Glioblastoma (GBM) is the most common and aggressive primary brain tumor in the adult population and it carries a dismal prognosis. Inefficient drug delivery across the blood brain barrier (BBB), an immunosuppressive tumor microenvironment (TME) and development of drug resistance are key barriers to successful glioma treatment. Since gliomas occur through sequential acquisition of genetic alterations, gene therapy, which enables to modification of the genetic make-up of target cells, appears to be a promising approach to overcome the obstacles encountered by current therapeutic strategies. Gene therapy is a rapidly evolving field with the ultimate goal of achieving specific delivery of therapeutic molecules using either viral or non-viral delivery vehicles. Gene therapy can also be used to enhance immune responses to tumor antigens, reprogram the TME aiming at blocking glioma-mediated immunosuppression and normalize angiogenesis. Nano-particles-mediated gene therapy is currently being developed to overcome the BBB for glioma treatment. Another approach to enhance the anti-glioma efficacy is the implementation of viro-immunotherapy using oncolytic viruses, which are immunogenic. Oncolytic viruses kill tumor cells due to cancer cell-specific viral replication, and can also initiate an anti-tumor immunity. However, concerns still remain related to off target effects, and therapeutic and transduction efficiency. In this review, we describe the rationale and strategies as well as advantages and disadvantages of current gene therapy approaches against gliomas in clinical and preclinical studies. This includes different delivery systems comprising of viral, and non-viral delivery platforms along with suicide/prodrug, oncolytic, cytokine, and tumor suppressor-mediated gene therapy approaches. In addition, advances in glioma treatment through BBB-disruptive gene therapy and anti-EGFRvIII/VEGFR gene therapy are also discussed. Finally, we discuss the results of gene therapy-mediated human clinical trials for gliomas. In summary, we highlight the progress, prospects and remaining challenges of gene therapies aiming at broadening our understanding and highlighting the therapeutic arsenal for GBM.

Breast cancer is the most common cancer in women all over the world. Furthermore, up to one third of breast tumors develop metastases that are resistant to standard therapies. Gene therapeutic strategies have been developed in order to specifically target cancer cells either directly or through the stimulation of antitumor immunity. Areas covered: This review describes the therapeutic strategies that are currently under development to treat this disease using engineered viral vectors including: adenovirus, adeno-associated virus, lentivirus, poxvirus, reovirus, baculovirus, herpesvirus and oncolytic viruses. Advantages and disadvantages of these multiple gene therapy platforms are discussed in detail. Expert opinion: Metastatic breast cancer is a perfect candidate for gene therapy approaches due to the presence of several tumor antigens and the aberrant expression of many molecular pathways. Oncolytic vectors are able to attack tumor cells while sparing normal cells and their activity is often enhanced by the administration of chemotherapy. However, more efforts are needed in order to reduce toxicity and to achieve better transduction efficiency. Improved preclinical models and a more critical patient selection for clinical trials, along with advances in gene therapy regulations, will surely facilitate the evolution of gene therapy for the treatment of metastatic breast cancer.

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Introduction: Gliomas are infiltrating brain tumors associated with high morbidity and mortality. Current standard of care includes radiation, chemotherapy and surgical resection. Today, survival rates for malignant glioma patients remain dismal and unchanged for decades. The glioma microenvironment is highly immunosuppressive and consequently this has motivated the development of immunotherapies for counteracting this condition, enabling the immune cells within the tumor microenvironment to react against this tumor. Areas covered: The authors discuss immunotherapeutic strategies for glioma in phase-I/II clinical trials and illuminate their mechanisms of action, limitations and key challenges. They also examine promising approaches under preclinical development. Expert opinion: In the last decade there has been an expansion in immune-mediated anti-cancer therapies. In the glioma field, sophisticated strategies have been successfully implemented in preclinical models. Unfortunately, clinical trials have not yet yielded consistent results for glioma patients. This could be attributed to our limited understanding of the complex immune cell infiltration and its interaction with the tumor cells, the selected time for treatment, the combination with other therapies and the route of administration of the agent. Applying these modalities to treat malignant glioma is challenging, but many new alternatives are emerging to bypass these hurdles.