AAV Vector Immunogenicity in Humans: A Long Journey to Successful Gene Transfer

Therapeutic advances in neural regeneration for Huntington's disease

Huntington's disease is a neurodegenerative disease caused by the expansion mutation of a cytosine-adenine-guanine triplet in the exon 1 of the HTT gene which is responsible for the production of the huntingtin (Htt) protein. In physiological conditions, Htt is involved in many cellular processes such as cell signaling, transcriptional regulation, energy metabolism regulation, DNA maintenance, axonal trafficking, and antiapoptotic activity. When the genetic alteration is present, the production of a mutant version of Htt (mHtt) occurs, which is characterized by a plethora of pathogenic activities that, finally, lead to cell death. Among all the cells in which mHtt exerts its dangerous activity, the GABAergic Medium Spiny Neurons seem to be the most affected by the mHtt-induced excitotoxicity both in the cortex and in the striatum. However, as the neurodegeneration proceeds ahead the neuronal loss grows also in other brain areas such as the cerebellum, hypothalamus, thalamus, subthalamic nucleus, globus pallidus, and substantia nigra, determining the variety of symptoms that characterize Huntington's disease. From a clinical point of view, Huntington's disease is characterized by a wide spectrum of symptoms spanning from motor impairment to cognitive disorders and dementia. Huntington's disease shows a prevalence of around 3.92 cases every 100,000 worldwide and an incidence of 0.48 new cases every 100,000/year. To date, there is no available cure for Huntington's disease. Several treatments have been developed so far, aiming to reduce the severity of one or more symptoms to slow down the inexorable decline caused by the disease. In this context, the search for reliable strategies to target the different aspects of Huntington's disease become of the utmost interest. In recent years, a variety of studies demonstrated the detrimental role of neuronal loss in Huntington's disease condition highlighting how the replacement of lost cells would be a reasonable strategy to overcome the neurodegeneration. In this view, numerous have been the attempts in several preclinical models of Huntington's disease to evaluate the feasibility of invasive and non-invasive approaches. Thus, the aim of this review is to offer an overview of the most appealing approaches spanning from stem cell-based cell therapy to extracellular vesicles such as exosomes in light of promoting neurogenesis, discussing the results obtained so far, their limits and the future perspectives regarding the neural regeneration in the context of Huntington's disease.

Unravelling the essential elements for recombinant adeno-associated virus (rAAV) production in animal cell-based platforms

Recombinant adeno-associated viruses (rAAVs) stand at the forefront of gene therapy applications, holding immense significance for their safe and efficient gene delivery capabilities. The constantly increasing and unmet demand for rAAVs underscores the need for a more comprehensive understanding of AAV biology and its impact on rAAV production. In this literature review, we delved into AAV biology and rAAV manufacturing bioprocesses, unravelling the functions and essentiality of proteins involved in rAAV production. We discuss the interconnections between these proteins and how they affect the choice of rAAV production platform. By addressing existing inconsistencies, literature gaps and limitations, this review aims to define a minimal set of genes that are essential for rAAV production, providing the potential to advance rAAV biomanufacturing, with a focus on minimizing the genetic load within rAAV-producing cells.

An Online Native Mass Spectrometry Approach for Fast, Sensitive, and Quantitative Assessment of Adeno-Associated Virus Capsid Content Ratios

Adeno-associated viruses (AAVs) have emerged as a leading platform for in vivo therapeutic gene delivery and offer tremendous potential in the treatment and prevention of human disease. The fast-paced development of this growing class of therapeutics, coupled with their intrinsic structural complexity, places a high demand on analytical methods capable of efficiently monitoring product quality to ensure safety and efficacy, as well as to support manufacturing and process optimization. Importantly, the presence and relative abundance of both empty and partially filled AAV capsid subpopulations are of principal concern, as these represent the most common product-related impurities in AAV manufacturing and have a direct impact on therapeutic potential. For this reason, the capsid content, or ratio of empty and partial capsids to those packaged with the full-length therapeutic genome, has been identified by regulatory agencies as a critical quality attribute (CQA) that must be carefully controlled to meet clinical specifications. Established analytical methods for the quantitation of capsid content ratios often suffer from long turnaround times, low throughput, and high sample demands that are not well-suited to the narrow timelines and limited sample availability typical of process development. In this study, we present an integrated online native mass spectrometry platform that aims to minimize sample handling and maximize throughput and robustness for rapid and sensitive quantitation of AAV capsid content ratios. The primary advantages of this platform for AAV analysis include the ability to perform online buffer exchange under low flow conditions to maintain sample stability with minimal sample dilution, as well as the ability to achieve online charge reduction via dopant-modified desolvation gas. By exploiting the latter, enhanced spectral resolution of signals arising from empty, partial, and full AAV capsids was accomplished in the m/z domain to facilitate improved spectral interpretation and quantitation that correlated well with the industry standard analytical ultracentrifugation (AUC) method for capsid content ratio determination. The utility of this approach was further demonstrated in several applications, including the rapid and universal screening of different AAV serotypes, evaluation of capsid content for in-process samples, and the monitoring of capsid stability when subjected to thermal stress conditions.

Innate Immune Sensing of AAV Vectors

Adeno-associated virus (AAV) based viral vectors are widely used in human gene therapy and form the basis of approved treatments for several genetic diseases. Immune responses to vector and transgene product, however, substantially complicate these applications in clinical practice. The role of innate immune recognition of AAV vectors was initially unclear, given that inflammatory responses early after vector administration were typically mild in animal models, including NHP studies. However, more recent research continues to identify innate immune pathways that are triggered by AAV vectors and that serve to provide activation signals for antigen-presenting cells and initiation of adaptive immune responses. Sensing of the AAV genome by the endosomal DNA receptor toll-like receptor 9 (TLR9) promotes early inflammatory response and interferon expression. Thus, activation of the TLR9>MyD88 pathway in plasmacytoid dendritic cells (pDCs) leads to the conditioning of antigen cross-presenting DCs via type I interferon (IFN I) and ultimately CD8+ T cell activation. Alternatively, pDCs may also promote CD8+ T cell responses in a TLR9-independent fashion by the production of IL-1 cytokines, thereby activating the IL-1R1>MyD88 signaling pathway. AAV can induce cytokine expression in monocyte-derived DCs, which in turn increases antibody formation. Binding of AAV capsid to complement components likely further elevates B cell activation. At high systemic vector doses in humans, AAV vectors can trigger complement activation, with contributions by classic and alternative pathways, leading to severe toxicities. Finally, evidence for activation of TLR2 by the capsid and of additional innate receptors for nucleic acids has been presented. These observations show that AAV vectors can initiate several and likely redundant innate immune pathways resulting in an exaggerated adaptive immune response.

Identifying Viral Vector Characteristics by Nanopore Sensing

Using viral vectors as gene delivery vehicles for gene therapy necessitates their quality control. Here, we report on nanopore sensing for nondestructively inspecting genomes inside the nanoscale cargoes at the single-molecule level. Using ionic current measurements, we motion-tracked the adeno-associated virus (AAV) vectors as they translocated through a solid-state nanopore. Considering the varying contributions of the electrophoretic forces from the negatively charged internal polynucleotides of different lengths, the nanocargoes carrying longer DNA moved more slowly in the nanochannel. Moreover, ion blockage characteristics revealed their larger volume by up to approximately 3600 nm3 in proportion to the length of single-stranded DNA packaged inside, thereby allowing electrical discriminations of AAV vectors by the gene-derived physical features. The present findings can be a promising tool for the enhanced quality control of AAV products by enabling the screening of empty and intermediate vectors at the single-particle level.

