Clinical applications of gene therapy for rare diseases: A review

Antisense oligonucleotides and their applications in rare neurological diseases

Rare diseases affect almost 500 million people globally, predominantly impacting children and often leading to significantly impaired quality of life and high treatment costs. While significant contributions have been made to develop effective treatments for those with rare diseases, more rapid drug discovery strategies are needed. Therapeutic antisense oligonucleotides can modulate target gene expression with high specificity through various mechanisms determined by base sequences and chemical modifications; and have shown efficacy in clinical trials for a few rare neurological conditions. Therefore, this review will focus on the applications of antisense oligonucleotides, in particular splice-switching antisense oligomers as promising therapeutics for rare neurological diseases, with key examples of Duchenne muscular dystrophy and spinal muscular atrophy. Challenges and future perspectives in developing antisense therapeutics for rare conditions including target discovery, antisense chemical modifications, animal models for therapeutic validations, and clinical trial designs will also be briefly discussed.

Construction of pVAX-1-based linear covalently closed vector with improved transgene expression

INTRODUCTION

This study presents a Mammalian Linear Expression System (MLES), a linear covalently closed (LCC) vector based on pVAX-1. The purpose of this system was to improve gene expression in mammalian cells and to test the efficacy of MLES in transient transfection and transgene expression using in vitro and in vivo models. Additionally, we aimed to evaluate potential inflammatory responses in vivo.

MATERIALS AND METHODS

MLES was developed by modifying pVAX-1, and the construct was confirmed by gel electrophoresis. Lipofectamine®2000 was used to assess the transfection efficiency and expression of MLES in various cell lines. In vivo studies were conducted in mice injected with MLES/EGFP, and the resulting transfection efficiency, gene expression, and inflammatory responses were analyzed.

RESULTS

MLES exhibited higher transfection efficiency and expression levels compared to pVAX-1 when tested on HEK-293, CHO-K1, and NIH-3T3 cells. When tested in vivo, MLES/EGFP showed elevated expression in the heart, kidney, liver, and spleen compared with pVAX-1/EGFP. Minimal changes are observed in the lungs. Additionally, MLES induced a reduced inflammatory response in mice compared with pVAX-1/EGFP.

CONCLUSIONS

MLES offer improved transfection efficiency and reduced inflammation, representing a significant advancement in gene therapy and recombinant protein production. Further research on MLES-mediated gene expression and immune modulation will enhance gene therapy strategies.

Burden of rare genetic disorders in India: twenty-two years' experience of a tertiary centre

BACKGROUND

Rare disorders comprise of ~ 7500 different conditions affecting multiple systems. Diagnosis of rare diseases is complex due to dearth of specialized medical professionals, testing labs and limited therapeutic options. There is scarcity of data on the prevalence of rare diseases in different populations. India being home to a large population comprising of 4600 population groups, of which several thousand are endogamous, is likely to have a high burden of rare diseases. The present study provides a retrospective overview of a cohort of patients with rare genetic diseases identified at a tertiary genetic test centre in India.

RESULTS

Overall, 3294 patients with 305 rare diseases were identified in the present study cohort. These were categorized into 14 disease groups based on the major organ/ organ system affected. Highest number of rare diseases (D = 149/305, 48.9%) were identified in the neuromuscular and neurodevelopmental (NMND) group followed by inborn errors of metabolism (IEM) (D = 47/305; 15.4%). Majority patients in the present cohort (N = 1992, 61%) were diagnosed under IEM group, of which Gaucher disease constituted maximum cases (N = 224, 11.2%). Under the NMND group, Duchenne muscular dystrophy (N = 291/885, 32.9%), trinucleotide repeat expansion disorders (N = 242/885; 27.3%) and spinal muscular atrophy (N = 141/885, 15.9%) were the most common. Majority cases of β-thalassemia (N = 120/149, 80.5%) and cystic fibrosis (N = 74/75, 98.7%) under the haematological and pulmonary groups were observed, respectively. Founder variants were identified for Tay-Sachs disease and mucopolysaccharidosis IVA diseases. Recurrent variants for Gaucher disease (GBA:c.1448T > C), β-thalassemia (HBB:c.92.+5G > C), non-syndromic hearing loss (GJB2:c.71G > A), albinism (TYR:c.832 C > T), congenital adrenal hyperplasia (CYP21A2:c.29-13 C > G) and progressive pseudo rheumatoid dysplasia (CCN6:c.298T > A) were observed in the present study.

