Gene Therapy Clinical Trials Research Articles

Gene Therapy for Non-Hereditary Retinal Disease: Age-Related Macular Degeneration, Diabetic Retinopathy, and Beyond.

Gene therapy holds promise as a transformative approach in the treatment landscape of age-related macular degeneration (AMD), diabetic retinopathy (DR), and diabetic macular edema (DME), aiming to address the challenges of frequent intravitreal anti-vascular endothelial growth factor (VEGF) injections. This manuscript reviews ongoing gene therapy clinical trials for these disorders, including ABBV-RGX-314, ixoberogene soroparvovec (ixo-vec), and 4D-150. ABBV-RGX-314 utilizes an adeno-associated virus (AAV) vector to deliver a transgene encoding a ranibizumab-like anti-VEGF antibody fragment, demonstrating promising results in Phase 1/2a and ongoing Phase 2b/3 trials. Ixo-vec employs an AAV2.7m8 capsid for intravitreal delivery of a transgene expressing aflibercept, showing encouraging outcomes in Phase 1 and ongoing Phase 2 trials. 4D-150 utilizes an evolved vector to express both aflibercept and a VEGF-C inhibitory RNAi, exhibiting positive interim results in Phase 1/2 studies. Other therapies reviewed include EXG102-031, FT-003, KH631, OLX10212, JNJ-1887, 4D-175, and OCU410. These therapies offer potential advantages of reduced treatment frequency and enhanced safety profiles, representing a paradigm shift in management towards durable and efficacious cellular-based biofactories. These advancements in gene therapy hold promise for improving outcomes in AMD and addressing the complex challenges of DME and DR, providing new avenues for the treatment of diabetic eye diseases.

Genetic alteration of SJ293TS cells and modification of serum-free media enhances lentiviral vector production

Successful cell and gene therapy clinical trials have resulted in the United States Food and Drug Administration and European Medicines Agency approving their use for treatment of patients with certain types of cancers and monogenetic diseases. These novel therapies, which rely heavily on lentiviral vectors to deliver therapeutic transgenes to patient cells, have driven additional investigations, increasing demand for both pre-clinical and current Good Manufacturing Practices-grade viral vectors. To better support novel studies by improving current production methods, we report the development of a genetically modified HEK293T-based cell line that is null for expression of both Protein Kinase R and Beta-2 microglobulin and grows in suspension using serum-free media, SJ293TS-DPB. Absence of Protein Kinase R increased anti-sense lentiviral vector titers by more than 7-fold, while absence of Beta-2 microglobulin, a key component of Major Histocompatibility Complex class I molecules, has been reported to reduce the immunogenicity of lentiviral particles. Furthermore, we describe an improved methodology for culturing SJ293TS-DPB which facilitates expansion, reduces handling, and increases titers by 2-fold compared to previous methods. SJ293TS-DPB stably produced lentiviral vectors for over four months and generated lentiviral vectors that efficiently transduce healthy human donor T cells and CD34+ hematopoietic stem cells.

Gene replacement therapy in Bietti crystalline corneoretinal dystrophy: an open-label, single-arm, exploratory trial

