Recombinant adenovirus shedding after intratumoral gene transfer in lung cancer patients

Alternative methods for local ablation-interventional pulmonology: a narrative review

OBJECTIVE

To discuss and summarise the background and recent advances in the approach to bronchoscopic ablative therapies for lung cancer, focusing on focal parenchymal lesions.

BACKGROUND

This series focusses on the challenges highlighted by increasing recognition of the prognostically more favourable oligometastatic disease rather than the more frequent, but prognostically poor, high tumour burden metastatic disease. While surgery, stereotactic body radiation therapy (SBRT), and trans-thoracic percutaneous ablative techniques such as microwave (MWA) and radiofrequency ablation (RFA) are well recognised options for selected cases of pulmonary oligometastasis, bronchoscopic approaches to pulmonary tumour ablation are becoming realistic alternatives. An underlying tenet driving research and implementation in this domain is that percutaneous ablative techniques are obliged to traverse the pleura leading to a high rate of pneumothorax, and risks also goes up for peri-vascular lesions. Historically low yield bronchoscopic targeting of isolated peripheral tumors have significantly improved by incorporating multi-modality high resolution imaging and processing, including navigation planning and real-time image guidances (ultrasound, electromagnetic navigation, cone-beam CT). Combining advanced image guidance with ablative technology adaptations for bronchoscopic delivery opens up the options for high dose local ablative therapies that may reduce transthoracic complications and provide palliative to curative options for limited stage primary and oligometastatic diseases.

METHODS

We conduct a narrative review of the literature summarizing the history of bronchoscopic tumor ablation approaches, technical details including biologic rational for their uses, and current evidence for each modality, as well as investigations into future applications. Because of the relative paucity of prospective studies, we have been very inclusive in our inclusion of experiences from the published clinical databases.

CONCLUSIONS

Whilst surgical resection and SBRT remain the current mainstay of curative therapies for peripheral cancers, in the foreseeable future, developments and further research will see bronchoscopic ablative therapies become viable lung sparing alternatives in those deemed suitable. The future is bright.

Neoadjuvant Gene-Mediated Cytotoxic Immunotherapy for Non-Small-Cell Lung Cancer: Safety and Immunologic Activity

Gene-mediated cytotoxic immunotherapy (GMCI) is an immuno-oncology approach involving local delivery of a replication-deficient adenovirus expressing herpes simplex thymidine kinase (AdV-tk) followed by anti-herpetic prodrug activation that promotes immunogenic tumor cell death, antigen-presenting cell activation, and T cell stimulation. This phase I dose-escalation pilot trial assessed bronchoscopic delivery of AdV-tk in patients with suspected lung cancer who were candidates for surgery. A single intra-tumoral AdV-tk injection in three dose cohorts (maximum 1012 viral particles) was performed during diagnostic staging, followed by a 14-day course of the prodrug valacyclovir, and subsequent surgery 1 week later. Twelve patients participated after appropriate informed consent. Vector-related adverse events were minimal. Immune biomarkers were evaluated in tumor and blood before and after GMCI. Significantly increased infiltration of CD8+ T cells was found in resected tumors. Expression of activation, inhibitory, and proliferation markers, such as human leukocyte antigen (HLA)-DR, CD38, Ki67, PD-1, CD39, and CTLA-4, were significantly increased in both the tumor and peripheral CD8+ T cells. Thus, intratumoral AdV-tk injection into non-small-cell lung cancer (NSCLC) proved safe and feasible, and it effectively induced CD8+ T cell activation. These data provide a foundation for additional clinical trials of GMCI for lung cancer patients with potential benefit if combined with other immune therapies.

Bronchoscopic intratumoural therapies for non-small cell lung cancer

The past decade has brought remarkable improvements in the treatment of non-small cell lung cancer (NSCLC) with novel therapies, such as immune checkpoint inhibitors, although response rates remain suboptimal. Direct intratumoural injection of therapeutic agents via bronchoscopic approaches poses the unique ability to directly target the tumour microenvironment and offers several theoretical advantages over systemic delivery including decreased toxicity. Increases in understanding of the tumour microenvironment and cancer immunology have identified many potential options for intratumoural therapy, especially combination immunotherapies. Herein, we review advances in the development of novel bronchoscopic treatments for NSCLC over the past decade with a focus on the potential of intratumoural immunotherapy alone or in combination with systemic treatments.

