Dendritic cells retrovirally transduced with a model antigen gene are therapeutically effective against established pulmonary metastases

Physical transfection technologies for macrophages and dendritic cells in immunotherapy

INTRODUCTION

Dendritic cells (DCs) and macrophages, two important antigen presenting cells (APCs) of the innate immune system, are being explored for the use in cell-based cancer immunotherapy. For this application, the therapeutic potential of patient-derived APCs is increased by delivering different types of functional macromolecules, such as mRNA and pDNA, into their cytosol. Compared to the use of viral and non-viral delivery vectors, physical intracellular delivery techniques are known to be more straightforward, more controllable, faster and generate high delivery efficiencies.

AREAS COVERED

This review starts with electroporation as the most traditional physical transfection method, before continuing with the more recent technologies such as sonoporation, nanowires and microfluidic cell squeezing. A description is provided of each of those intracellular delivery technologies with their strengths and weaknesses, especially paying attention to delivery efficiency and safety profile.

EXPERT OPINION

Given the common use of electroporation for the production of therapeutic APCs, it is recommended that more detailed studies are performed on the effect of electroporation on APC fitness, even down to the genetic level. Newer intracellular delivery technologies seem to have less impact on APC functionality but further work is needed to fully uncover their suitability to transfect APCs with different types of macromolecules.

A Novel Anti-PD-L1 Vaccine for Cancer Immunotherapy and Immunoprevention

Dendritic cells (DCs) are potent antigen-presenting cells that play a critical role in activating cellular and humoral immune responses. DC-based tumor vaccines targeting tumor-associated antigens (TAAs) have been extensively tested and demonstrated to be safe and potent in inducing anti-TAA immune responses in cancer patients. Sipuleucel-T (Provenge), a cancer vaccine of autologous DCs loaded with TAA, was approved by the United States Food and Drug Administration (FDA) for the treatment of castration-resistant prostate cancer. Sipuleucel-T prolongs patient survival, but has little or no effect on clinical disease progression or biomarker kinetics. Due to the overall limited clinical efficacy of tumor vaccines, there is a need to enhance their potency. PD-L1 is a key immune checkpoint molecule and is frequently overexpressed on tumor cells to evade antitumor immune destruction. Repeated administrations of PD-L1 or PD-1 antibodies have induced sustained tumor regression in a fraction of cancer patients. In this study, we tested whether vaccinations with DCs, loaded with a PD-L1 immunogen (PDL1-Vax), are able to induce anti-PD-L1 immune responses. We found that DCs loaded with PDL1-Vax induced anti-PD-L1 antibody and T cell responses in immunized mice and that PD-L1-specific CTLs had cytolytic activities against PD-L1⁺ tumor cells. We demonstrated that vaccination with PDL1-Vax DCs potently inhibited the growth of PD-L1⁺ tumor cells. In summary, this study demonstrates for the first time the principle and feasibility of DC vaccination (PDL1-Vax) to actively induce anti-PD-L1 antibody and T cell responses capable of inhibiting PD-L1⁺ tumor growth. This novel anti-PD-L1 vaccination strategy could be used for cancer treatment and prevention.

Lack of expression of hepatitis C virus core protein in human monocyte-erived dendritic cells using recombinant semliki forest virus

Hepatitis C Virus belongs to the Flaviviridae family.  One proposed mechanism of HCV persistence in the ability to infect hematopoietic cells, including Dendritic cells (DCs). HCV infection of DCs could impair their functions that represent one of the mechanisms, thus hampering viral clearance by the host immune system. Among HCV-encoded proteins, the highly conserved Core protein has been suggested to be responsible for the immunomodulatory properties of this Hepacivirus. Recombinant viral vectors expressing the HCV Core protein and allowing its transduction and therefore the expression of the protein into DCs could be useful tools for the analysis of the properties of the Core protein. Vaccinia Virus and retrovirus have been used to transduce human DCs. Likewise, gene transfer into DCs using Semliki Forest Virus has been reported. This study aimed to express the HCV Core protein in human monocyte-derived DCs using an SFV vector, in which the subgenomic RNA encoding the structural proteins was replaced by the HCV Core sequence and then analyze the effects of its expression on DCs functions.

Promoting the accumulation of tumor-specific T cells in tumor tissues by dendritic cell vaccines and chemokine-modulating agents

This protocol describes how to induce large numbers of tumor-specific cytotoxic T cells (CTLs) in the spleens and lymph nodes of mice receiving dendritic cell (DC) vaccines and how to modulate tumor microenvironments (TMEs) to ensure effective homing of the vaccination-induced CTLs to tumor tissues. We also describe how to evaluate the numbers of tumor-specific CTLs within tumors. The protocol contains detailed information describing how to generate a specialized DC vaccine with augmented ability to induce tumor-specific CTLs. We also describe methods to modulate the production of chemokines in the TME and show how to quantify tumor-specific CTLs in the lymphoid organs and tumor tissues of mice receiving different treatments. The combined experimental procedure, including tumor implantation, DC vaccine generation, chemokine-modulating (CKM) approaches, and the analyses of tumor-specific systemic and intratumoral immunity is performed over 30-40 d. The presented ELISpot-based ex vivo CTL assay takes 6 h to set up and 5 h to develop. In contrast to other methods of evaluating tumor-specific immunity in tumor tissues, our approach allows detection of intratumoral T-cell responses to nonmanipulated weakly immunogenic cancers. This detection method can be performed using basic laboratory skills, and facilitates the development and preclinical evaluation of new immunotherapies.

Dendritic Cells in Oncolytic Virus-Based Anti-Cancer Therapy

Dendritic cells (DCs) are specialized antigen-presenting cells that have a notable role in the initiation and regulation of innate and adaptive immune responses. In the context of cancer, appropriately activated DCs can induce anti-tumor immunity by activating innate immune cells and tumor-specific lymphocytes that target cancer cells. However, the tumor microenvironment (TME) imposes different mechanisms that facilitate the impairment of DC functions, such as inefficient antigen presentation or polarization into immunosuppressive DCs. These tumor-associated DCs thus fail to initiate tumor-specific immunity, and indirectly support tumor progression. Hence, there is increasing interest in identifying interventions that can overturn DC impairment within the TME. Many reports thus far have studied oncolytic viruses (OVs), viruses that preferentially target and kill cancer cells, for their capacity to enhance DC-mediated anti-tumor effects. Herein, we describe the general characteristics of DCs, focusing on their role in innate and adaptive immunity in the context of the TME. We also examine how DC-OV interaction affects DC recruitment, OV delivery, and anti-tumor immunity activation. Understanding these roles of DCs in the TME and OV infection is critical in devising strategies to further harness the anti-tumor effects of both DCs and OVs, ultimately enhancing the efficacy of OV-based oncotherapy.

Novel dendritic cell-based vaccination in late stage melanoma

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that play an important role in stimulating an immune response of both CD4(+) T helper cells and CD8(+) cytotoxic T lymphocytes (CTLs). As such, DCs have been studied extensively in cancer immunotherapy for their capability to induce a specific anti-tumor response when loaded with tumor antigens. However, when the most relevant antigens of a tumor remain to be identified, alternative approaches are required. Formation of a dentritoma, a fused DC and tumor cells hybrid, is one strategy. Although initial studies of these hybrid cells are promising, several limitations interfere with its clinical and commercial application. Here we present early experience in clinical trials and an alternative approach to manufacturing this DC/tumor cell hybrid for use in the treatment of late stage and metastatic melanoma.

