Immunotherapy with a posttranscriptionally modified DNA vaccine induces complete protection against metastatic neuroblastoma

Transcriptional Targeting of Dendritic Cells Using an Optimized Human Fascin1 Gene Promoter

Deeper knowledge about the role of the tumor microenvironment (TME) in cancer development and progression has resulted in new strategies such as gene-based cancer immunotherapy. Whereas some approaches focus on the expression of tumoricidal genes within the TME, DNA-based vaccines are intended to be expressed in antigen-presenting cells (e.g., dendritic cells, DCs) in secondary lymphoid organs, which in turn induce anti-tumor T cell responses. Besides effective delivery systems and the requirement of appropriate adjuvants, DNA vaccines themselves need to be optimized regarding efficacy and selectivity. In this work, the concept of DC-focused transcriptional targeting was tested by applying a plasmid encoding for the luciferase reporter gene under the control of a derivative of the human fascin1 gene promoter (pFscnLuc), comprising the proximal core promoter fused to the normally more distantly located DC enhancer region. DC-focused activity of this reporter construct was confirmed in cell culture in comparison to a standard reporter vector encoding for luciferase under the control of the strong ubiquitously active cytomegalovirus promoter and enhancer (pCMVLuc). Both plasmids were also compared upon intravenous administration in mice. The organ- and cell type-specific expression profile of pFscnLuc versus pCMVLuc demonstrated favorable activity especially in the spleen as a central immune organ and within the spleen in DCs.

A novel DNA platform designed for vaccine use with high transgene expression and immunogenicity

The development of new, low-cost vaccines and effective gene therapies requires accurate delivery and high-level expression of candidate genes. We developed a plasmid vector, pIDV-II, that allows for both easy manipulation and high expression of exogenous genes in mammalian cells. This plasmid is based upon the pVax1 plasmid and shares a common structure with typical mammalian transcription units. It is composed of a chicken β-actin promoter (CAG), followed by an intron and flanked by two restriction sites, and also includes a post-transcriptional regulatory element, followed by a transcriptional termination signal. While the modification of pVax1 elements either decreased eGFP expression levels or had no effect at all, replacement of the promoter, the poly-A signal, deletion of the T7 and AmpR promoters, and inversion of the ORI-Neo/Kan cassette, significantly increased in vitro eGFP expression with the modified plasmid called pIDV-II. To further evaluate our vector, expression levels of three viral antigens were compared in cell lines transfected either with pVax1 or pCAGGS backbones as controls. Higher transgene expression was consistently observed with pIDV-II. The humoral and cellular responses generated in mice immunized with pIDV-II vs pVax1 expressing each viral antigen individually were superior by 2-fold or more as measured by ELISA and ELISPOT assays. Overall these results indicate that pIDV-II induces robust transgene expression, with concomitant improved cellular and humoral immune responses against the transgene of interest over pVax1. The new vector, pIDV-II, offers an additional alternative for DNA based vaccination and gene therapy for animal and human use.

Genetically modified "obligate" anaerobic Salmonella typhimurium as a therapeutic strategy for neuroblastoma

Background

Neuroblastoma currently has poor prognosis, therefore we proposed a new strategy by targeting neuroblastoma with genetically engineered anaerobic Salmonella (Sal-YB1).

Methods

Nude and nonobese diabetic-severe combined immunodeficiency (NOD-SCID) orthotopic mouse models were used, and Sal-YB1 was administered via tail vein. The therapeutic effectiveness, bio-safety, and mechanisms were studied.

Results

No mice died of therapy-related complications. Tumor size reduction was 70 and 30 % in nude and NOD-SCID mice, respectively. No Salmonella was detected in the urine; 75 % mice had positive stool culture if diaminopimelic acid was added, but all turned negative subsequently. Tumor tissues had more Sal-YB1 infiltration, necrosis, and shrinkage in Sal-YB1-treated mice. Significantly higher expression of TLR4, TNF-stimulated gene 6 protein (TSG6), and cleaved caspase 1, 3, 8, and 9 was found in the tumor masses of the Sal-YB1-treated group with a decrease of interleukin 1 receptor-associated kinase (IRAK) and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα). There was a high release of TNFα both in human macrophages and mouse tumor tissues with Sal-YB1 treatment. The antitumor effect of the supernatant derived from macrophages treated with Sal-YB1 could be reversed with TNFα and pan-caspase inhibitors.

Conclusions

This new approach in targeting neuroblastoma by bio-engineered Salmonella with the assistance of macrophages indirectly may have a clinical therapeutic impact in the future.

MTDH/AEG-1-based DNA vaccine suppresses metastasis and enhances chemosensitivity to paclitaxel in pelvic lymph node metastasis

OBJECTIVE

MTDH/AEG-1 could act as an oncogene by regulating cellular transformation, proliferation, invasion, metastasis, and angiogenesis. This study aims to explore the mechanism by which MTDH/AEG-1 inhibits cancer growth and metastasis and enhances chemosensitivity.

