Tumour suppression induced by the macrophage activating lipopeptide MALP-2 in an ultrasound guided pancreatic carcinoma mouse model

Innovative Experimental Ultrasound and US-Related Techniques Using the Murine Model in Pancreatic Ductal Adenocarcinoma: A Systematic Review

Pancreatic ductal adenocarcinoma (PDAC) is a cancer with one of the highest mortality rates in the world. Several studies have been conductedusing preclinical experiments in mice to find new therapeutic strategies. Experimental ultrasound, in expert hands, is a safe, multifaceted, and relatively not-expensive device that helps researchers in several ways. In this systematic review, we propose a summary of the applications of ultrasonography in a preclinical mouse model of PDAC. Eighty-eight studies met our inclusion criteria. The included studies could be divided into seven main topics: ultrasound in pancreatic cancer diagnosis and progression (n: 21); dynamic contrast-enhanced ultrasound (DCE-US) (n: 5); microbubble ultra-sound-mediated drug delivery; focused ultrasound (n: 23); sonodynamic therapy (SDT) (n: 7); harmonic motion elastography (HME) and shear wave elastography (SWE) (n: 6); ultrasound-guided procedures (n: 9). In six cases, the articles fit into two or more sections. In conclusion, ultrasound can be a really useful, eclectic, and ductile tool in different diagnostic areas, not only regarding diagnosis but also in therapy, pharmacological and interventional treatment, and follow-up. All these multiple possibilities of use certainly represent a good starting point for the effective and wide use of murine ultrasonography in the study and comprehensive evaluation of pancreatic cancer.

Toll-like receptor-guided therapeutic intervention of human cancers: molecular and immunological perspectives

Toll-like receptors (TLRs) serve as the body's first line of defense, recognizing both pathogen-expressed molecules and host-derived molecules released from damaged or dying cells. The wide distribution of different cell types, ranging from epithelial to immune cells, highlights the crucial roles of TLRs in linking innate and adaptive immunity. Upon stimulation, TLRs binding mediates the expression of several adapter proteins and downstream kinases, that lead to the induction of several other signaling molecules such as key pro-inflammatory mediators. Indeed, extraordinary progress in immunobiological research has suggested that TLRs could represent promising targets for the therapeutic intervention of inflammation-associated diseases, autoimmune diseases, microbial infections as well as human cancers. So far, for the prevention and possible treatment of inflammatory diseases, various TLR antagonists/inhibitors have shown to be efficacious at several stages from pre-clinical evaluation to clinical trials. Therefore, the fascinating role of TLRs in modulating the human immune responses at innate as well as adaptive levels directed the scientists to opt for these immune sensor proteins as suitable targets for developing chemotherapeutics and immunotherapeutics against cancer. Hitherto, several TLR-targeting small molecules (e.g., Pam3CSK4, Poly (I:C), Poly (A:U)), chemical compounds, phytocompounds (e.g., Curcumin), peptides, and antibodies have been found to confer protection against several types of cancers. However, administration of inappropriate doses of such TLR-modulating therapeutics or a wrong infusion administration is reported to induce detrimental outcomes. This review summarizes the current findings on the molecular and structural biology of TLRs and gives an overview of the potency and promises of TLR-directed therapeutic strategies against cancers by discussing the findings from established and pipeline discoveries.

Pushing the envelope: Immune mechanism and application landscape of macrophage-activating lipopeptide-2

Mycoplasma fermentans can cause respiratory diseases, arthritis, genitourinary tract infections, and chronic fatigue syndrome and have been linked to the development of the human immunodeficiency virus. Because mycoplasma lacks a cell wall, its outer membrane lipoproteins are one of the main factors that induce inflammation in the organism and contribute to disease development. Macrophage-activating lipopeptide-2 (MALP-2) modulates the inflammatory response of monocytes/macrophages in a bidirectional fashion, indirectly enhances the cytotoxicity of NK cells, promotes oxidative bursts in neutrophils, upregulates surface markers on lymphocytes, enhances antigen presentation on dendritic cells and induces immune inflammatory responses in sebocytes and mesenchymal cells. MALP-2 is a promising vaccine adjuvant for this application. It also promotes vascular healing and regeneration, accelerates wound and bone healing, suppresses tumors and metastasis, and reduces lung infections and inflammation. MALP-2 has a simple structure, is easy to synthesize, and has promising prospects for clinical application. Therefore, this paper reviews the mechanisms of MALP-2 activation in immune cells, focusing on the application of MALP-2 in animals/humans to provide a basis for the study of pathogenesis in Mycoplasma fermentans and the translation of MALP-2 into clinical applications.

The Role of Toll-like Receptors (TLRs) Mediated Inflammation in Pancreatic Cancer Pathophysiology

Pancreatic cancer (PC) is one of the most lethal forms of cancer, characterized by its aggressiveness and metastatic potential. Despite significant improvements in PC treatment and management, the complexity of the molecular pathways underlying its development has severely limited the available therapeutic opportunities. Toll-like receptors (TLRs) play a pivotal role in inflammation and immune response, as they are involved in pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs). Activation of TLRs initiates a signaling cascade, which in turn, leads to the transcription of several genes involved in inflammation and anti-microbial defense. TLRs are also deregulated in several cancers and can be used as prognostic markers and potential targets for cancer-targeted therapy. In this review we discuss the current knowledge about the role of TLRs in PC progression, focusing on the available TLRs-targeting compounds and their possible use in PC therapy.

Cathelicidins Modulate TLR-Activation and Inflammation

Cathelicidins are short cationic peptides that are part of the innate immune system. At first, these peptides were studied mostly for their direct antimicrobial killing capacity, but nowadays they are more and more appreciated for their immunomodulatory functions. In this review, we will provide a comprehensive overview of the various effects cathelicidins have on the detection of damage- and microbe-associated molecular patterns, with a special focus on their effects on Toll-like receptor (TLR) activation. We review the available literature based on TLR ligand types, which can roughly be divided into lipidic ligands, such as LPS and lipoproteins, and nucleic-acid ligands, such as RNA and DNA. For both ligand types, we describe how direct cathelicidin-ligand interactions influence TLR activation, by for instance altering ligand stability, cellular uptake and receptor interaction. In addition, we will review the more indirect mechanisms by which cathelicidins affect downstream TLR-signaling. To place all this information in a broader context, we discuss how these cathelicidin-mediated effects can have an impact on how the host responds to infectious organisms as well as how these effects play a role in the exacerbation of inflammation in auto-immune diseases. Finally, we discuss how these immunomodulatory activities can be exploited in vaccine development and cancer therapies.

Toll-like Receptors from the Perspective of Cancer Treatment

Toll-like receptors (TLRs) represent a family of pattern recognition receptors that recognize certain pathogen-associated molecular patterns and damage-associated molecular patterns. TLRs are highly interesting to researchers including immunologists because of the involvement in various diseases including cancers, allergies, autoimmunity, infections, and inflammation. After ligand engagement, TLRs trigger multiple signaling pathways involving nuclear factor-κB (NF-κB), interferon-regulatory factors (IRFs), and mitogen-activated protein kinases (MAPKs) for the production of various cytokines that play an important role in diseases like cancer. TLR activation in immune as well as cancer cells may prevent the formation and growth of a tumor. Nonetheless, under certain conditions, either hyperactivation or hypoactivation of TLRs supports the survival and metastasis of a tumor. Therefore, the design of TLR-targeting agonists as well as antagonists is a promising immunotherapeutic approach to cancer. In this review, we mainly describe TLRs, their involvement in cancer, and their promising properties for anticancer drug discovery.

