Naked DNA transfer of Factor VIII induced transgene-specific, species-independent immune response in hemophilia A mice

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.

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.

CD4+ T cells engineered with FVIII-CAR and murine Foxp3 suppress anti-factor VIII immune responses in hemophilia a mice

Although protein replacement therapy provides effective treatment for hemophilia A patients, about a third of severe patients develop neutralizing inhibitor antibodies to factor VIII. Adoptive transfer of regulatory T cells (Tregs) has shown promise in treating unwanted immune responses. In previous studies, transferred polyclonal Tregs ameliorated the anti-factor VIII immune responses in hemophilia A mice. In addition, factor VIII-primed Tregs demonstrated increased suppressive function. However, antigen-specific Tregs are a small fraction of the total lymphocyte population. To generate large numbers of factor VIII-specific Tregs, the more abundant murine primary CD4⁺ T cells were lentivirally transduced ex vivo to express Foxp3 and a chimeric antigen receptor specific to factor VIII (F8CAR). Transduced cells significantly inhibited the proliferation of factor VIII-specific effector T cells in suppression assays. To monitor the suppressive function of the transduced chimeric antigen receptor expressing T cells in vivo, engineered CD4⁺CD25⁺Foxp3⁺F8CAR-Tregs were sorted and adoptively transferred into hemophilia A mice that are treated with hydrodynamically injected factor VIII plasmid. Mice receiving engineered F8CAR-Tregs showed maintenance of factor VIII clotting activity and did not develop anti-factor VIII inhibitors, while control CD4⁺T cell or PBS recipient mice developed inhibitors and had a sharp decrease in factor VIII activity. These results show that CD4⁺ cells lentivirally transduced to express Foxp3 and F8CAR can promote factor VIII tolerance in a murine model. With further development and testing, this approach could potentially be applied to human hemophilia patients.

Treatment of Hemophilia A Using Factor VIII Messenger RNA Lipid Nanoparticles

Hemophilia A (HemA) patients are currently treated with costly and inconvenient replacement therapy of short-lived factor VIII (FVIII) protein. Development of lipid nanoparticle (LNP)-encapsulated mRNA encoding FVIII can change this paradigm. LNP technology constitutes a biocompatible and scalable system to efficiently package and deliver mRNA to the target site. Mice intravenously infused with the luciferase mRNA LNPs showed luminescence signals predominantly in the liver 4 h after injection. Repeated injections of LNPs did not induce elevation of liver transaminases. We next injected LNPs carrying mRNAs encoding different variants of human FVIII (F8 LNPs) into HemA mice. A single injection of B domain-deleted F8 LNPs using different dosing regimens achieved a wide range of therapeutic activities rapidly, which can be beneficial for various usages in hemophilia treatment. The expression slowly declined yet remained above therapeutic levels up to 5–7 days post-injection. Furthermore, routine repeated injections of F8 LNPs in immunodeficient mice produced consistent expression of FVIII over time. In conclusion, F8 LNP treatment produced rapid and prolonged duration of FVIII expression that could be applied to prophylactic treatment and potentially various other treatment options. Our study showed potential for a safe and effective platform of new mRNA therapies for HemA.

Platelet Gene Therapy Promotes Targeted Peripheral Tolerance by Clonal Deletion and Induction of Antigen-Specific Regulatory T Cells

Delivery of gene therapy as well as of biologic therapeutics is often hampered by the immune response of the subject receiving the therapy. We have reported that effective gene therapy for hemophilia utilizing platelets as a delivery vehicle engenders profound tolerance to the therapeutic product. In this study, we investigated whether this strategy can be applied to induce immune tolerance to a non-coagulant protein and explored the fundamental mechanism of immune tolerance induced by platelet-targeted gene delivery. We used ovalbumin (OVA) as a surrogate non-coagulant protein and constructed a lentiviral vector in which OVA is driven by the platelet-specific αIIb promoter. Platelet-specific OVA expression was introduced by bone marrow transduction and transplantation. Greater than 95% of OVA was stored in platelet α-granules. Control mice immunized with OVA generated OVA-specific IgG antibodies; however, mice expressing OVA in platelets did not. Furthermore, OVA expression in platelets was sufficient to prevent the rejection of skin grafts from CAG-OVA mice, demonstrating that immune tolerance developed in platelet-specific OVA-transduced recipients. To assess the mechanism(s) involved in this tolerance we used OTII mice that express CD4⁺ effector T cells specific for an OVA-derived peptide. After platelet-specific OVA gene transfer, these mice showed normal thymic maturation of the T cells ruling against central tolerance. In the periphery, tolerance involved elimination of OVA-specific CD4⁺ effector T cells by apoptosis and expansion of an OVA-specific regulatory T cell population. These experiments reveal the existence of natural peripheral tolerance processes to platelet granule contents which can be co-opted to deliver therapeutically important products.

Immune tolerance induced by platelet-targeted factor VIII gene therapy in hemophilia A mice is CD4 T cell mediated

Essentials The immune response is a significant concern in gene therapy. Platelet-targeted gene therapy can restore hemostasis and induce immune tolerance. CD4 T cell compartment is tolerized after platelet gene therapy. Preconditioning regimen affects immune tolerance induction in platelet gene therapy.

SUMMARY

Background Immune responses are a major concern in gene therapy. Our previous studies demonstrated that platelet-targeted factor VIII (FVIII) (2bF8) gene therapy together with in vivo drug selection of transduced cells can rescue the bleeding diathesis and induce immune tolerance in FVIIInull mice. Objective To investigate whether non-selectable 2bF8 lentiviral vector (LV) for the induction of platelet-FVIII expression is sufficient to induce immune tolerance and how immune tolerance is induced after 2bF8LV gene therapy. Methods Platelet-FVIII expression was introduced by 2bF8LV transduction and transplantation. FVIII assays and tail bleeding tests were used to confirm the success of platelet gene therapy. Animals were challenged with rhF8 to explore if immune tolerance was induced after gene therapy. Treg cell analysis, T-cell proliferation assay and memory B-cell-mediated ELISPOT assay were used to investigate the potential mechanisms of immune tolerance. Results We showed that platelet-FVIII expression was sustained and the bleeding diathesis was restored in FVIIInull mice after 2bF8LV gene therapy. None of the transduced recipients developed anti-FVIII inhibitory antibodies in the groups preconditioned with 660 cGy irradiation or busulfan plus ATG treatment even after rhF8 challenge. Treg cells significantly increased in 2bF8LV-transduced recipients and the immune tolerance developed was transferable. CD4+ T cells from treated animals failed to proliferate in response to rhF8 re-stimulation, but memory B cells could differentiate into antibody secreting cells in 2bF8LV-transduced recipients. Conclusion 2bF8LV gene transfer without in vivo selection of manipulated cells can introduce immune tolerance in hemophilia A mice and this immune tolerance is CD4+ T cell mediated.