Liver gene transfer for metabolite detoxification in inherited metabolic diseases

Inherited metabolic disorders (IMDs) are a growing group of genetic diseases caused by defects in enzymes that mediate cellular metabolism, often resulting in the accumulation of toxic substrates. The liver is a highly metabolically active organ that hosts several thousands of chemical reactions. As such, it is an organ frequently affected in IMDs. In this article, we review current approaches for liver-directed gene-based therapy aimed at metabolite detoxification in a variety of IMDs. Moreover, we discuss current unresolved challenges in gene-based therapies for IMDs.

Durable transgene expression and efficient re-administration after rAAV2.5T-mediated fCFTRΔR gene delivery to adult ferret lungs

The dosing interval for effective recombinant adeno-associated virus (rAAV)-mediated gene therapy of cystic fibrosis lung disease remains unknown. Here, we assessed the durability of rAAV2.5T-fCFTRΔR-mediated transgene expression and neutralizing antibody (NAb) responses in lungs of adult wild-type ferrets. Within the first 3 months following rAAV2.5T-fCFTRΔR delivery to the lung, CFTRΔR transgene expression declined ∼5.6-fold and then remained stable to 5 months at ∼26% the level of endogenous CFTR. rAAV NAbs in the plasma and bronchoalveolar lavage fluid (BALF) peaked at 21 days, coinciding with peak ELISpot T cell responses to AAV capsid peptides, after which both responses declined and remained stable at 4-5 months post dosing. Administration of reporter vector rAAV2.5T-gLuc (gaussia luciferase) at 5 months following rAAV2.5T-fCFTRΔR dosing gave rise to similar levels of gLuc expression in the BALF as observed in age-matched reporter-only controls, demonstrating that residual BALF NAbs were functionally insignificant. Notably, the second vector administration led to a 2.6-fold greater ELISpot T cell response and ∼2.3-fold decline in fCFTRΔR mRNA and vector genomes derived from the initial rAAV2.5T-fCFTRΔR administration, suggesting selective destruction of transduced cells from the first vector dose. These findings provide insights into humoral and cellular immune response to rAAV that may be useful for optimizing gene therapy to the cystic fibrosis lung.

Strategies for enhanced gene delivery to the central nervous system

The delivery of genes to the central nervous system (CNS) has been a persistent challenge due to various biological barriers. The blood-brain barrier (BBB), in particular, hampers the access of systemically injected drugs to parenchymal cells, allowing only a minimal percentage (<1%) to pass through. Recent scientific insights highlight the crucial role of the extracellular space (ECS) in governing drug diffusion. Taking into account advancements in vectors, techniques, and knowledge, the discussion will center on the most notable vectors utilized for gene delivery to the CNS. This review will explore the influence of the ECS - a dynamically regulated barrier-on drug diffusion. Furthermore, we will underscore the significance of employing remote-control technologies to facilitate BBB traversal and modulate the ECS. Given the rapid progress in gene editing, our discussion will also encompass the latest advances focused on delivering therapeutic editing in vivo to the CNS tissue. In the end, a brief summary on the impact of Artificial Intelligence (AI)/Machine Learning (ML), ultrasmall, soft endovascular robots, and high-resolution endovascular cameras on improving the gene delivery to the CNS will be provided.

Optimization of systemic AAV9 gene therapy in Niemann-Pick disease type C1 mice

Niemann-Pick disease, type C1 (NPC1) is a rare, fatal neurodegenerative disorder caused by pathological variants in NPC1, which encodes a lysosomal cholesterol transport protein. There are no FDA approved treatments for this disorder. Both systemic and central nervous system delivery of AAV9-hNPC1 have shown significant disease amelioration in NPC1 murine models. To assess the impact of dose and window of therapeutic efficacy in Npc1 m1N mice, we systemically administered three different doses of AAV9-hNPC1 at 4 weeks old and the medium dose at pre-, early, and post-symptomatic timepoints. Higher vector doses and treatment earlier in life were associated with enhanced transduction in the nervous system and resulted in significantly increased lifespan. Similar beneficial effects were noted after gene therapy in Npc1 I1061T mice, a model that recapitulates a common human hypomorphic variant. Our findings help define dose ranges, treatment ages, and efficacy in severe and hypomorphic models of NPC1 deficiency and suggest that earlier delivery of AAV9-hNPC1 in a pre-symptomatic disease state is likely to yield optimal outcomes in individuals with NPC1.

Pancreas-directed AAV8-hSPINK1 gene therapy safely and effectively protects against pancreatitis in mice

OBJECTIVE

Currently, there is no cure for chronic pancreatitis (CP). Germline loss-of-function variants in SPINK1 (encoding trypsin inhibitor) are common in patients with CP and are associated with acute attacks and progression of the disease. This preclinical study was conducted to explore the potential of adeno-associated virus type 8 (AAV8)-mediated overexpression of human SPINK1 (hSPINK1) for pancreatitis therapy in mice.

DESIGN

A capsid-optimised AAV8-mediated hSPINK1 expression vector (AAV8-hSPINK1) to target the pancreas was constructed. Mice were treated with AAV8-hSPINK1 by intraperitoneal injection. Pancreatic transduction efficiency and safety of AAV8-hSPINK1 were dynamically evaluated in infected mice. The effectiveness of AAV8-hSPINK1 on pancreatitis prevention and treatment was studied in three mouse models (caerulein-induced pancreatitis, pancreatic duct ligation and Spink1 c.194+2T>C mouse models).

RESULTS

The constructed AAV8-hSPINK1 vector specifically and safely targeted the pancreas, had low organ tropism for the heart, lungs, spleen, liver and kidneys and had a high transduction efficiency (the optimal expression dose was 2×1011 vg/animal). The expression and efficacy of hSPINK1 peaked at 4 weeks after injection and remained at significant level for up to at least 8 weeks. In all three mouse models, a single dose of AAV8-hSPINK1 before disease onset significantly alleviated the severity of pancreatitis, reduced the progression of fibrosis, decreased the levels of apoptosis and autophagy in the pancreas and accelerated the pancreatitis recovery process.

CONCLUSION

One-time injection of AAV8-hSPINK1 safely targets the pancreas with high transduction efficiency and effectively ameliorates pancreatitis phenotypes in mice. This approach is promising for the prevention and treatment of CP.

Bilateral gene therapy in children with autosomal recessive deafness 9: single-arm trial results

Gene therapy is a promising approach for hereditary deafness. We recently showed that unilateral AAV1-hOTOF gene therapy with dual adeno-associated virus (AAV) serotype 1 carrying human OTOF transgene is safe and associated with functional improvements in patients with autosomal recessive deafness 9 (DFNB9). The protocol was subsequently amended and approved to allow bilateral gene therapy administration. Here we report an interim analysis of the single-arm trial investigating the safety and efficacy of binaural therapy in five pediatric patients with DFNB9. The primary endpoint was dose-limiting toxicity at 6 weeks, and the secondary endpoint included safety (adverse events) and efficacy (auditory function and speech perception). No dose-limiting toxicity or serious adverse event occurred. A total of 36 adverse events occurred. The most common adverse events were increased lymphocyte counts (6 out of 36) and increased cholesterol levels (6 out of 36). All patients had bilateral hearing restoration. The average auditory brainstem response threshold in the right (left) ear was >95 dB (>95 dB) in all patients at baseline, and the average auditory brainstem response threshold in the right (left) ear was restored to 58 dB (58 dB) in patient 1, 75 dB (85 dB) in patient 2, 55 dB (50 dB) in patient 3 at 26 weeks, and 75 dB (78 dB) in patient 4 and 63 dB (63 dB) in patient 5 at 13 weeks. The speech perception and the capability of sound source localization were restored in all five patients. These results provide preliminary insights on the safety and efficacy of binaural AAV gene therapy for hereditary deafness. The trial is ongoing with longer follow-up to confirm the safety and efficacy findings. Chinese Clinical Trial Registry registration: ChiCTR2200063181 .

