell-independent protective immunity

BACKGROUND

Virus-vectored vaccine is a powerful activator of CD8 T cell-mediated immunity and is especially amenable to respiratory mucosal immunization, offering hopes for use in humans with diminished helper CD4 T cell function. However, whether virus-mediated mucosal immunization can produce immune protective CD8 T cells without the CD4 T cell help remains to be investigated.

METHODS

We used a replication-deficient adenovirus vector expressing an Mycobacterium tuberculosis antigen Ag85A for intranasal vaccination and evaluated its effect on CD8 T cell activation and protection in mice depleted of CD4 T cells.

RESULTS

Intranasal vaccination of CD4 T cell-depleted mice led to suboptimal generation of Ag-specific tetramer(+) or interferon (IFN)-gamma-producing CD8 T cells in the lung and spleen but this was observed mainly at the early time after vaccination. Reduced CD8 T cell priming was also accompanied by decreased CD8 T cell responses (CTL). Nevertheless, the ratio of Ag-specific CD8 T cells to IFN-gamma-producing CD8 T cells in CD4 T cell-depleted hosts remained comparable to that in CD4 T cell-competent hosts. Furthermore, the 'unhelped' CD8 T cells also displayed a similar immune phenotype as the 'helped' counterparts. The animals with 'unhelped' CD8 T cells were as well-protected from pulmonary M. tuberculosis challenge as those with 'helped' CD8 T cells in the absence of CD4 T cells.

CONCLUSIONS

The data obtained in the present study suggest that the fully immune protective CD8 T cells can still be generated by respiratory mucosal viral-mediated immunization without CD4 T cells and that CD8 T cells, 'helped' or 'unhelped', can confer significant protection against pulmonary tuberculosis independent of CD4 T cells.

Adjuvants in tuberculosis vaccine development

Tuberculosis remains a major public health problem around the world. Because the Mycobacterium bovis Bacilli-Calmette-Guerin (BCG) vaccine fails to protect adults from pulmonary tuberculosis, there is an urgent need for improved vaccine formulations. Unlike BCG, recombinant vaccines purified from bacterial expression vectors, as well as naked DNA, require an additional adjuvant. Recent improvements in our understanding of disease immunopathology, together with advances in biochemical and molecular techniques, have permitted the successful development of promising tuberculosis vaccine delivery and adjuvant combinations for human use. Here, we summarize the current state of adjuvant development and its impact on tuberculosis vaccine progress.

GM-CSF Gene-Modifed Cancer Cell Immunotherapies: Of Mice and Men

GVAX cancer immunotherapies are composed of whole tumor cells genetically modified to secrete the immune stimulatory cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF), and then irradiated to prevent further cell division. Both autologous (patient specific) and allogeneic (non-patient specific) GVAX platforms have been evaluated either as single agents or in combination with other immunomodulatory strategies. Many early-phase clinical trials have now been completed. Results have consistently demonstrated a favorable safety profile manifested primarily by injection site reactions and flu-like symptoms. Consistent evidence of immune activation and clinical activity, including radiologic tumor regressions, has been seen across multiple cancer indications in both early- and late-stage disease. Phase 3 trials evaluating an allogeneic GVAX immunotherapy product in prostate cancer are under way.

Immunization with a bivalent adenovirus-vectored tuberculosis vaccine provides markedly improved protection over its monovalent counterpart against pulmonary tuberculosis

Recombinant virus-vectored vaccines hold great promise for tuberculosis (TB) vaccination strategies. However, there is a lack of side-by-side comparative investigations to dissect the functional differences and support the advantage of multivalent virus-vectored vaccine over its monovalent counterpart. We previously successfully developed a monovalent adenovirus (Ad)-vectored vaccine expressing Ag85a (AdAg85a) and demonstrated its superior protective efficacy in models of pulmonary TB. In this study, we have developed a bivalent Ad TB vaccine expressing Ag85a and TB10.4 antigens as a fusion protein (AdAg85a:TB10.4) and compared its T-cell-activating and immune protective efficacy with that by monovalent AdAg85a. A single intranasal (i.n.) administration of AdAg85a:TB10.4 induced robust T-cell responses toward the respective antigens within the airway lumen and spleen, although the level of Ag85a-specific T-cell responses in the airway lumen triggered by bivalent AdAg85a:TB10.4 was lower than that by its monovalent counterpart at earlier time points. Thus, a single i.n. delivery of AdAg85a:TB10.4 conferred a markedly improved and sustained level of protection in the lung against Mycobacterium tuberculosis (M.tb) challenge over that by AdAg85a or by conventional BCG immunization with similarly induced levels of protection in the spleen. Our results indicate a unique advantage of multivalent viral-vectored TB vaccines for immunization against pulmonary TB.