Key points of basic theories and clinical practice in rAd-p53 ( Gendicine ™) gene therapy for solid malignant tumors

INTRODUCTION

Wild-type p53 gene is an essential cancer suppressor gene which plays an important role in carcinogenesis and malignant progressions. The p53 gene family participates in almost all the key procedures of cancer biology, such as programmed cell death, angiogenesis, metabolism and epithelial-mesenchymal transition. The mutation or functional defects of the p53 gene family are detected in most of the solid malignant tumors, and the restoration of the p53 gene by adenovirus-mediated gene therapy becomes a promising treatment for cancer patients now.

AREAS COVERED

In the present review, the potential therapeutic effects of recombinant adenovirus p53 rAd-p53 ( Gendicine ™) were reviewed to explore the biological mechanism underlying the adenovirus-mediated p53 gene therapy. Then, the key points of the drug administration were discussed, including the routes of administration, dosage calculation and treatment cycles, based on findings of the preclinical and clinical trials in order to establish a standard treatment for the p53 gene therapy.

EXPERT OPINION

As an important part of the combined therapy for the cancer patients, the adenovirus-mediated p53 gene therapy was blossomed to be a promising treatment strategy. A new evaluation criteria and guideline for the gene therapy is urgently needed for the further clinical practice.

Immunomodulatory effects of polysaccharide from marine fungus Phoma herbarum YS4108 on T cells and dendritic cells

YCP, as a kind of natural polysaccharides from the mycelium of marine filamentous fungus Phoma herbarum YS4108, has great antitumor potential via enhancement of host immune response, but little is known about the molecular mechanisms. In the present study, we mainly focused on the effects and mechanisms of YCP on the specific immunity mediated by dendritic cells (DCs) and T cells. T cell /DC activation-related factors including interferon- (IFN-) γ, interleukin-12 (IL-12), and IL-4 were examined with ELISA. Receptor knock-out mice and fluorescence-activated cell sorting are used to analyze the YCP-binding receptor of T cells and DCs. RT-PCR is utilized to measure MAGE-A3 for analyzing the tumor-specific killing effect. In our study, we demonstrated YCP can provide the second signal for T cell activation, proliferation, and IFN-γ production through binding to toll-like receptor- (TLR-) 2 and TLR-4. YCP could effectively promote IL-12 secretion and expression of markers (CD80, CD86, and MHC II) via TLR-4 on DCs. Antigen-specific immunity against mouse melanoma cells was strengthened through the activation of T cells and the enhancement of capacity of DCs by YCP. The data supported that YCP can exhibit specific immunomodulatory capacity mediated by T cells and DCs.

Tracking and evaluation of dendritic cell migration by cellular magnetic resonance imaging

Cellular magnetic resonance imaging (MRI) is a means by which cells labeled ex vivo with a contrast agent can be detected and tracked over time in vivo. This technology provides a noninvasive method with which to assess cell-based therapies in vivo. Dendritic cell (DC)-based vaccines are a promising cancer immunotherapy, but its success is highly dependent on the injected DC migrating to a secondary lymphoid organ such as a nearby lymph node. There the DC can interact with T cells to elicit a tumor-specific immune response. It is important to verify DC migration in vivo using a noninvasive imaging modality, such as cellular MRI, so that important information regarding the anatomical location and persistence of the injected DC in a targeted lymph node can be provided. An understanding of DC biology is critical in ascertaining how to label DC with sufficient contrast agent to render them detectable by MRI. While iron oxide nanoparticles provide the best sensitivity for detection of DC in vivo, a clinical grade iron oxide agent is not currently available. A clinical grade (19) Fluorine-based perfluorcarbon nanoemulsion is available but is less sensitive, and its utility to detect DC migration in humans remains to be demonstrated using clinical scanners presently available. The ability to quantitatively track DC migration in vivo can provide important information as to whether different DC maturation and activation protocols result in improved DC migration efficiency which will determine the vaccine's immunogenicity and ultimately the tumor immunotherapy's outcome in humans.

Prolonged expression of MHC class I - peptide expression in bone marrow derived retrovirus transfected matured dendritic cells by continuous centrifugation in the presence of IL-4

Background & objectives:

Dendritic cells (DCs) are potent antigen presenting cells which proceed from immature to a mature stage during their differentiation. There are several methods of obtaining long lasting mature antigen expressing DCs and different methods show different levels of antigen expressions. We investigated bone marrow derived DCs for the degree of maturation and genetically engineered antigen presentation in the presence of interleukin-4 (IL-4) as a maturity enhancer.

Methods:

DCs and transfected retrovirus were cultured together in the presence of granulocyte-macrophage colony stimulating factor (GMCSF)-IL4, GMCSF +IL4, lipopolysaccharide (LPS). B 7.1, B7.2 and CD11c were measured by the degree of immune fluorescence using enhanced green fluorescent protein (EGFP) shuttled retrovirus transfected antigen. Degree of MHC class I molecule with antigen presentation of antigen was also evaluated by fluorescence activated cell sorting. The antigen presenting capacity of transfected DCs was investigated. Bone marrow DCs were generated in the presence of GMCSF and IL-4 in vitro. Dividing bone marrow cells were infected with EGFP shuttled retrovirus expressing SSP2 by prolonged centrifugation for three consecutive days from day 5, 6 and 7 and continued to culture in the presence of GMSCF and IL-4 until day 8.

Results:

IL-4 as a cytokine increased the maturation of retrovirus transfected DCs by high expression of B 7-1 and B 7-2. Also, IL-4 induced DC enhanced by the prolonged centrifugation and it was shown by increased antigen presentation of these dendric cells as antigen presenting cell (APC). Cytolytic effects were significantly higher in cytotoxic T cell response (CTLs) mixed with transfected DCs than CTLs mixed with pulsed DCs.

Interpretation & conclusions:

There was an enhanced antigen presentation by prolonged expression of antigen loaded MHC class I receptors in DCs in the presence of IL-4 by prolonged centrifugation.

HER-2/neu tolerant and non-tolerant mice for fine assessment of antimetastatic potency of dendritic cell-tumor cell hybrid vaccines

Main obstacles to cancer vaccine efficacy are pre-existing antigenic load and immunoescape mechanisms, including tolerance against self tumor-associated antigens. Here we explored the role of tolerance in an antimetastatic vaccine approach based on dendritic cell-tumor cell (DC-TC) hybrids, thanks to the comparison between BALB-neuT mice, transgenic for and tolerant to rat HER-2/neu, with their non-tolerant strain of origin BALB/c. Allogeneic DC-TC hybrid vaccine displayed a high antimetastatic activity in non-tolerant mice, but was far less effective in tolerant mice, even with intensified vaccine schedule. Tolerant BALB-neuT mice revealed a reduced ability to mount polarized Th1 responses. A further attempt to increase the antimetastatic activity by using LPS-matured DC hybrids failed. Allogeneic LPS-matured DC-TC hybrids induced high IFN-γ levels, but concomitantly also the highest production of IL-4 and IL-10 suggesting activation of mechanisms sustaining regulatory cells able to blunt vaccine efficacy. Our data in tolerant versus non-tolerant hosts suggest that clinical translation of effective DC-based strategies could benefit from more extensive investigations in tolerant transgenic models.

