Human factor VIII can be packaged and functionally expressed in an adeno-associated virus background: applicability to haemophilia A gene therapy

Gene therapy for hemophilia

Individuals with the inherited bleeding disorder hemophilia have achieved tremendous advances in clinical outcomes through widespread implementation of prophylactic replacement with safe and efficacious factor VIII and IX. However, despite this therapeutic approach, bleeds still occur, some with serious consequence, joint disease has not been eradicated, and patients have not yet been liberated from the need for regular intravenous infusions. The shift from protein replacement to gene replacement is offering great hope to achieve durable levels of plasma factor activity levels high enough to remove the risk for recurrent joint bleeding. For the first time, clinical trial results are showing promise for "curative" correction of the bleeding phenotype.

Evaluation of the biological differences of canine and human factor VIII in gene delivery: implications in human hemophilia treatment

The canine is the most important large animal model for testing novel hemophilia A (HA) treatment. It is often necessary to use canine factor VIII (cFIII) gene or protein for the evaluation of HA treatment in the canine model. However, different biological properties between cFVIII and human FVIII (hFVIII) indicated that the development of novel HA treatment may require careful characterization of non-human FVIII. To investigate whether the data obtained using cFVIII can translate to HA treatment in human, we analyzed the differential biological properties of canine heavy chain (cHC) and light chain (cLC) by comparing with human heavy chain (hHC) and light chain (hLC). The secretion of cHC was 5-30-fold higher than hHC, with or without light chains (LCs). cHC+hLC group exhibited ~18-fold increase in coagulation activity compared with hHC+hLC delivery by recombinant adeno-associated viral vectors. Unlike hHC, the secretion of cHC was independent of LCs. cLC improves the specific activity of FVIII by two- to threefold compared with hLC. Moreover, the cLC, but not cHC, contributes to the higher stability of cFVIII. Our results suggested that the cFVIII expression results in the canine model should be interpreted with caution as the cHC secreted more efficiently than hHC and cLC exhibited a more active and stable phenotype than hLC.

Efficient production of dual recombinant adeno-associated viral vectors for factor VIII delivery

Recombinant adeno-associated viral (rAAV) vectors have gained attention for human gene therapy because of their high safety and clinical efficacy profile. For factor VIII gene delivery, splitting the coding region between two AAV vectors remains a viable strategy to avoid the packaging capacity limitation (∼5.0 kb). However, it is time-consuming and labor-intensive to produce two rAAV vectors in separate batches. Here we demonstrated successful production of dual rAAV vectors for hemophilia A gene therapy in a single preparation. When the AAV vector plasmids carrying the human factor VIII heavy chain (hHC) and the light chain (hLC) expression cassettes were cotransfected into 293 cells along with the AAV rep&cap and mini-adenovirus helper plasmids, both rAAV-hHC and rAAV-hLC were produced at the desired ratio and in high titer. Interestingly, the rAAV-hHC vectors always yielded higher titers than rAAV-hLC vectors as a result of more efficient replication of rAAV-hHC genomes. The resulting vectors were effective in transducing the tissue culture cells in vitro. When these vectors were administered to hemophilia A mice, factor VIII was detected in the mouse plasma by both the activated partial thromboplastin time assay and enzyme-linked immunosorbent assay. The functional activity as well as the antigen levels of secreted factor VIII were similar to those of vectors produced by the traditional method. The dual-vector production method has been successfully extended to both AAV2 and AAV8 serotypes. In conclusion, cotransfection of vector plasmids presents an efficient method for producing dual or multiple AAV vectors at significantly reduced cost and labor.