Prolonged Expression of Secreted Enzymes in Dogs After Liver-Directed Delivery of Sleeping Beauty Transposons: Implications for Non-Viral Gene Therapy of Systemic Disease

The non-viral, integrating Sleeping Beauty (SB) transposon system is efficient in treating systemic monogenic disease in mice, including hemophilia A and B caused by deficiency of blood clotting factors and mucopolysaccharidosis types I and VII caused by α-L-iduronidase (IDUA) and β-glucuronidase (GUSB) deficiency, respectively. Modified approaches of the hydrodynamics-based procedure to deliver transposons to the liver in dogs were recently reported. Using the transgenic canine reporter secreted alkaline phosphatase (cSEAP), transgenic protein in the plasma was demonstrated for up to 6 weeks post infusion. This study reports that immunosuppression of dogs with gadolinium chloride (GdCl₃) prolonged the presence of cSEAP in the circulation up to 5.5 months after a single vector infusion. Transgene expression declined gradually but appeared to stabilize after about 2 months at approximately fourfold baseline level. Durability of transgenic protein expression in the plasma was inversely associated with transient increase of liver enzymes alanine transaminase and aspartate transaminase in response to the plasmid delivery procedure, which suggests a deleterious effect of hepatocellular toxicity on transgene expression. GdCl₃ treatment was ineffective for repeat vector infusions. In parallel studies, dogs were infused with potentially therapeutic transposons. Activities of transgenic IDUA and GUSB in plasma peaked at 50-350% of wildtype, but in the absence of immunosuppression lasted only a few days. Transposition was detectable by excision assay only when the most efficient transposase, SB100X, was used. Dogs infused with transposons encoding canine clotting factor IX (cFIX) were treated with GdCl₃ and showed expression profiles similar to those in cSEAP-infused dogs, with expression peaking at 40% wt (2 μg/mL). It is concluded that GdCl₃ can support extended transgene expression after hydrodynamic introduction of SB transposons in dogs, but that alternative regimens will be required to achieve therapeutic levels of transgene products.

Megakaryocyte- and megakaryocyte precursor-related gene therapies

Hematopoietic stem cells (HSCs) can be safely collected from the body, genetically modified, and re-infused into a patient with the goal to express the transgene product for an individual's lifetime. Hematologic defects that can be corrected with an allogeneic bone marrow transplant can theoretically also be treated with gene replacement therapy. Because some genetic disorders affect distinct cell lineages, researchers are utilizing HSC gene transfer techniques using lineage-specific endogenous gene promoters to confine transgene expression to individual cell types (eg, ITGA2B for inherited platelet defects). HSCs appear to be an ideal target for platelet gene therapy because they can differentiate into megakaryocytes which are capable of forming several thousand anucleate platelets that circulate within blood vessels to establish hemostasis by repairing vascular injury. Platelets play an essential role in other biological processes (immune response, angiogenesis) as well as diseased states (atherosclerosis, cancer, thrombosis). Thus, recent advances in genetic manipulation of megakaryocytes could lead to new and improved therapies for treating a variety of disorders. In summary, genetic manipulation of megakaryocytes has progressed to the point where clinically relevant strategies are being developed for human trials for genetic disorders affecting platelets. Nevertheless, challenges still need to be overcome to perfect this field; therefore, strategies to increase the safety and benefit of megakaryocyte gene therapy will be discussed.

Strategies to target long-lived plasma cells for treating hemophilia A inhibitors

Long-lived plasma cells (LLPCs) can persistently produce anti-factor VIII (FVIII) antibodies which disrupt therapeutic effect of FVIII in hemophilia A patients with inhibitors. The migration of plasma cells to BM where they become LLPCs is largely controlled by an interaction between the chemokine ligand CXCL12 and its receptor CXCR4. AMD3100 combined with G-CSF inhibit their interactions, thus facilitating the mobilization of CD34(+) cells and blocking the homing of LLPCs. These reagents were combined with anti-CD20 to reduce B-cells and the specific IL-2/IL-2mAb (JES6-1) complexes to induce Treg expansion for targeting anti-FVIII immune responses. Groups of mice primed with FVIII plasmid and protein respectively were treated with the combined regimen for six weeks, and a significant reduction of anti-FVIII inhibitor titers was observed, associated with the dramatic decrease of circulating and bone marrow CXCR4(+) plasma cells. The combination regimens are highly promising in modulating pre-existing anti-FVIII antibodies in FVIII primed subjects.

The immunogenicity of platelet-derived FVIII in hemophilia A mice with or without preexisting anti-FVIII immunity

Evidence shows that factor VIII (FVIII) ectopically expressed in platelets (2bF8) is therapeutic in FVIII(null) mice even with anti-FVIII inhibitory antibodies (inhibitors). If current efforts to generate platelets in vitro succeed, genetically manipulated platelets containing FVIII may be used therapeutically in hemophilia A patients with inhibitors. One important concern is the immunogenicity of platelet-derived FVIII. To address this concern, we infused 2bF8 transgenic (2bF8(Tg)) platelets into naïve FVIII(null) mice weekly for 8 weeks. No anti-FVIII antibodies were detected in the infused animals during the study course. We then explored whether platelet-derived FVIII is immunogenic in FVIII(null) mice with inhibitors. The 2bF8(Tg) platelets were transfused into rhF8-primed FVIII(null) mice, resulting in no augmentation of anti-FVIII antibodies. To investigate whether preconditioning affects the immune response, animals were sublethally irradiated and subsequently transfused with 2bF8(Tg) platelets. No anti-FVIII antibodies were detected in the recipients after platelet infusions. Following further challenge with rhF8, the inhibitor titer in this group was significantly lower than in naïve FVIII(null) mice utilizing the same immunization protocol. Thus, our data demonstrate that infusion of platelets containing FVIII triggers neither primary nor memory anti-FVIII immune response in FVIII(null) mice and that sublethal irradiation plus 2bF8(Tg) platelet infusion suppresses anti-FVIII immune response in FVIII(null) mice.

Donor antigen-primed regulatory T cells permit liver regeneration and phenotype correction in hemophilia A mouse by allogeneic bone marrow stem cells

INTRODUCTION

Cell replacement therapy may be considered as an alternate approach to provide therapeutic dose of plasma factor VIII (FVIII) in patients with hemophilia A (HA). However, immune rejection limits the use of allogeneic cells in this mode of therapy. Here, we have examined the role of donor major histocompatibility complex (MHC)-stimulated host CD4(+)CD25(+) regulatory T (Treg) cells in suppressing immune responses against allogeneic uncommitted (Lin(-)) bone marrow cells (BMCs) for correction of bleeding disorder in HA mice.