Clinical Pharmacology Perspective on Development of Adeno-Associated Virus Vector-Based Retina Gene Therapy

Adeno-associated virus (AAV) vector-based gene therapy is an innovative modality being increasingly investigated to treat diseases by modifying or replacing defective genes or expressing therapeutic entities. With its unique anatomic and physiological characteristics, the eye constitutes a very attractive target for gene therapy. Specifically, the ocular space is easily accessible and is generally considered "immune-privileged" with a low risk of systemic side effects following local drug administration. As retina cells have limited cellular turnover, a one-time gene delivery has the potential to provide long-term transgene expression. Despite the initial success with voretigene neparvovec (Luxturna), the first approved retina gene therapy, there are still challenges to be overcome for successful clinical development of these products and scientific questions to be answered. The current review paper aims to integrate published experience learned thus far for AAV-based retina gene therapy related to preclinical to clinical translation; first-in-human dose selection; relevant bioanalytical assays and strategies; clinical development considerations including trial design, biodistribution and vector shedding, immunogenicity, transgene expression, and pediatric populations; opportunities for model-informed drug development; and regulatory perspectives. The information presented herein is intended to serve as a guide to inform the clinical development strategy for retina gene therapy with a focus on clinical pharmacology.

Duchenne and Becker muscular dystrophy: Cellular mechanisms, image analysis, and computational models: A review

The muscle is the principal tissue that is capable to transform potential energy into kinetic energy. This process is due to the transformation of chemical energy into mechanical energy to enhance the movements and all the daily activities. However, muscular tissues can be affected by some pathologies associated with genetic alterations that affect the expression of proteins. As the muscle is a highly organized structure in which most of the signaling pathways and proteins are related to one another, pathologies may overlap. Duchenne muscular dystrophy (DMD) is one of the most severe muscle pathologies triggering degeneration and muscle necrosis. Several mathematical models have been developed to predict muscle response to different scenarios and pathologies. The aim of this review is to describe DMD and Becker muscular dystrophy in terms of cellular behavior and molecular disorders and to present an overview of the computational models implemented to understand muscle behavior with the aim of improving regenerative therapy.

Removal of empty capsids from high-dose adeno-associated virus 9 gene therapies

Recombinant adeno-associated virus, serotype 9 (rAAV9) has shown promise as a gene therapy vector for muscle and central nervous diseases. High-dose requirements of these therapies present critical safety considerations and biomanufacturing challenges. Notably, the reduction of empty capsids (ECs), which lack therapeutic transgene, from rAAV9 products is critical to maximize efficacy. Removal of rAAV ECs from full capsids is a major downstream challenge because of their highly similar biophysical characteristics. Ultracentrifugation (UC) reduces ECs but is laborious and difficult to scale. In this paper, to replace a poorly scalable UC process, we developed an anion exchange (AEX) chromatography for rAAV9 EC reduction from full capsids. AEX load preparation by dilution incurred major product loss. The addition of histidine and surfactants to dilution buffers increased yield and reduced aggregation. Elution salts were screened and sodium acetate was found to maximize yield and EC reduction. The most promising load dilution buffer and elution salt were used in combination to form an optimized AEX method. The process reduced ECs three-fold, demonstrated robustness to a broad range of EC load challenges, and was scaled for large-scale manufacture. Compared to UC, the AEX method simplified scale-up, reduced ECs to comparable levels (20%), afforded similar purity and product quality, and increased yield by 14%.

Clinical immunogenicity outcomes from GENEr8-1, a phase 3 study of valoctocogene roxaparvovec, an AAV5-vectored gene therapy for hemophilia A

Gene transfer therapies utilizing adeno-associated virus (AAV) vectors involve a complex drug design with multiple components that may impact immunogenicity. Valoctocogene roxaparvovec is an AAV serotype 5 (AAV5)-vectored gene therapy for the treatment of hemophilia A that encodes a B-domain-deleted human factor VIII (FVIII) protein controlled by a hepatocyte-selective promoter. Following previous results from the first-in-human phase 1/2 clinical trial, we assessed AAV5-capsid- and transgene-derived FVIII-specific immune responses with 2 years of follow-up data from GENEr8-1, a phase 3, single-arm, open-label study in 134 adult men with severe hemophilia A. No FVIII inhibitors were detected following administration of valoctocogene roxaparvovec. Immune responses were predominantly directed toward the AAV5 capsid, with all participants developing durable anti-AAV5 antibodies. Cellular immune responses specific for the AAV5 capsid were detected in most participants by interferon-γ enzyme-linked immunosorbent spot assay 2 weeks following dose administration and declined or reverted to negative over the first 52 weeks. These responses were weakly correlated with alanine aminotransferase elevations and showed no association with changes in FVIII activity. FVIII-specific cellular immune responses were less frequent and more sporadic compared with those specific for AAV5 and showed no association with safety or efficacy parameters.

Immunogenicity Risk Assessment of Process-Related Impurities in An Engineered T Cell Receptor Cellular Product

Cell therapies such as genetically modified T cells have emerged as a promising and viable treatment for hematologic cancers and are being aggressively pursued for a wide range of diseases and conditions that were previously difficult to treat or had no cure. The process development requires genetic modifications to T cells to express a receptor (engineered T cell receptor (eTCR)) of specific binding qualities to the desired target. Protein reagents utilized during the cell therapy manufacturing process, to facilitate these genetic modifications, are often present as process-related impurities at residual levels in the final drug product and can represent a potential immunogenicity risk upon infusion. This manuscript presents a framework for the qualification of an assay for assessing the immunogenicity risk of AA6 and Cas9 residuals. The same framework applies for other residuals; however, AAV6 and Cas9 were selected as they were residuals from the manufacturing of an engineered T cell receptor cellular product in development. The manuscript: 1) elucidates theoretical risks, 2) summarizes analytical data collected during process development, 3) describes the qualification of an in vitro human PBMC cytokine release assay to assess immunogenicity risk from cellular product associated process residuals; 4) identifies a multiplexed inflammatory innate and adaptive cytokine panel with pre-defined criteria using relevant positive controls; and 5) discusses qualification challenges and potential solutions for establishing meaningful thresholds. The assessment is not only relevant to establishing safe exposure levels of these residuals but also in guiding risk assessment and CMC strategy during the conduct of clinical trials.

Gene therapy: principles, challenges and use in clinical practice

INTRODUCTION

Gene therapy is an emerging topic in medicine. The first products have already been licensed in the European Union for the treatment of immune deficiency, spinal muscular atrophy, hemophilia, retinal dystrophy, a rare neurotransmitter disorder and some hematological cancers, while many more are being assessed in preclinical and clinical trials.

