Electrofusion of syngeneic dendritic cells and tumor generates potent therapeutic vaccine

Trial watch: Dendritic cell (DC)-based immunotherapy for cancer

Dendritic cell (DC)-based vaccination for cancer treatment has seen considerable development over recent decades. However, this field is currently in a state of flux toward niche-applications, owing to recent paradigm-shifts in immuno-oncology mobilized by T cell-targeting immunotherapies. DC vaccines are typically generated using autologous (patient-derived) DCs exposed to tumor-associated or -specific antigens (TAAs or TSAs), in the presence of immunostimulatory molecules to induce DC maturation, followed by reinfusion into patients. Accordingly, DC vaccines can induce TAA/TSA-specific CD8⁺/CD4⁺ T cell responses. Yet, DC vaccination still shows suboptimal anti-tumor efficacy in the clinic. Extensive efforts are ongoing to improve the immunogenicity and efficacy of DC vaccines, often by employing combinatorial chemo-immunotherapy regimens. In this Trial Watch, we summarize the recent preclinical and clinical developments in this field and discuss the ongoing trends and future perspectives of DC-based immunotherapy for oncological indications.

Trial watch: dendritic cell vaccination for cancer immunotherapy

Dendritic- cells (DCs) have received considerable attention as potential targets for the development of anticancer vaccines. DC-based anticancer vaccination relies on patient-derived DCs pulsed with a source of tumor-associated antigens (TAAs) in the context of standardized maturation-cocktails, followed by their reinfusion. Extensive evidence has confirmed that DC-based vaccines can generate TAA-specific, cytotoxic T cells. Nonetheless, clinical efficacy of DC-based vaccines remains suboptimal, reflecting the widespread immunosuppression within tumors. Thus, clinical interest is being refocused on DC-based vaccines as combinatorial partners for T cell-targeting immunotherapies. Here, we summarize the most recent preclinical/clinical development of anticancer DC vaccination and discuss future perspectives for DC-based vaccines in immuno-oncology.

Trial watch: Dendritic cell-based anticancer immunotherapy

Dendritic cell (DC)-based vaccines against cancer have been extensively developed over the past two decades. Typically DC-based cancer immunotherapy entails loading patient-derived DCs with an appropriate source of tumor-associated antigens (TAAs) and efficient DC stimulation through a so-called "maturation cocktail" (typically a combination of pro-inflammatory cytokines and Toll-like receptor agonists), followed by DC reintroduction into patients. DC vaccines have been documented to (re)activate tumor-specific T cells in both preclinical and clinical settings. There is considerable clinical interest in combining DC-based anticancer vaccines with T cell-targeting immunotherapies. This reflects the established capacity of DC-based vaccines to generate a pool of TAA-specific effector T cells and facilitate their infiltration into the tumor bed. In this Trial Watch, we survey the latest trends in the preclinical and clinical development of DC-based anticancer therapeutics. We also highlight how the emergence of immune checkpoint blockers and adoptive T-cell transfer-based approaches has modified the clinical niche for DC-based vaccines within the wide cancer immunotherapy landscape.

Tumor-dendritic cell fusion as a basis for cancer immunotherapy

OBJECTIVE: To establish the basis for use of allogeneic dendritic-tumor fusion cells.

STUDY DESIGN: Fusion cells were created by electrofusion. We used 2 allogeneic murine tumor lines (D5 and 4T1) that were virally transduced to express the antigen (β-galactosidase) as a surrogate tumor marker.

RESULTS: Cross-immunization was achieved with irradiated allogenic tumor cells. Successful electrofusion of dendritic cells and tumor cells was confirmed by using fluorescence-activated cell sorting and cytospin. Significant responses were shown in immunized mice against tumor challenge and established 3-day pulmonary metastasis with fusion cells.

CONCLUSIONS: Allogeneic tumor sharing a common tumor antigen can immunize against syngeneic tumor challenge. Fusion cells showed successful immunization against tumor challenge and showed regression of 3-day established pulmonary metastasis.