Intramuscular immunization with a monogenic plasmid DNA tuberculosis vaccine: Enhanced immunogenicity by electroporation and co-expression of GM-CSF transgene

Plasmid DNA vaccine has been widely explored for tuberculosis immunization but there is a need to develop the ways to improve its immunogenicity. In this study, we have constructed a plasmid DNA vaccine coding for Ag85A alone or for both Ag85A and GM-CSF and investigated the immune adjuvant effects of electroporation and GM-CSF co-expression, alone or in combination, on CD4 and CD8 T cell IFN-gamma responses, CTL activities and immune protection from pulmonary Mycobacterium tuberculosis challenge in a Balb/c mouse model. We have found that use of electroporation allows a single intramuscular (i.m.) DNA injection to be as effective as repeated i.m. DNA injections in activation of both Ag85A-specific CD4 and CD8 T cells. Co-expression of immune-enhancing cytokine GM-CSF by the same plasmid DNA TB vaccine could further enhance T cell activation including CTL activities on top of electroporation. With regard to immune protection from pulmonary M. tb challenge, use of electroporation also allows a single i.m. DNA injection to be as effective as repeated i.m. DNA injections. Co-expression of GM-CSF transgene also moderately enhances immune protection and such effect is more evident for systemic protection. However, GM-CSF expression has little added effect on immune protection by electroporation-aided immunization protocols. Our findings thus will help with the development of future DNA TB immunization strategies.

Phase 1/2 trial of autologous tumor mixed with an allogeneic GVAX vaccine in advanced-stage non-small-cell lung cancer

Tumor vaccines composed of autologous tumor cells genetically modified to secrete granulocyte-macrophage colony-stimulating factor (GM-CSF) (GVAX) have demonstrated clinical activity in advanced-stage non-small-cell lung cancer (NSCLC). In an effort to remove the requirement for genetic transduction of individual tumors, we developed a 'bystander' GVAX platform composed of autologous tumor cells mixed with an allogeneic GM-CSF-secreting cell line. We conducted a phase I/II trial of this vaccine (3-12 biweekly vaccinations) in advanced-stage NSCLC. Tumors were harvested from 86 patients, tumor cell processing was successful in 76, and 49 proceeded to vaccination. The most common toxicity was local vaccine injection site reactions. Serum GM-CSF pharmacokinetics were consistent with secretion of GM-CSF from vaccine cells for up to 4 days with associated transient leukocytosis confirming the bioactivity of vaccine-secreted GM-CSF. Evidence of vaccine-induced immune activation was demonstrated; however, objective tumor responses were not seen. Compared with autologous GVAX vaccines prepared by transduction of individual tumors with an adenoviral GM-CSF vector, vaccine GM-CSF secretion was approximately 25-fold higher with the bystander GVAX vaccine used in this trial. However, the frequency of vaccine site reactions, tumor response, time to disease progression, and survival were all less favorable in the current study.

Effect of different forms of adenylate cyclase toxin of Bordetella pertussis on protection afforded by an acellular pertussis vaccine in a murine model

Four recombinant forms of the cell-invasive adenylate cyclase toxin (CyaA) of Bordetella pertussis were compared for the ability to enhance protection against B. pertussis in mice when coadministered with an acellular pertussis vaccine (ACV). The four forms were as follows: fully functional CyaA, a CyaA form lacking adenylate cyclase enzymatic activity (CyaA*), and the nonacylated forms of these toxins, i.e., proCyaA and proCyaA*, respectively. None of these forms alone conferred significant (P > 0.05) protection against B. pertussis in a murine intranasal challenge model. Mice immunized with ACV alone showed significant (P < 0.05) reductions in bacterial numbers in the lungs after intranasal challenge compared with those for control mice. When administered with ACV, both CyaA and CyaA* further reduced bacterial numbers in the lungs of mice after intranasal challenge compared with those for ACV-immunized mice, but the enhanced protection was only significant (P < 0.05) with CyaA*. Coadministration of CyaA* with ACV caused a significant (P < 0.05) increase in immunoglobulin G2a antibody levels against pertactin compared with those in mice immunized with ACV alone. Spleen cells from mice immunized with ACV plus CyaA* secreted larger amounts of interleukin-5 (IL-5), IL-6, gamma interferon (IFN-gamma), and granulocyte-macrophage colony-stimulating factor (GM-CSF) than did cells from mice immunized with ACV plus CyaA or ACV alone after stimulation in vitro with a mixture of B. pertussis antigens. Spleen cells from mice immunized with ACV plus CyaA* also secreted larger amounts of IFN-gamma and GM-CSF than did cells from mice immunized with CyaA* alone after stimulation in vitro with CyaA*. Macrophages from mice immunized with ACV plus CyaA* produced significantly (P < 0.05) higher levels of nitric oxide than did macrophages from mice immunized with CyaA* alone, ACV alone, or ACV plus CyaA after stimulation in vitro with a mixture of B. pertussis antigens or heat-killed B. pertussis cells. These data suggest that the enhancement of protection provided by CyaA* was due to an augmentation of both Th1 and Th2 immune responses to B. pertussis antigens.

