Induction of specific antitumor immunity in the mouse with the electrofusion product of tumor cells and dendritic cells

A Novel Heat Shock Protein 70-Based Vaccine Prepared from DC Tumor Fusion Cells: An Update

We have developed an enhanced molecular chaperone-based vaccine through rapid isolation of Hsp70 peptide complexes after the fusion of tumor and dendritic cells (Hsp70.PC-F). In this approach, the tumor antigens are introduced into the antigen-processing machinery of dendritic cells through the cell fusion process, and thus we can obtain antigenic tumor peptides or their intermediates that have been processed by dendritic cells. Our results show that Hsp70.PC-F has increased immunogenicity compared to preparations from tumor cells alone and therefore constitutes an improved formulation of the chaperone protein-based tumor vaccine.

Cell pairing for biological analysis in microfluidic devices

Cell pairing at the single-cell level usually allows a few cells to contact or seal in a single chamber and provides high-resolution imaging. It is pivotal for biological research, including understanding basic cell functions, creating cancer treatment technologies, developing drugs, and more. Laboratory chips based on microfluidics have been widely used to trap, immobilize, and analyze cells due to their high efficiency, high throughput, and good biocompatibility properties. Cell pairing technology in microfluidic devices provides spatiotemporal research on cellular interactions and a highly controlled approach for cell heterogeneity studies. In the last few decades, many researchers have emphasized cell pairing research based on microfluidics. They designed various microfluidic device structures for different biological applications. Herein, we describe the current physical methods of microfluidic devices to trap cell pairs. We emphatically summarize the practical applications of cell pairing in microfluidic devices, including cell fusion, cell immunity, gap junction intercellular communication, cell co-culture, and other applications. Finally, we review the advances and existing challenges of the presented devices and then discuss the possible development directions to promote medical and biological research.

Combination of pioglitazone and dendritic cell to optimize efficacy of immune cell therapy in CT26 tumor models

Introduction

The maturation faith of dendritic cells is restrained by the inflammatory environment and cytokines, such as interleukin-6 and its downstream component. Therefore, introducing the suitable antigen to dendritic cells is crucial. However, reducing the severity of the suppressive tumor microenvironment is indispensable. The present study examined the combination therapy of lymphocyte antigen 6 family member E (LY6E) pulsed mature dendritic cells (LPMDCs) and pioglitazone against colorectal cancer (CRC) to elevate the effectiveness of cancer treatment through probable role of pioglitazone on inhibiting IL-6/STAT3 pathway.

Methods

Dendritic cells were generated from murine bone marrow and were pulsed with lymphocyte antigen 6 family member E peptide to assess antigen-specific T-cell proliferation and cytotoxicity assay with Annexin/PI. The effect of pioglitazone on interleukin (IL)-6/STAT3 was evaluated in vitro by real-time polymerase chain reaction (PCR). Afterward, the CRC model was established by subcutaneous injection of CT26, mouse colon carcinoma cell line, in female mice. After treatment, tumor, spleen, and lymph nodes samples were removed for histopathological, ELISA, and real-time PCR analysis.

Results

In vitro results revealed the potential of lysate-pulsed dendritic cells in the proliferation of double-positive CD3-8 splenocytes and inducing immunogenic cell death responses, whereas pioglitazone declined the expression of IL-6/STAT3 in colorectal cell lines. In animal models, the recipient of LPMDCs combined with pioglitazone demonstrated high tumor-infiltrating lymphocytes. Elevating the IL-12 and interferon-gamma (IFN-γ) levels and prolonged survival in lysate-pulsed dendritic cell and combination groups were observed.

Conclusion

Pioglitazone could efficiently ameliorate the immunosuppressive feature of the tumor microenvironment, mainly through IL-6. Accordingly, applying this drug combined with LPMDCs provoked substantial CD8 positive responses in tumor-challenged animal models.

Tumor cell-based vaccine: an effective strategy for eradication of cancer cells

Whole tumor cell-based vaccines include all potential antigen-rich cell lysates to target a specific type of tumor without the need to find the best antigen candidate in protein- or peptide-based vaccines. Preparation of whole tumor cell lysates inducing cell death and inactivating immunosuppressive cytokine secretion from the tumor cells is highly enviable. Generally, modified whole tumor cells, tumor cell-derived exosomes, autologous tumor cell-derived ribonucleic acid, and personalized mutanome-derived tumor antigen are promising immunotherapeutic approaches. Autologous dendritic cells loaded with tumor-associated antigens also induce the generation of immunological memory and antitumor response as an effective method for the treatment of cancer. The present review briefly describes tumor cell-based vaccines as a promising strategy for eradication of cancer cells.

A Novel Heat Shock Protein 70-based Vaccine Prepared from DC-Tumor Fusion Cells

We have developed an enhanced molecular chaperone-based vaccine through rapid isolation of Hsp70 peptide complexes after the fusion of tumor and dendritic cells (Hsp70.PC-F). In this approach, the tumor antigens are introduced into the antigen processing machinery of dendritic cells through the cell fusion process and thus we can obtain antigenic tumor peptides or their intermediates that have been processed by dendritic cells. Our results show that Hsp70.PC-F has increased immunogenicity compared to preparations from tumor cells alone and therefore constitutes an improved formulation of chaperone protein-based tumor vaccine.

A microfluidic approach towards hybridoma generation for cancer immunotherapy

Dendritic cells/tumor fusions have shown to elicit anti-cancer immunity in different cancer types. However, the application of these vaccines for human cancer immunotherapy are limited by the instable quality and insufficient quanity of fusion cells. We present a cell electrofusion chip fabricated using soft lithography technique, which combines the rapid and precise cell pairing microstructures and the high yield electrofusion micro-electrodes to improve the cell fusion. The design uses hydrodynamic trapping in combination with positive dielectrophoretic force (pDEP) to achieve cell fusion. The chip consists of total 960 pairs of trapping channels, which are capable of pairing and fusing both homogeneous and heterogeneous types of cells. The fused cells can be easily taken out of the chip that makes this device a distinguishable from other designs. We observe pairing efficiency of 68% with fusion efficiency of 64%.

The in vitro generation of multi-tumor antigen-specific cytotoxic T cell clones: Candidates for leukemia adoptive immunotherapy following allogeneic stem cell transplantation

Adoptive T-cell immunotherapy is a promising approach to manage and maintain relapse-free survival of leukemia patients, especially following allogeneic stem cell transplantation. Post-transplant adoptive immunotherapy using cytotoxic T lymphocytes (CTLs) of the donor origin provide graft-versus-tumor effects, with or without graft-versus-host disease. Myeloid leukemias express immunogenic leukemia associated antigens (LAAs); such as WT-1, PRAME, MAGE, h-TERT and others, most of them are able to induce specific T cell responses whenever associated with the proper co-stimulation. We investigated the ability of a LAA-expressing hybridoma cell line to induce CTL clones in PBMCs of HLA-matched healthy donors in vitro. The CTL clones were induced by repetitive co-culture with LAAs-expressing, HLA-A*0201(+) hybrid cell line, generated by fusion of leukemia blasts to human immortalized APC (EBV-sensitized B-lymphoblastoid cell line; HMy2). The induced cytotoxic T cell clones were phenotypically and functionally characterized by pentamer analysis, IFN-γ release ELISPOT and cellular cytotoxicity assays. All T cell lines showed robust peptide recognition and functional activity when sensitized with HLA-A*0201-restricted WT-1235-243, hTERT615-624 or PRAME100-108 peptides-pulsed T2 cells, in addition to partially HLA-matched leukemia blasts. This study demonstrates the feasibility of developing multi-tumor antigen-specific T cell lines in allogeneic PBMCs in vitro, using LAA-expressing tumor/HMy2 hybrid cell line model, for potential use in leukemia adoptive immunotherapy in partially matched donor-recipient setting.