SIGNIFICANCE: These preclinical studies provide evidence that an allogenic tumor-dendritic cell fusion vaccine is a valid approach for head and neck cancer immunotherapy. (Otolaryngol Head Neck Surg 2005;132:755-64.)

The Dark Side of Cell Fusion

Cell fusion is a physiological cellular process essential for fertilization, viral entry, muscle differentiation and placental development, among others. In this review, we will highlight the different cancer cell-cell fusions and the advantages obtained by these fusions. We will specially focus on the acquisition of metastatic features by cancer cells after fusion with bone marrow-derived cells. The mechanism by which cancer cells fuse with other cells has been poorly studied thus far, but the presence in several cancer cells of syncytin, a trophoblastic fusogen, leads us to a cancer cell fusion mechanism similar to the one used by the trophoblasts. The mechanism by which cancer cells perform the cell fusion could be an interesting target for cancer therapy.

Trial watch: Dendritic cell-based anticancer therapy

The use of patient-derived dendritic cells (DCs) as a means to elicit therapeutically relevant immune responses in cancer patients has been extensively investigated throughout the past decade. In this context, DCs are generally expanded, exposed to autologous tumor cell lysates or loaded with specific tumor-associated antigens (TAAs), and then reintroduced into patients, often in combination with one or more immunostimulatory agents. As an alternative, TAAs are targeted to DCs in vivo by means of monoclonal antibodies, carbohydrate moieties or viral vectors specific for DC receptors. All these approaches have been shown to (re)activate tumor-specific immune responses in mice, often mediating robust therapeutic effects. In 2010, the first DC-based preparation (sipuleucel-T, also known as Provenge®) has been approved by the US Food and Drug Administration (FDA) for use in humans. Reflecting the central position occupied by DCs in the regulation of immunological tolerance and adaptive immunity, the interest in harnessing them for the development of novel immunotherapeutic anticancer regimens remains high. Here, we summarize recent advances in the preclinical and clinical development of DC-based anticancer therapeutics.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

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.

Superior anti-tumor protection and therapeutic efficacy of vaccination with dendritic cell/tumor cell fusion hybrids for murine Lewis lung carcinoma

BACKGROUND

The development of protocols for the ex vivo generation of dendritic cells (DCs) has led to intensive research into their potential use in immunotherapy in the treatment of cancer. In this study, we examined the efficacy of dendritic cell-tumor cell fusion hybrid vaccines in eliciting an immune response against Lewis lung carcinoma (LLC) cells, as compared to other types of tumor vaccines. In addition, we also tested whether the efficacy of the vaccines was affected by the route of administration. Four different tumor vaccines were compared: (1) HC (hybrid cell), consisting of DC/LLC hybrids; (2) DC+LLC (DCs pulsed with apoptotic LLCs); (3) DC without antigen loading/pulsing; (4) LLC (apoptotic/irradiated tumor cells). We also compared four different routes of administration for each vaccine: (1) Preimmunization; (2) Vaccination therapy; (3) Adoptive immunotherapy; (4) Vaccination therapy combined with adoptive immunotherapy. Anti-tumor immunity was assessed in vivo and the CTL (cytotoxic T lymphocyte) response as well as the expression of key cytokines, IFN-γ and IL-10 were further evaluated using in vitro assays.

RESULTS

Our data demonstrate that vaccination with HC hybrids provides more effective anti-tumor protective immunity and significantly greater therapeutic immunity than vaccination with DC+LLC, DC or LLC. Most remarkably, vaccination therapy with HC hybrids was more successful than combination (vaccination + adoptive) therapy for the induction of anti-tumor responses. Splenocytes harvested from mice immunized with HC hybrids demonstrated the greatest cytotoxic T lymphocyte (CTL) activity and their production of IFN-γ was high, while their production of IL-10 was very low.