Dendritic cell-specific antigen delivery by coronavirus vaccine vectors induces long-lasting protective antiviral and antitumor immunity

Efficient vaccination against infectious agents and tumors depends on specific antigen targeting to dendritic cells (DCs). We report here that biosafe coronavirus-based vaccine vectors facilitate delivery of multiple antigens and immunostimulatory cytokines to professional antigen-presenting cells in vitro and in vivo. Vaccine vectors based on heavily attenuated murine coronavirus genomes were generated to express epitopes from the lymphocytic choriomeningitis virus glycoprotein, or human Melan-A, in combination with the immunostimulatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF). These vectors selectively targeted DCs in vitro and in vivo resulting in vector-mediated antigen expression and efficient maturation of DCs. Single application of only low vector doses elicited strong and long-lasting cytotoxic T-cell responses, providing protective antiviral and antitumor immunity. Furthermore, human DCs transduced with Melan-A-recombinant human coronavirus 229E efficiently activated tumor-specific CD8⁺ T cells. Taken together, this novel vaccine platform is well suited to deliver antigens and immunostimulatory cytokines to DCs and to initiate and maintain protective immunity.

Vaccination against infectious agents has protected many individuals from severe disease. In addition, prophylactic and, most likely, also therapeutic vaccination against tumors will save millions from metastatic disease. This study describes a novel vaccine approach that facilitates delivery of viral or tumor antigens to dendritic cells in vivo. Concomitant immunostimulation via the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) was achieved through delivery by the same viral vector. Single immunization with only low doses of coronavirus-based vaccine vectors was sufficient to elicit (i) vigorous expansion and optimal differentiation of CD8⁺ T cells, (ii) protective and long-lasting antiviral immunity, and (iii) prophylactic and therapeutic tumor immunity. Moreover, highly efficient antigen delivery to human DCs with recombinant human coronavirus 229E and specific stimulation of human CD8⁺ T cells revealed that this approach is exceptionally well suited for translation into human vaccine studies.

INGN-225: a dendritic cell-based p53 vaccine (Ad.p53-DC) in small cell lung cancer: observed association between immune response and enhanced chemotherapy effect

IMPORTANCE OF THE FIELD

Novel approaches are needed for patients with small cell lung cancer (SCLC), as response after relapse is poor with standard therapies. p53 gene mutations often occur, resulting in tumoral protein overexpression and allowing for their recognition by p53-specific cytotoxic T cells.

AREAS COVERED IN THIS REVIEW

We describe the characteristics and manufacturing of INGN-225, a p53-modified adenovirus-tranduced dendritic cell vaccine, and review available data, to understand INGN-225's role in SCLC treatment. We discuss our pre-clinical, early Phase I/II, and ongoing randomized Phase II studies.

WHAT THE READER WILL GAIN

INGN-225 was well tolerated (all toxicities <or=grade 2) in the Phase I/II trial (54 patients receiving at least 1 dose). Specific anti-p53 immune response was positive in 18/43 (41.8%) patients, with overall post-INGN-225 response observed in 17/33 (51.5%) and immune response data available in 29 (14 positive, 15 negative). Post-INGN-225 response was observed in 11/14 (78.6%) and 5/15 (33%) patients with positive and negative immune responses, respectively.

TAKE HOME MESSAGE

INGN-225 is safe, induces a significant immune response, and appears to sensitize SCLC to subsequent chemotherapy. Improvements in immune response induction and understanding the chemotherapy-immunotherapy synergism will determine INGN-225's future role as an anticancer therapy.

Identification of genetically modified Maraba virus as an oncolytic rhabdovirus

To expand our current array of safe and potent oncolytic viruses, we screened a variety of wild-type (WT) rhabdoviruses against a panel of tumor cell lines. Our screen identified a number of viruses with varying degrees of killing activity. Maraba virus was the most potent of these strains. We built a recombinant system for the Maraba virus platform, engineered a series of attenuating mutations to expand its therapeutic index, and tested their potency in vitro and in vivo. A double mutant (MG1) strain containing both G protein (Q242R) and M protein (L123W) mutations attenuated Maraba virus in normal diploid cell lines, yet appeared to be hypervirulent in cancer cells. This selective attenuation was mediated through interferon (IFN)-dependent and -independent mechanisms. Finally, the Maraba MG1 strain had a 100-fold greater maximum tolerable dose (MTD) than WT Maraba in vivo and resulted in durable cures when systemically administered in syngeneic and xenograft models. In summary, we report a potent new oncolytic rhabdovirus platform with unique tumor-selective attenuating mutations.

Dendritic cell/tumor hybrids enhances therapeutic efficacy against colorectal cancer liver metastasis in SCID mice

OBJECTIVE

Colorectal cancer (CRC) is one of the most common malignancies in the western world. More than 60% among patients will develop liver metastases. Although surgical resection is the first choice worldwide, at this point an effective approach for the treatment of patients with liver metastasis and cancer recurrence postoperation has not yet been found. The aim of this study is to investigate the role of the allogeneic dendritomas from fusion of DCs and metastatic colon cancer cells in the activation of anti-tumor immunity against colorectal cancer liver metastases.

MATERIAL AND METHODS

Hybrids were generated by fused allogeneic human peripheral blood dendritic cells with metastatic colon cancer SW620 cells using 50% polyethylene glycol (PEG). Induction of immune responses was assessed by ex vivo ELISPOT assays. A murine model of CRC liver metastasis was used by intrasplenic injection. The validity of the vaccine was observed by Vaccination CRC liver metastasis murine model with DC/tumor hybrids.

RESULTS

The hybrids highly express the major molecules of DCs and tumor cells. The number of hybrids pulsed CTL secreting IFN-gamma was significantly higher when compared to the DC controls (p < 0.01). In a therapeutic setting mice vaccinated with in vitro cultured hybrids produced strong cellular immune responses and significant inhibition of tumor growth, compared to sham vaccinated controls.

CONCLUSIONS

Vaccination with hybrids can induces strong cellular responses and significant protection from challenge in SCID mouse metastatic CRC model.

Current advances, problems and prospects for vaccine-based immunotherapy in follicular non-Hodgkin's lymphoma

Despite advances in chemotherapy, radiotherapy and combined modality treatment, a significant proportion of non-Hodgkin's lymphomas remain incurable. The disease usually responds well to chemotherapy or radiation, but relapses are observed within months to a few years, with frequent failure of subsequent therapies. High-dose chemotherapy with or without radiation and autologous or allogeneic hematopoietic stem cell transplantation provide higher cure rates and longer remissions in certain patients with aggressive lymphomas. However, the higher treatment-related morbidity and mortality of high-dose chemotherapy has driven a search for new and more tumor-specific treatment modalities, such as immunotherapy. Tumor antigens expressed by B-cell lymphomas, such as the "idiotype antigen", are seen as unique and specific target molecules for direct lymphoma immunotherapy. This review will delineate advances, problems and prospects for approaches to anti-B cell lymphoma immunotherapy where pre-clinical studies and proof of principle have been directly translated to patient care.