Liver-Directed Adeno-Associated Viral Gene Therapy for Hemophilia

Hemophilia A and B are monogenic bleeding disorders resulting from loss of functional coagulation factors VIII or IX, respectively. Prophylactic treatment requires frequent intravenous injections of exogenous factor VIII (F.VIII) or factor IX (F.IX), due to the short half-life of both factors. Hemophilia patients are at risk of developing neutralizing antibodies to F.VIII (~25-30%) or F.IX (~2-4%), which require the use of expensive bypass agents and immune tolerance induction protocols. Viral vector mediated liver gene transfer of F.VIII or F.IX offers an alternative treatment for hemophilia with easily defined clinical endpoints and no need for strict regulation of coagulation factor expression, as both proteins circulate as inactive zymogens. Adeno-associated viral (AAV) vectors are derived from a non-pathogenic human virus that efficiently transduce non-dividing cells, such as hepatocytes, and provide stable transgene expression. In vivo liver gene transfer of AAV-F.VIII and -F.IX vectors has restored hemostasis in murine and canine hemophilia models long-term, and has also been shown to induce immune tolerance. Consequently, two Phase I/II clinical trials have been conducted, based on hepatic AAV-FIX gene transfer to patients with severe hemophilia B. The first trial, utilizing serotype 2, demonstrated transient correction, which was limited by a cellular immune response against the viral capsid. However, sustained therapeutic expression has been achieved in a second trial, using AAV8 for expression of a codon-optimized F.IX transgene. Translation of F.VIII gene transfer studies into the clinic may require additional optimization of gene transfer and vector to effectively express the larger cDNA of F.VIII.

Engineering Factor Viii for Hemophilia Gene Therapy

Current treatment of hemophilia A by intravenous infusion of factor VIII (fVIII) concentrates is very costly and has a potential adverse effect of developing inhibitors. Gene therapy, on the other hand, can potentially overcome these limitations associated with fVIII replacement therapy. Although hemophilia B gene therapy has achieved promising outcomes in human clinical trials, hemophilia A gene therapy lags far behind. Compared to factor IX, fVIII is a large protein which is difficult to express at sustaining therapeutic levels when delivered by either viral or non-viral vectors. To improve fVIII gene delivery, numerous strategies have been exploited to engineer the fVIII molecule and overcome the hurdles preventing long term and high level expression. Here we reviewed these strategies, and discussed their pros and cons in human gene therapy of hemophilia A.

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.

Computationally designed adeno-associated virus (AAV) Rep 78 is efficiently maintained within an adenovirus vector

Adeno-associated virus (AAV) is a single-stranded parvovirus retaining the unique capacity for site-specific integration into a transcriptionally silent region of the human genome, a characteristic requiring the functional properties of the Rep 78/68 polypeptide in conjunction with AAV terminal repeat integrating elements. Previous strategies designed to assemble these genetic elements into adenoviral (Ad) backbones have been limited by the general intolerability of AAV Rep sequences, prompting us to computationally reengineer the Rep gene by using synonymous codon pair recoding. Rep mutants generated by using de novo genome synthesis maintained the polypeptide sequence and endonuclease properties of Rep 78, while dramatically enhancing Ad replication and viral titer yields, characteristics indistinguishable from adenovirus lacking coexpressed Rep. Parallel approaches using domain swaps encompassing WT and recoded genomic segments, coupled with iterative computational algorithms, collectively established that 3' cis-acting Rep genetic elements (and not the Rep 78 polypeptide) retain dominant-acting sequences inhibiting Ad replication. These data provide insights into the molecular relationships of AAV Rep and Ad replication, while expanding the applicability of synonymous codon pair reengineering as a strategy to effect phenotypic endpoints.

Gene therapy strategies for hemophilia: benefits versus risks

Hemophilia is an inherited bleeding disorder caused by a deficiency of functional clotting factors VIII or IX in the blood plasma. The drawbacks of the classical protein substitution therapy fueled interest in alternative treatments by gene therapy. Hemophilia has been recognized as an ideal target disease for gene therapy because a relatively modest increase in clotting factor levels can result in a significant therapeutic benefit. Consequently, introducing a functional FVIII or FIX gene copy into the appropriate target cells could ultimately provide a cure for hemophilic patients. Several cell types have been explored for hemophilia gene therapy, including hepatocytes, muscle, endothelial and hematopoietic cells. Both nonviral and viral vectors have been considered for the development of hemophilia gene therapy, including transposons, γ-retroviral, lentiviral, adenoviral and adeno-associated viral vectors. Several of these strategies have resulted in stable correction of the bleeding diathesis in hemophilia A and B murine as well as canine models, paving the way towards clinical trials. Although clotting factor expression has been detected in hemophilic patients treated by gene therapy, the challenge now lies in obtaining prolonged therapeutic FVIII or FIX levels in these patients. This review highlights the benefits and potential risks of the different gene therapy strategies for hemophilia that have been developed.