Bietti crystalline corneoretinal dystrophy is an inherited retinal disease caused by mutations in CYP4V2, which results in blindness in the working-age population, and there is currently no available treatment. Here, we report the results of the first-in-human clinical trial (NCT04722107) of gene therapy for Bietti crystalline corneoretinal dystrophy, including 12 participants who were followed up for 180–365 days. This open-label, single-arm exploratory trial aimed to assess the safety and efficacy of a recombinant adeno-associated-virus-serotype-2/8 vector encoding the human CYP4V2 protein (rAAV2/8-hCYP4V2). Participants received a single unilateral subretinal injection of 7.5 × 1010 vector genomes of rAAV2/8-hCYP4V2. Overall, 73 treatment-emergent adverse events were reported, with the majority (98.6%) being of mild or moderate intensity and considered to be procedure- or corticosteroid-related; no treatment-related serious adverse events or local/systemic immune toxicities were observed. Compared with that measured at baseline, 77.8% of the treated eyes showed improvement in best-corrected visual acuity (BCVA) on day 180, with a mean ± standard deviation increase of 9.0 ± 10.8 letters in the 9 eyes analyzed (p = 0.021). By day 365, 80% of the treated eyes showed an increase in BCVA, with a mean increase of 11.0 ± 10.6 letters in the 5 eyes assessed (p = 0.125). Importantly, the patients’ improvement observed using multifocal electroretinogram, microperimetry, and Visual Function Questionnaire-25 further supported the beneficial effects of the treatment. We conclude that the favorable safety profile and visual improvements identified in this trial encourage the continued development of rAAV2/8-hCYP4V2 (named ZVS101e).

Gene Therapy for Hypertension, Atherosclerosis, and Familial Hypercholesterolemia: The Old Concepts and the New Era

Cardiovascular disease remains the main cause of mortality in the 21st century. Hypertension, vessel atherosclerosis, and familial hypercholesterolemia (FH) are responsible for increased mortality and morbidity in patients. Therapies for cardiovascular disease are based on drug treatment options, but in the era of precision medicine, personalized treatments are being developed. Studies have shown that these conditions have a strong genetic background, creating an opportunity for the implementation of gene therapy for these diseases. Currently, gene therapy is not widely used in clinical practice. Recent advances in this research field are making gene therapy a very promising preventive and therapeutic tool for cardiovascular disease. Essential hypertension’s (EH) pathophysiology is mostly based on the activation of both the sympathetic nervous system and the renin angiotensin aldosterone system (RAAS), natriuretic peptide production, and endothelial dysfunction. Plasmid DNA and viral vectors can be used, targeting the main mechanisms in the pathogenesis of EH. Many preclinical studies have been developed across the years, presenting a significant decrease in blood pressure. Nevertheless, no clinical studies have been developed studying the implementation of gene therapy in EH. Atherosclerotic damage is caused by monogenic diseases or is deteriorated by the activation of inflammation in the vessel wall. Gene therapy studies have been developed in the pre- and clinical phases targeting the lipoprotein and cholesterol metabolism and the inflammation of the vessels. FH is a common inherited metabolic disease associated with high levels of cholesterol in the blood. Clinical trials of gene therapy have been developed and presented optimistic results. In this review, the challenges of gene therapy for cardiovascular disease are outlined. Nevertheless, more clinical trials are needed to be performed for the development of convenient and safe drug schemes for our patients.

236 Bilateral Intrathalamic Infusion of rAAVrh8-Hexa/Hexb in a Phase 1/2 Clinical Trial for Gene Therapy in Infantile and Juvenile Tay-Sachs and Sandhoff Disease; Surgical Technique

INTRODUCTION: Tay-Sachs (TSD) and Sandhoff (SD) diseases are rare,monogenic and severe neurodegenerative disorders due to Hexosaminidase A deficiency. We performed the first-in-human bilateral thalamic (BiTh) delivery of rAAVrh8-HEXA/HEXB in 8 children in a Phase 1/2 clinical trial. METHODS: Stereotactic infusion cannula placement was performed using ROSA robotic platform. Bilateral trajectories were planned via the trans-frontal route..Head stabilization was accomplished using radiolucent horse-shoe head rest and radiolucent pin-skull clamps. Flexible infusion cannulas were placed through small drill holes using ROSA guidance. Cannula stabilization was achieved using a construct which combined the Navigus brain biopsy platform and flexible cannula bolt. Insertion accuracy was verified with intraoperative CT images. Patients received one of the three doses in each thalamus: 180 mcl (5.87E + 12vg), 360 mcl (1.17E + 13vg) or 720 mcl (2.35E + 13vg). Drug infusion rate was 4 mcl/minute and completed in 90-360 minutes depending on drug dosage. RESULTS: Eight patients received treatment; 5 infants (6, 11, 13, 17, and 20 months) and 3 juvenile (5, 6, 12 years). Duration of follow up was 2-28 months. Outcome assessments included safety, CSF biochemistry, MRI/MRS/DTI, and neurodevelopmental observations. Surgery and drug infusions were well-tolerated. Post-infusion MRIs showed signal enhancement volume coverage in thalamus from 8%-44% parallel to escalating doses. The only surgery related complication was superficial wound dehiscence in two patients. Infants showed partial stabilization or improvement, including in oral feeding and myelination. In juveniles, dystonic posturing worsened after dosing in all 3 patients treated. Two patients died much later from reasons unrelated to surgery or drug infusion. CONCLUSIONS: Surgery for BiTh infusion of rAAVrh8-HEXA/HEXB for gene therapy in infants with TSD and SD is well-tolerated. Patients respond well to treatment with some stabilization or improvement.

