Somatic gene therapy for cancer: the utility of transferrinfection in generating 'tumor vaccines'

Targeting nucleic acid-based therapeutics to tumors: Challenges and strategies for polyplexes

The current medical reality of cancer gene therapy is reflected by more than ten approved products on the global market, including oncolytic and other viral vectors and CAR T-cells as ex vivo gene-modified cell therapeutics. The development of synthetic antitumoral nucleic acid therapeutics has been proceeding at a lower but steady pace, fueled by a plethora of alternative nucleic acid platforms (from various antisense oligonucleotides, siRNA, microRNA, lncRNA, sgRNA, to larger mRNA and DNA) and several classes of physical and chemical delivery technologies. This review summarizes the challenges and strategies for tumor-targeted nucleic acid delivery. Focusing primarily on polyplexes (polycation complexes) as nanocarriers, delivery options across multiple barriers into tumor cells are illustrated.

Drug targeting systems for cancer chemotherapy

Tumour specific drug targeting has been a very actively investigated area for over 2 decades. Various approaches have involved the use of drug delivery systems that can localise the anticancer agent at the tumour site without damaging the normal cells. For this purpose, various delivery systems that have been utilised are liposomes, microspheres and recently, nanoparticles. Two liposome formulations containing anticancer drugs for example, adriamycin and daunomycin are already on the market in the USA and Europe. Microspheres are also being investigated for delivering various anticancer drugs and protein/peptides for anticancer treatment, and several formulations are in Phase I/II clinical trials. Antitumour drugs have also been linked to tumour specific monoclonal antibodies via various chemical linkages. Doxorubicin was linked to a chimeric monoclonal antibody that was targeted to the Lewis Y antigen. Though this conjugate initially showed potential, it was recently dropped from Phase II clinical trials. Another approach with monoclonal antibodies has been the use of immunotoxins. Immunotoxins initially showed promise as potential anticancer agents at picomolar concentrations but several clinical and preclinical studies have not shown much promise in this regard. Drug containing liposomes and microspheres have been further linked to tumour specific monoclonal antibodies to enhance their tumour specificity. Most of the studies with immunoliposomes or targeted microspheres have not gone beyond the preclinical studies. New therapeutic approaches are presently emerging based on natural products like cytokines, peptide growth factor antagonists, antisense oligonucleotides and specific genes. These approaches need the help of delivery systems to deliver these complex molecules to tumour cells. One of the current pursued approaches is the use of cationic liposomes. Several clinical studies are undergoing with various cationic liposomes and the next few years will demonstrate the usefulness of this approach. In recent years, the problems in cancer treatment have been complicated with the emergence of resistance strains leading to resistant and cross-resistant tumour cells. Several agents have been used to overcome or reverse drug-resistance in solid tumours and it remains a highly pursued area in cancer treatment.

Gene therapy and reproductive medicine

OBJECTIVE

To review the literature on the principles of gene therapy and its potential application in reproductive medicine.

DESIGN

Literature review.

SETTING

Gene therapy involves transfer of genetic material to target cells using a delivery system, or vector. Attention has primarily focused on viral vectors. Significant problems remain to be overcome including low efficacy of gene transfer, the transient expression of some vectors, safety issues with modified adenoviruses and retroviruses, and ethical concerns. If these issues can be resolved, gene therapy will be applicable to an increasing spectrum of single and multiple gene disorders, as the Human Genome Project data are analyzed, and the genetic component of human disease becomes better understood. Gynecologic gene therapy has advanced to human clinical trials for ovarian carcinoma, and shows potential for the treatment of uterine leiomyomata. Obstetric applications of gene therapy, including fetal gene therapy, remain more distant goals.

CONCLUSION(S)

Concerns about the safety of human gene therapy research are being actively addressed, and remarkable progress in improving DNA transfer has been made. The first treatment success for a genetic disease (severe combined immunodeficiency disease) has been achieved, and ongoing research efforts will eventually yield clinical applications in many spheres of reproductive medicine.