Therapeutic bronchoscopy in the era of genotype directed lung cancer management

Lung cancer is the leading cause of cancer related deaths. Non-small cell lung cancer (NSCLC) accounts for ~85% of lung cancers. Our understanding of driver mutations and genotype directed therapy has revolutionized the management of advanced NSCLC. Commonly described mutations include mutations in epidermal growth factor (EGFR) & BRAF and translocations in anaplastic lymphoma kinase (ALK) & rat osteosarcoma (ROS1). Drugs directed against these translocations have significantly improved progression free survival individually and have shown a survival benefit when studied in the Lung Cancer Mutation Consortium (median survival 3.5 vs. 2.4 years compared to standard therapy). In a related yet parallel universe, the number of bronchoscopic ablative modalities available for management of cancer related airway obstruction have increased exponentially over the past decade. A wealth of literature has given us a better understanding of the technical aspects, benefits and risks associated with these procedures. While they all show benefits in terms of relieving airway obstruction, symptom control, quality of life and lung function testing, their complication rates vary based on the modality. The overall complication rate was ~4% in the AQuIRE registry. Bronchoscopic therapeutic modalities include rigid bronchoscopy with mechanical debulking, laser, thermo-coagulation [electrocautery & argon plasma coagulation (APC)], cryotherapy, endobronchial brachytherapy (EBT), photodynamic therapy (PDT), intratumoral chemotherapy (ITC) and transbronchial needle injection (TBNI) of chemotherapy. Intuitively, one would assume that the science of driver mutations would crisscross with the science of bronchoscopic ablation as they overlap in the same patient population. Sadly, this is not the case and there is a paucity of literature looking at these fields together. This results in several unanswered questions about the interplay between these two therapies.

Induction of PrPSc-specific systemic and mucosal immune responses in white-tailed deer with an oral vaccine for chronic wasting disease

The ongoing epidemic of chronic wasting disease (CWD) within cervid populations indicates the need for novel approaches for disease management. A vaccine that either reduces susceptibility to infection or reduces shedding of prions by infected animals, or a combination of both, could be of benefit for disease control. The development of such a vaccine is challenged by the unique nature of prion diseases and the requirement for formulation and delivery in an oral format for application in wildlife settings. To address the unique nature of prions, our group targets epitopes, termed disease specific epitopes (DSEs), whose exposure for antibody binding depends on disease-associated misfolding of PrP^C into PrP^Sc. Here, a DSE corresponding to the rigid loop (RL) region, which was immunogenic following parenteral vaccination, was translated into an oral vaccine. This vaccine consists of a replication-incompetent human adenovirus expressing a truncated rabies glycoprotein G recombinant fusion with the RL epitope (hAd5:tgG-RL). Oral immunization of white-tailed deer with hAd5:tgG-RL induced PrP^Sc-specific systemic and mucosal antibody responses with an encouraging safety profile in terms of no adverse health effects nor prolonged vector shedding. By building upon proven strategies of formulation for wildlife vaccines, these efforts generate a particular PrP^Sc-specific oral vaccine for CWD as well as providing a versatile platform, in terms of carrier protein and biological vector, for generation of other oral, peptide-based CWD vaccines.

Genetic Modification of the Lung Directed Toward Treatment of Human Disease

Genetic modification therapy is a promising therapeutic strategy for many diseases of the lung intractable to other treatments. Lung gene therapy has been the subject of numerous preclinical animal experiments and human clinical trials, for targets including genetic diseases such as cystic fibrosis and α1-antitrypsin deficiency, complex disorders such as asthma, allergy, and lung cancer, infections such as respiratory syncytial virus (RSV) and Pseudomonas, as well as pulmonary arterial hypertension, transplant rejection, and lung injury. A variety of viral and non-viral vectors have been employed to overcome the many physical barriers to gene transfer imposed by lung anatomy and natural defenses. Beyond the treatment of lung diseases, the lung has the potential to be used as a metabolic factory for generating proteins for delivery to the circulation for treatment of systemic diseases. Although much has been learned through a myriad of experiments about the development of genetic modification of the lung, more work is still needed to improve the delivery vehicles and to overcome challenges such as entry barriers, persistent expression, specific cell targeting, and circumventing host anti-vector responses.