B-Type Natriuretic Peptide Inhibits the Expression and Function of SERCA2a in Heart Failure.

B-type natriuretic peptide (BNP) possesses protective cardiovascular properties; however, there has not been sufficient serious consideration of the side effects of BNP. As for sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), it was once considered a new target for the treatment of heart failure (HF). Nevertheless, clinical trials of SERCA2a gene therapy in HF have finally become unsuccessful. Research has found that elevated BNP levels and decreased SERCA2a expression are two important HF characteristics, which are always negatively correlated. We hypothesize that BNP inhibits SERCA2a expression and, therefore, exerts negative effects on SERCA2a expression and function.The effects of BNP on endogenous SERCA2a expression and function were tested in mice with HF induced by transverse aortic constriction and neonatal rat cardiomyocytes (NRCM). Furthermore, to verify the effects of BNP on exogenous SERCA2a gene transduction efficacy, BNP was added to the myocardium and cardiomyocytes infected with an adenovirus overexpressing SERCA2a.In vivo, BNP levels were increased, SERCA2a expression was reduced in both the BNP intervention and HF groups, and BNP reduced the overexpressed exogenous SERCA2a protein in the myocardium. Our in vitro data showed that BNP dose-dependently inhibited the total and exogenous SERCA2a expression in NRCM by activating the cGMP-dependent protein kinase G. BNP also inhibited the effects of SERCA2a overexpression on Ca2+ transience in NRCM.The expression and function of endogenous and exogenous SERCA2a are inhibited by BNP. The opposite relationship between BNP and SERCA2a should be given serious attention in the treatment of HF via BNP or SERCA2a gene therapy.

Utilizing Adeno-Associated Virus Vectors for Advancing Cancer Gene Therapy

Adeno-associated virus (AAV) has proven highly effective as a delivery vector in clinical trials for gene therapy. The safety and efficacy of AAV have led to its application as a novel approach for cancer treatment. Many successful clinical trials of cancer have demonstrated the feasibility of this approach. This review mainly introduces the structure, characteristics and application of AAV in tumor models. The promise of gene therapy in addressing diverse diseases has become evident, with AAV vectors playing a pivotal role in its achievements. AAV's exceptional safety profile and efficacy in gene therapy have spurred their application as a novel approach in the realm of cancer treatment. Clinical trials in this area have yielded impressive results, underlining the potential of AAV in combating cancer. This review provides a comprehensive insight into AAV's structural attributes and unique characteristics, emphasizing their significance in the context of tumor models. AAV's ability to efficiently deliver therapeutic genes to cancer cells, coupled with minimal risk, marks a significant breakthrough in oncology.