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.

alpha-Galactosylceramide-loaded, antigen-expressing B cells prime a wide spectrum of antitumor immunity

Most of the current tumor vaccines successfully elicit strong protection against tumor but offer little therapeutic effect against existing tumors, highlighting the need for a more effective vaccine strategy. Vaccination with tumor antigen-presenting cells can induce antitumor immune responses. We have previously shown that NKT-licensed B cells prime cytotoxic T lymphocytes (CTLs) with epitope peptide and generate prophylactic/therapeutic antitumor effects. To extend our B cell vaccine approach to the whole antigen, and to overcome the MHC restriction, we used a nonreplicating adenovirus to transduce B cells with antigenic gene. Primary B cells transduced with an adenovirus-encoding truncated Her-2/neu (AdHM) efficiently expressed Her-2/neu. Compared with the moderate antitumor activity induced by vaccination with adenovirus-transduced B cells (B/AdHM), vaccination with alpha-galactosylceramide-loaded B/AdHM (B/AdHM/alpha GalCer) induced significantly stronger antitumor immunity, especially in the tumor-bearing mice. The depletion study showed that CD4(+), CD8(+) and NK cells were all necessary for the therapeutic immunity. Confirming the results of the depletion study, B/AdHM/alpha GalCer vaccination induced cytotoxic NK cell responses but B/AdHM did not. Vaccination with B/AdHM/alpha GalCer generated Her-2/neu-specific antibodies more efficiently than B/AdHM immunization. More importantly, B/AdHM/alpha GalCer could prime Her-2/neu-specific cytotoxic T cells more efficiently and durably than B/AdHM. CD4(+) cells appeared to be necessary for the induction of antibody and CTL responses. Our results demonstrate that, with the help of NKT cells, antigen-transduced B cells efficiently induce innate immunity as well as a wide range of adaptive immunity against the tumor, suggesting that they could be used to develop a novel cellular vaccine.

Tracking the migration of dendritic cells by in vivo optical imaging

We report herein a method to track the migration of dendritic cells (DCs) using optical imaging. With the assistance of the delivery module, fluorescein isothiocyanate (FITC) could internalize inside DCs within 15 minutes of incubation. The fluorescent signal was mostly cytoplasmic and could be detected using in vivo imaging. Furthermore, we observed that the probe did not interfere with the DCs maturation as we assessed the expression of several surface markers. The labeled DCs secreted interleukin-12 (IL-12) and tumor necrosis factor-alpha (TNF-alpha) and stimulated the proliferation of CD4+ T lymphocytes responding to lipopolysaccharide (LPS) stimulation. We have systematically compared the probe uptake between mature and immature DCs. The study showed that the latter phagocytosed the probe slightly better than the former. Intravital imaging of treated mice showed the migration of DCs to lymph nodes (LNs), which is confirmed by immunohistochemistry. Taken together, we demonstrated the potential use of optical imaging for tracking the migration of DCs and homing in vivo. The delivery molecules could also be used on other imaging modalities or for delivery of antigens.

Toll-like receptors in tumor immunotherapy

Lymphodepletion with chemotherapeutic agents or total body irradiation (TBI) before adoptive transfer of tumor-specific T cells is a critical advancement in the treatment of patients with melanoma. More than 50% of patients that are refractory to other treatments experience an objective or curative response with this approach. Emerging data indicate that the key mechanisms underlying how TBI augments the functions of adoptively transferred T cells include (a) the depletion of regulatory T cells (T(reg)) and myeloid-derived suppressor cells that limit the function and proliferation of adoptively transferred cells; (b) the removal of immune cells that act as "sinks" for homeostatic cytokines, whose levels increase after lymphodepletion; and (c) the activation of the innate immune system via Toll-like receptor 4 signaling, which is engaged by microbial lipopolysaccharide that translocated across the radiation-injured gut. Here, we review these mechanisms and focus on the effect of Toll-like receptor agonists in adoptive immunotherapy. We also discuss alternate regimens to chemotherapy or TBI, which might be used to safely treat patients with advanced disease and promote tumor regression.

Alphaviral vector-transduced dendritic cells are successful therapeutic vaccines against neu-overexpressing tumors in wild-type mice

While dendritic cell (DC) vaccines can protect hosts from tumor challenge, their ability to effectively inhibit the growth of established tumors remains indeterminate. Previously, we have shown that human DCs transduced with Venezuelan equine encephalitis virus replicon particles (VRPs) were potent stimulators of antigen-specific T cells in vitro. Therefore, we investigated the ability of VRP-transduced DCs (VRP-DCs) to induce therapeutic immunity in vivo against tumors overexpressing the neu oncoprotein. Transduction of murine DCs with VRPs resulted in high-level transgene expression, DC maturation and secretion of proinflammatory cytokines. Vaccination with VRP-DCs expressing a truncated neu oncoprotein induced robust neu-specific CD8(+) T cell and anti-neu IgG responses. Furthermore, a single vaccination with VRP-DCs induced the regression of large established tumors in wild-type mice. Interestingly, depletion of CD4(+), but not CD8(+), T cells completely abrogated inhibition of tumor growth following vaccination. Taken together, our results demonstrate that VRP-DC vaccines induce potent immunity against established tumors, and emphasize the importance of the generation of both CD4(+) T cell and B cell responses for efficient tumor inhibition. These findings provide the rationale for future evaluation of VRP-DC vaccines in the clinical setting.

Targeted delivery of CX3CL1 to multiple lung tumors by mesenchymal stem cells

MSCs are nonhematopoietic stem cells capable of differentiating into various mesoderm-type cells. MSCs have been considered to be a potential vehicle for cell-based gene therapy because MSCs are relatively easily expanded in vitro and have the propensity to migrate to and proliferate in the tumor tissue after systemic administration. Here, we demonstrated the tropism of mouse MSCs to tumor cells in vitro and multiple tumor tissues in the lung after i.v. injection of green fluorescent protein-positive MSCs in vivo. We transduced CX3CL1 (fractalkine), an immunostimulatory chemokine, to the mouse MSCs ex vivo using an adenoviral vector with the Arg-Gly-Asp-4C peptide in the fiber knob. Intravenous injection of CX3CL1-expressing MSCs to the mice bearing lung metastases of C26 and B16F10 cells strongly inhibited the development of lung metastases and thus prolonged the survival of these tumor-bearing mice. This antitumor effect depended on both innate and adaptive immunity. These results suggest that MSCs can be used as a vehicle for introducing biological agents into multiple lung tumor tissues. Disclosure of potential conflicts of interest is found at the end of this article.

Comparative analysis of DC fused with tumor cells or transfected with tumor total RNA as potential cancer vaccines against hepatocellular carcinoma

BACKGROUND

DC vaccination with the use of tumor cells provides the potential to generate a polyclonal immune response to multiple known and unknown tumor Ag. Our study comparatively analyzed DC fused with tumor cells or transfected with tumor total RNA as potential cancer vaccines against hepatocellular carcinoma (HCC).

METHODS

Immature DC generated from PBMC of patients with HCC were fused with HepG2-GFP (HepG2 cell line transfected stably with plasmid pEGFP-C3) cells or transfected with their total RNA. Matured DC were used to stimulate autologous T cells, and the resultant Ag-specific effector T cells were analyzed by IFN-gamma ELISPOT assay.

RESULTS

DC were capable of further differentiation into mature DC after fusion with HepG2-GFP cells or transfection with HepG2-GFP cell total RNA, and were able to elicit specific T-cell responses in vitro. Both methods of Ag loading could result in stimulating CD4+ and CD8+ T cells, but with the indication that fusion loading was more efficient than RNA loading in priming the Th1 response, while RNA loading was more effective in CTL priming.

DISCUSSION

Our results indicate that DC fused with tumor cells or transfected with tumor total RNA represent promising strategies for the development of cancer vaccines for treatment of HCC. They may have potential as an adjuvant immunotherapy for patients with HCC.