In Vivo Silencing of A20 via TLR9-Mediated Targeted SiRNA Delivery Potentiates Antitumor Immune Response

A20 is an ubiquitin-editing enzyme that ensures the transient nature of inflammatory signaling pathways induced by cytokines like TNF-α and IL-1 or pathogens via Toll-like receptor (TLR) pathways. It has been identified as a negative regulator of dendritic cell (DC) maturation and attenuator of their immunostimulatory properties. Ex vivo A20-depleted dendritic cells showed enhanced expression of pro-inflammatory cytokines and costimulatory molecules, which resulted in hyperactivation of tumor-infiltrating T lymphocytes and inhibition of regulatory T cells. In the present study, we demonstrate that a synthetic molecule consisting of a CpG oligonucleotide TLR9 agonist linked to A20-specific siRNAs silences its expression in TLR9⁺ mouse dendritic cells in vitro and in vivo. In the B16 mouse melanoma tumor model, silencing of A20 enhances the CpG-triggered induction of NFκB activity followed by elevated expression of IL-6, TNF-α and IL-12. This leads to potentiated antitumor immune responses manifested by increased numbers of tumor-specific cytotoxic T cells, high levels of tumor cell apoptosis and delayed tumor growth. Our findings confirm the central role of A20 in controlling the immunostimulatory potency of DCs and provide a strategy for simultaneous A20 silencing and TLR activation in vivo.

Antigen-loaded dendritic cell migration: MR imaging in a pancreatic carcinoma model

PURPOSE

To test the following hypotheses in a murine model of pancreatic cancer: (a) Vaccination with antigen-loaded iron-labeled dendritic cells reduces T2-weighted signal intensity at magnetic resonance (MR) imaging within peripheral draining lymph nodes ( LN lymph node s) and (b) such signal intensity reductions are associated with tumor size changes after dendritic cell vaccination.

MATERIALS AND METHODS

The institutional animal care and use committee approved this study. Panc02 cells were implanted into the flanks of 27 C57BL/6 mice bilaterally. After tumors reached 10 mm, cell viability was evaluated, and iron-labeled dendritic cell vaccines were injected into the left hind footpad. The mice were randomly separated into the following three groups (n = 9 in each): Group 1 was injected with 1 million iron-labeled dendritic cells; group 2, with 2 million cells; and control mice, with 200 mL of phosphate-buffered saline. T1- and T2-weighted MR imaging of labeled dendritic cell migration to draining LN lymph node s was performed before cell injection and 6 and 24 hours after injection. The signal-to-noise ratio ( SNR signal-to-noise ratio ) of the draining LN lymph node s was measured. One-way analysis of variance ( ANOVA analysis of variance ) was used to compare Prussian blue-positive dendritic cell measurements in LN lymph node s. Repeated-measures ANOVA analysis of variance was used to compare in vivo T2-weighted SNR signal-to-noise ratio LN lymph node measurements between groups over the observation time points.

RESULTS

Trypan blue assays showed no significant difference in mean viability indexes (unlabeled vs labeled dendritic cells, 4.32% ± 0.69 [standard deviation] vs 4.83% ± 0.76; P = .385). Thirty-five days after injection, the mean left and right flank tumor sizes, respectively, were 112.7 mm(2) ± 16.4 and 109 mm(2) ± 24.3 for the 1-million dendritic cell group, 92.2 mm(2) ± 9.9 and 90.4 mm(2) ± 12.8 for the 2-million dendritic cell group, and 193.7 mm(2) ± 20.9 and 189.4 mm(2) ± 17.8 for the control group (P = .0001 for control group vs 1-million cell group; P = .00007 for control group vs 2-million cell group). There was a correlation between postinjection T2-weighted SNR signal-to-noise ratio decreases in the left popliteal LN lymph node 24 hours after injection and size changes at follow-up for tumors in both flanks (R = 0.81 and R = 0.76 for left and right tumors, respectively).

CONCLUSION

MR imaging approaches can be used for quantitative measurement of accumulated iron-labeled dendritic cell-based vaccines in draining LN lymph node s. The amount of dendritic cell-based vaccine in draining LN lymph node s correlates well with observed protective effects.

Various ways to improve whole cancer cell vaccines

Immunotherapy based on whole cancer cell vaccines is regarded as a promising avenue for cancer treatment. However, limited efficacy in the first human clinical trials calls for more optimized whole cancer cell vaccines and better patient selection. It is suggested that whole cancer cell vaccines consist preferably of immunogenically killed autologous cancer stem cells associated with dendritic cells. Adjuvants should stimulate both immune effector cells and memory cells, which could be achieved through their correct dosage and timing of administration. There are indications that whole cancer cell vaccination is less effective in patients who are immunocompromised, who have specific genetic defects in their immune or cancer cells, as well as in patients in an advanced cancer stage. However, such patients form the bulk of enrolled patients in clinical trials, prohibiting an objective evaluation of the true potential of whole cancer cell immunotherapy. Each key point will be discussed.

Purified dendritic cell-tumor fusion hybrids supplemented with non-adherent dendritic cells fraction are superior activators of antitumor immunity

Background

Strong evidence supports the DC-tumor fusion hybrid vaccination strategy, but the best fusion product components to use remains controversial. Fusion products contain DC-tumor fusion hybrids, unfused DCs and unfused tumor cells. Various fractions have been used in previous studies, including purified hybrids, the adherent cell fraction or the whole fusion mixture. The extent to which the hybrids themselves or other components are responsible for antitumor immunity or which components should be used to maximize the antitumor immunity remains unknown.

Methods

Patient-derived breast tumor cells and DCs were electro-fused and purified. The antitumor immune responses induced by the purified hybrids and the other components were compared.

Results

Except for DC-tumor hybrids, the non-adherent cell fraction containing mainly unfused DCs also contributed a lot in antitumor immunity. Purified hybrids supplemented with the non-adherent cell population elicited the most powerful antitumor immune response. After irradiation and electro-fusion, tumor cells underwent necrosis, and the unfused DCs phagocytosed the necrotic tumor cells or tumor debris, which resulted in significant DC maturation. This may be the immunogenicity mechanism of the non-adherent unfused DCs fraction.