Management of malignant melanoma: new developments in immune and gene therapy

Thus far, the use of classical anti-cancer treatment modalities had only rarely a beneficial impact on the prognosis of patients with metastatic melanoma. We as physicians have therefore the obligation as well as the chance to develop and test new therapeutic strategies. Our growing knowledge about the genetic basis of melanoma provides one platform to fulfil this task. Another one comes from our increasing understanding of the molecular and cellular mechanisms involved in the induction/modulation of immune responses, as well as the progress made in the field of identification of melanoma antigens, and allows for the development of a new generation of vaccines. The aim of this article is to discuss several of these new concepts towards the use of immune and gene therapy of melanoma.

Liposomes containing interferon-gamma as adjuvant in tumor cell vaccines

PURPOSE

Liposomal systems may be useful as a cytokine supplement in tumor cell vaccines by providing a cytokine reservoir at the antigen presentation site. Here, we examined the effect of liposome incorporation of mIFNgamma on its potency as adjuvant in an established tumor cell vaccination protocol in the murine B16 melanoma model. Adjuvanticity of the mIFNgamma-liposomes was compared to that achieved by mIFNgamma-gene transfection of the B16 tumor cells. Furthermore, we studied whether liposomal incorporation of mIFNgamma indeed increases the residence time of the cytokine at the vaccination site.

METHODS

C57B1/6 mice were immunized with i) irradiated IFNgamma-gene transfected B16 melanoma cells or ii) irradiated wild type B16 cells supplemented with (liposomal) mIFNgamma, followed by a challenge with viable B16 cells. The residence time of the (liposomal) cytokine at the subcutaneous (s.c.) vaccination site was monitored using radiolabeled mIFNgamma and liposomes.

RESULTS

Immunization with irradiated tumor cells admixed with liposomal mIFNgamma generated comparable protection against B16 challenge as immunization with mIFNgamma-gene modified tumor cells. Irradiated tumor cells admixed with soluble mIFNgamma did not generate any protective responses. Radiolabeling studies indicated that free mIFNgamma rapidly cleared from the s.c. injection site. Association of [125I]-mIFNgamma with liposomes increased the local residence time substantially: liposomal association of mIFNgamma resulted in a prolonged local residence time of the cytokine as reflected by a 4-fold increase of the area under the curve. The amount of released cytokine in the optimal dose range corresponds to the amount released by the gene-transfected cells. Moderate but significant CTL-activity against B16 cells was found for mice immunized with irradiated cells supplemented with mIFNgamma-liposomes compared to untreated control animals.

CONCLUSIONS

Prolonged presence of mIFNgamma at the site of antigen presentation is crucial for the generation of systemic immune responses in the B16 melanoma model. These studies show that liposomal encapsulation of cytokines is an attractive strategy for paracrine cytokine delivery in tumor vaccine development.

Liposomes as cytokine-supplement in tumor cell-based vaccines

Subcutaneous vaccination of C57bl/6 mice with irradiated B16 melanoma cells supplemented with liposomal interleukin-2 (IL2) or murine interferon-gamma (mIFNgamma), resulted in systemic protection in 50% of the animals, against a subsequent tumor cell challenge in a dose dependent manner. The protective efficacy was comparable to the efficacy of cytokine gene-modified cells as tumor vaccine, whereas irradiated B16 cells supplemented with soluble cytokine did not result in protective responses. In vivo evidence was obtained that the beneficial effects mediated by liposome incorporation of the cytokine are the result of a depot function of the liposomal cytokine supplement at the vaccination site. In can be concluded that liposomal delivery of cytokines offers an attractive alternative to cytokine-gene transfection of tumor cells for therapeutic vaccination protocols.

The Tumorigenicity of IL-2 Gene-Transfected Murine M-3D Melanoma Cells Is Determined by the Magnitude and Quality of the Host Defense Reaction: NK Cells Play a Major Role