CONCLUSION

The present retrospective study of rare disease patients diagnosed at a tertiary genetic test centre provides first insight into the distribution of rare genetic diseases across the country. This information will likely aid in drafting future health policies, including newborn screening programs, development of target specific panel for affordable diagnosis of rare diseases and eventually build a platform for devising novel treatment strategies for rare diseases.

Manufacturing Cell and Gene Therapies: Challenges in Clinical Translation

The safety and efficacy of both cell and gene therapies have been demonstrated in numerous preclinical and clinical trials. Chimeric antigen receptor T (CAR-T) cell therapy, which leverages the technologies of both cell and gene therapies, has also shown great promise for treating various cancers. Advancements in pertinent fields have also highlighted challenges faced while manufacturing cell and gene therapy products. Potential problems and obstacles must be addressed to ease the clinical translation of individual therapies. Literature reviews of representative cell-based, gene-based, and cell-based gene therapies with regard to their general manufacturing processes, the challenges faced during manufacturing, and QC specifications are limited. We review the general manufacturing processes of cell and gene therapies, including those involving mesenchymal stem cells, viral vectors, and CAR-T cells. The complexities associated with the manufacturing processes and subsequent QC/validation processes may present challenges that could impede the clinical progression of the products. This article addresses these potential challenges. Further, we discuss the use of the manufacturing model and its impact on cell and gene therapy.

Impaired polyamine metabolism causes behavioral and neuroanatomical defects in a mouse model of Snyder-Robinson syndrome

Snyder-Robinson syndrome (SRS) is a rare X-linked recessive disorder caused by a mutation in the SMS gene, which encodes spermine synthase, and aberrant polyamine metabolism. SRS is characterized by intellectual disability, thin habitus, seizure, low muscle tone/hypotonia and osteoporosis. Progress towards understanding and treating SRS requires a model that recapitulates human gene variants and disease presentations. Here, we evaluated molecular and neurological presentations in the G56S mouse model, which carries a missense mutation in the Sms gene. The lack of SMS protein in the G56S mice resulted in increased spermidine/spermine ratio, failure to thrive, short stature and reduced bone density. They showed impaired learning capacity, increased anxiety, reduced mobility and heightened fear responses, accompanied by reduced total and regional brain volumes. Furthermore, impaired mitochondrial oxidative phosphorylation was evident in G56S cerebral cortex, G56S fibroblasts and Sms-null hippocampal cells, indicating that SMS may serve as a future therapeutic target. Collectively, our study establishes the suitability of the G56S mice as a preclinical model for SRS and provides a set of molecular and functional outcome measures that can be used to evaluate therapeutic interventions for SRS.

Studying the ssDNA loaded adeno-associated virus aggregation using coarse-grained molecular dynamics simulations

The aggregation of adeno-associated viral (AAV) capsids in an aqueous environment was investigated via coarse-grained molecular dynamics (CG-MD) simulations. The primary driving force and mechanism of the aggregation were investigated with or without single-strand DNA (ssDNA) loaded at various process temperatures. Capsid aggregation appeared to involve multiple residue interactions (i.e., hydrophobic, polar and charged residues) leading to complex protein aggregation. In addition, two aggregation mechanisms (i.e., the fivefold face-to-face contact and the edge-to-edge contact) were identified from this study. The ssDNA with its asymmetric structure could be the reason for destabilizing protein subunits and enhancing the interaction between the charged residues, and further result in the non-reversible face-to-face contact. At higher temperature, the capsid structure was found to be unstable with the significant size expansion of the loaded ssDNA which could be attributed to reduced number of intramolecular hydrogen bonds, the increased conformational deviations of protein subunits and the higher residue fluctuations. The CG-MD model was further validated with previous experimental and simulation data, including the full capsid size measurement and the capsid internal pressure. Thus, a good understanding of AAV capsid aggregation, instability and the role of ssDNA were revealed by applying the developed computational model.