Protein trans-splicing based dual-vector delivery of the coagulation factor VIII gene

A dual-vector system was explored for the delivery of the coagulation factor VIII gene, using intein-mediated protein trans-splicing as a means to produce intact functional factor VIII post-translationally. A pair of eukaryotic expression vectors, expressing Ssp DnaB intein-fused heavy and light chain genes of B-domain deleted factor VIII (BDD-FVIII), was constructed. With transient co-transfection of the two vectors into 293 and COS-7 cells, the culture supernatants contained (137+/-23) and (109+/-22) ng mL(-1) spliced BDD-FVIII antigen with an activity of (1.05+/-0.16) and (0.79+/-0.23) IU mL(-1) for 293 and COS-7 cells, respectively. The spliced BDD-FVIII was also detected in supernatants from a mixture of cells transfected with inteinfused heavy and light chain genes. The spliced BDD-FVIII protein bands from cell lysates were visualized by Western blotting. The data demonstrated that intein could be used to transfer the split factor VIII gene and provided valuable information on factor VIII gene delivery by dual-adeno-associated virus in hemophilia A gene therapy.

Evaluation of the oral health situation of a group of Egyptian haemophilic children and their re-evaluation following an oral hygiene and diet education programme

Haemophilic children in Egypt have received minimal dental intervention and their dental needs required assessment. The purpose of this study was to assess the oral health needs of a sample (n = 60) of Egyptian haemophilic children (6-12 years), so as to develop, implement and evaluate an oral hygiene education programme over an 8-month period on the experimental group (n = 30) vs. the control group (n = 30). The oral hygiene index simplified (OHI-S) index was used for baseline data and at the end of the study, while DMFS and defs were used to collect caries experience baseline data on each subject. The results showed that the DMFT and deft were significantly higher than those of the non-haemophilic population in Egypt and also higher than those of haemophilic children in developed countries and that the decayed component represented most of the index values. At phase I, the mean value of the OHI-S of experimental and the control groups was 2.67 +/- 0.45 and 2.53 +/- 0.53, respectively, but the difference was not significant (P > 0.05), both values were in the 'fair' category (1.3-3.0). At phase II, the end of the 8 months follow-up period and after the application of a strict oral care programme in the experimental group, there was a significant decrease from 2.67 to 1.20 (P < 0.001), a shift of values occurred from the 'fair' category to the 'good' category (0.1-1.2) while there was no significant difference in the control group. It can be concluded that professional plaque control, education and access to oral hygiene aids is paramount to improve oral health of these children.

Total correction of hemophilia A mice with canine FVIII using an AAV 8 serotype

Despite the popularity of adeno-associated virus 2 (AAV2) as a vehicle for gene transfer, its efficacy for liver-directed gene therapy in hemophilia A or B has been suboptimal. Here we evaluated AAV serotypes 2, 5, 7, and 8 in gene therapy of factor VIII (FVIII) deficiency in a hemophilia A mouse model and found that AAV8 was superior to the other 3 serotypes. We expressed canine B domain-deleted FVIII cDNA either in a single vector or in 2 separate AAV vectors containing the heavy- and light-chain cDNAs. We also evaluated AAV8 against AAV2 in intraportal and tail vein injections. AAV8 gave 100% correction of plasma FVIII activity irrespective of the vector type or route of administration.