TLR1/2 ligand enhances antitumor efficacy of CTLA-4 blockade by increasing intratumoral Treg depletion

Immune checkpoint inhibitors such as anti-CTLA-4 antibody are widely accepted therapeutic options for many cancers, but there is still a considerable gap in achieving their full potential. We explored the potential of activating the innate and adaptive immune pathways together to improve tumor reduction and survival outcomes. We treated a mouse model of melanoma with intratumoral injections of Toll-like receptor 1/2 (TLR1/2) ligand Pam3CSK4 plus i.p. injections of anti-CTLA-4 antibody. This combination treatment enhanced antitumor immune responses both qualitatively and quantitatively over anti-CTLA-4 alone, and its efficacy depended on CD4 T cells, CD8 T cells, Fcγ receptor IV, and macrophages. Interestingly, our results suggest a unique mechanism by which TLR1/2 ligand increased Fcγ receptor IV expression on macrophages, leading to antibody-dependent macrophage-mediated depletion of regulatory T cells in the tumor microenvironment and increasing efficacy of anti-CTLA-4 antibody in the combination treatment. This mechanism could be harnessed to modulate the clinical outcome of anti-CTLA-4 antibodies and possibly other antibody-based immunotherapies.

In vivo cancer vaccination: Which dendritic cells to target and how?

The field of cancer immunotherapy has been revolutionized with the use of immune checkpoint blockade antibodies such as anti-programmed cell death 1 protein (PD-1) and chimeric antigen receptor T cells. Significant clinical benefits are observed in different cancer types with these treatments. While considerable efforts are made in augmenting tumor-specific T cell responses with these therapies, other immunotherapies that actively stimulate endogenous anti-tumor T cells and generating long-term memory have received less attention. Given the high cost of cancer immunotherapies especially with chimeric antigen receptor T cells, not many patients will have access to such treatments. The next-generation of cancer immunotherapy could entail in vivo cancer vaccination to activate both the innate and adaptive anti-tumor responses. This could potentially be achieved via in vivo targeting of dendritic cells which are an indispensable link between the innate and adaptive immunities. Dendritic cells highly expressed toll-like receptors for recognizing and eliminating pathogens. Synthetic toll-like receptors agonists could be synthesized at a low cost and have shown promise in preclinical and clinical trials. As different subsets of human dendritic cells exist in the immune system, activation with different toll-like receptor agonists could exert profound effects on the quality and magnitude of anti-tumor T cell responses. Here, we reviewed the different subsets of human dendritic cells. Using published preclinical and clinical cancers studies available on PubMed, we discussed the use of clinically approved and emerging toll-like receptor agonists to activate dendritic cells in vivo for cancer immunotherapy. Finally, we searched www.clinicaltrials.gov and summarized the active cancer trials evaluating toll-like receptor agonists as an adjuvant.

Natural killer cells and their therapeutic role in pancreatic cancer: A systematic review

Pancreatic cancer is among the three deadliest cancers worldwide with the lowest 5-year survival of all cancers. Despite all efforts, therapeutic improvements have barely been made over the last decade. Even recent highly promising targeted and immunotherapeutic approaches did not live up to their expectations. Therefore, other horizons have to be explored. Natural Killer (NK) cells are gaining more and more interest as a highly attractive target for cancer immunotherapies, both as pharmaceutical target and for cell therapies. In this systematic review we summarise the pathophysiological adaptions of NK cells in pancreatic cancer and highlight possible (future) therapeutic NK cell-related targets. Furthermore, an extensive overview of recent therapeutic approaches with an effect on NK cells is given, including cytokine-based, viro- and bacteriotherapy and cell therapy. We also discuss ongoing clinical trials that might influence NK cells. In conclusion, although several issues regarding NK cells in pancreatic cancer remain unsolved and need further investigation, extensive evidence is already provided that support NK cell oriented approaches in pancreatic cancer.

Type I Interferon-Independent Dendritic Cell Priming and Antitumor T Cell Activation Induced by a Mycoplasma fermentans Lipopeptide

Mycoplasma fermentans-derived diacylated lipoprotein M161Ag (MALP404) is recognized by human/mouse toll-like receptor (TLR) 2/TLR6. Short proteolytic products including macrophage-activating lipopeptide 2 (MALP2) have been utilized as antitumor immune-enhancing adjuvants. We have chemically synthesized a short form of MALP2 named MALP2s (S-[2,3-bis(palmitoyloxy)propyl]-CGNNDE). MALP2 and MALP2s provoke natural killer (NK) cell activation in vitro but only poorly induce tumor regression using in vivo mouse models loading NK-sensitive tumors. Here, we identified the functional mechanism of MALP2s on dendritic cell (DC)-priming and cytotoxic T lymphocyte (CTL)-dependent tumor eradication using CTL-sensitive tumor-implant models EG7 and B16-OVA. Programmed death ligand-1 (PD-L1) blockade therapy in combination with MALP2s + ovalbumin (OVA) showed a significant additive effect on tumor growth suppression. MALP2s increased co-stimulators CD80/86 and CD40, which were totally MyD88-dependent, with no participation of toll-IL-1R homology domain-containing adaptor molecule-1 or type I interferon signaling in DC priming. MALP2s + OVA consequently augmented proliferation of OVA-specific CTLs in the spleen and at tumor sites. Chemokines and cytolytic factors were upregulated in the tumor. Strikingly, longer duration and reinvigoration of CTLs in spleen and tumors were accomplished by the addition of MALP2s + OVA to α-PD-L1 antibody (Ab) therapy compared to α-PD-L1 Ab monotherapy. Then, tumors regressed better in the MALP2s/OVA combination than in the α-PD-L1 Ab monotherapy. Hence, MALP2s/tumor-associated antigens combined with α-PD-L1 Ab is a good therapeutic strategy in some mouse models. Unfortunately, numerous patients are still resistant to PD-1/PD-L1 blockade, and good DC-priming adjuvants are desired. Cytokine toxicity by MALP2s remains to be settled, which should be improved by chemical modification in future studies.

Myeloid-derived macrophages and secreted HSP90α induce pancreatic ductal adenocarcinoma development

We detected a significant elevation of serum HSP90α levels in pancreatitis patients and even more in pancreatic ductal adenocarcinoma (PDAC) patients. However, there was no significant difference in the serum HSP90α levels between patients with early-stage and late-stage PDAC. To study whether elevation of serum HSP90α levels occurred early during PDAC development, we used LSL-KrasG12D/Pdx1-Cre transgenic mice as a studying model. Elevated serum HSP90α levels were detected before PDAC formation and an extracellular HSP90α (eHSP90α) inhibitor effectively prevented PDAC development. Both serum HSP90α level and pancreatic lesion were suppressed when the mice were administered a CD11b-antagonizing antibody, suggesting that CD11b⁺-myeloid cells were associated with eHSP90α levels and pancreatic carcinogenesis. Consistently, in CD11b-DTR-EGFP transgenic mouse model with CD11b⁺-myeloid cells depletion, serum HSP90α levels were suppressed and Panc-02 cell grafts failed to develop tumors. Macrophages and granulocytes are two common tissue-infiltrating CD11b⁺-myeloid cells. Duplex in situ hybridization assays suggested that macrophages were predominant HSP90α-expressing CD11b⁺-myeloid cells during PDAC development. Immunohistochemical and immunohistofluorescent staining results revealed that HSP90α-expressing cells included not only macrophages but also pancreatic ductal epithelial (PDE) cells. Cell culture studies also indicated that eHSP90α could be produced by macrophages and macrophage-stimulated PDE cells. Macrophages not only secreted significant amount of HSP90α, but also secreted interleukin-6 and interleukin-8 to induce a JAK2−STAT3 signaling axis in PDE cells, stimulating them to express and secrete HSP90α. eHSP90α further promoted cellular epithelial-mesenchymal transition, migration, and invasion in PDE cells. Besides myeloid cells, eHSP90α can be potentially taken as a target to suppress PDAC pathogenesis.

