Enhanced antigen-presenting activity and tumour necrosis factor-alpha-independent activation of dendritic cells following treatment with Mycobacterium bovis bacillus Calmette-Guérin

A Novel Protozoa Parasite-Derived Protein Adjuvant Is Effective in Immunization with Cancer Cells to Activate the Cancer-Specific Protective Immunity and Inhibit the Cancer Growth in a Murine Model of Colorectal Cancer

Cancer-specific CD8+ cytotoxic T cells play important roles in preventing cancer growth, and IFN-γ, in addition to IL-12 and type I interferon, is critical for activating CD8+ cytotoxic T cells. We recently identified the capability of the amino-terminus region of dense granule protein 6 (GRA6Nt) of Toxoplasma gondii, an intracellular protozoan parasite, to activate IFN-γ production of microglia, a tissue-resident macrophage population. Therefore, in the present study, we examined whether recombinant GRA6Nt protein (rGRA6Nt) functions as an effective adjuvant to potently activate cancer-specific protective immunity using a murine model of MC38 colorectal cancer (CRC). When mice were immunized with non-replicable (either treated with mitomycin C or irradiated by X-ray) MC38 CRC cells in combination with rGRA6Nt adjuvant and received a challenge implantation of replication-capable MC38 tumor cells, those mice markedly inhibited the growth of the implanted tumors in association with a two-fold increase in CD8+ T cell density within the tumors. In addition, CD8+ T cells of the immunized mice secreted significantly increased amounts of granzyme B, a key mediator of the cytotoxic activity of CD8+ T cells, and IFN-γ in response to MC38 CRC cells in vitro when compared to the T cells from unimmunized mice. Notably, the protective effects of the immunization were specific to MC38 CRC cells, as the immunized mice did not exhibit a significantly inhibited growth of EL4 lymphoma tumors. These results indicate that rGRA6Nt is a novel and effective protein adjuvant when used in immunizations with non-replicable cancer cells to potently activate the protective immunity specifically against the cancer cells employed in the immunization.

A century of BCG: Impact on tuberculosis control and beyond

BCG turns 100 this year and while it might not be the perfect vaccine, it has certainly contributed significantly towards eradication and prevention of spread of tuberculosis (TB). The search for newer and better vaccines for TB is an ongoing endeavor and latest results from trials of candidate TB vaccines such as M72AS01 look promising. However, recent encouraging data from BCG revaccination trials in adults combined with studies on mucosal and intravenous routes of BCG vaccination in non-human primate models have renewed interest in BCG for TB prevention. In addition, several well-demonstrated non-specific effects of BCG, for example, prevention of viral and respiratory infections, give BCG an added advantage. Also, BCG vaccination is currently being widely tested in human clinical trials to determine whether it protects against SARS-CoV-2 infection and/or death with detailed analyses and outcomes from several ongoing trials across the world awaited. Through this review, we attempt to bring together information on various aspects of the BCG-induced immune response, its efficacy in TB control, comparison with other candidate TB vaccines and strategies to improve its efficiency including revaccination and alternate routes of administration. Finally, we discuss the future relevance of BCG use especially in light of its several heterologous benefits.

Induction of Trained Immunity by Recombinant Vaccines

Vaccines represent an important strategy to protect humans against a wide variety of pathogens and have even led to eradicating some diseases. Although every vaccine is developed to induce specific protection for a particular pathogen, some vaccine formulations can also promote trained immunity, which is a non-specific memory-like feature developed by the innate immune system. It is thought that trained immunity can protect against a wide variety of pathogens other than those contained in the vaccine formulation. The non-specific memory of the trained immunity-based vaccines (TIbV) seems beneficial for the immunized individual, as it may represent a powerful strategy that contributes to the control of pathogen outbreaks, reducing morbidity and mortality. A wide variety of respiratory viruses, including respiratory syncytial virus (hRSV) and metapneumovirus (hMPV), cause serious illness in children under 5 years old and the elderly. To address this public health problem, we have developed recombinant BCG vaccines that have shown to be safe and immunogenic against hRSV or hMPV. Besides the induction of specific adaptive immunity against the viral antigens, these vaccines could generate trained immunity against other respiratory pathogens. Here, we discuss some of the features of trained immunity induced by BCG and put forward the notion that recombinant BCGs expressing hRSV or hMPV antigens have the capacity to simultaneously induce specific adaptive immunity and non-specific trained immunity. These recombinant BCG vaccines could be considered as TIbV capable of inducing simultaneously the development of specific protection against hRSV or hMPV, as well as non-specific trained-immunity-based protection against other pathogenic viruses.

Bladder cancer, a unique model to understand cancer immunity and develop immunotherapy approaches

With the mechanistic understanding of immune checkpoints and success in checkpoint blockade using antibodies for the treatment of certain cancers, immunotherapy has become one of the hottest areas in cancer research, with promise of long‐lasting therapeutic effect. Currently, however, only a proportion of cancers have a good response to checkpoint inhibition immunotherapy. Better understanding of the cancer response and resistance mechanisms is essential to fully explore the potential of immunotherapy to cure the majority of cancers. Bladder cancer, one of the most common and aggressive malignant diseases, has been successfully treated both at early and advanced stages by different immunotherapeutic approaches, bacillus Calmette–Guérin (BCG) intravesical instillation and anti‐PD‐1/PD‐L1 immune checkpoint blockade, respectively. Therefore, it provides a good model to investigate cancer immune response mechanisms and to improve the efficiency of immunotherapy. Here, we review bladder cancer immunotherapy with equal weight on BCG and anti‐PD‐1/PD‐L1 therapies and demonstrate why and how bladder cancer can be used as a model to study the predictors and mechanisms of cancer immune response and shine light on further development of immunotherapy approaches and response predictive biomarkers to improve immunotherapy of bladder cancer and other malignancies. We review the success of BCG and anti‐PD‐1/PD‐L1 treatment of bladder cancer, the underlying mechanisms and the therapeutic response predictors, including the limits to our knowledge. We then highlight briefly the adaptation of immunotherapy approaches and predictors developed in other cancers for bladder cancer therapy. Finally, we explore the potential of using bladder cancer as a model to investigate cancer immune response mechanisms and new therapeutic approaches, which may be translated into immunotherapy of other human cancers. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Early vaccination protects against childhood leukemia: A systematic review and meta-analysis

Leukemia is the most commonly diagnosed childhood cancer, although its etiology is still largely unknown. Growing evidence supports a role for infection in the etiology of acute lymphocytic leukemia (ALL), and the involvement of the immune system suggests that vaccination may also play a role. However, the findings presented in the published literature are inconsistent. Therefore, we conducted a PRISMA systematic review and meta-analysis. 14 studies were identified and meta-analyzed. Vaccinations studied comprised Bacillus Calmette-Guérin (BCG) vaccine, Triple vaccine, Hepatitis B vaccine (HBV), Polio, Measles, Rubella, Mumps, trivalent MMR vaccine and Haemophilus influenza type B (HiB) vaccine. We observed a protective association between any vaccination in the first year of life and risk of childhood leukemia (summary odds ratio (OR) 0.58 [95% confidence interval (CI) 0.36-0.91]). When individual vaccines were analysed, some evidence of an association was seen only for BCG (summary OR 0.73 [95% CI 0.50-1.08]). In conclusion, early vaccination appears to be associated with a reduced risk of childhood leukemia. This finding may be underpinned by the association observed for BCG. Given the relatively imprecise nature of the results of this meta-analysis, our findings should be interpreted cautiously and replicated in future studies.

Immune Responses to Bacillus Calmette-Guérin Vaccination: Why Do They Fail to Protect against Mycobacterium tuberculosis?

Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis (TB), is the current leading cause of death due to a single infectious organism. Although curable, the broad emergence of multi-, extensive-, extreme-, and total-drug resistant strains of M.tb has hindered eradication efforts of this pathogen. Furthermore, computational models predict a quarter of the world’s population is infected with M.tb in a latent state, effectively serving as the largest reservoir for any human pathogen with the ability to cause significant morbidity and mortality. The World Health Organization has prioritized new strategies for improved vaccination programs; however, the lack of understanding of mycobacterial immunity has made it difficult to develop new successful vaccines. Currently, Mycobacterium bovis bacillus Calmette–Guérin (BCG) is the only vaccine approved for use to prevent TB. BCG is highly efficacious at preventing meningeal and miliary TB, but is at best 60% effective against the development of pulmonary TB in adults and wanes as we age. In this review, we provide a detailed summary on the innate immune response of macrophages, dendritic cells, and neutrophils in response to BCG vaccination. Additionally, we discuss adaptive immune responses generated by BCG vaccination, emphasizing their specific contributions to mycobacterial immunity. The success of future vaccines against TB will directly depend on our understanding of mycobacterial immunity.

Murine Flt3 ligand-generated plasmacytoid and conventional dendritic cells display functional differentiation in activation, inflammation, and antigen presentation during BCG infection in vitro

Dendritic cells (DCs) are composed of distinct subsets. Their immunologic functions (especially in pathogenic infection, such as with mycobacteria) are poorly understood, largely because of their rarity and difficulty of preparation. We used the murine Fms-like tyrosine kinase 3 (Flt3) ligand to generate conventional DCs (FL-cDCs) and plasmacytoid DCs (FL-pDCs) and further evaluated their immunological responses to bacillus Calmette-Guérin (BCG) infection in vitro. BCG cells were observed inside both FL-cDCs and FL-pDCs by confocal microscopy, as confirmed by flow cytometric analysis showing a low infection rate of approximately 6 %, which was similar to in vivo results. The CD40, CD80, CD86, and MHC-II proteins were significantly upregulated in both FL-cDCs and -pDCs beginning at 4 h post-BCG exposure. FL-pDCs secreted TNF-α and IL-6 earlier and at significantly higher levels in the first 12 h following infection, but demonstrated delayed and weak activation and maturation compared to FL-cDCs. Although both subsets proved capable of presenting a mycobacterial antigen, FL-pDCs exhibited weaker activity in this respect than did FL-cDCs. In summary, the existence of FL-generated cDCs and pDCs imply functional differentiation in activation, inflammation, and antigen presentation, although both cells types participated extensively in the immune response to BCG infection.

The Effect of Traditional Chinese Formula Danchaiheji on the Differentiation of Regulatory Dendritic Cells

Recently, regulatory dendritic cells (DCregs), a newly described dendritic cell subset with potent immunomodulatory function, have attracted increased attention for their utility in treating immune response-related diseases, such as graft-versus-host disease, hypersensitivity, and autoimmune diseases. Danchaiheji (DCHJ) is a traditional Chinese formula that has been used for many years in the clinic. However, whether DCHJ can program dendritic cells towards a regulatory phenotype and the underlying mechanism behind this process remain unknown. Herein, we investigate the effects of traditional Chinese DCHJ on DCregs differentiation and a mouse model of skin transplantation. The current study demonstrates that DCHJ can induce dendritic cells to differentiate into DCregs, which are represented by high CD11b and low CD86 and HLA-DR expression as well as the secretion of IL-10 and TGF-β. In addition, DCHJ inhibited DC migration and T cell proliferation, which correlated with increased IDO expression. Furthermore, DCHJ significantly prolonged skin graft survival time in a mouse model of skin transplantation without any liver or kidney toxicity. The traditional Chinese formula DCHJ has the potential to be a potent immunosuppressive agent with high efficiency and nontoxicity.

Lipoarabinomannan, and its related glycolipids, induce divergent and opposing immune responses to Mycobacterium tuberculosis depending on structural diversity and experimental variations

Exposure to Mycobacterium tuberculosis (Mtb) may lead to active or latent tuberculosis, or clearance of Mtb, depending essentially on the quality of the host's immune response. This response is initiated through the interaction of Mtb cell wall surface components, mostly glycolipids, with cells of the innate immune system, particularly macrophages (Mφs) and dendritic cells (DCs). The way Mφs and DC alter their cytokine secretome, activate or inhibit different microbicidal mechanisms and present antigens and consequently trigger the T cell-mediated immune response impacts the host immune response against Mtb. Lipoarabinomannan (LAM) is one of the major cell wall components of Mtb. Mannosyl-capped LAM (ManLAM), and its related cell wall-associated types of glycolipids/lipoglycans, namely phosphatidylinositol mannosides (PIMs) and lipomannan (LM), exhibit important and distinct immunomodulatory properties. The structure, internal heterogeneity and abundance of these molecules vary between Mtb strains exhibiting distinct degrees of virulence. Thus ManLAM, LM and PIMs may be considered crucial Mtb-associated virulence factors in the pathogenesis of tuberculosis. Of particular relevance for this review, there is controversy about the specific immunomodulatory properties of these distinct glycolipids, particularly when tested as purified molecules in vitro. In addition to the variability in the glycolipid composition conflicting reports may also result from differences in the protocols used for glycolipid isolation and for in vitro experiments including immune cell types and procedures to generate them. Understanding the immunomodulatory properties of these cell wall glycolipids, how they differ between distinct Mtb strains, and how they influence the degree of Mtb virulence, is of utmost relevance to understand how the host mounts a protective or otherwise pathologic immune response. This is essential for the design of preventive strategies against tuberculosis. Thus, since clarifying the controversy on this matter is crucial we here review, summarize and discuss reported data from in vitro stimulation with the three major Mtb complex cell wall glycolipids (ManLAM, PIMs and LM) in an attempt to conciliate the conflicting findings.

The contribution of non-conventional T cells and NK cells in the mycobacterial-specific IFNγ response in Bacille Calmette-Guérin (BCG)-immunized infants

BACKGROUND

The Mycobacterium bovis Bacille Calmette-Guérin (BCG) vaccine is given to >120 million infants each year worldwide. Most studies investigating the immune response to BCG have focused on adaptive immunity. However the importance of TCR-gamma/delta (γδ) T cells and NK cells in the mycobacterial-specific immune response is of increasing interest.

METHODS

Participants in four age-groups were BCG-immunized. Ten weeks later, in vitro BCG-stimulated blood was analyzed for NK and T cell markers, and intracellular IFNgamma (IFNγ) by flow cytometry. Total functional IFNγ response was calculated using integrated median fluorescence intensity (iMFI).

RESULTS

In infants and children, CD4 and CD4-CD8- (double-negative (DN)) T cells were the main IFNγ-expressing cells representing 43-56% and 27-37% of total CD3+ IFNγ+ T cells respectively. The iMFI was higher in DN T cells compared to CD4 T cells in all age groups, with the greatest differences seen in infants immunized at birth (p=0.002) or 2 months of age (p<0.0001). When NK cells were included in the analysis, they accounted for the majority of total IFNγ-expressing cells and, together with DN Vδ2 γδ T cells, had the highest iMFI in infants immunized at birth or 2 months of age.

CONCLUSION

In addition to CD4 T cells, NK cells and DN T cells, including Vδ2 γδ T cells, are the key populations producing IFNγ in response to BCG immunization in infants and children. This suggests that innate immunity and unconventional T cells play a greater role in the mycobacterial immune response than previously recognized and should be considered in the design and assessment of novel tuberculosis vaccines.

Divergent effects of mycobacterial cell wall glycolipids on maturation and function of human monocyte-derived dendritic cells

BACKGROUND

Mycobacterium tuberculosis (Mtb) is able to evade the immune defenses and may persist for years, decades and even lifelong in the infected host. Mtb cell wall components may contribute to such persistence by modulating several pivotal types of immune cells. Dendritic cells (DCs) are the most potent antigen-presenting cells and hence play a crucial role in the initial immune response to infections by connecting the innate with the adaptive immune system.

PRINCIPAL FINDINGS

We investigated the effects of two of the major mycobacterial cell wall-associated types of glycolipids, mannose-capped lipoarabinomannan (ManLAM) and phosphatidylinositol mannosides (PIMs) purified from the Mtb strains H37Rv and Mycobacterium bovis, on the maturation and cytokine profiles of immature human monocyte-derived DCs. ManLAM from Mtb H37Rv stimulated the release of pro-inflammatory cytokines TNF, IL-12, and IL-6 and expression of co-stimulatory (CD80, CD86) and antigen-presenting molecules (MHC class II). ManLAM from M. bovis also induced TNF, IL-12 and IL-6 but at significantly lower levels. Importantly, while ManLAM was found to augment LPS-induced DC maturation and pro-inflammatory cytokine production, addition of PIMs from both Mtb H37Rv and M. bovis strongly reduced this stimulatory effect.