METHODS

Allogeneic donor Lin(-) BMCs were co-transplanted with allo-antigen sensitized Treg cells in HA mice having acetaminophen-induced acute liver injury. Plasma FVIII activity was determined by in vitro functional assay, and correction of bleeding phenotype was assessed on the basis of capillary blood clotting time and tail-clip challenge. The immunosuppression potential of the sensitized Treg cells on CD4(+) T cells was studied both in vitro and in vivo. Suppression of inflammatory reactions in the liver against the homed donor cells by sensitized Treg cells was analysed by histopathological scoring. Allo-specificity of sensitized Treg cells and long-term retention of immunosuppression were examined against a third-party donor and by secondary challenge of allogeneic donor cells, respectively. The engraftment and phenotype change of donor BMCs in the liver and their role in synthesis of FVIII and liver regeneration were also determined.

RESULTS

Co-transplantation of allogeneic Lin(-) BMCs with sensitized Treg cells led to systemic immune modulation and suppression of inflammatory reactions in the liver, allowing better engraftment of allogeneic cells in the liver. Allo-antigen priming led to allo-specific immune suppression even after 1 year of transplantation. Donor-derived endothelial cells expressed FVIII in HA mice, leading to the correction of bleeding phenotype. Donor-derived hepatocyte-like cells, which constitute the major fraction of engrafted cells, supported regeneration of the liver after acute injury.

CONCLUSIONS

A highly proficient FVIII secreting core system can be created in regenerating liver by transplanting allogeneic Lin(-) BMCs in HA mice where transplantation tolerance against donor antigens can be induced by in vitro allo-antigen primed Treg cells. This strategy can be beneficial in treatment of genetic liver disorders for achieving prophylactic levels of the missing proteins.

Gene therapy for hemophilia

Hemophilia is an X-linked inherited bleeding disorder consisting of two classifications, hemophilia A and hemophilia B, depending on the underlying mutation. Although the disease is currently treatable with intravenous delivery of replacement recombinant clotting factor, this approach represents a significant cost both monetarily and in terms of quality of life. Gene therapy is an attractive alternative approach to the treatment of hemophilia that would ideally provide life-long correction of clotting activity with a single injection. In this review, we will discuss the multitude of approaches that have been explored for the treatment of both hemophilia A and B, including both in vivo and ex vivo approaches with viral and nonviral delivery vectors.

In vivo enrichment of genetically manipulated platelets corrects the murine hemophilic phenotype and induces immune tolerance even using a low multiplicity of infection

BACKGROUND

Our previous studies have demonstrated that platelet-specific gene delivery to hematopoietic stem cells can induce sustained therapeutic levels of platelet factor VIII (FVIII) expression in mice with hemophilia A.

OBJECTIVE

In this study, we aimed to enhance platelet FVIII expression while minimizing potential toxicities.

METHODS

A novel lentiviral vector (LV), which harbors dual genes, the FVIII gene driven by the αIIb promoter (2bF8) and a drug-resistance gene, the MGMT(P140K) cassette, was constructed. Platelet FVIII expression in mice with hemophilia A was introduced by transduction of hematopoietic stem cells and transplantation. The recipients were treated with O(6)-benzylguanine followed by 1,3-bis-2 chloroethyl-1-nitrosourea monthly three or four times. Animals were analyzed by using polymerase chain reaction (PCR), quantitative PCR, FVIII:C assays, and inhibitor assays. Phenotypic correction was assessed by tail clipping tests and rotational thromboelastometry analysis.

RESULTS

Even using a low multiplicity of infection of 1 and a non-myeloablative conditioning regimen, after in vivo selection, the levels of platelet FVIII expression in recipients increased to 4.33 ± 5.48 mU per 10(8) platelets (n = 16), which were 19.7-fold higher than the levels obtained from the recipients before treatment. Quantitative PCR results confirmed that 2bF8/MGMT-LV-transduced cells were effectively enriched after drug-selective treatment. Fifteen of 16 treated animals survived tail clipping. Blood loss and whole blood clotting time were normalized in the treated recipients. Notably, no anti-FVIII antibodies were detected in the treated animals even after recombinant human B-domain deleted FVIII challenge.

CONCLUSION

we have established an effective in vivo selective system that allows us to enrich 2bF8LV-transduced cells, enhancing platelet FVIII expression while reducing the potential toxicities associated with platelet gene therapy.

Anti-CD20 as the B-Cell Targeting Agent in a Combined Therapy to Modulate Anti-Factor VIII Immune Responses in Hemophilia a Inhibitor Mice

Neutralizing antibody formation against transgene products can represent a major complication following gene therapy with treatment of genetic diseases, such as hemophilia A. Although successful approaches have been developed to prevent the formation of anti-factor VIII (FVIII) antibodies, innovative strategies to overcome pre-existing anti-FVIII immune responses in FVIII-primed subjects are still lacking. Anti-FVIII neutralizing antibodies circulate for long periods in part due to persistence of memory B-cells. Anti-CD20 targets a variety of B-cells (pre-B-cells to mature/memory cells); therefore, we investigated the impact of B-cell depletion on anti-FVIII immune responses in hemophilia A mice using anti-CD20 combined with regulatory T (Treg) cell expansion using IL-2/IL-2mAb complexes plus rapamycin. We found that anti-CD20 alone can partially modulate anti-FVIII immune responses in both unprimed and FVIII-primed hemophilia A mice. Moreover, in mice treated with anti-CD20+IL-2/IL-2mAb complexes+rapamycin+FVIII, anti-FVIII antibody titers were significantly reduced in comparison to mice treated with regimens targeting only B or T cells. In addition, titers remained low after a second challenge with FVIII plasmid. Treg cells and activation markers were transiently and significantly increased in the groups treated with IL-2/IL-2mAb complexes; however, significant B-cell depletion was obtained in anti-CD20-treated groups. Importantly, both FVIII-specific antibody-secreting cells and memory B-cells were significantly reduced in mice treated with combination therapy. This study demonstrates that a combination regimen is highly promising as a treatment option for modulating anti-FVIII antibodies and facilitating induction of long-term tolerance to FVIII in hemophilia A mice.

