A novel gene expression system: non-viral gene transfer for hemophilia as model systems

Ultrasound-mediated gene delivery specifically targets liver sinusoidal endothelial cells for sustained FVIII expression in hemophilia A mice

The ability to target the native production site of factor VIII (FVIII)-liver sinusoidal endothelial cells (LSECs)-can improve the outcome of hemophilia A (HA) gene therapy. By testing a matrix of ultrasound-mediated gene delivery (UMGD) parameters for delivering a GFP plasmid into the livers of HA mice, we were able to define specific conditions for targeted gene delivery to different cell types in the liver. Subsequently, two conditions were selected for experiments to treat HA mice via UMGD of an endothelial-specific human FVIII plasmid: low energy (LE; 50 W/cm2, 150 μs pulse duration) to predominantly target endothelial cells or high energy (HE; 110 W/cm2, 150 μs pulse duration) to predominantly target hepatocytes. Both groups of UMGD-treated mice achieved persistent FVIII activity levels of ∼10% over 84 days post treatment; however, half of the HE-treated mice developed low-titer inhibitors while none of the LE mice did. Plasma transaminase levels and histological liver examinations revealed minimal transient liver damage that was lower in the LE group than in the HE group. These results indicate that UMGD can safely target LSECs with a lower-energy condition to achieve persistent FVIII gene expression, demonstrating that this novel technology is highly promising for therapeutic correction of HA.

Influence of N-glycosylation in the A and C domains on the immunogenicity of factor VIII

The most significant complication in hemophilia A treatment is the formation of inhibitors against factor VIII (FVIII) protein. Glycans and glycan-binding proteins are central to a properly functioning immune system. This study focuses on whether glycosylation of FVIII plays an important role in induction and regulation of anti-FVIII immune responses. We investigated the potential roles of 4 N-glycosylation sites, including N41 and N239 in the A1 domain, N1810 in the A3 domain, and N2118 in the C1 domain of FVIII, in moderating its immunogenicity. Glycomics analysis of plasma-derived FVIII revealed that sites N41, N239, and N1810 contain mostly sialylated complex glycoforms, while high mannose glycans dominate at site N2118. A missense variant that substitutes asparagine (N) to glutamine (Q) was introduced to eliminate glycosylation on each of these sites. Following gene transfer of plasmids encoding B domain deleted FVIII (BDD-FVIII) and each of these 4 FVIII variants, it was found that specific activity of FVIII in plasma remained similar among all treatment groups. Slightly increased or comparable immune responses in N41Q, N239Q, and N1810Q FVIII variant plasmid-treated mice and significantly decreased immune responses in N2118Q FVIII plasmid-treated mice were observed when compared with BDD-FVIII plasmid-treated mice. The reduction of inhibitor response by N2118Q FVIII variant was also demonstrated in AAV-mediated gene transfer experiments. Furthermore, a specific glycopeptide epitope surrounding the N2118 glycosylation site was identified and characterized to activate T cells in an FVIII-specific proliferation assay. These results indicate that N-glycosylation of FVIII can have significant impact on its immunogenicity.

Transcutaneous ultrasound mediated gene delivery into canine livers achieves therapeutic levels of FVIII expression

Nonviral UMGD can achieve therapeutic levels of FVIII gene expression in a large animal model.

UMGD targeting liver is safe without evidence of any lasting damage.

A safe, effective, and inclusive gene therapy will significantly benefit a large population of patients with hemophilia. We used a minimally invasive transcutaneous ultrasound-mediated gene delivery (UMGD) strategy combined with microbubbles (MBs) to enhance gene transfer into 4 canine livers. A mixture of high-expressing, liver-specific human factor VIII (hFVIII) plasmid and MBs was injected into the hepatic vein via balloon catheter under fluoroscopy guidance with simultaneous transcutaneous UMGD treatment targeting a specific liver lobe. Therapeutic levels of hFVIII expression were achieved in all 4 dogs, and hFVIII levels were maintained at a detectable level in 3 dogs throughout the 60-day experimental period. Plasmid copy numbers correlated with hFVIII antigen levels, and plasmid-derived messenger RNA (mRNA) was detected in treated livers. Liver transaminase levels and histology analysis indicated minimal liver damage and a rapid recovery after treatment. These results indicate that liver-targeted transcutaneous UMGD is promising as a clinically feasible therapy for hemophilia A and other diseases.