Dysregulation of signaling pathways associated with innate antibacterial immunity in patients with pancreatic cancer

Disorders of innate antibacterial response are of fundamental importance in the development of gastrointestinal cancers, including pancreatic cancer. Multi-regulatory properties of the Toll-like receptors (TLRs) (e.g., regulation of proliferation, the activity of NF-κB, gene transcription of apoptosis proteins, regulation of angiogenesis, HIF-1α protein expression) are used in experimental studies to better understand the pathogenesis of pancreatic cancer, for early diagnosis, and for more effective therapeutic intervention. There are known numerous examples of TLR agonists (e.g., TLR2/5 ligands, TLR6, TLR9) of antitumor effect. The direction of these studies is promising, but a small number of them does not allow for an accurate assessment of the impact of TLR expression disorders, proteins of these signaling pathways, or attempts to block or stimulate them, on the results of treatment of pancreatic cancer patients. It is known, however, that the expression disorders of proteins of innate antibacterial response signaling pathways occur not only in tumor tissue but also in peripheral blood leukocytes of pancreatic cancer patients (e.g., increased expression of TLR4, NOD1, TRAF6), which is one of the most important factors facilitating further tumor development. This review mainly focuses on the genetic aspects of signaling pathway disorders associated with innate antibacterial response in the pathogenesis and diagnosis of pancreatic cancer.

Metastasis regulation by PPARD expression in cancer cells

Peroxisome proliferator-activated receptor-δ (PPARD) is upregulated in many major human cancers, but the role that its expression in cancer cells has in metastasis remains poorly understood. Here, we show that specific PPARD downregulation or genetic deletion of PPARD in cancer cells significantly repressed metastasis in various cancer models in vivo. Mechanistically, PPARD promoted angiogenesis via interleukin 8 in vivo and in vitro. Analysis of transcriptome profiling of HCT116 colon cancer cells with or without genetic deletion of PPARD and gene expression patterns in The Cancer Genome Atlas colorectal adenocarcinoma database identified novel pro-metastatic genes (GJA1, VIM, SPARC, STC1, SNCG) as PPARD targets. PPARD expression in cancer cells drastically affected epithelial-mesenchymal transition, migration, and invasion, further underscoring its necessity for metastasis. Clinically, high PPARD expression in various major human cancers (e.g., colorectal, lung, breast) was associated with significantly reduced metastasis-free survival. Our results demonstrate that PPARD, a druggable protein, is an important molecular target in metastatic cancer.

Clinically feasible approaches to potentiating cancer cell-based immunotherapies

The immune system exerts both tumor-destructive and tumor-protective functions. Mature dendritic cells (DCs), classically activated macrophages (M1), granulocytes, B lymphocytes, aβ and ɣδ T lymphocytes, natural killer T (NKT) cells, and natural killer (NK) cells may be implicated in antitumor immunoprotection. Conversely, tolerogenic DCs, alternatively activated macrophages (M2), myeloid-derived suppressor cells (MDSCs), and regulatory T (Tregs) and B cells (Bregs) are capable of suppressing antitumor immune responses. Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. To potentiate immunotherapy, vaccinations can be combined with other modalities that target different immune pathways. These modalities include 1) genetic or chemical modification of cell-based vaccines; 2) cross-priming TAAs to T cells by engaging dendritic cells; 3) T-cell adoptive therapy; 4) stimulation of cytotoxic inflammation by non-specific immunomodulators, toll-like receptor (TLR) agonists, cytokines, chemokines or hormones; 5) reduction of immunosuppression and/or stimulation of antitumor effector cells using antibodies, small molecules; and 6) various cytoreductive modalities. The authors envisage that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

The TLR-2/TLR-6 agonist macrophage-activating lipopeptide-2 augments human NK cell cytotoxicity when PGE2 production by monocytes is inhibited by a COX-2 blocker

Macrophage-activating lipopeptide-2 (MALP-2) is a potent inducer of proinflammatory cytokine secretion by macrophages, monocytes, and dendritic cells. MALP-2 was reported to be involved in natural killer (NK) cell activation and ensuing tumor rejection. However, the mechanism of MALP-2-mediated NK cell activation remained unclear. Therefore, we studied the effects of MALP-2 on cultured human NK cells. We found that MALP-2 had no direct effect on NK cells. Instead, MALP-2 acted on monocytes and triggered the release of different molecules such as interleukin (IL)-1β, IL-6, IL-10, IL-12, IL-15, interferon gamma-induced protein (IP-10), and prostaglandin (PG)-E2. Our data show that monocyte-derived IP-10 could significantly induce NK cell cytotoxicity as long as the immunosuppression by PGE2 is specifically inhibited by cyclooxygenase (COX)-2 blockade. In summary, our results show that MALP-2-mediated stimulation of monocytes results in the production of several mediators which, depending on the prevailing conditions, affect the activity of NK cells in various ways. Hence, MALP-2 administration with concurrent blocking of COX-2 can be considered as a promising approach in MALP-2-based adjuvant tumor therapies.

Locally applied macrophage-activating lipopeptide-2 (MALP-2) promotes early vascularization of implanted porous polyethylene (Medpor®)

Porous polyethylene (Medpor®) is frequently used in craniofacial reconstructive surgery. Rapid vascularization of the biomaterial crucially contributes to its adequate incorporation without complications. Macrophage-activating lipopeptide-2 (MALP-2) is a toll-like receptor (TLR)-2/6 agonist with pro-angiogenic properties. Herein we analyzed whether local single-shot application of MALP-2 improves the angiogenic host tissue response to Medpor®. Medpor® (3 mm×3 mm×0.25 mm) was implanted into dorsal skinfold chambers of BALB/c mice topically exposed to different MALP-2 doses (0.1 and 0.5 μg) or vehicle (control). The vascularization of the implants and the inflammatory foreign body reaction was analyzed using intravital fluorescence microscopy, histology and immunohistochemistry over 14 days. MALP-2 treatment dose-dependently improved the vascularization of Medpor®, as indicated by a significantly higher functional microvessel density at the border and center of the implants when compared to controls. This was associated with a temporary increase of adherent leukocytes in host tissue venules during the first 3 days after implantation. At day 14, implants in MALP-2-treated chambers were surrounded by granulation tissue, which exhibited a significantly higher density of CD31-positive microvessels and number of F4/80-positive macrophages when compared to controls. Additional biomaterial-free chambers did not show any signs of angiogenesis when treated with MALP-2. This indicates that locally applied MALP-2 effectively stimulates the early vascularization of Medpor® without inducing any local or systemic side effects. Accordingly, this easy approach may further improve the rapid incorporation of this biomaterial at the implantation site.