Abstract 7250: Serial assessment of GEN2, a retroviral vector for gene transfer of an optimized thymidine kinase and GM-CSF, for genomic integration into peripheral blood mononuclear cells (PBMCs) in a Phase 1 clinical trial in adult patients with solid tumors

Abstract GEN2 is a non-replicating retroviral gene transfer vector encoding a sequence-optimized herpes simplex thymidine kinase (HSV-TK), which activates the antiherpetic pro-drug ganciclovir (GCV), resulting in chain termination during DNA replication, triggering cancer cell apoptosis and release of neoantigens (NA). GEN2 also encodes hGM-CSF, which may augment antitumor immunity by enhancing NA presentation to immune effector cells. GEN2 in combination with valganciclovir (an oral formulation of GCV) was evaluated in a dose-escalating Phase 1 clinical trial in 61 adult patients (pts) with an advanced solid tumor (NCT04313868), with serial assessment of PBMCs to detect any GEN2 integration and replication competent retrovirus (RCR). Methods: PBMCs were obtained in Cycle 1 (following 1st/3rd dose), prior to and 2 hours after Cycle 2, and thereafter at 6-month intervals for 15 years, or until death or withdrawal of consent. Digital droplet PCR (ddPCR) for psi and envelope gene sequences in extracted genomic DNA from PBMCs was used to detect vector genome integration and replication competent retrovirus (RCR), respectively. Results: All 82 samples obtained from the intravenous cohorts 1-12 were below LOD (Limit of Detection) for RCR. All results for integration were BLOQ (Below Limit of Quantitation), whereas 4 samples collected at two hours following the end of infusion were above LOD, likely resulting from non-integrated cDNA. GEN2 continues to be studied in clinical trials in adult patients with solid tumors. Per the 2020 FDA Guidance for Industry (Long Term Follow-Up After Administration of Human Gene Therapy Products), serial assessment of vector integration is mandated throughout a pt’s participation in a gene therapy clinical trial and for 15 years following the last dose. These guidance documents were originally conceived when gene therapy was developed for treatment of rare hereditary diseases in pediatric pts; however, adult pts enrolled in early-stage clinical trials for cancer typically do not have a prolonged life expectancy (BMC Cancer 2011 11:426). In the context of proper and warranted usage of pts’ blood for testing, attention should be drawn to the limited expectation for a 2nd malignancy within the lifespan of this pt population, and the absence of detectable RCR in cancer patients receiving retroviral vectors over decades. A recent review noted no evidence of RCR in 1,595 post-treatment PBMCs obtained from 60 clinical trials (Mol Ther 2023 31(3):801). Our results confirm that GEN2 also shows negligible genotoxic risk for gene therapy of cancer at doses tested to date. Citation Format: Alison L. Hannah, Noriyuki Kasahara, Li Liu, Allen Wang, Joe McNulty, Robert G. Johnson. Serial assessment of GEN2, a retroviral vector for gene transfer of an optimized thymidine kinase and GM-CSF, for genomic integration into peripheral blood mononuclear cells (PBMCs) in a Phase 1 clinical trial in adult patients with solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7250.

Clinical practice guidelines for gene therapy to treat hereditary hearing loss

AbstractHereditary deafness is a common neurosensory disorder, and 148 non‐syndromic deafness genes have been identified to date. Gene therapy has been used to treat a variety of genetic diseases, but no gene therapy drug for hereditary deafness has been approved for clinical use. At present, several clinical trials of gene therapy for hereditary deafness are underway. However, few normative documents have been issued to guide the standardization of gene therapy for hearing loss, and this document is the first global gene therapy guideline for hereditary hearing loss. The guidelines were jointly developed and drafted by experienced audiologists, virologists and biologists who are vigorously involved in inner ear gene therapy research in the Hearing, Speech and Communication Subsociety of Biophysical Society of China, Audiology Development Foundation Of China and Audiology Subsociety of Jiangsu Medical Association. These guidelines cover preclinical research and clinical practice of gene therapy for hereditary deafness, including indications, key points of pre‐clinical research, patient selection criteria, pre‐clinical preparation, drug efficacy, drug safety evaluation criteria, ethical review, etc. We hope that the guidelines will promote the standardization of clinical practice related to gene therapy for hereditary deafness in China and around the world.

