Development of immunoadjuvants for immunotherapy of cancer

Peptidoglycan-Like Components in Z-100, Extracted from Mycobacterium tuberculosis Strain Aoyama B, Increase IL-12p40 via NOD2

Background. Z-100 is a hot-water extract of the human-type Mycobacterium tuberculosis strain Aoyama B. While Z-100’s macrophage-mediated immunomodulatory effects have been reported, the mechanistic details have not been fully clarified. Here, we studied the immunomodulatory effects of Z-100 on mouse bone marrow-derived cells, human CD14+ cells, and skin. Methods. Mouse bone marrow-derived cells and CD14+ cells were cultured in the presence of granulocyte-macrophage colony-stimulating factor, differentiated into macrophage-like cells, and then stimulated with Z-100. Furthermore, since Z-100 is subcutaneously administered clinically, we injected Z-100 into mice and measured gene expression in the skin. Results. While Z-100 stimulation increased the production of interleukin- (IL-) 12p40 and IL-1β in mouse bone marrow-derived macrophages, levels of IL-1β were low. In contrast, TNF-α production did not increase. Meanwhile, stimulation of human CD14+ cells with Z-100 increased production of IL-12p40, TNF-α, and IL-1β. Because Z-100 appeared to have the most stable effect on IL-12p40, we examined the components of Z-100 that induce IL-12p40 production. We found that Z-100 contained peptidoglycan-like components. In addition, an siRNA study showed that Z-100 increased the production of IL-12p40 via nucleotide-binding oligomerization domain 2 (NOD2). Further, subcutaneous administration of Z-100 to mice significantly elevated expression of IL-12p40 and IL-1β and showed a trend towards increasing TNF-α in the skin. Conclusion. Z-100 induced the production of immunomodulatory cytokines from various types of macrophages and specifically increased IL-12p40 production through peptidoglycan-like components via NOD2.

Application of nanotechnology in the diagnosis and treatment of bladder cancer

Bladder cancer (BC) is a common malignancy in the genitourinary system and the current theranostic approaches are unsatisfactory. Sensitivity and specificity of current diagnosis methods are not ideal and high recurrence and progression rates after initial treatment indicate the urgent need for management improvements in clinic. Nanotechnology has been proposed as an effective method to improve theranosis efficiency for both non-muscle invasive bladder cancer (NMIBC) and muscle invasive bladder cancer (MIBC). For example, gold nanoparticles (AuNPs) have been developed for simple, fast and sensitive urinary sample test for bladder cancer diagnosis. Nanoparticles targeting bladder cancers can facilitate to distinguish the normal and abnormal bladder tissues during cystoscopy and thus help with the complete removal of malignant lesions. Both intravenous and intravesical agents can be modified by nanotechnology for targeted delivery, high anti-tumor efficiency and excellent tolerability, exhibiting encouraging potential in bladder cancer treatment. Photosensitizers and biological agents can also be delivered by nanotechnology, intermediating phototherapy and targeted therapy. The management of bladder cancer remained almost unchanged for decades with unsatisfactory effect. However, it is likely to change with the fast-developed nanotechnology. Herein we summarized the current utility of nanotechnology in bladder cancer diagnosis and treatment, providing insights for the future designing and discovering novel nanoparticles for bladder cancer management.

Tumor-Associated Mast Cells in Urothelial Bladder Cancer: Optimizing Immuno-Oncology

Urothelial bladder cancer (UBC) is one of the most prevalent and aggressive malignancies. Recent evidence indicates that the tumor microenvironment (TME), including a variety of immune cells, is a critical modulator of tumor initiation, progression, evolution, and treatment resistance. Mast cells (MCs) in UBC are possibly involved in tumor angiogenesis, tissue remodeling, and immunomodulation. Moreover, tumor-infiltration by MCs has been reported in early-stage UBC patients. This infiltration is linked with a favorable or unfavorable prognosis depending on the tumor type and location. Despite the discrepancy of MC function in tumor progression, MCs can modify the TME to regulate the immunity and infiltration of tumors by producing an array of mediators. Nonetheless, the precise role of MCs in UBC tumor progression and evolution remains unknown. Thus, this review discusses some critical roles of MCs in UBC. Patients with UBC are treated at both early and late stages by immunotherapeutic methods, including intravenous bacillus Calmette–Guérin instillation and immune checkpoint blockade. An understanding of the patient response and resistance mechanisms in UBC is required to unlock the complete potential of immunotherapy. Since MCs are pivotal to understand the underlying processes and predictors of therapeutic responses in UBC, our review also focuses on possible immunotherapeutic treatments that involve MCs.

Combination of PEG-decorated black phosphorus nanosheets and immunoadjuvant for photoimmunotherapy of melanoma

Photoimmunotherapy, which combines local photothermal therapy (PTT) with immunological stimulation, is a promising modality for cancer treatment. Herein, we have reported a photothermal-immunotherapy of melanoma using pegylated black phosphorus nanosheets (BP-PEG NSs) and imiquimod (R837) as the photothermal conversion agent and the immunoadjuvant, respectively. The photothermal stability of BP NSs was remarkably enhanced after the modification of poly(ethylene glycol) (PEG) by electrostatic interactions. The in situ generation of tumor-associated antigens by PTT elicited a strong immune response in the presence of R837, achieving a photoimmunotherapy of B16 melanoma. This photoimmunotherapy stimulated a stronger immune response both in vitro and in vivo than monotherapy, inducing a much greater release of cytokines such as IL-6, IL-12, and TNF-α. In vivo antitumor studies in B16 tumor-bearing mice demonstrated that photoimmunotherapy showed the best tumor inhibition effects. Our study suggested that BP-PEG NS-based PTT primed with an immunoadjuvant can be used for synergistic photoimmunotherapy of melanomas.

Suppression of MD2 inhibits breast cancer in vitro and in vivo

Purpose

To explore the effects of the intervening measure targeting myeloid differentiation 2 (MD2) on breast cancer progression in vitro and in vivo.

Methods

The expression of MD2 in normal breast cells (Hs 578Bst) and three kinds of breast carcinoma cell lines (MCF-7, MDA-MB-231 s and 4T1) were detected by western blot. MTT assay was used to detect the proliferation of 4T1 cells treated by L6H21, cell migration and invasion was measured by wound healing assay and trans-well matrigel invasion assay, respectively. In addition, to further study the role of MD2 in tumor progression, we assessed the effects of inhibition of MD2 on the progression of xenograft tumors in vivo.