Dendritic cells, pulsed with lysate of allogeneic tumor cells, are capable of stimulating MHC-restricted antigen-specific antitumor T cells

A variety of approaches have been used to deliver tumor-associated antigens (TAA) in conjunction with dendritic cells (DC) as cellular adjuvants. DC derived from monocytic precursors have been pulsed with whole tumor antigen using a variety of strategies and have been demonstrated to induce CD4+ and CD8+ antitumor responses. In the present study, monocyte-derived DC have been pulsed with lysate from an allogeneic melanoma cell line, A-375, and used to repeatedly stimulate T cells. The resultant T cells were examined for cytotoxic activity against A-375 targets as well as the HLA A2-positive melanoma cell line DFW. Uptake of FITC-labeled melanoma lysate by DC established that lysate of melanoma cells was efficiently endocytosed. Stimulation with lysate-pulsed DC resulted in strong proliferative responses by T cells, which could be inhibited by antibodies against both MHC class I and class II. T cells stimulated in vitro with lysate-pulsed DC demonstrated potent cytotoxicity against the melanoma targets which were blocked by antibodies against MHC class I. Lysate-pulsed DC also elicited IFN-gamma secretion by T cells as measured in an ELISPOT assay. We have also examined the ability of lysate-pulsed DC to present melanoma-associated antigens to T cells. ELISPOT assays with synthetic peptides of melanoma-associated antigens, such as gp100, mage1, NY-ESO, and MART-1, revealed that lysate-pulsed DC could stimulate T cells in an antigen-specific manner. The results demonstrate that lysate from allogeneic tumor cells may be used as a source of antigens to stimulate tumor-specific T cells in melanoma.

Immunologic and clinical responses after vaccinations with peptide-pulsed dendritic cells in metastatic renal cancer patients

A phase I trial was conducted to evaluate the feasibility, safety, and efficacy of a dendritic cell-based vaccination in patients with metastatic renal cell carcinoma (RCC). Autologous mature dendritic cells derived from peripheral blood monocytes were pulsed with the HLA-A2-binding MUC1 peptides (M1.1 and M1.2). For the activation of CD4(+) T-helper lymphocytes, dendritic cells were further incubated with the PAN-DR-binding peptide PADRE. Dendritic cell vaccinations were done s.c. every 2 weeks for four times and repeated monthly until tumor progression. After five dendritic cell injections, patients additionally received three injections weekly of low-dose interleukin-2 (1 million IE/m(2)). The induction of vaccine-induced T-cell responses was monitored using enzyme-linked immunospot and Cr release assays. Twenty patients were included. The treatment was well tolerated with no severe side effects. In six patients, regression of the metastatic sites was induced after vaccinations with three patients achieving an objective response (one complete response, two partial responses, two mixed responses, and one stable disease). Additional four patients were stable during the treatment for up to 14 months. MUC1 peptide-specific T-cell responses in vivo were detected in the peripheral blood mononuclear cells of the six patients with objective responses. Interestingly, in patients responding to the treatment, T-cell responses to antigens not used for vaccinations, such as adipophilin, telomerase, or oncofetal antigen, could be detected, indicating that epitope spreading might occur. This study shows that MUC1 peptide-pulsed dendritic cells can induce clinical and immunologic responses in patients with metastatic RCC.

Adenoviral gene transfer of stromal cell-derived factor-1 to murine tumors induces the accumulation of dendritic cells and suppresses tumor growth

The human CXC chemokine, stromal cell-derived factor 1 (SDF-1alpha), is known to function in vitro as a chemotactic factor for lymphocytes, monocytes, and dendritic cells. In the context that dendritic cells are powerful antigen-presenting cells, we hypothesized that adenoviral gene transfer of SDF-1alpha to tumors might inhibit growth of preexisting tumors through attracting dendritic cells to the tumor. AdSDF-1alpha mediated the expression of SDF-1alpha mRNA and protein in A549 cells in vitro, and the supernatant of the AdSDF-1alpha-infected A549 cells showed chemotactic activity for dendritic cells. When syngeneic murine CT26 colon carcinoma tumors (BALB/c) and B16 melanoma and Lewis lung cell carcinoma (C57Bl/6) were injected with AdSDF-1alpha (5 x 10(8) plaque-forming units), there was an accumulation of dendritic cells and CD8(+) cells within the tumor and significant inhibition of tumor growth compared with tumors injected with PBS or AdNull (control vector). The injection of AdSDF-1alpha into tumors induced the inflammatory enlargement and the accumulation of dendritic cells in the draining lymph node. Intratumoral AdSDF-1alpha administration elicited tumor-specific CTLs and adoptive transfer of splenocytes from AdSDF-1alpha-treated mice resulted in the elongation of survival after tumor challenge. Interestingly, in wild-type and CD4(-/-) mice but not in CD8(-/-) mice, AdSDF-1alpha inhibited the growth of the tumor. These observations suggest that adenoviral gene transfer of SDF-1alpha may be a useful strategy to accumulate dendritic cells in tumors and evoke antitumor immune responses to inhibit tumor growth.

Dendritic cell generated from CD34+ hematopoietic progenitors can be transfected with adenovirus containing gene of HBsAg and induce antigen-specific cytotoxic T cell responses

Dendritic cells (DCs) are professional antigen presenting cells that are being considered as potential immunotherapeutic agents to promote host immune responses against tumor antigens. The use of such modified antigen-presenting cells for research or therapeutic have been limited by several factors, including maintaining DCs in a highly activated state, efficient transduction and expression, stable expression, identification of appropriate tumor-associated antigens, and absence of unintended functional changes or cytotoxicity. In this study, the feasibility of using CD34-DCs for tumor immunotherapy after transduction with a recombinant adenovirus containing HBsAg gene (AdVHBsAg), an HCC-associated antigen, was investigated. The gene transfer with recombinant adenovirus vectors (AdV) can obtained high levels of stable expression of HBsAg and its efficiency was increased in a multiplicity of infection (MOI)-dependent manner. Moreover, the AdVHBsAg infection had no appreciable effect on apoptosis of DCs compared with that of mock-infected DCs. The T cell lines, primed by the recombinant AdVHBsAg-infected DCs in vitro, recognized HBsAg-expressing tumor cell lines in a human leukocyte antigen (HLA) class I-restricted manner, and evoked a higher CTL response, which indicated that high potent and specific antitumor immune response could be induced by AdVHBsAg DC vaccine. It may be a promising the therapeutic modality for the treatment of HBsAg-expressing tumors, and will be a foundation for further study on DC vaccines and gene therapy for HCC.

Induction of α-fetoprotein-specific CD4- and CD8-mediated T-cell response using RNA-transfected dendritic cells

alpha-Fetoprotein (AFP) may be a possible target for a hepatocellular carcinoma (HCC)-specific vaccination. But some studies have demonstrated that dendritic cells (DCs) treated with AFP become dysfunctional. So in this study, we try to transfect AFP mRNA into DCs and observe the ability of DCs to induce AFP-specific CD4(+) and CD8(+) T cells. We hope that AFP can be processed and presented by DCs directly, rather than released to the cultures. So there will be no AFP negative effect on the function of DCs. In the study, immature DCs generated from peripheral blood mononuclear cells (PBMCs) of HLA-A2(+) HCC patients were transfected with AFP mRNA. Then the transfected, matured DCs were used to stimulate autologous T cells. The results showed that the expressions of membrane molecules of DCs after transfection were increased dramatically, and interleukin-12 (IL-12) p70 release in the supernatant was elevated significantly. There was only a minority of AFP release in the supernatants of transfected DCs. CTLs induced by the transfected DCs recognized HLA-matched AFP positive HepG2 cell line specifically and the AFP-specific proliferative T-cell responses could also be induced. These findings indicate that this AFP mRNA transfection strategy could generate fully functional DCs, which could induce specific T cells to recognize AFP(+) HCC cells.