Contract development and manufacturing organization selection: critical considerations that can make or break your cell and gene therapy development

Background aimsWith the increase in cell and gene therapy (CGT) clinical trials in recent years has come a subsequent increase in the number of contract development and manufacturing organizations (CDMOs). Successful transition from development and early-phase clinical trials to commercialization of a CGT product often depends on selecting the best-suited CDMO. However, many CGT companies are small biotech companies that lack expertise in the field or do not have experience selecting and transferring a process to a CDMO. MethodsGiven the interest in this topic, a roundtable with CGT developers and CDMO members at the 2023 annual meeting of the International Society of Cell and Gene Therapy Paris discussed these critical aspects of product development, including technical expertise, risk sharing and timing of partnerships. Results and ConclusionsHere, we'll analyze the considerations discussed by the panel and elaborate on other factors crucial for CGT development.

ShRNA Targeting Lentiviral Vector Minus-Strand Product Improves the Viral Titer During Viral Packaging.

Lentiviral vector (LVV) has been used as one of the common carriers for gene therapy in clinical trials. LVV-mediated clinical trials have being reported in successfully treating hundreds of β-thalassemia cases. These LVVs bear an inversely placed β-hemoglobin (HBB) gene expression cassette for preserving introns during the viral RNA packaging. Consequently, these LVVs often produce a small amount of negatively orientated transcript driven by its internal gene promoter and would lower the viral titer by the minus-strand complemented with the viral backbone. To overcome this problem, we designed shRNAs specifically target the minus-strand RNA driven by the LVV internal promoter that resulted in a notable increase in the viral titer. This report demonstrates a simple and positive mean for increasing the effectiveness for gene therapy with the LVV system.

Does gene therapies clinical research in rare diseases reflects the competitivity of the country: Example of France

Rare diseases are chronic, serious and generally genetic conditions affecting a small number of people, and their therapeutic management is a real challenge. They represent a considerable burden for patients, caregivers and society alike. Compared with existing symptomatic treatments, gene therapies represent a promising new approach aimed at treating these diseases by replacing a defective gene, or by abolishing or reviving a gene-derived function. France is considered one of the leading countries in the research and development of drugs for rare diseases, yet the position of French public and private stakeholders in the research and development of gene therapies for rare diseases at global and European level remains unclear. To answer this question, we used the GENOTRIAL FR database developed by OrphanDev to clarify France's involvement and competitiveness in this field. The results show that France is actively involved in gene therapy clinical trials, with a dense international collaboration network and solid expertise. However, the French medical infrastructure is mainly involved in clinical research on gene therapy candidates sponsored by several foreign countries. To a lesser extent, French public and private entities are also developing their own gene therapy candidates for various rare diseases, some of which have already reached advanced clinical phases. In conclusion, a number of technical and financial challenges need to be overcome if France is to maintain its position as a European and world leader and increase its contribution to reducing the economic and social burden of rare diseases by developing revolutionary and effective new therapies.

Results from GALILEO-1, a first-in-human clinical trial of FLT201 gene therapy in patients with Gaucher disease type 1

Results from GALILEO-1, a first-in-human clinical trial of FLT201 gene therapy in patients with Gaucher disease type 1

RGX-381: Interim results from the first-in-human clinical trial of an investigational gene therapy for the treatment of ocular manifestations of CLN2 Batten disease

RGX-381: Interim results from the first-in-human clinical trial of an investigational gene therapy for the treatment of ocular manifestations of CLN2 Batten disease

Advancements and future prospects of adeno-associated virus-mediated gene therapy for sensorineural hearing loss.

