Anti-tumor effect of an intratumoral administration of dendritic cells in combination with TS-1, an oral fluoropyrimidine anti-cancer drug, and OK-432, a streptococcal immunopotentiator: involvement of toll-like receptor 4

Dendritic cell-based vaccine for pancreatic cancer in Japan

“Vaccell” is a dendritic cell (DC)-based cancer vaccine which has been established in Japan. The DCs play central roles in deciding the direction of host immune reactions as well as antigen presentation. We have demonstrated that DCs treated with a streptococcal immune adjuvant OK-432, produce interleukin-12, induce Th1-dominant state, and elicit anti-tumor effects, more powerful than those treated with the known DC-maturating factors. We therefore decided to mature DCs by the OK-432 for making an effective DC vaccine, Vaccell. The 255 patients with inoperable pancreatic cancer who received standard chemotherapy combined with DC vaccines, were analyzed retrospectively. Survival time of the patients with positive delayed type hypersensitivity (DTH) skin reaction was significantly prolonged as compared with that of the patients with negative DTH. The findings strongly suggest that there may be “Responders” for the DC vaccine in advanced pancreatic cancer patients. We next conducted a small-scale prospective clinical study. In this trial, we pulsed HLA class II-restricted WT1 peptide (WT1-II) in addition to HLA class I-restricted peptide (WT1-I) into the DCs. Survival of the patients received WT1-I and -II pulsed DC vaccine was significantly extended as compared to that of the patients received DCs pulsed with WT1-I or WT1-II alone. Furthermore, WT1-specific DTH positive patients showed significantly improved the overall survival as well as progression-free survival as compared to the DTH negative patients. The activation of antigen-specific immune responses by DC vaccine in combination with standard chemotherapy may be associated with a good clinical outcome in advanced pancreatic cancer. We are now planning a pivotal study of the Vaccell in appropriate protocols in Japan.

Immunocompromised and immunocompetent mouse models for head and neck squamous cell carcinoma

Mouse models can closely mimic human oral squamous epithelial carcinogenesis, greatly expand the in vivo research possibilities, and play a critical role in the development of diagnosis, monitoring, and treatment of head and neck squamous cell carcinoma. With the development of the recent research on the contribution of immunity/inflammation to cancer initiation and progression, mouse models have been divided into two categories, namely, immunocompromised and immunocompetent mouse models. And thus, this paper will review these two kinds of models applied in head and neck squamous cell carcinoma to provide a platform to understand the complicated histological, molecular, and genetic changes of oral squamous epithelial tumorigenesis.

Immunochemoradiotherapy for patients with oral squamous cell carcinoma: augmentation of OK-432-induced helper T cell 1 response by 5-FU and X-ray irradiation

Eighty-one patients with oral squamous cell carcinoma (OSCC) received oral fluoropyrimidine UFT and radiotherapy (RT) with or without an immunotherapeutic agent OK-432. Both overall survival and progression-free survival of patients who received RT + UFT + OK-432 were significantly longer than those of patients who received RT + UFT (P = .0075 and P = .0175, respectively). Clinical response was also more favorable in RT + UFT + OK-432 group than in RT + UFT group (P = .0066). Next, in vitro experiments were conducted to examine the effect of 5-fluorouracil (5-FU) and X-ray irradiation in OK-432-induced immunity. Human peripheral blood mononuclear cells stimulated with OK-432 produced helper T cell 1 (Th1)-type cytokines as well as interleukin-10 (IL-10) and transforming growth factor-β (TGF-β), which are produced by Th2 and regulatory T cells (Tregs), respectively, and are inhibitory in antitumor immunity. OK-432-induced IL-10 and TGF-β but not Th1 cytokines were significantly inhibited by 5-FU and/or X-ray. 5-FU and X-ray also inhibited the expression of mRNAs for GATA-3 and Foxp3, which are transcription factors for Th2 and Tregs, respectively, but not for T-bet, a transcription factor for Th1. In addition, 5-FU and X-ray decreased the expression of mRNAs for suppressor of cytokine signaling 1 (SOCS1) and SOCS3. Antisense oligonucleotides for SOCS1 and SOCS3 markedly reduced OK-432-induced IL-10 and TGF-β. This is the first report clearly demonstrating that OK-432-based immunotherapy significantly enhanced the therapeutic effects of chemoradiotherapy in patients with OSCC as well as elucidating the mechanism of the synergistic effect of immunochemoradiotherapy in which 5-FU and radiation enhanced OK-432-induced Th1 response mediated by the inhibition of SOCS1 and SOCS3 gene expression.

