Prednisolone reduces the interferon response to AAV in cynomolgus macaques and may increase liver gene expression

Progress in skin gene therapy: From the inside and out

The skin is the largest organ of the body and forms and serves as the barrier for preventing external material from accessing and damaging internal organs. As the outward interface to the environment, it is accessible for the application of therapeutic agents and cellular and gene therapy represent attractive and promising options to treat severe genetic conditions for which palliation has long been the main stay. However, because of its barrier function, transit across and to the subdermal compartment can be challenging. This commentary examines the current approaches of cell and gene therapies for genetic skin disorders. We write this from a local and systemic "outside and inside." perspective. Delivery from the outside encompasses topical, intradermal, and transdermal strategies for cell and vector delivery and ex vivo cell expansion and grafting. The inside approach details systemic delivery via infusion of cells or agents toward providing benefit to the skin. We use recessive dystrophic epidermolysis bullosa (RDEB) as a representative and paradigmatic disease to showcase these approaches as a means to highlight potential broader applicability to other conditions.

Safety and efficacy of valoctocogene roxaparvovec with prophylactic glucocorticoids: 1-year results from the phase 3b, single-arm, open-label GENEr8-3 study

BACKGROUND

Valoctocogene roxaparvovec, an adeno-associated virus vector that transfers a human factor (F)VIII (FVIII) coding sequence to hepatocytes, provides bleeding protection for people with severe hemophilia A.

OBJECTIVES

Determine the efficacy and safety of valoctocogene roxaparvovec with concomitant prophylactic glucocorticoids in the open-label, single-arm, phase 3b GENEr8-3 trial.

METHODS

Participants with severe hemophilia A who were using hemophilia A prophylaxis received one 6 × 1013 vg/kg infusion of valoctocogene roxaparvovec concomitantly with daily prophylactic glucocorticoids (40 mg prednisolone equivalent/d weeks 0-8; taper to 5 mg/d weeks 9-19). The primary efficacy endpoint was change from baseline in FVIII activity (chromogenic substrate assay) at week 52. Secondary efficacy endpoints included annualized rate of FVIII use and annualized bleeding rate for treated bleeds. Safety was assessed by adverse events (AEs). Analysis populations were intent-to-treat (ITT; received valoctocogene roxaparvovec) for safety analyses and modified ITT (≥52 FVIII infusions in the year before dosing) for efficacy analyses.

RESULTS

Overall, 22 participants with severe hemophilia A received valoctocogene roxaparvovec. In the modified ITT population (n = 21), mean week 52 FVIII activity increased from baseline (imputed as 1 IU/dL) to 16.1 IU/dL (SD, 22.4; P = .0057); posthemophilia A prophylaxis, mean treated annualized bleeding rate and mean annualized FVIII use decreased 67.1% and 91.6% from baseline, respectively (P < .05). The most common AE was alanine aminotransferase elevation (20/22 participants). Glucocorticoid-related AEs occurred in 19 of 22 participants. No participants discontinued the study.

CONCLUSION

Based on cross-trial comparisons, prophylactic glucocorticoids do not confer safety or efficacy benefits compared with reactive glucocorticoid regimens.

The combination of rAAV pseudo-lipid nanoparticle and triamcinolone acetonide enables multi-administration to liver

The multi-administration of recombinant adeno-associated virus (rAAV) is limited largely by immunological barriers. Herein, a novel strategy, named rAAV pseudo-lipid nanoparticle combined with triamcinolone acetonide (LNP-rAAV + TAC), has been described in mice. We showed successful but low efficient triple trafficking by LNP-rAAV2 carrying EGFP, human factor IX (hFIX), and luciferase (luc), due to its encapsulation characteristic. Additionally, sustained TAC treatment, which dose-dependently downregulated the anti-rAAV2 antibodies, permitted rAAV2 re-administration at dosages of ≥45 mg/kg/3 days. Furthermore, to improve the efficiency and safety, LNP-rAAV + TAC was evaluated, using LNP-rAAV2 carrying EGFP, hFIX, and luc co-treating with 45 mg/kg/3 days TAC before and after treatment with LNP-rAAV2 injections. Notable neutralizing antibody reductions of 37.8-fold and 12.7-fold were observed by the combinatorial strategy compared with the independent LNP encapsulation and TAC treatment approaches. The plasma hFIX protein was enhanced to 15.1 μg/mL and the liver bioluminescence was elevated to 1.4 × 108 p/s/cm2/sr following the second and third administrations, with weaker levels in LNP encapsulation (1.9 μg/mL, 2.1 × 104 p/s/cm2/sr) and TAC treatment (3.0 μg/mL, 6.1 × 104 p/s/cm2/sr) groups. Thus, this combination strategy is an attractive candidate for enabling multi-dosing of rAAV vector and warrants further study on the underlying mechanism.