OBJECTIVE

The purpose of this review is to provide an overview of the core principles of gene therapy along with information on challenges and risks. Benefits, adverse effects and potential risks are illustrated based on the examples of hemophilia and spinal muscular atrophy.

RESULTS

At present, in-vitro and in-vivo gene addition or gene augmentation is the most commonly established type of gene therapy. More recently, more sophisticated and precise approaches such as in situ gene editing have moved into focus. However, all types of gene therapy require long-term observation of treated patients to ensure safety, efficacy, predictability and durability. Important safety concerns include immune reactions to the vector, the foreign DNA or the new protein resulting from gene therapy, and a remaining low cancer risk based on insertional mutagenesis. Ethical and regulatory issues need to be addressed, and new reimbursement models are called for to ease the financial burden that this new treatment poses for the health care system.

CONCLUSION

Gene therapy holds great promise for considerable improvement or even cure of genetic diseases with serious clinical consequences. However, a number of questions and issues need to be clarified to ensure broad accessibility of safe and efficacious products.

Gene therapy for age-related macular degeneration: potential, feasibility, and pitfalls

PURPOSE OF REVIEW

The landscape for age-related macular degeneration (AMD) is rapidly changing with addition of biosimilars and now United States Food and Drug Administration (FDA) approved nonneovascular AMD (nnAMD) treatment options. These developments have inspired a burgeoning pipeline of gene therapy approaches focused on similar antivascular endothelial growth factors (VEGF) and complement related pathways. Historic and more recent setbacks in the gene therapy pipeline, including intraocular inflammatory reactions, have raised important concerns for adverse events related to AMD therapeutics both for gene and nongene approaches. The specific clinical profile of these therapeutics approaching later stage clinical trials are complex and under active investigation; however, these options hold promise to disrupt the current landscape and change management paradigms for one of the leading causes of vision loss worldwide.

RECENT FINDINGS

This review covers current gene therapy approaches for neovascular AMD (nAMD) and nnAMD. Intravitreal, suprachoroidal, and subretinal delivery routes are discussed with attention to technical procedure, capabilities for transgene delivery to target tissue, immunogenicity, and collateral effects. Suprachoroidal delivery is an emerging approach which may bridge some of the practical drawbacks for intravitreal and subretinal methods, though with less elaborated immunologic profile. In parallel to delivery modification, viral vectors have been cultivated to target specific cells, with promising enhancements in adeno-associated viral (AAV) vectors and persistent interest in alternate viral and nonviral delivery vectors. Ongoing questions such as steroid or immunosuppressive regimen and economic considerations from a payer and societal perspective are discussed.

SUMMARY

The present review discusses emerging gene therapy options which could foster new, more durable nAMD and nnAMD therapeutics. These options will need refinement with regards to route, vector, and dosage, and specialists must decipher the specific clinical risk benefit profile for individual patients. Ongoing concerns for immunogenicity or dosage related adverse events could stifle progress, while further vector development and refined delivery techniques have the potential to change the safety and efficacy of currently options in the pipeline.

In vivo LNP-CRISPR Approaches for the Treatment of Hemophilia

Hemophilia is a genetic disorder that is caused by mutations in coagulation factor VIII (hemophilia A) or IX (hemophilia B) genes resulting in blood clotting disorders. Despite advances in therapies, such as recombinant proteins and products with extended half-lives, the treatment of hemophilia still faces two major limitations: the short duration of therapeutic effect and production of neutralizing antibodies against clotting factors (inhibitor). To overcome these limitations, new hemophilia treatment strategies have been established such as gene therapy, bispecific antibody, and rebalancing therapy. Although these strategies have shown promising results, it is difficult to achieve a permanent therapeutic effect. Advances in the clustered regularly interspaced short palindromic repeat (CRISPR) technology have allowed sustainable treatment by correcting mutated genes. Since genome editing generates irreversible changes in host genome, safety must be ensured by delivering target organs. Therefore, the delivery tool of the CRISPR system is crucial for safe, accurate, and efficient genome editing. Recently, non-viral vector lipid nanoparticles (LNPs) have emerged as safer tools for delivering CRISPR systems than other viral vectors. Several previous hemophilia pre-clinical studies using LNP-CRISPR showed that sufficient and sustainable therapeutic effects, which means that LNP-CRISPR-mediated genome-editing therapy can be a valid option for the treatment of hemophilia. In this paper, we summarize the latest advancements in the successful treatment of hemophilia and the potential of CRISPR-mediated genome-editing therapy using LNPs.

Humanized mice for studying HIV latency and potentially its eradication

PURPOSE OF THE REVIEW

The quest for an HIV cure faces a formidable challenge: the persistent presence of latent viral infections within the cells and tissues of infected individuals. This review provides a thorough examination of discussions surrounding HIV latency, the use of humanized mouse models, and strategies aimed at eliminating the latent HIV reservoir. It explores the hurdles and advancements in understanding HIV pathogenesis, mainly focusing on establishing latent reservoirs in CD4 + T cells and macrophages. Introducing the concepts of functional and sterile cures, the review underscores the indispensable role of humanized mouse models in HIV research, offering crucial insights into the efficacy of cART and the ongoing pursuit of an HIV cure.

RECENT FINDINGS

Here, we highlight studies investigating molecular mechanisms and pathogenesis related to HIV latency in humanized mice and discuss novel strategies for eradicating latent HIV. Emphasizing the importance of analytical cART interruption in humanized mouse studies to gauge its impact on the latent reservoir accurately, the review underlines the ongoing progress and challenges in harnessing humanized mouse models for HIV research.

SUMMARY

This review suggests that humanized mice models provide valuable insights into HIV latency and potential eradication strategies, contributing significantly to the quest for an HIV cure.

Adeno-associated virus-mediated trastuzumab delivery to the central nervous system for human epidermal growth factor receptor 2+ brain metastasis

Trastuzumab improves overall survival for HER2+ breast cancer, but its short half-life in the cerebrospinal fluid (~2-4 days) and delivery limitations restrict the ability to target HER2+ central nervous system (CNS) disease. We developed an adeno-associated virus (AAV) vector expressing a codon-optimized, ubiquitin C (UbC)-promoter-driven trastuzumab sequence (AAV9.UbC.trastuzumab) for intrathecal administration. Transgene expression was evaluated in adult Rag1 knockout mice and rhesus nonhuman primates (NHPs) after a single intracerebroventricular (ICV) or intra-cisterna magna (ICM) AAV9.UbC.trastuzumab injection, respectively, using real-time PCR, ELISA, Western blot, in situ hybridization, single-nucleus RNA sequencing, and liquid chromatography-mass spectrometry; antitumor efficacy was evaluated in brain xenografts using HER2+ breast cancer cell lines (BT-474, MDA-MB-453). Transgene expression was detected in brain homogenates of Rag1 knockout mice following a single ICV injection of AAV9.UbC.trastuzumab (1 × 1011 vector genome copies [GC]/mouse) and tumor progression was inhibited in xenograft models of breast-to-brain metastasis. In NHPs, ICM delivery of AAV9.UbC.trastuzumab (3 × 1013 GC/animal) was well tolerated (36-37 days in-life) and resulted in transgene expression in CNS tissues and cerebrospinal fluid at levels sufficient to induce complete tumor remission in MDA-MB-453 brain xenografts. With AAV9's proven clinical safety record, this gene therapy may represent a viable approach for targeting HER2 + CNS malignancies.