Conclusions

The non-adherent cell fraction (containing mainly unfused DCs) from total DC/tumor fusion products had enhanced immunogenicity that resulted from apoptotic/necrotic tumor cell phagocytosis and increased DC maturation. Purified fusion hybrids supplemented with the non-adherent cell population enhanced the antitumor immune responses, avoiding unnecessary use of the tumor cell fraction, which has many drawbacks. Purified hybrids supplemented with the non-adherent cell fraction may represent a better approach to the DC-tumor fusion hybrid vaccination strategy.

Microarray of non-connected gold pads used as high density electric traps for parallelized pairing and fusion of cells

Cell fusion consists of inducing the formation of a hybridoma cell containing the genetic properties of the progenitor cells. Such an operation is usually performed chemically or electrically. The latter method, named electrofusion, is considered as having a strong potential, due to its efficiency and non-toxicity, but deserves further investigations prior to being applicable for key applications like antibody production and cancer immunotherapy. Indeed, to envision such applications, a high amount of hybrid cells is needed. In this context, we present in this paper a device for massive cell pairing and electrofusion, using a microarray of non-connected conductive pads. The electrofusion chamber--or channel--exposes cells to an inhomogeneous electric field, caused by the pads array, enabling the trapping and pairing of cells with dielectrophoresis (DEP) forces prior to electrofusion. Compared to a mechanical trapping, such electric trapping is fully reversible (on/off handling). The DEP force is contactless and thus eases the release of the produced hybridoma. Moreover, the absence of wire connections on the pads permits the high density trapping and electrofusion of cells. In this paper, the electric field mapping, the effect of metallic pads thickness, and the transmembrane potential of cells are studied based on a numerical model to optimize the device. Electric calculations and experiments were conducted to evaluate the trapping force. The structure was finally validated for cell pairing and electrofusion of arrays of cells. We believe that our approach of fully electric trapping with a simple structure is a promising method for massive production of electrofused hybridoma.

Antigen presenting cell/ tumor cell fusion vaccines for cancer immunotherapy

Fusions of antigen presenting cells and tumor cells have been investigated in animal models and phase I/II clinical trials as candidate cancer vaccines. In animal studies there have been numerous reports of induction of protective immunity against a wide range of tumor types. Results of clinical trials have been less dramatic, but tumor-specific immune responses have been reported in many patients, with clinical responses to the vaccination in a subset. In this commentary article, I review the current status of antigen presenting cell/tumor cell fusion vaccines for cancer immunotherapy.

Allogeneic mRNA-based electrotransfection of autologous dendritic cells and specific antitumor effects against osteosarcoma in rats

Vaccination with dendritic cells (DCs) transfected with tumor-derived mRNA antigen has emerged as a promising strategy for generating protective immunity in mammals. However, the integration of allogeneic osteosarcoma mRNA and autologous DCs has not been fully examined. This study was designed to investigate the antitumor effects of tumor vaccine produced by autologous DCs transfected of allogeneic osteosarcoma mRNA through electroporation in tumor-bearing rats model. In the present study, extraction of Wistar rat tumor mRNA was performed as a two-step procedure. First, total RNA was extracted by use of Trizol; then, mRNA purification was performed by use of polyT-coated magnetic beads. Then, we transfected the allogeneic-derived tumor mRNA to Sprague-Dawley (SD) rat bone marrow-derived DCs through electroporation. The tumor vaccine was applied to tumor-bearing rats model, and the specific antitumor effects of the tumor vaccine were observed. The immunization using autologous DCs electrotransfected with allogeneic osteosarcoma total RNA induced specific CTL responses, which were statistically significant (P < 0.05), and the cytotoxic activity was confirmed in cold target inhibition assays and using mAbs blocking MHC class I molecules. In in vivo experiments, 70 % of the rats immunized with allogeneic osteosarcoma RNA transfected to DCs were typically able to reject tumor challenge and remained tumor-free. Vaccinated survivors developed long immunological memory and were able to reject a subsequent rechallenge with the same tumor cells but not a syngeneic unrelated tumor line. In the present study, we demonstrated that allogeneic tumor mRNA isolated from rat osteosarcoma cell line could be applied to produce tumor vaccine inducing specific antitumor effects, especially in DC-based immunotherapy strategy. This study also provides the foundations for an effective and broadly applicable treatment to a wide range of cancer indications for which tumor-associated antigens have not been identified.

Anti-glioma response of autologous T cells stimulated by autologous dendritic cells electrofused with CD133+ or CD133- glioma cells

Glioma, the most common tumor of the central nervous system (CNS), currently results in a high rate of morbidity and mortality. The expression of CD133, a stem-like cell marker expressed in the glioma cells, is believed to lead to tumorigenesis in the human brain. Thus, it is necessary to find a proper method to specifically kill the CD133(+) glioma cells. Dendritic cell (DC)/tumor hybrids are proven to be able to induce an effective immune response, leading to killing of glioma cells in vitro. We isolated CD133(+) cells from a population of primary glioma cells, and cultured autologous DCs and T cells at the same time. Next, we electrofused the DCs with the CD133(+) glioma cells and with CD133- ones, in order to explore a new strategy for glioma therapy. We then exposed the T cells to five separate groups of cells: DC/CD133(+) hybrids, DC/CD133(-) hybrids, DCs alone, unsorted glioma cells alone and mixed DCs-glioma cells. A cytotoxicity assay showed that T cells stimulated by either type of hybrid were able to kill cultured autologous glioma cells significantly more effectively than those stimulated by the other three cell types (P<0.05). The amounts of IFN-γ secreted by T cells stimulated by the two types of fused cells were obviously increased compared to those stimulated by the other three cell types (P<0.05). However, no significant differences were noted between the effects of the two hybrids, neither in the cytotoxicity assay nor in the IFN-γ release assay (P>0.05). Therefore, both DC/CD133(+) and DC/CD133(-) hybrids can cause significant T cell immune responses in vitro. There were no significant differences between the immune responses caused by the two types of hybrids.

Allogeneic tumor vaccine produced by electrofusion between osteosarcoma cell line and dendritic cells in the induction of antitumor immunity

OBJECTIVE

Fusion of dendritic cells, DCs, with tumor cells is an effective approach for delivering tumor antigens to DCs, and DC-tumor fusion cells are potent stimulators of T cells. However, the integration of allogeneic DC-osteosarcoma fusion cells has not been fully examined. This study was designed to investigate the antitumor effects of tumor vaccine produced by electrofusion between rat osteosarcoma cells and allogeneic DCs.

METHODS

In the present study, we electrofused Wistar rat bone marrow-derived DCs to SD rat osteosarcoma cells (UMR106) and purified them by monoclonal antibody OX62 and magnetic beads. Coculture of SD or Wistar bone marrow derived T lymphocytes with DC-tumor fusion cells resulted in activation of T cells, and the proportion of CD8(+), CD4(+) cells was determined using flow cytometry. Then cytotoxic T lymphocytes, CTLs, assay was assessed according to results of MTT assay.