CONCLUSIONS

Our results suggest that vaccination therapy with DC-tumor cell fusion hybrids provides more effective protection against lung cancer.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a privileged position at the interface between innate and adaptive immunity, orchestrating a large panel of responses to both physiological and pathological cues. In particular, whereas the presentation of antigens by immature DCs generally results in the development of immunological tolerance, mature DCs are capable of priming robust, and hence therapeutically relevant, adaptive immune responses. In line with this notion, functional defects in the DC compartment have been shown to etiologically contribute to pathological conditions including (but perhaps not limited to) infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. Thus, the possibility of harnessing the elevated immunological potential of DCs for anticancer therapy has attracted considerable interest from both researchers and clinicians over the last decade. Alongside, several methods have been developed not only to isolate DCs from cancer patients, expand them, load them with tumor-associated antigens and hence generate highly immunogenic clinical grade infusion products, but also to directly target DCs in vivo. This intense experimental effort has culminated in 2010 with the approval by the US FDA of a DC-based preparation (sipuleucel-T, Provenge®) for the treatment of asymptomatic or minimally symptomatic metastatic castration-refractory prostate cancer. As an update to the latest Trial Watch dealing with this exciting field of research (October 2012), here we summarize recent advances in DC-based anticancer regimens, covering both high-impact studies that have been published during the last 13 mo and clinical trials that have been launched in the same period to assess the antineoplastic potential of this variant of cellular immunotherapy.

Dendritic cell-based vaccines: barriers and opportunities

Dendritic cells (DCs) have several characteristics that make them an ideal vehicle for tumor vaccines, and with the first US FDA-approved DC-based vaccine in use for the treatment of prostate cancer, this technology has become a promising new therapeutic option. However, DC-based vaccines face several barriers that have limited their effectiveness in clinical trials. A major barrier includes the activation state of the DC. Both DC lineage and maturation signals must be selected to optimize the antitumor response and overcome immunosuppressive effects of the tumor microenvironment. Another barrier to successful vaccination is the selection of target antigens that will activate both CD8(+) and CD4(+) T cells in a potent, immune-specific manner. Finally, tumor progression and immune dysfunction limit vaccine efficacy in advanced stages, which may make DC-based vaccines more efficacious in treating early-stage disease. This review underscores the scientific basis and advances in the development of DC-based vaccines, focuses on current barriers to success and highlights new research opportunities to address these obstacles.

Membrane and actin reorganization in electropulse-induced cell fusion

When cells of Dictyostelium discoideum are exposed to electric pulses they are induced to fuse, yielding motile polykaryotic cells. By combining electron microscopy and direct recording of fluorescent cells, we have studied the emergence of fusion pores in the membranes and the localization of actin to the cell cortex. In response to electric pulsing, the plasma membranes of two contiguous cells are turned into tangles of highly bent and interdigitated membranes. Live-imaging of cells double-labeled for membranes and filamentous actin revealed that actin is induced to polymerize in the fusion zone to temporally bridge the gaps in the vesiculating membrane. The diffusion of green fluorescent protein (GFP) from one fusion partner to the other was scored using spinning disc confocal microscopy. Fusion pores that allowed intercellular exchange of GFP were formed after a delay, which may last up to 24 seconds after exposure of the cells to the electric field. These data indicate that the membranes persist in a fusogenic state before pores of about 3 nm diameter are formed.

Semiallogenic fusions of MSI(+) tumor cells and activated B cells induce MSI-specific T cell responses

Background

Various strategies have been developed to transfer tumor-specific antigens into antigen presenting cells in order to induce cytotoxic T cell responses against tumor cells. One approach uses cellular vaccines based on fusions of autologous antigen presenting cells and allogeneic tumor cells. The fusion cells combine antigenicity of the tumor cell with optimal immunostimulatory capacity of the antigen presenting cells.

Microsatellite instability caused by mutational inactivation of DNA mismatch repair genes results in translational frameshifts when affecting coding regions. It has been shown by us and others that these mutant proteins lead to the presentation of immunogenic frameshift peptides that are - in principle - recognized by a multiplicity of effector T cells.

Methods

We chose microsatellite instability-induced frameshift antigens as ideal to test for induction of tumor specific T cell responses by semiallogenic fusions of microsatellite instable carcinoma cells with CD40-activated B cells. Two fusion clones of HCT116 with activated B cells were selected for stimulation of T cells autologous to the B cell fusion partner. Outgrowing T cells were phenotyped and tested in functional assays.