Transfection of a variety of tumor lines with the IL-2 gene strongly reduces their tumorigenic potential when applied to either euthymic or athymic animals. To elucidate the mechanisms underlying this phenomenon, we inoculated IL-2-transfected M-3D melanoma (M-3D-IL-2) cells into DBA/2 mice immunosuppressed by γ-irradiation. Animals thus treated developed pigmented tumors, suggesting that IL-2 transfection of melanoma cells, instead of altering their neoplastic growth properties, renders them capable of evoking a tumoricidal host response. To define the critical effector cell, we injected M-3D-IL-2 and, for control purposes, nontransfected M-3D cells into DBA/2 recipients and analyzed the injection site. We found that 1) IL-2-expressing M-3D cells induce a much stronger inflammatory reaction than wild-type cells, 2) in both instances the infiltrate consists mainly of macrophages (40–60%) and granulocytes (30–40%), and 3) only the infiltrate of M-3D-IL-2 cell deposits contains a minor fraction of NK cells (∼1–2%). When we reconstituted sublethally irradiated animals with various leukocyte subsets, we found that unfractionated as well as macrophage-depleted peritoneal lavage cells but not NK cell-depleted peritoneal lavage cells were able to suppress the growth of IL-2-expressing M-3D cells. In vivo leukocyte depletion experiments showed that the NK cell-depleting asialo-GM1 antiserum, but not anti-macrophage and/or anti-granulocyte reagents, restored the tumorigenicity of M-3D-IL-2 cells. Our results indicate that the inflammatory tissue response evoked by IL-2-transfected cancer cells includes the attraction and/or activation of NK cells and that, in the experimental system used, these cells are critically needed for successfully controlling cancer growth in vivo.

Redox-mediated gene therapies for environmental injury: approaches and concepts

Cellular redox state has been increasingly recognized as a critical component of stress-induced cellular responses and disease. Inherent in these responses are reactive oxygen species (ROS), which inflict direct cellular damage in addition to acting as intracellular second messengers modulating signal transduction pathways. These intracellular highways of communication are critical in determining cell fates and whole-organ responses following environmental injury. Although gene therapy for inherited and acquired disorders has exploded in the last decade, the application of gene therapeutic approaches for transient pathologic conditions resulting from environmental stress is just beginning to be recognized. This review will summarize the theoretical and practical applications of gene therapy for the treatment of environmental injury by modulating redox-activated cellular responses. Several approaches can be utilized to achieve this goal. These include the application of gene targeting to modulate the cellular redox state directly by expressing recombinant genes capable of degrading ROS at pathophysiologic important subcellular sites. The use of mitochondrial superoxide dismutase (MnSOD), which degrades superoxides arising from ischemia/reperfusion injury, is one example of this approach. MnSOD serves as a "garbage disposal" for potentially toxic ROS prior to cellular injury and the activation of signal transduction cascades important in whole-organ pathology and inflammation. In contrast, some ROS have been suggested to have beneficial effects on cellular responses following environmental injury. Hence, expressing the nitrogen oxygen synthetase gene (NOS) to enhance the levels of nitric oxide (NO.) and augment the beneficial effects of this compound has also been suggested as a useful redox-modulating gene therapy approach. Lastly, indirect intervention in signal transduction pathways following environmental stress by expressing dominant inhibitory proteins of redox-activated signal transduction cascades has also been useful in modulating cellular responses to redox stress. Two such examples have utilized dominant inhibitory forms of the retinoblastoma gene product (Rb) and IkappaBalpha which prevent activation of cyclin-dependent protein kinases and NF-kappaB, respectively. Ultimately, the most efficacious therapeutic approach or combination of approaches that alter the redox responsiveness of cells and organs to environmental injury will be determined through a comprehensive understanding of the relevant pathophysiologic processes.

DNA-antiviral vaccines: new developments and approaches--a review

Current vaccines can be divided into "live," "recombinant" and "killed" vaccines. Live vaccines are traditionally composed of attenuated viruses or bacteria, selected for their reduced pathogenicity. Recombinant vaccines, driven by a viral or bacterial vector express foreign antigens, or only recombinant proteins injected as antigen. Killed vaccines consist of inactivated whole pathogens. But all these traditional vaccines have some disadvantages: Attenuated live vaccine are able to undergo mutation and as mutated viruses or bacteria can now provoke the diseases against which the vaccine should protect the organism. A further disadvantage of live vaccines is the possibility of shedding which is a real problem especially in veterinary medicine. Clearly, there is a need for better vaccines to protect against diseases without the disadvantages associated with vaccines presently in use. Modern vaccines might be characterized as safe, no risk of reversion to pathogenicity, and they should be stable without the necessity of a "cold chain." Production should be simple, standardized and inexpensive. Vaccine development has now been improved by the ability to use direct inoculations of plasmid DNA encoding viral or bacterial proteins. One of the major benefits of DNA-vaccines, variously termed "DNA-, genetic- or nucleic acid-immunization," is the endogenous synthesis of the encoded protein. Therefore DNA vaccines mimic natural infection and provoke both strong humoral and cellular immune response. This review summarizes new developments and approaches of DNA vaccination and explains the construction of expression plasmids as well as possible mechanisms of immune responses.