RESULTS

After T cells were cultured with allogeneic DC-osteosarcoma fusion cells, DOF, and effective activation of T cells was observed. The proportion of CD8(+) cells in the SD T cell group increases from 34.16% before induction to 74.85%, while that of CD4(+) cells is from 63.35% to 71.75% in Wistar T cell group. The immunization using allogeneic DC-osteosarcoma vaccine induced UMR106-specific CTL responses which were statistically significant (P < 0.05) and the cytotoxic activity was inhibited by the treatment with anti-CD8 and anti-MHC-class I monoclonal antibodies but not with anti-CD4 and anti-MHC-class II antibodies.

CONCLUSION

The present study provided valid evidence of integration of rat allogeneic DCs electrofused with tumor cells and analyzed their properties in T cell activation. The fusion cells may thus represent a promising strategy for DC-based immunotherapy of patients with osteosarcoma.

Immunologic monitoring of cellular responses by dendritic/tumor cell fusion vaccines

Although dendritic cell (DC)- based cancer vaccines induce effective antitumor activities in murine models, only limited therapeutic results have been obtained in clinical trials. As cancer vaccines induce antitumor activities by eliciting or modifying immune responses in patients with cancer, the Response Evaluation Criteria in Solid Tumors (RECIST) and WHO criteria, designed to detect early effects of cytotoxic chemotherapy in solid tumors, may not provide a complete assessment of cancer vaccines. The problem may, in part, be resolved by carrying out immunologic cellular monitoring, which is one prerequisite for rational development of cancer vaccines. In this review, we will discuss immunologic monitoring of cellular responses for the evaluation of cancer vaccines including fusions of DC and whole tumor cell.

Cancer immunotherapy by fusions of dendritic cells and tumor cells

Dendritic cells (DCs) are potent professional antigen-presenting cells and play a critical role in the induction of primary immune responses. DC-based vaccination represents a potentially powerful strategy for cancer immunotherapy. Thus, the use of cancer vaccines to eliminate residual tumor cells is a promising area of investigation. The immunotherapy of tumor antigen-loaded DCs has now been demonstrated in cancer patients and some clinical responses without any significant toxicity. Fusions of DCs and tumor cells represent an alternative but promising approach to overcome the inability of tumor antigens to induce a sustainable T-cell response. This review deals with recent progress in the immunotherapy of cancer with fusions of DCs and tumor cells.

Preparation of a heat-shock protein 70-based vaccine from DC-tumor fusion cells

We have developed an enhanced molecular chaperone-based vaccine through rapid isolation of heat-shock protein 70 peptide complexes (Hsp70.PC) after the fusion of tumor and dendritic cells (DCs) (Hsp70.PC-F). In this approach, the tumor antigens are introduced into the antigen-processing machinery of dendritic cells through the cell fusion process and, thus, we can obtain antigenic tumor peptides or their intermediates that have been processed by dendritic cells. Our results show that Hsp70.PC-F has increased immunogenicity compared to preparations from tumor cells alone and, therefore, constitutes an improved formulation of chaperone protein-based tumor vaccine.

Regulation of tumor immunity by tumor/dendritic cell fusions

The goal of cancer vaccines is to induce antitumor immunity that ultimately will reduce tumor burden in tumor environment. Several strategies involving dendritic cells- (DCs)- based vaccine incorporating different tumor-associated antigens to induce antitumor immune responses against tumors have been tested in clinical trials worldwide. Although DCs-based vaccine such as fusions of whole tumor cells and DCs has been proven to be clinically safe and is efficient to enhance antitumor immune responses for inducing effective immune response and for breaking T-cell tolerance to tumor-associated antigens (TAAs), only a limited success has occurred in clinical trials. This paper reviews tumor immune escape and current strategies employed in the field of tumor/DC fusions vaccine aimed at enhancing activation of TAAs-specific cytotoxic T cells in tumor microenvironment.

Human myeloid dendritic cells for cancer therapy: does maturation matter?

Dendritic cells form the connection between innate and adoptive mechanisms of the immune system. As antigen-presenting cells, dendritic cells are capable of presenting tumour antigen and effectively stimulating immune response targeted against a tumour. A number of preclinical and clinical studies document dendritic cells' potential in anti-cancer treatment. Increasing knowledge of dendritic cell biology is leading to improved methods for their preparation for clinical application. Unfortunately, there is to date no consensus specifying optimal conditions for dendritic cell preparation in vitro. This review summarizes the methods used for preparing myeloid dendritic cells derived from monocytic precursors while focusing on cytokine cocktails used for their growth, maturation, and functional adjustment.

Induction of antitumor immunity by semi-allogeneic and fully allogeneic electrofusion products of tumor cells and dendritic cells

Immunization with the electrofusion product of tumor cells and dendritic cells (DCs) is a promising approach to cancer immunotherapy. Production of electrofusion vaccines currently requires the acquisition of tumor material and must be tailored to each individual. Alternative vaccine configurations were explored in this study. Results indicated that fusion vaccines with fully syngeneic, semi-allogeneic or fully allogeneic components, were all effective in inducing specific, long-lasting antitumor immunity. This previously undescribed activity of a fully allogeneic fusion product introduces the possibility of using defined allogeneic tumor and DC lines to simplify vaccine manufacturing.

Antigen-specific polyclonal cytotoxic T lymphocytes induced by fusions of dendritic cells and tumor cells

The aim of cancer vaccines is induction of tumor-specific cytotoxic T lymphocytes (CTLs) that can reduce the tumor mass. Dendritic cells (DCs) are potent antigen-presenting cells and play a central role in the initiation and regulation of primary immune responses. Thus, DCs-based vaccination represents a potentially powerful strategy for induction of antigen-specific CTLs. Fusions of DCs and whole tumor cells represent an alternative approach to deliver, process, and subsequently present a broad spectrum of antigens, including those known and unidentified, in the context of costimulatory molecules. Once DCs/tumor fusions have been infused back into patient, they migrate to secondary lymphoid organs, where the generation of antigen-specific polyclonal CTL responses occurs. We will discuss perspectives for future development of DCs/tumor fusions for CTL induction.

Cancer vaccine by fusions of dendritic and cancer cells

Dendritic cells (DCs) are potent antigen-presenting cells and play a central role in the initiation and regulation of primary immune responses. Therefore, their use for the active immunotherapy against cancers has been studied with considerable interest. The fusion of DCs with whole tumor cells represents in many ways an ideal approach to deliver, process, and subsequently present a broad array of tumor-associated antigens, including those yet to be unidentified, in the context of DCs-derived costimulatory molecules. DCs/tumor fusion vaccine stimulates potent antitumor immunity in the animal tumor models. In the human studies, T cells stimulated by DC/tumor fusion cells are effective in lysis of tumor cells that are used as the fusion partner. In the clinical trials, clinical and immunological responses were observed in patients with advanced stage of malignant tumors after being vaccinated with DC/tumor fusion cells, although the antitumor effect is not as vigorous as in the animal tumor models. This review summarizes recent advances in concepts and techniques that are providing new impulses to DCs/tumor fusions-based cancer vaccination.