Results

The fusion clones expressed frameshift antigens as well as high amounts of MHC and costimulatory molecules. Autologous T cells stimulated with these fusions were predominantly CD4⁺, activated, and reacted specifically against the fusion clones and also against the tumor cell fusion partner. Interestingly, a response toward 6 frameshift-derived peptides (of 14 tested) could be observed.

Conclusion

Cellular fusions of MSI⁺ carcinoma cells and activated B cells combine the antigen-presenting capacity of the B cell with the antigenic repertoire of the carcinoma cell. They present frameshift-derived peptides and can induce specific and fully functional T cells recognizing not only fusion cells but also the carcinoma cells. These hybrid cells may have great potential for cellular immunotherapy and this approach should be further analyzed in preclinical as well as clinical trials. Moreover, this is the first report on the induction of frameshift-specific T cell responses without the use of synthetic peptides.

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.

Immunotherapy using allogeneic squamous cell tumor-dendritic cell fusion hybrids

BACKGROUND

Tumor-associated antigens (TAAs) are known to be immunotherapy targets; thus tumor-sharing TAA may be used as a fusion hybrid partner to confer protection against subsequent tumor challenge.

METHODS

The squamous cell carcinomas (SCCs), SCCVII and B4B8, were used in C3H/HEN mice: SCCVII (H-2(k)) is syngeneic, B4B8 (H-2(d)) is allogeneic. Experiments using tumor alone included hyperimmunization schedule, subdermal and intranodal routes. Mice were challenged 2 weeks later. Fusion hybrids were created from both SCC tumor cell lines and syngeneic dendritic cells (DCs). These were delivered intranodally for immunization, and mice were challenged with tumor 2 weeks later.

RESULTS

Only syngeneic tumor given subdermally was able to protect after tumor challenge 2 weeks later. Hyperimmunization schedule did not alter these findings. However, fusion hybrid immunization from both allogeneic and syngeneic SCCs conferred protection after tumor challenge.

CONCLUSIONS

Allogeneic tumor-DC fusion hybrids targeting TAA can protect against subsequent tumor challenge.

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.

Toll-like receptor agonists as third signals for dendritic cell-tumor fusion vaccines

BACKGROUND

The aim of the present study was to evaluate the therapeutic efficacy of dendritic cell (DC)-tumor fusion hybrids with Toll-like receptor (TLR) agonists.

METHODS

DC-tumor fusion hybrids were generated by electrofusion and injected into the inguinal lymph nodes of C57BL/6 mice with 3-day established pulmonary metastases. Paired TLR agonists polyinosine:polycytadilic acid [poly(I:C)] and cytosine-phosphate-guanine (CpG) were then injected intraperitoneally. Enzyme-linked immunosorbent assay (ELISA) was used to evaluate interleukin (IL)-12 production from the DC-tumor fusion hybrids in vitro.

RESULTS

Fusion + TLR agonists (60 metastases) had significantly fewer metastases than did the untreated control (262 metastases, p = .0001) and fusion alone (150 metastases, p = .02). ELISA showed that the DC-tumor fusion hybrids yielded 90 pg of IL-12 after TLR stimulation compared with 1610 pg from dendritic cells alone.

CONCLUSIONS

CpG and poly(I:C) administered as a third signal with fusion hybrids as described significantly reduce melanoma metastasis compared with fusion hybrids alone. Fusion hybrids do not appear to be a significant source for IL-12 secretion.

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.

Paired Toll-like receptor agonists enhance vaccine therapy through induction of interleukin-12