Characterization of a novel conditional knockout mouse model to assess efficacy of mRNA therapy in the context of severe OTC deficiency

Ornithine transcarbamylase deficiency (OTCD) is the most common urea-cycle disorder, characterized by hyperammonemia and accompanied by a high unmet patient need. mRNA therapies have been shown to be efficacious in hypomorphic Sparse-fur abnormal skin and hair (Spf-ash) mice, a model of late-onset disease. However, studying the efficacy of ornithine transcarbamylase (OTC) mRNA therapy in traditional knockout mice, a model for severe early-onset OTCD, is hampered by the rapid lethality of the model and poor lipid nanoparticle (LNP) uptake into neonatal mouse liver. We developed a novel tamoxifen-inducible mouse to study the effect of mRNA therapy in the context of complete or near-complete OTC loss in adult animals. Characterization of the model showed that it is highly reproducible, 100% penetrant, and phenocopies hallmarks of human disease, with animals exhibiting decreased body weight, hyperammonemia, and brain edema. Delivery of OTC mRNA increased survival, maintained body weight, delayed the onset of hyperammonemia, and reduced brain edema. Therefore, this model provides a platform to study LNP-mediated mRNA therapies for the treatment of late-onset OTCD.

Gene Therapy for Inherited Liver Disease: To Add or to Edit

Patients suffering from an inherited severe liver disorder require lifelong treatment to prevent premature death. Until recently, the only curative treatment option was liver transplantation, which requires lifelong immune suppression. Now, liver-directed gene therapy, which is a much less invasive procedure, has become a market-approved treatment for hemophilia A and B. This may pave the way for it to become the treatment of choice for many other recessive inherited liver disorders with loss-of-function mutations. Inherited liver disease with toxic-gain-of-function or intrinsic hepatocyte damage may require alternative applications, such as integrating vectors or genome editing technologies, that can provide permanent or specific modification of the genome. We present an overview of currently available gene therapy strategies, i.e., gene supplementation, gene editing, and gene repair investigated in preclinical and clinical studies to treat inherited severe liver disorders. The advantages and limitations of these gene therapy applications are discussed in relation to the underlying disease mechanism.

Current landscape of cystic fibrosis gene therapy

Cystic fibrosis is a life-threatening disease that is caused by mutations in CFTR, a gene which encodes an ion channel that supports proper function of several epithelial tissues, most critically the lung. Without CFTR, airway barrier mechanisms are impaired, allowing for chronic, recurrent infections that result in airway remodeling and deterioration of lung structure and function. Small molecule modulators can rescue existing, defective CFTR protein; however, they still leave a subset of people with CF with no current disease modifying treatments, aside from lung transplantation. Gene therapy directed to the lung is a promising strategy to modify CF disease in the organ most associated with morbidity and mortality. It is accomplished through delivery of a CFTR transgene with an airway permissive vector. Despite more than three decades of research in this area, a lung directed gene therapy has yet to be realized. There is hope that with improved delivery vectors, sufficient transduction of airway cells can achieve therapeutic levels of functional CFTR. In order to do this, preclinical programs need to meet a certain level of CFTR protein expression in vitro and in vivo through improved transduction, particularly in relevant airway cell types. Furthermore, clinical programs must be designed with sensitive methods to detect CFTR expression and function as well as methods to measure meaningful endpoints for lung structure, function and disease. Here, we discuss the current understanding of how much and where CFTR needs to be expressed, the most advanced vectors for CFTR delivery and clinical considerations for detecting CFTR protein and function in different patient subsets.

Integrated vector genomes may contribute to long-term expression in primate liver after AAV administration

The development of liver-based adeno-associated virus (AAV) gene therapies is facing concerns about limited efficiency and durability of transgene expression. We evaluated nonhuman primates following intravenous dosing of AAV8 and AAVrh10 vectors for over 2 years to better define the mechanism(s) of transduction that affect performance. High transduction of non-immunogenic transgenes was achieved, although expression declined over the first 90 days to reach a lower but stable steady state. More than 10% of hepatocytes contained single nuclear domains of vector DNA that persisted despite the loss of transgene expression. Greater reductions in vector DNA and RNA were observed with immunogenic transgenes. Genomic integration of vector sequences, including complex concatemeric structures, were detected in 1 out of 100 cells at broadly distributed loci that were not in proximity to genes associated with hepatocellular carcinoma. Our studies suggest that AAV-mediated transgene expression in primate hepatocytes occurs in two phases: high but short-lived expression from episomal genomes, followed by much lower but stable expression, likely from integrated 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.