Pegylated bisacycloxypropylcysteine, a diacylated lipopeptide ligand of TLR6, plays a host-protective role against experimental Leishmania major infection

TLRs recognize pathogen-expressed Ags and elicit host-protective immune response. Although TLR2 forms heterodimers with TLR1 or TLR6, recognizing different ligands, differences in the functions of these heterodimers remain unknown. In this study, we report that in Leishmania major-infected macrophages, the expression of TLR1 and TLR2, but not TLR6, increased; TLR2-TLR2 association increased, but TLR2-TLR6 association diminished. Lentivirus-expressed TLR1-short hairpin RNA (shRNA) or TLR2-shRNA administration reduced, but TLR6-shRNA increased L. major infection in BALB/c mice. Corroboratively, Pam3CSK4 (TLR1-TLR2 ligand) and peptidoglycan (TLR2 ligand) increased L. major infection but reduced TLR9 expression, whereas pegylated bisacycloxypropylcysteine (BPPcysMPEG; TLR2-TLR6 ligand) reduced L. major number in L. major-infected macrophages, accompanied by increased TLR9 expression, higher IL-12 production, and inducible NO synthase expression. Whereas MyD88, Toll/IL-1R adaptor protein, and TNFR-α-associated factor 6 recruitments to TLR2 were not different in Pam3CSK4-, peptidoglycan-, or BPPcysMPEG-treated macrophages, only BPPcysMPEG enhanced p38MAPK and activating transcription factor 2 activation. BPPcysMPEG conferred antileishmanial functions to L. major-infected BALB/c-derived T cells in a macrophage-T cell coculture and in BALB/c mice; the protection was TLR6 dependent and IL-12 dependent, and it was accompanied by reduced regulatory T cell number. BPPcysMPEG administration during the priming with fixed L. major protected BALB/c mice against challenge L. major infection; the protection was accompanied by low IL-4 and IL-10, but high IFN-γ productions and reduced regulatory T cells. Thus, BPPcysMPEG, a novel diacylated lipopeptide ligand for TLR2-TLR6 heterodimer, induces IL-12-dependent, inducible NO synthase-dependent, T-reg-sensitive antileishmanial protection. The data reveal a novel dimerization partner-dependent duality in TLR2 function.

Systemic injection of TLR1/2 agonist improves adoptive antigen-specific T cell therapy in glioma-bearing mice

Adoptive immunotherapy is an attractive strategy for glioma treatment. However, some obstacles still need be overcome. In this study, GL261-bearing mice treated with adoptively transferred antigen-specific T cells and systemic injection of bacterial lipoprotein (BLP), a TLR1/2 agonist, got a long-term survival and even immune protection. By analyzing adoptive T cells, it was found that BLP maintained T cell survival, proliferation and anti-tumor efficacy in the brains of tumor-bearing hosts. Moreover, tumor microenvironment was modified by up-regulating IFN-γ-secreting CD8+ T cells and down-regulating MDSC, which might be related with high CXCL10 and low CCL2 expression. In addition, TLR2 deficiency abrogated therapeutic effect with increased MDSC accumulation and decreased IFN-γ-secreting CD8+ T cells in the brains. Thus, the systemic injection of BLP could improve the adoptive T cell therapy by maintaining T cell persistence, modifying the tumor microenvironment and even inducing systemic anti-tumor immunity, which might offer a clinically promising immunotherapeutic strategy for glioma.

Intervention on toll-like receptors in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a devastating disease with pronounced morbidity and a high mortality rate. Currently available treatments lack convincing cost-efficiency determinations and are in most cases not associated with relevant success rate. Experimental stimulation of the immune system in murine PDA models has revealed some promising results. Toll-like receptors (TLRs) are pillars of the immune system that have been linked to several forms of malignancy, including lung, breast and colon cancer. In humans, TLRs are expressed in the pancreatic cancer tissue and in several cancer cell lines, whereas they are not expressed in the normal pancreas. In the present review, we explore the current knowledge concerning the role of different TLRs associated to PDA. Even if almost all known TLRs are expressed in the pancreatic cancer microenvironment, there are only five TLRs suggested as possible therapeutic targets. Most data points at TLR2 and TLR9 as effective tumor markers and agonists could potentially be used as e.g. future adjuvant therapies. The elucidation of the role of TLR3 in PDA is only in its initial phase. The inhibition/blockage of TLR4-related pathways has shown some promising effects, but there are still many steps left before TLR4 inhibitors can be considered as possible therapeutic agents. Finally, TLR7 antagonists seem to be potential candidates for therapy. Independent of their potential in immunotherapies, all existing data indicate that TLRs are strongly involved in the pathophysiology and development of PDA.

Synthesis and immunological evaluation of self-adjuvanting MUC1-macrophage activating lipopeptide 2 conjugate vaccine candidates

The synthesis and immunological evaluation of self-adjuvanting cancer vaccine candidates comprising of mucin 1 (MUC1) (glyco)peptides linked to macrophage activating lipopeptide 2 (MALP2) is described.

The use of dendritic cells for peptide-based vaccination in cancer immunotherapy

Effective antitumor immunity requires the generation and persistence of functional tumor-specific T-cell responses. Among the critical factors that often control these responses is how the antigen is delivered and presented to T cells. The use of peptide-based vaccination has been found to be a promising means to induce antitumor T-cell responses but with limited effects even if the peptide is co-delivered with a potent adjuvant. This limited response could be due to cancer-induced dysfunction in dendritic cells (DC), which play a central role in shaping the quantity and quality of antitumor immunity. Therefore, DC-based peptide delivery of tumor antigen is becoming a potential approach in cancer immunotherapy. In this approach, autologous DC are generated from their precursors in bone marrow or peripheral blood mononuclear cells, loaded with tumor antigen(s) and then infused back to the tumor-bearing host in about 7 days. This DC-based vaccination can act as an antigen delivery vehicle as well as a potent adjuvant, resulting in measurable antitumor immunity in several cancer settings in preclinical and clinical studies. This chapter focuses on DC-based vaccination and how this approach can be more efficacious in cancer immunotherapy.Effective antitumor immunity requires the generation and persistence of functional tumor-specific T-cell responses. Among the critical factors that often control these responses is how the antigen is delivered and presented to T cells. The use of peptide-based vaccination has been found to be a promising means to induce antitumor T-cell responses but with limited effects even if the peptide is co-delivered with a potent adjuvant. This limited response could be due to cancer-induced dysfunction in dendritic cells (DC), which play a central role in shaping the quantity and quality of antitumor immunity. Therefore, DC-based peptide delivery of tumor antigen is becoming a potential approach in cancer immunotherapy. In this approach, autologous DC are generated from their precursors in bone marrow or peripheral blood mononuclear cells, loaded with tumor antigen(s) and then infused back to the tumor-bearing host in about 7 days. This DC-based vaccination can act as an antigen delivery vehicle as well as a potent adjuvant, resulting in measurable antitumor immunity in several cancer settings in preclinical and clinical studies. This chapter focuses on DC-based vaccination and how this approach can be more efficacious in cancer immunotherapy.

Antioxidant N-acetylcysteine attenuates hepatocarcinogenesis by inhibiting ROS/ER stress in TLR2 deficient mouse

Hepatocellular carcinoma (HCC) remains one of the most deadly solid tumor malignancies worldwide. We recently find that the loss of toll-like receptor 2 (TLR2) activities promotes the diethylnitrosamine (DEN) induced hepatocellular carcinogenesis and tumor progression, which associates with an abundant accumulation of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. This finding suggests that the ROS/ER stress plays a role in TLR2 modulated carcinogenesis of HCC. To investigate the mechanism of TLR2 activity defending against hepatocarcinogenesis, the TLR2-deficient mice were treated with or without antioxidant N-acetylcysteine (NAC) before DEN administration. We found that pretreatment of these animals with NAC attenuated carcinogenesis and progression of HCC in the TLR2-deficient mice, declined ROS/ER stress, and alleviated the unfold protein response and inflammatory response in TLR2-deficient liver tissue. Moreover, the NAC treatment significantly reduced the enhanced aggregation of p62 and Mallory-Denk bodies in the DEN-induced HCC liver tissue, suggesting that NAC treatment improves the suppressive autophagic flux in the TLR2-deficient liver. These findings indicate that TLR2 activity defends against hepatocarcinogenesis through diminishing the accumulation of ROS and alleviating ER stress and unfold protein response mediated inflammatory response in the liver.