Optimizing dendritic cell-based immunotherapy for cancer

Dendritic cells (DCs) are the most powerful professional antigen-presenting cells and are unique in their capability to initiate, maintain and regulate the intensity of primary immune responses, including specific antitumor responses. Development of practical procedures to prepare sufficient numbers of functional human DCs in culture from the peripheral blood precursors, paved the way for clinical trials to evaluate various DC-based strategies in patients with malignant diseases. However, no definite conclusions regarding the clinical and even immunological efficacy of DC vaccination can be stated, despite the fact that 12 years have passed since the first clinical trial utilizing DCs in cancer patients. Many unanswered questions hamper the development of DC-based vaccines, including the source of DC preparation and protocols for DC generation, activation and loading with tumor antigens, source of tumor antigens, route of vaccine administration and methods of immunomonitoring. Fortunately, in spite of the many obstacles, DC vaccines continue to hold promise for cancer therapy.

OK-432 synergizes with IFN-γ to confer dendritic cells with enhanced antitumor immunity

Generation of functional dendritic cells (DCs) with boosted immunity after the withdrawal of initial activation/maturation conditions remains a significant challenge. In this study, we investigated the impact of a newly developed maturation cocktail consisting of OK-432 and interferon-gamma (IFN-γ) on the function of human monocyte-derived DCs (MoDCs). We found that OK-432 plus IFN-γ stimulation could induce significantly stronger expression of surface molecules, production of cytokines, as well as migration of DCs compared with OK-432 stimulation alone. Most importantly, DCs matured with OK-432 plus IFN-γ-induced maintained secretion of interleukin-12 (IL-12)p70 in secondary culture after stimulus withdrawal. Functionally, OK-432 plus IFN-γ-conditioned DCs induce remarkable Th1 and Tc1 responses more effectively than OK-432 alone, even more than the use of α-type-1 cytokine cocktail. As a result, DCs matured with OK-432 plus IFN-γ can prime stronger cytotoxic lymphocyte (CTL) and natural killer (NK) cell response against tumor cells in vitro. Peripheral blood mononuclear cells activated by DCs matured with OK-432 plus IFN-γ also showed greater tumor growth inhibition in vivo in null mice. Molecular mechanistic analysis showed that DC maturation using IFN-γ in concert with OK-432 involves the activation of p38 and nuclear factor-kappa B (NF-κB) pathways. This study provided a novel strategy to generate more potent immune segments in DC vaccine.

Prognostic impact of expression of Bcl-2 and Bax genes in circulating immune cells derived from patients with head and neck carcinoma

Antitumor functions of the host immune system are frequently compromised in patients with malignancies. In the current study, we evaluated the relationship between expression ratio of mRNAs for the antiapoptotic protein Bcl-2 and the proapoptotic protein Bax (the Bcl-2/Bax ratio) in peripheral blood mononuclear cells and clinical outcomes in patients with head and neck carcinomas. The overall survival (OS) time of patients with Bcl-2/Bax ratios ≥ 1.2 tended to be longer than that of patients with Bcl-2/Bax ratios < 1.2 but not significantly so (P = .084, n = 61). Disease-free survival (DFS) of patients with Bcl-2/Bax ratios ≥ 1.2 was statistically significantly longer than that of patients with Bcl-2/Bax ratios < 1.2 (P = .001, n = 76). All of the patients whose Bcl-2/Bax ratio is ≥ 2.0 were alive after 36 months and survived without any evidence of disease for 24 months (Bcl-2/Bax ≥ 2.0 versus Bcl-2/Bax < 2.0; P = .035, n = 61 in OS, P < .001, n = 76 in DFS, respectively). In 56 patients who received immunochemoradiotherapy using UFT and OK-432 in combination with radiotherapy, a statistically significant relationship between the Bcl-2/Bax ratio and the therapeutic effect estimated using Response Evaluation Criteria in Solid Tumors was observed, as well as a relation with interferon-γ (IFN-γ) induction in response to the therapy [P = .002 in complete response versus partial response + stable disease; P = .046 in IFN-γ(+) versus IFN-γ(-)]. In addition, there were significant correlations of the Bcl-2/Bax ratio with both the absolute number of CD4(+) T cells and the rate of CD4(+) T cell and natural killer cell activity. These findings strongly suggest that the balance of expression of Bcl-2 and Bax genes in circulating immune cells has a high prognostic value in head and neck cancer patients.