Novel 19 F-MRS β-galactosidase reporter molecules incorporated nitrogen mustard analogues

In this study, we propose a novel molecular platform-integrated fluorinated antitumor nitrogen mustards for ¹⁹ F-MRS assay of β-galactosidase (β-gal) activity. Following this idea, we have designed, synthesized, and characterized 2-fluoro-4-[bis(2'-chloroethyl)amino]phenyl β-D-galactopyranoside 5, 2-fluoro-4-{bis[2'-O-(β-D-galactopyranosyl)ethyl]amino}phenyl β-D-galactopyranoside 8, 2-fluoro-4-{bis[[1″-(β-D-galactopyranosyl)-1″, 2″, 3″-triazol-4″-yl]methyl] amino}phenyl β-D-galactopyranoside 14 and 2-fluoro-4-{bis[[1″-(β-D-glucopyranosyl)-1″, 2″, 3″-triazol-4″-yl]methyl]amino}phenyl β-D-galactopyranoside 15 through glycosylation and click reaction strategies, and their structures were confirmed by NMR and HRMS or elemental analysis data. Among them, 2-fluoro-4-[bis(2'-chloroethyl)amino]phenyl β-D-galacto-pyranoside 5 was found very sensitive to β-gal (E801A) in PBS at 37°C with big Δδ_F response. Here, we demonstrated the feasibility of this platform for assessing β-gal activity in solution, and in vitro with lacZ-transfected human MCF7 breast and PC3 prostate tumor cells, by the characterization of β-gal-responsive ¹⁹ F-chemical shift changes Δδ_F and hydrolytic kinetics.

Surgical immune interventions for solid malignancies

BACKGROUND

The purpose of this study was to systematically review clinically translatable immunotherapeutic agents that are delivered regionally for solid malignancies.

DATA SOURCES

PubMed and ClinicalTrials.gov were searched for published and registered clinical trials, respectively. The search yielded 334 relevant publications, of which 116 articles were included for review after exclusion criteria were applied.

CONCLUSIONS

There has been an increase in the regional administration of cell-based and viral vector-based clinical trials over the last 5 years. Surgical interventions have been developed for intrapleural, intracranial, intraperitoneal, and intratumoral routes of access to enhance the local delivery of these therapies. Multimodality therapies that combine regional immunotherapy with other local and systemic therapies are demonstrating continued growth as the field of immunotherapy continues to expand.

Oncolytic viruses: From bench to bedside with a focus on safety

Oncolytic viruses are a relatively new class of anti-cancer immunotherapy agents. Several viruses have undergone evaluation in clinical trials in the last decades, and the first agent is about to be approved to be used as a novel cancer therapy modality. In the current review, an overview is presented on recent (pre)clinical developments in the field of oncolytic viruses that have previously been or currently are being evaluated in clinical trials. Special attention is given to possible safety issues like toxicity, environmental shedding, mutation and reversion to wildtype virus.

Targeting the tumor microenvironment to enhance antitumor immune responses

The identification of tumor-specific antigens and the immune responses directed against them has instigated the development of therapies to enhance antitumor immune responses. Most of these cancer immunotherapies are administered systemically rather than directly to tumors. Nonetheless, numerous studies have demonstrated that intratumoral therapy is an attractive approach, both for immunization and immunomodulation purposes. Injection, recruitment and/or activation of antigen-presenting cells in the tumor nest have been extensively studied as strategies to cross-prime immune responses. Moreover, delivery of stimulatory cytokines, blockade of inhibitory cytokines and immune checkpoint blockade have been explored to restore immunological fitness at the tumor site. These tumor-targeted therapies have the potential to induce systemic immunity without the toxicity that is often associated with systemic treatments. We review the most promising intratumoral immunotherapies, how these affect systemic antitumor immunity such that disseminated tumor cells are eliminated, and which approaches have been proven successful in animal models and patients.