Toll-like receptor 2/6 agonist macrophage-activating lipopeptide-2 promotes reendothelialization and inhibits neointima formation after vascular injury

OBJECTIVE

Reendothelialization after vascular injury (ie, balloon angioplasty or stent implantation) is clinically extremely relevant to promote vascular healing. We here investigated the therapeutic potential of the toll-like receptor 2/6 agonist macrophage-activating lipopeptide (MALP)-2 on reendothelialization and neointima formation in a murine model of vascular injury.

APPROACH AND RESULTS

The left common carotid artery was electrically injured, and reendothelialization was quantified by Evans blue staining after 3 days. A single injection of MALP-2 (1 or 10 µg, IV) after vascular injury accelerated reendothelialization (P<0.001). Proliferation of endothelial cells at the wound margins determined by 5-ethynyl-2'-deoxyuridine incorporation was significantly higher in MALP-2-treated animals (P<0.05). Furthermore, wire injury-induced neointima formation of the left common carotid artery was completely prevented by a single injection of MALP-2 (10 µg, IV). In vitro, MALP-2 induced proliferation (BrdU incorporation) and closure of an artificial wound of endothelial cells (P<0.05) but not of smooth muscle cells. Protein array and ELISA analysis of isolated primary endothelial cells and ex vivo stimulated carotid segments revealed that MALP-2 stimulated the release of multiple growth factors and cytokines predominantly from endothelial cells. MALP-2 induced a strong activation of the mitogen-activated protein kinase cascade in endothelial cells, which was attenuated in smooth muscle cells. Furthermore, MALP-2 significantly enhanced circulating monocytes and hematopoietic progenitor cells.

CONCLUSIONS

The toll-like receptor 2/6 agonist MALP-2 promotes reendothelialization and inhibits neointima formation after experimental vascular injury via enhanced proliferation and migration of endothelial cells. Thus, MALP-2 represents a novel therapeutic option to accelerate reendothelialization after vascular injury.

TLR agonists: our best frenemy in cancer immunotherapy

Various TLR agonists are currently under investigation in clinical trials for their ability to orchestrate antitumor immunity. The antitumor responses are largely attributed to their aptitude to stimulate APCs such as DCs which in turn, activate tumor-specific T cell responses. However, there is a potential for TLR signaling to occur on cells other than professional APCs that could negate antitumor responses or even worse, promote tumor growth. The impetus for this review is twofold. First, there is accumulating data demonstrating that the engagement of TLRs on different T cell subsets and different cancer types could promote tumor growth or conversely, contribute to antitumor responses. Second, the efficacy of TLR agonists as monotherapies to treat cancer patients has been limited. In this review, we discuss how TLR signaling within different T cell subsets and cancer cells can potentially impact the generation of antitumor responses. Based on evidence from preclinical models and clinical trials, we draw attention to several criteria that we believe must be considered when selecting TLR agonists for developing effective immunotherapeutic strategies against cancer.

Current developments, problems and solutions in the non-surgical treatment of pancreatic cancer

Pancreatic cancer is a common malignant neoplasm of the pancreas with an increasing incidence, a low early diagnostic rate and a fairly poor prognosis. To date, the only curative therapy for pancreatic cancer is surgical resection, but only about 20% patients have this option at the time of diagnosis and the mean 5-year survival rate after resection is only 10%-25%. Therefore, developing new treatments to improve the survival rate has practical significance for patients with this disease. This review deals with a current unmet need in medical oncology: the improvement of the treatment outcome of patients with pancreatic cancer. We summarize and discuss the latest systemic chemotherapy treatments (including adjuvant, neoadjuvant and targeted agents), radiotherapy, interventional therapy and immunotherapy. Besides discussing the current developments, we outline some of the main problems, solutions and prospects in this field.

Recombinant lipidated HPV E7 induces a Th-1-biased immune response and protective immunity against cervical cancer in a mouse model

The E7 oncoprotein of human papillomavirus (HPV) is an ideal target for developing immunotherapeutic strategies against HPV-associated tumors. However, because protein-based immunogens alone are poor elicitors of the cytotoxic T-lymphocyte (CTL) responses, they have been difficult to exploit for therapeutic purposes. In this study, we report that a recombinant lipoprotein consisting of inactive E7 (E7m) biologically linked to a bacterial lipid moiety (rlipo-E7m) induces the maturation of mouse bone marrow-derived dendritic cells through toll-like receptor 2 (TLR2), skews the immune responses toward the Th1 responses and induces E7-specific CTL responses. We further studied the ability of rlipo-E7m to provide protection against a TC-1 tumor cell challenge in an animal model. Mice prophylactically immunized with two 10-µg doses of rlipo-E7m were found to be free of TC-1 tumor growth. Experiments in a therapeutic immunization model showed that the tumor volume in mice receiving a single dose of rlipo-E7m was less than 0.01 cm³ on day 40, whereas the tumor volume in mice treated with rE7m was 2.28±1.21 cm³. The tumor volume of the entire control group was over 3 cm³. In addition, we demonstrated that the CD8+ T cells play a major role in anti-tumor immunity when administration of rlipo-E7m. These results demonstrate that rlipo-E7m could be a promising candidate for treating HPV-associated tumors.

Stimulation of pulmonary immune responses by the TLR2/6 agonist MALP-2 and effect on melanoma metastasis to the lung

Given that metastasized melanoma is a fatal disease in most cases, it is tempting to develop strategies to a priori prevent metastasis. We have stimulated the pulmonary innate immune system by macrophage-activating lipopeptide-2 (MALP-2), a specific agonist at Toll-like receptor (TLR) 2/6, and investigated its impact on experimental melanoma metastasis. In C57BL/6 mice, intratracheal application of MALP-2 induced a profound influx of neutrophils and macrophages into the lung, which peaked after 24 h (sixfold increase) and returned to baseline within 72 h. Further analysis revealed that MALP-2 also markedly induced VCAM-1 expression on pulmonary blood vessels. In vitro experiments demonstrated that this adhesion molecule mediates binding of B16F10 melanoma cells. Furthermore, in vivo or in vitro treatment with MALP-2 did not significantly affect the ability of immune cells to lyse melanoma cells. As a consequence, notwithstanding the profound pulmonary immune response induction and in contrast to conclusions drawn from some previous publications, the net extent of experimental metastasis did not change significantly, regardless of the application regimen of MALP-2 prior to, concomitant with or after tumor cell inoculation. Melanoma cells stably transfected with green fluorescent protein allowed tracking of early events after tumor cell dissemination and showed that MALP-2-mediated TLR2/6 activation did not interfere with pulmonary melanoma cell arrest. Likewise, boosting the immune induction after establishment of metastases did not change the clinical outcome. These unexpected results vividly counsel caution regarding predictions of immunomodulating therapies, as multiple intertwined effects may influence the net outcome.