CONCLUSIONS

These results indicate that the mycobacterial cell wall contains macromolecules of glycolipid nature which are able to induce strong and divergent effects on human DCs; i.e while ManLAM is immune-stimulatory, PIMs act as powerful inhibitors of DC cytokine responses. Thus PIMs may be important Mtb-associated virulence factors contributing to the pathogenesis of tuberculosis disease. These findings may also aid in the understanding of some earlier conflicting reports on the immunomodulatory effects exerted by different ManLAM preparations.

Fibroblast and T cells conditioned media induce maturation dendritic cell and promote T helper immune response

Dendritic cells (DCs) induce pathogen-specific T cell responses. We comprehensively studied the effects of addition of maturation stimulus, fibroblasts (fibroblast conditioned medium), PHA activated T cells (T cell conditioned medium), and mixture of fibroblast & PHA activated T cells (FCM-TCCM) conditioned media on maturation of DCs. Monocytes were cultured with GM-CSF and IL-4 for five days. Maturation factors included MCM and TNF-α as control group. FCM and TCCM, or FCM-TCCM supernatant were considered as the treatment group. Tumor antigens were added at day five. Matured DCs were harvested at day seven. Phenotypic and functional analyses were carried out using anti (CD14, CD80, CD86, CD83 and HLA-DR) monoclonal antibodies. Phagocytic activity, mixed lymphocyte reaction (MLR) and cytokine production were also evaluated. At the end of culturing period, significantly fully matured DCs with large amount cytoplasm and copious dendritic projections were found in the presence of MCM, TNF-α with or without FCM, TCCM, FCM as well as TCCM. Flow cytometric analysis revealed that expression of CD14 decreased in particular in treated DCs, at the 5(th) day and expression of CD80, CD86 and HLA-DR was higher when FCM, TCCM, FCM plus TCCM were added to maturation factor. This study demonstrated that DCs matured with these methods had optimum function in comparison with either factor alone.

Mixture of fibroblast, epithelial and endothelial cells conditioned media induce monocyte-derived dendritic cell maturation

Fully matured DCs with large amount cytoplasm and copious dendritic projections were visible at the end of culturing period in the presence of MCM, TNF-α and poly (I:C), with or without FEECM. Thus, DCs generated with these maturation factors are nonadherent and have typical satellite morphology. Flow cytometric analysis using anti-CD14, -CD80, -CD86, -HLA-DR and -CD83 revealed that expression of CD14 is decreased in particular in FEECM treated DCs, on day 5 and expression of CD80, CD86 and HLA-DR was the higher when FEECM are added to maturation factor. Functionally, when DCs matured in the presence of FEECM elicited stronger MLR, reduced phagocytic activity. These results support the use of the FEECM with MCM, TNF-α and poly (I-C) as maturation factor in DC generation that could result in functionally mature monocyte-derived DCs in comparison to either alone.

Mycobacterium bovis bacillus Calmette-Guerin treated human cord blood monocyte-derived dendritic cells polarize naïve T cells into a tolerogenic phenotype in newborns

BACKGROUND

As one of the first infectious challenges of life, the impact of neonatal Mycobacterium bovis bacillus Calmette-Guerin (BCG) vaccination on the polarization of neonatal T helper subset has not been well defined.

METHODS

We investigated the effect of BCG-treated cord blood (CB) dendritic cells (DCs) on naïve CD4+ T cells polarization compared with that of adult blood DCs.

RESULTS

BCG-treated CB DCs had significantly lower expression of CD83 and a higher ratio of CD47/Fas than BCG-treated adult blood DCs. BCG induced significantly lower IL-12 but relatively higher IL-10 production from CB DCs than adult blood DCs. Moreover, in comparison with BCG-treated adult blood DCs, BCG-treated CB DCs induced higher IL-10 production and cytotoxic T-lymphocyte antigen 4 (CTLA-4) expression, and lower interferon-gamma (IFN-gamma) production from naïve CD4+ T cells. On the other hand, lipopolysaccharide-treated CB DCs had similar capacity as prime naïve CD4+ T cells did to produce higher IFN-gamma, lower IL-10 production, and CTLA-4 expression compared with their adult counterparts.

CONCLUSION

These results suggested that BCG-treated CB DCs might be semi-mature DCs which polarize naïve T cells into a tolerogenic T cell phenotype in newborns.

Spotlight on Mycobacteria and dendritic cells: will novel targets to fight tuberculosis emerge?

Over thousands of years microbes and mammals have co-evolved, resulting in extraordinarily sophisticated molecular mechanisms permitting the organisms to survive together. Mycobacterium tuberculosis is one of the best examples of successful co-evolution, since the bacilli have infected one third of the human population, but in 90% of the cases without causing overt disease. Despite this, increasing incidence of Human Immunodeficiency Virus (HIV) infection and the emergence of drug-resistant strains means that tuberculosis is in fact an extremely serious emerging threat to global health. Decades of work have focused on the interaction of this pathogen with its established cellular host, the macrophage, but still novel therapeautics remain elusive. While the macrophage is clearly important, recent evidence suggests that understanding the role of dendritic cells, which are key regulators of immunity, may be a crucial step in identifying new means of controlling this disease. Novel technologies, in particular genome-wide transcriptome analyses, are advancing our ability to dissect the complex dynamic relationships between dendritic cells and mycobacteria, highlighting new areas for study that have not been previously explored.

Role of apoptosis-regulating signal kinase 1 in innate immune responses by Mycobacterium bovis bacillus Calmette-Guérin

Mycobacterium bovis bacillus Calmette-Guérin (BCG) induces innate immune responses through Toll-like receptor (TLR) 2 and TLR4. We investigated the role of apoptosis-regulating signal kinase (ASK) 1 in reactive oxygen species (ROS)-mediated innate immune responses induced by BCG mycobacterial infection. In macrophages, M. bovis BCG stimulation resulted in rapid activation of mitogen-activated protein kinases (MAPKs), secretion of inflammatory cytokines, such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-6, and ROS generation in a TLR2- and TLR4-dependent manner. M. bovis BCG-induced ROS production led to robust activation of ASK1 upstream of the c-jun-N-terminal kinase and p38 MAPK, but not extracellular-regulated kinase 1/2. Blocking ASK1 activity markedly attenuated M. bovis BCG-induced TNF-alpha and IL-6 production by macrophages. Both TLR2 and TLR4 were required for optimal activation of ASK1 in response to M. bovis BCG. Furthermore, we present evidence that TNF receptor-associated factor (TRAF) 6 activities were essential for ROS-mediated ASK1 activation by M. bovis BCG. Finally, ASK1 activities were required for effective control of intracellular mycobacterial survival. Thus, the results of this study suggest a novel role of the TLR-ROS-TRAF6-ASK1 axis in the innate immune response to mycobacteria as a signaling intermediate.

Mycobacterium bovis Bacillus Calmette-Guérin suppresses inflammatory Th2 responses by inducing functional alteration of TSLP-activated dendritic cells

Allergic diseases such as atopic dermatitis and asthma develop as a consequence of dysregulated T(h)2 responses. Recently, it has been demonstrated that interaction between dendritic cells (DCs) and thymic stromal lymphopoietin (TSLP), an IL-7-like cytokine, is essential for evoking T(h)2 responses in allergy. In this study, we investigated whether Mycobacterium bovis Bacillus Calmette-Guérin (BCG), a strong T(h)1 response-inducing adjuvant, can alter the function of DCs activated by TSLP (TSLP-DCs). We demonstrated that BCG redirects TSLP-DCs away from inducing inflammatory T(h)2 cells that produce IL-4, IL-5, IL-13 and tumor necrosis factor (TNF)-alpha and toward regulatory T(h)1 cells that produce IFN-gamma and IL-10. We also demonstrated that this functional alteration of TSLP-DCs by BCG depended on both production of IL-12 from DCs and down-regulation of OX40 ligand, a member of the TNF family, on DCs. These findings suggest that BCG might be a useful adjuvant for the treatment of allergic diseases that are triggered by TSLP.

