The treatment of hemophilia A: from protein replacement to AAV-mediated gene therapy

Advancements in gene transfer-based therapy for hemophilia A

Gene therapy has promised clinical benefit to those suffering with hemophilia A, but this benefit has not yet been realized. However, during the past two decades, basic and applied gene therapy research has progressed and the goal of gene therapy for hemophilia A is once again in our sights. The hemophilia A patient population suffers from a disease that requires invasive, lifelong management, is exorbitantly expensive to treat, has geographically limited treatment access and can become untreatable due to immune reactions to the treatment product. Subsequent to the cloning of the factor VIII gene and cDNA in the early 1980s, academic and commercial research laboratories began to pursue gene transfer-based therapies to supplement or supplant the available protein replacement therapy. However, to date, clinical trials for gene therapy of hemophilia A have been unsuccessful. Three trials have been conducted with each having tested a different gene-transfer strategy and each demonstrating that there is a considerable barrier to achieving sustained expression of therapeutic amounts of factor VIII. Recent progress has been made in gene-transfer technology and, relevant to hemophilia A, towards increasing the biosynthetic efficiency of factor VIII. These advances are now being combined to develop novel strategies to treat and possibly cure hemophilia A.

Haemophilia B: current pharmacotherapy and future directions

INTRODUCTION

Hemophilia B is a rare hereditary hemorrhagic disorder characterized by deficiency of the clotting factor IX (FIX). Hemophilia B patients experience mild to severe bleeding complications according to the degree of FIX defect. Nowadays, the most challenging complication of individuals with hemophilia B is the development of alloantibodies, which render the standard replacement therapy with FIX concentrates ineffective, exposing them to a significantly increased morbidity and mortality.

AREAS COVERED

This review summarizes the most important events leading to the development of the current FIX products available for the treatment of hemophilia B patients. In addition, it focuses on the more recent advances in the production of new FIX molecules aimed at improving the clinical management of such patients.

EXPERT OPINION

Although the availability of plasma-derived FIX concentrates has greatly improved the clinical management of hemophilia B patients, the introduction of FIX products using recombinant DNA technology has represented the most significant therapeutic progress in hemophilia B therapy, ensuring an advanced level of safety. The development of rFIX products with extended half lives will further improve the therapeutic armamentarium for hemophilia B patients.

Past, present and future of hemophilia: a narrative review

Over the past forty years the availability of coagulation factor replacement therapy has greatly contributed to the improved care of people with hemophilia. Following the blood-borne viral infections in the late 1970s and early 1980, caused by coagulation factor concentrates manufactured using non-virally inactivated pooled plasma, the need for safer treatment became crucial to the hemophilia community. The introduction of virus inactivated plasma-derived coagulation factors and then of recombinant products has revolutionized the care of these people. These therapeutic weapons have improved their quality of life and that of their families and permitted home treatment, i.e., factor replacement therapy at regular intervals in order to prevent both bleeding and the resultant joint damage (i.e. primary prophylaxis). Accordingly, a near normal lifestyle and life-expectancy have been achieved. The main current problem in hemophilia is the onset of alloantibodies inactivating the infused coagulation factor, even though immune tolerance regimens based on long-term daily injections of large dosages of coagulation factors are able to eradicate inhibitors in approximately two-thirds of affected patients. In addition availability of products that bypass the intrinsic coagulation defects have dramatically improved the management of this complication. The major challenges of current treatment regimens, such the short half life of hemophilia therapeutics with need for frequent intravenous injections, encourage the current efforts to produce coagulation factors with more prolonged bioavailability. Finally, intensive research is devoted to gene transfer therapy, the only way to ultimately obtain cure in hemophilia.

Efficient Nonviral Gene Therapy Using Folate-Targeted Chitosan-DNA Nanoparticles In Vitro

Nonviral cationic polymers like chitosan can be combined with DNA to protect it from degradation. The chitosan is a biocompatible, biodegradable, nontoxic, and cheap polycationic polymer with low immunogenicity. The objective of this study was to synthesize and then assess different chitosan-DNA nanoparticles and to select the best ones for selective in vitro transfection in human epidermoid carcinoma (KB) cell lines. It revealed that different combinations of molecular weight, the presence or absence of folic acid ligand, and different plasmid DNA sizes can lead to nanoparticles with various diameters and diverse transfection efficiencies. The intracellular trafficking, nuclear uptake, and localization are also studied by confocal microscopy, which confirmed that DNA was delivered to cell nuclei to be expressed.