Structural biology of the Toll-like receptor family

Innate immune receptors respond to common structural patterns in microbial molecules and are called pattern recognition receptors. Toll-like receptors (TLRs) play critical roles in the innate immune system by recognizing microbial lipids, carbohydrates, nucleic acids, and proteins. Precise definition of the ligand "pattern" of TLRs has been difficult to determine primarily owing to a lack of high-resolution structures. Recently, the structures of several TLR-ligand complexes and the intracellular signaling domains have been determined by X-ray crystallography. This new structural information, combined with extensive biochemical and immunological data accumulated over decades, sheds new light on ligand-recognition and -activation mechanisms. In this review, we summarize the TLR structures and discuss proposed ligand-recognition and -activation mechanisms.

Adjuvants for enhancing the immunogenicity of whole tumor cell vaccines

Whole tumor cell lysates can serve as excellent multivalent vaccines for priming tumor-specific CD8(+) and CD4(+) T cells. Whole cell vaccines can be prepared with hypochlorous acid oxidation, UVB-irradiation and repeat cycles of freeze and thaw. One major obstacle to successful immunotherapy is breaking self-tolerance to tumor antigens. Clinically approved adjuvants, including Montanide™ ISA-51 and 720, and keyhole-limpet proteins can be used to enhance tumor cell immunogenicity by stimulating both humoral and cellular anti-tumor responses. Other potential adjuvants, such as Toll-like receptor agonists (e.g., CpG, MPLA and PolyI:C), and cytokines (e.g., granulocyte-macrophage colony stimulating factor), have also been investigated.

Development of an orthotopic human pancreatic cancer xenograft model using ultrasound guided injection of cells

Mice have been employed as models of cancer for over a century, providing significant advances in our understanding of this multifaceted family of diseases. In particular, orthotopic tumor xenograft mouse models are emerging as the preference for cancer research due to increased clinical relevance over subcutaneous mouse models. In the current study, we developed orthotopic pancreatic cancer xenograft models in mice by a minimally invasive method, ultrasound guided injection (USGI) comparable to highly invasive surgical orthotopic injection (SOI) methods. This optimized method prevented injection complications such as recoil of cells through the injection canal or leakage of cells out of the pancreas into the peritoneal cavity. Tumor growth was monitored in vivo and quantified by ultrasound imaging weekly, tumors were also detected by in vivo fluorescence imaging using a tumor targeted molecular probe. The mean tumor volumes for the USGI and SOI models after 2 weeks of tumor growth were 205 mm(3) and 178 mm(3) respectively. By USGI of human pancreatic cancer cell lines, human orthotopic pancreatic cancer xenografts were established. Based on ultrasound imaging, the orthotopic human pancreatic cancer xenograft take rate was 100% for both human pancreatic cancer cell lines used, MiaPaCa-2 and Su86.86, with mean tumor volumes of 28 mm(3)and 30 mm(3). We demonstrated that this USGI method is feasible, reproducible, facile, minimally invasive and improved compared to the highly-invasive SOI method for establishing orthotopic pancreatic tumor xenograft models suitable for molecular imaging.

TLR1/TLR2 agonist induces tumor regression by reciprocal modulation of effector and regulatory T cells

Using TLR agonists in cancer treatment can have either beneficial or detrimental effects. Therefore, it is important to determine their effect on the tumor growth and understand the underlying mechanisms in animal tumor models. In this study, we report a general immunotherapeutic activity of a synthetic bacterial lipoprotein (BLP), a TLR1/TLR2 agonist, on established lung carcinoma, leukemia, and melanoma in mice. Systemic treatment of 3LL tumor-bearing mice with BLP, but not LPS, led to a dose-dependent tumor regression and a long-lasting protective response against tumor rechallenge. The BLP-mediated tumor remission was neither mediated by a direct tumoricidal activity nor by innate immune cells, because it lacked therapeutic effect in immunodeficient SCID mice. Instead, BLP treatment reduced the suppressive function of Foxp3(+) regulatory T cells (Tregs) and enhanced the cytotoxicity of tumor-specific CTL in vitro and in vivo. Furthermore, adoptive cotransfer of BLP-pretreated but not untreated CTL and Tregs from wild-type but not from TLR2(-/-) mice was sufficient to restore antitumor immunity in SCID mice by reciprocally modulating Treg and CTL function. These results demonstrate that the TLR1/TLR2 agonist BLP may have a general tumor therapeutic property involving reciprocal downregulation of Treg and upregulation of CTL function. This property may play an important role in the development of novel antitumor strategies.

A critical role for mast cells and mast cell-derived IL-6 in TLR2-mediated inhibition of tumor growth

Several TLR agonists are effective in tumor immunotherapy, but their early innate mechanisms of action, particularly those of TLR2 agonists, are unclear. Mast cells are abundant surrounding solid tumors where they are often protumorigenic and enhance tumor angiogenesis. However, antitumor roles for mast cells have also been documented. The impact of mast cells may be dependent on their activation status and mediator release in different tumors. Using an orthotopic melanoma model in wild-type C57BL/6 and mast cell-deficient Kit(W-sh/W-sh) mice and a complementary Matrigel-tumor model in C57BL/6 mice, mast cells were shown to be crucial for TLR2 agonist (Pam(3)CSK(4))-induced tumor inhibition. Activation of TLR2 on mast cells reversed their well-documented protumorigenic role. Tumor growth inhibition after peritumoral administration of Pam(3)CSK(4) was restored in Kit(W-sh/W-sh) mice by local reconstitution with wild-type, but not TLR2-deficient, mast cells. Mast cells secrete multiple mediators after Pam(3)CSK(4) activation, and in vivo mast cell reconstitution studies also revealed that tumor growth inhibition required mast cell-derived IL-6, but not TNF. Mast cell-mediated anticancer properties were multifaceted. Direct antitumor effects in vitro and decreased angiogenesis and recruitment of NK and T cells in vivo were observed. TLR2-activated mast cells also inhibited the growth of lung cancer cells in vivo. Unlike other immune cells, mast cells are relatively radioresistant making them attractive candidates for combined treatment modalities. This study has important implications for the design of immunotherapeutic strategies and reveals, to our knowledge, a novel mechanism of action for TLR2 agonists in vivo.

Adjuvant engineering for cancer immunotherapy: Development of a synthetic TLR2 ligand with increased cell adhesion

The development of effective immunoadjuvants for tumor immunotherapy is of fundamental importance. The use of Mycobacterium bovis bacillus Calmette-Guérin cell wall skeleton (BCG-CWS) in tumor immunotherapy has been examined in various clinical applications. Because BCG-CWS is a macromolecule that cannot be chemically synthesized, the development of an alternative synthetic molecule is necessary to ensure a constant supply of adjuvant. In the present study, a new adjuvant was designed based on the structure of macrophage-activating lipopeptide (MALP)-2, which is a Toll-like receptor (TLR)-2 ligand similar to BCG-CWS. Macrophage-activating lipopeptide-2, [S-(2,3-bispalmitoyloxypropyl)Cys (P2C) - GNNDESNISFKEK], originally identified in a Mycoplasma species, is a lipopeptide that can be chemically synthesized. A MALP-2 peptide was substituted with a functional motif, RGDS, creating a novel molecule named P2C-RGDS. RGDS was selected because its sequence constitutes an integrin-binding motif and various integrins are expressed in immune cells including dendritic cells (DCs). Thus, this motif adds functionality to the ligand. P2C-RGDS activated DCs and splenocytes more efficiently than MALP-2 over short incubation times in vitro, and the RGDS motif contributed to their activation. Furthermore, P2C-RGDS showed higher activity than MALP-2 in inducing migration of DCs to draining lymph node, and in inhibiting tumor growth in vivo. This process of designing and developing synthetic adjuvants has been named "adjuvant engineering," and the evaluation and improvement of P2C-RGDS constitutes a first step in the development of stronger synthetic adjuvants in the future.