Cell fusion: from hybridoma to dendritic cell-based vaccine

The deployment of dendritic cell (DC) and tumor cell fusions is increasing in tumor immunotherapy. In animal and human studies, fusion cell vaccines have been shown to possess the elements essential for processing and presenting tumor antigens to host immune cells, for inducing effective immune response and for breaking T-cell tolerance to tumor-associated antigens. Moreover, fusion cell vaccines provide protection against challenge with tumor cells and mediate regression of established tumors. Despite these unique features of fusion cell vaccines and the observation of tumor eradication in animal studies, limited success has occurred in clinical trials. This article reviews the methods used for optimizing the preparation and selection of DC-tumor fusion cells and analyzes factors influencing the success or failure of fusion cell-mediated immunotherapy. In addition, we discuss the challenges facing effective fusion cell vaccine production, including factors in preparation, selection and quality control of fusion cell vaccines, as well as approaches for enhancing anti-tumor immunity.

HVJ envelope vector, a versatile delivery system: its development, application, and perspectives

An efficient and minimally invasive vector system is the "bottle neck" of both gene transfer and drug delivery. Numerous viral and non-viral (synthetic) delivery systems have been developed and improved. Hemagglutinating virus of Japan (HVJ, Sendai virus) envelope vector is a novel and unique system which combined the advantages of viral and non-viral vectors with the following features and advantages: (1) safe and easy as a "non-viral" transfection reagent; (2) delivery of various molecules including plasmid DNA, siRNA, protein, antisense oligonucleotide; (3) wide usability from in vitro to in vivo. In this review, the development, application, and perspectives of the HVJ envelope vector will be discussed.

Whole-cell cancer vaccination: from autologous to allogeneic tumor- and dendritic cell-based vaccines

The field of tumor vaccination is currently undergoing a shift in focus, from individualized tailor-made vaccines to more generally applicable vaccine formulations. Although primarily predicated by financial and logistic considerations, stemming from a growing awareness that clinical development for wide-scale application can only be achieved through backing from major pharmaceutical companies, these new approaches are also supported by a growing knowledge of the intricacies and minutiae of antigen presentation and effector T-cell activation. Here, the development of whole-cell tumor and dendritic cell (DC)-based vaccines from an individualized autologous set-up to a more widely applicable allogeneic approach will be discussed as reflected by translational studies carried out over the past two decades at our laboratories and clinics in the vrije universiteit medical center (VUmc) in Amsterdam, The Netherlands.

Phase I/II study of vaccination with electrofused allogeneic dendritic cells/autologous tumor-derived cells in patients with stage IV renal cell carcinoma

In the present study, we assessed the feasibility, toxicity, immunologic response, and clinical efficacy of vaccination with allogeneic dendritic cell (DC)/tumor fusions in patients with metastatic renal cell carcinoma (RCC). Patients with stage IV RCC with accessible tumor lesions or independent therapeutic indications for nephrectomy were eligible for enrollment. Tumors were processed into single cell suspensions and cryopreserved. DCs were generated from adherent peripheral blood mononuclear cells isolated from normal volunteers and cultured with granulocyte macrophage colony-stimulating factor, interleukin-4, and tumor necrosis factor-alpha. DCs were fused to patient derived RCC with serial electrical pulses. Patients received up to 3 vaccinations at a fixed dose of 4x10(7) to 1x10(8) cells administered at 6-week intervals. Twenty-four patients underwent vaccination. Twenty-one and 20 patients were evaluable for immunologic and clinical response, respectively. DCs demonstrated a characteristic phenotype with prominent expression of HLA class II and costimulatory molecules. A mean fusion efficiency of 20% was observed, determined by the percent of cells coexpressing DC and tumor antigens. No evidence of significant treatment related toxicity or auto-immunity was observed. Vaccination resulted in antitumor immune responses in 10/21 evaluable patients as manifested by an increase in CD4 and/or CD8 T-cell expression of interferon-gamma after ex vivo exposure to tumor lysate. Two patients demonstrated a partial clinical response by Response Evaluation Criteria in Solid Tumors criteria and 8 patients had stabilization of their disease. Vaccination of patients with RCC with allogeneic DC/tumor fusions was feasible, well tolerated, and resulted in immunologic and clinical responses in a subset of patients.

Autologous versus allogeneic peptide-pulsed dendritic cells for anti-tumour vaccination: expression of allogeneic MHC supports activation of antigen specific T cells, but impairs early naïve cytotoxic priming and anti-tumour therapy

BACKGROUND

Dendritic cells (DC) pulsed with MHC class I-restricted tumour associated antigen (TAA) peptides have been widely tested in pre-clinical models and early clinical studies for their ability to prime cytotoxic T cell (CTL) responses. The effect of co-expression of allogeneic MHC antigens on DC immunogenicity has not been addressed, and has implications for the feasibility of clinical applications.

OBJECTIVE

This study compared DC from autologous H-2(b) or semi-allogeneic F1 H-2(bxk) mice pulsed with the H-2(b)-restricted model ovalbumin (OVA) peptide SIINFEKL, and compared in vitro and in vivo their ability to (i) activate specific OT1 cells, (ii) prime naïve CTL, and (iii) protect against B16.OVA challenge. Peptide-pulsed autologous and allogeneic DC were also tested in naïve human CTL priming assays.

RESULTS

Semi-allogeneic DC expressed higher levels of co-stimulatory molecules. On pulsing with SIINFEKL they triggered greater proliferation of OT1 cells in vitro and in vivo, but were less effective at naïve CTL priming and tumour protection. Autologous human DC were similarly more potent at naïve CTL priming against the melanoma-associated TAA MART-1 in vitro.

CONCLUSION

The expression of allogeneic MHC antigens on peptide-pulsed DC impairs naïve CTL priming and anti-tumour effects, despite effective TAA presentation both in vitro and in vivo.

Semi-allogeneic dendritic cells can induce antigen-specific T-cell activation, which is not enhanced by concurrent alloreactivity

BACKGROUND

Alloreactive T-cell responses are known to result in the production of large amounts of proinflammatory cytokines capable of activating and maturing dendritic cells (DC). However, it is unclear whether these allogeneic responses could also act as an adjuvant for concurrent antigen-specific responses.

OBJECTIVE

To examine effects of simultaneous alloreactive and antigen-specific T-cell responses induced by semi-allogeneic DC.

METHODS

Semi-allogeneic DC were generated from the F(1) progeny of inbred strains of mice (C57BL/6 and C3H, or C57BL/6 and DBA). We directly primed antigen-specific CD8(+) and CD4(+) T-cells from OT-I and OT-II mice, respectively, in the absence of allogeneic responses, in vitro, and in the presence or absence of alloreactivity in vivo.

RESULTS

In vitro, semi-allogeneic DC cross-presented ovalbumin (OVA) to naïve CD8(+) OT-I transgenic T-cells, primed naïve CD4(+) OT-II transgenic T-cells and could stimulate strong alloreactive T-cell proliferation in a primary mixed lymphocyte reaction (MLR). In vivo, semi-allogeneic DC migrated efficiently to regional lymph nodes but did not survive there as long as autologous DC. In addition, they were not able to induce cytotoxic T-lymphocyte (CTL) activity to a target peptide, and only weakly stimulated adoptively transferred OT-II cells. The CD4(+) response was unchanged in allo-tolerized mice, indicating that alloreactive T-cell responses could not provide help for concurrently activated antigen-specific responses. In an EL4 tumour-treatment model, vaccination with semi-allogeneic DC/EL4 fusion hybrids, but not allogeneic DC/EL4 hybrids, significantly increased mouse survival.