Perioperative haemostatic management of haemophilic mice using normal mouse plasma

Intense haemostatic interventions are required to avoid bleeding complications when surgical procedures are performed on haemophilia patients. The objective of this study was to establish an appropriate protocol for perioperative haemostatic management of haemophilic mice. We assessed the prophylactic haemostatic effects of normal mouse plasma (NMP) on haemophilia B (HB) mice for both a skin flap procedure and a laparotomy. When 500 μL of NMP was administered to the mice, plasma factor IX (FIX:C) levels peaked at 15.1% immediately after intravenous (IV) administration, at 6.1% 2 h after intraperitoneal (IP) administration and at 2.7% 6 h after subcutaneous administration. Administering 500 μL of NMP via IP or IV 30 min in advance enabled the skin flap procedure to be performed safely without any complications. After the laparotomy procedure, several mice in the IP administration group exhibited lethal bleeding, but all mice survived in the IV administration group. Anti-mouse FIX inhibitors did not develop, even after repetitive administrations of NMP. However, human FIX concentrates, especially plasma-derived concentrates, elicited the anti-human FIX inhibitors. The results show that administering 500 μL of NMP via IV or IP 30 min in advance enables surgical procedures to be safely performed on HB mice, and that IV administration is more desirable than IP if the procedure requires opening of the abdominal wall.

In vitro and in vivo evaluation of the effect of elevated factor VIII on the thrombogenic process

Factor VIII (FVIII), a procoagulant cofactor, plays a crucial role in the intrinsic coagulation cascade. A causal association between elevated FVIII levels and venous thrombosis incidence has been established; no such association has been confirmed with arterial thrombosis. The independent role of elevated FVIII levels in arteriolar thrombosis was evaluated in a mouse model to determine the thrombogenic potential of elevated levels of FVIII. The in vitro thrombogenic effect of elevated FVIII levels was examined using thrombin-antithrombin (TAT) complex generation and thromboelastography (TEG) assays. The thrombogenic potential of acute and extended elevation of circulating FVIII levels was assessed using ferric chloride induced injury of the cremaster arterioles. The rate of TAT complex formation, and the final concentration of TAT complexes, significantly increased as FVIII levels were elevated from 100% to 400% FVIII activity. TEG analysis of fibrin and clot formation showed that as FVIII levels were elevated, the time to initial fibrin formation decreased and the rate of fibrin formation increased. The acute elevation of circulating FVIII to 400% FVIII activity resulted in significantly decreased times to vessel occlusion. Prolonged elevation of FVIII activity did not significantly affect time to vessel occlusion. In conclusion, acute elevations in FVIII levels result in a non-linear thrombogenic effect, with non-significant increases in thrombogenic risk within the physiological range (FVIII levels up to 200%). Prolonged elevation of plasma FVIII did not further increase the thrombogenic potential of elevated FVIII levels.

Long-term expression of human coagulation factor VIII in a tolerant mouse model using the φC31 integrase system

We generated a mouse model for hemophilia A that combines a homozygous knockout for murine factor VIII (FVIII) and a homozygous addition of a mutant human FVIII (hFVIII). The resulting mouse, having no detectable FVIII protein or activity and tolerant to hFVIII, is useful for evaluating FVIII gene-therapy protocols. This model was used to develop an effective gene-therapy strategy using the φC31 integrase to mediate permanent genomic integration of an hFVIII cDNA deleted for the B-domain. Various plasmids encoding φC31 integrase and hFVIII were delivered to the livers of these mice by using hydrodynamic tail-vein injection. Long-term expression of therapeutic levels of hFVIII was observed over a 6-month time course when an intron was included in the hFVIII expression cassette and wild-type φC31 integrase was used. A second dose of the hFVIII and integrase plasmids resulted in higher long-term hFVIII levels, indicating that incremental doses were beneficial and that a second dose of φC31 integrase was tolerated. We observed a significant decrease in the bleeding time after a tail-clip challenge in mice treated with plasmids expressing hFVIII and φC31 integrase. Genomic integration of the hFVIII expression plasmid was demonstrated by junction PCR at a known hotspot for integration in mouse liver. The φC31 integrase system provided a nonviral method to achieve long-term FVIII gene therapy in a relevant mouse model 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.

Hepatic control elements promote long-term expression of human coagulation factor IX gene in hydrodynamically transfected mice

BACKGROUND

Long-term expression of the delivered target gene is critical for successful gene therapy. Recently, hepatic control region I (HCR I) originating from the apolipoprotein (apo)C-I pseudogene was shown to be a critical element for long-term gene expression in the liver of mice. HCR II is another hepatic control region of apoC-I.

METHODS

HCR I, HCR II and HCR I/II-containing plasmids encoding factor IX were prepared and hydrodynamically transferred into the liver of normal and hemophilia B mice. Factor IX expression, clotting activity and formation of antibodies against the expressed gene product were compared.

RESULTS

HCR I-, HCR II- and HCR I/II-containing plasmids all induced long-term gene expression in both normal and hemophilia B mice. Post-transfection factor IX expression in the hemophilia B mice remained above 500 ng/ml for 210 days. Antibodies against human factor IX were detected at a low level in the serum, although they had no effect on the levels and clotting activity of the expressed factor IX.

CONCLUSIONS

We have shown in mouse models that hydrodynamic transfection of pBS-HCRII-HP-FIXA and pBS-HCRI/II-HP-FIXA was able to induce and maintain the expression and clotting activity of human factor IX for a long period of time at a potentially therapeutic level. With an appropriate delivery system, this type of plasmid vector could be clinically useful for the hepatic expression of therapeutic genes including human factor IX.

In vivo expansion of regulatory T cells with IL-2/IL-2 mAb complexes prevents anti-factor VIII immune responses in hemophilia A mice treated with factor VIII plasmid-mediated gene therapy

Generation of transgene-specific immune responses can constitute a major complication following gene therapy treatment. An in vivo approach to inducing selective expansion of Regulatory T (Treg) cells by injecting interleukin-2 (IL-2) mixed with a specific IL-2 monoclonal antibody (JES6-1) was adopted to modulate anti-factor VIII (anti-FVIII) immune responses. Three consecutive IL-2 complexes treatments combined with FVIII plasmid injection prevented anti-FVIII formation and achieved persistent, therapeutic-level of FVIII expression in hemophilia A (HemA) mice. The IL-2 complexes treatment expanded CD4(+)CD25(+)Foxp3(+) Treg cells five- to sevenfold on peak day, and they gradually returned to normal levels within 7-14 days without changing other lymphocyte populations. The transiently expanded Treg cells are highly activated and display suppressive function in vitro. Adoptive transfer of the expanded Treg cells protected recipient mice from generation of high-titer antibodies following FVIII plasmid challenge. Repeated plasmid transfer is applicable in tolerized mice without eliciting immune responses. Mice treated with IL-2 complexes mounted immune responses against both T-dependent and T-independent neoantigens, indicating that IL-2 complexes did not hamper the immune system for long. These results demonstrate the important role of Treg cells in suppressing anti-FVIII immune responses and the potential of developing Treg cell expansion therapies that induce long-term tolerance to FVIII.