Results

The expression of MD2 is much higher in MDA-MB-231 s and 4T1cells than that in normal breast cells (Hs 578Bst) or MCF-7 cells (p < 0.05). In vitro, suppression of MD2 by L6H21 has a significant inhibition of proliferation, migration and invasion in 4T1 cells in dose-dependent manner. In vivo, L6H21 pretreatment significantly improved survival of 4T1-bearing mice (p < 0.05). Additionally, we also observed that none of the mice died from the toxic effect of 10 mg kg⁻¹ L6H21 in 60 days.

Conclusion

Overall, this work indicates that suppression of MD2 shows progression inhibition in vitro and significantly prolong survival in vivo. These findings provide the potential experimental evidence for using MD2 as a therapeutic target of breast carcinoma.

Liposome-Encapsulated Bacillus Calmette-Guérin Cell Wall Skeleton Enhances Antitumor Efficiency for Bladder Cancer In Vitro and In Vivo via Induction of AMP-Activated Protein Kinase

Simple Summary

We engineered novel nanoparticles consisting of liposome-encapsulated Bacillus Calmette–Guérin cell well skeleton (BCG-CWS) for intravesical instillation in bladder cancer. The liposome-encapsulated BCG-CWS nanoparticles had antitumoral effects in an orthotopic bladder cancer mouse model, and the BCG-CWS nanoparticles can be further developed as a non-toxic substitute for live BCG with improved dispensability, stability, and size compatibility. This is significant because we succeeded in the intravesical delivery of BCG-CWS through the intravesical route using a catheter in an orthotopic bladder cancer mouse model to specifically target tumor cells. This is the first study on the BCG-CWS-induced activation of AMPK in urothelial carcinoma cells, suggesting that AMPK-mediated reactive oxygen species (ROS) production and ER stress is a cellular signaling pathway in tumors sensitive to BCG-CWS. These results have the potential for significant ramifications in targeted therapy using a predictive marker for bladder cancer.

Abstract

The Mycobacterium Bacillus Calmette-Guérin cell wall skeleton (BCG-CWS), the main immune active center of BCG, is a potent candidate non-infectious immunotherapeutic drug and an alternative to live BCG for use against urothelial carcinoma. However, its application in anticancer therapy is limited, as BCG-CWS tends to aggregate in both aqueous and non-aqueous solvents. To improve the internalization of BCG-CWS into bladder cancer cells without aggregation, BCG-CWS was nanoparticulated at a 180 nm size in methylene chloride and subsequently encapsulated with conventional liposomes (CWS-Nano-CL) using an emulsified lipid (LEEL) method. In vitro cell proliferation assays showed that CWS-Nano-CL was more effective at suppressing bladder cancer cell growth compared to nonenveloped BCG-CWS. In an orthotopic implantation model of luciferase-tagged MBT2 bladder cancer cells, encapsulated BCG-CWS nanoparticles could enhance the delivery of BCG-CWS into the bladder and suppress tumor growth. Treatment with CWS-Nano-CL induced the inhibition of the mammalian target of rapamycin (mTOR) pathway and the activation of AMP-activated protein kinase (AMPK) phosphorylation, leading to apoptosis, both in vitro and in vivo. Furthermore, the antitumor activity of CWS-Nano-CL was mediated predominantly by reactive oxygen species (ROS) generation and AMPK activation, which induced endoplasmic reticulum (ER) stress, followed by c-Jun N-terminal kinase (JNK) signaling-mediated apoptosis. Therefore, our data suggest that the intravesical instillation of liposome-encapsulated BCG-CWS nanoparticles can facilitate BCG-CW cellular endocytosis and provide a promising drug-delivery system as a therapeutic strategy for BCG-mediated bladder cancer treatment.

Clinical and molecular insights into BCG immunotherapy for melanoma

The incidence of cutaneous melanoma and the mortality rate of advanced melanoma patients continue to rise globally. Despite the recent success of immunotherapy including ipilimumab and pembrolizumab checkpoint inhibitors, a large proportion of patients are refractory to such treatment modalities. The application of mycobacteria such as Bacillus Calmette-Guérin (BCG) in the treatment of various malignancies, including cutaneous melanoma, has been clearly demonstrated after almost a century of observations and experimentation. Intralesional BCG (IL-BCG) immunotherapy is a highly efficient and cost-effective treatment option for inoperable stage III in-transit melanoma, as recommended in the National Comprehensive Cancer Network Guidelines. IL-BCG has shown great efficacy in the regression of directly injected metastatic melanoma lesions, as well as distal noninjected nodules in immunocompetent patients. Clinical and preclinical studies have shown that BCG serves as a strong immune modulator, inducing the recruitment of various immune cells that contribute to antitumour immunity. However, the specific mechanism of BCG-mediated tumour immunity remains poorly understood. Comparative genome analyses have revealed that different BCG strains exhibit distinct immunological activity and virulence, which might impact the therapeutic response and clinical outcome of patients. In this review, we discuss the immunostimulatory potential of different BCG substrains and highlight clinical studies utilizing BCG immunotherapy for the treatment of cutaneous melanoma. Furthermore, the review focuses on the cellular and molecular mechanisms of the BCG-induced immune responses of both the innate and adaptive arms of the immune system. Furthermore, the review discussed the administration of BCG as a monotherapy or in combination with other immunotherapeutic or chemotherapeutic agents.

Immunoadjuvants for cancer immunotherapy: A review of recent developments

Cancer immunotherapy evolved as a new treatment modality to eradicate tumor cells and has gained in popularity after its successful clinical transition. By activating antigen-presenting cells (APCs), and thus, inducing innate or adaptive immune responses, immunoadjuvants have become promising tools for cancer immunotherapy. Different types of immunoadjuvants such as toll-like receptor (TLR) agonists, exosomes, and metallic and plant-derived immunoadjuvants have been studied for their immunological effects. However, the clinical use of immunoadjuvants is limited by short response rates and various side-effects. The rapid progress made in the development of nanoparticle systems as immunoadjuvant carrier vehicles has provided potential carriers for cancer immunotherapy. In this review article, we describe different types of immunoadjuvants, their limitations, modes of action, and the reasons for their clinical adoption. In addition, we review recent progress made in the nanoparticle-based immunoadjuvant field and on the combined use of nanoparticle-based immunoadjuvants and chemotherapy, phototherapy, radiation therapy, and immune checkpoint inhibitor-based therapy. STATEMENT OF SIGNIFICANCE: Cancer immunotherapy emerged as a new hope for treating malignant tumors. Different types of immunoadjuvants serve as an important tool for cancer immunotherapy by activating an innate or adaptive immune response. Limitation of free immunoadjuvant has paved the path for the development of nanoparticle-based immunoadjuvant therapy with the hope of prolonging the therapeutic efficacy. This review highlights the recent advancement made in nanoparticle-based immunoadjuvant therapy in modulating the adaptive and innate immune system. The application of the combinatorial approach of chemotherapy, phototherapy, radiation therapy adds synergy in nanoparticle-based immunoadjuvant therapy. It will broaden the reader's understanding on the recent progress made in immunotherapy with the aid of immunoadjuvant-based nanosystem.

