DNA vaccines against cancer: from genes to therapy

Analysis of physical and biological delivery systems for DNA cancer vaccines and their translation to clinical development

DNA cancer vaccines as an approach in tumor immunotherapy are still being investigated in preclinical and clinical settings. Nevertheless, only a small number of clinical studies have been published so far and are still active. The investigated vaccines show a relatively stable expression in in-vitro transfected cells and may be favorable for developing an immunologic memory in patients. Therefore, DNA vaccines could be suitable as a prophylactic or therapeutic approach against cancer. Due to the low efficiency of these vaccines, the administration technique plays an important role in the vaccine design and its efficacy. These DNA cancer vaccine delivery systems include physical, biological, and non-biological techniques. Although the pre-clinical studies show promising results in the application of the different delivery systems, further studies in clinical trials have not yet been successfully proven.

A Nanoplasmonic Assay of Oligonucleotide-Cargo Delivery from Cationic Lipoplexes

A powerful new biophysical model is reported to assay nanocarrier lipid membrane permeability. The approach employs a nanophotonic biophysical membrane model as an assay to study oligonucleotide escape from delivery vector following fusion with endosomal membrane that relies on plasmonic hotspots within the receptor well, below the membrane to follow cargo arrival. Through the combined use of surface enhanced Raman spectroscopy and fluorescence lifetime correlation spectroscopy (FLCS), the model enables identification of a lipoplex-mediated endosomal-escape mechanism facilitated by DOTAP-oligonucleotide interaction that dictates the rate of oligonucleotide release. This work reveals a hitherto unreported release mechanism as a complex multistep interplay between the oligonucleotide cargo and the target membrane, rather than a process based solely on lipid mixing at the fusing site as previously proposed. This substantiates the observations that lipid mixing is not necessarily followed by cargo release. The approach presents a new paradigm for assessment of vector delivery at model membranes that promises to have wide application within the drug delivery design application space. Overall, this plasmonic membrane model offers a potential solution to address persistent challenges in engineering the release mechanism of large therapeutic molecules from their nanocarrier, which is a major bottleneck in intracellular delivery.

Prophylactic DNA vaccine targeting Foxp3+ regulatory T cells depletes myeloid-derived suppressor cells and improves anti-melanoma immune responses in a murine model

Regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) are the two important and interactive immunosuppressive components of the tumor microenvironment that hamper anti-tumor immune responses. Therefore, targeting these two populations together might be beneficial for overcoming immune suppression in the tumor microenvironment. We have recently shown that prophylactic Foxp3 DNA/recombinant protein vaccine (Foxp3 vaccine) promotes immunity against Treg in tumor-free conditions. In the present study, we investigated the immune modulatory effects of a prophylactic regimen of the redesigned Foxp3 vaccine in the B16F10 melanoma model. Our results indicate that Foxp3 vaccination continuously reduces Treg population in both the tumor site and the spleen. Surprisingly, Treg reduction was associated with a significant decrease in the frequency of MDSC, both in the spleen and in the tumor environment. Furthermore, Foxp3 vaccination resulted in a significant reduction of arginase-1(Arg-1)-induced nitric oxide synthase (iNOS), reactive oxygen species (ROS) and suppressed MDSC activity. Moreover, this concurrent depletion restored production of inflammatory cytokine IFN-γ and enhanced tumor-specific CTL response, which subsequently resulted in the reduction of tumor growth and the improved survival rate of vaccinated mice. In conclusion, our results revealed that Foxp3 vaccine promotes an immune response against tumor by targeting both Treg and MDSC, which could be exploited as a potential immunotherapy approach.

Immunization by particle bombardment of antigen-loaded poly-(DL-lactide-co-glycolide) microspheres in mice

In the present study, we investigated whether poly-(DL-lactide-co-glycolide) (50:50) microspheres (PLG MS) containing a model antigen, ovalbumin (OVA), were delivered into mouse skin and the immune responses induced using a microparticulate bombardment system, Helios gene gun system, which can painlessly deliver the powdered drug through the stratum corneum to the epidermal-dermal interface using a high velocity supersonic flow of helium gas to accelerate the particles. The introduction of OVA-loaded PLG MS shows helium pressure-dependence, so that improved introduction can be achieved by a higher helium pressure used, thereby inducing sufficient anti-OVA IgG level. Moreover, in order to determine the type of immune system induced using particle bombardment, we investigated helper T-cell response characterized by the cytokine production in the isolated splenocytes 6 weeks after immunization and consequent production of the anti-OVA IgG subclasses in the serum in mice. As a result, IL-4 production in splenocytes and anti-OVA IgG1 level were preferentially elicited by particle bombardment with OVA-loaded PLG MS compared with IFN-gamma and anti-OVA IgG2a level. It seemed likely that particle bombardment using this system led to a Th-2 type immune response, i.e. a humoral immune response. In conclusion, this microparticulate bombardment system is a promising immunization method, expected to become an alternative to needle injection used to administer a broad range of vaccines for the treatment of various diseases.

