Gene therapy for haemophilia

Minimizing the inhibitory effect of neutralizing antibody for efficient gene expression in the liver with adeno-associated virus 8 vectors

Neutralizing antibodies (NAbs) against adeno-associated viruses (AAVs) are known to interfere with AAV vector-mediated gene transfer by intravascular delivery. Evading the inhibitory effects of antibodies against AAV vectors is necessary for efficient transfer of therapeutic genes clinically. For this purpose, we tested the efficacy of saline flushing in order to avoid contact of vectors with NAbs present in blood. Direct injection of the AAV8 vector carrying the factor IX (FIX) gene into the portal vein of macaques using saline flushing achieved transgene-derived FIX expression (4.7 ± 2.10-10.1 ± 5.45% of normal human FIX concentration) in the presence of NAbs. Expression was as efficient as that (5.43 ± 2.59-12.68 ± 4.83%) in macaques lacking NAbs. We next tested the efficacy of saline flushing using less invasive balloon catheter-guided injection. This approach also resulted in efficient expression of transgene-derived FIX (2.5 ± 1.06-9.0 ± 2.37%) in the presence of NAbs (14-56× dilutions). NAbs at this range of titers reduced the efficiency of transduction in the macaque liver by 100-fold when the same vector was injected into mesenteric veins without balloon catheters. Our results suggest that portal vein-directed vector delivery strategies with flushing to remove blood are efficacious for minimizing the inhibitory effect of anti-AAV antibodies.

Liver-restricted expression of the canine factor VIII gene facilitates prevention of inhibitor formation in factor VIII-deficient mice

BACKGROUND

Gene therapy for hemophilia A with adeno-associated virus (AAV) vectors involves difficulties in the efficient expression of factor VIII (FVIII) and in antibody formation against transgene-derived FVIII.

METHODS

AAV8 vectors carrying the canine B domain deleted FVIII (cFVIII) gene under the control of the ubiquitous beta-actin promoter, the liver-specific human alpha1 anti-trypsin promoter (HAAT) and the liver-specific hepatic control region (HCR) enhancer/human alpha1 anti-trypsin promoter complex (HCRHAAT) were used for the expression of cFVIII in FVIII deficient (fviii(-/-)) mice.

RESULTS

Addition of the hepatic control region enhancer element to the HAAT promoter successfully augmented HAAT promoter activity without loss of liver-specificity in vivo. Using this enhancer/promoter complex, a high cFVIII transgene expression was achieved, resulting in increased blood cFVIII activities to more than 100% of the normal canine FVIII levels in fviii(-/-) mice at a 1 : 10 lower dose of the AAV8 vector carrying the cFVIII gene driven by the HAAT promoter. Under short-term immunosuppression, neutralizing antibodies against cFVIII developed in only one out of six mice when the HAAT promoter was used for cFVIII expression, whereas all the mice developed neutralizing antibodies against cFVIII when the beta-actin promoter was used for cFVIII expression. No neutralizing antibodies against cFVIII developed in fviii(-/-) mice that received the AAV8 vector carrying the cFVIII gene driven by the HCRHAAT enhancer/promoter complex without immunosuppression.

CONCLUSIONS

These data suggest that AAV8 vector-mediated liver-restricted cFVIII gene expression is sufficient for immune hypo-responsiveness to transgene-derived cFVIII in fviii(-/-) mice.

Protein replacement therapy and gene transfer in canine models of hemophilia A, hemophilia B, von willebrand disease, and factor VII deficiency

Dogs with hemophilia A, hemophilia B, von Willebrand disease (VWD), and factor VII deficiency faithfully recapitulate the severe bleeding phenotype that occurs in humans with these disorders. The first rational approach to diagnosing these bleeding disorders became possible with the development of reliable assays in the 1940s through research that used these dogs. For the next 60 years, treatment consisted of replacement of the associated missing or dysfunctional protein, first with plasma-derived products and subsequently with recombinant products. Research has consistently shown that replacement products that are safe and efficacious in these dogs prove to be safe and efficacious in humans. But these highly effective products require repeated administration and are limited in supply and expensive; in addition, plasma-derived products have transmitted bloodborne pathogens. Recombinant proteins have all but eliminated inadvertent transmission of bloodborne pathogens, but the other limitations persist. Thus, gene therapy is an attractive alternative strategy in these monogenic disorders and has been actively pursued since the early 1990s. To date, several modalities of gene transfer in canine hemophilia have proven to be safe, produced easily detectable levels of transgene products in plasma that have persisted for years in association with reduced bleeding, and correctly predicted the vector dose required in a human hemophilia B liver-based trial. Very recently, however, researchers have identified an immune response to adeno-associated viral gene transfer vector capsid proteins in a human liver-based trial that was not present in preclinical testing in rodents, dogs, or nonhuman primates. This article provides a review of the strengths and limitations of canine hemophilia, VWD, and factor VII deficiency models and of their historical and current role in the development of improved therapy for humans with these inherited bleeding disorders.