Bovine TB and the development of new vaccines

Bovine tuberculosis (bTB) is caused by Mycobacterium bovis. The incidence of bTB is increasing in cattle herds of developed countries that have a wild life reservoir of M. bovis, such as the UK, New Zealand and the USA. The increase in the incidence of bTB is thought to be due, at least in part, to a wildlife reservoir of M. bovis. M. bovis is also capable of infecting humans and on a worldwide basis, M. bovis is thought to account for up to 10% of cases of human TB [Cosivi O, Grange JM, Daborn CJ et al. Zoonotic tuberculosis due to Mycobacterium bovis in developing countries. Emerg Infect Dis 1998;4(1):59-70]. Thus, the increased incidence of bTB, besides being a major economic problem, poses an increased risk to human health. In the UK, the incidence of bTB continues to rise despite the use of the tuberculin test and slaughter control policy, highlighting the need for improved control strategies. Vaccination of cattle, in combination with more specific and sensitive diagnostic tests, is suggested as the most effective strategy for bovine TB control. The only vaccine currently available for human and bovine TB is the live attenuated Bacille Calmette Guerin (BCG). BCG is thought to confer protection through the induction of Th1 responses against mycobacteria. However, protection against TB conferred by BCG is variable and to this date the reasons for the successes and failures of BCG are not clear. Therefore, there is a need to develop vaccines that confer greater and more consistent protection against bTB than that afforded by BCG. Given that BCG is currently the only licensed vaccine against human TB, it is likely that any new vaccine or vaccination strategy will be based around BCG. In this review we discuss immune responses elicited by mycobacteria in cattle and the novel approaches emerging for the control of bovine TB based on our increasing knowledge of protective immune responses.

Vdelta2 T-lymphocyte responses in cord blood samples from Italy and Côte d'Ivoire

Cord blood T lymphocytes are immature and their functional defect partially reflects a suboptimal level of costimulatory signals provided by neonatal antigen-presenting cells. Neonatal Vdelta2 T lymphocytes, a small component of cellular immunity involved in the response against bacteria, protozoa, virus-infected cells and tumours, are also considered to be immature. Cord blood Vdelta2 T lymphocytes are mostly naïve, proliferate poorly and do not produce cytokines in response to the model phosphoantigen isopentenyl pyrophosphate. We cultured cord blood mononuclear cells with the aminobisphosphonate Pamidronate or with live bacille Calmette-Guérin, and showed that both elicit a strong cord blood Vdelta2 T-cell proliferative response, inducing the expression of activation markers and promoting the differentiation from naïve to memory cells. Our results suggest that cord blood Vdelta2 T cells are not inherently unresponsive and can mount strong responses to aminobisphosphonates and mycobacteria. Neonatal Vdelta2 T lymphocytes may be important participants in responses to microbial infections early in life.

Innate-immunity cytokines induced by very small size proteoliposomes, a Neisseria-derived immunological adjuvant

Neisserial outer membrane proteins have been combined with monosialoganglioside GM3 to form very small size proteoliposomes (VSSP), a nanoparticulated formulation used as a cancer vaccine for the treatment of cancer patients with GM3-positive tumours. VSSP were shown to elicit anti-GM3 and anti-tumour immune responses. VSSP have also been shown to be an efficient adjuvant for tumour-cell and peptide-antigen vaccines in mice. In vitro studies showed that VSSP promote maturation of both murine and human dendritic cells, suggesting that VSSP could be used as efficient adjuvants. In order to study further the capacity of VSSP to elicit innate immune responses, human peripheral blood mononuclear cells and monocytes derived thereof were assessed for in vitro secretion of interleukin (IL)-10, IL-6, IL-12 and interferon (IFN)-gamma. VSSP most prominently induced the secretion of IL-6. IL-10 was secreted at a lower level. IL-12 p40 (but no p70) was also detected. IFN-gamma response was observed in 56% of the tested samples. Cytokine secretion was not related to lipopolysaccharide (LPS) content and involved Toll-like receptor 2 (TLR2)-mediated signal transduction. VSSP also induced DC maturation and a cytokine secretion pattern (high IL-6/low IL-10) which differs from that induced by LPS. The observed proinflammatory cytokine secretion pattern and the capacity of VSSP to drive DC maturation are examined in the light of the properties of other bacterial derivatives currently being user for immunotherapy purposes. Our results suggest that VSSP could be tested in clinical settings where T helper 1-type immune responses would be beneficial.

Enhancement of BCG-induced Th1 immune response through Vγ9Vδ2 T cell activation with non-peptidic drugs

Since drug-activated gammadelta T cells promote dendritic cell (DC) maturation, we analyzed the effect of combining gammadelta T cell specific drugs with BCG in vitro. BCG-induced DC maturation was increased by bromohydrin-pirophosphate (BrHPP) or zoledronate (Zol)-activated gammadelta T cells. Specifically, the co-culture with activated Vgamma9Vdelta2 T cells with BCG-infected DC resulted in a significant increase of the expression of CD80, CD86, CD40 and CD25 molecules on DC. Moreover, DC were able to produce increased levels of TNF-alpha and synthesize ex novo IL-15 without altering the IL-10/IL-12 immunoregulatory pathway. Finally, the Th1 immunity induced by BCG-infected DC on naïve CD4 T cells was increased by gammadelta T cell activation with BrHpp or Zol. These data indicate that gammadelta T cell triggering drugs could be used to enhance the BCG induced Th1 immunity.

gammadelta T cells condition dendritic cells in vivo for priming pulmonary CD8 T cell responses against Mycobacterium tuberculosis

gammadelta T cells and dendritic cells are quickly recruited to the lungs shortly after intranasal vaccination with BCG, but the functional in vivo interplay between these two cell populations and its role in the induction of adaptive immune responses is unclear. Using TCR-deficient mice and bone marrow chimeras, we show here that gammadelta T cells provide a non-redundant early source of IFN-gamma in vivo, which enhances IL-12 production by lung dendritic cells. The in vivo-conditioned dendritic cells, in turn, prime a more efficient lung CD8 T cell response against Mycobacterium tuberculosis. Thus, strategies exploiting gammadelta T cell function and IFN-gamma production could be valuable for the design and testing of mucosal vaccines.

Evaluación de la capacidad invasiva de las micobacterias no pigmentadas de crecimiento rápido mediante el estudio de la morfología de las microcolonias en fibroblastos

OBJECTIVE

The invasive capacity of rapidly-growing nonpigmented mycobacteria strains was evaluated by means of a fibroblast microcolony assay and related to the colony phenotype on Middlebrook 7H11 and to the clinical significance of the isolates.

METHODS

Twenty-nine strains [Mycobacterium chelonae (8), M. fortuitum (6), M. peregrinum (5), M. abscessus (5), M. mucogenicum (4) and M. septicum (1)], proceeding from a bacterial collection and clinical isolates, were evaluated. The smooth or rough phenotype of the colonies was assessed in Middlebrook 7H11 medium. Intracellular invasiveness was determined by the fibroblast-microcolony assay described by Shepard. Quantitative culture characteristics were compared with Student's t-test, and qualitative characteristics with Fisher's exact test.

RESULTS

No significant differences were found between colonies with different phenotypes or strains having a different clinical significance, except for two strains of Mycobacterium chelonae isolated from cases of catheter-related bacteremia, which showed elongated microcolonies. M. fortuitum and M. peregrinum strains showed larger microcolonies than M. chelonae, M. abscessus and M. mucogenicum, and displayed a fluffy appearance, while the latter two strains showed rounded colonies.

CONCLUSION

Very few strains of mycobacteria had invasive capacity and the majority of strains isolated from human infections do not show this characteristic; hence this trait is not essential for mycobacteria to cause infection in humans.