METHODS

Mouse model was established using orally immunized mice exposed to attenuated Salmonella containing vectors carrying full length MTDH/AEG-1 gene, and we were able to enhance the immune response and inhibit the growth and metastasis of prostate cancer through activation of cellular and humoral immunities and induction of CD8+ T cells. Immunohistochemistry and TUNEL assay, CD4+ and CD8+ T cell analysis by flow cytometry, HE staining, RT-PCR analysis, Western-blot analysis and quantitative polymerase chain reaction were performed.

RESULTS

The MTDH/AEG-1 gene vaccine induced the anti-tumor function of cytotoxic T lymphocytes and CD8+ T cells and inhibited tumor growth and metastasis of prostate cancer. In the therapy model, the MTDH/AEG-1 gene vaccine significantly enhanced chemosensitivity to paclitaxel, inhibited tumor growth, promoted tumor cell apoptosis, and prolonged the survival time of tumor-bearing mice without any apparent side effects.

CONCLUSIONS

Our results demonstrated that MTDH/AEG-1-based DNA vaccines could used for the treatment of prostate cancer in terms of the inhibition of tumor growth, the lifespan of tumor-bearing animals. Combined with chemotherapy, MTDH/AEG-1-based DNA vaccines may produce highly favorable outcomes in the prevention and treatment of prostate cancer, suggesting the immune efficacy of MTDH/AEG-1-based DNA should be further analyzed in other cancers.

Effective cancer vaccine platform based on attenuated salmonella and a type III secretion system

Vaccines explored for cancer therapy have been based generally on injectable vector systems used to control foreign infectious pathogens, to which the immune system evolved to respond naturally. However, these vectors may not be effective at presenting tumor-associated antigens (TAA) to the immune system in a manner that is sufficient to engender antitumor responses. We addressed this issue with a novel orally administered Salmonella-based vector that exploits a type III secretion system to deliver selected TAA in the cytosol of professional antigen-presenting cells in situ. A systematic comparison of candidate genes from the Salmonella Pathogenicity Island 2 (SPI2) locus was conducted in the vaccine design, using model antigens and a codon-optimized form of the human TAA survivin (coSVN), an oncoprotein that is overexpressed in most human cancers. In a screen of 20 SPI2 promoter:effector combinations, a PsifB::sseJ combination exhibited maximal potency for antigen translocation into the APC cytosol, presentation to CD8 T cells, and murine immunogenicity. In the CT26 mouse model of colon carcinoma, therapeutic vaccination with a lead PsifB::sseJ-coSVN construct (p8032) produced CXCR3-dependent infiltration of tumors by CD8 T cells, reversed the CD8:Treg ratio at the tumor site, and triggered potent antitumor activity. Vaccine immunogenicity and antitumor potency were enhanced by coadministration of the natural killer T-cell ligand 7DW8-5, which heightened the production of IL12 and IFNγ. Furthermore, combined treatment with p8032 and 7DW8-5 resulted in complete tumor regression in A20 lymphoma-bearing mice, where protective memory was demonstrated. Taken together, our results demonstrate how antigen delivery using an oral Salmonella vector can provide an effective platform for the development of cancer vaccines.

The role of AEG-1/MTDH/LYRIC in the pathogenesis of central nervous system disease

Astrocyte-elevated gene-1 (AEG-1/MTDH/LYRIC) is a potent oncogene that regulates key cellular processes underlying disease of the central nervous system (CNS). From its involvement in human immunodeficiency virus (HIV)-1 infection to its role in neurodegenerative disease and malignant brain tumors, AEG-1/MTDH/LYRIC facilitates cellular survival and proliferation through the control of a multitude of molecular signaling cascades. AEG-1/MTDH/LYRIC induction by HIV-1 and TNF highlights its importance in viral infection, and its incorporation into viral vesicles supports its potential role in active viral replication. Overexpression of AEG-1/MTDH/LYRIC in the brains of Huntington's disease patients suggests its function in neurodegenerative disease, and its association with genetic polymorphisms in large genome-wide association studies of migraine patients suggests a possible role in the pathogenesis of migraine headaches. In the field of cancer, AEG-1/MTDH/LYRIC promotes angiogenesis, migration, invasion, and enhanced tumor metabolism through key oncogenic signaling cascades. In response to external stress cues and cellular mechanisms to inhibit further growth, AEG-1/MTDH/LYRIC activates pathways that bypass cell checkpoints and potentiates signals to enhance survival and tumorigenesis. As an oncogene that promotes aberrant cellular processes within the CNS, AEG-1/MTDH/LYRIC represents an important therapeutic target for the treatment of neurological disease.