Sensorineural hearing loss (SNHL), a highly prevalent sensory impairment, results from a multifaceted interaction of genetic and environmental factors. As we continually gain insights into the molecular basis of auditory development and the growing compendium of deafness genes identified, research on gene therapy for SNHL has significantly deepened. Adeno-associated virus (AAV), considered a relatively secure vector for gene therapy in clinical trials, can deliver various transgenes based on gene therapy strategies such as gene replacement, gene silencing, gene editing, or gene addition to alleviate diverse types of SNHL. This review delved into the preclinical advances in AAV-based gene therapy for SNHL, spanning hereditary and acquired types. Particular focus is placed on the dual-AAV construction method and its application, the vector delivery route of mouse inner ear models (local, systemic, fetal, and cerebrospinal fluid administration), and the significant considerations in transforming from AAV-based animal model inner ear gene therapy to clinical implementation.

Mannose-coupled AAV2: A second-generation AAV vector for increased retinal gene therapy efficiency

Inherited retinal diseases are a leading and untreatable cause of blindness and are therefore candidate diseases for gene therapy. Recombinant vectors derived from adeno-associated virus (rAAV) are currently the most promising vehicles for in vivo therapeutic gene delivery to the retina. However, there is a need for novel AAV-based vectors with greater efficacy for ophthalmic applications, as underscored by recent reports of dose-related inflammatory responses in clinical trials of rAAV-based ocular gene therapies. Improved therapeutic efficacy of vectors would allow for decreases in the dose delivered, with consequent reductions in inflammatory reactions. Here, we describe the development of new rAAV vectors using bioconjugation chemistry to modify the rAAV capsid, thereby improving the therapeutic index. Covalent coupling of a mannose ligand, via the formation of a thiourea bond, to the amino groups of the rAAV capsid significantly increases vector transduction efficiency of both rat and nonhuman primate retinas. These optimized rAAV vectors have important implications for the treatment of a wide range of retinal diseases.

N-terminal titin fragment: a non-invasive, pharmacodynamic biomarker for microdystrophin efficacy

BackgroundMultiple clinical trials to assess the efficacy of AAV-directed gene transfer in participants with Duchenne muscular dystrophy (DMD) are ongoing. The success of these trials currently relies on standard functional outcome measures that may exhibit variability within and between participants, rendering their use as sole measures of drug efficacy challenging. Given this, supportive objective biomarkers may be useful in enhancing observed clinical results. Creatine kinase (CK) is traditionally used as a diagnostic biomarker of DMD, but its potential as a robust pharmacodynamic (PD) biomarker is difficult due to the wide variability seen within the same participant over time. Thus, there is a need for the discovery and validation of novel PD biomarkers to further support and bolster traditional outcome measures of efficacy in DMD.MethodPotential PD biomarkers in DMD participant urine were examined using a proteomic approach on the Somalogic platform. Findings were confirmed in both mdx mice and Golden Retriever muscular dystrophy (GRMD) dog plasma samples.ResultsChanges in the N-terminal fragment of titin, a well-known, previously characterized biomarker of DMD, were correlated with the expression of microdystrophin protein in mice, dogs, and humans. Further, titin levels were sensitive to lower levels of expressed microdystrophin when compared to CK.ConclusionThe measurement of objective PD biomarkers such as titin may provide additional confidence in the assessment of the mechanism of action and efficacy in gene therapy clinical trials of DMD.Trial registrationClinicalTrials.gov NCT03368742.

Advances in delivery systems for CRISPR/Cas-mediated cancer treatment: a focus on viral vectors and extracellular vesicles.