A microRNA-regulated and GP64-pseudotyped lentiviral vector mediates stable expression of FVIII in a murine model of Hemophilia A

The objective to use gene therapy to provide sustained, therapeutic levels of factor VIII (FVIII) for hemophilia A is compromised by the emergence of inhibitory antibodies that prevent FVIII from performing its essential function as a cofactor for factor IX (FIX). FVIII appears to be more immunogenic than FIX and an immune response is associated more frequently with FVIII than FIX gene therapy strategies. We have evaluated a modified lentiviral delivery strategy that facilitates liver-restricted transgene expression and prevents off-target expression in hematopoietic cells by incorporating microRNA (miRNA) target sequences. In contrast to outcomes using this strategy to deliver FIX, this modified delivery strategy was in and of itself insufficient to prevent an anti-FVIII immune response in treated hemophilia A mice. However, pseudotyping the lentivirus with the GP64 envelope glycoprotein, in conjunction with a liver-restricted promoter and a miRNA-regulated FVIII transgene resulted in sustained, therapeutic levels of FVIII. These modifications to the lentiviral delivery system effectively restricted FVIII transgene expression to the liver. Plasma levels of FVIII could be increased to around 9% that of normal levels when macrophages were depleted prior to treating the hemophilia A mice with the modified lentiviral FVIII delivery system.

Codon optimization of human factor VIII cDNAs leads to high-level expression

Gene therapy for hemophilia A would be facilitated by development of smaller expression cassettes encoding factor VIII (FVIII), which demonstrate improved biosynthesis and/or enhanced biologic properties. B domain deleted (BDD) FVIII retains full procoagulant function and is expressed at higher levels than wild-type FVIII. However, a partial BDD FVIII, leaving an N-terminal 226 amino acid stretch (N6), increases in vitro secretion of FVIII tenfold compared with BDD-FVIII. In this study, we tested various BDD constructs in the context of either wild-type or codon-optimized cDNA sequences expressed under control of the strong, ubiquitous Spleen Focus Forming Virus promoter within a self-inactivating HIV-based lentiviral vector. Transduced 293T cells in vitro demonstrated detectable FVIII activity. Hemophilic mice treated with lentiviral vectors showed expression of FVIII activity and phenotypic correction sustained over 250 days. Importantly, codon-optimized constructs achieved an unprecedented 29- to 44-fold increase in expression, yielding more than 200% normal human FVIII levels. Addition of B domain sequences to BDD-FVIII did not significantly increase in vivo expression. These significant findings demonstrate that shorter FVIII constructs that can be more easily accommodated in viral vectors can result in increased therapeutic efficacy and may deliver effective gene therapy for hemophilia A.

Immunomodulation for inhibitors in hemophilia A: the important role of Treg cells

Approximately 25-30% of the hemophilia A patients develop inhibitory antibodies against Factor VIII (FVIII) following protein-replacement therapy. This problem is also thought to occur following gene-replacement therapy. Recently, many approaches have been investigated to modulate FVIII-specific immune responses in either protein-replacement or gene therapy hemophilia A mouse models. Several promising protocols have been demonstrated to successfully prevent or modulate the formation of anti-FVIII antibodies, including methods to manipulate antigen presentation, development of less immunogenic FVIII proteins, or formulations or gene therapy protocols to evade immune responses, as well as immunomodulation strategies to target either T- and/or B-cell responses. Most of these successful protocols involve the induction of activated Treg cells to create a regulatory immune environment during tolerance induction. Innovative strategies to overcome pre-existing anti-FVIII immune responses and induce long-term tolerance in primed subjects still need to be developed.

CD4+FOXP3+ regulatory T cells confer long-term regulation of factor VIII-specific immune responses in plasmid-mediated gene therapy-treated hemophilia mice

Gene transfer of a factor VIII (FVIII) plasmid into hemophilia A (HemA) mice achieved supraphysiologic FVIII expression, but triggered production of high-titer FVIII-specific antibodies and loss of functional FVIII activity. To test whether FVIII-specific regulatory T cells (Tregs) can modulate immune responses against FVIII, we developed a HemA mouse model in which all T cells overexpressed Foxp3 (HemA/Foxp3-Tg). FVIII plasmid therapy did not induce antibody production in HemA/Foxp3-Tg mice. CD4(+)Foxp3(+) T cells isolated from plasmid-treated HemA/Foxp3-Tg mice significantly suppressed proliferation of FVIII-stimulated CD4(+) effector T cells. The percentage of CD4(+) T cells expressing CD25, glucocorticoid-induced tumor necrosis factor receptor, and cytotoxic T lymphocyte antigen 4 increased significantly in spleen and peripheral blood for 9 weeks. Mice receiving adoptively transferred Tregs from FVIII-exposed HemA/Foxp3-Tg mice produced significantly reduced antibody titers compared with controls after initial challenge with FVIII plasmid and second challenge 16 weeks after first plasmid treatment. Adoptively transferred Tregs engrafted and distributed at 2% to 4% in the Treg compartment of blood, lymph nodes, and spleens of the recipient mice and induced activation of endogenous Tregs; the engraftment decreased to negligible levels over 8 to 12 weeks. Antigen-specific Tregs can provide long-lasting protection against immune responses in vivo and limit recall responses induced by a second challenge via infectious tolerance.

Anti-CD3 antibodies modulate anti-factor VIII immune responses in hemophilia A mice after factor VIII plasmid-mediated gene therapy

One major obstacle in gene therapy is the generation of immune responses directed against transgene product. Five consecutive anti-CD3 treatments concomitant with factor VIII (FVIII) plasmid injection prevented the formation of inhibitory antibodies against FVIII and achieved persistent, therapeutic levels of FVIII gene expression in treated hemophilia A mice. Repeated plasmid gene transfer is applicable in tolerized mice without eliciting immune responses. Anti-CD3 treatment significantly depleted both CD4+ and CD8+ T cells, whereas increased transforming growth factor-beta levels in plasma and the frequency of both CD4+CD25+FoxP3+ and CD4+CD25-Foxp3+ regulatory T cells in the initial few weeks after treatment. Although prior depletion of CD4+CD25+ cells did not abrogate tolerance induction, adoptive transfer of CD4+ cells from tolerized mice at 6 weeks after treatment protected recipient mice from anti-FVIII immune responses. Anti-CD3-treated mice mounted immune responses against both T-dependent and T-independent neo-antigens, indicating that anti-CD3 did not hamper the immune systems in the long term. Concomitant FVIII plasmid + anti-CD3 treatment induced long-term tolerance specific to FVIII via a mechanism involving the increase in transforming growth factor-beta levels and the generation of adaptive FVIII-specific CD4+Foxp3+ regulatory T cells at the periphery. Furthermore, anti-CD3 can reduce the titers of preexisting anti-FVIII inhibitory antibodies in hemophilia A mice.