Enhanced Dendritic Cell-Mediated Antigen-Specific CD4+ T Cell Responses: IFN-Gamma Aids TLR Stimulation

Phenotypic maturation and T cell stimulation are two functional attributes of DCs critical for immune induction. The combination of antigens, including those from cancer, with Toll-like receptor (TLR) ligands induces far superior cellular immune responses compared to antigen alone. In this study, IFN-gamma treatment of bone marrow-derived DC, followed by incubation with the TLR2, TLR4, or TLR9 agonists, enhanced DC activation compared to TLR ligation alone. Most notably, the upregulation of CD40 with LPS stimulation and CD86 with CpG stimulation was observed in in vitro cultures. Similarly, IFN-gamma coinjected with TLR ligands was able to promote DC activation in vivo, with DCs migrating from the site of immunization to the popliteal lymph nodes demonstrating increased expression of CD80 and CD86. The heightened DC activation translated to a drastic increase in T cell stimulatory capacity in both antigen independent and antigen dependent fashions. This is the first time that IFN-gamma has been shown to have a combined effect with TLR ligation to enhance DC activation and function. The results demonstrate the novel use of IFN-gamma together with TLR agonists to enhance antigen-specific T cell responses, for applications in the development of enhanced vaccines and drug targets against diseases including cancer.

Immune-maximizing (IMAX) therapy for cancer: Combination of dendritic cell vaccine and intensity-modulated radiation

A dendritic cell (DC)-based vaccine was combined with intensity-modulated radiotherapy (IMRT) or other conformal radiotherapy (RT), assuming minimal immunosuppression by such RT modalities. In this study, the outcomes in the first 40 patients are presented. The patients had recurrent, metastatic or locally advanced tumors. Nine had previously undergone full-course RT. Peripheral blood mononuclear cells obtained by leukapheresis were cultured with granulocyte-macrophage colony-stimulating factor, interleukin-4, OK-432 and prostaglandin E2 to generate DCs, which were pulsed with autologous tumor lysates or tumor-specific peptides, such as WT1. IMRT using tomotherapy, stereotactic irradiation or 3-dimensional conformal RT (3DCRT) was initially administered. The standard dose was 30 and 60 Gy in patients with and without previous RT, respectively. Every other week thereafter, up to a total of 7 times, DC vaccines were injected directly into the tumor (n=15) or administered intradermally when DCs were pulsed with tumor lysates or peptides. The tumor response was evaluated according to the response evaluation criteria in solid tumors (RECIST). RT and DC vaccines were well tolerated and there were no major complications. Three patients were not able to complete the planned DC therapy due to disease progression. For the 31 patients receiving full-dose RT, the response rate was 61% and for the 9 patients who had previously received RT, the response rate was 55%. In 9 patients, the tumor response outside the RT target volume was evaluable: 22% had a partial response (PR), 33% had stable disease (SD) and 44% had progressive disease (PD). In conclusion, a combination of IMRT (or 3DCRT) and DC vaccine is feasible and requires further investigation.

Clinical and immunologic evaluation of dendritic cell-based immunotherapy in combination with gemcitabine and/or S-1 in patients with advanced pancreatic carcinoma

OBJECTIVES

In the current study, we have evaluated the clinical and immunological responses in patients with advanced pancreatic carcinoma who received dendritic cell (DC)-based immunotherapy in combination with gemcitabine and/or S-1.

METHODS

Dendritic cell-based immunotherapy (DC vaccine alone or DC vaccine plus lymphokine-activated killer [LAK] cell therapy) in combination with gemcitabine and/or S-1 has been carried out in 49 patients with inoperable pancreatic carcinoma refractory to standard treatment.

RESULTS

Of 49 patients, 2 patients had complete remission, 5 had partial remission, and 10 had stable disease. Prolongation of survival in this cohort was highly likely (median survival, 360 days). Survival of patients receiving DC vaccine and chemotherapy plus LAK cell therapy was longer than those receiving DC vaccine in combination with chemotherapy but no LAK cells. Increased numbers of cancer antigen-specific cytotoxic T cells and decreased regulatory T cells were observed in several patients on immunotherapy, but increased overall survival time tended to be associated only with the latter. None of the patients experienced grade 3 or worse adverse events during the treatment period.