Effective Gene Therapy for Metachromatic Leukodystrophy Achieved with Minimal Lentiviral Genomic Integrations

Metachromatic leukodystrophy (MLD) is a fatal lysosomal storage disease (LSD) characterized by the deficient enzymatic activity of arylsulfatase A (ARSA). Combined autologous hematopoietic stem cell transplant (HSCT) with lentiviral (LV) based gene therapy has great potential to treat MLD. However, if enzyme production is inadequate, this could result in continued loss of motor function, implying a high vector copy number (VCN) requirement for optimal enzymatic output. This may place children at increased risk for genomic toxicity due to higher VCN. We increased the expression of ARSA cDNA at single integration by generating novel LVs, optimizing ARSA expression, and enhancing safety. In addition, our vectors achieved optimal transduction in mouse and human HSC with minimal multiplicity of infection (MOI). Our top-performing vector (EA1) showed at least 4X more ARSA activity than the currently EU-approved vector and a superior ability to secrete vesicle-associated ARSA, a critical modality to transfer functional enzymes from microglia to oligodendrocytes. Three-month-old Arsa -KO MLD mice transplanted with Arsa -KO BM cells transduced with 0.6 VCN of EA1 demonstrated behavior and CNS histology matching WT mice. Our novel vector boosts efficacy while improving safety as a robust approach for treating early symptomatic MLD patients.

Focused ultrasound gene delivery for the treatment of neurological disorders

The transformative potential of gene therapy has been demonstrated in humans. However, there is an unmet need for non-invasive targeted gene delivery and regulation in the treatment of brain disorders. Transcranial focused ultrasound (FUS) has gained tremendous momentum to address these challenges. FUS non-invasively modulates brain cells and their environment, and is a powerful tool to facilitate gene delivery across the blood-brain barrier (BBB) with millimeter precision and promptly regulate transgene expression. This review highlights technical aspects of FUS-mediated gene therapies for the central nervous system (CNS) and lessons learned from discoveries in other organs. Understanding the possibilities and remaining obstacles of FUS-mediated gene therapy will be necessary to harness remarkable technologies and create life-changing treatments for neurological disorders.

Recent landscape and trends for industry-sponsored pediatric clinical trials in China from 2013 to 2022

Importance

Pediatric medication is a challenging issue globally. Promoting trials of medications for children and implementing measures to encourage innovation for addressing unmet medical and health needs are important.

Objective

To explore the recent landscape of pediatric clinical trials of new investigational drugs conducted by pharmaceutical enterprises in China from 2013 to 2022 to provide insight into pediatric drug development in the pharmaceutical industry and regulatory policy formulation.

Methods

We performed a cross-sectional observational investigation of pediatric clinical trials registered from January 1, 2013, to December 31, 2022, on the Registration and Information Disclosure Platform for Drug Clinical Trials, the official registration platform established in 2013 for trials of new investigational drugs initiated by biopharmaceutical enterprises. Trials that included pediatric participants (under 18 years old) were retrieved, and their relevant characteristics were extracted and analyzed.

Results

In total, 895 pediatric clinical trials were collected, accounting for 5.1% of the total registered clinical trials initiated prior to January 1, 2023. The overall average annual growth rate for the number of pediatric clinical trials was 12% (P < 0.001). Phase III trials accounted for the highest proportion (49.1%, 439). Of the 895 trials included, 736 (82.2%) were domestic trials, and 159 (17.8%) were international multicenter trials. In terms of tested drugs, investigations of biological products accounted for the largest proportion of trials (67.4%, 603). Among pediatric clinical trials, studies of vaccines accounted for the largest proportion of trials (41.0%, 367), followed by trials for rare diseases (17.2%, 154). Furthermore, geographical distribution analysis revealed that the largest and smallest numbers of trials were conducted in North China (35.7%, 320) and Northeast China (0.8%, 7), respectively.

Interpretation

The growth trends for industry-sponsored clinical trials involving children illustrate the progress and increasing capability of pediatric drug development achieved in China since 2013. Current challenges and potential areas of focus for policymakers and stakeholders include investigating orphan drugs for rare diseases according to the unique epidemiological characteristics of Chinese children, expanding the scope of pediatric clinical trials, and improving the uneven geographical distribution of leading research centers.