AML-loaded DC generate Th1-type cellular immune responses in vitro

BACKGROUND

The generation of AML-specific T-lymphocyte responses by leukemia-derived DC has been documented by multiple investigators and is being pursued clinically. An obstacle to widespread use of this strategy is that it has not been possible to generate leukemic DC from all patients, and an alternative approach is needed if the majority of leukemia patients are to receive therapeutic vaccination in conjunction with other treatment protocols.

METHODS

In the present study, we generated DC from CD14-selected monocytes isolated from healthy donor PBPC and loaded them with a total cell lysate from AML patient blasts.

RESULTS

Immature in vitro-derived DC exhibited robust phagocytic activity, and mature DC demonstrated high expression of CD80, CD83, CD86 and the chemokine receptor CCR7, important for DC migration to local lymph nodes. Mature, Ag-loaded DC were used as APC for leukemia-specific cytotoxic T-lymphocyte (CTL) induction and demonstrated cytotoxic activity against leukemic targets. CTL lysis was Ag-specific, with killing of both allogeneic leukemic blasts and autologous DC loaded with allogeneic AML lysate. HLA-matched controls were not lysed in our system.

DISCUSSION

These data support further research into the use of this strategy as an alternative approach to leukemia-derived DC vaccination.

Expression of hepatitis C virus-derived core or NS3 antigens in human dendritic cells leads to induction of pro-inflammatory cytokines and normal T-cell stimulation capabilities

The majority of hepatitis C virus (HCV)-infected individuals become chronically infected, which can result in liver cirrhosis and hepatocellular carcinoma. Patients with chronic HCV are unable to prime and maintain vigorous T-cell responses, which are required to rid the body of the viral infection. Dendritic cells (DCs) are the professional antigen-presenting cells that probably play a dominant role in priming and maintaining vigorous T-cell responses in HCV infection. Furthermore, inefficient DC function may play an important role in HCV chronicity. In order to determine the effect of HCV NS3 and core proteins on phenotype and function of human DCs, recombinant adenoviral vectors containing NS3 or core genes were used to infect human DCs. HCV NS3- or core-protein expression in DCs was confirmed by Western blotting and immunofluorescence staining. The DCs expressing HCV NS3 or core proteins expressed several inflammatory cytokine mRNAs, had a normal phenotype and effectively stimulated allogeneic T cells, as well as T cells specific for another foreign antigen (tetanus toxoid). These findings are important for rational design of cellular-vaccine approaches for the immunotherapy of chronic HCV.

B cell tumor vaccine enhanced by covalent attachment of immunoglobulin to surface proteins on dendritic cells

Protein antigens have been covalently linked randomly to surface proteins on immature dendritic cells (DC). This has been achieved under physiological conditions using a heterobifunctional reagent that couples antigens to free thiol groups expressed on DC surface proteins. This results in a significant increase in the amount of antigen that is bound to DC, and the antigen/membrane protein complexes that are formed are rapidly internalized. DC, loaded covalently with either beta-galactosidase (beta-gal) or a tumor-associated immunoglobulin (Ig) when injected into mice, induce a beta-gal- or Ig-specific T cell response, and a protective anti-tumor immunity for tumors expressing either beta-gal or the targeted Ig. This response is shown here to be significantly greater than that which is induced by DC that are loaded with these antigens via the conventional antigen pulse protocol. These results establish a novel, safe, and viable approach of enhancing the effectiveness of DC-based vaccination strategies for B cell lymphoma.

Immunization with dendritic cells retrovirally transduced with mycobacterial antigen 85A gene elicits the specific cellular immunity including cytotoxic T-lymphocyte activity specific to an epitope on antigen 85A

In the present study, we evaluated antigen 85A (Ag85A) gene-transduced dendritic cells (DCs) vaccine against Mycobacterium tuberculosis. Murine bone marrow-derived DCs were retrovirally transduced with mycobacterial Ag85A gene and injected to BALB/c mice intravenously. The DC vaccine was capable of inducing purified protein derivative (PPD)- and the antigen-specific spleen cell proliferation and IFN-gamma production from both CD4+ and CD8+ T cells in spleens of the immune mice. In addition, the DC vaccination induced cytotoxic T-lymphocytes (CTL) and IFN-gamma-producing cells specific for a 9-mer CTL epitope on Ag85A molecule. This eliciting cellular immunity led to protection against wasting disease due to M. tuberculosis infection and induction of moderate bacterial clearance.

Specific antihepatocellular carcinoma T cells generated by dendritic cells pulsed with hepatocellular carcinoma cell line HepG2 total RNA

Dendritic cell (DC) vaccination with the use of total tumor RNA provides the potential to generate a polyclonal immune response to multiple known and unknown tumor antigens without HLA restriction. Our study evaluated this approach as potential immunotherapy for patients with hepatocellular carcinoma (HCC). Immature DCs generated from peripheral blood mononuclear cells of patients with HCC were transfected with HepG2-GFP (HepG2 cells transfected stably with plasmid pEGFP-C3) cells total RNA. Transfected, matured DCs were used to stimulate autologous T cells. Results revealed that DCs transfected with HepG2-GFP cells total RNA expressed EGFP when observed by flow cytometry. Compared with those before transfection, the expressions of membrane molecules were increased dramatically, and interleukin-12p70 release in the supernatant was elevated significantly. Specific T cells generated by DCs transfected with HepG2-GFP total RNA recognized HLA-matched HepG2 cell lines specifically. These findings indicate that these RNA-transfected DCs successfully generate specific T cells that specifically recognize HCC cells. Total tumor RNA-pulsed DCs may have potential as an adjuvant immunotherapy for patients with HCC.

Polyethylenimine-based non-viral gene delivery systems

Gene therapy has become a promising strategy for the treatment of many inheritable or acquired diseases that are currently considered incurable. Non-viral vectors have attracted great interest, as they are simple to prepare, rather stable, easy to modify and relatively safe, compared to viral vectors. Unfortunately, they also suffer from a lower transfection efficiency, requiring additional effort for their optimization. The cationic polymer polyethylenimine (PEI) has been widely used for non-viral transfection in vitro and in vivo and has an advantage over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. Here, we give some insight into strategies developed for PEI-based non-viral vectors to overcome intracellular obstacles, including the improvement of methods for polyplex preparation and the incorporation of endosomolytic agents or nuclear localization signals. In recent years, PEI-based non-viral vectors have been locally or systemically delivered, mostly to target gene delivery to tumor tissue, the lung or liver. This requires strategies to efficiently shield transfection polyplexes against non-specific interaction with blood components, extracellular matrix and untargeted cells and the attachment of targeting moieties, which allow for the directed gene delivery to the desired cell or tissue. In this context, materials, facilitating the design of novel PEI-based non-viral vectors are described.