Toll-like receptors as therapeutic targets in gastrointestinal diseases

IMPORTANCE OF THE FIELD

Toll-like receptors (TLRs) are innate immunity receptors that recognize several different antigens, initiating immunological/inflammatory responses. Recent evidence associates numerous pathophysiological processes and diseases with dysregulated activation of these receptors, conferring a potential therapeutic value to their modulation.

AREAS COVERED IN THIS REVIEW

The aim of this systematic review that covers literature from the past 10 years is to address the role of TLRs in the pathophysiology of gastrointestinal (GI) diseases as well as the therapeutic potential of modulating TLRs' signaling pathways in GI pathology.

WHAT THE READER WILL GAIN

This review shows that TLRs play an important role in the pathophysiology of several GI diseases and that modulating TLRs signaling pathways may have an enormous therapeutic potential. Different methods for modulation of TLRs' activity in GI tract, with direct agonists/antagonists but also with non-specific substances, like antibiotics or probiotics, are presented.

TAKE HOME MESSAGE

Even though TLRs modulators have been used for therapy in some GI diseases, further research, particularly in humans, is needed in order to establish the precise role of the different TLRs in the diverse GI diseases and to motivate clinical trials that consider TLRs as therapeutic targets in GI pathology.

Local treatment with BPPcysMPEG reduces allergic airway inflammation in sensitized mice

According to the hygiene hypothesis, triggering the immune system with microbial components during childhood balances the inherent Th2 bias. In contrast, specific immunotherapy involves exposure of the patient to the allergen in order to achieve desensitization to subsequent contact. In a human in vitro allergy model the potential of the TLR2/6 agonist BPPcysMPEG to modulate antigen presenting cells and allergen-specific immune responses was evaluated. Specific immunomodulation via co-administration of the allergen and BPPcysMPEG enhanced expression of co-stimulatory molecules on DC and increased secretion of the proinflammatory cytokine TNF-α. Acting as an adjuvant, BPPcysMPEG elevated allergen-specific immune responses in co-culture with autologous lymphocytes. Although administration of BPPcysMPEG alone enhanced expression of co-stimulatory molecules on DC, proliferation of autologous lymphocytes was not induced. Based on this finding, the potential of BPPcysMPEG to reduce allergic airway inflammation by preventive modulation of the innate immune system via TLR2/6 agonization was investigated in mice. Local administration of BPPcysMPEG altered cellular influx and cell composition in BAL fluid. Furthermore, the Th2-associated cytokines IL-4 and IL-5 were diminished. Allergen-specific restimulation of cells from mediastinal lymph nodes and splenocytes suggested an alteration of immune responses. The treatment with BPPcysMPEG induced a Th1-dominated cytokine milieu in mediastinal lymph nodes, while allergen-specific immune responses in splenocytes were diminished. The co-administration of allergen and BPPcysMPEG reduced cytokine secretion upon restimulation in mediastinal lymph nodes and splenocytes. From these data we conclude that BPPcysMPEG was able to influence the immune system with regard to subsequent allergen contact by TLR2/6 agonization.

Toll-like receptor 2/6 stimulation promotes angiogenesis via GM-CSF as a potential strategy for immune defense and tissue regeneration

Toll-like receptors (TLRs) are known primarily as pathogen recognition receptors of the innate immunity, initiating inflammatory pathways to organize the immune defense. More recently, an involvement of TLRs in various physiologic and pathologic processes has been reported. Because many of these processes implicate angiogenesis, we here elucidated the role of a TLR2/6-dependent pathway on angiogenesis using the TLR2/6 agonist macrophage-activating lipopeptide of 2 kDa (MALP-2), a common bacterial lipopeptide. In vivo and in vitro Matrigel assays demonstrated that MALP-2 promoted angiogenesis in a TLR2/6-dependent manner. Moreover, MALP-2 induced endothelial cell proliferation and migration and a strong secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF release in response to MALP-2 from isolated vascular segments was completely prevented when the endothelium was removed. MALP-2 containing Matrigel implants exhibited vascular structures as well as CD45(+) cells. MALP-2 induced migration of leukocytes and likewise GM-CSF release, particularly from the monocyte population. Inhibition of GM-CSF by siRNA or antibodies suppressed MALP-2-induced angiogenesis in vitro and in vivo. These results clearly identified a TLR2/6-dependent induction of angiogenesis by the bacterial lipopeptide MALP-2, which is mediated by GM-CSF. This might represent a general mechanism to enhance or restore blood flow and recruit immune cells for pathogen defense and tissue regeneration.

Increase of in vivo antitumoral activity by CD40L (CD154) gene transfer into pancreatic tumor cell-dendritic cell hybrids

OBJECTIVES

Fusion of dendritic cells (DC) with tumor cells is an approach in immunotherapy combining antigenicity and capacity of antigen presentation to activate T cells for the induction of tumor-specific cytotoxic immunity. Although there have been reports of clinical benefit, response rates have been limited and further improvements are warranted.

METHODS

We used murine DC and a novel protocol for an effective fusion of those cells with the murine pancreatic cell line Panc02.

RESULTS

We observed 2 events: only moderate in vitro and in vivo cytotoxicity of tumor cell/DC hybrids and a down-regulation of costimulatory molecules on fused cells. Therefore, we transfected tumor cell/DC hybrids with an adenovirus expressing CD154 to improve DC activation and generating antitumor immune response without the need of CD4 T cells. High CD154 expression could be obtained by transfection of DC and Panc02 cells prior fusion. Furthermore, vaccination with CD154-transfected tumor cell/DC hybrid led to a significantly increased induction of cytotoxic T cells in vitro and to an improved antitumoral effect in an orthotopic in vivo mouse model.

CONCLUSIONS

CD154-transfected tumor cell/DC hybrids are a promising approach to increase the efficiency of antitumoral response.

Activation of Toll-like receptor 2 by a novel preparation of cell wall skeleton from Mycobacterium bovis BCG Tokyo (SMP-105) sufficiently enhances immune responses against tumors

The cell wall skeleton of Mycobacterium bovis BCG has been investigated as an immunopotentiating adjuvant for immuno-therapy of malignant tumors via Toll-like receptor (TLR) 2 and TLR4. However, due to its high molecular weight, highly complicated lipoglycan structure, and complicated purification and isolation procedure, its exact structure-activity relationship has not been well established. We have newly isolated the cell wall skeleton from M. bovis BCG Tokyo (SMP-105) and examined the binding of SMP-105 with TLR. It was revealed that highly purified SMP-105 activates the nuclear factor-kB promoter in a TLR2-dependent manner, not a TLR4-dependent manner, using a reporter gene assay system. Peritoneal exudated cells of TLR2 and MyD88 knockout mice severely reduced the induction of tumor necrosis factor-alpha and interleukin-6 in the presence of SMP-105, whereas cells from TLR4 knockout mice produced similar levels of cytokines to wild-type mice. Dendritic cells and macrophages accumulated in the draining lymph nodes of treated mice. When mice were administered both SMP-105 and mitomycin C-inactivated Lewis lung carcinoma cells simultaneously, interferon-gamma-producing cells reacting to the tumor were increased distinctly in draining lymph nodes. When C57BL/6 mice, into which splenocytes from OT-I transgenic mice had been transferred, were administered with both SMP-105 and E.G7-OVA, OVA-specific cytotoxic T lymphocytes (CTL) increased markedly. Mice treated with SMP-105 and inactivated Lewis lung carcinoma cells suppressed the growth of implanted tumors. These results suggest that the activation of TLR2 by SMP-105 sufficiently enhanced immune responses, such as the number of interferon-gamma-producing cells and CTL, and prevented the growth of tumors without the contribution of TLR4.