Suppression of FVIII inhibitor formation in hemophilic mice by delivery of transgene modified apoptotic fibroblasts

The development of inhibitory antibodies to factor VIII (FVIII) is currently the most significant complication of FVIII replacement therapy in the management of patients with severe hemophilia A. Immune tolerance protocols for the eradication of inhibitors require daily delivery of intravenous FVIII for at least 6 months and are unsuccessful in 20-40% of treated patients. We hypothesize that tolerance can be induced more efficiently and reliably by delivery of FVIII antigen within autologous apoptotic cells (ACs). In this study, we demonstrated suppression of the T cell and inhibitor responses to FVIII by infusion of FVIII expression vector modified apoptotic syngeneic fibroblasts in both naive and preimmunized hemophilia A mice. ACs without FVIII antigen exerted modest generalized immune suppression mediated by anti-inflammatory signals. However, FVIII expressing apoptotic syngeneic fibroblasts produced much stronger antigen-specific immune suppression. Mice treated with these fibroblasts generated CD4+ T cells that suppressed the immune response to FVIII after adoptive transfer into naive recipients and antigen-specific CD4+CD25+ regulatory T cells (Tregs) that inhibited the proliferation of FVIII responsive effector T cells in vitro. These preclinical results demonstrate the potential for using FVIII vector modified autologous ACs to treat high-titer inhibitors in patients with hemophilia A.

Strategies to modulate immune responses: a new frontier for gene therapy

The success of gene therapy strategies to cure disease relies on the control of unwanted immune responses to transgene products, genetically modified cells and/or to the vector. Effective treatment of an established immune response is much harder to achieve than prevention of a response before it has had a chance to develop. However, preventive strategies are not always effective in avoiding immune responses, thus the use of drugs to induce immunosuppression (IS) is required. The growing discovery of novel drugs provides a conceptual shift from using generalized, moderately intensive immunosuppressive regimens towards a refined approach to attain the optimal balance of naive cells, effector cells, memory cells, and regulatory cells, harnessing the natural tolerance mechanisms of the body. We review several strategies based on transient IS coupled with gene therapy for sustained immune tolerance induction to the therapeutic transgene.

Nanocapsule-delivered Sleeping Beauty mediates therapeutic Factor VIII expression in liver sinusoidal endothelial cells of hemophilia A mice

Liver sinusoidal endothelial cells are a major endogenous source of Factor VIII (FVIII), lack of which causes the human congenital bleeding disorder hemophilia A. Despite extensive efforts, gene therapy using viral vectors has shown little success in clinical hemophilia trials. Here we achieved cell type-specific gene targeting using hyaluronan- and asialoorosomucoid-coated nanocapsules, generated using dispersion atomization, to direct genes to liver sinusoidal endothelial cells and hepatocytes, respectively. To highlight the therapeutic potential of this approach, we encapsulated Sleeping Beauty transposon expressing the B domain-deleted canine FVIII in cis with Sleeping Beauty transposase in hyaluronan nanocapsules and injected them intravenously into hemophilia A mice. The treated mice exhibited activated partial thromboplastin times that were comparable to those of wild-type mice at 5 and 50 weeks and substantially shorter than those of untreated controls at the same time points. Further, plasma FVIII activity in the treated hemophilia A mice was nearly identical to that in wild-type mice through 50 weeks, while untreated hemophilia A mice exhibited no detectable FVIII activity. Thus, Sleeping Beauty transposon targeted to liver sinusoidal endothelial cells provided long-term expression of FVIII, without apparent antibody formation, and improved the phenotype of hemophilia A 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.

Progress toward liver-based gene therapy

The liver is involved in the synthesis of serum proteins, regulation of metabolism and maintenance of homeostasis and provides a variety of opportunities for gene therapy. The enriched vasculature and blood circulation, fenestrated endothelium, abundant receptors on the plasma membranes of the liver cells, and effective transcription and translation machineries in the hepatocytes are some unique features that have been explored for delivery, and functional analysis, of genetic sequences in the liver. Both viral and non-viral methods have been developed for effective gene delivery and liver-based gene therapy. This review describes the fundamentals of gene delivery, and the preclinical and clinical progress that has been made toward gene therapy using the liver as a target.

Gene transfer to hemophilia A mice via oral delivery of FVIII-chitosan nanoparticles

Effective oral delivery of a non-viral gene carrier would represent a novel and attractive strategy for therapeutic gene transfer. To evaluate the potential of this approach, we studied the oral gene delivery efficacy of DNA polyplexes composed of chitosan and Factor VIII DNA. Transgene DNA was detected in both local and systemic tissues following oral administration of the chitosan nanoparticles to hemophilia A mice. Functional factor VIII protein was detected in plasma by chromogenic and thrombin generation assays, reaching a peak level of 2-4% FVIII at day 22 after delivery. In addition, a bleeding challenge one month after DNA administration resulted in phenotypic correction in 13/20 mice given 250-600 microg of FVIII DNA in chitosan nanoparticles, compared to 1/13 mice given naked FVIII DNA and 0/6 untreated mice. While further optimization would be required to render this type of delivery system practical for hemophilia A gene therapy, the findings suggest the feasibility of oral, non-viral delivery for gene medicine applications.

Transient blockade of the inducible costimulator pathway generates long-term tolerance to factor VIII after nonviral gene transfer into hemophilia A mice

Formation of inhibitory antibodies is a common problem encountered in clinical treatment for hemophilia. Human factor VIII (hFVIII) plasmid gene therapy in hemophilia A mice also leads to strong humoral responses. We demonstrate that short-term therapy with an anti-ICOS monoclonal antibody to transiently block the inducible costimulator/inducible costimulator ligand (ICOS/ICOSL) signaling pathway led to sustained tolerance to hFVIII in hFVIII plasmid-treated hemophilia A mice and allowed persistent, high-level FVIII functional activity (100%-300% of normal). Anti-ICOS treatment resulted in depletion of ICOS(+)CD4(+) T cells and activation of CD25(+)Foxp3(+) Tregs in the peripheral blood, spleen, and lymph nodes. CD4(+) T cells from anti-ICOS-treated mice did not proliferate in response to hFVIII stimulation and produced high levels of regulatory cytokines, including interleukin-10 and transforming growth factor-beta. Moreover, CD4(+)CD25(+) Tregs from tolerized mice adoptively transferred dominant tolerance in syngeneic hFVIII plasmid-treated hemophilia A mice and reduced the production of antibodies against FVIII. Anti-ICOS-treated mice tolerized to hFVIII generated normal primary and secondary antibody responses after immunization with the T-dependent antigen, bacteriophage Phix 174, indicating maintenance of immune competency. Our data indicate that transient anti-ICOS monoclonal antibody treatment represents a novel single-agent immunomodulatory strategy to overcome the immune responses against transgene product after gene therapy.