CONCLUSIONS

Dendritic cell vaccine-based immunotherapy combined with chemotherapy was shown to be safe and possibly effective in patients with advanced pancreatic cancer refractory to standard treatment.

The bacterial preparation OK432 induces IL-12p70 secretion in human dendritic cells in a TLR3 dependent manner

Dendritic cells (DC) used in therapeutic cancer immunotherapy have to be able to stimulate T cells resulting in an immune response that can efficiently target the cancer cells. One of the critical hurdles has been the lack of IL-12p70 production when maturating the DC, which is rectified by using the bacterial preparation OK432 (trade name Picibanil) to mature the cells. In order to identify the mechanism behind OK432 stimulation of DC, we investigated the contribution of different TLR to examine their involvement in IL-12p70 production. By combining different inhibitors of TLR signaling, we demonstrate here that TLR3 is responsible for the IL-12p70 production of DC induced by OK432. Moreover, our data suggest that the ligand triggering IL-12p70 secretion upon TLR3 stimulation is sensitive to proteinase and partly also RNAse treatment. The fact that a bacterial compound like OK432 can activate the TLR3 pathway in human DC is a novel finding. OK432 demonstrates a critical ability to induce IL-12p70 production, which is of great relevance in DC based cancer immunotherapy.

Combining bacterial-immunotherapy with therapeutic antibodies: a novel therapeutic concept

Immunotherapeutic strategies become more and more important for cancer treatment. Therapeutic monoclonal antibodies (mAbs) like Panitumumab binding and blocking the EGF-receptor are in routine clinical use for the treatment of colorectal carcinoma (CRC). Also, bacterial therapy proved beneficial for experimental treatment of different tumor entities. The latter has been attributed to an activation of the immune system. Here, we describe a combination of both immunotherapeutic approaches in order to develop a novel targeted therapy for CRC. The therapeutic mAbs Trastuzumab and Panitumumab were conjugated to heat-inactivated bacteria expressing protein A or protein G. The potential of the conjugates was tested in comparison to the single components both in vitro and in vivo using a panel of patient-derived CRC cell lines. Antitumoral effects observed in vitro were strictly dependent on the presence of bacteria. Generally, effects could be enhanced by the addition of human lymphocytes. Detailed analysis of effector cells in autologous and allogeneic long-term stimulated lymphocyte cultures revealed the predominance of NK-cell-like cytolytic effectors. Reactivity was observed both against CRC target cells but also against the NK cell target K562. Similarly, in a subsequent in vivo study we observed substantial tumor growth delay accompanied by an increase in circulating NK cells. Contrary to this, the monotherapy with mAb alone caused only marginal effects and the treatment with bacteria was comparable to the mock-treated control. These data demonstrate successful targeting of CRC by bacteria/mAb conjugates. This novel concept may be interesting for future clinical approaches. Additionally, it illustrates the effectiveness of NK cells for cancer immunotherapy.

Lipopolysacchride-treated mammary carcinomas secrete proinflammatory chemokines and exhibit reduced growth rates in vivo, but not in vitro

Toll-like receptors (TLR) are pattern recognition receptors that play a pivotal role in the initiation of immune responses. Here we report that the murine mammary carcinoma 4T1 constitutively expressed genes encoding TLR2, 3, 4 and 5. Moreover, treatment of the 4T1 cell line with peptidoglycan (PGN), polyinosinic-polycytidylic acid (Poly(I:C)) or lipopolysaccharide (LPS), agonists for TLR2, 3 or 4 respectively, induced nuclear translocation of NFkappaB and secretion of CCL2, CCL5 and CXCL1 in a dose dependent manner. Although treating the tumor cells with the TLR agonists did not modulate growth or viability of the tumor cells in vitro, 4T1 exhibited a decreased growth rate in vivo following treatment with LPS that was dependent upon the presence of CD8(+) T cells. Analysis of 3 additional murine mammary carcinomas revealed that they also secreted CCL2, CCL5 and CXCL1 in response to TLR agonist treatment, and LPS treated 168 and SM1 tumors exhibited decreased growth rates in vivo, but not in vitro. These data indicated that 4 out of 4 murine mammary carcinomas secreted proinflammatory chemokines following treatment with TLR agonists, and 3 out of 4 of the mammary carcinomas responded to LPS treatment in a manner that decreased tumor growth in vivo.