Minimal requirements for generating effective immunity include the delivery of antigenic (signal 1) and costimulatory (signal 2) signals to T lymphocytes. Recently, a class of third signals, often delivered by antigen-presenting dendritic cells, has been shown to greatly enhance immune responses, especially against tumors. Among signal 3 factors, interleukin (IL)-12 is particularly effective and can be conditionally induced by agonists of Toll-like transmembrane receptors (TLR). In this study, we assessed the therapeutic effect of adjuvant TLR agonist administration upon the capacity of dendritic cell (DC)-tumor electrofusion hybrids to eradicate established MCA205 sarcomas in syngeneic mice. Paired, but not solitary combinations of polyinosine:polycytadilic acid (P[I:C]; TLR3 agonist) and CpG DNA (ODN1826l; TLR9 agonist) stimulated IL-12 secretion from DCs in vitro and synergized with vaccination to achieve potent tumor rejection. Therapeutic effects, however, required coadministration of paired TLR agonists and DC-tumor fusion hybrids. The administration of TLR agonists alone or with fusion vaccine induced transient splenomegaly but without apparent toxicity. The therapeutic effects of this immunization regimen were significantly abrogated through the neutralization of IL-12p70, indicating that production of this third signal was essential to the observed tumor regression. These results show the profound functional consequences of TLR cooperativity and further highlight the critical role of IL-12 in antitumor immunity.

IL-12 is required for anti-OX40-mediated CD4 T cell survival

Engagement of OX40 greatly improves CD4 T cell function and survival. Previously, we showed that both OX40 engagement and CTLA-4 blockade led to enhanced CD4 T cell expansion, but only OX40 signaling increased survival. To identify pathways associated with OX40-mediated survival, the gene expression of Ag-activated CD4 T cells isolated from mice treated with anti-OX40 and -CTLA-4 was compared. This comparison revealed a potential role for IL-12 through increased expression of the IL-12R-signaling subunit (IL-12Rbeta2) on T cells activated 3 days previously with Ag and anti-OX40. The temporal expression of IL-12Rbeta2 on OX40-stimulated CD4 T cells was tightly regulated and peaked approximately 4-6 days after initial activation/expansion, but before the beginning of T cell contraction. IL-12 signaling, during this window of IL-12Rbeta2 expression, was required for enhanced T cell survival and survival was associated with STAT4-specific signaling. The findings from these observations were exploited in several different mouse tumor models where we found that the combination of anti-OX40 and IL-12 showed synergistic therapeutic efficacy. These results may lead to the elucidation of the molecular pathways involved with CD4 T cell survival that contribute to improved memory, and understanding of these pathways could lead to greater efficacy of immune stimulatory Abs in tumor-bearing individuals.

Generation of anti-tumour effector T cells from naïve T cells by stimulation with dendritic/tumour fusion cells

Tumour-draining lymph node T cells are an excellent source of effector T cells that can be used in adoptive tumour immunotherapy because they have already been sensitized to tumour-associated antigens in vivo. However, such tumour-specific immune cells are not readily obtained from the host due to poor immunogenicity of tumours and reduced host immune responses. One obstacle in implementation of adoptive immunotherapy has been insufficient sensitization and expansion of tumour-specific effector cells. In this study, we aim to improve adoptive immunotherapy by generating anti-tumour effector T cells from naïve T lymphocytes. We attempted to achieve this by harnessing the advantages of dendritic cell (DC)-based anti-cancer vaccine strategies. Electrofusion was routinely employed to produce fusion cells with 30-40% efficiency by using the poorly immunogenic murine B16/F10 cell line, D5 cells, and DC generated from bone marrow cells. CD62L-positive T cells from spleens of naïve mice and the fusion cells were cocultured with a low concentration of IL-2. After 9 days of culture, the antigen-specific T cells were identified with an upregulation of CD25 and CD69 expression and a downregulation of CD62L expression. These cells secreted IFN-gamma upon stimulation with irradiated tumour cells. Moreover, when transferred into mice with 3-day established pulmonary metastases, these cells with coadministration of IL-2 exhibited anti-tumour efficacy. In contrast, naïve T cells cocultured with a mixture of unfused DC and irradiated tumour cells did not exhibit anti-tumour efficacy. Our strategy provides the basis for a new approach in adoptive T cell immunotherapy for cancer.

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.