Immune characterization of clinical grade-dendritic cells generated from cancer patients and genetically modified by an ALVAC vector carrying MAGE minigenes

Gene delivery into dendritic cells (DC) is most efficiently achieved by viral vectors. Recombinant canarypox viruses (ALVAC) were validated safe and efficient in humans. We aimed firstly to evaluate DC transduction by ALVAC vectors, then to investigate if such infection induced or not the maturation of the DC, and finally to assess the efficiency of ALVAC-MAGE-transduced DC to activate specific CTL clones. Clinical grade DC from melanoma patients were generated from blood monocytes and infected with a recombinant ALVAC virus encoding either a marker gene (EGFP) or the MAGE-1-MAGE-3 minigenes. According to the patient-donor, 22+/-16% of immature DC were successfully transduced. Flow cytometry analysis of surface markers expressed on DC after ALVAC infection did not reveal a mature phenotype. Moreover, ALVAC transduction did not interfere with the capacity of the DC to further mature under poly:IC stimulation. But most importantly, our results demonstrated that DC from HLA-A1 patient-donors infected with the recombinant ALVAC MAGE-1-MAGE-3 minigenes virus were capable of activating a MAGE 3/A1 CTL clone more efficiently than same DC loaded with MAGE 3/A1 peptide, as shown by increased IFN-gamma secretion. These results could be the basis for the development of a new clinical strategy in melanoma patient's immunotherapy.

Continuous Presence of Th1 Conditions Is Necessary for Longer Lasting Tumor-Specific CTL Activity in Stimulation Cultures With PBL

The generation of tumor-associated, but self-antigen specific cytotoxic T lymphocytes (CTL) response is possible by vaccination even in patients at the advanced stages of the disease. The in vivo expansion of such CTLs is now the most important objective of the immunotherapy. In human melanoma, we show here that MART-1(27-35)-specific CTLs generated with purified CD8+ cells survive and maintain their activity longer in culture than those CTLs generated by using total peripheral blood lymphocytes (PBL) taken either from patients or from normal donors. When PBL are grown under Th1 conditioning the quantity and quality of CTL with total PBL are comparable with that of the CTLs generated with purified CD8+ cells. For patients either autologous melanoma tumor cells or MART-1(27-35) peptide pulsed autologous DC were used to generate CTL responses. For normal donors MART-1(27-35) peptide pulsed autologous DC were used. For both normal donors or patients, polarization of PBL with Th1 conditioning with interleukin (IL)-12 (250 U/ml) and anti IL-4 antibody 1 mug/ml for 7 days before CTL generation, induced better and longer living CTL response and prevented the expansion of CD4+ T cells that have downregulatory activity. We show that continuous presence of Th1 conditioning in cultures with total PBL generated significantly higher number of antigen-specific CTLs as detected by MART-1 HLA-A2 tetramer staining. The antigen specificity of such CTLs were determined by IFN-gamma secretion in response to target cells bearing the specific antigen. Our observations indicate that Th1 conditioning results in a longer lasting CTL response in vitro and points toward a newer approach for vaccine strategy.

Rationale for antiangiogenic cancer therapy with vaccination using epitope peptides derived from human vascular endothelial growth factor receptor 2

Angiogenesis is a critical mechanism for tumor progression. Multiple studies have suggested that tumor growth can be suppressed if tumor angiogenesis can be inhibited using various types of antiangiogenic agents. Recent studies in mouse systems have shown that tumor angiogenesis can also be inhibited if cellular immune response could be induced against vascular endothelial growth factor receptor 2 (VEGFR2), which is one of the key factors in tumor angiogenesis. In this study, we examined the possibility of developing this novel immunotherapy in clinical setting. We first identified the epitope peptides of VEGFR2 and showed that stimulation using these peptides induces CTLs with potent cytotoxicity in the HLA class I-restricted fashion against not only peptide-pulsed target cells but also endothelial cells endogenously expressing VEGFR2. In A2/Kb transgenic mice that express alpha1 and alpha2 domains of human HLA-A*0201, vaccination using these epitope peptides in vivo was associated with significant suppression of the tumor growth and prolongation of the animal survival without fatal adverse effects. In antiangiogenesis assay, tumor-induced angiogenesis was significantly suppressed with the vaccination using these epitope peptides. Furthermore, CTLs specific to the epitope peptides were successfully induced in cancer patients, and the specificities of the CTLs were confirmed using functional and HLA-tetramer analysis. These results in vitro and in vivo strongly suggest that the epitope peptides derived from VEGFR2 could be used as the agents for antiangiogenic immunotherapy against cancer in clinical settings.

Therapeutic potential of dendritic-based vaccines

Involving a delicate balance of cell types, the interaction between the immune system and disease or abnormality in the human body is complex. Moreover, the mere presence of antigen and immune cells is necessary, yet insufficient to elicit immune reactivity. In order to elicit an immune response, an antigen in some form must be processed and presented to the immune system. Arguably, the most efficient antigen-presenting cell, the dendritic cell (DC), is the centre of intense investigation. The elicitation or cessation of an immune response is not a simple matter. The body must be able either to up-regulate (e.g., in the case of infectious disease) or down-regulate (e.g., in the case of transplantation) immunity to antigens located anywhere in the body. This sentinel role is capably filled via the distribution of Langerhans cells in the epidermis of the skin, and the migration of DCs throughout the lymphatic and circulatory systems. DCs are potent, as well as efficient: small numbers of cells and low levels of antigen still induce clinically relevant immunity. Lastly, they are capable of tolerance induction to self components by helping to delete self-reactive thymocytes and generating anergy in committed T-cells. Since DCs both initiate and modulate immunity, they are a component of a vast array of vaccines. This review highlights some of the intriguing basic research involving the development of DC-based therapeutics. Furthermore, whenever an area of study has progressed to human treatment, recent and on-going clinical trials are discussed.

New developments in dendritic cell-based vaccinations: RNA translated into clinics

Dendritic cells (DCs) are the most powerful antigen-presenting cells that induce and maintain primary immune responses in vitro and in vivo. The development of protocols for the ex vivo generation of DCs provided a rationale for designing and developing DC-based vaccination studies for the treatment of infectious and malignant diseases. Recently, it was shown that DCs transfected with ribonucleic acid (RNA) coding for a tumour-associated antigen or whole tumour RNA are able to induce potent antigen and tumour-specific T-cell responses directed against multiple epitopes. The first RNA-transfected-DC-based clinical studies have shown that this form of vaccination is feasible and safe. In some cases, clinical responses were observed, but the preliminary data require further extensive investigations that should address the technical and biological problems of manipulating human DCs, as well as the development of standardised protocols and definitions of clinical settings.

Immunization with lentiviral vector-transduced dendritic cells induces strong and long-lasting T cell responses and therapeutic immunity

Dendritic cell (DC) therapies are currently being evaluated for the treatment of cancer. The majority of ongoing clinical trials use DCs loaded with defined antigenic peptides or proteins, or tumor-derived products, such as lysates or apoptotic cells, as sources of Ag. Although several theoretical considerations suggest that DCs expressing transgenic protein Ags may be more effective immunogens than protein-loaded cells, methods for efficiently transfecting DCs are only now being developed. In this study we directly compare the immunogenicity of peptide/protein-pulsed DCs with lentiviral vector-transduced DCs, and their comparative efficacy in tumor immunotherapy. Maturing, bone marrow-derived DCs can be efficiently transduced with lentiviral vectors, and transduction does not affect DC maturation, plasticity, or Ag presentation function. Transduced DCs efficiently process and present both MHC class I- and II-restricted epitopes from the expressed transgenic Ag OVA. Compared with peptide- or protein-pulsed DCs, lentiviral vector-transduced DCs elicit stronger and longer-lasting T cell responses in vivo, as measured by both in vivo killing assays and intracellular production of IFN-gamma by Ag-specific T cells. In the B16-OVA tumor therapy model, the growth of established tumors was significantly inhibited by a single immunization using lentiviral vector-transduced DCs, resulting in significantly longer survival of immunized animals. These results suggest that compared with Ag-pulsed DCs, vaccination with lentiviral vector-transduced DCs may achieve more potent antitumor immunity. These data support the further development of lentiviral vectors to transduce DCs with genes encoding Ags or immunomodulatory adjuvants to generate and control systemic immune responses.