Feasibility of clinical dendritic cell vaccination in acute myeloid leukemia

Dendritic cells (DC) are increasingly being utilized for anti-cancer therapy. Acute myeloid leukemia (AML) blasts are able to differentiate towards leukemia-derived DC enabling efficient presentation of known and unknown leukemic antigens. Advances in culture techniques and AML-DC characterization justify clinical application. However, clinical trials using AML-DC are hampered by patient inclusion criteria which allow selective entering of patients in second complete remission. Clinical relevant responses to DC-based immunotherapy are likely to only occur in non-end-stage patients. Application in early stage disease is mandatory to permit ultimate proof of clinical benefit of AML-DC vaccination strategy.

Plasmid interleukin-23 (IL-23), but not plasmid IL-27, enhances the protective efficacy of a DNA vaccine against Mycobacterium tuberculosis infection

Protection against intracellular pathogens such as Mycobacterium tuberculosis requires the development of Th1-like T-cell responses. This in turn is dependent on the pattern of cytokine produced from dendritic cells (DCs) after infection. Three heterodimeric cytokines, interleukin-12 (IL-12), IL-23, and IL-27, as well as IL-18, contribute to the differentiation and expansion of naive CD4(+) T cells. In this study we compared the effects of plasmids expressing both chains of IL-12, IL-23, or IL-27 as adjuvants for DNA immunization against M. tuberculosis infection. The genes encoding p19 and p40 chains of IL-23 or EBI3 and p28 chains of IL-27 were cloned on either side of a self-cleaving peptide from the FMDV2A protein. The secretion of functional cytokines from transfected cells was detected with bioassays. Supernatant from p2AIL-23-transfected cells induced the release of IL-17 from activated lymphocytes, confirming the presence of bioactive IL-23. Further, supernatant from p2AIL-27-transfected cells stimulated a significant increase in the proliferation of peptide-stimulated transgenic CD4(+) T cells. In initial experiments, M. tuberculosis infection of DCs was more potent at inducing IL-12 and IL-23 secretion than infection with the vaccine strain Mycobacterium bovis bacille Calmette-Guérin (BCG), and no significant upregulation of IL-27 was observed. Coimmunization of C57BL/6 mice with DNA expressing M. tuberculosis antigen 85B (Ag85B; DNA85B) and plasmids expressing IL-23 or IL-12 stimulated stronger Ag85B-specific T-cell proliferative and IFN-gamma responses than DNA85B alone, whereas the addition of p2AIL-27 had no effect. Interestingly, DNA85B codelivered with p2AIL-12, but not p2AIL-23, reduced the immunoglobulin G antibody response. Both p2AIL-23 and p2AIL-12, but not p2AIL-27, enhanced the protective efficacy of DNA85B against aerosol M. tuberculosis challenge. Therefore, both p2AIL-23 and p2AIL-12 are valuable as cytokine adjuvants for increasing the protective antituberculosis immunity induced by DNA vaccines.

Time course of mycobacterial infection of dendritic cells in the lungs of intranasally infected mice

SETTING

Dendritic cells (DC) could regulate between the protective and pathogenic immune responses following tuberculous infection. In this paper we investigated if their early infection in the lungs represents a plausible alternative to cross-priming with mycobacterial antigens acquired from infected macrophages.

OBJECTIVE

To determine the extent and time course of infection of lung DCs following intranasal inoculation of BALB/c mice with green fluorescent protein (GFP) tagged Bacillus Calmette-Guerin (BCG).

RESULTS

A fraction of GFP-BCG infected lung cells were classified as monocytic DCs with the CD11c+IA+33D1+CD8a- phenotype. These cells represented 5-18% of the total GFP+ cells, the bulk of which were macrophages. The infected DCs could be separated by cell size into two fractions with similar cell surface staining properties during the 2-72 h period after infection. An unexpected difference was observed for the time course of infection between DCs and macrophages: DC infection peaked at 48 h followed by decline at 72 h, while the proportion of infected macrophages remained steady during the same period.

CONCLUSION

The presented results are direct evidence that monocytic DCs are recruited to the lungs and take up live bacilli within 48 h of intranasal infection with GFP-BCG. This finding is pertinent for the regulation of pulmonary and systemic immune responses and possibly for the dissemination of mycobacterial infection by DCs.

Reciprocal stimulation of gammadelta T cells and dendritic cells during the anti-mycobacterial immune response

Gammadelta T cells and dendritic cells (DC) are two distinct cell types of innate immunity that participate in early phases of immune response against Mycobacterium tuberculosis infection. Here we show that a close functional relationship exists between these cell populations. Using an in vitro coculture system, Vgamma1 T cells from Tcrb(-/- )mice were found to be activated by DC infected in vitro with BCG, as indicated by the elevated CD69 expression, IFN-gamma secretion and cytotoxic activity. This activation process was due to a non-cognate mechanism since it required neither cell to cell contact nor interaction between the TCR and a specific antigen, but was mediated by DC-derived IL-12. Reciprocally, Vgamma1 T cells provided a key cytokine, IFN-gamma, which increased IL-12 production by BCG-infected DC. Moreover, exposure of BCG-infected DC to Vgamma1 T cells conditioned the former to prime a significantly stronger anti-mycobacterial CD8 T cell response. Consequently, stimulation of gammadelta T cells and their non-cognate interaction with DC could be applied as an immune adjuvant strategy to optimize vaccine-induced CD8 T cell immunity.

Effects of cytokine milieu secreted by BCG-treated dendritic cells on allergen-specific Th immune response

Bacillus Calmette-Guerin (BCG) is reported to suppress Th2 response and asthmatic reaction. Dendritic cells (DCs), the major antigen-presenting cells, infections with BCG are known to result in inducing various cytokines. Thus, DCs are likely to play a role in the effects of BCG on asthma. This study aims at investigating that cytokine milieu secreted by BCG-treated DCs directly enhances allergen-specific Th1 response and/or suppresses Th2 response in allergic asthma. DCs and CD3+ T cells were generated from Dermatophagoides farinae-sensitive asthmatics. DCs were cultured with and without BCG and subjected to flow cytometric analysis. IL-12 and IL-10 were determined from the culture supernatants. Some DCs were cocultured with T cells in the presence of D. farinae extracts after adding the culture supernatants from BCG-treated DCs, and IL-5 and IFN-gamma were determined. BCG-treated DCs enhanced significantly the expressions of CD80, CD86, and CD40, and the productions of IL-12 and IL-10. Addition of culture supernatants from BCG-treated DCs up-regulated production of IFN-gamma by T cells stimulated by DCs and D. farinae extracts (p<0.05), but did not down-regulate production of IL-5 (p>0.05). The cytokine milieu secreted by BCG-treated DCs directly enhanced allergen-specific Th1 response, although did not suppress Th2 response.

Tolerance associated with cord blood transplantation may depend on the state of host dendritic cells

Allogeneic cord blood (CB) transplantation is associated with less severe graft-versus-host disease (GvHD), thought to be due to the immaturity of CB T cells, but how T cells interact with host and donor-derived dendritic cells (DCs) to initiate GvHD has not been elucidated. We therefore investigated the responses of CB and adult blood CD4(+) T cells co-cultured with adult host DCs of different maturities. Primed by adult host DCs, CB and adult blood CD4(+) T cells underwent similar changes in the expression of CD45RA/45RO, CD25, CD40L and CTLA-4. However, CB CD4(+) T cells, when primed by either immature or Bacillus Calmette-Guerin mycobacteria-treated adult host DCs, produced lower interferon-gamma (IFN-gamma) and higher interleukin-10 (IL-10), which is a regulatory T cell-like cytokine profile, as compared with adult blood CD4(+) T cells. In contrast, lipopolysaccharide (LPS)-treated adult host DCs significantly up-regulated IFN-gamma and down-regulated IL-10 production levels from CB CD4(+) T cells to that from adult blood CD4(+) T cells. The sustained low IFN-gamma and high IL-10 production from CB CD4(+) T cells co-cultured with adult blood DCs might account for the less severe GvHD occurrence after CB transplantation, which could be reversed by LPS-treated adult blood DCs.