Vaccine therapy in NHL: future promises and current limitations

Recent advances in genomics are revealing new molecular targets for vaccination strategies in cancer, and unraveling the immune pathways that must be activated. Initially, work focused on idiotypic antigen expressed by the clonal immunoglobulin (Ig) of B-cell tumors. This involved assembling the encoding V(H) and V(L) genes as single-chain Fv (scFv), which has been fused to Fragment C (FrC) of tetanus toxin to enhance recognition and response. The fusion gene induces strong anti-idiotypic protection against lymphoma in experimental models, and is now in clinical trials with encouraging results emerging. This principle of fusing a pathogen-derived sequence is widely applicable. A coat protein from a potato virus substituted for the FrC sequence has also been found to be capable of promoting anti-tumor immunity. The current design is effective in inducing anti-idiotypic (Id) antibody and CD4+ T-cell attack. For intracellular tumor antigens expressed as MHC Class I-associated peptides, a design consisting of a gene encoding a single domain of FrC linked to a candidate peptide sequence has been developed. This induces fast cytotoxic T-cell attack on peptide-expressing tumor cells. Injection of DNA appears safe and clinical trials will test the efficacy of this approach, and probably lead to improvements in these flexible vaccines.

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Vaccine therapy in melanoma today

Melanoma is the most significant malignant tumor of the melanocyte system. It is characterized by a high malignant potential and an outstanding possibility for giving metastasis. Despite all investigations and progress concerning molecular genetics and immunology melanoma is a therapeutic problem even today. Vaccines are being developed with an intention not only to prevent but also to cure the disease, and the most important aim of clinical trails is to develop corresponding antitumor immunotherapy based on vaccine.

Optimizing the efficacy of epitope-directed DNA vaccination

An increasing number of clinical trials has been initiated to test the potential of prophylactic or curative vaccination with tumor Ag-encoding DNA vaccines. However, in the past years it has become apparent that for many Ags and in particular for tumor Ags the intracellular processing and presentation are suboptimal. To improve epitope-directed DNA vaccines we have developed a murine model system in which epitope-specific, DNA vaccine-induced T cell immunity can be followed by MHC tetramer technology directly ex vivo. We have used this well-defined model to dissect the parameters that are crucial for the induction of strong cytotoxic T cell immunity using two independent model Ags. These experiments have led to a set of five guidelines for the design of epitope-directed DNA vaccines, indicating that carboxyl-terminal fusion of the epitope to a carrier protein of foreign origin is the most favorable strategy. DNA vaccines that are based on these guidelines induce high-magnitude CD8(+) T cell responses in >95% of vaccinated animals. Moreover, T cell immunity induced by this type of optimized DNA vaccine provides long-term protection against otherwise lethal tumor challenges.

Oral DNA vaccination: antigen uptake and presentation by dendritic cells elicits protective immunity

Melanoma differentiation antigens, such as glycoprotein 100 (gp100), have been shown to induce both cellular and humoral immune responses against melanoma in mouse and man. They are therefore considered as potential targets for melanoma immunotherapy. In this study, we have used the attenuated auxotrophic mutant strain SL7207 of Salmonella typhimurium as vehicle for a human gp100 (hgp100) DNA vaccine against melanoma. In vitro studies indicate that Salmonella/pCMV-hgp100 is efficiently scavenged by dendritic cells, resulting in the expression of the hgp100 transcription unit in the DC. In addition, oral administration of Salmonella/pCMV-hgp100 results in the expression of hgp100 RNA and protein by cells exhibiting DC-morphology in mesenteric lymph nodes as soon as 3 days after vaccination. Analysis of the efficacy of the Salmonella/pCMV-hgp100 vaccine in the B16/hgp100 model demonstrated the induction of strong anti-hgp100 CTL responses and protective immunity in 70% of the vaccinated mice, but not in control mice. Based on these data, we consider S. typhimurium as a useful vehicle for the design of recombinant DNA based anti-cancer vaccines.