Computationally guided AAV engineering for enhanced gene delivery

Gene delivery vehicles based on adeno-associated viruses (AAVs) are enabling increasing success in human clinical trials, and they offer the promise of treating a broad spectrum of both genetic and non-genetic disorders. However, delivery efficiency and targeting must be improved to enable safe and effective therapies. In recent years, considerable effort has been invested in creating AAV variants with improved delivery, and computational approaches have been increasingly harnessed for AAV engineering. In this review, we discuss how computationally designed AAV libraries are enabling directed evolution. Specifically, we highlight approaches that harness sequences outputted by next-generation sequencing (NGS) coupled with machine learning (ML) to generate new functional AAV capsids and related regulatory elements, pushing the frontier of what vector engineering and gene therapy may achieve.

Deciphering conundrums of adeno-associated virus liver-directed gene therapy: focus on hemophilia

Adeno-associated virus gene therapy has been the subject of intensive investigation for monogenic disease gene addition therapy for more than 25 years, yet few therapies have been approved by regulatory agencies. Most have not progressed beyond phase 1/2 due to toxicity, lack of efficacy, or both. The liver is a natural target for adeno-associated virus since most serotypes have a high degree of tropism for hepatocytes due to cell surface receptors for the virus and the unique liver sinusoidal geometry facilitating high volumes of blood contact with hepatocyte cell surfaces. Recessive monogenic diseases such as hemophilia represent promising targets since the defective proteins are often synthesized in the liver and secreted into the circulation, making them easy to measure, and many do not require precise regulation. Yet, despite initiation of many disease-specific clinical trials, therapeutic windows are often nonexistent, resulting in excess toxicity and insufficient efficacy. Iterative progress built on these attempts is best illustrated by hemophilia, with the first regulatory approvals for factor IX and factor VIII gene therapies eventually achieved 25 years after the first gene therapy studies in humans. Although successful gene transfer may result in the production of sufficient transgenic protein to modify the disease, many emerging questions on durability, predictability, reliability, and variability of response have not been answered. The underlying biology accounting for these heterogeneous responses and the interplay between host and virus is the subject of intense investigation and the subject of this review.

The science and practice of current environmental risk assessment for gene therapy: a review

Gene therapy is a fast-growing field showing great potential to treat genetic diseases and cancer. With accelerating gene therapy development and approval, their environment risk assessment (ERA) becomes increasingly important. An ERA is an assessment of the risks to human health and the environment upon exposure to a medicinal product as the result of its release during clinical development or after entering the market. Because ERA is an important component of regulatory submission, drug developers must perform a robust assessment to ensure the safety of unintended persons, animal, plants, microorganisms and environment at large. Global regulations on gene therapy ERA continue to evolve. Gene therapy ERAs are carried out according to general principles as provided in regulatory guidelines for application of clinical trials and marketing authorizations. The current review intends to summarize regulations and content requirements on gene therapy ERA in European Union, the USA and Japan. The approved gene therapy products by EMA and US Food and Drug Administration are analyzed for the critical aspects of their ERAs to provide the current status and practice of gene therapy ERAs by drug developers. For this purpose, the main contents of these gene therapy ERAs are summarized. Critical safety factors of gene therapy ERAs are described. With more experience and knowledge to be accumulated, gene therapy ERAs are expected to be less challenging with commonly used viral vectors.

Adeno-associated virus as a delivery vector for gene therapy of human diseases

Adeno-associated virus (AAV) has emerged as a pivotal delivery tool in clinical gene therapy owing to its minimal pathogenicity and ability to establish long-term gene expression in different tissues. Recombinant AAV (rAAV) has been engineered for enhanced specificity and developed as a tool for treating various diseases. However, as rAAV is being more widely used as a therapy, the increased demand has created challenges for the existing manufacturing methods. Seven rAAV-based gene therapy products have received regulatory approval, but there continue to be concerns about safely using high-dose viral therapies in humans, including immune responses and adverse effects such as genotoxicity, hepatotoxicity, thrombotic microangiopathy, and neurotoxicity. In this review, we explore AAV biology with an emphasis on current vector engineering strategies and manufacturing technologies. We discuss how rAAVs are being employed in ongoing clinical trials for ocular, neurological, metabolic, hematological, neuromuscular, and cardiovascular diseases as well as cancers. We outline immune responses triggered by rAAV, address associated side effects, and discuss strategies to mitigate these reactions. We hope that discussing recent advancements and current challenges in the field will be a helpful guide for researchers and clinicians navigating the ever-evolving landscape of rAAV-based gene therapy.

Long-Term Downregulation of the Sodium Channel Gene Scn8a Is Therapeutic in Mouse Models of SCN8A Epilepsy

OBJECTIVE

De novo mutations of the voltage-gated sodium channel gene SCN8A cause developmental and epileptic encephalopathy (DEE). Most pathogenic variants result in gain-of-function changes in activity of the sodium channel Nav1.6, poorly controlled seizures, and significant comorbidities. In previous work, an antisense oligonucleotide (ASO) reduced Scn8a transcripts and increased lifespan after neonatal administration to a mouse model. Here, we tested long-term ASO treatment initiated after seizure onset, as required for clinical application.

METHODS

ASO treatment was initiated after observation of a convulsive seizure and repeated at 4 to 6 week intervals for 1 year. We also tested the long-term efficacy of an AAV10-short hairpin RNA (shRNA) virus administered on P1.

RESULTS

Repeated treatment with the Scn8a ASO initiated after seizure onset provided long-term survival and reduced seizure frequency during a 12 month observation period. A single treatment with viral shRNA was also protective during 12 months of observation.

INTERPRETATION

Downregulation of Scn8a expression that is initiated after the onset of seizures is effective for long-term treatment in a model of SCN8A-DEE. Repeated ASO administration or a single dose of viral shRNA prevented seizures and extended survival through 12 months of observation. ANN NEUROL 2024;95:754-759.

Recent Progress in the Endosomal Escape Mechanism and Chemical Structures of Polycations for Nucleic Acid Delivery

Nucleic acid-based therapies are seeing a spiralling surge. Stimuli-responsive polymers, especially pH-responsive ones, are gaining widespread attention because of their ability to efficiently deliver nucleic acids. These polymers can be synthesized and modified according to target requirements, such as delivery sites and the nature of nucleic acids. In this regard, the endosomal escape mechanism of polymer-nucleic acid complexes (polyplexes) remains a topic of considerable interest owing to various plausible escape mechanisms. This review describes current progress in the endosomal escape mechanism of polyplexes and state-of-the-art chemical designs for pH-responsive polymers. The importance is also discussed of the acid dissociation constant (i.e., pKa) in designing the new generation of pH-responsive polymers, along with assays to monitor and quantify the endosomal escape behavior. Further, the use of machine learning is addressed in pKa prediction and polymer design to find novel chemical structures for pH responsiveness. This review will facilitate the design of new pH-responsive polymers for advanced and efficient nucleic acid delivery.

Hemophilia and hepatology, back to the future

Years ago, patients with hemophilia were often cared for because of liver issues. The use of hemoderivatives in the 1970s and 1980s, and the natural history of chronic hepatitis B and C, led to a surge of patients with cirrhosis and related complications after two or three decades. It was not until the approval of entecavir and tenofovir (2005-2008) against the B virus, and of direct-acting antiviral agents (2015) against the C virus, that a truly effective treatment became available for liver disease. Since then, patients with hemophilia disappeared from hepatology clinics and wards, apart from specific isolated problems.