Sustained phenotypic correction of canine hemophilia A using an adeno-associated viral vector

Gene therapy for hemophilia A requires efficient delivery of the factor VIII gene and sustained protein expression at circulating levels of at least 1% to 2% of normal. Adeno-associated viral type 2 (AAV2) vectors have a number of advantages over other viral vectors, including an excellent safety profile and persistent gene expression. However, a major disadvantage is their small packaging capacity, which has hampered their use in treating diseases such as hemophilia A, cystic fibrosis, and muscular dystrophy, which are caused by mutations in large genes. Here we demonstrate that this can be overcome by using small regulatory elements to drive expression of a B-domain-deleted form of FVIII. The use of this vector for hepatic gene transfer in a canine model of hemophilia A resulted in the sustained (> 14 months) expression of biologically active FVIII. FVIII activity levels of 2% to 4% were achieved. These levels correlated with a partial correction in the whole-blood clotting time and cuticle bleeding time. In addition, immunoprecipitation analysis demonstrated the expression of canine FVIII of the predicted size in the plasma of injected animals. These data support the use of AAV2 vectors in human clinical trials to treat hemophilia A patients.

Expression of human factor VIII under control of the platelet-specific alphaIIb promoter in megakaryocytic cell line as well as storage together with VWF

Hemophilia A, which results in defective or deficient factor VIII (FVIII) protein, is one of the genetic diseases that has been addressed through gene therapy trials. FVIII synthesis does not occur in normal megakaryocytes. In hemophilia patients who have inhibitors to FVIII activity, megakaryocytes could be a protected site of FVIII synthesis and subsequent release. Since von Willebrand factor (VWF) is a carrier protein for FVIII, we hypothesize that by directing FVIII synthesis to megakaryocytes, it would traffick together with VWF to storage in megakaryocyte alpha-granules and the platelets derived from these cells. Such synthesis would establish a protected, releasable alpha-granule pool of FVIII together with VWF. When platelets are activated in a region of local vascular damage, FVIII and VWF could potentially be released together to provide improved local hemostatic effectiveness. To direct FVIII expression to the megakaryocyte lineage, we designed a FVIII expression cassette where the human B-domain deleted FVIII cDNA was placed under the control of the megakaryocytic/platelet-specific glycoprotein IIb (alphaIIb) promoter. We demonstrated by means of a functional FVIII activity assay that the biosynthesis of FVIII occurred normally in Dami cells transfected with FVIII. FVIII production was higher when driven by the alphaIIb promoter compared to the CMV promoter, and was increased about 8-fold following PMA treatment of the transfected Dami cells. Immunofluorescence staining of the transfected cells showed that FVIII stored together with VWF in the granules. The data indicate that the megakaryocytic compartment of hematopoietic cells may represent a potential target of gene therapy for hemophilia A-especially in those patients who have developed inhibitors to plasma FVIII.

A single adeno-associated virus (AAV)-murine factor VIII vector partially corrects the hemophilia A phenotype

A major obstacle for delivery of factor (F)VIII using adeno-associated virus (AAV) vectors is the large size of FVIII cDNA, which is well above the 5 kb packaging limit for AAV. Here we construct a < 5 kb FVIII-AAV vector using murine FVIII cDNA and a strong liver-specific albumin promoter. We assessed the efficacy of this vector using three different routes of administration, intraportal, intrasplenic and tail vein injection, in FVIII knockout (FVIII KO) mice. The peak level of FVIII observed was about 8% of normal mouse FVIII activity. Even at 9 months, post vector injection, 14 of 19 mice receiving FVIII-AAV demonstrated phenotypic correction and roughly 2% FVIII activity. The transgene copy number ranged from 0.001 to 0.1 copies per cell, depending upon the somatic tissue. The potential for germline transmission of AAV was assayed in 34 pups obtained from five pairs of treated, phenotypically corrected adult hemophilic mice. Although the parents harbored the transgene in liver, spleen, and gonads, none of the 34 offspring was positive for the transgene, suggesting that the risk of inadvertent germline transmission is low.