A combination hybrid-based vaccination/adoptive cellular therapy to prevent tumor growth by involvement of T cells

Cancer immunotherapy with dendritic cell-tumor cell fusion hybrids induces polyclonal stimulation against a variety of tumor antigens, including unknown antigens. Hybrid cells can prime CTLs, which subsequently develop antitumor responses. The aim of this study was to enhance the known antitumor effect of hybrid vaccination (HC-Vacc) and hybrid-primed adoptive T-cell therapy (HC-ACT) using the poorly immunogenic Lewis lung carcinoma (LLC1) model. The strategy used was a combination of a double HC-Vacc alternating with HC-ACT (HC-Vacc/ACT). Using flat-panel volumetric computer tomography and immunohistochemistry, we showed a significant retardation of tumor growth (85%). In addition, a significant delay in tumor development, a reduction in the number of pulmonary metastases, and increased survival times were observed. Furthermore, the tumors displayed significant morphologic changes and increased apoptosis, as shown by up-regulation of gene expression of the proapoptotic markers Fas, caspase-8, and caspase-3. The residual tumor masses seen in the HC-Vacc/ACT-treated mice were infiltrated with CD4+ and CD8+ lymphocytes and showed elevated IFNgamma expression. Moreover, splenic enlargement observed in HC-Vacc/ACT-treated mice reflected the increased functionality of T cells, as also indicated by increased expression of markers for CTL activation, differentiation, and proliferation (Cd28, Icosl, Tnfrsf13, and Tnfsf14). Our findings indicate that the combination therapy of dendritic cell-tumor cell HC-Vacc/ACT is a very effective and a promising immunotherapeutic regimen against poorly immunogenic carcinomas.

Mechanism of third signals provided by IL-12 and OX-40R ligation in eliciting therapeutic immunity following dendritic-tumor fusion vaccination

Dendritic-tumor heterokaryons generated by electrofusion are highly immunogenic. In animal studies, a single vaccination was therapeutic for tumors established in the lung, skin, and brain. However, effective therapy required a third signal which could be provided by exogenous IL-12 or the agonistic anti-OX-40R monoclonal antibody (mAb). In this study, we investigated the mechanism and mode of actions of these two seemingly distinct adjuvants. In immunotherapy of the MCA205 sarcoma, administration of the neutralizing anti-IL-12 mAb nearly completely blocked the adjuvant effect of IL-12, but had minimal inhibitory effects on anti-OX-40R mAb. By contrast, in vivo administration of the antagonistic anti-OX-40L mAb inhibited the adjuvant effects of both IL-12 and anti-OX-40R mAb. Thus, a common pathway of endogenous OX-40 interaction is critical for the development of a therapeutic immune response. Analysis of the third signal mechanism revealed that in the absence of an adjuvant, vaccination with fusion hybrids led to IL-10 production without eliciting IFN-gamma secreting cells. The addition of IL-12 to vaccination suppressed IL-10 production and initiated sensitization of specific IFN-gamma secreting cells, resulting in a type 1-like antitumor immunity. These findings underscore the significance of the third signal in the design of dendritic cell-based cancer vaccines.

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.

Generation of cell hybrids via a fusogenic cell line

BACKGROUND

Hybrids obtained by fusion between tumour cells (TC) and dendritic cells (DC) have been proposed as anti-tumour vaccines because of their potential to combine the expression of tumour-associated antigens with efficient antigen presentation. The classical methods used for fusion, polyethylene glycol (PEG) and electrofusion, are cytotoxic and generate cell debris that can be taken up by DC rendering the identification of true hybrids difficult.

METHODS

We have established a stable cell line expressing a viral fusogenic membrane glycoprotein (FMG) that is not itself susceptible to fusion. This cell line has been used to generate hybrids and to evaluate the relevance of tools used for hybrid detection.

RESULTS

This FMG-expressing cell line promotes fusion between autologous or allogeneic TC and DC in any combination, generating 'tri-parental hybrids'. At least 20% of TC are found to be integrated into hybrids.

CONCLUSIONS

It is speculated that this tri-parental hybrid approach offers new possibilities to further modulate the anti-tumour effect of the DC/TC hybrids since it allows the expression of relevant immunostimulatory molecules by appropriate engineering of the fusogenic cell line.