Prospects for the use of artificial chromosomes and minichromosome-like episomes in gene therapy

Artificial chromosomes and minichromosome-like episomes are large DNA molecules capable of containing whole genomic loci, and be maintained as nonintegrating, replicating molecules in proliferating human somatic cells. Authentic human artificial chromosomes are very difficult to engineer because of the difficulties associated with centromere structure, so they are not widely used for gene-therapy applications. However, OriP/EBNA1-based episomes, which they lack true centromeres, can be maintained stably in dividing cells as they bind to mitotic chromosomes and segregate into daughter cells. These episomes are more easily engineered than true human artificial chromosomes and can carry entire genes along with all their regulatory sequences. Thus, these constructs may facilitate the long-term persistence and physiological regulation of the expression of therapeutic genes, which is crucial for some gene therapy applications. In particular, they are promising vectors for gene therapy in inherited diseases that are caused by recessive mutations, for example haemophilia A and Friedreich's ataxia. Interestingly, the episome carrying the frataxin gene (deficient in Friedreich's ataxia) has been demonstrated to rescue the susceptibility to oxidative stress which is typical of fibroblasts from Friedreich's ataxia patients. This provides evidence of their potential to treat genetic diseases linked to recessive mutations through gene therapy.

Physicochemical and biological properties of self-assembled antisense/poly(amidoamine) dendrimer nanoparticles: the effect of dendrimer generation and charge ratio

To gain a deeper understanding of the physicochemical phenomenon of self-assembled nanoparticles of different generations and ratios of poly (amidoamine) dendrimer (PAMAM) dendrimer and a short-stranded DNA (antisense oligonucleotide), multiple methods were used to characterize these nanoparticles including photon correlation spectroscopy (PCS); zeta potential measurement; and atomic force microscopy (AFM). PCS and AFM results revealed that, in contrast to larger molecules of DNA, smaller molecules produce more heterodisperse and large nanoparticles when they are condensed with a cationic dendrimer. AFM images also showed that such nanoparticles were spherical. The stability of the antisense content of the nanoparticles was investigated over different charge ratios using polyacrylamide gel electrophoresis. It was clear from such analyses that much more than charge neutrality point was required to obtain stable nanoparticles. For cell uptake, self-assembled nanoparticles were prepared with PAMAM G5 and 5’-FITC labeled antisense and the uptake experiment was carried out in T47D cell culture. This investigation also shows that the cytotoxicity of the nanoparticles was dependent upon the generation and charge ratio of the PAMAM dendrimer, and the antisense concentration had no significant effect on the cytotoxicity.

Efficient AAV1-AAV2 hybrid vector for gene therapy of hemophilia

Adeno-associated virus (AAV) serotype 1 (AAV1) has been shown to be more effective than the well-studied AAV serotype 2 (AAV2) in muscle gene transfer. Replacement of amino acids 350 to 430 of AAV2 VP1 with the corresponding amino acids from VP1 of AAV1 resulted in a hybrid vector, termed AAV-221-IV, which behaved similarly to AAV1 in vitro and in vivo in muscle. Intramuscular injection of 1x10(11) vector particles per mouse of hybrid vector carrying a human FIX transgene in CD4 knockout mice resulted in an average level of human FIX in the plasma of 450 ng/ml, 4- to 10-fold higher than in mice injected with an AAV2 vector carrying the same transgene, and 80% of the transgene levels in animals treated with the same dose of AAV1. DNA analysis of injected muscle showed a 10-fold higher copy number after gene delivery by the hybrid vector compared with AAV2. A comparison of total DNA versus DNA from intact virus particles suggests a higher stability of hybrid virus particles. These results suggest that changes in the AAV capsid have an effect on virus-cell receptor interaction, and also influence trafficking and processing of the virus particle in the cell. This "hybrid vector" retains the heparin-binding sites of AAV2 and, therefore, can be purified by passage through a heparin-Sepharose column with the same efficiency as AAV2. When tested in vivo, either in CD4 knockout mice or in a hemophilic mouse model, the heparin-purified hybrid vector showed >10-fold higher activity than similarly purified AAV2. This demonstrates the utility of this hybrid vector in the performance of large-scale heparin column purification to generate a vector with a high expression profile for muscle-directed gene delivery. Initiation of clinical studies with this hybrid vector may be facilitated because it differs from AAV2 by only nine amino acids.