Interaction of antigen presenting cells with mycobacteria

The interaction of mycobacteria with antigen presenting cells is a key feature in the pathogenesis of tuberculosis and the outcome of this interaction is pivotal in determining whether immunity or disease ensues. Human and mouse macrophages and dendritic cells (DC) have been shown to become infected with mycobacteria and to produce a response to infection that reflects their suggested role in immunity. Thus, macrophages elicit anti-microbial mechanisms for elimination of mycobacteria and DC up-regulate expression of molecules that aid their stimulation of T lymphocytes. We have examined the effects of infection with the avirulent strain Mycobacterium bovis BCG and with virulent M. bovis on bovine antigen presenting cells. Differences in the intracellular survival of bacteria within DC and macrophages were observed with higher numbers of bacteria maintained within DC following infection compared to macrophages. BCG was killed more effectively than M. bovis. Alterations in the expression of cell surface molecules involved in antigen presentation and the stimulation of T cells, including MHC II and CD40, were observed following infection of bovine antigen presenting cells. In addition infected DC secreted IL-12, TNFalpha and IL-10 whereas macrophages produced TNFalpha, IL-10 and little IL-12. Generally responses were more marked when virulent M. bovis was used compared to BCG. These studies indicate that infection of bovine antigen presenting cells by mycobacterial species results in the induction of both innate and adaptive immune responses that are critical for the outcome of infection.

Platelet factor 4 in conjunction with IL‐4 directs differentiation of human monocytes into specialized antigen‐ presenting cells

Recent evidence suggests that platelets are not only involved in haemostatic processes but also modulate immune responses. As antigen-presenting cells (APC) are of crucial importance for the regulation of immunity, in this study we wanted to define the role of platelet factor 4 (PF-4) as one of the major platelet-derived chemokines on the transition of monocytes into APCs. Our experiments show that within 3 days PF-4 in conjunction with IL-4 induces a rapid differentiation of monocytes into APC. These PFAPC (PF-4/IL-4 differentiated APC) display unique phenotypical and functional characteristics setting them apart from macrophages and conventional dendritic cells. Functional studies revealed that PFAPC preferentially stimulated proliferation of lymphocytes and lytic NK activity while they induced only moderate cytokine responses. Beyond day 3 of differentiation, PFAPC became less immunostimulatory and maintained their capacity to phagocytose particulate material even after LPS-induced maturation. These experiments uncover a previously unknown role for the platelet-derived CXC-chemokine PF-4 in differentiation of human APC. Our data further support the newly discovered function of platelets in immunomodulation and provide new evidence for a rapid transition of monocytes into APC under the influence of inflammatory stimuli.

Dendritic cells derived from BCG-infected precursors induce Th2-like immune response

Human monocytes can differentiate into dendritic cells (DCs) according to the nature of environmental signals. We tested here whether the infection with the live tuberculosis vaccine bacillus Calmette-Guerin (BCG), which is known to be limited in preventing pulmonary tuberculosis, modulates monocyte and DC differentiation. We found that monocytes infected with BCG differentiate into CD1a- DCs (BCG-DCs) in the presence of granulocyte macrophage-colony stimulating factor and interleukin (IL)-4 and acquired a mature phenotype in the absence of maturation stimuli. In addition, BCG-DCs produced proinflammatory cytokines (tumor necrosis factor alpha, IL-1beta, IL-6) and IL-10 but not IL-12. BCG-DCs were able to stimulate allogeneic T lymphocytes to a similar degree as DCs generated in the absence of infection. However, BCG-DCs induced IL-4 production when cocultured with human cord-blood mononuclear cells. The induction of IL-4 production by DCs generated by BCG-infected monocytes could explain the failure of the BCG vaccine to prevent pulmonary tuberculosis.

Interferon-gamma Added During Bacillus Calmette-Guerin Induced Dendritic Cell Maturation Stimulates Potent Th1 Immune Responses

Dendritic cells (DC) are increasingly prepared in vitro for use in immunotherapy trials. Mature DC express high levels of surface molecules needed for T cell activation and are superior at antigen-presentation than immature DC. Bacillus Calmette-Guerin (BCG) is one of several products known to induce DC maturation, and interferon (IFN)-gamma has been shown to enhance the activity of DC stimulated with certain maturation factors. In this study, we investigated the use of IFN-gamma in combination with the powerful maturation agent, BCG. The treatment of immature DC with IFN-gamma plus BCG led to the upregulation of CD54, CD80, and CD86 in comparison with BCG treatment alone. In MLR or recall immune responses, the addition of IFN-gamma at the time of BCG-treatment did not increase the number of antigen-specific T cells but enhanced the development of IFN-gamma-producing Th1 cells. In primary immune responses, on the other hand, BCG and IFN-gamma co-treated DC stimulated higher proportions of specific T cells as well as IFN-gamma secretion by these T cells. Thus the use of IFN-gamma during BCG-induced DC maturation differentially affects the nature of recall versus naïve antigen-specific T-cell responses. IFN-gamma co-treatment with BCG was found to induce IL-12 and, in some instances, inhibit IL-10 secretion by DC. These findings greatly enhance the potential of BCG-matured dendritic cells for use in cancer immunotherapy.

Maturation of bovine dendritic cells by lipopeptides

The response of DC, and the subsequent stimulation of T cells, is an essential part of the initiation of immune responses following microbial challenge. The response of human DC to bacterial lipopeptides is mediated by toll-like receptor 2, and is characterised by DC maturation and the enhanced capacity to stimulate of T cells. We report here that bovine DC are also induced to mature following lipopeptide stimulation. Exposure of DC to the model lipopeptide Pam3CSK4 was associated with increased expression of MHC, costimulatory molecules, and enhanced secretion of IL-12 and TNFalpha. Lipopeptide-matured DC were superior in their ability to induce T cell activation and IFNgamma secretion. In contrast, exposure of MPhi to lipopeptides induced down-regulation of MHC expression and much lower increases in IL-12 secretion. A lipopeptide derived from the sequence of a relevant mycobacterial lipoprotein, MPB83, also influenced bovine DC by stimulating increases in IL-12 and TNFalpha secretion. These different changes in bovine DC and MPhi may have important implications for immune responses induced following bacterial infection with uptake of microbes by DC resulting in potentiation of their immunostimulatory capacity and uptake by MPhi having a much less marked effect on immune responses.

BCG promotes cord blood monocyte-derived dendritic cell maturation with nuclear Rel-B up-regulation and cytosolic I kappa B alpha and beta degradation

Mycobacterium bovis bacillus Calmette-Guerin (BCG) is given to millions of neonates in developing countries as a vaccine against Mycobacterium tuberculosis; however, little is known about the initiation of response in neonatal dendritic cells (DCs) to BCG. To address this issue, the interaction of BCG with human cord blood monocyte-derived DCs was studied. We showed that BCG could promote cord blood monocyte-derived DC maturation by up-regulation of CD80, CD83, CD86, CD40, and MHC class II molecules and down-regulation of mannose receptor. BCG was able to induce similar levels of tumor necrosis factor-alpha and IL-10 but no bioactive IL-12p70 production from cord blood DCs as from adult blood DCs. Functionally BCG-treated cord blood DCs had higher ability to induce mixed lymphocyte reaction than non-BCG-treated cord blood DCs. Both non-BCG-treated and BCG-treated cord blood DCs efficiently induced a high level of IL-10, medium level of interferon-gamma, but little IL-4 production by cord blood naïve CD4+ T cells. Heat shock protein 65, a key component of BCG, had no effect on cord blood DC maturation in terms of CD86, MHC class II, and mannose receptor up-regulation. During the BCG-induced maturation process of cord blood DCs, nuclear transcription factor Rel-B was up-regulated and cytosolic Rel-B down-regulated with cytosolic IkappaB alpha and beta degradation. These results suggest that BCG can promote cord blood monocyte-derived DC maturation, and that the mechanism is through the up-regulation of nuclear Rel-B secondary to the degradation of cytosolic IkappaB alpha and beta.

Cytotoxic lymphocytes primed by DC based hepatocellular carcinoma vaccine against growth of carcinoma xenograft on nude mice

AIM

To investigate the cytotoxic lymphocyte (CTL) primed by DC based hepatocellular carcinoma (HCC) vaccine against the growth of the carcinoma xenograft on nude mice.