Evolution of drug delivery system from viewpoint of controlled intracellular trafficking and selective tissue targeting toward future nanomedicine

Due to the rapid changes that have occurred in the field of drug discovery and the recent developments in the early 21st century, the role of drug delivery systems (DDS) has become increasingly more important. For the past 20 years, our laboratory has been developing gene delivery systems based on lipid-based delivery systems. One of our efforts has been directed toward developing a multifunctional envelope-type nano device (MEND) by modifying the particle surface with octaarginine, which resulted in a remarkably enhanced cellular uptake and improved intracellular trafficking of plasmid DNA (pDNA). When we moved to in vivo applications, however, we were faced with the PEG-dilemma and we shifted our strategy to the incorporation of ionizable cationic lipids into our system. This resulted in some dramatic improvements over our original design and this can be attributed to the development of a new lipid library. We have also developed a mitochondrial targeting system based on a membrane fusion mechanism using a MITO-Porter, which can deliver nucleic acids/pDNA into the matrix of mitochondria. After the appearance of antibody medicines, Opdivo, an immune checkpoint inhibitor, has established cancer immunology as the 4th strategy in cancer therapy. Our DDS technologies can also be applied to this new field of cancer therapy to cure cancer by controlling our immune mechanisms. The latest studies are summarized in this review article.

Myeloid C-Type Lectin Receptors in Tuberculosis and HIV Immunity: Insights Into Co-infection?

C-type lectin receptors (CLRs) are carbohydrate binding pattern recognition receptors (PRRs) which play a central role in host recognition of pathogenic microorganisms. Signaling through CLRs displayed on antigen presenting cells dictates important innate and adaptive immune responses. Several pathogens have evolved mechanisms to exploit the receptors or signaling pathways of the CLR system to gain entry or propagate in host cells. CLR responses to high priority pathogens such as Mycobacterium tuberculosis (Mtb), HIV, Ebola, and others are described and considered potential avenues for therapeutic intervention. Mtb and HIV are the leading causes of death due to infectious disease and have a synergistic relationship that further promotes aggressive disease in co-infected persons. Immune recognition through CLRs and other PRRs are important determinants of disease outcomes for both TB and HIV. Investigations of CLR responses to Mtb and HIV, to date, have primarily focused on single infection outcomes and do not account for the potential effects of co-infection. This review will focus on CLRs recognition of Mtb and HIV motifs. We will describe their respective roles in protective immunity and immune evasion or exploitation, as well as their potential as genetic determinants of disease susceptibility, and as avenues for development of therapeutic interventions. The potential convergence of CLR-driven responses of the innate and adaptive immune systems in the setting of Mtb and HIV co-infection will further be discussed relevant to disease pathogenesis and development of clinical interventions.

Adjuvant activity of Mycobacteria-derived mycolic acids

Successful vaccination, especially with safe vaccines such as component/subunit vaccines, requires proper activation of innate immunity and, for this purpose, adjuvant is used. For clinical use, alum is frequently used while, for experimental use, CFA, containing Mycobacterial components, was often used. In this report, we demonstrated that mycolic acids (MA), major and essential lipid components of the bacterial cell wall of the genus Mycobacterium, has adjuvant activity. MA plus model antigen-immunization induced sufficient humoral response, which was largely comparable to conventional CFA plus antigen-immunization. Importantly, while CFA plus antigen-immunization induced Th17-biased severe and destructive inflammatory responses at the injected site, MA plus antigen-immunization induced Th1-biased mild inflammation at the site. MA induced dendritic cell activation by co-stimulatory molecule induction as well as inflammatory cytokine/chemokine induction. MA plus antigen-immunization successfully protected mice from tumor progression both in prevention and in therapy models. We thus submit that MA is a promising adjuvant candidate material for clinical purposes and for experimental purposes from a perspective of animal welfare.

Enhanced Intracellular Delivery of BCG Cell Wall Skeleton into Bladder Cancer Cells Using Liposomes Functionalized with Folic Acid and Pep-1 Peptide

Although bacillus Calmette–Guérin cell wall skeleton (BCG-CWS) might function as a potential substitute for live BCG, its use in the treatment of bladder cancer remains limited owing to issues such as insolubility and micrometer-size following exposure to an aqueous environment. Thus, to develop a novel nanoparticulate system for efficient BCG-CWS delivery, liposomal encapsulation was carried out using a modified emulsification-solvent evaporation method (targets: Size, <200 nm; encapsulation efficiency, ~60%). Further, the liposomal surface was functionalized with specific ligands, folic acid (FA), and Pep-1 peptide (Pep1), as targeting and cell-penetrating moieties, respectively. Functionalized liposomes greatly increased the intracellular uptake of BCG-CWS in the bladder cancer cell lines, 5637 and MBT2. The immunoactivity was verified through elevated cytokine production and a THP-1 migration assay. In vivo antitumor efficacy revealed that the BCG-CWS-loaded liposomes effectively inhibited tumor growth in mice bearing MBT2 tumors. Dual ligand-functionalized liposome was also superior to single ligand-functionalized liposomes. Immunohistochemistry supported the enhanced antitumor effect of BCG-CWS, with IL-6 production and CD4 infiltration. Thus, we conclude that FA- and Pep1-modified liposomes encapsulating BCG-CWS might be a good candidate for bladder cancer treatment with high target selectivity.

Application of BCG-CWS as a Systemic Adjuvant by Using Nanoparticulation Technology

The intravesical instillation of live Bacillus Calmette-Guerin (BCG) for treating bladder cancer is a powerful cancer immunotherapy. The BCG cell wall skeleton (BCG-CWS) is the main component of the adjuvant, leading to the induction of antitumor immunity. However, the use of live BCG and BCG-CWS is currently limited to local administration because of the infectiousness of live BCG and the insolubility of BCG-CWS. We previously developed a water-dispersible nanoparticle (NP) formulation of BCG-CWS (CWS-NP), which could be used to apply BCG components for use as a systemically injected adjuvant for the treatment of cancers other than bladder cancer. In the present study, we examined the possible use of CWS-NP for cancer immunotherapy, when intravenously administered. The CWS-NP was a highly uniform dispersion and showed no aggregation in serum. The intravenously injected CWS-NP accumulated in the spleen and was efficiently taken up by dendritic cells, leading to their maturation. The coadministration of CWS-NP and ovalbumin (OVA) loaded NP resulted in the generation of OVA-specific cytotoxic T cells and inhibited the growth of E.G7-OVA tumors. These results represent the first findings related to the use of systemically injected CWS-NP as an adjuvant for cancer immunotherapy.