Immune responses in the draining lymph nodes against cancer: implications for immunotherapy

Regional lymph nodes are the first site for melanoma metastases. The sentinel node (SN), on the direct lymphatic drainage pathway, which usually harbors first metastases, demonstrates significant suppression in its ability to respond to antigenic stimulation. This down-regulation of SN immunity is likely the basis of its susceptibility to tumor metastases, suggesting a potential role of the immune system in the control of malignant tumors. Despite immune dysfunction in the SN, phase II trials of systemic post-operative immunotherapy with a polyvalent melanoma vaccine developed at the John Wayne Cancer Institute showed improved 5-year overall survival in patients with melanoma metastatic to regional nodes. However, most immunotherapy clinical trials have failed to demonstrate a significant clinical response, and analyses of immune responses to tumor-associated antigens that correlate clinical responses have not been established. Therefore, refinements in assay methodologies and improvements in vaccine designs are critical to the success of cancer immunotherapy. Antigen presentation by dendritic cells (DCs) is the most potent means to initiate a T cell immunity. Dendritic cell-based immunotherapies have been vigorously attempted in the past decade. To improve the immunogenicity of cancer vaccines, we recently generated heterokaryons of DCs and tumor cells by electrofusion. The fusion hybrids retained their full antigen-presenting capacity and all natural tumor antigens. In pre-clinical animal experiments, a single injection of the DC-tumor fusion hybrids was sufficient to mediate the regression of tumors established in the lung, skin and brain. Most interestingly, successful therapy required the delivery of fusion hybrids directly into lymphoid organs such as lymph nodes. A clinical trial is now being carried out to test the immunogenicity and therapeutic effects of fusion hybrids for the treatment of metastatic melanoma.

Hybrid-primed lymphocytes and hybrid vaccination prevent tumor growth of lewis lung carcinoma in mice

Dendritic cell (DC)-tumor cell hybrids are currently being evaluated as a novel antitumor vaccination strategy. We have explored in an animal model whether administration of DCs fused with poorly immunogenic carcinoma cells could elicit an antitumor response. Fusion of C57/BL6 mice bone marrow-derived DCs with Lewis lung carcinoma (LLC1) cells resulted in approximately 50% fusion efficiency. Hybrid cells (HCs) were used to explore 3 potential tumor therapy strategies: protective immunization, vaccination, and adoptive cellular therapy. Immunization with HCs induced activation of proliferating cytotoxic T cells, upregulation of distinct cytokines genes, and a significant retardation of tumor growth. Similar results were observed by vaccination with HCs in the tumor-bearing host. Finally, when T cells from HC-vaccinated mice were transferred into naive tumor-bearing mice, tumor growth was strongly retarded and an efficient proliferative and cytotoxic T-cell response was observed. Tumor growth was reduced by more than 50%, and tumor development was significantly delayed. Taken together, we demonstrate that HCs offer effective immunotherapy of poorly immunogenic carcinomas. This is independent of whether the HCs are taken for adoptive transfer or as a vaccine.

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.

The impact of electrical charge on the viability and physiology of dendritic cells

The use of electrical charge for electroporation or electrofusion is widely applied to customize dendritic cells (DC) and their immunological properties as anticancer vaccines. The aim of this study was to evaluate the influence of various electrical field strengths on the recovery, viability and physiology of DC. Immature DC were transferred into low-conductive medium and electrically charged within a range of 0-1500 V/cm. Viability was assessed by Trypan Blue dye exclusion or staining with impermeant nucleic acid stains and fluorescence-activated cell sorter analysis. Additionally, apoptosis was determined by flow cytometry after staining with Annexin-V, endocytosis by uptake of fluorescein isothiocyanate-dextran and metabolic activity by a standardized fluorescent live/dead assay. There was a strong correlation between the electrical field strength and the viability and physiology of DC. Field strengths > or =1000 V/cm significantly impaired viability, metabolism and endocytotic activity. Dual fluorescence with 7-7-amino-actinomycin D and Annexin-V demonstrated that loss of viability was predominantly due to necrosis rather than apoptosis. Field strengths < or =500 V/cm allowed to maintain good cell viability and recovery of DC and did not cause alterations of metabolism and endocytosis. Therefore, the frequently used amplification of field strengths to improve the efficacy of electroporation and electrofusion requires critical re-evaluation.