Syngeneic transplantation of hematopoietic stem cells that are genetically modified to express factor VIII in platelets restores hemostasis to hemophilia A mice with preexisting FVIII immunity

Although genetic induction of factor VIII (FVIII) expression in platelets can restore hemostasis in hemophilia A mice, this approach has not been studied in the clinical setting of preexisting FVIII inhibitory antibodies to determine whether such antibodies would affect therapeutic engraftment. We generated a line of transgenic mice (2bF8) that express FVIII only in platelets using the platelet-specific alphaIIb promoter and bred this 2bF8 transgene into a FVIII(null) background. Bone marrow (BM) from heterozygous 2bF8 transgenic (2bF8(tg+/-)) mice was transplanted into immunized FVIII(null) mice after lethal or sublethal irradiation. After BM reconstitution, 85% of recipients survived tail clipping when the 1100-cGy (myeloablative) regimen was used, 85.7% of recipients survived when 660-cGy (nonmyeloablative) regimens were used, and 60% of recipients survived when the recipients were conditioned with 440 cGy. Our further studies showed that transplantation with 1% to 5% 2bF8(tg+/-) BM cells still improved hemostasis in hemophilia A mice with inhibitors. These results demonstrate that the presence of FVIII-specific immunity in recipients does not negate engraftment of 2bF8 genetically modified hematopoietic stem cells, and transplantation of these hematopoietic stem cells can efficiently restore hemostasis to hemophilic mice with preexisting inhibitory antibodies under either myeloablative or nonmyeloablative regimens.

Altered thrombus formation in von Willebrand factor-deficient mice expressing von Willebrand factor variants with defective binding to collagen or GPIIbIIIa

The role of von Willebrand factor (VWF) in thrombosis involves its binding to a number of ligands. To investigate the relative importance of these particular interactions in the thrombosis process, we have introduced mutations into murine VWF (mVWF) cDNA inhibiting VWF binding to glycoprotein (Gp) Ib, GPIIbIIIa, or to fibrillar collagen. These VWF mutants were expressed in VWF-deficient mice (VWF(-/-)) by using an hydrodynamic injection approach, and the mice were studied in the ferric chloride-induced injury model. Expression of the collagen and the GPIIbIIIa VWF-binding mutants in VWF(-/-) mice resulted in delayed thrombus growth and significantly increased vessel occlusion times compared with mice expressing wild-type (WT) mVWF (30 +/- 3 minutes and 38 +/- 4 minutes for the collagen and GPIIbIIIa mutants, respectively, vs 19 +/- 3 minutes for WT mVWF). Interestingly, these mutants were able to correct bleeding time as efficiently as WT mVWF. In contrast, VWF(-/-) mice expressing the GPIb binding mutant failed to restore thrombus formation and were bleeding for as long as they were observed, confirming the critical importance of the VWF-GPIb interaction. Our observations suggest that targeting the VWF-collagen or VWF-GPIIbIIIa interactions could be an interesting alternative for new antithrombotic strategies.

Ultrasound with microbubbles enhances gene expression of plasmid DNA in the liver via intraportal delivery

Current ultrasound (US)-mediated gene delivery methods are inefficient due, in part, to a lack of US optimization. We systematically explored the use of microbubbles (MBs), US parameters and plasmid delivery routes to improve gene transfer into the mouse liver. Co-presentation of plasmid DNA (pDNA), 10% Optison MBs and pulsed 1-MHz US at a peak negative pressure of 4.3 MPa significantly increased luciferase gene expression with pDNA delivered by intrahepatic injection to the left liver lobe. Intraportal injection delivered pDNA and MBs to the whole liver; with insonation, all lobes expressed the transgene, thus increasing total gene expression. Gene expression was also dependent on acoustic pressure over the range of 0-4.3 MPa, with a peak effect at 3 MPa. An average of 85-fold enhancement in gene delivery was achieved. No enhancement was observed below 0.25 MPa. Increasing pulse length while decreasing pulse repetition frequency and exposure time to maintain a constant total energy during exposure did not further improve transfection efficiency, nor did extend the US exposure pre- or postinjection of pDNA. The results indicate that coupled with MBs, US can more efficiently and dose-dependently enhance gene expression from pDNA delivered via portal vein injection by an acoustic mechanism of inertial cavitation.

Naked plasmid DNA-based alpha-galactosidase A gene transfer partially reduces systemic accumulation of globotriaosylceramide in Fabry mice

Fabry disease is an X-linked recessive inborn metabolic disorder in which a deficiency in lysosomal enzyme alpha-galactosidase A (Gal A) causes the systemic accumulation of globotriaosylceramide (Gb3). Although many investigators have attempted to treat alpha-Gal A knock-out mice (Fabry mice) with gene therapy, no report has demonstrated therapeutic effects by the retrograde renal vein injection of naked DNA. We recently developed a naked plasmid vector-mediated kidney-targeted gene transfer technique. A solution containing naked plasmid DNA encoding human alpha-Gal A (pKSCX-alpha-Gal A) was rapidly injected into the left kidney of Fabry mice (pKSCX-alpha-Gal A mice). pKSCX was used for mock transfections (pKSCX mice). We confirmed that vector-derived human alpha-Gal A mRNA was present in the left kidney but not in other tissues, by reverse transcriptase polymerase chain reaction. Compared with the pKSCX mice, the pKSCX-alpha-Gal A mice showed partial therapeutic effects: increased alpha-Gal A activity in the injected kidney and in the liver, heart, and plasma, and decreased Gb3 in the injected kidney, contralateral kidney, liver, heart, and spleen. Our results demonstrated that, although further studies are needed to improve the outcome, this method has promise as a potential treatment option for Fabry disease.

Lentivirus-mediated platelet-derived factor VIII gene therapy in murine haemophilia A

BACKGROUND

Previous studies from our laboratory have demonstrated that lineage-targeted synthesis of factor VIII (FVIII) under the direction of the platelet-specific integrin alphaIIb gene promoter (2bF8) can correct the murine haemophilia A phenotype even in the presence of high titer inhibitory antibodies in a transgenic mouse model.

OBJECTIVE

In this study, we assessed the efficacy of using a genetic therapy approach to correct haemophilia A in FVIII-deficient (FVIII(null)) mice by transplantation of bone marrow (BM) transduced with a lentivirus (LV)-based gene transfer cassette encoding 2bF8.

RESULTS

Functional FVIII activity (FVIII:C) was detected in platelet lysates from treated mice and the levels were similar to 2bF8 heterozygous transgenic mice. Mice transplanted with 2bF8 LV-transduced BM survived tail clipping and we did not detected inhibitory or non-inhibitory FVIII antibodies over the period of this study (11 months). Furthermore, BM transferred from the primary transplant recipients into FVIII(null) secondary recipients demonstrated sustained platelet-FVIII expression leading to correction of the haemophilia A phenotype showing that gene transfer occurred within long-term repopulating haematopoietic stem cells.