Persistent transgene expression in peripheral tissues one year post intravenous and intramuscular administration of AAV vectors containing the alphaherpesvirus latency-associated promoter 2

Significant progress has been made in enhancing recombinant adeno-associated virus (rAAV) for clinical investigation. Despite its versatility as a gene delivery platform, the inherent packaging constraint of 4.7 kb imposes restrictions on the range of diseases it can address. In this context, we present findings of an exceptionally compact and long-term promoter that facilitates the expression of larger genes compared to conventional promoters. This compact promoter originated from the genome of the alphaherpesvirus pseudorabies virus, latency-associated promoter 2 (LAP2, 404 bp). Promoter driving an mCherry reporter was packaged into single strand (ss) AAV8 and AAV9 vectors and injected into adult C57BL/6 mice at a dose of 5 × 1011 vg/mouse by single intravenous or intramuscular administration. An ssAAV8 and ssAAV9 vector with elongation factor-1α promoter (EF1α, 1264 bp) was injected side-by-side for comparison. After 400 days, we sacrificed the mice and examined mCherry expression in liver, kidney, heart, lung, spleen, pancreas, skeletal muscle, and brain. We found that LAP2 exhibited robust transgene expression across a wide range of cells and tissues comparable to the larger EF1α, which is currently recognized as a rather potent and ubiquitous promoter. The AAV8-LAP2 and AAV9-LAP2 constructs displayed strong transduction and transcription in liver, kidney, and skeletal muscle on both route of administration. However, no expression was detected in the heart, lung, spleen, pancreas, and brain. The outcomes of our investigation propose the viability of LAP2 for gene therapy applications demanding the expression of large or multiple therapeutic genes following a single viralvector administration.

Novel assay format for total anti-adeno-associated virus antibody detection with low capsid consumption and built-in specificity control

Aim: To develop an assay format for detection of total anti-adeno-associated virus 2 (AAV2) antibodies with low capsid material consumption. Methods: An immune complex (IC) assay format was developed. The format is based on the formation of ICs in solution and their subsequent detection using an anti-AAV2 antibody for capture and an antibody against the study species IgG for detection. Results: The feasibility of the IC assay for detection of preexisting and treatment-emergent anti-AAV2 antibodies was demonstrated in cynomolgus monkey and human serum samples, including samples from a preclinical study with AAV2-based therapies. Conclusion: The presented IC assay is an easy-to-perform total anti-AAV2 antibody assay that requires a small amount of unlabeled capsid material and provides an intrinsic specificity control.

Advancements in Viral Gene Therapy for Gaucher Disease

Gaucher disease, an autosomal recessively inherited lysosomal storage disorder, results from biallelic mutations in the GBA1 gene resulting in deficient activity of the enzyme glucocerebrosidase. In Gaucher disease, the reduced levels and activity of glucocerebrosidase lead to a disparity in the rates of formation and breakdown of glucocerebroside and glucosylsphingosine, resulting in the accumulation of these lipid substrates in the lysosome. This gives rise to the development of Gaucher cells, engorged macrophages with a characteristic wrinkled tissue paper appearance. There are both non-neuronopathic (type 1) and neuronopathic (types 2 and 3) forms of Gaucher disease, associated with varying degrees of severity. The visceral and hematologic manifestations of Gaucher disease respond well to both enzyme replacement therapy and substrate reduction therapy. However, these therapies do not improve the neuronopathic manifestations, as they cannot cross the blood-brain barrier. There is now an established precedent for treating lysosomal storage disorders with gene therapy strategies, as many have the potential to cross into the brain. The range of the gene therapies being employed is broad, but this review aimed to discuss the progress, advances, and challenges in developing viral gene therapy as a treatment for Gaucher disease.

B cell focused transient immune suppression protocol for efficient AAV readministration to the liver

Adeno-associated virus (AAV) vectors are used for correcting multiple genetic disorders. Although the goal is to achieve lifelong correction with a single vector administration, the ability to redose would enable the extension of therapy in cases in which initial gene transfer is insufficient to achieve a lasting cure, episomal vector forms are lost in growing organs of pediatric patients, or transgene expression is diminished over time. However, AAV typically induces potent and long-lasting neutralizing antibodies (NAbs) against capsid that prevents re-administration. To prevent NAb formation in hepatic AAV8 gene transfer, we developed a transient B cell-targeting protocol using a combination of monoclonal Ab therapy against CD20 (for B cell depletion) and BAFF (to slow B cell repopulation). Initiation of immunosuppression before (rather than at the time of) vector administration and prolonged anti-BAFF treatment prevented immune responses against the transgene product and abrogated prolonged IgM formation. As a result, vector re-administration after immune reconstitution was highly effective. Interestingly, re-administration before the immune system had fully recovered achieved further elevated levels of transgene expression. Finally, this immunosuppression protocol reduced Ig-mediated AAV uptake by immune cell types with implications to reduce the risk of immunotoxicities in human gene therapy with AAV.

mitoTALEN reduces the mutant mtDNA load in neurons

Mutations within mtDNA frequently give rise to severe encephalopathies. Given that a majority of these mtDNA defects exist in a heteroplasmic state, we harnessed the precision of mitochondrial-targeted TALEN (mitoTALEN) to selectively eliminate mutant mtDNA within the CNS of a murine model harboring a heteroplasmic mutation in the mitochondrial tRNA alanine gene (m.5024C>T). This targeted approach was accomplished by the use of AAV-PHP.eB and a neuron-specific synapsin promoter for effective neuronal delivery and expression of mitoTALEN. We found that most CNS regions were effectively transduced and showed a significant reduction in mutant mtDNA. This reduction was accompanied by an increase in mitochondrial tRNA alanine levels, which are drastically reduced by the m.5024C>T mutation. These results showed that mitochondrial-targeted gene editing can be effective in reducing CNS-mutant mtDNA in vivo, paving the way for clinical trials in patients with mitochondrial encephalopathies.

Gene Delivery From Granular Scaffolds for Tunable Biologics Manufacturing

The understanding of the molecular basis for disease has generated a myriad of therapeutic biologics, including therapeutic proteins, antibodies, and viruses. However, the promise that biologics can resolve currently incurable diseases hinges in their manufacturability. These therapeutics require that their genetic material be introduced to mammalian cells such that the cell machinery can manufacture the biological components. These are then purified, validated, and packaged. Most manufacturing uses batch processes that collect the biologic a few days following genetic modification, due to toxicity or difficulty in separating product from cells in a continuous operation, limiting the amount of biologic that can be produced and resulting in yearlong backlogs. Here, a scaffold-based approach for continuous biologic manufacturing is presented, with sustained production of active antibodies and viruses for 30 days. The use of scaffold-based biologic production enabled perfusion-based bioreactors to be used, which can be incorporated into a fully continuous process.

Prednisolone and rapamycin reduce the plasma cell gene signature and may improve AAV gene therapy in cynomolgus macaques

Adeno-associated virus (AAV) vector gene therapy is a promising approach to treat rare genetic diseases; however, an ongoing challenge is how to best modulate host immunity to improve transduction efficiency and therapeutic outcomes. This report presents two studies characterizing multiple prophylactic immunosuppression regimens in male cynomolgus macaques receiving an AAVrh10 gene therapy vector expressing human coagulation factor VIII (hFVIII). In study 1, no immunosuppression was compared with prednisolone, rapamycin (or sirolimus), rapamycin and cyclosporin A in combination, and cyclosporin A and azathioprine in combination. Prednisolone alone demonstrated higher mean peripheral blood hFVIII expression; however, this was not sustained upon taper. Anti-capsid and anti-hFVIII antibody responses were robust, and vector genomes and transgene mRNA levels were similar to no immunosuppression at necropsy. Study 2 compared no immunosuppression with prednisolone alone or in combination with rapamycin or methotrexate. The prednisolone/rapamycin group demonstrated an increase in mean hFVIII expression and a mean delay in anti-capsid IgG development until after rapamycin taper. Additionally, a significant reduction in the plasma cell gene signature was observed with prednisolone/rapamycin, suggesting that rapamycin's tolerogenic effects may include plasma cell differentiation blockade. Immunosuppression with prednisolone and rapamycin in combination could improve therapeutic outcomes in AAV vector gene therapy.