Intratumoural injection of the toll-like receptor-2/6 agonist 'macrophage-activating lipopeptide-2' in patients with pancreatic carcinoma: a phase I/II trial

This phase I/II trial examined safety and efficacy of the toll-like receptor 2/6 agonist MALP-2 in combination with gemcitabine in patients with incompletely resectable pancreas carcinomas. MALP-2 is a toll-like receptor 2/6 agonist, acts as an immunological adjuvant, and has been described recently to prolong survival in a mouse model of an orthotopic, syngeneic pancreas tumour. Male and female patients with incompletely resectable pancreas carcinomas were eligible while those with R0 or R1 resections or with peritoneal carcinosis were excluded. Ten patients were injected intratumourally during surgery with 20-30 microg MALP-2 followed by postoperative chemotherapy. Samples were taken from peripheral blood and wound secretion, and assayed for cell content, cytokine and CRP levels, and NK activity. An MALP-2 dose of 20 microg was well tolerated. Clear signs of local MALP-2 effects were presented by the influx of lymphocytes and monocytes in wound secretions, and abolishment of inhibition of NK activity. The actual mean survival is 17.1+/-4.2 months; the median survival being 9.3 months. Two patients are still alive after 31 months. Up to 20 microg MALP-2 was well tolerated, and no systemic side effects were noted. The mean survival of 17.1 months is remarkably high.

Cancer relapse under chemotherapy: why TLR2/4 receptor agonists can help

Liver or lung metastases usually relapse under chemotherapy. Such life-threatening condition urgently needs new, systemic anticancer compounds, with original and efficient mechanisms of action. In B16 melanoma mice treated with cyclophosphamide, D'Agostini et al. [D'Agostini, C., Pica, F., Febbraro, G., Grelli, S., Chiavaroli, C., Garaci, E., 2005. Antitumour effect of OM-174 and Cyclophosphamide on murine B16 melanoma in different experimental conditions. Int. Immunopharmacol. 5, 1205-1212.] recently found that OM-174, a chemically defined Toll-like receptor(TLR)2/4 agonist, reduces tumor progression and prolongs survival. Here we review 149 articles concerning molecular mechanisms of TLR2/4 agonists, alone or in combination with chemotherapy. It appears that TLR2/4 agonists induce a well controlled tumor necrosis factor-alpha (TNF-alpha) secretion, at plasma levels known to permeabilize neoangiogenic tumor vessels to the passage of cytotoxic drugs. Moreover, TLR2/4 agonists induce inducible nitric oxide synthase (iNOS) expression, and nitric oxide is able to induce apoptosis of chemotherapy-resistant tumor cell clones. Finally, TLR2/4-stimulation activates dendritic cell traffic and its associated tumor-specific, cytotoxic T-cell responses. Therefore, parenteral TLR2/4 agonists seem promising molecules to prolong survival in cancer patients who relapse under chemotherapy.

Telomerase-specific T-cells kill pancreatic tumor cells in vitro and in vivo

BACKGROUND

Adoptive cell transfer is described as an innovative and challenging option for the treatment of malignant melanoma. In the current study, the generation and expansion of telomerase-specific T-cells for adoptive cell transfer and their use in a syngeneic pancreatic carcinoma mouse model was investigated.

METHODS

Telomerase-specific T-cells were generated either in vitro by coculture of human lymphocytes with telomerase-peptide-pulsed dendritic cells or in vivo by injection of peptide plus adjuvant into C57BL/6 mice. Spleens were harvested after immunization and lymphocytes were expanded in the presence of feeder cells. T-cells were tested in vitro against human leukocyte antigen (HLA)-matched, telomerase-positive pancreatic carcinoma cells. Tumor-bearing (subcutaneous) mice pretreated with cyclophosphamide were injected intravenously with the expanded cells.

RESULTS

It was possible to generate and expand telomerase-specific T-cells with cytotoxic activity. The protocol did not work as well in the murine setting. However, adoptive cell transfer with murine antigen-specific T-cells delayed disease progression in tumor-bearing mice significantly.

CONCLUSIONS

Generation of antigen-specific T-cells is feasible; the expansion of these cells could be accomplished without loss of function. Antigen-specific T-cells demonstrated significant cytotoxic activity in a syngeneic, subcutaneous mouse model. However, further optimization of the expansion protocol is warranted.

Decreased total lymphocyte counts in pancreatic cancer: an index of adverse outcome

OBJECTIVES

An impaired host immunity might concur in determining the dismal prognosis of patients with pancreatic cancer (PC). Our aim was to ascertain whether the immunophenotype pattern of blood lymphocytes in PC correlates with tumor stage, grade, or survival.

METHODS

We studied 115 patients with PC, 44 with chronic pancreatitis (CP), 23 with tumors of the pancreatico-biliary tract, and 34 healthy controls (CS). Survival data were available for 77 patients with PC. Lymphocyte subsets were determined by fluorescent activated cell sorter (FACS) analysis.

RESULTS

In patients with PC, total lymphocyte counts were lower than in CP or CS, and CD8 lymphocyte subset levels were higher with respect to CS. Lower circulating lymphocytes were found in advanced PC stages (IIB-IV; chi2 = 11.55, P < 0.05) compared with stages 0 to IIA. Cox regression analysis, made considering total lymphocyte counts and tumor stage as covariates, was found to be significant for both tumor stage (P < 0.001) and total lymphocyte counts (P < 0.05).

CONCLUSIONS

The reduction of total lymphocytes in blood is the main immunologic change in advanced PC. The survival of these patients depends mainly on tumor stage, but it is also affected by the number of circulating lymphocytes, suggesting that the immune system plays an important role in pancreatic adenocarcinoma immunosurveillance and immunoediting.

Therapeutic synergism of gemcitabine and CpG-oligodeoxynucleotides in an orthotopic human pancreatic carcinoma xenograft

CpG-oligodeoxynucleotides (CpG-ODN) exhibit potent immunostimulatory activity by binding with Toll-like receptor 9 (TLR9). Based on the finding that TLR9 is highly expressed and functional in pancreatic tissue, we evaluated the antitumor effects of chemotherapy combined with CpG-ODNs in the orthotopic mouse model of a human pancreatic tumor xenograft. Chemotherapy consisted of the maximum tolerated dose of gemcitabine (i.v., 100 mg/kg, q3dx4). CpG-ODNs were delivered (i.p., 20 microg/mouse), weekly, after the end of chemotherapy. CpG-ODNs alone had little effect on tumor growth, whereas gemcitabine alone significantly delayed the median time of disease onset (palpable i.p. tumor) and of bulky disease development (extensive peritoneal tumor burden), but did not enhance survival time. When the gemcitabine regimen was followed by administration of the immunostimulator, development of bulky disease was delayed, survival time was significantly improved (median survival time, 106 days; P < 0.02 versus gemcitabine-treated mice). Autoptic examination showed that tumor spread in the peritoneal cavity was reduced to a greater extent than with gemcitabine alone. All treatment regimens were well-tolerated. The use of nude mice excluded a T cell-mediated immune response, whereas the high pancreatic expression of TLR9 might have contributed to the tumor response. The clear improvement of survival observed in an orthotopic murine model of human pancreatic cancer by the combined use of CpG-ODNs with chemotherapy suggests the promise of this therapeutic regimen in the clinical setting.