Magnetic resonance imaging-guided adoptive cellular immunotherapy of central nervous system tumors with a T1 contrast agent

Dendritic cells (DCs) are the most effective antigen-presenting cells (APCs) and are used in a variety of immunotherapeutic approaches. Adoptive cellular immunotherapy (ACI) of cancer using DCs has attracted much interest due to their capacity to promote immunity in prophylactic and therapeutic protocols. As one approach, DCs are injected into patients or tumor-bearing animals, to trigger specific antitumor immunity. In that framework, several approaches to DC delivery have been reported, including direct intratumoral injection; this has yielded positive but variable results. The underlying reasons for this have not been fully determined, but major hypotheses include technical difficulties in delivering cells into tumors and tumor-mediated immunosuppression. Image-guided ACI offers the potential to establish that DCs are efficiently delivered to the tumor site, which might eliminate some of the variability. Therefore, we developed highly sensitive methods for monitoring the injection or trafficking of DCs into tumors using a clinically approved formulation of a gadolinium-based magnetic resonance imaging (MRI) contrast agent, Gd(III)-HP-DO3A (ProHance). We determined the labeling efficiency of DCs with this formulation; that labeling DCs with this agent did not inhibit expression of surface markers important for antigen presentation and activation of naive T cells; that their capacity to interact with natural killer (NK) cells was not reduced; and that their migration was not diminished. Further, we determined that ProHance-labeled DCs can be effectively imaged in vivo in established central nervous system tumors.

Enhancement of T-cell-mediated anti-tumour immunity via the ectopically expressed glucocorticoid-induced tumour necrosis factor receptor-related receptor ligand (GITRL) on tumours

Glucocorticoid-induced tumour necrosis factor receptor-related receptor (GITR) costimulates functions of both effector and regulatory T cells. The administration of agonistic anti-GITR monoclonal antibodies efficiently enhances various T-cell-mediated immune responses; however, it is unknown to what extent the ligand of GITR (GITRL) contributes to T-cell responses. We investigated the involvement of endogenously expressed GITRL on dendritic cells and ectopically expressed GITRL on tumours in T-cell-mediated immunity. Expression of GITRL on dendritic cells in secondary lymphoid organs was limited, and treatment with anti-GITRL monoclonal antibodies did not substantially affect T-cell-mediated immunity to alloantigens, a specific protein antigen (ovalbumin), or tumour antigens. The introduction of GITRL promoted anti-tumour immunity in four tumour models. Tumour-associated GITRL greatly augmented the effector function of CD8(+) T cells and enhanced the contribution of CD8(+) T cells. These events reduced the crucial contribution of CD25(+) CD4(+) regulatory T cells, which were found to inhibit immunity against tumours lacking GITRL. Peritumoral injection of GITRL tumour vaccine efficiently inhibited the growth of established tumours. Our results suggest that the ectopic expression of GITRL in tumour cells enhances anti-tumour immunity at peripheral tumour sites. Consequently, the combined use of a GITRL tumour vaccine with methods aimed at enhancing the activation of host antigen-presenting cells in secondary lymphoid tissues may be a promising strategy for tumour immunotherapy.

Oral administration of poly-gamma-glutamate induces TLR4- and dendritic cell-dependent antitumor effect