FVIII gene delivery by muscle electroporation corrects murine hemophilia A

BACKGROUND

Hemophilia A treatment relies on costly factor VIII (FVIII) replacement that may transmit iatrogenic viral diseases. Viral vectors and cell implants are being developed as improvements. We investigated in vivo electroporation of naked DNA as a safe and simple method for correcting FVIII deficiency.

METHODS

B-domain-deleted murine FVIII cDNA expression plasmids were constructed with CMV and elongation factor 1alpha promoters for characterisation in murine C2C12 myoblasts. The construct conferring highest in vitro FVIII secretion was electroporated into skeletal muscle of FVII null mice in vivo for phenotypic correction using a protocol that minimised tissue injury.

RESULTS

B-domain-deleted murine FVIII cDNA plasmids induced FVIII secretion from stably transfected C2C12 myoblasts (0.54+/-0.20 mU/day/10(5) cells). Phenotypic correction of hemophilic mice was more consistently achieved using a protocol for in vivo electroporation of gastrocnemius muscle with FVIII cDNA that reduced tissue injury by the use of plate electrodes, hyaluronidase pre-treatment and lower field strength. This technique was associated with <10% muscle necrosis. Activated partial thromboplastin time decreased from 51.4+/-3.3 to 34.7+/-1.1 (mean+/-s.e.m.) seconds (p=0.0004) following in vivo electroporation (0.1 mg plasmid/limb; 8x20 ms pulses, 175 V/cm, 1 Hz) of hemophilic mice. All hemophilic mice (8/8) survived hemostatic challenge after muscle electroporation with FVIII cDNA, whereas all (9/9) untreated hemophilic mice died. Plasmid DNA was detectable only in electroporated muscle and not in all other organs tested, including gonads.

CONCLUSION

In vivo intramuscular electroporation of naked FVIII plasmid successfully corrects murine hemophilia.

Preclinical experiment of auxiliary partial orthotopic liver transplantation as a curative treatment for hemophilia

The cause of hemophilia is deficiency of coagulation factor VIII production in the liver, which can be cured by liver transplantation. Because the hepatic function of hemophilia patients is quite normal except for production of factor VIII, auxiliary partial orthotopic liver transplantation (APOLT) is beneficial in that patient survival is secured by preserving native liver even in the event of graft loss. However, it is not known whether the graft of APOLT would be enough to cure hemophilia. We evaluated the efficacy and feasibility of APOLT for hemophilia in a canine hemophilia A model that we established. Partial left liver graft was taken from the normal donor (blood factor VIII activity > 60%). The graft was transplanted to the hemophilia beagle dog (blood factor VIII activity < 5%) after resection of the left lobe preserving native right lobe. Changes in time of blood factor VIII activity and liver function parameters were observed after APOLT. APOLT and perioperative hemostatic management were successfully performed. The blood factor VIII activity increased to 30% after APOLT, and was sustained at least 6 weeks throughout the observation period without symptoms of bleeding. The result demonstrated sustained production of factor VIII in the hemophilia recipient after APOLT. Transplantation of approximately one third of whole liver resulted in cure of hemophilia. In conclusion, it is suggested that APOLT would be feasible as a curative treatment of hemophilia A to improve quality of life of the patients.