Development of Cell and Gene Therapies for Clinical Use in the US and EU: Summary of Regulatory Guidelines

Recent decades have seen advancements in the management and treatment of difficultto- treat diseases such as cancer. A special class of therapeutics called cell and gene therapy has been introduced in the past 10 years. Cell and gene therapy products have strengthened the treatment options for life-threatening diseases with unmet clinical needs and also provided the possibility of a potential cure for the disease in some of the patients. Cell and gene therapy products are gaining recognition, and the interest in clinical development of cell and gene therapy products is increasing. Moreover, as the class of cell and gene therapy products is relatively new, there is a limited regulatory experience in the development, and the developers of the cell and gene therapy products can often be puzzled with an array of questions on regulations. The current review intends to provide a basic understanding of regulatory guidelines from the FDA and EMA that are applicable to cell and gene therapy products. Essentials such as which office is responsible for the evaluation of applications, which regulatory class/pathway is appropriate for development, and what are the quality, nonclinical and clinical studies that are needed to support the application are discussed in the article. In addition, a summary of regulatory designations and the post-approval requirements, such as Risk Evaluation and Mitigation Strategies (REMS) and long-term follow- up, is included in the article. Developers (referred to as 'sponsors' in this article) of cell and gene therapies can use the respective guidance documents and other specific review articles cited in this review for detailed information on the topics.

Exploration of the Noncoding Genome for Human-Specific Therapeutic Targets-Recent Insights at Molecular and Cellular Level

While it is well known that 98-99% of the human genome does not encode proteins, but are nevertheless transcriptionally active and give rise to a broad spectrum of noncoding RNAs [ncRNAs] with complex regulatory and structural functions, specific functions have so far been assigned to only a tiny fraction of all known transcripts. On the other hand, the striking observation of an overwhelmingly growing fraction of ncRNAs, in contrast to an only modest increase in the number of protein-coding genes, during evolution from simple organisms to humans, strongly suggests critical but so far essentially unexplored roles of the noncoding genome for human health and disease pathogenesis. Research into the vast realm of the noncoding genome during the past decades thus lead to a profoundly enhanced appreciation of the multi-level complexity of the human genome. Here, we address a few of the many huge remaining knowledge gaps and consider some newly emerging questions and concepts of research. We attempt to provide an up-to-date assessment of recent insights obtained by molecular and cell biological methods, and by the application of systems biology approaches. Specifically, we discuss current data regarding two topics of high current interest: (1) By which mechanisms could evolutionary recent ncRNAs with critical regulatory functions in a broad spectrum of cell types (neural, immune, cardiovascular) constitute novel therapeutic targets in human diseases? (2) Since noncoding genome evolution is causally linked to brain evolution, and given the profound interactions between brain and immune system, could human-specific brain-expressed ncRNAs play a direct or indirect (immune-mediated) role in human diseases? Synergistic with remarkable recent progress regarding delivery, efficacy, and safety of nucleic acid-based therapies, the ongoing large-scale exploration of the noncoding genome for human-specific therapeutic targets is encouraging to proceed with the development and clinical evaluation of novel therapeutic pathways suggested by these research fields.

Application of Electrophysiology in Non-Macular Inherited Retinal Dystrophies

Inherited retinal dystrophies encompass a diverse group of disorders affecting the structure and function of the retina, leading to progressive visual impairment and, in severe cases, blindness. Electrophysiology testing has emerged as a valuable tool in assessing and diagnosing those conditions, offering insights into the function of different parts of the visual pathway from retina to visual cortex and aiding in disease classification. This review provides an overview of the application of electrophysiology testing in the non-macular inherited retinal dystrophies focusing on both common and rare variants, including retinitis pigmentosa, progressive cone and cone-rod dystrophy, bradyopsia, Bietti crystalline dystrophy, late-onset retinal degeneration, and fundus albipunctatus. The different applications and limitations of electrophysiology techniques, including multifocal electroretinogram (mfERG), full-field ERG (ffERG), electrooculogram (EOG), pattern electroretinogram (PERG), and visual evoked potential (VEP), in the diagnosis and management of these distinctive phenotypes are discussed. The potential for electrophysiology testing to allow for further understanding of these diseases and the possibility of using these tests for early detection, prognosis prediction, and therapeutic monitoring in the future is reviewed.