Structure-based design of peptides that self-assemble into regular polyhedral nanoparticles

Artificial particulate systems such as polymeric beads and liposomes are being applied in drug delivery, drug targeting, antigen display, vaccination, and other technologies. Here we used computer modeling to design a novel type of nanoparticles composed of peptides as building blocks. We verified the computer models via solid-phase peptide synthesis and biophysical analyses. We describe the structure-based design of a novel type of nanoparticles with regular polyhedral symmetry and a diameter of about 16 nm, which self-assembles from single polypeptide chains. Each peptide chain is composed of two coiled coil oligomerization domains with different oligomerization states joined by a short linker segment. In aqueous solution the peptides form nanoparticles of about 16 nm diameter. Such peptide nanoparticles are ideally suited for medical applications such as drug targeting and drug delivery systems, such as imaging devices, or they may be used for repetitive antigen display.

Manipulation of dendritic cells for host defence against intracellular infections

Dendritic cells (DCs) are an important innate immune cell type which is the bridge between innate and adaptive immunity. Mounting experimental evidence suggests that manipulating DCs represents a powerful means to enhance host defence against intracellular infectious diseases. We have developed several strategies to manipulate DCs either in vivo or in vitro for the purpose of enhancing the effect of vaccination or immunotherapeutics. In vivo delivery of transgene encoding GM-CSF (granulocyte/macrophage colony-stimulating factor), a DC-activating cytokine, increases the number and activation status of DCs at various tissue sites and enhances antimicrobial immune responses in murine models. Co-expression or co-delivery of GM-CSF gene transfer vector with an antimicrobial vaccine enhances microbial antigen-specific T-cell responses and immune protection. Murine bone marrow-derived DCs are being manipulated in vitro and exploited as a vaccine delivery system. Transduction of DCs with a virus-vectored tuberculosis vaccine is a powerful way to activate T-cells in vivo. Such genetically modified DC vaccines can be administered either parenterally or mucosally via the respiratory tract.

SLPI and elafin: one glove, many fingers

Elafin and SLPI (secretory leucocyte protease inhibitor) have multiple important roles both in normal homoeostasis and at sites of inflammation. These include antiprotease and antimicrobial activity as well as modulation of the response to LPS (lipopolysaccharide) stimulation. Elafin and SLPI are members of larger families of proteins secreted predominantly at mucosal sites, and have been shown to be modulated in multiple pathological conditions. We believe that elafin and SLPI are important molecules in the controlled functioning of the innate immune system, and may have further importance in the integration of this system with the adaptive immune response. Recent interest has focused on the influence of inflamed tissues on the recruitment and phenotypic modulation of cells of the adaptive immune system and, indeed, the local production of elafin and SLPI indicate that they are ideally placed in this regard. Functionally related proteins, such as the defensins and cathelicidins, have been shown to have direct effects upon dendritic cells with potential alteration of their phenotype towards type I or II immune responses. This review addresses the multiple functions of elafin and SLPI in the inflammatory response and discusses further their roles in the development of the adaptive immune response.

Use of cytokines in infection

Infectious disease remains an ever-growing health concern worldwide due to increasing antibiotic-resistant microbial strains, immune-compromised populations, international traffic and globalisation, and bioterrorism. There exists an urgent need to develop novel prophylactic and therapeutic strategies. In addition to classic antibiotic therapeutics, immune-modulatory molecules such as cytokines or their inhibitors represent a promising form of antimicrobial therapeutics or immune adjuvant used for the purpose of vaccination. These molecules, in the form of either recombinant protein or transgene, exert their antimicrobial effect by enhancing infectious agent-specific immune activation or memory development, or by dampening undesired inflammatory and immune responses resulting from infection and host defence mechanisms. In the last two decades, a number of cytokine therapy-based experimental and clinical trials have been conducted, and some of these efforts have led to the routine clinical use of cytokines. For instance, although IFNs have been used to treat hepatitis C with great success, many other cytokines are yet to be fully evaluated for their antimicrobial potential. This review discusses the biology and therapeutic potential of selected immune modulatory cytokines and their inhibitors, including granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, IFN-gamma, IL-12 and TNF.