Dual vectors expressing murine factor VIII result in sustained correction of hemophilia A mice

Hemophilia A is a sex-linked disorder that results from a deficiency of functional factor VIII and is currently treated by protein replacement therapies. Within the past decade, gene therapy efforts have come to the forefront of novel therapeutics. In this work, a dual-vector approach was employed in which recombinant adeno-associated viral (rAAV) vectors expressing the heavy and light chains of the murine factor VIII gene were delivered either intramuscularly or intravenously to a mouse model of hemophilia A. From in vitro work, it was determined that coinfection with both vectors is required as heterodimerization of the heavy and light chains occurs intracellularly. In vivo, therapeutic levels of factor VIII expression were achieved throughout the duration of the study (22 weeks). Intravenous and intramuscular delivery resulted in a maximal average expression of 31.4 +/- 6.4 and 29 +/- 6.5% of normal murine factor VIII levels, respectively. Western blots of cryoprecipitate as well as immunostaining of injection sites with an anti-murine factor VIII light chain antibody also confirmed the expression of factor VIII. Because the murine form of the gene was used in the mouse model, less than 1 Bethesda unit of inhibitors was noted. This work demonstrates the feasibility of using rAAV vectors for the long-term treatment of hemophilia A.

Use of blood outgrowth endothelial cells for gene therapy for hemophilia A

A culture of human blood outgrowth endothelial cells (BOECs) was established from a sample of peripheral blood and was transfected using a nonviral plasmid carrying complementary DNA for modified human coagulation factor VIII (B domain deleted and replaced with green fluorescence protein). BOECs were then chemically selected, expanded, cryopreserved, and re-expanded in culture. Stably transfected BOECs were administered intravenously daily for 3 days to NOD/SCID mice at 4 cell dose levels (from 5 x 10(4) to 40 x 10(4) cells per injection). In 156 days of observation, mice showed levels of human FVIII that increased with cell dose and time. Mice in all cell dose groups achieved therapeutic levels (more than 10 ng/mL) of human FVIII, and mice in the 3 highest dose groups acquired levels that were normal (100-200 ng/mL) or even above the normal range (highest observed value, 1174 ng/mL). These levels indicate that the BOECs expanded in vivo after administration. When the mice were killed, it was found that BOEC accumulated only in bone marrow and spleen and that these cells retained endothelial phenotype and transgene expression. Cell doses used here would make scale-up to humans feasible. Thus, the use of engineered autologous BOECs, which here resulted in sustained and therapeutic levels of FVIII, may comprise an effective therapeutic strategy for use in gene therapy for hemophilia A.

Toxicity of a first-generation adenoviral vector in rhesus macaques

We constructed a first-generation adenovirus vector (AVC3FIX5) that we used to assess the rhesus macaque as a nonhuman primate model for preclinical testing of hemophilia B gene therapy vectors. Although we succeeded in our primary objective of demonstrating expression of human factor IX we encountered numerous toxic side effects that proved to be dose limiting. Following intravenous administration of AVC3FIX5 at doses of 3.4 x 10(11) vector particles/kg to 3.8 x 10(12) vector particles/kg, the animals in our study developed antibodies against human factor IX, and dose-dependent elevations of enzymes specific for liver, muscle, and lung injury. In addition, these animals showed dose-dependent prolongation of clotting times as well as acute, dose-dependent decreases in platelet counts and concomitant elevation of fibrinogen and von Willebrand factor. These abnormalities may be caused by the direct toxic effects of the adenovirus vector itself, or may result indirectly from the accompanying acute inflammatory response marked by elevations in IL-6, a key regulator of the acute inflammatory response. The rhesus macaque may be a useful animal model in which to evaluate mechanisms of adenovirus toxicities that have been encountered during clinical gene therapy trials.

Gene therapy for hemophilia

Hemophilia A and B are X-chromosome linked recessive bleeding disorders that result from a deficiency in factor VIII (FVIII) and factor IX (FIX) respectively. Though factor substitution therapy has greatly improved the lives of hemophiliac patients, there are still limitations to the current treatment that have triggered interest in alternative treatments by gene therapy. Significant progress has recently been made in the development of gene therapy for the treatment of hemophilia A and B. These advances parallel the technical improvements of existing vector systems including MoMLV-based retroviral, adenoviral and AAV vectors, and the development of new delivery methods such as lentiviral vectors, helper-dependent adenoviral vectors and improved non-viral gene delivery methods. Therapeutic and physiologic levels of FVIII and FIX could be achieved in FVIII- and FIX-deficient mice and hemophilia dogs by different gene therapy approaches. Long-term correction of the bleeding disorders and in some cases a permanent cure has been realized in these preclinical studies. However, the induction of neutralizing antibodies often precludes stable phenotypic correction. Another complication is that certain promoters are prone to transcriptional inactivation in vivo, precluding long-term FVIII or FIX expression. Several gene therapy phase I clinical trials are currently ongoing in patients suffering from severe hemophilia A or B. No significant adverse side-effects were reported, and semen samples were negative for vector sequences by sensitive PCR assays. Most importantly, some subjects report fewer bleeding episodes and occasionally have very low levels of clotting factor activity detected. The results from the extensive preclinical studies in normal and hemophilic animal models and encouraging preliminary clinical data indicate that the simultaneous development of different strategies is likely to bring a permanent cure for hemophilia one step closer to reality.