T cell-mediated immunotherapy of metastases: state of the art in 2005

Advances in cellular and molecular immunology have led to the development of strategies for effective augmentation of antitumour immune responses in cancer patients. This review focuses on the manipulation of T cell immunity either by active specific immunotherapy (ASI) using tumour vaccines, or by adoptive immunotherapy (ADI) with immune T cells. Such therapies offer exquisite specificity of tumour recognition based on the ability of the T cell to distinguish single amino acid differences in any protein from any compartment of the tumour cell. Examples are presented of clinical survival benefits for cancer patients by postoperative ASI with a modified autologous tumour vaccine of high quality. Furthermore, clinical studies employing ADI with T cells activated and expanded ex vivo have demonstrated 'proof of principle' that tumour-specific T cells are capable of mediating anticancer activity in vivo, as measured by regression of metastatic tumours. Translation of these findings into a standardised immunotherapy is, however, not easy and will require coordination and cooperation among academic, private and federal sectors.

Active immunotherapy for advanced intracranial murine tumors by using dendritic cell-tumor cell fusion vaccines

OBJECT

Immunotherapy for malignant brain tumors by active immunization or adoptive transfer of tumor antigen-specific T lymphocytes has the potential to make up for some of the limitations of current clinical therapy. In this study, the authors tested whether active immunotherapy is curative in mice bearing advanced, rapidly progressive intracranial tumors.

METHODS

Tumor vaccines were created through electrofusion of dendritic cells (DCs) and irradiated tumor cells to form multinucleated heterokaryons that retained the potent antigen processing and costimulatory function of DCs as well as the entire complement of tumor antigens. Murine hosts bearing intracranial GL261 glioma or MCA 205 fibrosarcoma were treated with a combination of local cranial radiotherapy, intrasplenic vaccination with DC/tumor fusion cells, and anti-OX40R (CD134) monoclonal antibody (mAb) 7 days after tumor inoculation. Whereas control mice had a median survival of approximately 20 days, the treated mice underwent complete tumor regression that was immunologically specific. Seven days after vaccination treated mice demonstrated robust infiltration of CD4+ and CD8+ T cells, which was exclusively confined to the tumor without apparent neurological toxicity. Cured mice survived longer than 120 days with no evidence of tumor recurrence and resisted intracranial tumor challenge.

CONCLUSIONS

These data indicate a strategy to achieve an antitumor response against tumors in the central nervous system that is highly focused from both immunological and anatomical perspectives.

Comparative Analysis of Antigen Loading Strategies of Dendritic Cells for Tumor Immunotherapy

Dendritic cells (DCs) loaded with antigens can effectively stimulate host immune responses to syngeneic tumors, but there is considerable controversy as to which forms of antigen-loading are most immunogenic. Here, the authors compared immunotherapeutic reactivities of DCs loaded with a variety of antigen preparations. Because DC maturation stages affect their capacities of antigen processing and presentation, two DC populations were used for the current analysis: in vivo Flt-3 ligand-induced mature DCs and in vitro bone marrow-derived DCs, which were less mature. To facilitate a direct comparison, the LacZ gene-transduced B16 melanoma model system was used, where beta-galactosidase served as the surrogate tumor-rejection antigen. DC loading strategies included pulsing with the beta-galactosidase protein, H-2K restricted peptide, tumor cell lysate, and irradiated tumor cells and fusion of DCs with tumor cells. Our results demonstrated that electrofusion of DCs and tumor cells generated a therapeutic vaccine far superior to other methods of DC loading. For the treatment of 3-day established pulmonary tumor nodules, a single intranodal vaccination plus IL-12 resulted in a significant reduction of metastatic nodules, while other DC preparations were only marginally effective. Immunotherapy mediated by the fusion cells was tumor antigen-specific. Consistent with their therapeutic activity, fusion hybrids were the most potent stimulators to induce specific IFN-gamma secretion from immune T cells. Furthermore, fusion cells also stimulated a small amount of IL-10 production from immune T cells. However, this IL-10 secretion was also induced by other DC preparations and did not correlate with in vivo therapeutic reactivity.