Augmenting Vaccine Immunogenicity through the Use of Natural Human Anti-rhamnose Antibodies

Utilizing natural antibodies to augment vaccine immunogenicity is a promising approach toward cancer immunotherapy. Anti-rhamnose (anti-Rha) antibodies are some of the most common natural anti-carbohydrate antibodies present in human serum. Therefore, rhamnose can be utilized as a targeting moiety for a rhamnose-containing vaccine to prepare an effective vaccine formulation. It was shown previously that anti-Rha antibody generated in mice binds effectively with Rha-conjugated vaccine and is picked up by antigen presenting cells (APCs) through stimulatory Fc receptors. This leads to the effective uptake and processing of antigen and eventually presentation by major histocompatibility complex (MHC) molecules. In this article, we show that natural human anti-Rha antibodies can also be used in a similar mechanism and immunogenicity can be enhanced by targeting Rha-conjugated antigens. In doing so, we have purified human anti-Rha antibodies from human serum using a rhamnose affinity column. In vitro, human anti-Rha antibodies are shown to enhance the uptake of a model antigen, Rha-ovalbumin (Rha-Ova), by APCs. In vivo, they improved the priming of CD4+ T cells to Rha-Ova in comparison to non-anti-Rha human antibodies. Additionally, increased priming of both CD4+ and CD8+ T cells toward the cancer antigen MUC1-Tn was observed in mice that received human anti-Rha antibodies prior to vaccination with a rhamnose-modified MUC1-Tn cancer vaccine. The vaccine conjugate contained Pam₃CysSK₄, a Toll-like receptor (TLR) agonist linked via copper-free cycloaddition chemistry to a 20-amino-acid glycopeptide derived from the tumor marker MUC-1 containing the tumor-associated carbohydrate antigen α-N-acetyl galactosamine (GalNAc). The primed CD8+ T cells released IFN-γ and killed tumor cells. Therefore, we have confirmed that human anti-Rha antibodies can be effectively utilized as a targeting moiety for making an effective vaccine.

Integration of nano drug-delivery system with cancer immunotherapy

Immune checkpoint therapy represents a new, revolutionary type of cancer therapy, but emerging evidence indicates that only a minority of patients will benefit from it. The issue of how to improve and widen the clinical response is a pivotal issue, and combining other types of therapy with immune checkpoint inhibitors is currently under development. A nanotechnology-based drug-delivery system (nano DDS) could be an important contribution to the development of an effective combination therapy. In this document, we review recent findings in the field of tumor immunology, which provide a strategy for an efficient combination therapy, and discuss nano DDS that are associated with cancer immunotherapy and nano DDS strategies based on the immune status in tumor microenvironments.

Nonpyrogenic Molecular Adjuvants Based on norAbu-Muramyldipeptide and norAbu-Glucosaminyl Muramyldipeptide: Synthesis, Molecular Mechanisms of Action, and Biological Activities in Vitro and in Vivo

Fatty acyl analogues of muramyldipeptide (MDP) (abbreviated N-L18 norAbuGMDP, N-B30 norAbuGMDP, norAbuMDP-Lys(L18), norAbuMDP-Lys(B30), norAbuGMDP-Lys(L18), norAbuGMDP-Lys(B30), B30 norAbuMDP, L18 norAbuMDP) are designed and synthesized comprising the normuramyl-l-α-aminobutanoyl (norAbu) structural moiety. All new analogues show depressed pyrogenicity in both free (micellar) state and in liposomal formulations when tested in rabbits in vivo (sc and iv application). New analogues are also shown to be selective activators of NOD2 and NLRP3 (inflammasome) in vitro but not NOD1. Potencies of NOD2 and NLRP3 stimulation are found comparable with free MDP and other positive controls. Analogues are also demonstrated to be effective in stimulating cellular proliferation when the sera from mice are injected sc with individual liposome-loaded analogues, causing proliferation of bone marrow-derived GM-progenitors cells. Importantly, vaccination nanoparticles prepared from metallochelation liposomes, His-tagged antigen rOspA from Borrelia burgdorferi, and lipophilic analogue norAbuMDP-Lys(B30) as adjuvant, are shown to provoke OspA-specific antibody responses with a strong Th1-bias (dominance of IgG2a response). In contrast, the adjuvant effects of Alum or parent MDP show a strong Th2-bias (dominance of IgG1 response).

Synthesis of synthetic mannan backbone polysaccharides found on the surface of Mycobacterium tuberculosis as a vaccine adjuvant and their immunological properties

Surface components of Mycobacterium tuberculosis (Mtb) play crucial roles in modulating host immune responses. Thorough understandings of immunological properties of the Mtb's surface components are essential for the development of tuberculosis treatment and prevention. Unfortunately, the accessibility to the molecules on the surface of Mtb is limited by the structural complexity due to their various macromolecular nature and the hazard of culturing Mtb. In this study, we reveal a practical synthesis of lipomannan (LM) backbone polysaccharides - the core glycans found on Mtb's surface. A rapid synthetic approach based on a controlled polymerization was developed for the chemical synthesis of mannopyranans, the core structure of LM. The size of the LM glycans can be controlled by using specific monomer concentrations in addition to stereo- and regioselectivity derived from the versatile tricyclic orthoester mannose monomer. The immunological properties of the synthesized mannopyranans were investigated and their adjuvant potential was revealed. The adjuvanticity mechanism of the synthetic mannopyranans appears to involve the NF-κB and inflammasome pathways.

Recent Advances in Subunit Vaccine Carriers

The lower immunogenicity of synthetic subunit antigens, compared to live attenuated vaccines, is being addressed with improved vaccine carriers. Recent reports indicate that the physio-chemical properties of these carriers can be altered to achieve optimal antigen presentation, endosomal escape, particle bio-distribution, and cellular trafficking. The carriers can be modified with various antigens and ligands for dendritic cells targeting. They can also be modified with adjuvants, either covalently or entrapped in the matrix, to improve cellular and humoral immune responses against the antigen. As a result, these multi-functional carrier systems are being explored for use in active immunotherapy against cancer and infectious diseases. Advancing technology, improved analytical methods, and use of computational methodology have also contributed to the development of subunit vaccine carriers. This review details recent breakthroughs in the design of nano-particulate vaccine carriers, including liposomes, polymeric nanoparticles, and inorganic nanoparticles.