Update on epidemiology and therapeutics for non-Hodgkin's lymphoma

This chapter presents updated information on the trends and patterns of non-Hodgkin's lymphoma (NHL) diagnoses as well as new information on chemotherapeutic and immunotherapeutic options for NHL treatment. In Section I, Dr. Brian Chiu summarizes the current knowledge regarding the etiologic factors and patterns of NHL as well as suggests future epidemiologic studies based on these preliminary results. In Section II, Dr. Bruce Cheson and colleagues outline new chemotherapeutic and small molecule antineoplastic agents with unique mechanisms of action such as protease inhibitors, farnesyl transferase or histone deacetylase inhibitors, and antisense oligonucleotides. In Section III, Dr. Julie Vose reviews the anti-lymphoma effects of monoclonal antibodies, radioimmunoconjugates, idiotype vaccines, and immunologic enhancing adjuvants with respect to mechanisms of action, clinical trials, and their potential for patient therapy.

Concurrent administration of high-dose chemotherapy and rituximab is a feasible and effective chemo/immunotherapy for patients with high-risk non-Hodgkin's lymphoma

The aim of this study was to investigate feasibility, tolerability and efficacy of rituximab-supplemented high-dose sequential chemotherapy (R-HDS) with peripheral blood progenitor cell autografting as frontline or salvage treatment in patients with advanced non-Hodgkin's lymphoma (NHL). Thirty-two patients have been treated: 14 at disease onset and 18 with relapsed or progressive disease. R-HDS regimens included six courses of rituximab. Rituximab was delivered either concurrently with high-dose chemotherapy to exploit the in vivo purging properties of the drug as well as at the end of the treatment plan to target minimal residual disease. All patients treated at disease onset completed their treatment with no life-threatening toxicity, while two toxic deaths due to severe bilateral pneumonia were observed among patients treated due to relapsed or refractory disease. Thirteen of 14 patients treated up-front achieved CR. Among pre-treated patients 10 of 18 achieved CR with better results in patients with relapsed (seven of eight) compared to progressive disease (three of 10). PCR analysis was carried out in indolent lymphoma patients: nine of nine follicular lymphomas and three of six CD5-positive NHL collected PCR-negative peripheral blood progenitor cell harvests. The results of this pilot study show that R-HDS is feasible and effective with acceptable toxicity when used at disease onset. In pre-treated patients this treatment also showed promising results, although the risk of severe infections needs to be considered.

Immunotherapy of multiple myeloma

The failure of chemotherapy to cure a significant proportion of multiple myeloma (MM) patients and increasing knowledge of tumor immunology and MM biology have generated considerable interest in immunotherapy for this lethal disease. Immunotherapy for MM can be divided into three broad categories: passive antibody-mediated immunotherapy, active specific immunization (vaccination), and adoptive T-cell immunotherapy. Early clinical trials using anti-CD20 monoclonal antibodies (mAbs) have met with limited success so far but have also suggested that selected patient subgroups may benefit from this treatment. The availability of a truly tumor-specific antigen such as immunoglobulin idiotype, the recent demonstration that MM cells process and present idiotype to T lymphocytes, and formal evidence of an antitumor effect of idiotypic vaccination in follicular lymphoma provide the framework for applying idiotypic vaccination in MM. The ability to generate ex vivo functional dendritic cells has made it possible to fuse them with patients' MM cells, thus producing a different type of customized vaccine. Dendritic cells are also a pivotal reagent to generate ex vivo MM-specific cytotoxic T lymphocytes (CTLs) to be reinfused into the patient for adoptive immunotherapy. This review summarizes achievements in MM immunotherapy based on data reported since 1998.

Developing non-viral DNA delivery systems for cancer and infectious disease

Efforts to deliver therapeutic genes are frequently rebuffed by the body's adaptive immune response against viral delivery vectors. Attempts to circumvent this problem using non-viral delivery systems have encountered problems with transient expression and inflammatory responses induced by reaction of the innate immune system reacting against bacterial DNA. However, within the past decade, these barriers to non-viral DNA delivery have been recognized as potential allies in the development of novel vaccines for cancer and infectious disease. This review summarizes preclinical and current clinical studies testing the formulation, delivery route and adjuvant options in the development of novel DNA-based vaccines.