Ultrasound-mediated gene delivery of factor VIII plasmids for hemophilia A gene therapy in mice

Gene therapy offers great promises for a cure of hemophilia A resulting from factor VIII (FVIII) gene deficiency. We have developed and optimized a non-viral ultrasound-mediated gene delivery (UMGD) strategy. UMGD of reporter plasmids targeting mice livers achieved high levels of transgene expression predominantly in hepatocytes. Following UMGD of a plasmid encoding human FVIII driven by a hepatocyte-specific promoter/enhancer (pHP-hF8/N6) into the livers of hemophilia A mice, a partial phenotypic correction was achieved in treated mice. In order to achieve persistent and therapeutic FVIII gene expression, we adopted a plasmid (pHP-hF8-X10) encoding an FVIII variant with significantly increased FVIII secretion. By employing an optimized pulse-train ultrasound condition and immunomodulation, the treated hemophilia A mice achieved 25%–150% of FVIII gene expression on days 1–7 with very mild transient liver damage, as indicated by a small increase of transaminase levels that returned to normal within 3 days. Therapeutic levels of FVIII can be maintained persistently without the generation of inhibitors in mice. These results indicate that UMGD can significantly enhance the efficiency of plasmid DNA transfer into the liver. They also demonstrate the potential of this novel technology to safely and effectively treat hemophilia A.

Modulation of Immune Reaction in Hydrodynamic Gene Therapy for Hemophilia A

Hemophilia A (HA) is a monogenic disease characterized by plasma clotting factor 8 (F8) deficiency due to F8 mutation. We have been attempting to cure HA permanently using a CRISPR-Cas9 gene-editing strategy. Here, we induced targeted integration of BDDF8 (B-domain-deleted F8) gene into the albumin locus of HA mice by hydrodynamic tail vein injection of editing plasmid vectors. One week after treatment, a high F8 activity ranging from 70% to 280% of normal serum levels was observed in all treated HA mice but dropped to background levels 3-5 weeks later. We found that the humoral immune reaction targeting F8 is the predominant cause of the decreased F8 activity. We hypothesized that hydrodynamic injection-induced liver damage triggered the release of large quantities of inflammatory cytokines. However, co-injection of plasmids expressing a dozen immunomodulatory factors failed to curtail the immune reaction and stabilize F8 activity. The spCas9 plasmid carrying a miR-142-3p target sequence alleviated the cellular immune response but was unable to deliver therapeutic efficacy. Strikingly, immunosuppressant cyclo-phosphamide virtually abolished the immune response, leading to a year-long stable F8 level. Our findings should have important implications in developing therapies in mouse models using the hydrodynamic gene delivery approach, highlighting the ne-cessity of modulating the innate immune response triggered by liver damage.

Physical methods for gene transfer

The key impediment to the successful application of gene therapy in clinics is not the paucity of therapeutic genes. It is rather the lack of nontoxic and efficient strategies to transfer therapeutic genes into target cells. Over the past few decades, considerable progress has been made in gene transfer technologies, and thus far, three different delivery systems have been developed with merits and demerits characterizing each system. Viral and chemical methods of gene transfer utilize specialized carrier to overcome membrane barrier and facilitate gene transfer into cells. Physical methods, on the other hand, utilize various forms of mechanical forces to enforce gene entry into cells. Starting in 1980s, physical methods have been introduced as alternatives to viral and chemical methods to overcome various extra- and intracellular barriers that limit the amount of DNA reaching the intended cells. Accumulating evidence suggests that it is quite feasible to directly translocate genes into cytoplasm or even nuclei of target cells by means of mechanical force, bypassing endocytosis, a common pathway for viral and nonviral vectors. Indeed, several methods have been developed, and the majority of them share the same underlying mechanism of gene transfer, i.e., physically created transient pores in cell membrane through which genes get into cells. Here, we provide an overview of the current status and future research directions in the field of physical methods of gene transfer.

In vivo screening for secreted proteins that modulate glucose handling identifies interleukin-6 family members as potent hypoglycemic agents

Diabetes is a disease of abnormal glucose homeostasis characterized by chronic hyperglycemia and a broad array of consequent organ damage. Because normal glucose homeostasis is maintained by a complex interaction between behavior (feeding and physical activity) and metabolic activity that is modulated by inter-organ signaling through secreted factors, disease modeling in vitro is necessarily limited. In contrast, in vivo studies allow complex metabolic phenotypes to be studied but present a barrier to high throughput studies. Here we present the development of a novel in vivo screening platform that addresses this primary limitation of in vivo experimentation. Our platform leverages the large secretory capacity of the liver and the hepatocyte transfection technique of hydrodynamic tail vein injection to achieve supraphysiologic blood levels of secreted proteins. To date, the utility of hydrodynamic transfection has been limited by the deleterious impact of the variable transfection efficiency inherent to this technique. We overcome this constraint by co-transfection of a secreted luciferase cDNA whose product can be easily monitored in the blood of a living animal and used as a surrogate marker for transfection efficiency and gene expression levels. To demonstrate the utility of our strategy, we screened 248 secreted proteins for the ability to enhance glucose tolerance. Surprisingly, interleukin-6 and several of its family members but not other well-recognized insulin sensitizing agents were identified as potent hypoglycemic factors. We propose this experimental system as a powerful and flexible in vivo screening platform for identifying genes that modulate complex behavioral and metabolic phenotypes.