Use of attenuated bacteria as delivery vectors for DNA vaccines

Live, attenuated bacterial vaccines (LBV) are promising candidates for the induction of a broad-based immune response directed at recombinant heterologous antigens and the corresponding pathogen. LBVs allow vaccination through the mucosal surfaces and specific targeting of professional antigen-presenting cells located at the inductive sites of the immune system. A novel approach exploits attenuated intracellular bacteria as delivery vectors for eukaryotic antigen-expression plasmids (so-called DNA vaccines). Candidate carrier bacteria include attenuated strains of Gram-positive and Gram-negative bacteria. These bacteria have been shown to deliver DNA vaccines to human cells in vitro and have also proven their in vivo efficacy in several experimental animal models of infectious diseases and different cancers. The clinical assessment of the safety, immunogenicity and efficacy of these candidate strains will be the next challenging step towards live bacterial DNA vaccines.

Targeting tumors with salmonella Typhimurium- potential for therapy

When one considers the organism Salmonella enterica serotype Typhimurium (S. Typhimurium), one usually thinks of the Gram-negative enteric pathogen that causes the severe food borne illness, gastroentertitis. In this context, the idea of Salmonella being exploited as a cancer therapeutic seems pretty remote. However, there has been an escalating interest in the development of tumor-therapeutic bacteria for use in the treatment of a variety of cancers. This strategy takes advantage of the remarkable ability of certain bacteria to preferentially replicate and accumulate within tumors. In the case of S. Typhimurium, this organism infects and selectively grows within implanted tumors, achieving tumor/normal tissue ratios of approximately 1,000:1. Salmonella also has some attractive properties well suited for the design of a chemotherapeutic agent. In particular, this pathogen can easily be manipulated to carry foreign genes, and since this species is a facultative anaerobe, it is able to survival in both oxygenated and hypoxic conditions, implying this organism could colonize both small metastatic lesions as well as larger tumors. These observations are the impetus to a burgeoning field focused on the development of Salmonella as a clinically useful anti-cancer agent. We will discuss three cutting edge technologies employing Salmonella to target tumors.

MTDH/AEG-1-based DNA vaccine suppresses lung metastasis and enhances chemosensitivity to doxorubicin in breast cancer

The gene MTDH/AEG-1 is overexpressed in more than 40% of breast cancer patients, and it is associated with poor clinical outcomes. Previous studies have indicated that MTDH/AEG-1 could promote metastatic lung-seeding and enhance chemoresistance. Therefore, MTDH/AEG-1 could be a candidate target against breast cancer lung metastasis. We demonstrated that MTDH/AEG-1-based DNA vaccine, delivered by attenuated Salmonella typhimurium, could evoke strong CD8(+) cytotoxic-T-cell mediated immune responses against breast cancer. This vaccine showed anti-tumor growth and metastasis efficacy in a prophylactic setting. Importantly, in a therapeutic model, MTDH/AEG-1 vaccine was proved to increase chemosensitivity to doxorubicin and inhibit breast cancer lung metastasis. This vaccine could also prolong the life span of tumor-bearing mice without significant side effects in vivo. These results suggested that this novel DNA vaccine was effective in the inhibition of breast cancer growth and metastasis, and this vaccine in combination with chemotherapies offered new strategies for the clinical therapeutics of breast cancer metastasis.

DNA vaccination: using the patient's immune system to overcome cancer

Cancer is one of the most challenging diseases of today. Optimization of standard treatment protocols consisting of the main columns of chemo- and radiotherapy followed or preceded by surgical intervention is often limited by toxic side effects and induction of concomitant malignancies and/or development of resistant mechanisms. This requires the development of therapeutic strategies which are as effective as standard therapies but permit the patients a life without severe negative side effects. Along this line, the development of immunotherapy in general and the innovative concept of DNA vaccination in particular may provide a venue to achieve this goal. Using the patient's own immune system by activation of humoral and cellular immune responses to target the cancer cells has shown first promising results in clinical trials and may allow reduced toxicity standard therapy regimen in the future. The main challenge of this concept is to transfer the plethora of convincing preclinical and early clinical results to an effective treatment of patients.

Targeting tumors with salmonella Typhimurium- potential for therapy

When one considers the organism Salmonella enterica serotype Typhimurium (S. Typhimurium), one usually thinks of the Gram-negative enteric pathogen that causes the severe food borne illness, gastroentertitis. In this context, the idea of Salmonella being exploited as a cancer therapeutic seems pretty remote. However, there has been an escalating interest in the development of tumor-therapeutic bacteria for use in the treatment of a variety of cancers. This strategy takes advantage of the remarkable ability of certain bacteria to preferentially replicate and accumulate within tumors. In the case of S. Typhimurium, this organism infects and selectively grows within implanted tumors, achieving tumor/normal tissue ratios of approximately 1,000:1. Salmonella also has some attractive properties well suited for the design of a chemotherapeutic agent. In particular, this pathogen can easily be manipulated to carry foreign genes, and since this species is a facultative anaerobe, it is able to survival in both oxygenated and hypoxic conditions, implying this organism could colonize both small metastatic lesions as well as larger tumors. These observations are the impetus to a burgeoning field focused on the development of Salmonella as a clinically useful anti-cancer agent. We will discuss three cutting edge technologies employing Salmonella to target tumors.