Ethics of Cancer Gene Transfer Clinical Research

Translation of cancer gene transfer confronts many familiar-and some distinctive-ethical challenges. In what follows, I survey three major ethical dimensions of cancer gene transfer development. Subheading 1 centers on the ethics of planning, designing, and reporting animal studies. Subheading 2 describes basic elements of human subjects protection as pertaining to cancer gene transfer. In Subheading 3, I describe how cancer gene transfer researchers have obligations to downstream consumers of the evidence they produce.

Novel molecular platform integrated iron chelation therapy for 1H-MRI detection of β-galactosidase activity

Targeting the increased Fe(3+) content in tumors, we propose a novel molecular platform integrated cancer iron chelation therapy for (1)H-magnetic resonance imaging (MRI) detection of β-galactosidase (β-gal) activity. Following this idea, we have designed, synthesized, and characterized a series of β-d-galactosides conjugated with various chelators and demonstrated the feasibility of this concept for assessing β-gal activity in solution by (1)H-MRI T1 and T2 relaxation mapping.

Gene therapy for lung neoplasms

Both advanced-stage lung cancer and malignant pleural mesothelioma are associated with a poor prognosis. Advances in treatment regimens for both diseases have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in several clinical trials. Strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review considers the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

Enhanced tumor therapy using vaccinia virus strain GLV-1h68 in combination with a β-galactosidase-activatable prodrug seco-analog of duocarmycin SA

Breast cancer is the most common cause of cancer-related death worldwide, thus remaining a crucial health problem among women despite advances in conventional therapy. Therefore, new alternative strategies are needed for effective diagnosis and treatment. One approach is the use of oncolytic viruses for gene-directed enzyme prodrug therapy. Here, the lacZ-carrying vaccinia virus (VACV) strain GLV-1h68 was used in combination with a β-galactosidase-activatable prodrug derived from a seco-analog of the natural antibiotic duocarmycin SA. Tumor cell infection with the VACV strain GLV-1h68 led to production of β-galactosidase, essential for the conversion of the prodrug to the toxic compound. Furthermore, drug-dependent cell kill and induction of the intrinsic apoptosis pathway in tumor cells was also observed on combination therapy using the prodrug and the GLV-1h68 strain, despite the fact that VACV strains encode antiapoptotic proteins. Moreover, GI-101A breast cancer xenografts were effectively treated by the combination therapy. In conclusion, the combination of a β-galactosidase-activatable prodrug with a tumor-specific vaccinica virus strain encoding this enzyme, induced apoptosis in cultures of the human GI-101A breast cancer cells, in which a synergistic oncolytic effect was observed. Moreover, in vivo, additional prodrug treatment had beneficial effects on tumor regression in GLV-1h68-treated GI-101A-xenografted mice.

Advances in viral-vector systemic cytokine gene therapy against cancer

Current strategies for cancer gene therapy consist mainly of direct inhibition of tumor cell growth and activation of systemic host defense mechanisms. Cytokine gene-transduced tumor cells have been used as vaccines in clinical trials, which have shown good safety profiles and some local responses but substantial lack of systemic efficacy. Cytokines should be directed at the level of gene selection and delivery, in order to identify the optimal cytokine and achieve efficient and durable cytokine expression at the level of improving immune stimulation. In this review, we will summarize the current achievements of cytokine gene therapy, especially viral-vector, and their applications in cancer treatment. Additionally, we will also discuss and propose future perspectives about cancer gene therapy.

Gene therapy for mesothelioma and lung cancer

Both malignant pleural mesothelioma and advanced stage lung cancer are associated with a poor prognosis. Unfortunately, current treatment regimens have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in a number of clinical trials over the last two decades. Using viral vectors or anti-sense RNA, strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review will consider the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

Viral shedding after p53 adenoviral gene therapy in 10 cases of esophageal cancer

We detected adenoviral DNA fragments in excretions of 10 esophageal cancer patients by DNA-PCR after tumor injection of Ad-CMV-vector. A total of 220 samples consisting of feces, gargling saliva, urine, and blood plasma were assessed. A total of 29.7% of feces samples and 13.2% of gargling saliva samples were positive for adenoviral DNA fragments, but 89.7% of the positive feces samples and all of the positive gargling saliva samples turned negative on day 12 after tumor injection. Although adenoviral DNA fragments may be pathogen-free, patients' feces and gargling saliva contain adenoviral DNA fragments for 12 days after injection.