CONCLUSION

Expression of self-Major histocompatibility complex (MHC) by semi-allogeneic DC can cause the induction of antigen-specific immunity, however, concurrently activated allogeneic bystander responses do not provide helper or adjuvant effects.

Enhancement of dendritic cell-tumor fusion vaccine potency by indoleamine-pyrrole 2,3-dioxygenase inhibitor, 1-MT

PURPOSE

Dendritic cell (DC)-based cancer vaccines are currently being evaluated as novel anti-tumor vaccination strategies, but in some cases, they are demonstrated to have poor clinical efficacies than anticipated. A potential reason is immune tolerance due to the immunosuppressive enzyme, indoleamine-pyrrole 2,3-dioxygenase (IDO). The aim of this study was to determine whether blocking the activity of IDO might improve the anti-tumor efficacy of DC/Lewis lung carcinoma (LLC) fusion vaccine applied to the mouse LLC model.

METHODS

To prepare the DC/LLC fusion vaccine, DCs were fused with LLC using polyethylene glycol (PEG) as described. The IDO expression in the DC/LLC fusion vaccine and in the vaccinated mice was detected by western blot (WB) and/or immunohistochemical (IHC) analysis. This fusion vaccine, as a single agent or in combination with 1-methyl-tryptophan (1-MT, an IDO inhibitor), was administered to LLC mice. The anti-tumor efficacy in different treatment was determined by regular observation of tumor development and the level of splenic cytotoxic T lymphocyte (CTL) response, which was examined by lactate dehydrogenase (LDH) release.

RESULTS

In the LLC mice, we observed that IDO-positive cells were extensively accumulated in tumor draining lymph nodes (TDLNs). Furthermore, WB and IHC analysis results showed that vaccination with fusion DC/LLC cells alone caused significant up-regulation of IDO in spleens. 1-MT enhanced the anti-tumor efficacy elicited by DC/LLC fusion vaccine via delaying the tumor development and inducing stronger splenic CTL responses.

CONCLUSIONS

Our results indicate an IDO-mediated immunosuppressive mechanism might be involved in weakening the anti-tumor efficacy elicited by DC/LLC fusion vaccine, and specific inhibition of IDO activity might be required for development of cancer vaccines.

Superior anti-tumor protection and therapeutic efficacy of vaccination with allogeneic and semiallogeneic dendritic cell/tumor cell fusion hybrids for murine colon adenocarcinoma

Cancer immunotherapy by dendritic cell (DC)/tumor cell fusion hybrids (DC/TC hybrids) has been shown to elicit potent anti-tumor effects via the induction of immune responses against multiple tumor-associated antigens. In the present study, we compared the anti-tumor effects of vaccinating Balb/c mice (H-2(d)) with CT26CL25 colon carcinoma cells that had been fused with either syngeneic DCs from Balb/c mice, allogeneic DCs from C57BL/6 mice (H-2(b)) or semiallogeneic DCs from B6D2F1 mice (H-2(b/d)). Preimmunization with either semiallogeneic or allogeneic DC/TC hybrids induced complete protection from tumor challenge, whereas mice preimmunized with syngeneic DC/TC hybrids were only partially protected (75% tumor rejection). The average number of pulmonary metastases after intravenous tumor injection decreased significantly following immunization with semiallogeneic or allogeneic DC/TC hybrids (8.3 +/- 7.9 or 16.3 +/- 3.5, mean +/- SD) relative to syngeneic DC/TC hybrids (67.8 +/- 6.3). These data demonstrate that vaccination with semiallogeneic DC/TC hybrids resulted in the greatest anti-tumor efficacy. Anti-tumor effects showed by in vivo studies were virtually accomplished by the frequency of induced CTLs specific to both gp70 and beta-galactosidase assessed by using pentameric assay. Among the fusion vaccines tested, semiallogeneic DC/TC hybrids induced the highest ratio of Th1 cytokine IFN-gamma to Th2 cytokine IL-10. In addition, allogeneic or semiallogeneic DC/TC hybrids elicited a significantly stronger NK activity than syngeneic DC/TC hybrids. These findings suggest that in clinical settings, DCs derived from a healthy donor (which are generally characterized as more semiallogeneic than allogeneic) may be more capable than autologous DCs of inducing promising anti-tumor effects in vaccinations with DC/TC hybrids.

Dendritic cells pulsed or fused with AML cellular antigen provide comparable in vivo antitumor protective responses

OBJECTIVE

To investigate whether syngeneic BM-derived DCs generated in vitro and fused with syngeneic C1498 tumor cells (murine AML line) could induce a better antitumor protective effect compared to similarly generated DCs pulsed with C1498 lysate with or without co-injection of a class B CpG oligodeoxynucleotide (CpG 7909) in vivo.

METHODS

DCs were pulsed with C1498 lysate prior to intravenous administration 14 and 7 days prior to tumor challenge. Separate cohorts received DCs electrically fused to irradiated C1498 cells. Cohorts were administered DCs that were lysate-pulsed or fused with tumor cells on days 14 and 7 prior to tumor injection. Some cohorts were co-injected with CpG 7909 at the time of DC administration.

RESULTS

All DC vaccines significantly improved survival (p < 0.01) vs nonvaccinated controls. There was no difference in the antitumor protective response between mice that received pulsed vs fused DCs (47% vs 45% survival). Both DC vaccines generated a fivefold increase in splenic tumor-reactive cytotoxic T-lymphocyte precursor cells and significantly (p < 0.05) higher mean frequencies of IFN-gamma-producing splenocytes compared to controls. CpG 7909 improved the survival of mice receiving the fused DCs (p < 0.05) but not the pulsed DCs. Surviving mice were rechallenged and found to be resistant to lethal tumor injection.

CONCLUSIONS

DC vaccine strategies may be effective in generating anti-AML responses. No advantage was observed between lysate-pulsed and tumor cell-fused DCs. CpGs may provide an adjuvant effect depending on the type of DC vaccine administered.

Vaccination therapy in malignant disease

Improvement in survival among patients with early malignancy is well established in various cancers. However, long-term survival in those with advanced malignancy has changed little and this poses a major therapeutic challenge to clinicians. Anti-cancer immunotherapy is a novel approach, which is still experimental, but offers a new therapeutic strategy. In this review, we discuss the basic immunological interplay between the host immune system and the tumour, mechanisms of anti-tumour immune responses induced by immunotherapy and key in vivo pilot studies of active specific immunotherapy in various sold cancers, carried out during the last five years.