Allogeneic Dendritomas Induce Anti-tumour Immunity Against Metastatic Colon Cancer

Colon cancer (CC) is one of the most common malignancies in the Western world. Although surgical resection is the first choice worldwide, at this point an effective approach for the treatment of patients with metastasis and cancer recurrence post-operation has not yet been found. The aim of this study was to investigate the role of the allogeneic dendritomas from fusion of dendritic cells (DC) and metastatic CC cells in the activation of anti-tumour immunity against metastatic CC. Dendritomas were generated by fused allogeneic human peripheral blood DC with metastatic CC cells using 50% polyethylene glycol. The proliferation of the T cells and the toxicity of the cytotoxic T lymphocytes were observed after T cell pulsed with allogeneic dendritomas. The activated ratios of CD4+T helper 1 and CD8+Tc1 cells were about 51.55 and 65.60% after T cells were mixed with fusions for 24 h, which higher than those of controls. The proliferation of T cells were significantly higher than those of control after T cell pulsed with dendritomas (P < 0.01). Significantly, the activated CD8+ T lymphocytes effectively lysed the CC cells. These results demonstrate that allogeneic dendritomas activate T-cell responses against metastatic CC cells.

Vaccines for human papillomavirus-associated anogenital disease and cervical cancer: practical and theoretical approaches

The association of genital warts, cervical dysplasia and cervical cancer with certain human papillomavirus (HPV) types indicates that vaccine strategies that target the virus could be effective in controlling disease onset and progression. Three vaccine strategies are available. Firstly, a prophylactic approach of immunisation with HPV virus-like particles to elicit neutralising antibody would prevent infection. Secondly, vaccination targeting replicating virus in suprabasal cells of infected anogenital epithelium would be an effective therapy for infection and early dysplasias. Thirdly, immunotherapy directed to the oncoprotein products of the HPV E6 and E7 open reading frames would be effective in the control of cervical carcinoma. We examine how these strategies may be augmented by contemporary vaccine technologies, in particular through the use of live recombinant vaccine vectors, specific targeting of antigen processing pathways, dendritic cell and 'polytope' approaches, to produce 'designer' vaccines of maximum specificity and efficacy. How these approaches are being exploited by vaccine manufacturers and in clinical trials is discussed.

Efficient transfer of PSA and PSMA cDNAs into DCs generates antibody and T cell antitumor responses in vivo

Gene therapy for prostate cancer may be realized through transduction of whole genes, such as PSA or PSMA, into immunotherapeutic dendritic cells (DCs). An oncoretroviral vector encoding human PSMA and a bicistronic oncoretroviral vector encoding human PSA and cell surface CD25 cDNAs were constructed. Remarkably, transfer of PSA/CD25 or PSMA cDNA during murine hematopoietic cell differentiation into DCs occurred with approximately 80% efficiency. In vitro, transduced DCs retained allostimulatory function and primed syngeneic T cells for tumor antigen-specific IFN-gamma secretion. In test experiments designed to elucidate mechanisms in vivo, syngeneic recipients of transduced DCs had increased anti-human PSA antibody titers and tumor-specific CD8(+) T cell IFN-gamma secretion with no detectable immune response to CD25. Gene-modified DC recipients had increased protection from specific tumor challenge for at least 18 weeks post-vaccination. DC vaccination also protected both male and female recipients. Gene-modified DC vaccination mediated regression of established, specific gene-expressing, TRAMP-C1 prostate cancer cell tumors. These findings indicate that antibody and cellular responses generated through PSA and PSMA gene transfer into DC yielded protective immunity, thereby providing further preclinical support for the implementation of immuno-gene therapy approaches for prostate cancer.

Embryonic stem cells: a novel source of dendritic cells for clinical applications

As arbitrators of the immune response, dendritic cells (DC) are uniquely placed to negotiate the balance between the opposing forces of tolerance and immunity, making them attractive candidates for clinical applications. Accordingly, DC have been used successfully in the treatment of cancer, enhancing immune responses to tumour-associated antigens (TAA) in experimental animal models and phase I clinical trials. A novel source of DC that has recently been described is the embryonic stem (ES) cell whose differentiation in vitro may be directed along multiple lineage pathways. Such pluripotency offers unparalleled opportunities for the treatment of chronic and degenerative disease states by the replacement of affected tissues, a vision which has inspired the emerging field of regenerative medicine. By sharing the genotype of therapeutic cell types, such as cardiomyocytes and dopaminergic neurons derived from the same ES cell line, so-called esDC may offer prospects for reprogramming the immune system to tolerate the grafted tissues. Here, we describe how the unique properties of esDC and the ES cells from which they derive, make them eminently suited to clinical applications, overcoming many of the issues that currently limit the effectiveness of DC-based immune intervention.

Intratumoral immunotherapy: using the tumour against itself

Summary Diverse immunotherapy approaches have achieved success in controlling individual aspects of immune responses in animal models. Transfer of such immunotherapies to clinical trials has obtained some success in patients, with clinical responses observed or effective antigen specific immune responses achieved, but has had limited impact on patient survival. Key elements required to generate de novo cell-mediated antitumour immune responses in vivo include recruitment of antigen-presenting cells to the tumour site, loading these cells with antigen, and their migration and maturation to full antigen-presenting function. In addition, it is essential for antigen-specific T cells to locate the tumour to mediate cytotoxicity, emphasizing the need for local inflammation to target effector cell recruitment. We review those therapies that involve the tumour site as a target and source of antigen for the initiation of immune responses, and discuss strategies to generate and co-ordinate an optimal cell-mediated immune response to control tumours locally.

Dendritic cells strongly boost the antitumor activity of adoptively transferred T cells in vivo

Dendritic cells (DCs) have been well characterized for their ability to initiate cell-mediated immune responses by stimulating naive T cells. However, the use of DCs to stimulate antigen-activated T cells in vivo has not been investigated. In this study, we determined whether DC vaccination could improve the efficacy of activated, adoptively transferred T cells to induce an enhanced antitumor immune response. Mice bearing B16 melanoma tumors expressing the gp100 tumor antigen were treated with cultured, activated T cells transgenic for a T-cell receptor specifically recognizing gp100, with or without concurrent peptide-pulsed DC vaccination. In this model, antigen-specific DC vaccination induced cytokine production, enhanced proliferation, and increased tumor infiltration of adoptively transferred T cells. Furthermore, the combination of DC vaccination and adoptive T-cell transfer led to a more robust antitumor response than the use of each treatment individually. Collectively, these findings illuminate a new potential application for DCs in the in vivo stimulation of adoptively transferred T cells and may be a useful approach for the immunotherapy of cancer.