The delivery of CRISPR/Cas systems holds immense potential for revolutionizing cancer treatment, with recent advancements focusing on extracellular vesicles (EVs) and viral vectors. EVs, particularly exosomes, offer promising opportunities for targeted therapy due to their natural cargo transport capabilities. Engineered EVs have shown efficacy in delivering CRISPR/Cas components to tumor cells, resulting in inhibited cancer cell proliferation and enhanced chemotherapy sensitivity. However, challenges such as off-target effects and immune responses remain significant hurdles. Viral vectors, including adeno-associated viruses (AAVs) and adenoviral vectors (AdVs), represent robust delivery platforms for CRISPR/Cas systems. AAVs, known for their safety profile, have already been employed in clinical trials for gene therapy, demonstrating their potential in cancer treatment. AdVs, capable of infecting both dividing and non-dividing cells, offer versatility in CRISPR/Cas delivery for disease modeling and drug discovery. Despite their efficacy, viral vectors present several challenges, including immune responses and off-target effects. Future directions entail refining delivery systems to enhance specificity and minimize adverse effects, heralding personalized and effective CRISPR/Cas-mediated cancer therapies. This article underscores the importance of optimized delivery mechanisms in realizing the full therapeutic potential of CRISPR/Cas technology in oncology. As the field progresses, addressing these challenges will be pivotal for translating CRISPR/Cas-mediated cancer treatments from bench to bedside.

Family and caregiver perspectives on gene therapy for Rett syndrome

IntroductionRett syndrome (RTT) is a neurodevelopmental disorder that primarily affects females and can result in cognitive impairment, seizures, spasticity, breathing problems, gastrointestinal issues, motor impairment, and behavioral concerns. Gene therapy may be a potential treatment in the future as clinical trials are underway. AimThis study evaluates the attitudes and opinions of family members and caregivers of patients with RTT towards gene therapy using a mixed-method approach. MethodsSixty-six caregivers of individuals with RTT completed an online survey asking about their previous experience in research and questions about their understanding of gene therapy, their expectations, as well as their hopes and concerns for treating RTT. Ten respondents also participated in online focus groups, which were evaluated using thematic analysis. ResultsOverall, most participants (95.5 %) had heard about gene therapy. More than half of the respondents (68.2 %) reported being somewhat knowledgeable about gene therapy, and 18.2 % reported no understanding of gene therapy. When asked the highest level of risk they would accept when enrolling the individual with Rett syndrome in a gene therapy clinical trial, 47.7 % stated they would accept a low risk, and 7.7 % indicated they would accept a high risk. In the focus groups, individuals discussed barriers to gene therapy, their hopes and concerns regarding gene therapy treatment, and how they would like to receive information about future research and therapies. Participants had concerns about possible side effects of gene therapy, including physical and mental harm, a potential decrease in quality of life, whether individuals with RTT would want to “change who they are,” and the irreversibility of the treatment. ConclusionAlthough most participants have heard about gene therapy, many caregivers would only accept a low risk when considering gene therapy for the individual with RTT. This could be in part due to concerns about side effects and potential harm to the patient as well as anticipated barriers related to cost and accessibility to appropriate follow-up care. Understanding caregiver opinions is important in setting goals and evaluating the success of current studies, identifying and addressing barriers to trials and treatment, and in the development and implementation of educational resources for gene therapy in RTT.

Liver-directed gene therapy for inherited metabolic diseases.

Gene therapy clinical trials are rapidly expanding for inherited metabolic liver diseases whilst two gene therapy products have now been approved for liver based monogenic disorders. Liver-directed gene therapy has recently become an option for treatment of haemophilias and is likely to become one of the favoured therapeutic strategies for inherited metabolic liver diseases in the near future. In this review, we present the different gene therapy vectors and strategies for liver-targeting, including gene editing. We highlight the current development of viral and nonviral gene therapy for a number of inherited metabolic liver diseases including urea cycle defects, organic acidaemias, Crigler-Najjar disease, Wilson disease, glycogen storage disease Type Ia, phenylketonuria and maple syrup urine disease. We describe the main limitations and open questions for further gene therapy development: immunogenicity, inflammatory response, genotoxicity, gene therapy administration in a fibrotic liver. The follow-up of a constantly growing number of gene therapy treated patients allows better understanding of its benefits and limitations and provides strategies to design safer and more efficacious treatments. Undoubtedly, liver-targeting gene therapy offers a promising avenue for innovative therapies with an unprecedented potential to address the unmet needs of patients suffering from inherited metabolic diseases.