Adjuvant for vaccine immunotherapy of cancer--focusing on Toll-like receptor 2 and 3 agonists for safely enhancing antitumor immunity

Immune‐enhancing adjuvants usually targets antigen (Ag)‐presenting cells to tune up cellular and humoral immunity. CD141⁺ dendritic cells (DC) represent the professional Ag‐presenting cells in humans. In response to microbial pattern molecules, these DCs upgrade the maturation stage sufficient to improve cross‐presentation of exogenous Ag, and upregulation of MHC and costimulators, allowing CD4/CD8 T cells to proliferate and liberating cytokines/chemokines that support lymphocyte attraction and survival. These DCs also facilitate natural killer‐mediated cell damage. Toll‐like receptors (TLRs) and their signaling pathways in DCs play a pivotal role in DC maturation. Therefore, providing adjuvants in addition to Ag is indispensable for successful vaccine immunotherapy for cancer, which has been approved in comparison with antimicrobial vaccines. Mouse CD8α⁺DCs express TLR7 and TLR9 in addition to the TLR2 family (TLR1, 2, and 6) and TLR3, whereas human CD141⁺DCs exclusively express the TLR2 family and TLR3. Although human and mouse plasmacytoid DCs commonly express TLR7/9 to respond to their agonists, the results on mouse adjuvant studies using TLR7/9 agonists cannot be simply extrapolated to human adjuvant immunotherapy. In contrast, TLR2 and TLR3 are similarly expressed in both human and mouse Ag‐presenting DCs. Bacillus Calmette–Guerin peptidoglycan and polyinosinic–polycytidylic acid are representative agonists for TLR2 and TLR3, respectively, although they additionally stimulate cytoplasmic sensors: their functional specificities may not be limited to the relevant TLRs. These adjuvants have been posted up to a certain achievement in immunotherapy in some cancers. We herein summarize the history and perspectives of TLR2 and TLR3 agonists in vaccine‐adjuvant immunotherapy for cancer.

Perioperative treatment with the new synthetic TLR-4 agonist GLA-SE reduces cancer metastasis without adverse effects

The use of TLR agonists as an anti-cancer treatment is gaining momentum given their capacity to activate various host cellular responses through the secretion of inflammatory cytokines and type-I interferons. It is now also recognized that the perioperative period is a window of opportunity for various interventions aiming at reducing the risk of cancer metastases-the major cause of cancer related death. However, immune-stimulatory approach has not been used perioperatively given several contraindications to surgery. To overcome these obstacles, in this study, we used the newly introduced, fully synthetic TLR-4 agonist, Glucopyranosyl Lipid-A (GLA-SE), in various models of cancer metastases, and in the context of acute stress or surgery. Without exerting evident adverse effects, a single systemic administration of GLA-SE rapidly and dose dependently elevated both innate and adaptive immunity in the circulation, lungs and the lymphatic system. Importantly, GLA-SE treatment led to reduced metastatic development of a mammary adenocarcinoma and a colon carcinoma by approximately 40-75% in F344 rats and BALB/c mice, respectively, at least partly through elevating marginating-pulmonary NK cell cytotoxicity. GLA-SE is safe and well tolerated in humans, and currently is used as an adjuvant in phase-II clinical trials. Given that the TLR-4 receptor and its signaling cascade is highly conserved throughout evolution, our current results suggest that GLA-SE may be a promising immune stimulatory agent in the context of oncological surgeries, aiming to reduce long-term cancer recurrence.

Trehalose 6,6'-dimycolate--a coat to regulate tuberculosis immunopathogenesis

Tuberculosis (TB) remains a significant public health burden worldwide. Treatment of this disease requires a minimum of six months and there is no vaccine available for the most common form of the disease. Increasing evidence suggests that the mycobacterial glycolipid trehalose 6,6' dimycolate (TDM; cord factor) plays a key role in the pathogenesis of TB disease. TDM protects the TB bacilli from macrophage-mediated killing, inhibits effective antigen presentation, and reduces the formation of protective T-cell responses. TDM promotes initiation of granuloma formation and likely plays a role in caseation. Furthermore, TDM may contribute to the development of post primary disease. Receptors for TDM were recently described and are expected to contribute to our knowledge of the molecular pathogenesis of TB disease. In this manner, understanding TDM may prove promising towards development of targeted TB therapeutics to limit clinical pathologies.

Effects of some natural immunomodulatory compounds in combination with thalidomide on survival rate and tumor size in fibrosarcoma-bearing mice

PURPOSE

Despite significant advances have been achieved in cancer therapy, response to conventional treatments like surgery, radiotherapy and chemotherapy varies among individuals. Immunotherapy is known to be an effective strategy for patients who are resistant to the currently available interventions.

METHODS

Ninety-six male Balb/c mice (aged 6-8 weeks) were selected and divided into twelve groups of eight. Approximately, 1&times;10(6)of WEHI-164 cells were injected to each mouse for tumor genesis. Five immunotherapy treatments were considered in this study, including Heat Shock Proteins (HSP), Bacillus Calmette-Gu&eacute;rin (BCG), Bifidobacterium, Immuno-Modulator Drug (IMOD) and Thalidomide. After tumor formation, the groups were treated with one or more of these therapies. Tumor size and survival rate was regularly monitored.

RESULTS

Depending on the treatment group, tumor sizes were different. In some groups, combined treatments demonstrated more inhibitory effects on tumor growth rate. The mice in group (IMOD+ Thalidomide) had the lowest survival rate but group (BCG+ HSP+ Thalidomide) survived until the end of the experiment.

CONCLUSION

The (HSP+ BCG+ Thalidomide) group exhibited satisfactory outcomes and two third of the mice in this group went into complete remission. Some combination therapies in test groups had significant impacts on survival and tumor growth rate.

Self and nonself recognition through C-type lectin receptor, Mincle

Mincle (also called as Clec4e or Clecsf9) is a C-type lectin receptor expressed in activated macrophages. Recently, we have reported that Mincle transduces the activation signals through ITAM-containing adaptor protein, FcRγ and induces the secretion of inflammatory cytokines. Furthermore, we and other groups have identified that Mincle recognizes a wide variety of ligands such as damaged cells, fungus, yeast and mycobacteria. These results indicate that Mincle acts as a multi-task danger receptor for both self and nonself ligands. This review summarizes the recent discoveries about the ligands and immunological roles of Mincle.