Harnessing whole human liver ex situ normothermic perfusion for preclinical AAV vector evaluation

Developing clinically predictive model systems for evaluating gene transfer and gene editing technologies has become increasingly important in the era of personalized medicine. Liver-directed gene therapies present a unique challenge due to the complexity of the human liver. In this work, we describe the application of whole human liver explants in an ex situ normothermic perfusion system to evaluate a set of fourteen natural and bioengineered adeno-associated viral (AAV) vectors directly in human liver, in the presence and absence of neutralizing human sera. Under non-neutralizing conditions, the recently developed AAV variants, AAV-SYD12 and AAV-LK03, emerged as the most functional variants in terms of cellular uptake and transgene expression. However, when assessed in the presence of human plasma containing anti-AAV neutralizing antibodies (NAbs), vectors of human origin, specifically those derived from AAV2/AAV3b, were extensively neutralized, whereas AAV8- derived variants performed efficiently. This study demonstrates the potential of using normothermic liver perfusion as a model for early-stage testing of liver-focused gene therapies. The results offer preliminary insights that could help inform the development of more effective translational strategies.

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.

Treatment and management for children with urea cycle disorder in chronic stage

Urea cycle disorder (UCD) is a group of inherited metabolic diseases with high disability or fatality rate, which need long-term drug treatment and diet management. Except those with Citrin deficiency or liver transplantation, all pediatric patients require lifelong low protein diet with safe levels of protein intake and adequate energy and lipids supply for their corresponding age; supplementing essential amino acids and protein-free milk are also needed if necessary. The drugs for long-term use include nitrogen scavengers (sodium benzoate, sodium phenylbutyrate, glycerol phenylbutyrate), urea cycle activation/substrate supplementation agents (N-carbamylglutamate, arginine, citrulline), etc. Liver transplantation is recommended for pediatric patients not responding to standard diet and drug treatment, and those with severe progressive liver disease and/or recurrent metabolic decompensations. Gene therapy, stem cell therapy, enzyme therapy and other novel technologies may offer options for treatment in UCD patients. The regular biochemical assessments like blood ammonia, liver function and plasma amino acid profile are needed, and physical growth, intellectual development, nutritional intake should be also evaluated for adjusting treatment in time.

Immunosuppression reduces rAAV2.5T neutralizing antibodies that limit efficacy following repeat dosing to ferret lungs

The efficacy of redosing the recombinant adeno-associated virus (rAAV) vector rAAV2.5T to ferret lung is limited by AAV neutralizing antibody (NAb) responses. While immunosuppression strategies have allowed for systemic rAAV repeat dosing, their utility for rAAV lung-directed gene therapy is largely unexplored. To this end, we evaluated two immunosuppression (IS) strategies to improve repeat dosing of rAAV2.5T to ferret lungs: (1) a combination of three IS drugs (Tri-IS) with broad coverage against cellular and humoral responses (methylprednisolone [MP], azathioprine, and cyclosporine) and (2) MP alone, which is typically used in systemic rAAV applications. Repeat dosing utilized AAV2.5T-SP183-fCFTRΔR (recombinant ferret CFTR transgene), followed 28 days later by AAV2.5T-SP183-gLuc (for quantification of transgene expression). Both the Tri-IS and MP strategies significantly improved transgene expression following repeat dosing and reduced AAV2.5T NAb responses in the bronchioalveolar lavage fluid (BALF) and plasma, while AAV2.5T binding antibody subtypes and cellular immune responses by ELISpot were largely unchanged by IS. One exception was the reduction in plasma AAV2.5T binding immunoglobulin G (IgG) in both IS groups. Only the Tri-IS strategy significantly suppressed splenocyte expression of IFNA (interferon α [IFN-α]) and IL4. Our studies suggest that IS strategies may be useful in clinical application of rAAV targeting lung genetic diseases such as cystic fibrosis.