Combination vaccine of dendritic cells (DCs) and T cells effectively suppressed preestablished malignant melanoma in mice

The study aims at establishing a novel vaccine procedure, using bone marrow-derived DCs that have ingested apoptotic B16 melanoma (DCs(+)), alone or in combination with splenic T lymphocytes from a syngenic donor. Co-immunization with DCs(+) and T cells showed the highest antitumor potential against preestablished B16 tumor in mice, in which CTL and NK cytotoxicities were drastically elevated, while either DCs(+) alone, naive DCs (DCs(-)) alone, or a mixture of DCs(-) and T cells induced less significant therapeutic outcomes. Use of extracellular matrix proteins elevated antitumor activity of DC(-)/T cell vaccine. Compared with the CD8(+) cells, the CD4(+)T cells more remarkably improved the efficacy of DC-based immunotherapy. The present system may be a feasible therapeutic modality to eradicate malignancies including melanoma.

Early manifestations of NNK-induced lung cancer: role of lung immunity in tumor susceptibility

A strong correlation exists between smoking and lung cancer; however, susceptibility to lung cancer among smokers is not uniform. Similarly, mice show differential susceptibility to the tobacco carcinogen nitrosamine 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which produces lung tumors in A/J but not in C3H mice. Host immunity may play a role in the susceptibility to cancer, and cigarette smoke/nicotine suppresses the immune system through activation of nicotinic acetylcholine receptors (nAChRs). Mammalian lungs express alpha7-nAChRs, and NNK is a high-affinity agonist for alpha7-nAChRs. To examine whether NNK differentially modulates lung immunity in susceptible and resistant mouse strains, A/J and C3H mice were treated with NNK and/or immunized with sheep red blood cells. Lung tissues and RNA of treated and untreated animals were analyzed by immunohistochemistry and RT-PCR for alpha7-nAChR and COX-2 expression. Spleen- and the lung-associated lymph node cells from control and immunized animals were assessed for immunologic responses, including anti-sheep red blood cell antibody plaque-forming cells, concanavalin A-induced T-cell proliferation, and the anti-CD3/CD28 antibody-induced rise in intracellular calcium. NNK strongly suppressed these responses in A/J but not in C3H mice. Similar NNK-induced immunologic changes were seen in another pair of carcinogen-sensitive (NGP) and relatively carcinogen-resistant (B10.A) mouse strains. Moreover, NNK stimulates a significantly higher expression of COX-2 and alpha7-nAChRs in A/J than in C3H lungs. These results suggest that the susceptibility to chemical carcinogenesis among various mouse strains might be influenced by their immunologic response to the carcinogen.

Nonviral delivery of cancer genetic vaccines

The potential use of genetic vaccines to address numerous diseases including cancer is promising, but currently unrealized. Here, we review advances in the nonviral delivery of antigen-encoded plasmid DNA for the purpose of treating cancer through the human immune system, as this disease has drawn the most attention in this field to date. Brief overviews of dendritic cell immunobiology and the mechanism of immune activation through genetic vaccines set the stage for the desirability of delivery technology. Several promising nonviral delivery techniques are discussed along with a mention of targeting strategies aimed at improving the potency of vaccine formulations. Implications for the future of genetic vaccines are also presented.

Chick embryo lethal orphan virus can be polymer-coated and retargeted to infect mammalian cells

Non-human adenovirus vectors have attractive immunological properties for gene therapy but are frequently restricted by inefficient transduction of human target cells. Using chicken embryo lethal orphan (CELO) virus, we employed a nongenetic mechanism of polymer coating and retargeting with basic fibroblast growth factor (bFGF-pc-CELOluc), a strategy that permits efficient tropism modification of human adenovirus. bFGF-pc-CELOluc showed efficient uptake and transgene expression in chick embryo fibroblasts (CEF), and increased levels of binding and internalization in a variety of human cell lines. Transgene expression was also greater than unmodified CELOluc in PC-3 human prostate cells, although the specific activity (RLU per internalized viral genome) was decreased. In CEF, the specific activity of bFGF-pc-CELOluc was considerably higher than in the human prostate cell line PC-3. Retargeted virus was fully resistant to inhibition by human serum with known adenovirus-neutralizing activity in vitro, while in mice CELOluc was cleared less rapidly from the blood than Adluc following i.v. administration in the presence of adenovirus neutralizing serum. Polymer coating and retargeting with bFGF further reduced rates of clearance for both viruses, suggesting protection against both neutralizing and opsonizing factors. The data indicate that CELO virus may be retargeted to infect human cells via alternative, potentially disease-specific, receptors and resist the effects of pre-existing humoral immunity.

Directed differentiation of human embryonic stem cells into functional dendritic cells through the myeloid pathway

We have established a system for directed differentiation of human embryonic stem (hES) cells into myeloid dendritic cells (DCs). As a first step, we induced hemopoietic differentiation by coculture of hES cells with OP9 stromal cells, and then, expanded myeloid cells with GM-CSF using a feeder-free culture system. Myeloid cells had a CD4+CD11b+CD11c+CD16+CD123(low)HLA-DR- phenotype, expressed myeloperoxidase, and included a population of M-CSFR+ monocyte-lineage committed cells. Further culture of myeloid cells in serum-free medium with GM-CSF and IL-4 generated cells that had typical dendritic morphology; expressed high levels of MHC class I and II molecules, CD1a, CD11c, CD80, CD86, DC-SIGN, and CD40; and were capable of Ag processing, triggering naive T cells in MLR, and presenting Ags to specific T cell clones through the MHC class I pathway. Incubation of DCs with A23187 calcium ionophore for 48 h induced an expression of mature DC markers CD83 and fascin. The combination of GM-CSF with IL-4 provided the best conditions for DC differentiation. DCs obtained with GM-CSF and TNF-alpha coexpressed a high level of CD14, and had low stimulatory capacity in MLR. These data clearly demonstrate that hES cells can be used as a novel and unique source of hemopoietic and DC precursors as well as DCs at different stages of maturation to address essential questions of DC development and biology. In addition, because ES cells can be expanded without limit, they can be seen as a potential scalable source of cells for DC vaccines or DC-mediated induction of immune tolerance.

Dendritic cell fusion vaccines for cancer immunotherapy

The use of tumour vaccines is being explored as a means of generating effective antitumour immune responses in patients with cancer. Dendritic cells (DCs) are the most potent antigen-presenting cells that are essential for initiating primary immune responses. As such, DCs are being studied as a platform for the design of cancer vaccines. DCs loaded with tumour antigens or whole tumour cell derivatives stimulate tumour-specific immunity. A promising vaccine strategy involves the fusion of DCs with whole tumour cells. DC/tumour fusions express a broad array of tumour antigens, including those yet to be identified, in the context of DC-mediated costimulation. Animal models have demonstrated that vaccination with fusion cells is protective against tumour challenge and results in the regression of established metastatic disease. In vitro human studies have demonstrated that DC/tumour fusions potently stimulate antitumour immunity and lysis of autologous tumour cells. Vaccination of cancer patients with DC/tumour fusions is being studied in Phase I/II clinical trials. Preliminary results demonstrate that generation of a vaccine is feasible and that vaccination is associated with minimal toxicity. Immunological and clinical responses have been found in a subset of patients.