Targeting lentiviral vector expression to hepatocytes limits transgene-specific immune response and establishes long-term expression of human antihemophilic factor IX in mice

Stable gene replacement by in vivo administration of lentiviral vectors (LVs) has therapeutic potential for metabolic disorders and other systemic diseases. We studied the expression of intracellular and secreted proteins by LVs in immunocompetent mice. Liver, spleen, and bone marrow cells were efficiently transduced. However, transgene expression, driven by a ubiquitous promoter, was limited by transgene-specific cellular and humoral immune responses, leading to the clearance of transduced cells. After green fluorescent protein (GFP) gene transfer, the liver showed infiltration of CD8(+) cytotoxic T cells, and GFP-specific CD8(+) T cells were isolated from the spleen. After human factor IX (hF.IX) gene transfer, anti-hF.IX antibodies were induced. These immune responses were not detected in mice injected with heat-inactivated or genome-lacking LVs or in GFP-transgenic mice, indicating that they were specifically triggered by transgene expression in vivo. Intriguingly, selective targeting of LV expression to hepatocytes limited the immune responses to the transgenes. By this approach, high levels of hF.IX, potentially in the therapeutic range, were reached and maintained long term in immunocompetent mice, without inducing antibody formation. These results prompt further studies in relevant animal models to explore the potential of in vivo LV administration for the gene therapy of hemophilias and other liver-based diseases.

Phase 1 trial of FVIII gene transfer for severe hemophilia A using a retroviral construct administered by peripheral intravenous infusion

In a phase 1 dose escalation study, 13 subjects with hemophilia A received by peripheral intravenous infusion a retroviral vector carrying a B-domain-deleted human factor VIII (hFVIII) gene. Infusions were well tolerated. Tests for replication competent retrovirus have been negative. Polymerase chain reaction (PCR) analyses demonstrate the persistence of vector gene sequences in peripheral blood mononuclear cells in 3 of 3 subjects tested. Factor VIII was measured in serial samples using both a one-stage clotting assay and a chromogenic assay. While no subject had sustained FVIII increases, 9 subjects had FVIII higher than 1% on at least 2 occasions 5 or more days after infusion of exogenous FVIII, with isolated levels that ranged from 2.3% to 19%. Pharmacokinetic parameters of exogenous FVIII infused into subjects 13 weeks after vector infusion showed an increased half-life (T1/2; P <.02) and area under the curve (AUC, P <.04) compared with prestudy values. Bleeding frequency decreased in 5 subjects compared with historical rates. These results demonstrate that this retroviral vector (hFVIII(V)) is safe and, in some subjects, persists more than a year in peripheral blood mononuclear cells, with measurable factor VIII levels and with increased available FVIII activity (increased T1/2 and AUC) after infusion of exogenous FVIII concentrate.

Haemophilias A and B

The haemophilias are inherited disorders in which one of the coagulation factors is deficient. Although deficiencies of factor VIII (haemophilia A) and factor IX (haemophilia B) are well recognised, von Willebrand's disease is much more common. Rare defects can occur in any of the coagulation factors. In the past, men with haemophilia were likely to die in their youth. With advances in diagnosis, and especially with development of safe and effective treatment, affected individuals can now look forward to a normal life expectancy. Complications of the disorder, particularly the development of antibodies that make treatment ineffective, and of treatment, such as transfusion-transmitted infections, have taken a severe toll on these patients. The future holds the realistic possibility of gene therapy. However, we must not forget that haemophilia is a worldwide disorder that requires significant economic resources not available for the majority.

Haemophilia B: from molecular diagnosis to gene therapy

Thanks to its typical expression, haemophilia can be identified in writings from the second century AD. Haemophilia B, an X-linked recessive bleeding disorder due to factor IX (FIX) deficiency, has an incidence of about 1:30,000 live male births. The factor 9 (F9) gene was mapped in 1984 on Xq27.1. Haemophilia is diagnosed from prothrombin time, activated partial thromboplastin time, and FIX levels. Carrier females are usually asymptomatic and must be identified only with molecular analysis. Linkage analysis of F9 polymorphisms is rapid and inexpensive but limited by non-informative families, recombinant events, and the high incidence of germline mutations; thus, various procedures have been used for the direct scan of F9 mutations. We set up a novel denaturing high performance liquid chromatographic procedure to scan the F9 gene. This rapid, reproducible procedure detected F9 mutations in 100% of a preliminary cohort of 18 haemophilia B patients. Parallel to the development of more efficient diagnostic tools, the life expectancy and reproductive fitness of haemophilic patients have greatly improved and will continue to improve thanks to the use of less immunogenic recombinant FIX. Hopefully, new approaches based on gene therapy now being evaluated in clinical trials will revolutionise haemophilia B treatment.