Previously, we reported that the oral administration of high molecular mass poly-gamma-glutamate (gamma-PGA) induced antitumor immunity but the mechanism underlying this antitumor activity was not understood. In the present study, we found that application of high molecular mass gamma-PGA induced secretion of tumor necrosis factor (TNF)-alpha from the bone-marrow-derived macrophages of wild type (C57BL/6 and C3H/HeN) and Toll-like receptor 2 knockout (TLR2(-/-)) mice, but not those of myeloid differentiation factor 88 knockout (MyD88(-/-)) and TLR4-defective mice (C3H/HeJ). Production of interferon (IFN)-gamma-inducible protein 10 (IP-10) in response to treatment with gamma-PGA was almost abolished in C3H/HeJ mice. In contrast to LPS, gamma-PGA induced productions of TNF-alpha and IP-10 could not be blocked by polymyxin B. Furthermore, gamma-PGA-induced interleukin-12 production was also impaired in immature dendritic cells (iDCs) from MyD88(-/-) and C3H/HeJ mice. Downregulation of MyD88 and TLR4 expression using small interfering RNA (siRNA) significantly inhibited gamma-PGA-induced TNF-alpha secretion from the RAW264.7 cells. Gamma-PGA-mediated intracellular signaling was markedly inhibited in C3H/HeJ cells. The antitumor effect of gamma-PGA was completely abrogated in C3H/HeJ mice compared with control mice (C3H/HeN) but significant antitumor effect was generated by the intratumoral administration of C3H/HeN mice-derived iDCs followed by 2,000 kDa gamma-PGA in C3H/HeJ. These findings strongly suggest that the antitumor activity of gamma-PGA is mediated by TLR4.

Mechanism of antitumor effect on mouse hepatocellular carcinoma by intratumoral injection of OK-432, a streptococcal preparation

Intratumoral (i.t.) injection of OK-432, a streptococcal preparation, into implanted tumors of mouse hepatocellular carcinoma (MIH-2) showed antitumor effect including tumor eradication. Intraperitoneal administration of same dose OK-432 did not exhibit tumor suppressive effect. In vitro cytotoxic test suggested that direct cytotoxic effect of OK-432 was not associated with antitumor activity by i.t.-OK-432 treatment. It was also found that Toll-like receptor 4 signaling was not involved in i.t.-OK-432 treatment. Three mice out of five, which had shown tumor eradication by i.t.-OK-432 treatment did not reject re-challenge of MIH-2 cells. Splenocytes from i.t.-OK-432 treated mice did not produce IFN-gamma by stimulation with MIH-2 cells in vitro, but produced abundant IFN-gamma by stimulation with OK-432. Immunofluorescence microscopy demonstrated that CD4+T cells, but not CD8+T cells, infiltrated to i.t.-OK-432 treated tumor tissue produced IFN-gamma. Tumor-infiltrating CD4+T cells from i.t.-OK-432 treated tumor tissue produced IFN-gamma by in vitro stimulation with OK-432 higher than those from untreated tumor tissue. IFN-gamma directly induced apoptosis of MIH-2 cells in vitro. Collectively, i.t.-OK-432 treatment induced priming of CD4+T cells to antigenecity of OK-432, and repetitive i.t.-OK-432 treatment induced IFN-gamma production from OK-432-sensitized CD4+T cells in tumor site, leading to apoptosis of MIH-2 cells susceptible to IFN-gamma.

Intratumoral cytokines/chemokines/growth factors and tumor infiltrating dendritic cells: friends or enemies?

The tumor microenvironment consists of a variable combination of tumor cells, stromal fibroblasts, endothelial cells and infiltrating leukocytes, such as macrophages, T lymphocytes, and dendritic cells. A variety of cytokines, chemokines and growth factors are produced in the local tumor environment by different cells accounting for a complex cell interaction and regulation of differentiation, activation, function and survival of multiple cell types. The interaction between cytokines, chemokines, growth factors and their receptors forms a comprehensive network at the tumor site, which is primary responsible for overall tumor progression and spreading or induction of antitumor immune responses and tumor rejection. Although the general thought is that dendritic cells are among the first cells migrating to the tumor site and recognizing tumor cells for the induction of specific antitumor immunity, the clinical relevance of dendritic cells at the site of the tumor remains a matter of debate regarding their role in the generation of successful antitumor immune responses in human cancers. While several lines of evidence suggest that intratumoral dendritic cells play an important role in antitumor immune responses, understanding the mechanisms of dendritic cell/tumor cell interaction and modulation of activity and function of different dendritic cell subtypes at the tumor site is incomplete. This review is limited to discussing the role of intratumoral cytokine network in the understanding immunobiology of tumor-associated dendritic cells, which seems to possess different regulatory functions at the tumor site.