Bacteria-induced gap junctions in tumors favor antigen cross-presentation and antitumor immunity

Antigen-presenting dendritic cells (DCs) trigger the activation of cytotoxic CD8 T cells that target and eliminate cells with the antigen on their surface. Although DCs usually pick up and process antigens themselves, they can also receive peptide antigens from other cells via gap junctions. We demonstrate here that infection with Salmonella can induce, in both human and murine melanoma cells, the up-regulation of connexin 43 (Cx43), a ubiquitous protein that forms gap junctions and that is normally lost during melanoma progression. Bacteria-treated melanoma cells can establish functional gap junctions with adjacent DCs. After bacterial infection, these gap junctions transferred preprocessed antigenic peptides from the tumor cells to the DCs, which then presented those peptides on their surface. These peptides activated cytotoxic T cells against the tumor antigen, which could control the growth of distant uninfected tumors. Melanoma cells in which Cx43 had been silenced, when infected in vivo with bacteria, failed to elicit a cytotoxic antitumor response, indicating that this Cx43 mechanism is the principal one used in vivo for the generation of antitumor responses. The Cx43-dependent cross-presentation pathway is more effective than standard protocols of DC loading (peptide, tumor lysates, or apoptotic bodies) for generating DC-based tumor vaccines that both inhibit existing tumors and prevent tumor establishment. In conclusion, we exploited an antimicrobial response present in tumor cells to activate cytotoxic CD8 T cells specific for tumor-generated peptides that could directly recognize and kill tumor cells.

Targets for active immunotherapy against pediatric solid tumors

The potential role of antibodies and T lymphocytes in the eradication of cancer has been demonstrated in numerous animal models and clinical trials. In the last decennia new strategies have been developed for the use of tumor-specific T cells and antibodies in cancer therapy. Effective anti-tumor immunotherapy requires the identification of suitable target antigens. The expression of tumor-specific antigens has been extensively studied for most types of adult tumors. Pediatric patients should be excellent candidates for immunotherapy since their immune system is more potent and flexible as compared to that of adults. So far, these patients do not benefit enough from the progresses in cancer immunotherapy, and one of the reasons is the paucity of tumor-specific antigens identified on pediatric tumors. In this review we discuss the current status of cancer immunotherapy in children, focusing on the identification of tumor-specific antigens on pediatric solid tumors.

Posttranscriptional regulatory elements enhance antigen expression and DNA vaccine efficacy

In higher eukaryotes, introns are usually required for efficient pre-mRNA processing. However, some viruses have alternative approaches involving posttranscriptional regulatory elements (PREs) to enhance intronless heterologous gene expression through enabling stability and 3' end formation, and to facilitate the nucleocytoplasmic export of unspliced mRNAs. In the current study, we compared the human cytomegalovirus (hCMV) immediate/early (IE) intronA, as well as virus-derived PREs-the PRE of Hepatitis B virus (HPRE) and Woodchuck Hepatitis virus (WPRE) on their ability to enhance antigen gene expression in vitro and immune responses induced by DNA vaccination in animal. Among all the constructs, the plasmids carrying the HPRE element showed the highest gene expression level in both in vivo and in vitro models. During immunization of mice with low doses (10 microg) of HIV-1 DNA vaccine, only -intronA/+HPRE and +intronA/+HPRE vaccine constructs induced anti-Gag antibodies, although the -intronA/+WPRE construct also elicited antigen-specific cellular immune responses. In addition, pInHGag (+intronA/+HPRE) at a 10 mug dose could induce higher anti-Gag antibody level than that induced by pGag (-intronA/-HPRE) or pInGag (+intronA/-HPRE) at 40 microg dose (p < 0.05). Our data are useful for the optimization of heterologous expression and immunogenicity of DNA vaccines.

Immunotherapy of neuroblastoma by an Interleukin-21-secreting cell vaccine involves survivin as antigen

AIM

IL-21 is the most recently identified member of the IL-2 cytokine family. Here we studied the therapeutic efficacy of IL-21-gene-modified cells (Neuro2a/IL-21) in a syngeneic metastatic neuroblastoma (NB) model.