METHODS

High purity of dendritic cells (DCs) were obtained and the immune responses of lymphocytes primed by BCG HSP70 activated DCs were loaded with HCC associated antigens to prepare DC based HCC vaccine. The nude mouse model bearing human HCC xenografts was established and the characteristics of the tumor were identified with immunohistochemical techniques. Transplanted human HCC on nude mouse was treated with freezing and anabiotic HCC specific lymphocytes.

RESULTS

Lymphocytes primed by DCs based HC vaccine had the specific cytotoxicity against HCC lines. The CTL after freezing and anabiotics could prevent and treat HCC xenograft on nude mice with a preventive rate of 97 %.

CONCLUSION

DCs not only inhibit the growth of human HCC and other cancer cells in vitro, but also prevent the growth of HCC xenograft on nude mice in vivo.

Mycobacteria target DC-SIGN to suppress dendritic cell function

Mycobacterium tuberculosis represents a world-wide health risk and immunosuppression is a particular problem in M. tuberculosis infections. Although macrophages are primarily infected, dendritic cells (DCs) are important in inducing cellular immune responses against M. tuberculosis. We hypothesized that DCs represent a target for M. tuberculosis and that the observed immuno-suppression results from modulation of DC functions. We demonstrate that the DC-specific C-type lectin DC-SIGN is an important receptor on DCs that captures and internalizes intact Mycobacterium bovis bacillus Calmette-Guérin (BCG) through the mycobacterial cell wall component ManLAM. Antibodies against DC-SIGN block M. bovis BCG infection of DCs. ManLAM is also secreted by M. tuberculosis-infected macrophages and has been implicated as a virulence factor. Strikingly, ManLAM binding to DC-SIGN prevents mycobacteria- or LPS-induced DC maturation. Both mycobacteria and LPS induce DC maturation through Toll-like receptor (TLR) signaling, suggesting that DC-SIGN, upon binding of ManLAM, interferes with TLR-mediated signals. Blocking antibodies against DC-SIGN reverse the ManLAM-mediated immunosuppressive effects. Our results suggest that M. tuberculosis targets DC-SIGN both to infect DCs and to down-regulate DC-mediated immune responses. Moreover, we demonstrate that DC-SIGN has a broader pathogen recognition profile than previously shown, suggesting that DC-SIGN may represent a molecular target for clinical intervention in infections other than HIV-1.

Mycobacterium bovis bacillus Calmette-Guérin-infected dendritic cells potently activate autologous T cells via a B7 and interleukin-12-dependent mechanism

Mycobacteria are potent adjuvants, can survive intracellularly and have been safely used for many years as vaccines against tuberculosis and leprosy. They are thus important potential vectors for recombinant vaccines. Many of their adjuvant properties are mediated following phagocytosis by dendritic cells (DC), which are in turn critical for priming naïve T cells. Although the maturation of DC in response to mycobacteria, such as Mycobacterium bovis bacillus Calmette-Guérin (BCG), is well described the subsequent responses of autologous T cells to mycobacterium-infected DC remains uncharacterized. In our experiments DC infected with BCG expressed more co-stimulatory molecules than tumour-necrosis factor-alpha (TNF-alpha) -treated DC and stimulated more potent mixed leucocyte reactions. When autologous T cells were co-cultured with BCG-exposed DC they became highly activated, as determined by display of CD25, CD54 and CD71 on both CD4+ and CD8+ cells. In contrast, the response of T cells to TNF-alpha-matured DC was significantly less. Cytokine production from T cells cultured with BCG-exposed DC was enhanced with elevated secretion of interleukin-2 (IL-2), IL-10 and interferon-gamma (IFN-gamma) and was produced by both CD4+ and CD8+ lymphocytes as determined by intracellular staining. In particular, IFN-gamma secretion was increased from 50 pg/ml to 25 000 pg/ml and IL-10 secretion increased from 20 pg/ml to 300 pg/ml in BCG-exposed DC co-cultures. Blocking antibodies to B7.1 and B7.2 or IL-12 significantly reduced the secretion of IFN-gamma and reductions were also seen in the expression of CD25 and CD71 by CD4+ cells. These data demonstrate that mycobacterially infected DC are particularly potent activators of autologous T cells compared to TNF-alpha-exposed DC and that the resultant T cells are functionally superior.

Mycobacterium leprae infection in monocyte-derived dendritic cells and its influence on antigen-presenting function

Host defense against Mycobacterium leprae infection is chiefly mediated by gamma interferon (IFN-gamma)-secreting cytotoxic T cells. Since which antigen-presenting cell populations act to stimulate these T cells is not fully understood, we addressed the role of monocyte-derived dendritic cells (DCs). The DCs phagocytosed M. leprae and expressed bacterially derived antigens (Ags), such as phenolic glycolipid 1 (PGL-1), in the cytoplasm, as well as on the cell surface. The expression of HLA-ABC and -DR Ags on DCs was down-regulated by M. leprae infection, and that of CD86 was up-regulated, but not as fully as by Mycobacterium bovis BCG infection. Induction of CD83 expression required a large number of M. leprae cells. When a multiplicity of infection of >40 was used, the DCs induced a significant proliferative and IFN-gamma-producing response in autologous T cells. However, these responses were significantly lower than those induced by BCG- or Mycobacterium avium-infected DCs. A CD40-mediated signaling in M. leprae-infected DCs up-regulated the expression of HLA Ags, CD86, and CD83 but did not enhance T-cell-stimulating ability. Therefore, M. leprae-infected DCs are less efficient at inducing T-cell responses. However, when the surface PGL-1 on M. leprae-infected DCs was masked by a monoclonal antibody, the DCs induced enhanced responses in both CD4(+)- and CD8(+)-T-cell subsets. M. leprae is a unique pathogen which remains resistant to DC-mediated T-cell immunity, at least in the early stages of infection.

Identification of a clinical-grade maturation factor for dendritic cells

Dendritic cells (DC) are essential for the generation of primary adaptive immune responses, but their full immunostimulatory capacities are only reached upon maturation. The authors compared several clinical-grade adjuvants of bacterial origin to determine their ability to induce phenotypic and functional maturation of monocyte-derived DC (Dendritophages, Dphi; IDM, Paris, France) differentiated with granulocyte-macrophage colony-stimulating factor and interleukin-13 in single-use cell processors (VacCell; IDM, Paris, France). Monophosphoryl lipid A, Mycobacterium bovis bacillus Calmette-Guerin, and Ribomunyl (Pierre Fabre Medicament, Boulogne, France) all appeared able to provide the signal necessary to initiate Dphi maturation. However, only Ribomunyl (Pierre Fabre Medicament) (containing membrane and ribosomal fractions from four bacterial strains) allowed the authors to obtain a significant enhancement of allostimulatory abilities and cytokine production by Dphi in the absence of active cellular infection. Addition of interferon-gamma (IFN-gamma) to Ribomunyl resulted in more pronounced upregulation of CD83, major histocompatibility complex class I, and B7 molecules by Dphi. Moreover, the IFN-gamma addition modulated their cytokine secretion, allowing higher levels of bioactive interleukin-12 concomitant with lower levels of interleukin-10. In kinetic studies, Dphi contact with Ribomunyl and IFN-gamma for 6 hours was sufficient to trigger a maturation process that completed spontaneously. Thus, Ribomunyl in association with IFN-gamma represents a suitable agent for the ex vivo production of mature monocyte-derived DC that can be used as cellular vaccines to promote a potent type I immune response.

Protein tyrosine kinase regulates FAS-mediated apoptosis in human BCG-infected monocytes

Apoptosis of monocytes/macrophages has emerged as a central regulatory event in the defense against mycobacterial infections. The involvement of protein tyrosine kinases (PTK) in Fas-mediated apoptosis in T cells is well established, but the possible role of PTK in Fas-dependent death of human bacillus Calmette-Guerin (BCG)-infected monocytes remains unclear. Here, we first examined the expression and function of Fas on BCG-infected human monocytes by flow cytometry. The results demonstrated that BCG-infected monocytes expressed significant Fas protein levels. In addition, engagement of the Fas antigen with its agonistic antibody (Ab) resulted in apoptosis of monocytes, as monitored by DNA analysis and fluorescence-activated cell sorter (FACS) analysis. The apoptotic action of Fas was suppressed significantly by genistein, indicating a role for PTK in this death process. Consistent with this observation, herbimycin A and tyrphostin, two selective tyrosine kinase inhibitors with different mechanisms of action, effectively inhibited Fas-mediated apoptosis of BCG-infected monocytes, as demonstrated by DNA content analysis. Moreover, we confirmed the effect of genistein, herbimycin A, and tyrphostin by examining apoptosis with the terminal transferase dUTP nick endlabeling (TUNEL) assay. Collectively, these data demonstrate that Fas-induced apoptosis may represent an important mechanism for eliminating BCG-activated human monocytes and that this apoptosis is due, at least in part, to signaling via a PTK pathway.