Receptor-Mediated Delivery of Antigens to Dendritic Cells: Anticancer Applications

Recently, there has been a surge of interest in the use of ex vivo antigen-pulsed dendritic cells (DCs) in the immunotherapy for cancer. DCs are powerful adjuvants with the ability to prime naive CD4+ and CD8+ T cells. As antigen sources, various preparations, including peptides, proteins, crude tumor lysates, and DCs transfected or transformed with various viruses, have been used. These procedures that involve the isolation of patient DCs and reintroduction after in vitro manipulation are time-consuming and expensive. The DC populations used frequently in ex vivo clinical studies are IL-4 and GM-CSF cultured DCs that may not represent the in vivo DC populations. An attractive method of targeting in vivo DCs is to utilize various ligands or antibodies that bind discrete populations of DCs. These cell surface receptors will direct the antigen to different antigen processing pathways depending on the targeted receptor to induce cytotoxic T cell or T helper responses. This review will discuss the various approaches and receptors that have been used for antigen targeting that may eventually be translated to alternative DC-based immunotherapies.

Pathogen recognition and development of particulate vaccines: does size matter?

The use of particulate carriers holds great promise for the development of effective and affordable recombinant vaccines. Rational development requires a detailed understanding of particle up-take and processing mechanisms to target cellular pathways capable of stimulating the required immune responses safely. These mechanisms are in turn based on how the host has evolved to recognize and process pathogens. Pathogens, as well as particulate vaccines, come in a wide range of sizes and biochemical compositions. Some of these also provide 'danger signals' so that antigen 'senting cells (APC), usually dendritic cells (DC), acquire specific stimulatory activity. Herein, we provide an overview of the types of particles currently under investigation for the formulation of vaccines, discuss cellular uptake mechanisms (endocytosis, macropinocytosis, phagocytosis, clathrin-dependent and/or caveloae-mediated) for pathogens and particles of different sizes, as well as antigen possessing and presentation by APC in general, and DC in particular. Since particle size and composition can influence the immune response, inducing humoral and/or cellular immunity, activating CD8 T cells and/or CD4 T cells of T helper 1 and/or T helper 2 type, particle characteristics have a major impact on vaccine efficacy. Recently developed methods for the formulation of particulate vaccines are presented in this issue of Methods, showcasing a range of "cutting edge" particulate vaccines that employ particles ranging from nano to micro-sized. This special issue of Methods further addresses practical issues of production, affordability, reproducibility and stability of formulation, and also includes a discussion of the economic and regulatory challenges encountered in developing vaccines for veterinary use and for common Third World infectious diseases.

Antitumor effect of OK-432-derived DNA: one of the active constituents of OK-432, a streptococcal immunotherapeutic agent

OK-432 is a Streptococcus-derived immunotherapeutic agent for malignancies. Our group has tried to identify the effective components of OK-432 and has succeeded in isolating a lipoteichoic acid-related preparation designated as OK-PSA, which is a strong inducer of T helper 1 (T(H)1) cells, and elicits an anticancer effect via Toll-like receptor (TLR) 4. Conversely, bacterial DNA with unmethylated CpG motifs can stimulate a T(H)1-type host response via TLR9. The unmethylated CpG DNA contained in OK-432 may play a role in its anticancer effect. In the current study, we investigated the effect of OK-432-derived DNA (OK-DNA) in augmenting the anticancer immune response. Analysis of OK-DNA with the restriction enzymes Hpa II and MspI revealed that OK-DNA contained unmethylated CpG motifs. OK-DNA induced TH1-type cytokines such as interferon-gamma, tumor necrosis factor-alpha, interleukin (IL)-12, and IL-18 and augmented killer cell activities in vitro on human peripheral blood mononuclear cells, whereas the methylated OK-DNA did not. Cytokines were also produced by OK-DNA-stimulated splenocytes derived from wild-type mice but not from TLR9-deficient mice. In the in vivo study, peritumoral administration of OK-DNA resulted in a significant inhibition of tumor growth in syngeneic tumor-bearing wild-type and TLR4-deficient mice but not in TLR9-deficient mice. The antitumor effect of OK-432 in TLR9-deficient mice was significantly but partially reduced compared with that in wild-type mice, whereas the effect of OK-432 was almost completely eliminated in TLR4-deficient mice. These findings suggest that unmethylated CpG DNA in OK-432 functions as an active component in OK-432-induced anticancer immunity via TLR9.