MATERIALS AND METHODS

Neuro2a/IL-21 cells were tested as subcutaneous (sc) vaccine both in prophylactic and therapeutic settings. Depletion studies, cytotoxicity assay and immunohistochemical analyses were carried out to evaluate the mechanisms involved in tumor rejection.

RESULTS

When injected sc in syngeneic A/J mice viable Neuro2a/IL-21 cells were rejected and induced resistance to a subsequent iv challenge with Neuro2a parental cells (Neuro2a/pc), suggesting the involvement of an immune response. More importantly, in mice bearing Neuro2a/pc micrometastases, a single sc injection of Neuro2a/IL-21 cells significantly increased the mean tumor-free survival of treated animals (43 vs. 22 days) and cured 14% of them. The administration of two or three doses of Neuro2a/IL-21 cell vaccine further increased the mean survival time to 54 and 75 days, and the cure rate to 27 and 33%, respectively, whereas the use of unmodified Neuro2a or mock-transfected cells had no effect. In vivo cell subset depletion and a Winn-assay indicated the involvement of CD8 + CTLs. Immunohistochemical analysis indicated a reduction of CD31+ and VEGFR2+ microvessels in late metastases from therapeutically vaccinated mice. A role of survivin as antigen was suggested by in vitro assays using survivin-synthetic CTL-epitopes.

CONCLUSIONS

Our present data indicate that IL-21-secreting NB cells are effective as therapeutic vaccine in mice bearing metastatic NB, through a specific CTL response involving survivin as antigen, and suggest a potential interest for IL-21 in NB immuno-gene therapy.

AttenuatedSalmonellaandShigellaas Carriers for DNA Vaccines

The discovery that genes can be functionally transferred from bacteria to mammalian cells has suggested the possible use of bacterial vectors as gene delivery vehicles for vaccines. Attenuated invasive human intestinal bacteria, such as Salmonella and Shigella, have been used as plasmid DNA vaccine carriers and their potency has been evaluated in several animal models. This delivery system allows the administration of DNA vaccines together with associated bacterial immunostimulators directly to professional antigen presenting cells via human mucosal surfaces. Various strategies have been taken to improve the use of this delivery system to achieve robust immune responses at both mucosal and systemic sites of the immunized animals.

Heterologous viral RNA export elements improve expression of severe acute respiratory syndrome (SARS) coronavirus spike protein and protective efficacy of DNA vaccines against SARS

The SARS-CoV spike glycoprotein (S) is the main target of the protective immune response in humans and animal models of SARS. Here, we demonstrated that efficient expression of S from the wild-type spike gene in cultured cells required the use of improved plasmid vectors containing donor and acceptor splice sites, as well as heterologous viral RNA export elements, such as the CTE of Mazon-Pfizer monkey virus or the PRE of Woodchuck hepatitis virus (WPRE). The presence of both splice sites and WPRE markedly improved the immunogenicity of S-based DNA vaccines against SARS. Upon immunization of mice with low doses (2 microg) of naked DNA, only intron and WPRE-containing vectors could induce neutralizing anti-S antibodies and provide protection against challenge with SARS-CoV. Our observations are likely to be useful for the construction of plasmid and viral vectors designed for optimal expression of intronless genes derived from cytoplasmic RNA viruses.

DNA vaccination against VEGF receptor 2 reduces atherosclerosis in LDL receptor-deficient mice

OBJECTIVE

Similarities between neovascular ingrowth in atherosclerotic plaques and angiogenesis in tumors suggest that antiangiogenic factors that target tumor expansion may prove efficacious in the treatment of atherosclerosis. This study examined whether an oral DNA vaccine against the murine VEGF receptor 2 (Flk-1) with demonstrated antitumor effect through inhibition of pathological neovascularization can prevent or retard progression of atherosclerosis in hyperlipidemic low density lipoprotein receptor-deficient (LDLr-/-) mice.

METHODS AND RESULTS

Vaccination against Flk-1 resulted in T cell activation, suppression of neoangiogenesis, and a marked reduction in atherosclerosis which was independent of hypercholesterolemia in both male and female mice. Immunohistochemical characterization of aortic sinus lesions showed that the decreased lesion area was not associated with reduced plaque stability and had a lower density of microvessels.

CONCLUSIONS

These findings demonstrate for the first time that a DNA vaccine targeting activated endothelial cells in atherosclerotic lesions provides direct atheroprotective effects.