Granulocyte-macrophage colony-stimulating factor does not increase the potency or efficacy of a foot-and-mouth disease virus subunit vaccine

Foot-and-mouth disease (FMD) is one of the most feared diseases of livestock worldwide. Vaccination has been a very effective weapon in controlling the disease, however a number of concerns with the current vaccine including the inability of approved diagnostic tests to reliably distinguish vaccinated from infected animals and the need for high containment facilities for vaccine production, have limited its use during outbreaks in countries previously free of the disease. A number of FMD vaccine candidates have been tested and a replication-defective human adenovirus type 5 (Ad5) vector containing the FMDV capsid (P1-2A) and 3C protease coding regions has been shown to completely protect pigs against challenge with the homologous virus (FMDV A12 and A24). An Ad5-P1-2A+3C vaccine for FMDV O1 Campos (Ad5-O1C), however, only induced a low FMDV-specific neutralizing antibody response in swine potency tests. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been successfully used to stimulate the immune response in vaccine formulations against a number of diseases, including HIV, hepatitis C and B. To attempt to improve the FMDV-specific immune response induced by Ad5-O1C, we inoculated swine with Ad5-O1C and an Ad5 vector containing the gene for porcine GM-CSF (pGM-CSF). However, in the conditions used in this trial, pGM-CSF did not improve the immune response to Ad5-O1C and adversely affected the level of protection of swine challenged with homologous FMDV.

Mechanisms of mucosal and parenteral tuberculosis vaccinations: adenoviral-based mucosal immunization preferentially elicits sustained accumulation of immune protective CD4 and CD8 T cells within the airway lumen

The mechanisms underlying better immune protection by mucosal vaccination have remained poorly understood. In our current study we have investigated the mechanisms by which respiratory virus-mediated mucosal vaccination provides remarkably better immune protection against pulmonary tuberculosis than parenteral vaccination. A recombinant adenovirus-based tuberculosis (TB) vaccine expressing Mycobacterium tuberculosis Ag85A (AdAg85A) was administered either intranasally (i.n.) or i.m. to mice, and Ag-specific CD4 and CD8 T cell responses, including frequency, IFN-gamma production, and CTL, were examined in the spleen, lung interstitium, and airway lumen. Although i.m. immunization with AdAg85A led to activation of T cells, particularly CD8 T cells, in the spleen and, to a lesser extent, in the lung interstitium, it failed to elicit any T cell response in the airway lumen. In contrast, although i.n. immunization failed to effectively activate T cells in the spleen, it uniquely elicited higher numbers of Ag-specific CD4 and CD8 T cells in the airway lumen that were capable of IFN-gamma production and cytolytic activities, as assessed by an intratracheal in vivo CTL assay. These airway luminal T cells of i.n. immunized mice or splenic T cells of i.m. immunized mice, upon transfer locally to the lungs of naive SCID mice, conferred immune protection against M. tuberculosis challenge. Our study has demonstrated that the airway luminal T cell population plays an important role in immune protection against pulmonary TB, thus providing mechanistic insights into the superior immune protection conferred by respiratory mucosal TB vaccination.

Single mucosal, but not parenteral, immunization with recombinant adenoviral-based vaccine provides potent protection from pulmonary tuberculosis

Bacillus Calmette-Guerin (BCG) vaccine has failed to control the global tuberculosis (TB) epidemic, and there is a lack of safe and effective mucosal vaccines capable of potent protection against pulmonary TB. A recombinant replication-deficient adenoviral-based vaccine expressing an immunogenic Mycobacterium tuberculosis Ag Ag85A (AdAg85A) was engineered and evaluated for its potential to be used as a respiratory mucosal TB vaccine in a murine model of pulmonary TB. A single intranasal, but not i.m., immunization with AdAg85A provided potent protection against airway Mycobacterium tuberculosis challenge at an improved level over that by cutaneous BCG vaccination. Systemic priming with an Ag85A DNA vaccine and mucosal boosting with AdAg85A conferred a further enhanced immune protection which was remarkably better than BCG vaccination. Such superior protection triggered by AdAg85 mucosal immunization was correlated with much greater retention of Ag-specific T cells, particularly CD4 T cells, in the lung and was shown to be mediated by both CD4 and CD8 T cells. Thus, adenoviral TB vaccine represents a promising novel vaccine platform capable of potent mucosal immune protection against TB. Our study also lends strong evidence that respiratory mucosal vaccination is critically advantageous over systemic routes of vaccination against TB.

