Noncarrier naked antigen-specific DNA vaccine generates potent antigen-specific immunologic responses and antitumor effects

Plasmid DNA for Therapeutic Applications in Cancer

Recently, the interest in using nucleic acids for therapeutic applications has been increasing. DNA molecules can be manipulated to express a gene of interest for gene therapy applications or vaccine development. Plasmid DNA can be developed to treat different diseases, such as infections and cancer. In most cancers, the immune system is limited or suppressed, allowing cancer cells to grow. DNA vaccination has demonstrated its capacity to stimulate the immune system to fight against cancer cells. Furthermore, plasmids for cancer gene therapy can direct the expression of proteins with different functions, such as enzymes, toxins, and cytotoxic or proapoptotic proteins, to directly kill cancer cells. The progress and promising results reported in animal models in recent years have led to interesting clinical results. These DNA strategies are expected to be approved for cancer treatment in the near future. This review discusses the main strategies, challenges, and future perspectives of using plasmid DNA for cancer treatment.

Fusion protein vaccines targeting two tumor antigens generate synergistic anti-tumor effects

Introduction

Human papillomavirus (HPV) has been consistently implicated in causing several kinds of malignancies, and two HPV oncogenes, E6 and E7, represent two potential target antigens for cancer vaccines. We developed two fusion protein vaccines, PE(ΔIII)/E6 and PE(ΔIII)/E7 by targeting these two tumor antigens to test whether a combination of two fusion proteins can generate more potent anti-tumor effects than a single fusion protein.

Materials and Methods

Invivo antitumor effects including preventive, therapeutic, and antibody depletion experiments were performed. Invitro assays including intracellular cytokine staining and ELISA for Ab responses were also performed.

Results

PE(ΔIII)/E6+PE(ΔIII)/E7 generated both stronger E6 and E7-specific immunity. Only 60% of the tumor protective effect was observed in the PE(ΔIII)/E6 group compared to 100% in the PE(ΔIII)/E7 and PE(ΔIII)/E6+PE(ΔIII)/E7 groups. Mice vaccinated with the PE(ΔIII)/E6+PE(ΔIII)/E7 fusion proteins had a smaller subcutaneous tumor size than those vaccinated with PE(ΔIII)/E6 or PE(ΔIII)/E7 fusion proteins alone.

Conclusion

Fusion protein vaccines targeting both E6 and E7 tumor antigens generated more potent immunotherapeutic effects than E6 or E7 tumor antigens alone. This novel strategy of targeting two tumor antigens together can promote the development of cancer vaccines and immunotherapy in HPV-related malignancies.

A pestivirus DNA vaccine based on a non-antibiotic resistance Escherichia coli essential gene marker

Antibiotic resistance genes are widely used to produce plasmid DNA vaccines, but risk unwanted exposure to antibiotic residues and the spread of resistance genes. To overcome the limitations of existing selection technologies, we developed an alternative system applying the widely used household biocide triclosan as the selective agent and an endogenous growth essential target gene, fabI, as the plasmid-borne marker in Escherichia coli. The fabI/triclosan system enables efficient, non-antibiotic selection of transformed bacteria, with improved safety and plasmid production features. Here we aimed to evaluate the performance of this non-antibiotic selection system using a plasmid DNA vaccine against bovine viral diarrhoea virus as an example. The new system displayed high-yield plasmid DNA production in a standard E. coli host strain and growth media. Notably, the purified pDNA provided efficient in vitro protein expression and a strong in vivo neutralising antibody response in a mouse model, with measures comparable to that of the parental plasmid DNA based on ampicillin resistance. The fabI/triclosan system requires only low levels of triclosan for selection (1 μM) and residual triclosan in isolated DNA was below the limit of detection (< 20 parts per trillion). The fabI/triclosan selection system provides a simple, non-antibiotic resistance marker for plasmid selection, applicable to DNA vaccines and possibly other recombinant vaccine applications.