Antitumor Activity of the TLR-5 Ligand Flagellin in Mouse Models of Cancer

Flagellin, the structural protein subunit of the bacterial flagellum, is specifically recognized by TLR-5 and has potent immunomodulatory effects. The antitumor effects of purified Salmonella typhimurium flagellin were evaluated in mice transplanted s.c. with a weakly immunogenic murine tumor or with its variant stably transfected to express the highly antigenic human HER-2 oncoprotein. Peritumoral administration of flagellin 8-10 days after tumor implantation did not affect the growth rate of the weakly immunogenic tumor but significantly inhibited growth of the antigenic variant tumor. In contrast, flagellin administered at the time of implantation of the antigenic tumor led to accelerated tumor growth. These contrasting effects of flagellin on tumor growth correlated with the type of immune response induced; i.e., late flagellin administration was associated with an increased IFN-gamma:IL-4 ratio and the decreased frequency of CD4+CD25+ T regulatory cells, whereas flagellin treatment at the time of tumor implantation decreased the IFN-gamma:IL-4 ratio and increased CD4+CD25+ T cell frequency. When the early flagellin treatment was combined with administration of CpG-containing oligodeoxynucleotides, tumor growth was completely suppressed, indicating synergy between flagellin and CpG-containing oligodeoxynucleotides. Together, these data provide evidence that flagellin can have contrasting effects on tumor growth.

Mechanism of anticancer host response induced by OK-432, a streptococcal preparation, mediated by phagocytosis and Toll-like receptor 4 signaling

It has previously been reported by our group that Toll-like receptor (TLR) 4 is involved in anticancer immunity induced by OK-432, a Streptococcus-derived immunotherapeutic agent. However the detailed mechanism of the OK-432-induced immune response via TLR4 remained uncertain, because it may not be possible for OK-432, which consists of whole bacterial bodies, to bind directly to TLR4. In the current study, we conducted in vitro and in vivo experiments to investigate the hypothesis that OK-432 may first be captured and dissolved by phagocytes and that the active components released by the cells may then induce host responses via TLR4. TS-2 monoclonal antibody, which recognizes an active component of OK-432 designated OK-PSA was used in the current study. First, it was observed that OK-432-induced cytokine production by dendritic cells (DCs) and macrophages was significantly inhibited in vitro by cytochalasin B, a phagocytosis inhibitor. Immunofluorescence staining using TS-2 demonstrated that OK-432 was captured and dissolved by phagocytes. OK-PSA was detected in the supernatants derived from OK-432-treated DC culture by enzyme-linked immunosorbent assay using TS-2. Supernatants from OK-432-treated DC culture increased nuclear factor (NF)-kappaB activity in TLR4-expressing cells, and the increased activity was inhibited by TS-2 antibody. OK-432 itself did not activate NF-kappaB in these cells. In in vivo experiments, the anticancer effect of OK-432 was significantly inhibited by suppression of phagocytosis activity by cytochalasin B. In this case, the amount of OK-PSA, an active component of OK-432, in the sera was also reduced by cytochalasin B. These findings elucidated the mechanism mediated by phagocytosis and TLR4 signaling in the immune effect of OK-432.

Involvement of nitric oxide in anti-tumor effects of OK-432, a streptococcal anti-tumor immunotherapeutic agent

We examined the role of nitric oxide (NO) induced by OK-432, a streptococcal immunotherapeutic agent, in anti-tumor effects of the OK-432 by in vitro and in vivo experiments using an NO synthase inhibitor, N-monomethyl-l-arginine acetate (NMA). The in vitro treatment of mouse splenocytes with OK-432 increased the expression of inducible NO synthase (iNOS) gene and NO production in a dose-dependent manner. Although it is well known that OK-432 induces cytokines such as interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, both of which are known to be potent NO inducers, we observed only a partial reduction of OK-432-induced NO production with the addition of anti-IFN-gamma and/or anti-TNF-alpha neutralizing antibodies. The cytotoxicity of the splenocytes increased by in vitro OK-432 stimulation was almost completely inhibited by the treatment with NMA. OK-432 administration resulted in a marked prolongation of survival and a significant inhibition of tumor growth in syngeneic tumor-bearing mice, whereas NMA significantly inhibited the anti-tumor effects of OK-432. Although the increased cytotoxicity of adherent splenocytes derived from OK-432-treated tumor-bearing mice was almost completely inhibited by NMA, only partial inhibition by NMA was observed in the cytotoxicity of the nonadherent splenocytes. These findings strongly suggest that the iNOS/NO induced by OK-432 is intimately involved in the anti-tumor effects of OK-432.