Mechanism responsible for the antitumor effect of BCG-CWS using the LEEL method in a mouse bladder cancer model

We previously reported on the development of a water soluble formulation of the cell wall skeleton of BCG (BCG-CWS), a major immune active center of BCG, by encapsulating it into a nanoparticle (CWS-NP). The CWS-NP allowed us to clarify the machinery associated with the BCG mediated anti-bladder tumor effect, especially the roles of bladder cancer cells and dendritic cells (DCs) in the initial step, which remains poorly understood. We show herein that the internalization of BCG-CWS by bladder cancer cells, but not DCs, is indispensable for the induction of an antitumor effect against bladder cancer. Tumor growth was significantly inhibited in mice that had been inoculated with mouse bladder cancer (MBT-2) cells containing internalized BCG-CWS. On the other hand, the internalization of BCG-CWS by DCs had only a minor effect on inducing an antitumor effect against MBT-2 tumors. This was clarified for the first time by using the CWS-NP. This finding provides insights into our understanding of the role of bladder cancer cells and DCs in BCG therapy against bladder cancer.

Vizantin inhibits endotoxin-mediated immune responses via the TLR 4/MD-2 complex

Vizantin has immunostimulating properties and anticancer activity. In this study, we investigated the molecular mechanism of immune activation by vizantin. THP-1 cells treated with small interfering RNA for TLR-4 abolished vizantin-induced macrophage activation processes such as chemokine release. In addition, compared with wild-type mice, the release of MIP-1β induced by vizantin in vivo was significantly decreased in TLR-4 knockout mice, but not in TLR-2 knockout mice. Vizantin induced the release of IL-8 when HEK293T cells were transiently cotransfected with TLR-4 and MD-2, but not when they were transfected with TLR-4 or MD-2 alone or with TLR-2 or TLR-2/MD-2. A dipyrromethene boron difluoride-conjugated vizantin colocalized with TLR-4/MD-2, but not with TLR-4 or MD-2 alone. A pull-down assay with vizantin-coated magnetic beads showed that vizantin bound to TLR-4/MD-2 in extracts from HEK293T cells expressing both TLR-4 and MD-2. Furthermore, vizantin blocked the LPS-induced release of TNF-α and IL-1β and inhibited death in mice. We also performed in silico docking simulation analysis of vizantin and MD-2 based on the structure of MD-2 complexed with the LPS antagonist E5564; the results suggested that vizantin could bind to the active pocket of MD-2. Our observations show that vizantin specifically binds to the TLR-4/MD-2 complex and that the vizantin receptor is identical to the LPS receptor. We conclude that vizantin could be an effective adjuvant and a therapeutic agent in the treatment of infectious diseases and the endotoxin shock caused by LPS.

Synergistic effects of glycated chitosan with high-intensity focused ultrasound on suppression of metastases in a syngeneic breast tumor model

Stimulation of the host immune system is crucial in cancer treatment. In particular, nonspecific immunotherapies, when combined with other traditional therapies such as radiation and chemotherapy, may induce immunity against primary and metastatic tumors. In this study, we demonstrate that a novel, non-toxic immunoadjuvant, glycated chitosan (GC), decreases the motility and invasion of mammalian breast cancer cells in vitro and in vivo. Lung metastatic ratios were reduced in 4T1 tumor-bearing mice when intratumoral GC injection was combined with local high-intensity focused ultrasound (HIFU) treatment. We postulate that this treatment modality stimulates the host immune system to combat cancer cells, as macrophage accumulation in tumor lesions was detected after GC-HIFU treatment. In addition, plasma collected from GC-HIFU-treated tumor-bearing mice exhibited tumor-specific cytotoxicity. We also investigated the effect of GC on epithelial–mesenchymal transition-related markers. Our results showed that GC decreased the expression of Twist-1 and Slug, proto-oncogenes commonly implicated in metastasis. Epithelial-cadherin, which is regulated by these genes, was also upregulated. Taken together, our current data suggest that GC alone can reduce cancer cell motility and invasion, whereas GC-HIFU treatment can induce immune responses to suppress tumor metastasis in vivo.

Natural products and synthetic compounds as immunomodulators

Research on immunomodulation by natural products or synthetic derivatives is of key interest for anti-infective therapy for a number of reasons. Many plant remedies well-known in traditional medicine or refined natural products in clinical use exert their anti-infective effects not only (if at all) by directly affecting the pathogen. At least part of their effect is indirect, by stimulating natural and adaptive defense mechanisms of the host. These findings have now given many empirical therapies a rationale, scientific basis and thereby a means for 'intelligent' improvement. In discovering the molecular mechanisms by which known remedies exert their effects, chosen elements further down the 'chain of command' might be synthesized and applied directly for more rapid and selective cure, omitting unwanted side effects. The direct use of recombinant cytokines, often in combination with antibiotics, is one consequence of this rationale.

Should a Toll-like receptor 4 (TLR-4) agonist or antagonist be designed to treat cancer? TLR-4: its expression and effects in the ten most common cancers

Toll-like receptor 4 (TLR-4) is well known for its host innate immunity. Despite the fact that TLR-4 activation confers antitumor responses; emerging evidence suggests that TLR-4 is associated with tumor development and progression. It is now clear that overactivation of TLR-4, through various immune mediators, may cause immune response dysfunction, resulting in tumorigenesis. Different cancers could have different extents of TLR-4 involvement during tumorigenesis or tumor progression. In this review, we focus on infection- and inflammation-related TLR-4 activation in noncancer and cancer cells, as well as on the current evidence about the role of TLR-4 in ten of the most common cancers, viz, head and neck cancer, lung cancer, gastrointestinal cancer, liver cancer, pancreatic cancer, skin cancer, breast cancer, ovarian cancer, cervical cancer, and prostate cancer.