New Approaches to Immunotherapy for HPV Associated Cancers

Cervical cancer is the second most common cancer of women worldwide and is the first cancer shown to be entirely induced by a virus, the human papillomavirus (HPV, major oncogenic genotypes HPV-16 and -18). Two recently developed prophylactic cervical cancer vaccines, using virus-like particles (VLP) technology, have the potential to prevent a large proportion of cervical cancer associated with HPV infection and to ensure long-term protection. However, prophylactic HPV vaccines do not have therapeutic effects against pre-existing HPV infections and do not prevent their progression to HPV-associated malignancy. In animal models, therapeutic vaccines for persisting HPV infection can eliminate transplantable tumors expressing HPV antigens, but are of limited efficacy in inducing rejection of skin grafts expressing the same antigens. In humans, clinical trials have reported successful immunotherapy of HPV lesions, providing hope and further interest. This review discusses possible new approaches to immunotherapy for HPV associated cancer, based on recent advances in our knowledge of the immunobiology of HPV infection, of epithelial immunology and of immunoregulation, with a brief overview on previous and current HPV vaccine clinical trials.

Therapeutic HPV DNA vaccines

It is now well established that most cervical cancers are causally associated with HPV infection. This realization has led to efforts to control HPV-associated malignancy through prevention or treatment of HPV infection. Currently, commercially available HPV vaccines are not designed to control established HPV infection and associated premalignant and malignant lesions. To treat and eradicate pre-existing HPV infections and associated lesions which remain prevalent in the U.S. and worldwide, effective therapeutic HPV vaccines are needed. DNA vaccination has emerged as a particularly promising form of therapeutic HPV vaccines due to its safety, stability and ability to induce antigen-specific immunity. This review focuses on improving the potency of therapeutic HPV vaccines through modification of dendritic cells (DCs) by [1] increasing the number of antigen-expressing/antigen-loaded DCs, [2] improving HPV antigen expression, processing and presentation in DCs, and [3] enhancing DC and T cell interaction. Continued improvement in therapeutic HPV DNA vaccines may ultimately lead to an effective DNA vaccine for the treatment of HPV-associated malignancies.

Immunotherapy for cervical cancer: Research status and clinical potential

The high-risk types of human papillomavirus (HPV) have been found to be associated with most cervical cancers and play an essential role in the pathogenesis of the disease. Despite recent advances in preventive HPV vaccine development, such preventive vaccines are unlikely to reduce the prevalence of HPV infections within the next few years, due to their cost and limited availability in developing countries. Furthermore, preventive HPV vaccines may not be capable of treating established HPV infections and HPV-associated lesions, which account for high morbidity and mortality worldwide. Thus, it is important to develop therapeutic HPV vaccines for the control of existing HPV infection and associated malignancies. Therapeutic vaccines are quite different from preventive vaccines in that they require the generation of cell-mediated immunity, particularly T cell-mediated immunity, instead of the generation of neutralizing antibodies. The HPV-encoded early proteins, the E6 and E7 oncoproteins, form ideal targets for therapeutic HPV vaccines, since they are consistently expressed in HPV-associated cervical cancer and its precursor lesions and thus play crucial roles in the generation and maintenance of HPV-associated disease. Our review covers the various therapeutic HPV vaccines for cervical cancer, including live vector-based, peptide or protein-based, nucleic acid-based, and cell-based vaccines targeting the HPV E6 and/or E7 antigens. Furthermore, we review the studies using therapeutic HPV vaccines in combination with other therapeutic modalities and review the latest clinical trials on therapeutic HPV vaccines.

Metronomic chemotherapy enhances antitumor effects of cancer vaccine by depleting regulatory T lymphocytes and inhibiting tumor angiogenesis

Although cancer vaccines are emerging as innovative methods for cancer treatment, these alone have limited potential for treating measurable tumor burden. Thus, the importance of identifying anticancer strategies with greater potency is necessary. The chimeric DNA vaccine CTGF/E7 (connective tissue growth factor linked to the tumor antigen human papillomavirus 16 E7) generates potent E7-specific immunity and antitumor effects. We tested immune-modulating doses of chemotherapy in combination with the CTGF/E7 DNA vaccine to treat existing tumors in mice. Metronomic low doses of paclitaxel, not the maximal tolerable dose, are synergistic with the antigen-specific DNA vaccine. Paclitaxel, given in metronomic sequence with the CTGF/E7 DNA vaccine enhanced the vaccine's potential to delay tumor growth and decreased metastatic tumors in vivo better than the CTGF/E7 DNA vaccine alone. The two possible mechanisms of metronomic paclitaxel chemotherapy are the depletion of regulatory T cells and the inhibition of tumor angiogenesis rather than direct cancer cell cytolytic effects. Results indicate that combination treatment of metronomic chemotherapy and antigen-specific DNA vaccine can induce more potent antigen-specific immune responses and antitumor effects. This provides an immunologic basis for further testing in cancer patients.