Gene therapy vector-related myocarditis

Gene therapy is a technique to correct genetic abnormalities, through introduction of a functional gene or through direct genome editing. Adeno-associated virus (AAV)-mediated gene replacement shows promise for targeted therapies in treatment of inherited cardiomyopathies and is the most used approach in clinical trials. However, immune responses from the host to the virus and gene product pose delivery and safety challenges. This review explores the immunological reactions to AAV-based gene therapy, their potential toxic effects, with a focus on myocarditis, and future directions for gene therapy.

Annexin A1 in the nervous and ocular systems

The therapeutic potential of Annexin A1, an important member of the Annexin superfamily, has become evident in results of experiments with multiple human systems and animal models. The anti-inflammatory and pro-resolving effects of Annexin A1 are characteristic of pathologies involving the nervous system. In this review, we initially describe the expression sites of Annexin A1, then outline the mechanisms by which Annexin A1 maintains the neurological homeostasis through either formyl peptide receptor 2 or other molecular approaches; and, finally, we discuss the neuroregenerative potential qualities of Annexin A1. The eye and the nervous system are anatomically and functionally connected, but the association between visual system pathogenesis, especially in the retina, and Annexin A1 alterations has not been well summarized. Therefore, we explain the beneficial effects of Annexin A1 for ocular diseases, especially for retinal diseases and glaucoma on the basis of published findings, and we explore present and future delivery strategies for Annexin A1 to the retina.

Advanced strategies for CRISPR/Cas9 delivery and applications in gene editing, therapy, and cancer detection using nanoparticles and nanocarriers

Cancer remains one of the deadliest diseases, and is characterised by the uncontrolled growth of modified human cells. Unlike infectious diseases, cancer does not originate from foreign agents. Though a variety of diagnostic procedures are available; their cost-effectiveness and accessibility create significant hurdles. Non-specific cancer symptoms further complicate early detection, leading to belated recognition of certain cancer. The lack of reliable biomarkers hampers effective treatment, as chemotherapy, radiation therapy, and surgery often result in poor outcomes and high recurrence rates. Genetic and epigenetic mutations play a crucial role in cancer pathogenesis, necessitating the development of alternate treatment methods. The advent of CRISPR/Cas9 technology has transformed molecular biology and exhibits potential for gene modification and therapy in various cancer types. Nonetheless, obstacles such as safe transport, off-target consequences, and potency must be overcome before widespread clinical use. Notably, this review delves into the multifaceted landscape of cancer research, highlighting the pivotal role of nanoparticles in advancing CRISPR/Cas9-based cancer interventions. By addressing the challenges associated with cancer diagnosis and treatment, this integrated approach paves the way for innovative solutions and improved patient outcomes.

Gene therapy for monogenic disorders: challenges, strategies, and perspectives

Monogenic disorders refer to a group of human diseases caused by mutations in single genes. While disease-modifying therapies have offered some relief from symptoms and delayed progression for some monogenic diseases, most of these diseases still lack effective treatments. In recent decades, gene therapy has emerged as a promising therapeutic strategy for genetic disorders. Researchers have developed various gene manipulation tools and gene delivery systems to treat monogenic diseases. Despite this progress, concerns about inefficient delivery, persistent expression, immunogenicity, toxicity, capacity limitation, genomic integration, and limited tissue specificity still need to be addressed. This review gives an overview of commonly used gene therapy and delivery tools, along with the challenges they face and potential strategies to counter them.

Mucopolysaccharidosis type IIIB: a current review and exploration of the AAV therapy landscape

Mucopolysaccharidoses type IIIB is a rare genetic disorder caused by mutations in the gene that encodes for N-acetyl-alpha-glucosaminidase. This results in the aggregation of heparan sulfate polysaccharides within cell lysosomes that leads to progressive and severe debilitating neurological dysfunction. Current treatment options are expensive, limited, and presently there are no approved cures for mucopolysaccharidoses type IIIB. Adeno-associated virus gene therapy has significantly advanced the field forward, allowing researchers to successfully design, enhance, and improve potential cures. Our group recently published an effective treatment using a codon-optimized triple mutant adeno-associated virus 8 vector that restores N-acetyl-alpha-glucosaminidase levels, auditory function, and lifespan in the murine model for mucopolysaccharidoses type IIIB to that seen in healthy mice. Here, we review the current state of the field in relation to the capsid landscape, adeno-associated virus gene therapy and its successes and challenges in the clinic, and how novel adeno-associated virus capsid designs have evolved research in the mucopolysaccharidoses type IIIB field.

Adeno-associated viruses for gene therapy - clinical implications and liver-related complications, a guide for hepatologists

Gene therapy has garnered increasing interest over recent decades. Several therapies employing gene transfer mechanisms have been developed, and, of these, adeno-associated virus (AAV) vectors have demonstrated viability for use with in vivo gene therapy. Several AAV-based therapeutics have received regulatory approval in the last few years including those for retinal disease, spinal muscular atrophy or aromatic L-amino acid decarboxylase deficiency. Lately, with the introduction of novel liver-directed AAV vector-based therapeutics for the treatment of haemophilia A and B, gene therapy has attracted significant attention in the hepatology community, with the liver increasingly recognised as a target for gene therapy. However, the introduction of foreign DNA into hepatocytes is associated with a risk of hepatic reactions, with raised ALT (alanine aminotransferase) and AST (aspartate aminotransferase) being - so far - the most commonly reported side effects. The complete mechanisms underlying the ALT flairs remain to be determined and the long-term risks associated with these new treatments is not yet known. The liver community is increasingly being asked to support liver-directed gene therapy to mitigate potential liver associated harm. In this review, we focus on AAV vector-based gene therapy, shedding light on this promising technique and its remarkable success in haemophilia, with a special focus on hepatic complications and their management in daily clinical practice.

Rational immunosilencing of a promiscuous T-cell epitope in the capsid of an adeno-associated virus

Owing to the immunogenicity of adeno-associated viruses (AAVs), gene therapies using AAVs face considerable obstacles. Here, by leveraging ex vivo T-cell assays, the prediction of epitope binding to major histocompatibility complex class-II alleles, sequence-conservation analysis in AAV phylogeny and site-directed mutagenesis, we show that the replacement of amino acid residues in a promiscuous and most immunodominant T-cell epitope in the AAV9 capsid with AAV5 sequences abrogates the immune responses of peripheral blood mononuclear cells to the chimaeric vector while preserving its functions, potency, cellular specificity, transduction efficacy and biodistribution. This rational approach to the immunosilencing of capsid epitopes promiscuously binding to T cells may be applied to other AAV vectors and epitope regions.