Activation of CD8 T cells by mycobacterial vaccination protects against pulmonary tuberculosis in the absence of CD4 T cells

We have investigated whether both primary CD8 T cell activation and CD8 T cell-mediated protection from Mycobacterium tuberculosis challenge could occur in mycobacterial-vaccinated CD4 T cell-deficient (CD4KO) mice. Different from wild-type C57BL/6 mice, s.c. vaccination with bacillus Calmette-Guérin (BCG) in CD4KO mice failed to provide protection from secondary M. tuberculosis challenge at 3 wk postvaccination. However, similar to C57BL/6 mice, CD4KO mice were well protected from M. tuberculosis at weeks 6 and 12 postvaccination. This protection was mediated by CD8 T cells. The maintenance of protective effector/memory CD8 T cells in CD4KO mice did not require the continuous presence of live BCG vaccine. As in C57BL/6 mice, similar levels of primary activation of CD8 T cells in CD4KO mice occurred in the draining lymph nodes at 3 wk after BCG vaccination, but different from C57BL/6 mice, the distribution of these cells to the spleen and lungs of CD4KO mice was delayed, which coincided with delayed acquisition of protection in CD4KO mice. Our results suggest that both the primary and secondary activation of CD8 T cells is CD4 T cell independent and that the maintenance of these CD8 T cells is also independent of CD4 T cells and no longer requires the presence of live mycobacteria. However, the lack of CD4 T cells may result in delayed distribution of activated CD8 T cells from draining lymph nodes to distant organs and consequently a delayed acquisition of immune protection. Our findings hold implications in rational design of tuberculosis vaccination strategies for humans with impaired CD4 T cell function.

Immobilisation of GM-CSF onto particulate vaccine carrier systems

Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption of GM-CSF to aluminium hydroxide adjuvants and PLGA microparticulates provides a simple and efficient possibility to physically connect the cytokine with these commonly used and potential vaccine carriers and may enable its localised delivery to the side of action.

Single intranasal mucosal Mycobacterium bovis BCG vaccination confers improved protection compared to subcutaneous vaccination against pulmonary tuberculosis

Whether the intranasal (i.n.) route of Mycobacterium bovis BCG vaccination provides better protection against pulmonary tuberculosis than subcutaneous (s.c.) vaccination remains an incompletely solved issue. In the present study, we compared both immune responses and protection elicited by single BCG vaccinations via the i.n. or s.c. route in BALB/c mice. While both i.n. and s.c. vaccination triggered comparable levels of primary immune activation in the spleen and draining lymph nodes, i.n. vaccination led to a greater antigen-specific gamma interferon recall response in splenocytes than s.c. vaccination upon secondary respiratory mycobacterial challenge, accompanied by an increased frequency of antigen-specific lymphocytes. There was also a quicker cellular response in the lungs of i.n. vaccinated mice upon mycobacterial challenge. Mice vaccinated i.n. were found to be much better protected, particularly in the lung, than s.c. vaccinated counterparts against pulmonary tuberculosis at both 3 and 6 months postvaccination. These results suggest that the i.n. route of vaccination improves the protective effect of the current BCG vaccine.

Dendritic cells, new tools for vaccination

Our rapidly expanding knowledge of the biology of the dendritic cell (DC), a major antigen-presenting cell connecting innate and adaptive immunity, suggests new possibilities for the development of vaccines and therapeutic strategies against pathogens, through the manipulation of their function in vivo, or the injection of the DC itself, once properly instructed ex vivo.

Tuberculosis vaccines: the past, present and future

Tuberculosis still remains a leading infectious cause of death worldwide, although the BCG vaccine has been used for 80 years. There is an urgent need to develop improved BCG or new tuberculosis vaccines. This apparently represents a daunting task, since it will take a long time before a vaccine can be declared to be better than the current BCG vaccine, both in experimental and human studies. The current review takes a brief historic look at the use of current BCG vaccine and provides an overview on what are considered to be the key immunologic criteria that have to be met by a new generation of tuberculosis vaccines. It also provides the most up-to-date information on the latest developments in tuberculosis vaccine research, with a focus on mycobacterial organism-based and Mycobacterium tuberculosis antigen-based vaccines. Consideration is also given to the mucosal route of immunization and 'prime and boost' regimens. This review also presents several important tables, highlighting critical components of antituberculosis immunity, the most commonly tested immune adjuvants, the types of novel tuberculosis antigen-based vaccines and the outcome of different heterologous 'prime and boost' vaccination regimens.