Interaction between photodynamic therapy and BCG immunotherapy responsible for the reduced recurrence of treated mouse tumors

Subcutaneous mouse EMT6 tumors were treated by individual or combined regimens of a single Bacillus Calmette-Guérin (BCG) vaccine administration and photodynamic therapy (PDT). Six clinically relevant photosensitizers characterized by different action mechanisms were used: Photofrin, benzoporphyrin derivative, tetra(m-hydroxyphenyl)chlorin (foscan), mono-L-aspartylchlorin e6, lutetium texaphyrin or zinc phthalocyanine. Irrespective of the type of photosensitizer used, the optimized BCG protocols improved the cure rate of PDT-treated tumors. This indicates that the interaction does not take place during the early phase of tumor ablation but at later events involved in preventing tumor recurrence. Beneficial effects on tumor cure were observed even when the BCG injection was delayed to 7 days after PDT. The accumulation of activated myeloid cells that markedly increases in tumors treated by Photofrin-based PDT was not additionally affected by BCG treatment. However, the incidence of immune memory T cells in tumor-draining lymph nodes that almost doubled at 6 days after Photofrin-PDT further increased close to three-fold with adjuvant BCG. This suggests that BCG immunotherapy amplifies the T-lymphocyte-mediated immune response against PDT-treated tumors. Since both these modalities are established for the treatment of superficial bladder carcinomas, use of their combination for this condition should be clinically tested.

The response of human dendritic cells to recombinant adenovirus, recombinant Mycobacterium bovis Bacillus Calmette Guerin and biolistic methods of antigen delivery: different induction of contact-dependant and soluble signals

Dendritic cells (DCs) are the most potent antigen presenting cells for inducing T-cell immune responses. The ability to grow human DCs from monocyte precursors provides an abundant source of these cells, which can be modified in vitro to present antigens. Re-administration of modified DCs to patients as vaccines has been shown in some cases to induce immune responses against cancer and infectious disease. Gene delivery to DCs provides an intracellular source of antigen for efficient and persistent loading of major histocompatibility complex (MHC) class I molecules. The aim of this study was to use monocyte-derived DCs (MD-DCs) from healthy donors to compare in vitro gene transfer, mediated by adenovirus, M. bovis Bacillus Calmette Guerin (BCG) and biolistic delivery. Efficiency of transfection and effect on DC phenotype, allostimulatory capacity and cytokine secretion was investigated. Adenovirus and BCG both showed a comparable ability to transfect MD-DCs, whereas the biolistic delivery by gene gun was unsuccessful in the reporter gene delivery. BCG transfection promoted MD-DC maturation as is apparent in the surface phenotype, allostimulatory capacity and cytokine secretion from cells. In comparison, adenovirus and biolistic delivery had a reduced effect on MD-DCs although enhancement of co-stimulatory and MHC molecule expression occurred in the cells of some donors. Both BCG and adenovirus represent useful vectors for gene transfer to human DCs. The effect of BCG on DC maturation may provide additional signals for the induction of antigen-specific T-cell responses.

Microbial lipopeptides stimulate dendritic cell maturation via Toll-like receptor 2

The ability of dendritic cells (DC) to initiate immune responses in naive T cells is dependent upon a maturation process that allows the cells to develop their potent Ag-presenting capacity. Although immature DC can be derived in vitro by treatment of peripheral blood monocytes with GM-CSF and IL-4, additional signals such as those provided by TNF-alpha, CD40 ligand, or LPS are required for complete maturation and maximum APC function. Because we recently found that microbial lipoproteins can activate monocytes and DC through Toll-like receptor (TLR) 2, we also investigated whether lipoproteins can drive DC maturation. Immature DC were cultured with or without lipoproteins and were monitored for expression of cell surface markers indicative of maturation. Stimulation with lipopeptides increased expression of CD83, MHC class II, CD80, CD86, CD54, and CD58, and decreased CD32 expression and endocytic activity; these lipopeptide-matured DC also displayed enhanced T cell stimulatory capacity in MLR, as measured by T cell proliferation and IFN-gamma secretion. The lipid moiety of the lipopeptide was found to be essential for induction of maturation. Preincubation of maturing DC with an anti-TLR2 blocking Ab before addition of lipopeptide blocked the phenotypic and functional changes associated with DC maturation. These results demonstrate that lipopeptides can stimulate DC maturation via TLR2, providing a mechanism by which products of bacteria can participate in the initiation of an immune response.

Maturation of human dendritic cells by cell wall skeleton of Mycobacterium bovis bacillus Calmette-Guérin: involvement of toll-like receptors

The constituents of mycobacteria are an effective immune adjuvant, as observed with complete Freund's adjuvant. In this study, we demonstrated that the cell wall skeleton of Mycobacterium bovis bacillus Calmette-Guérin (BCG-CWS), a purified noninfectious material consisting of peptidoglycan, arabinogalactan, and mycolic acids, induces maturation of human dendritic cells (DC). Surface expression of CD40, CD80, CD83, and CD86 was increased by BCG-CWS on human immature DC, and the effect was similar to those of interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), heat-killed BCG, and viable BCG. BCG-CWS induced the secretion of TNF-alpha, IL-6, and IL-12 p40. CD83 expression was increased by a soluble factor secreted from BCG-CWS-treated DC and was completely inhibited by monoclonal antibodies against TNF-alpha. BCG-CWS-treated DC stimulated extensive allogeneic mixed lymphocyte reactions. The level of TNF-alpha secreted through BCG-CWS was partially suppressed in murine macrophages with no Toll-like receptor 2 (TLR 2) or TLR4 and was completely lost in TLR2 and TLR4 double-deficient macrophages. These results suggest that the BCG-CWS induces TNF-alpha secretion from DC via TLR2 and TLR4 and that the secreted TNF-alpha induces the maturation of DC per se.

Human dendritic cells discriminate between viable and killed Toxoplasma gondii tachyzoites: dendritic cell activation after infection with viable parasites results in CD28 and CD40 ligand signaling that controls IL-12-dependent and -independent T cell production of IFN-gamma

We studied how the interaction between human dendritic cells (DC) and Toxoplasma gondii influences the generation of cell-mediated immunity against the parasite. We demonstrate that viable, but not killed, tachyzoites of T. gondii altered the phenotype of immature DC. DC infected with viable parasites up-regulated the expression of CD40, CD80, CD86, and HLA-DR and down-regulated expression of CD115. These changes are indicative of DC activation induced by T. gondii. Viable and killed tachyzoites had contrasting effects on cytokine production. DC infected with viable T. gondii rather than DC that phagocytosed killed parasites induced secretion of high amounts of IFN-gamma by T cells from T. gondii-seronegative donors. IFN-gamma production in response to DC infected with viable parasites required CD28 and CD40 ligand (CD40L) signaling. In addition, this IFN-gamma response was dependent in part on IL-12 secretion. Production of IL-12 p70 occurred after interaction between T cells and DC infected with viable T. gondii, but not after incubation of T cells with DC plus killed tachyzoites. IL-12 synthesis was inhibited by blockade of CD40L signaling. IL-12-independent IFN-gamma production required CD80/CD86-CD28 interaction and, to a lesser extent, CD40-CD40L signaling. Taken together, T. gondii-induced activation of human DC is associated with T cell production of IFN-gamma through CD40-CD40L-dependent release of IL-12 and through CD80/CD86-CD28 and CD40-CD40L signaling that mediate IFN-gamma secretion even in the absence of bioactive IL-12.