A 19F-NMR approach using reporter molecule pairs to assess beta-galactosidase in human xenograft tumors in vivo

Gene therapy has emerged as a promising strategy for treatment of various diseases. However, widespread implementation is hampered by difficulties in assessing the success of transfection in the target tissue and the longevity of gene expression. Thus, there is increasing interest in the development of non-invasive in vivo reporter techniques to assay gene expression. We recently demonstrated the ability to detect beta-galactosidase activity in stably transfected human prostate tumor xenografts in mice in vivo using 19F NMR. We now extend the studies to human MCF7 breast cancer cells growing as xenografts in nude mice. Moreover, by using two spectrally resolved reporters (o-fluoro-p-nitrophenyl-beta-D-galactopyranoside and an isomer), two tumors could be interrogated simultaneously revealing lacZ transgene activity in a stably transfected tumor versus no activity in a wild-type tumor. Most significantly, hydrolytic activity observed by 19F NMR corresponded to differential activity in lacZ-expressing tumors.

An inventory of shedding data from clinical gene therapy trials

Viruses are the most commonly used vectors for clinical gene therapy. The risk of dissemination of a viral vector into the environment via excreta from the treated patient, a phenomenon called shedding, is a major safety concern for the environment. Despite the significant number of clinical gene therapy trials that have been conducted worldwide, there is currently no overview of actual shedding data available. In this article, an inventory of shedding data obtained from a total of 100 publications on clinical gene therapy trials using retroviral, adenoviral, adeno-associated viral and pox viral vectors is presented. In addition, the experimental set-up for shedding analysis including the assays used and biological materials tested is summarized. The collected data based on the analysis of 1619 patients in total demonstrate that shedding of these vectors occurs in practice, mainly determined by the type of vector and the route of vector administration. Due to the use of non-quantitative assays, the lack of information on assay sensitivity in most publications, and the fact that assay sensitivity is expressed in various ways, general conclusions cannot be made as to the level of vector shedding. The evaluation of the potential impact and consequences of the observations is complicated by the high degree of variety in the experimental design of shedding analysis between trials. This inventory can be supportive to clinical gene therapy investigators for the establishment of an evidence-based risk assessment to be included in a clinical protocol application, as well as to national regulatory authorities for the ongoing development of regulatory guidelines regarding gene therapy.

Improvement of Antitumor Activity by Gene Amplification with a Replicating but Nondisseminating Adenovirus

Gene therapy is a promising approach for cancer treatment; however, efficacy of current vectors remains insufficient. To improve the success of suicide gene therapy, we constructed a replication-competent adenoviral vector that has its protease gene deleted and expresses bacterial cytosine deaminase fused with bacterial uracil phosphoribosyltransferase (CU). The prodrug, 5-fluorocytosine, is transformed into the highly toxic and tissue-diffusible 5-fluorouracil by CU in infected cells. This vector is incapable of producing infectious particles but is able to undergo a single round of replication, thereby increasing transgene copy number and expression. In the presence of 5-FC, compared with the first-generation vector (AdCU), the replication-competent vector, Ad(dPS)CU-IRES-E1A, was significantly more efficacious for in vitro tumor cell killing and in bystander assays, whereas 25-fold fewer viral particles were required in a three-dimensional spheroid model. For in vivo experiments, in which virus was injected into preestablished intracranial glioma xenografts, followed by 5-FC treatment, mice receiving Ad(dPS)CU-IRES-E1A had significantly smaller tumors at 35 days postinjection as well as significantly longer median survival than mice treated with the replication-deficient, protease-deleted vector [Ad(dPS)CU]. In an immunocompetent syngeneic model, Ad(dPS)CU + 5-FC-treated mice had a median survival of only 23 days, whereas Ad(dPS)CU-IRES-E1A + 5-FC-treated animals had a survival of 57.1% at 365 days. In conclusion, Ad(dPS)CU-IRES-E1A in the presence of 5-FC produces more potent tumoricidal effects than its replication-deficient counterparts.