Characterization of GD2 peptide mimotope DNA vaccines effective against spontaneous neuroblastoma metastases

Disialoganglioside GD2 is an established target for immunotherapy in neuroblastoma. We tested the hypothesis that active immunization against the glycolipid GD2 using DNA vaccines encoding for cyclic GD2-mimicking decapeptides (i.e., GD2 mimotopes) is effective against neuroblastoma. For this purpose, two GD2 peptide mimotopes (MA and MD) were selected based on docking experiments to anti-GD2 antibody ch14.18 (binding free energy: -41.23 kJ/mol for MA and -48.06 kJ/mol for MD) and Biacore analysis (K(d) = 12.3 x 10(-5) mol/L for MA and 5.3 x 10(-5) mol/L for MD), showing a higher affinity of MD over MA. These sequences were selected for DNA vaccine design based on pSecTag2-A (pSA) also including a T-cell helper epitope. GD2 mimicry was shown following transfection of CHO-1 cells with pSA-MA and pSA-MD DNA vaccines, with twice-higher signal intensity for cells expressing MD over MA. Finally, these DNA vaccines were tested for induction of tumor protective immunity in a syngeneic neuroblastoma model following oral DNA vaccine delivery with attenuated Salmonella typhimurium (SL 7207). Only mice receiving the DNA vaccines revealed a reduction of spontaneous liver metastases. The highest anti-GD2 humoral immune response and natural killer cell activation was observed in mice immunized with the pSA-MD, a finding consistent with superior calculated binding free energy, dissociation constant, and GD2 mimicry potential for GD2 mimotope MD over MA. In summary, we show that DNA immunization with pSA-MD may provide a useful strategy for active immunization against neuroblastoma.

Recombinant Escherichia coli expressing invasin targets the Peyer's patches: the basis for a bacterial formulation for oral vaccination

We have investigated the tropism of nonpathogenic recombinant invasive Escherichia coli in the gastrointestinal tract and the efficacy of this invasive E. coli as an oral vaccine for cancer immunotherapy. E. coli expressing invasin from Yersinia pseudotuberculosis selectively invade nonphagocytic cells in which beta(1)-integrin is expressed and accessible. Following internalization the E. coli are degraded in the phagosome. Coexpression of listeriolysin O (LLO) mediates release of the content of the bacteria into the cytosol of the invaded cell. In vitro and in vivo experiments demonstrated that gut epithelial cells failed to be invaded by invasive E. coli, due to a basolateral localization of beta(1)-integrin. By contrast, selective uptake of invasive bacteria from the intestinal lumen into Peyer's patches was observed ex vivo. Once in this structure, invasive E. coli colocalized with dendritic cells and possibly B cells. Oral administration of invasive E. coli coexpressing the model antigen ovalbumin and LLO from Listeria monocytogenes was able to elicit systemic protection against a lethal challenge of B16 tumor cells expressing ovalbumin. These data demonstrate the selectivity of invasin-mediated invasion to the Peyer's patches and indicate the potential of nonpathogenic, invasive E. coli as an oral vaccine with applications in immunotherapy.

Bacterial gene therapy strategies

The ability of bacteria to mediate gene transfer has only recently been established and these observations have led to the utilization of various bacterial strains in gene therapy. The types of bacteria used include attenuated strains of Salmonella, Shigella, Listeria, and Yersinia, as well as non-pathogenic Escherichia coli. For some of these vectors, the mechanism of DNA transfer from the bacteria to the mammalian cell is not yet fully understood but their potential to deliver therapeutic molecules has been demonstrated in vitro and in vivo in experimental models. Therapeutic benefits have been observed in vaccination against infectious diseases, immunotherapy against cancer, and topical delivery of immunomodulatory cytokines in inflammatory bowel disease. In the case of attenuated Salmonella, used as a tumour-targeting vector, clinical trials in humans have demonstrated the proof of principle but they have also highlighted the need for the generation of strains with reduced toxicities and improved colonization properties. Altogether, the encouraging results obtained in the studies presented in this review justify further development of bacteria as a therapeutic vector against many types of pathology.

Multicolor fluorescence-based approaches for imaging cytokine-induced alterations in the neovascularization, growth, metastasis, and apoptosis of murine neuroblastoma tumors

Neuroblastoma is one of the most common solid tumors in children. The prognosis of patients with advanced neuroblastoma is poor overall despite standard therapeutic modalities and has stimulated substantial interest in the potential role for biologics such as immunotherapeutic and/or antiangiogenic agents for the treatment of neuroblastoma. To facilitate preclinical investigation of the efficacy and mechanisms of action of new biologic agents for the treatment of neuroblastoma, a comprehensive panel of disease-specific fluorescence-based model systems has been developed by our group to image the growth, neovascularization, metastasis, and apoptosis of neuroblastoma tumors. These model systems use fluorescent proteins to monitor cytokine-induced alterations in the growth and metastasis of neuroblastoma and allow for monitoring and/or quantitation of even minimal residual disease that is localized to visceral organ sites such as the liver, lung, and/or bone marrow. Further, based on the differential spectra of red fluorescent protein, green fluorescent protein (GFP), and agents such as 4'-6-diamidino-2-phenylindole (DAPI) (blue) and fluorescein isothiocyanate-dextran (green), multicolor systems have now been established by our group that allow for combined assessment of parameters, including the macroscopic relation of tumors to their associated vasculature and, within tissue sections, simultaneous quantitation of tumor neovascularization and evaluation of therapy-induced apoptosis within the tumor and vascular endothelial compartments. Further, by engineering cells to express specific mediators of apoptosis that have been linked to GFP (ie, BID-EGFP), these systems can also be used to dissect mechanisms by which neuroblastoma cells are induced to undergo apoptosis in vitro as well as in vivo. Collectively, these model systems provide important tools for investigation of the biology of neuroblastoma tumors and evaluation of mechanisms that mediate the regression of these tumors in response to novel therapeutic agents, including cytokines such as interleukin-12.