Antitumor effect of new multiple antigen peptide based on HLA-A0201-restricted CTL epitopes of human telomerase reverse transcriptase (hTERT)

The development of peptide vaccines aimed at enhancing immune responses against tumor cells is becoming a promising area of research. Human telomerase reverse transcriptase (hTERT) is an ideal universal target for novel immunotherapies against cancers. The aim of this work was to verify whether the multiple antigen peptides (MAP) based on HLA-A0201-restricted CTL epitopes of hTERT could trigger a better and more sustained CTL response and kill multiple types of hTERT-positive tumor cells in vitro and ex vivo. Dendritic cells (DC) pulsed with MAP based on HLA-A0201-restricted CTL epitopes of hTERT (hTERT-540, hTERT-865 and hTERT-572Y) were used to evaluate immune responses against various tumors and were compared to the immune responses resulting from the use of corresponding linear epitopes and a recombinant adenovirus-hTERT vector. A 4-h standard (51) Cr-release assay and an ELISPOT assay were used for both in vitro and ex vivo analyses. Results demonstrated that targeting hTERT with an adenovector was the most effective way to stimulate a CD8(+) T cell response. When compared with linear hTERT epitopes, MAP could trigger stronger hTERT-specific CTL responses against tumor cells expressing hTERT and HLA-A0201. In contrast, the activated CTL could neither kill the hTERT-negative tumor cells, such as U2OS cells, nor kill HLA-A0201 negative cells, such as HepG2 cells. We also found that these peptide-specific CTL could not kill autologous lymphocytes and DC with low telomerase activity. Our results indicate that MAP from hTERT can be exploited for cancer immunotherapy.

Sensing necrotic cells

Multicellular organisms have developed ways to recognize potentially life-threatening events (danger signals). Classically, danger signals have been defined as exogenous, pathogen-associated molecular patterns (PAMPs) such as bacterial cell wall components (e.g., lipopolysaccharide and peptideglycan) or viral DNA/RNA. PAMPs interact with dedicated receptors on immune cells, so-called pattern recognition receptors (PRRs) and activate immune systems. A well-known family of PRRs is the toll-like receptors (TLRs) in which each member recognizes a specific set of PAMPs. However, not only exogenous pathogens but also several endogenous molecules released from necrotic cells (damaged self) also activate immune systems. These endogenous adjuvants are called damage-associated molecular patterns (DAMPs). It has been reported that high-mobility group box 1 protein (HMGB1), uric acid, heat shock proteins (HSPs) and nucleotides act as endogenous adjuvants. DAMPs are recognized by specific receptors (danger receptors) expressed mainly on antigen-presenting cells such as dendritic cells and macrophages and induce cell maturation and the production of inflammatory cytokines by activating the NF-kB pathway. In this chapter, we will review danger signals released from necrotic cells and its recognition receptors.

Bacterial immunotherapy of gastrointestinal tumors

Background

Cancer immunotherapy using bacteria dates back over 150 years. The deeper understanding on how the immune system interferes with the tumor microenvironment has led to the re-emergence of bacteria or their related products in immunotherapeutic concepts. In this review, we discuss recent approaches on experimental bacteriolytic therapy, emphasizing the specific interplay between bacteria, immune cells and tumor cells to break the tumor-induced tolerance.

Results

Experimental research during the last decades demonstrated beneficial but also adverse influence of bacteria on tumor growth. There is a strong correlation between chronic infections and tumor incidence. However, acute bacterial infections have favourable effects on tumor growth often contributing to complete remission. Tumor regression is usually attributable to both direct tumor cell killing (via apoptosis and/or necrosis, depending on the applied bacteria) and indirect immune stimulation. This includes (I) elimination of immunosuppressive immune cells (i.e. tumor-associated macrophages, myeloid-derived suppressor, and regulatory T cells), (II) suppression of Th2-directed cytokine secretion (TGFα, IL10), (III) providing a pro-inflammatory micro-milieu (tumor infiltrating neutrophils) and (IV) supporting the influx of cytotoxic T cells into tumors. This finally forces the development of an immunological memory and may provide long-term protection against cancer.

Conclusion

Immunotherapy using bacteria is still a double-edged sword. Experiences from the last years have substantially contributed to when bacteria and defined components thereof might be integrated into immunotherapeutic concepts. Attempts in transferring this approach into the clinics are on their way.

Anti-protease and immunomodulatory activities of bacteria associated with Caribbean sponges

Marine sponges and their associated bacteria have been proven to be a rich source of novel secondary metabolites with therapeutic usefulness in cancer, infection, and autoimmunity. In this study, 79 strains belonging to 20 genera of the order Actinomycetales and seven strains belonging to two genera of the order Sphingomonadales were cultivated from 18 different Caribbean sponges and identified by 16S rRNA gene sequencing. Seven of these strains are likely to represent novel species. Crude extracts from selected strains were found to exhibit protease inhibition against cathepsins B and L, rhodesain, and falcipain-2 as well as immunomodulatory activities such as induction of cytokine release by human peripheral blood mononuclear cells. These results highlight the significance of marine sponge-associated bacteria to produce bioactive secondary metabolites with therapeutic potential in the treatment of infectious diseases and disorders of the immune system.

TLR2-dependent induction of IL-10 and Foxp3+ CD25+ CD4+ regulatory T cells prevents effective anti-tumor immunity induced by Pam2 lipopeptides in vivo

16 S-[2,3-bis(palmitoyl)propyl]cysteine (Pam2) lipopeptides act as toll-like receptor (TLR)2/6 ligands and activate natural killer (NK) cells and dendritic cells (DCs) to produce inflammatory cytokines and cytotoxic NK activity in vitro. However, in this study, we found that systemic injection of Pam2 lipopeptides was not effective for the suppression of NK-sensitive B16 melanomas in vivo. When we investigated the immune suppressive mechanisms, systemic injection of Pam2 lipopeptides induced IL-10 in a TLR2-dependent manner. The Pam2 lipopeptides increased the frequencies of Foxp3⁺CD4⁺ regulatory T (T reg) cells in a TLR2- and IL-10- dependent manner. The T reg cells from Pam2-lipopeptide injected mice maintained suppressor activity. Pam2 lipopeptides, plus the depletion of T reg with an anti-CD25 monoclonal antibody, improved tumor growth compared with Pam2 lipopeptides alone. In conclusion, our data suggested that systemic treatment of Pam2 lipopeptides promoted IL-10 production and T reg function, which suppressed the effective induction of anti-tumor immunity in vivo. It is necessary to develop an adjuvant that does not promote IL-10 and T reg function in vivo for the future establishment of an anti-cancer vaccine.