Exposure to the electrofusion process can increase the immunogenicity of human cells

The cellular products obtained following electrofusion (EF) of dendritic cells (DC) and tumour cells have shown promise as cancer vaccines. The immunogenicity of these preparations has been attributed to the presence of small numbers of DC-tumour hybrids and the contribution of the non-hybrid tumour cells present has received little attention. In this report, we investigated the effect of the EF process on the immunogenicity of allogeneic human cells, in particular the colorectal cell line, SW620. EF conditions were optimised to yield the maximum number of DC-SW620 hybrids co-expressing tumour associated antigen (TAA) and DC associated antigens. Exposure of SW620 to EF induced significant increases (P < 0.05) in apoptosis and necrosis. Pre-exposure of SW620 to the EF buffer alone [0.3 M glucose, 0.1 mM Ca(CH3COO)2 and 0.5 mM Mg(CH3COO)(2)] resulted in significant increases in TAA uptake by DC during co-culture (P < 0.05). DC phenotype was, however, not altered by exposure to EF treated tumour cells. In co-cultures of PBMC responders with SW620, the levels of IFNgamma release and cytotoxic activity were significantly increased (P < 0.05) by pre-exposure of the SW620 to EF. Pre-exposure of allogeneic non-T cells, the colorectal cell line Lovo and a breast cancer cell line (MCF7) to EF also significantly (P < 0.05) increased the levels of IFNgamma release by responding PBMC. These results demonstrate that the EF process itself can increase the immunogenicity of at least some human cell types independently of hybrid formation. These findings suggest that EF protocols should be evaluated with regard to the possibility that DC-tumour hybrids may not contribute all, or even most, of the immunostimulatory capacity present in preparations of EF treated cells.

Potentiation of a Dendritic Cell Vaccine for Murine Renal Cell Carcinoma by CpG Oligonucleotides

Purpose: An ideal vaccine therapy for tumors should activate both effector and memory immune responses against tumor-specific antigens. Here we investigated the effect of CpG oligodeoxynucleotides (CpG-ODN) for their ability to potentiate the activity of tumor antigen–pulsed bone marrow–derived dendritic cells (DC) in a vaccine model for the treatment of murine renal cell carcinoma (RENCA).

Experimental Design: First we evaluated the effects of a murine renal cell carcinoma (RENCA) on immune cell activity in a mouse model using in vitro assays for T-cell proliferation and natural killer cell activation. To overcome the immune suppression of the tumor, we s.c. injected groups of 10 mice with dendritic cells and tumor cells. We compared the effect of different conditioning regimens of the DCs with RENCA antigen and/or CpG-ODNs before injection by measuring tumor size twice a week.

Results: Tumor growth was shown to negatively affect spleen cell and T-cell proliferation, IFN-γ production, natural killer cell activity, and NF-κB activation in T cells. In this model, we have shown that RENCA-pulsed CpG-ODN-treated DCs were able not only to significantly reduce tumor growth but also to prevent tumor implantation in 60% of mice. Tumor-free mice were resistant to tumor challenge and the immunity conferred by the vaccine was transferable and tumor specific.

Conclusions: This data show that RENCA down-modulates the immune response, and DC vaccine therapy, in conjunction with CpG-ODN, can restore tumor-specific immunity.

Vaccination of Dendritic Cells Loaded with Interleukin-12-Secreting Cancer Cells Augments In vivo Antitumor Immunity: Characteristics of Syngeneic and Allogeneic Antigen-Presenting Cell Cancer Hybrid Cells

Cancer immunotherapy by fusion of antigen-presenting cells and tumor cells has been shown to induce potent antitumor immunity. In this study, we characterized syngeneic and allogeneic, murine macrophage/dendritic cell (DC)-cancer fusion cells for the antitumor effects. The results showed the superiority of allogeneic cells as fusion partners in both types of antigen-presenting cells in an in vivo immunotherapy model. A potent induction of tumor-specific CTLs was observed in these immunized conditions. In addition, the immunization with DC-cancer fusion cells was better than that with macrophage-cancer fusion cells. Both syngeneic and allogeneic DC-cancer fusion cells induced higher levels of IFN-γ production than macrophage-cancer fusion cells. Interestingly, allogeneic DC-cancer fusion cells were superior in that they efficiently induced Th1-type cytokines but not the Th2-type cytokines interleukin (IL)-10 and IL-4, whereas syngeneic DC-cancer fusion cells were powerful inducers of both Th1 and Th2 cytokines. These results suggest that allogeneic DCs are suitable as fusion cells in cancer immunotherapy. To further enhance the antitumor immunity in the clinical setting, we prepared DCs fused with IL-12 gene-transferred cancer cells and thus generated IL-12-secreting DC-cancer fusion cells. Immunization with these gene-modified DC-cancer fusion cells was able to elicit a markedly enhanced antitumor effect in the in vivo therapeutic model. This novel IL-12-producing fusion cell vaccine might be one promising intervention for future cancer immunotherapy.

Enhanced tumor-specific long-term immunity of hemagglutinating [correction of hemaggluttinating] virus of Japan-mediated dendritic cell-tumor fused cell vaccination by coadministration with CpG oligodeoxynucleotides

Immunization with dendritic cells (DCs) using various Ag-loading approaches has shown promising results in tumor-specific immunotherapy and immunoprevention. Fused cells (FCs) that are generated from DCs and tumor cells are one of effective cancer vaccines because both known and unknown tumor Ags are presented on the FCs and recognized by T cells. In this study, we attempted to augment antitumor immunity by the combination of DC-tumor FC vaccination with immunostimulatory oligodeoxynucleotides containing CpG motif (CpG ODN). Murine DCs were fused with syngeneic tumor cells ex vivo using inactivated hemagglutinating virus of Japan (Sendai virus). Mice were intradermally (i.d.) immunized with FCs and/or CpG ODN. Coadministration of CpG ODN enhanced the phenotypical maturation of FCs and unfused DCs, and the production of Th1 cytokines, such as IFN-gamma and IL-12, leading to the induction of tumor-specific CTLs without falling into T cell anergy. In addition, immunization with FCs + CpG ODN provided significant protection against lethal s.c. tumor challenge and spontaneous lung metastasis compared with that with either FCs or CpG ODN alone. Furthermore, among mice that rejected tumor challenge, the mice immunized with FCs + CpG ODN, but not the mice immunized with FCs or CpG ODN alone, completely rejected tumor rechallenge, indicating that CpG ODN provided long-term maintenance of tumor-specific immunity induced by FCs. Thus, the combination of DC-tumor FCs and CpG ODN is an effective and feasible cancer vaccine to prevent the generation and recurrence of cancers.

Progress on new vaccine strategies for the immunotherapy and prevention of cancer

In recent years, great strides in understanding and regulating the immune system have led to new hope for harnessing its exquisite specificity to destroy cancer cells without affecting normal tissues. This review examines the fundamental immunologic advances and the novel vaccine strategies arising from these advances, as well as the early clinical trials studying new approaches to treat or prevent cancer.