Angiogenesis meets immunology: Cytokine gene therapy of cancer

Delivery of cytokine genes at the tumor site in pre-clinical models has been shown to recruit host inflammatory cells followed by inhibition of tumor growth. This local effect is often accompanied by systemic protection mediated by the immune system, mainly by CD8(+) T and NK cells. On this basis, cytokine gene-transduced tumor cells have widely been used as vaccines in clinical trials, which have shown good safety profiles and some local responses but substantial lack of systemic efficacy. Are these findings the end of the story? Possibly not, if major improvements will be attained in the coming years. These should be directed at the level of gene selection and delivery, in order to identify the optimal cytokine and achieve efficient and durable cytokine expression, and at the level of improving immune stimulation, i.e. by co-administration of co-stimulatory molecules including B7 and CD40, or boosting the expression of tumor antigens or MHC class I molecules. Interestingly, some of the cytokines which have shown encouraging anti-tumor activity, including IFNs, IL-4, IL-12 and TNF-alpha, are endowed with anti-angiogenic or vasculotoxic effects, which may significantly contribute to local tumor control. Therapeutic exploitation of this property may result in the design of novel approaches which, by maximizing immune-stimulating and anti-angiogenic effects, could possibly lead to starvation of established tumors in patients.

Transbronchial Needle Injection: A Systematic Review of a New Diagnostic and Therapeutic Paradigm

BACKGROUND AND OBJECTIVE

Transbronchial needle catheters are commonly used during flexible and rigid bronchoscopy for needle aspiration. The use of these catheters can be expanded by employing the technique of transbronchial needle injection.

METHODS AND RESULTS

By injecting lesions in the airways, peribronchial structures, mediastinum, or lung parenchyma, transbronchial needle injection has been applied to the treatment of lung cancer, inflammatory disorders of the airways, recurrent respiratory papillomatosis, as well as bronchopleural fistulas. Diagnostic applications have included the localization of peripheral lung nodules as well as sentinel lymph nodes.

CONCLUSIONS

Our review defines this bronchoscopic technique and summarizes its various reported applications.

Adenoviral Strategies for the Gene Therapy of Cancer

Despite slow clinical progress, efforts to develop specific nontoxic cancer gene therapies are increasing exponentially. Adenoviral vectors are one of the most popular vehicles for gene transfer currently being used in worldwide clinical trials for cancer. Over the past decade our knowledge of the adenoviral life cycle together with the discovery of novel tumor antigens has permitted the targeting of adenoviral vectors to specific tumors. Targeting adenoviral vectors to tumors is crucial for their use in clinical applications in order to allow for systemic administration and the use of reduced vector doses. In addition, novel approaches to tumor killing have also been explored, which will have greater potency and selectivity than currently available treatments such as chemotherapy or radiation. This review discusses the basic concepts behind the use of adenoviral vectors for cancer gene therapy and their potential for clinical application, as well as ongoing and completed clinical trials.

WWOX gene restoration prevents lung cancer growth in vitro and in vivo

The WWOX (WW domain containing oxidoreductase) gene at the common fragile site, FRA16D, is altered in many types of cancer, including lung cancer. We have examined the tumor suppressor function of WWOX in preclinical lung cancer models. The WWOX gene was expressed in lung cancer cell lines through recombinant adenovirus (Ad) infection (Ad-WWOX), and through a drug [ponasterone A, (ponA)]-inducible system. After WWOX restoration in vitro, endogenous Wwox protein-negative cell lines (A549, H460, and H1299) underwent apoptosis through activation of the intrinsic apoptotic caspase cascade in A549 and H460 cells. Ectopic expression of Wwox caused dramatic suppression of tumorigenicity of A549, H460, and H1299 cells in nude mice after Ad-WWOX infection and after ponA induction of Wwox expression in H1299 lung cancer cells. Tumorigenicity and in vitro growth of U2020 (Wwox-positive) lung cancer cells was unaffected by Wwox overexpression. This study confirms that WWOX is a tumor suppressor gene and is highly effective in preventing growth of lung cancer xenografts, whether introduced through viral infection or by induction of a silent WWOX transgene.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.