Mycobacterial cell-wall skeleton as a universal vaccine vehicle for antigen conjugation

Mycobacterial cell-wall skeleton (CWS) is an immunoactive and biodegradable particulate adjuvant and has been used for immunotherapy in patients with cancer. The CWS of Mycobacterium bovis bacillus Calmette-Guérin (BCG-CWS) was studied as a universal vaccine vehicle for antigen conjugation, to develop potentially effective and safe vaccines. Here, we describe experiments in which protein antigens, such as keyhole limpet haemocyanin (KLH), ovalbumin (OVA) and bovine serum albumin (BSA) were highly efficiently coupled to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS)-activated carboxyl groups of BCG-CWS, and tested the immunogenicity of OVA-conjugated BCG-CWS vaccine. We found that a strong immune response was induced in mice immunised with OVA-conjugated BCG-CWS, which was similar to the enhancement of the immune responses in mice immunised with OVA and complete Freund's adjuvant. Covalent conjugation of OVA to BCG-CWS was essential for Th1-skewed immune responses, with prominent expression of IFN-γ. Furthermore, antigen-conjugated BCG-CWS vaccine is simple to manufacture, safe, and easy to use. Our results suggest that mycobacterial CWS as a universal vaccine vehicle for conjugation of a wide variety of antigens constitutes a breakthrough for development of the most promising vaccines for infections, allergic diseases, and cancer.

A synthetic analogue of phosphatidylinositol mannoside is an efficient adjuvant

We recently described the synthesis of an ether linked analogue of phosphatidylinositol dimannoside (PIM(2)ME). In the current study, PIM(2)ME was found to significantly enhance the release of the key Th1 cytokine interleukin-12 (IL-12) by dendritic cells (DCs) of naive mice in vitro, but not interleukin-10 (IL-10). Based on this result, it was hypothesized that PIM(2)ME would be an effective adjuvant for cell-mediated immune responses. Injections of PIM(2)ME alone did not lead to weight loss and did not have toxic side effects, based on biomarkers of toxicity in serum,demonstrating that the compound induced no apparent adverse side effects. Mice were vaccinated with the core antigens of the hepatitis C virus by itself or with three different adjuvants, namely PIM(2)ME, a commercial preparation of monophosphoryl lipid A (MPL) or a preparation of aluminium hydroxide gel (alum). A control group of animals received the antigen only with no adjuvants. Immune responses to the Hepatitis C viral antigens were monitored by measuring antigen-specific production of interferon-gamma (IFN-gamma), the p40 subunit of interleukin-12 (IL-12) and interleukin-10 (IL-10) to assess cell-mediated immune responses. Vaccination of mice with Hepatitis C viral antigens with the adjuvant PIM(2)ME led to a significant increase in cell-mediated immune responses (IFN-gamma and IL-12). Injection of Hepatitis C viral antigens in alum led to no enhancement of the cell-mediated immune response. We conclude that PIM(2)ME is an efficacious adjuvant for enhancing cell-mediated immunity, and induces no observable adverse effects.

Gerbu adjuvant modulates the immune response and thus the course of infection in C56BL/6 mice immunised with Echinococcus multilocularis rec14-3-3 protein

Vaccination with Echinococcus multilocularis 14-3-3 protein can protect mice against primary E. multilocularis infection. The present study investigated the efficacy and efficiency of the adjuvant muramyl dipeptide Gerbu, alone or together with recombinant 14-3-3 protein, to modulate the course of secondary E. multilocularis infection in C56BL/6 mice. The application of Gerbu alone already resulted in a parasite weight reduction when compared with infected control mice, while rec14-3-3 did not add to this effect. Immunological parameters were concurrently assessed with a mixed cell reaction including bone marrow-derived dendritic cells (BMDCs) together with lymph node cells from mice with or without immunisation and/or infection. While mice having received Gerbu adjuvant were found to highly proliferate in response to co-cultivation with 14-3-3-stimulated bone marrow dendritic cells, a sensitisation of BMDCs with vesicle fluid (VF) antigen lead to a striking decrease of the lymphoproliferative response in comparison to that of control mice, raising the hypothesis that immunosuppressive components may be part of this VF-antigen. Anti-14-3-3 antibody production was only found in those mice that had been previously 14-3-3-immunised, whereas all other only-infected mice failed to produce such antibodies. Conclusively, Gerbu adjuvant appears to directly generate a non-specific immune response that contributes to the control of the metacestode growth, putatively in association with a BMDC activity suppressed by components of the VF-antigen.

Direct recognition of the mycobacterial glycolipid, trehalose dimycolate, by C-type lectin Mincle

Tuberculosis remains a fatal disease caused by Mycobacterium tuberculosis, which contains various unique components that affect the host immune system. Trehalose-6,6′-dimycolate (TDM; also called cord factor) is a mycobacterial cell wall glycolipid that is the most studied immunostimulatory component of M. tuberculosis. Despite five decades of research on TDM, its host receptor has not been clearly identified. Here, we demonstrate that macrophage inducible C-type lectin (Mincle) is an essential receptor for TDM. Heat-killed mycobacteria activated Mincle-expressing cells, but the activity was lost upon delipidation of the bacteria; analysis of the lipid extracts identified TDM as a Mincle ligand. TDM activated macrophages to produce inflammatory cytokines and nitric oxide, which are completely suppressed in Mincle-deficient macrophages. In vivo TDM administration induced a robust elevation of inflammatory cytokines in sera and characteristic lung inflammation, such as granuloma formation. However, no TDM-induced lung granuloma was formed in Mincle-deficient mice. Whole mycobacteria were able to activate macrophages even in MyD88-deficient background, but the activation was significantly diminished in Mincle/MyD88 double-deficient macrophages. These results demonstrate that Mincle is an essential receptor for the mycobacterial glycolipid, TDM.

Advances in saponin-based adjuvants

Saponins are natural glycosides of steroid or triterpene which exhibited many different biological and pharmacological activities. Notably, saponins can also activate the mammalian immune system, which have led to significant interest in their potential as vaccine adjuvants. The most widely used saponin-based adjuvants are Quil A and its derivatives QS-21, isolated from the bark of Quillaja saponaria Molina, which have been evaluated in numerous clinical trials. Their unique capacity to stimulate both the Th1 immune response and the production of cytotoxic T-lymphocytes (CTLs) against exogenous antigens makes them ideal for use in subunit vaccines and vaccines directed against intracellular pathogens as well as for therapeutic cancer vaccines. However, Quillaja saponins have serious drawbacks such as high toxicity, undesirable haemolytic effect and instability in aqueous phase, which limits their use as adjuvant in vaccination. It has driven much research for saponin-based adjuvant from other kinds of natural products. This review will summarize the current advances concerning adjuvant effects of different kinds of saponins. The structure-activity relationship of saponin adjuvants will also be discussed in the light of recent findings. It is hoped that the information collated here will provide the reader with information regarding the adjuvant potential applications of saponins and stimulate further research into these compounds.