Animal models of hemophilia

The X-linked bleeding disorder hemophilia is caused by mutations in coagulation factor VIII (hemophilia A) or factor IX (hemophilia B). Unless prophylactic treatment is provided, patients with severe disease (less than 1% clotting activity) typically experience frequent spontaneous bleeds. Current treatment is largely based on intravenous infusion of recombinant or plasma-derived coagulation factor concentrate. More effective factor products are being developed. Moreover, gene therapies for sustained correction of hemophilia are showing much promise in preclinical studies and in clinical trials. These advances in molecular medicine heavily depend on availability of well-characterized small and large animal models of hemophilia, primarily hemophilia mice and dogs. Experiments in these animals represent important early and intermediate steps of translational research aimed at development of better and safer treatments for hemophilia, such a protein and gene therapies or immune tolerance protocols. While murine models are excellent for studies of large groups of animals using genetically defined strains, canine models are important for testing scale-up and for long-term follow-up as well as for studies that require larger blood volumes.

Gene therapy for haemophilia...yes, but...with non-viral vectors?

High-purity plasma-derived and recombinant factors are currently safe and efficient treatment for haemophilia. The mid-term future of haemophilia treatment will involve the use of modified recombinant factors to achieve advantages such as decreased immunogenicity in inhibitor formation and enhanced efficacy as a result of their longer half-life. In the long-term, gene therapy and cell therapy strategies will have to be considered. Achievements in cell therapy to date have been using embryonic stem cells and hepatic sinusoidal endothelial cells. Current gene therapy strategies for haemophilia are based on gene transfer using adeno-associated viruses and non-viral vectors. Gene therapy for haemophilia is justified because it is a chronic disease and because a very regular factor infusion is required that may involve fatal risks and because it is very expensive. Haemophilia is a very good candidate for use of gene therapy protocols because it is a monogenic disease, and even low expression is able to achieve reversion from a severe to a moderate phenotype. The current trends in haemophilia using adeno-associated viral vectors are safe but also involve immunogenicity problems. The other alternatives are non-viral vectors. There have been in recent years relevant advances in non-viral transfection that raise hope for considering this possibility. Several research groups are opting for this experimental alternative. An expression over 5%, representing a moderate phenotype, for a few months with a high safety, regarding vector, transfected cells, and implantation procedure, would already be a great success. This may represent an intermediate protocol in which the expression levels and times obtained are lower and shorter respectively as compared to viral vectors, but which provide a potential greater patient safety. This may more readily win acceptance among both patients and haematologists because fatal events in the past due to HIV/HCV infection may constrain the implementation of viruses as vectors.

Hydrodynamic gene delivery: its principles and applications

Efficient and safe methods for delivering genetic materials into cells must be developed before the clinical potential of gene therapy can be fully realized. Recently, hydrodynamic gene delivery using a rapid injection of a relatively large volume of DNA solution has opened up a new avenue for gene therapy studies in vivo. This method is superior to the existing delivery systems because of its simplicity, efficiency, and versatility. Wide success in applying hydrodynamic principles to delivery of DNA, RNA, proteins, and synthetic compounds, into the cells in various tissues of small animals, has inspired the recent attempts at establishing a hydrodynamic procedure for clinical use. In this review, we provide an overview of the theory and practice of hydrodynamic gene delivery so as to aid researchers for the use of this method in their pre-clinical and translational gene therapy studies.

Gene therapy progress and prospects: hydrodynamic gene delivery

Over the last few years, hydrodynamic tail vein delivery has established itself as a simple, yet very effective method for gene transfer into small rodents. Hydrodynamic delivery of plasmid DNA expression vectors or small interfering RNA allows for a broad range of in vivo experiments, including the testing of regulatory elements, antibody generation, evaluation of gene therapy approaches, basic biology and disease model creation (non-heritable transgenics). The recent development of the hydrodynamic limb vein procedure provides a safe nucleic acid delivery technique with equally high efficiency in small and large research animals and, importantly, the prospects for clinical translation.

Polymers for gene delivery across length scales

A number of human diseases stem from defective genes. One approach to treating such diseases is to replace, or override, the defective genes with normal genes, an approach called 'gene therapy'. However, the introduction of correctly functioning DNA into cells is a non-trivial matter, and cells must be coaxed to internalize, and then use, the DNA in the desired manner. A number of polymer-based synthetic systems, or 'vectors', have been developed to entice cells to use exogenous DNA. These systems work across the nano, micro and macro length scales, and have been under continuous development for two decades, with varying degrees of success. The design criteria for the construction of more-effective delivery vectors at each length scale are continually evolving. This review focuses on the most recent developments in polymer-based vector design at each length scale.