Receptor-targeted recombinant adenovirus conglomerates: a novel molecular conjugate vector with improved expression characteristics

To develop improved strategies for gene transfer to hematopoietic cells, we have explored targeted gene transfer using molecular conjugate vectors (MCVs). MCVs are constructed by condensing plasmid DNA containing the gene of interest with polylysine (PL), PL linked to a replication-incompetent adenovirus (endosomolytic agent), and PL linked to streptavidin for targeting with biotinylated ligands. In this report, we compare gene transfer to K562 cells by using the previously described transferrin-targeted MCV (Trans-MCV) to a novel transferrin-targeted MCV. In the novel MCV, the transferred gene (luciferase) is in the genome of recombinant replication-incompetent adenovirus (recMCV), which also acts as the endosomolytic agent. The level of luciferase gene expression was fivefold higher in K562 cells transfected with Trans-recMCV than in cells transfected with Trans-MCV. Furthermore, targeted transfection with recMCV resulted in prolonged luciferase expression that declined 14 to 20 days after transfection, in comparison with Trans-MCV, where luciferase expression declined by 4 to 8 days. Moreover, targeted transfection of K562 cells with the Trans-recMCV resulted in persistent luciferase gene expression for 6 months. Analysis of luciferase gene expression in K562 single-cell clones that were subcloned 5 weeks after transfection with Trans-recMCV showed that 35 to 50% of the single-cell clones had intermediate to high levels of luciferase gene expression that was stable for 6 months, with the remaining clones showing low or no luciferase gene expression. Stable gene expression was associated with integration of adenovirus sequences into genomic DNA.

Cell-free tumor antigen peptide-based cancer vaccines

The central role that tumor antigen-derived peptides play in induction of antitumor immunity makes them ideal candidates for peptide-based cancer vaccines. We have demonstrated that "transloading" is an efficient strategy for importing short peptide ligands into antigen-presenting cells in vitro. Postulating that the transloading procedure might effect peptide uptake by antigen-presenting cells in vivo as well, we tested this approach for the generation of peptide-based cancer vaccines. In the P815 mastocytoma system, we vaccinated mice by s.c. injection of a single, known natural peptide derived from JAK-1 kinase. Whereas vaccination with peptide alone or mixed with incomplete Freund's adjuvant was ineffective, application of the peptide in conjunction with the polycation poly-L-lysine protected a significant number of animals against tumor challenge. Dependent upon the type of poly-L-lysine applied, protection against tumor take was comparable to that achieved with irradiated whole-cell vaccines, genetically modified to secrete granulocyte-macrophage colony-stimulating factor. In the murine melanoma M-3, a combination of four putative tumor antigen-derived peptides was tested as a cancer vaccine. Administered in combination with polycations, these peptides evoked potent antitumor immunity that could not be obtained with the peptides alone or peptides emulsified in incomplete Freund's adjuvant. However, peptide-polycation vaccines applied to the M-3 model were not as efficient as cellular control vaccines, consisting of irradiated interleukin 2 or granulocyte-macrophage colony-stimulating factor-secreting tumor cells.

Tumor cells expressing a recall antigen are powerful cancer vaccines

Tumor cells were engineered to express a specific recall antigen molecule to serve as a target for the host's existing memory response, and then used as immunogens as a novel form of cancer vaccine. As recall antigen, the efficiently expressible hybrid protein Heat1 was employed, that contains an antigenic fragment of the Mycobacterium bovis 65-kDa heat shock protein (hsp65), and thus can be recognized in mice immunized with live Bacillus Calmette-Guérin (BCG) or its derivatives. Mouse M-3 melanoma cells were transfected to express Heat1, irradiated, and used as anti-melanoma vaccines. Vaccination elicited anti-tumor immunity in mice, i.e. a subsequent challenge with the parental wild-type M-3 melanoma cells was rejected. Successful vaccination was dependent on the correct recognition of the recall antigen, since vaccination failed to prevent outgrowth of the challenge in mice possessing no memory response against the recall antigen. The results indicate that expression of a recall antigen can turn tumor cells into powerful vaccines. By using the Heat1 protein or other appropriate antigens, this general concept may be applied for human therapy.