Immunotherapy: on the edge between experimental and clinical oncology

Cancer immunotherapy is still largely confined to the laboratory bench and experimental animal models. Yet the field is rapidly moving forward and some immunological tools are now entering into clinical use. The first and perhaps best example of such progress is given by bioengineered humanized monoclonal antibodies of which some have been already approved for therapy in B-cell lymphoma and breast cancer. Unexpectedly, another remarkable form of immunotherapy has turned out to derive from T-cell adoptive therapy associated with allogeneic bone marrow transplantation. Its benefits render such an approach the first choice therapy for a large number of hematological malignancies and it is now being adapted also for treatment of advanced solid tumors. Finally, harnessing the immune system against the autologous tumor remains the most ambitious but still distant design for immunotherapy. Recent technical advances and a better understanding of the immune system in cancer patients should concur in defining the best strategy for active immunotherapy in clinical oncology.

Identification of a ras oncogene peptide that contains both CD4(+) and CD8(+) T cell epitopes in a nested configuration and elicits both T cell subset responses by peptide or DNA immunization

Mutations in ras proto-oncogenes are commonly found in a diversity of malignancies and may encode unique, non-self epitopes for T cell-mediated antitumor activity. In a BALB/c (H-2(d)) murine model, we have identified a single peptide sequence derived from the ras oncogenes that contained both CD8(+) and CD4(+) T cell epitopes in a nested configuration. This peptide reflected ras sequence 4-16, and contained the substitution of Gly to Val at position 12 ¿i.e., 4-16(Val12)¿. Mice immunized with this 13-mer peptide induced a strong antigen (Ag)-specific CD4(+) proliferative response in vitro. In contrast, mice inoculated with the wild-type ras sequence failed to generate a peptide-specific T cell response. Additionally, mice immunized with the ras 4-16(Val12) peptide concomitantly displayed an Ag-specific CD8(+) cytotoxic T lymphocyte (CTL) response, as determined by lysis of syngeneic tumor target cells incubated with the nominal 9-mer nested epitope peptide ¿i.e., 4-12(Val12)¿, as well as lysis of tumor target cells expressing the corresponding ras codon 12 mutation. Analysis of the Valpha- and Vbeta-chains of the T cell receptor (TCR) expressed by these CTL revealed usage of the Valpha1 and Vbeta9 subunits, consistent with the TCR phenotype of anti-ras Val12 CTL lines produced by in vivo immunization with the nominal peptide epitope alone. Moreover, immunization with the nested epitope peptide, as compared to immunization with either the 9-mer CTL peptide alone or an admixture of the 9-mer CTL peptide with an overlapping 13-mer CD4(+) T cell helper peptide ¿i.e., 5-17(Val12)¿ lacking the class I N-terminus anchor site, enhanced the production of the CD8(+) T cell response. Finally, immunization with plasmid DNA encoding the ras 4-16(Val12) sequence led to the induction of both Ag-specific proliferative and cytotoxic responses. Overall, these results suggested that a single peptide immunogen containing nested mutant ras-specific CD4(+) and CD8(+) T cell epitopes: (1) can be processed in vivo to induce both subset-specific T lymphocyte responses; and (2) leads to the generation of a quantitatively enhanced CD8(+) CTL response, likely due to the intimate coexistence of CD4(+) help, which may have implications in peptide- or DNA-based immunotherapies.

Strategies to reduce the risk of virus-related cancers

BACKGROUND

Experimental and epidemiological evidence has established an association between at least eight viruses and various cancer sites. Recent estimates (at least 10% of cancer worldwide) have revealed that viruses, together with tobacco and diet, account for the largest proportion of cancer in the world.

RESULTS

Improvements in the detection of viruses and biomarkers of chronic infection have led to the identification of strong associations with cancer, particularly for human papillomavirus (HPV), hepatitis B virus (HBV), and human immunodeficiency virus (HIV). For some cancer viruses (e.g., HIV and hepatitis C virus, HCV), the spectrum of malignancies involved has still to be well defined. For HBV and HPV, vaccination aimed at cancer prevention is already a reality or a possibility. Whereas HBV vaccination already emerged as one of the most cost-effective ways to reduce adult cancer mortality, for HPV vaccination some technical problems still await a solution. For other infectious agents (e.g., HCV, HIV) prospects for a vaccine are not immediate.

CONCLUSIONS

In order to apply new knowledge on viruses to cancer prevention, large vaccination trials are warranted. These will have to be large (many thousands of people), prolonged (5-10 years), and match scientific excellence with a feasible design. Mistrust between scientists and the public will have to be prevented by means of absolute openness in scientific information and economical interests involved.