Adeno-associated virus vector-based gene therapies for pediatric diseases

Gene therapy using adeno-associated virus (AAV) is a rapidly developing technology with widespread treatment potential. AAV2 vectors injected directly into the brain by stereotaxic brain surgery have shown good results in treating aromatic l-amino acid decarboxylase deficiency. Moreover, gene therapy using the AAV9 vector, which crosses the blood-brain barrier, has been performed in more than 2000 patients worldwide as a disease-modifying therapy for spinal muscular atrophy. AAV vectors have been applied to the development of gene therapies for various pediatric diseases. Gene therapy trials for hemophilia and ornithine transcarbamylase deficiency are underway. Clinical trials are planned for glucose transporter I deficiency, Niemann-Pick disease type C, and spinocerebellar ataxia type 1. The genome of AAV vectors is located in the episome and is rarely integrated into chromosomes, making the vectors safe. However, serious adverse events such as hepatic failure and thrombotic microangiopathy have been reported, and ongoing studies are focusing on developing more efficient vectors to reduce required dosages.

Gene therapy for liver diseases - progress and challenges

Gene therapy is poised to revolutionize modern medicine, with seemingly unlimited potential for treating and curing genetic disorders. For otherwise incurable indications, including most inherited metabolic liver disorders, gene therapy provides a realistic therapeutic option. In this Review, we discuss gene supplementation and gene editing involving the use of recombinant adeno-associated virus (rAAV) vectors for the treatment of inherited liver diseases, including updates on several ongoing clinical trials that are producing promising results. Clinical testing has been essential in highlighting many key translational challenges associated with this transformative therapy. In particular, the interaction of a patient's immune system with the vector raises issues of safety and the duration of treatment efficacy. Furthermore, several serious adverse events after the administration of high doses of rAAVs suggest greater involvement of innate immune responses and pre-existing hepatic conditions than initially anticipated. Finally, permanent modification of the host genome associated with rAAV genome integration and gene editing raises concerns about the risk of oncogenicity that require careful evaluation. We summarize the main progress, challenges and pathways forward for gene therapy for liver diseases.

Pathogenic variants of ornithine transcarbamylase deficiency: Nation-wide study in Japan and literature review

Ornithine transcarbamylase deficiency (OTCD) is an X-linked disorder. Several male patients with OTCD suffer from severe hyperammonemic crisis in the neonatal period, whereas others develop late-onset manifestations, including hyperammonemic coma. Females with heterozygous pathogenic variants in the OTC gene may develop a variety of clinical manifestations, ranging from asymptomatic conditions to severe hyperammonemic attacks, owing to skewed lyonization. We reported the variants of CPS1, ASS, ASL and OTC detected in the patients with urea cycle disorders through a nation-wide survey in Japan. In this study, we updated the variant data of OTC in Japanese patients and acquired information regarding genetic variants of OTC from patients with OTCD through an extensive literature review. The 523 variants included 386 substitution (330 missense, 53 nonsense, and 3 silent), eight deletion, two duplication, one deletion-insertion, 55 frame shift, two extension, and 69 no category (1 regulatory and 68 splice site error) mutations. We observed a genotype-phenotype relation between the onset time (neonatal onset or late onset), the severity, and genetic mutation in male OTCD patients because the level of deactivation of OTC significantly depends on the pathogenic OTC variants. In conclusion, genetic information about OTC may help to predict long-term outcomes and determine specific treatment strategies, such as liver transplantation, in patients with OTCD.

Novel Gene-Correction-Based Therapeutic Modalities for Monogenic Liver Disorders

The majority of monogenic liver diseases are autosomal recessive disorders, with few being sex-related or co-dominant. Although orthotopic liver transplantation (LT) is currently the sole therapeutic option for end-stage patients, such an invasive surgical approach is severely restricted by the lack of donors and post-transplant complications, mainly associated with life-long immunosuppressive regimens. Therefore, the last decade has witnessed efforts for innovative cellular or gene-based therapeutic strategies. Gene therapy is a promising approach for treatment of many hereditary disorders, such as monogenic inborn errors. The liver is an organ characterized by unique features, making it an attractive target for in vivo and ex vivo gene transfer. The current genetic approaches for hereditary liver diseases are mediated by viral or non-viral vectors, with promising results generated by gene-editing tools, such as CRISPR-Cas9 technology. Despite massive progress in experimental gene-correction technologies, limitations in validated approaches for monogenic liver disorders have encouraged researchers to refine promising gene therapy protocols. Herein, we highlighted the most common monogenetic liver disorders, followed by proposed genetic engineering approaches, offered as promising therapeutic modalities.