Bacteria-mediated DNA transfer in gene therapy and vaccination

The use of live attenuated bacterial vaccine strains allows the targeted delivery of macromolecules to mammalian cells and tissues via the mucosal route. Depending on their specific virulence mechanisms and inherent metabolic preferences, bacteria invade certain cell types and body niches where they consequently deliver their cargo. Recently, the ability of attenuated strains of Salmonella, Shigella and Yersinia spp., as well as Listeria monocytogenes and invasive Escherichia coli, to deliver eukaryotic expression plasmids into mammalian cells in vitro and in vivo has been discovered. The great potential of bacteria-mediated transfer of plasmid DNA encoding vaccine antigens and/or therapeutic molecules was demonstrated in experimental animal models of infectious diseases, tumours and gene deficiencies. The exact mechanism of DNA transfer from the bacterial vector into the mammalian host is not yet completely known. The understanding of molecular events during bacterial DNA transfer, however, will further the development of bacterial vector systems with great promise for various clinical applications.

Enhanced activity of hu14.18-IL2 immunocytokine against murine NXS2 neuroblastoma when combined with interleukin 2 therapy

Established s.c. NXS2 murine neuroblastoma tumors exhibited transient resolution after suboptimal therapy using the hu14.18-IL2 immunocytokine (IC). The hu14.18-IL2 IC is a fusion protein that has linked a molecule of interleukin 2 (IL-2) to the COOH terminus of each of the IgG heavy chains on the humanized anti-GD(2) monoclonal antibody hu14.18. To induce more potent and longer lasting in vivo antitumor effects, we tested hu14.18-IL2 IC in a regimen combining it with constant infusion IL-2 in NXS2 tumor-bearing mice. The addition of the constant infusion IL-2 augmented the antitumor response induced by treatment with the hu14.18-IL2 IC in animals with experimentally induced hepatic metastases and in animals bearing localized s.c. tumors. The combined treatment induced prolonged tumor eradication in most animals bearing s.c. tumors and involved both natural killer cells and T cells. The enhanced ability of this combined treatment to prevent tumor recurrence was not observed when a larger dose of hu14.18-IL2 IC, similar in IL-2 content to the IC plus systemic IL-2 regimen, was tested as single-agent therapy. Animals showing prolonged tumor eradication of established tumors after the combined hu14.18-IL2 plus IL-2 regimen exhibited a protective T-cell-dependent antitumor memory response against NXS2 rechallenge.

Bacteria as DNA vaccine carriers for genetic immunization

Genetic immunization with plasmid DNA vaccines has proven to be a promising tool in conferring protective immunity in various experimental animal models of infectious diseases or tumors. Recent research focuses on the use of bacteria, in particular enteroinvasive species, as effective carriers for DNA vaccines. Attenuated strains of Shigella flexneri, Salmonella spp., Yersinia enterocolitica or Listeria monocytogenes have shown to be attractive candidates to target DNA vaccines to immunological inductive sites at mucosal surfaces. This review summarizes recent progress in bacteria-mediated delivery of plasmid DNA vaccines in the field of infectious diseases and cancer.

The hybrid cytomegalovirus enhancer/chicken beta-actin promoter along with woodchuck hepatitis virus posttranscriptional regulatory element enhances the protective efficacy of DNA vaccines

DNA vaccines represent a novel and powerful alternative to conventional vaccine approaches. They are extremely stable and can be produced en masse at low cost; more importantly, DNA vaccines against emerging pathogens or bioterrorism threats can be quickly constructed based solely upon the pathogen's genetic code. The main drawback of DNA vaccines is that they often induce lower immune responses than traditional vaccines, particularly in nonrodent species. Thus, improving the efficacy of DNA vaccines is a critical issue in vaccine development. In this study we have enhanced the efficacy of DNA vaccines by adopting strategies that increase gene expression. We generated influenza-hemagglutinin (HA)-encoding DNA vaccines that contain the hybrid CMV enhancer/chicken beta-actin (CAG) promoter and/or the mRNA-stabilizing post-transcriptional regulatory element from the woodchuck hepatitis virus (WPRE). Mice were immunized with these DNA vaccines, and the influenza-HA-specific cellular and humoral immune responses were compared with a conventional, HA-encoding DNA vaccine whose gene expression was driven by the CMV immediate-early promoter (pCMV-HA). CAG promoter-driven DNA vaccines elicited significantly higher humoral and cellular immune responses compared with the pCMV-HA vaccine. DNA vaccines consisting of both CAG and WPRE elements (pCAG-HA-WPRE) induced the highest level of protective immunity, such that immunization with 10-fold lower DNA doses prevented death in 100% of the mice upon lethal viral challenge, whereas all mice immunized with the conventional pCMV-HA vaccine succumbed to influenza infection.