Haemophilias: advances towards genetic engineering replacement therapy

Both haemophilia A and B are X-linked recessive disorders and therefore occur almost exclusively in males. The genes for both factors VIII and IX have been mapped to the distal end of the long arm of the X chromosome, bands Xq28 and Xq27.1, respectively. The Factor VIII gene comprises 186 kb DNA with 9 kb of exon of DNA which encodes an mRNA of nearly 9 kb. The Factor IX gene is 34 kb in length and the essential genetic information is present in eight exons which encode 1.6 kb mRNA. In gene therapy, genetic modification of the target cells can be either ex vivo or in vivo. The advantage of the ex vivo approach is that the genetic modification is strictly limited to the isolated cells. In the in vivo approach, the integrity of the target tissue is maintained but the major challenge is to deliver the gene to the target tissue. The use of improved retroviral and adenovirus-based vectors for gene therapy has produced clinically relevant levels of human factor VIII in mice and haemophilic dogs. If further improvements can increase the persistence of expression and decrease the immunological responses, phase I clinical trials in patients can be considered.

Biotechnology: alternatives to human plasma-derived therapeutic proteins

Proteins derived from human plasma have become critically important therapeutic products since their introduction in the 1940s. In the last 20 years, the tools of molecular biology have provided alternatives to the administration of the natural products. Recombinant analogues of Factor VIII and Factor IX are commercially available, and recombinant forms of other plasma proteins are under development. Genetic engineering also provides the opportunity to modify a natural protein to improve the efficiency with which it can be produced in vitro, or to change its therapeutic profile. More efficient production systems, such as transgenic plants or animals, may yield less costly therapies and a wider availability of products that are now in limited supply. Finally, gene therapy offers the prospect of permanently correcting conditions arising from deficiencies in any one of several plasma proteins, freeing individuals from the need to undergo periodic treatments with exogenous proteins.

Sustained expression of human factor VIII in mice using a parvovirus-based vector

Persistent therapeutic levels of human factor VIII (hFVIII) would signify a major advance in the treatment of hemophilia A. Here we report sustained expression of hFVIII in immunocompetent mice using recombinant adeno-associated virus (rAAV) vectors. AAV can stably transduce liver cells, the target tissue for efficient hFVIII production. Because of rAAV packaging constraints, we tested 2 constructs using small regulatory elements designed for liver-specific transgene expression linked to B-domain–deleted hFVIII (BDD-hFVIII) cDNA. More than 1012/mL rAAV/BDD-hFVIII virion particles were generated using a transfection scheme that eliminates adenovirus. Coatest and APTT assays confirmed the production of functional BDD-hFVIII protein after transduction of 293 and HepG2 cells. In vivo experiments were performed in C57BL/6 and NOD/scid mice receiving 1010–11 rAAV/hFVIII particles via portal vein injection. All C57BL/6 mice tested developed anti-hFVIII antibody. In contrast, NOD/scid mice expressed hFVIII reaching 27% of normal human plasma levels. As expected, we could not detect hFVIII antigen from plasma samples isolated from control animals receiving equivalent doses of rAAV expressing enhanced green fluorescent protein (EGFP). Transgene mRNA expression was detected primarily in the liver and histologic analysis of the liver revealed no pathologic abnormalities. These results demonstrate a promising approach for treatment of hemophilia A.