Priming of tumor-specific T cells in the draining lymph nodes after immunization with interleukin 2-secreting tumor cells: three consecutive stages may be required for successful tumor vaccination

Although both CD4+ and CD8+ T cells are clearly required to generate long-lasting anti-tumor immunity induced by s.c. vaccination with interleukin 2 (IL-2)-transfected, irradiated M-3 clone murine melanoma cells, some controversy continues about the site and mode of T-cell activation in this system. Macrophages, granulocytes, and natural killer cells infiltrate the vaccination site early after injection into either syngeneic euthymic DBA/2 mice or athymic nude mice and eliminate the inoculum within 48 hr. We could not find T cells at the vaccination site, which argues against the concept that T-cell priming by the IL-2-secreting cancer cells occurs directly at that location. However, reverse transcription-PCR revealed transcripts indicative of T-cell activation and expansion in the draining lymph nodes of mice immunized with the IL-2-secreting vaccine but not in mice vaccinated with untransfected, irradiated M-3 cells. We therefore propose that the antigen-presenting cells, which invade the vaccination site, process tumor-derived antigens and, subsequently, initiate priming of tumor-specific T lymphocytes in lymphoid organs. These findings suggest a three-stage process for the generation of effector T cells after vaccination with IL-2-secreting tumor cells: (i) tumor-antigen uptake and processing at the site of injection by antigen-presenting cells, (ii) migration of antigen-presenting cells into the regional draining lymph nodes, where T-cell priming occurs, and (iii) circulation of activated T cells that either perform or initiate effector mechanisms leading to tumor cell destruction.

Cancer vaccines: the interleukin 2 dosage effect

Cancer vaccines genetically engineered to produce interleukin 2 have been investigated intensively in a series of animal models and are at the point of entering into clinical trials. In this study we demonstrate a strong correlation between the rate of interleukin 2 production and the protection efficiency of murine S91 melanoma cell (clone M-3) vaccines. Best immunization is achieved with vaccines producing medium interleukin 2 levels of 1000-3000 units per 10(5) cells per day. Reduced interleukin 2 production evokes a corresponding decline in the number of successfully treated animals. Unexpectedly, when interleukin 2 expression is raised to high levels of 5000-7500 units per 10(5) cells per day, protection is completely absent because of impaired generation of tumor-specific cytotoxic T lymphocytes. In comparison, granulocyte-macrophage colony-stimulating factor as immunomodulator induces substantial immunization even at a moderate level of secretion and protects all animals at the maximal obtainable level of secretion. Our findings demonstrate the importance of the interleukin 2 level produced by genetically modified tumor cells and may have substantial impact for the clinical application of cancer vaccines.

Tumor vaccines: effects and fate of IL-2 transfected murine melanoma cells in vivo

We have previously demonstrated the general usefulness of the adenovirus-enhanced transferrinfection (AVET) in the generation of IL-2 producing tumor vaccines. By optimizing different parameters of the transfection protocol we were able to transform the poorly immunogenic M-3 mouse melanoma cell line into a potent immunogen. A long-lasting immunity was demonstrated after administration of the IL-2 releasing vaccine, since immunized animals successfully rejected native M-3 melanoma cells even after a period of more than 6 months. We also demonstrated that in vivo administration of such a vaccine is safe since transmission of the transfected IL-2 gene in host organs was not detected. IL-2 production ceased 2 days after injection because the engineered cells were destroyed. However, RT-PCR analysis of the site of vaccine injection suggests that IL-2 exerts its effects not only directly but also by inducing a set of other immunomodulator cytokines in situ that are probably indispensable in inducing a host response. We conclude that AVET of IL-2 into tumor cells is a safe and efficient method for the generation of tumor vaccines.