Detection and treatment of minimal residual disease in high-risk neuroblastoma

Intensive, myeloablative therapy supported by autologous hematopoietic stem-cell transplantation (AHSCT) has improved the outcome for children with high-risk neuroblastoma. However, >50% of patients develop recurrent neuroblastoma, often from minimal residual disease (MRD). Immunocytological and reverse transcriptase polymerase chain reaction (RT-PCR) for genes highly expressed in neuroblastoma both can detect small amounts of MRD in blood and bone marrow, and detection of MRD at certain levels during therapy has prognostic value. Radionucleotide scans using meta-iodobenzaguanidine (MIBG) imaging allows sensitive detection of neuroblastoma in patients, but whether or not all MIBG-positive disease detected after AHSCT will progress remains to be defined and is complicated by use of post-AHSCT therapy. Selective removal of tumor cells from marrow or blood stem cells harvested for AHSCT could decrease recurrence by preventing infusion of tumorigenic cells with AHSCT. Treating MRD after AHSCT with the differentiation-inducing retinoid 13-cis-retinoic acid significantly /improved EFS of high-risk neuroblastoma patients. Randomized clinical trials in the Children's Oncology Group are testing the value of purging blood stem cells and also whether post-AHSCT therapy with an anti-GD2 monoclonal antibody (combined with cytokines) improves outcome over use of 13-cis-retinoic acid alone. New approaches to treating neuroblastoma MRD that are in early clinical trials include the cytotoxic retinoid fenretinide and the hu14.18-IL2 immunocytokine. It is anticipated that testing novel approaches to treating neuroblastoma MRD will be the subject of future phase-III randomized trials.

Clinical applications of DNA microarray analysis

Microarray technology provides a revolutionary macro-genetic and bioinformatic-rich platform for understanding human diseases. DNA microarrays facilitate the study of complex diseases, enabling several observations simultaneously that can become foundations for newer hypotheses-shifting us towards a non-reductionist approach to biological phenomenon. This appears of particular value for scientific and clinical dissection of tumor pathologies. Despite the tremendous potential presented by microarray technology for the investigation of disease, concrete insights and advances that translate to the clinical setting are only recently beginning to be tapped. Here, we discuss specific examples of how microarray technology is being integrated into our ever-evolving approach to clinical disease. We focus on molecular strategies for (a) disease classification, (b) disease outcome, and (c) disease mechanisms.

Immunotherapy of cancer by active vaccination: does allogeneic bone marrow transplantation after non-myeloablative conditioning provide a new option?

The critical role of antigen-specific T cells in cancer immunotherapy has been amply demonstrated in many model systems. Though success of clinical trials still remains far behind expectation, the continuous improvement in our understanding of the biology of the immune response will provide the basis of optimized cancer vaccines and allow for new modalities of cancer treatment. This review focuses on the current status of active therapeutic vaccination and future prospects. The latter will mainly be concerned with allogeneic bone marrow cell transplantation after non-myeloablative conditioning, because it is my belief that this approach could provide a major breakthrough in cancer immunotherapy. Concerning active vaccination protocols the following aspects will be addressed: i) the targets of immunotherapeutic approaches; ii) the response elements needed for raising a therapeutically successful immune reaction; iii) ways to achieve an optimal confrontation of the immune system with the tumor and iv) supportive regimen of immunomodulation. Hazards which one is most frequently confronted with in trials to attack tumors with the inherent weapon of immune defense will only be briefly mentioned. Many question remain to be answered in the field of allogeneic bone marrow transplantation after non-myeloablative conditioning to optimize the therapeutic setting for this likely very powerful tool of cancer therapy. Current considerations to improve engraftment and to reduce graft versus host disease while strengthening graft versus tumor reactivity will be briefly reviewed. Finally, I will discuss whether tumor-reactive T cells can be "naturally" maintained during the process of T cell maturation in the allogeneic host. Provided this hypothesis can be substantiated, a T cell vaccine will meet a pool of virgin T cells in the allogeneically reconstituted host, which are tolerant towards the host, but not anergised towards tumor antigens presented by MHC molecules of the host.