Neuronal Replenishment via Hydrogel-Rationed Delivery of Reprogramming Factors

The central nervous system's limited capacity for regeneration often leads to permanent neuronal loss following injury. Reprogramming resident reactive astrocytes into induced neurons at the site of injury is a promising strategy for neural repair, but challenges persist in stabilizing and accurately targeting viral vectors for transgene expression. In this study, we employed a bioinspired self-assembling peptide (SAP) hydrogel for the precise and controlled release of a hybrid adeno-associated virus (AAV) vector, AAVDJ, carrying the NeuroD1 neural reprogramming transgene. This method effectively mitigates the issues of high viral dosage at the target site, off-target delivery, and immunogenic reactions, enhancing the vector's targeting and reprogramming efficiency. In vitro, this vector successfully induced neuron formation, as confirmed by morphological, histochemical, and electrophysiological analyses. In vivo, SAP-mediated delivery of AAVDJ-NeuroD1 facilitated the trans-differentiation of reactive host astrocytes into induced neurons, concurrently reducing glial scarring. Our findings introduce a safe and effective method for treating central nervous system injuries, marking a significant advancement in regenerative neuroscience.

The glucocorticoid receptor as a master regulator of the Müller cell response to diabetic conditions in mice

Diabetic retinopathy (DR) is considered a primarily microvascular complication of diabetes. Müller glia cells are at the centre of the retinal neurovascular unit and play a critical role in DR. We therefore investigated Müller cell-specific signalling pathways that are altered in DR to identify novel targets for gene therapy. Using a multi-omics approach on purified Müller cells from diabetic db/db mice, we found the mRNA and protein expression of the glucocorticoid receptor (GR) to be significantly decreased, while its target gene cluster was down-regulated. Further, oPOSSUM TF analysis and ATAC- sequencing identified the GR as a master regulator of Müller cell response to diabetic conditions. Cortisol not only increased GR phosphorylation. It also induced changes in the expression of known GR target genes in retinal explants. Finally, retinal functionality was improved by AAV-mediated overexpression of GR in Müller cells. Our study demonstrates an important role of the glial GR in DR and implies that therapeutic approaches targeting this signalling pathway should be aimed at increasing GR expression rather than the addition of more ligand.

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.

Understanding AAV vector immunogenicity: from particle to patient

Gene therapy holds promise for patients with inherited monogenic disorders, cancer, and rare genetic diseases. Naturally occurring adeno-associated virus (AAV) offers a well-suited vehicle for clinical gene transfer due to its lack of significant clinical pathogenicity and amenability to be engineered to deliver therapeutic transgenes in a variety of cell types for long-term sustained expression. AAV has been bioengineered to produce recombinant AAV (rAAV) vectors for many gene therapies that are approved or in late-stage development. However, ongoing challenges hamper wider use of rAAV vector-mediated therapies. These include immunity against rAAV vectors, limited transgene packaging capacity, sub-optimal tissue transduction, potential risks of insertional mutagenesis and vector shedding. This review focuses on aspects of immunity against rAAV, mediated by anti-AAV neutralizing antibodies (NAbs) arising after natural exposure to AAVs or after rAAV vector administration. We provide an in-depth analysis of factors determining AAV seroprevalence and examine clinical approaches to managing anti-AAV NAbs pre- and post-vector administration. Methodologies used to quantify anti-AAV NAb levels and strategies to overcome pre-existing AAV immunity are also discussed. The broad adoption of rAAV vector-mediated gene therapies will require wider clinical appreciation of their current limitations and further research to mitigate their impact.

The Road towards Gene Therapy for X-Linked Juvenile Retinoschisis: A Systematic Review of Preclinical Gene Therapy in Cell-Based and Rodent Models of XLRS

X-linked juvenile retinoschisis (XLRS) is an early-onset progressive inherited retinopathy affecting males. It is characterized by abnormalities in the macula, with formation of cystoid retinal cavities, frequently accompanied by splitting of the retinal layers, impaired synaptic transmission of visual signals, and associated loss of visual acuity. XLRS is caused by loss-of-function mutations in the retinoschisin gene located on the X chromosome (RS1, MIM 30083). While proof-of-concept studies for gene augmentation therapy have been promising in in vitro and rodent models, clinical trials in XLRS patients have not been successful thus far. We performed a systematic literature investigation using search strings related to XLRS and gene therapy in in vivo and in vitro models. Three rounds of screening (title/abstract, full text and qualitative) were performed by two independent reviewers until consensus was reached. Characteristics related to study design and intervention were extracted from all studies. Results were divided into studies using (1) viral and (2) non-viral therapies. All in vivo rodent studies that used viral vectors were assessed for quality and risk of bias using the SYRCLE's risk-of-bias tool. Studies using alternative and non-viral delivery techniques, either in vivo or in vitro, were extracted and reviewed qualitatively, given the diverse and dispersed nature of the information. For in-depth analysis of in vivo studies using viral vectors, outcome data for optical coherence tomography (OCT), immunohistopathology and electroretinography (ERG) were extracted. Meta-analyses were performed on the effect of recombinant adeno-associated viral vector (AAV)-mediated gene augmentation therapies on a- and b-wave amplitude as well as the ratio between b- and a-wave amplitudes (b/a-ratio) extracted from ERG data. Subgroup analyses and meta-regression were performed for model, dose, age at injection, follow-up time point and delivery method. Between-study heterogeneity was assessed with a Chi-square test of homogeneity (I2). We identified 25 studies that target RS1 and met our search string. A total of 19 of these studies reported rodent viral methods in vivo. Six of the 25 studies used non-viral or alternative delivery methods, either in vitro or in vivo. Of these, five studies described non-viral methods and one study described an alternative delivery method. The 19 aforementioned in vivo studies were assessed for risk of bias and quality assessments and showed inconsistency in reporting. This resulted in an unclear risk of bias in most included studies. All 19 studies used AAVs to deliver intact human or murine RS1 in rodent models for XLRS. Meta-analyses of a-wave amplitude, b-wave amplitude, and b/a-ratio showed that, overall, AAV-mediated gene augmentation therapy significantly ameliorated the disease phenotype on these parameters. Subgroup analyses and meta-regression showed significant correlations between b-wave amplitude effect size and dose, although between-study heterogeneity was high. This systematic review reiterates the high potential for gene therapy in XLRS, while highlighting the importance of careful preclinical study design and reporting. The establishment of a systematic approach in these studies is essential to effectively translate this knowledge into novel and improved treatment alternatives.

Synthetically mannosylated antigens induce antigen-specific humoral tolerance and reduce anti-drug antibody responses to immunogenic biologics

Immunogenic biologics trigger an anti-drug antibody (ADA) response in patients that reduces efficacy and increases adverse reactions. Our laboratory has shown that targeting protein antigen to the liver microenvironment can reduce antigen-specific T cell responses; herein, we present a strategy to increase delivery of otherwise immunogenic biologics to the liver via conjugation to a synthetic mannose polymer, p(Man). This delivery leads to reduced antigen-specific T follicular helper cell and B cell responses resulting in diminished ADA production, which is maintained throughout subsequent administrations of the native biologic. We find that p(Man)-antigen treatment impairs the ADA response against recombinant uricase, a highly immunogenic biologic, without a dependence on hapten immunodominance or control by T regulatory cells. We identify increased T cell receptor signaling and increased apoptosis and exhaustion in T cells as effects of p(Man)-antigen treatment via transcriptomic analyses. This modular platform may enhance tolerance to biologics, enabling long-term solutions for an ever-increasing healthcare problem.