CONCLUSIONS

These results demonstrate that ectopic expression of FVIII in platelets by lentivirus-mediated bone marrow transduction/transplantation may be a promising strategy for gene therapy of haemophilia A in humans.

Sleeping beauty transposon-mediated nonviral gene therapy

Safe and effective delivery of genetic material to mammalian tissues would significantly expand the therapeutic possibilities for a large number of medical conditions. Unfortunately, the promise of gene therapy has been hampered by technical challenges, the induction of immune responses, and inadequate expression over time. Despite these setbacks, progress continues to be made and the anticipated benefits may come to fruition for certain disorders. In terms of delivery, nonviral vector systems are particularly attractive as they are simple to produce, can be stored for long periods of time, and induce no specific immune responses. A significant drawback to nonviral systems has been the lack of persistent expression, as plasmids are lost or degraded when delivered to living tissues. The recent application of integrating transposons to nonviral gene delivery has significantly helped to overcome this obstacle, because it allows for genomic integration and long-term expression. Recent advances in transposon-based vector systems hold promise as new technologies that may unlock the potential of gene therapy; however, technical and safety issues still need refinement.

Structural impact of hydrodynamic injection on mouse liver

The impact of hydrodynamic injection on liver structure was evaluated in mice using various microscopic techniques. Upon hydrodynamic injection of approximately 9% of body weight by volume, the liver rapidly expanded, reaching maximal size at the end of the injection and returned to its original size in 30 min. Histological analysis revealed a swollen appearance in the peri-central region of the liver where delivery of genes and fluorescence-labeled markers was observed. Scanning and transmission electron microscopy showed enlargement and rupture of endothelium that in about 24-48 h regains its morphology and normal function as a barrier against infection by adenovirus viral particles. At the cellular level in hydrodynamically treated animals, four types of hepatocytes were seen: cells with normal appearance; cells with enriched vesicles in the cytoplasm; cells with lightly stained cytosol; and cells with significant dilution of the cytoplasm. In addition, red blood cells and platelets were observed in the space of Disse and even inside hepatocytes. Vesicle formation is triggered by hydrodynamic injection and resembles the process of macropinocytosis. These results, whereas confirming the physical nature of hydrodynamic delivery, are important for a better understanding of this efficient method for intrahepatic gene and small interfering RNA delivery.

Factor VIII ectopically targeted to platelets is therapeutic in hemophilia A with high-titer inhibitory antibodies

Inhibitory immune response to exogenously infused factor VIII (FVIII) is a major complication in the treatment of hemophilia A. Generation of such inhibitors has the potential to disrupt gene therapy for hemophilia A. We explore what we believe to be a novel approach to overcome this shortcoming. Human B-domain-deleted FVIII (hBDDFVIII) was expressed under the control of the platelet-specific alphaIIb promoter in platelets of hemophilic (FVIIInull) mice to create 2bF8trans mice. The FVIII transgene product was stored in platelets and released at the site of platelet activation. In spite of the lack of FVIII in the plasma of 2bF8trans mice, the bleeding phenotype of FVIIInull mice was corrected. More importantly, the bleeding phenotype was corrected in the presence of high inhibitory antibody titers introduced into the mice by infusion or by spleen cell transfer from recombinant hBDDFVIII-immunized mice. Our results demonstrate that this approach to the targeted expression of FVIII in platelets has the potential to correct hemophilia A, even in the presence of inhibitory immune responses to infused FVIII.

Genetic engineering for haemophilia A

At first sight, haemophilia A would appear to be an ideal candidate for treatment by gene therapy. There is a single gene defect; cells in different parts of the body, but especially the liver, produce Factor VIII, and only 5% of normal levels of Factor VIII are necessary to prevent the serious symptoms of bleeding. This review attempts to outline the status of gene therapy at present and efforts that have been made to overcome the difficulties and remaining problems that require solving. Undoubtedly, success will be achieved, but it is likely that considerably more work will be necessary before experimental models can be introduced into the clinic with any likelihood of success. The most successful results in animals that may have clinical application were from introducing the Factor VIII gene to newborn animals before antibodies are produced, presumably inducing a state of tolerance.

Immunomodulation of transgene responses following naked DNA transfer of human factor VIII into hemophilia A mice

A robust humoral immune response against human factor VIII (hFVIII) following naked DNA transfer into immunocompetent hemophilia A mice completely inhibits circulating FVIII activity despite initial high-level hFVIII gene expression. To prevent this undesirable response, we compared transient immunomodulation strategies. Eight groups of mice (n = 4-9 per group) were treated with naked DNA transfer of pBS-HCRHPI-hFVIIIA simultaneously with immunosuppressive reagents that included cyclosporine A (CSA), rapamycin (RAP), mycophenylate mofetil (MMF), a combination of CSA and MMF, a combination of RAP and MMF, a monoclonal antibody against murine CD40 ligand (MR1), recombinant murine Ctla4Ig, and a combination of MR1 and Ctla4Ig. All animals except those receiving only CSA exhibited delayed or absent immune responses against hFVIII. The most effective immunosuppressive regimen, the combination of Ctla4Ig and MR1, prevented inhibitor formation in 8 of 9 animals; the ninth had transient low-titer antibodies. All 9 mice of this group produced persistent, therapeutic levels of hFVIII for more than 6 months. When challenged with the T-dependent antigen bacteriophage Phix174, tolerized mice exhibited normal primary and secondary antibody responses, suggesting that transient immunomodulation to disrupt B/T-cell interaction at the time of plasmid injection effectively promoted long-term immune tolerance specific for hFVIII.

Multiyear therapeutic benefit of AAV serotypes 2, 6, and 8 delivering factor VIII to hemophilia A mice and dogs

Hemophilia A, a deficiency of functional coagulation factor VIII (FVIII), is treated via protein replacement therapy. Restoring 1% to 5% of normal blood FVIII activity prevents spontaneous bleeding, making the disease an attractive gene therapy target. Previously, we have demonstrated short-term activity of a liver-specific AAV2 vector expressing canine B-domain-deleted FVIII (cFVIII) in a hemophilia canine model. Here, we report the long-term efficacy and safety of AAV-cFVIII vectors of serotypes 2, 5, 6, and 8 in both hemophilia A mice and dogs. AAV6-cFVIII and AAV8-cFVIII restored physiologic levels of plasma FVIII activity in hemophilia A mice. The improved efficacy is attributed to more efficient gene transfer in liver compared with AAV2 and AAV5. However, supraphysiologic cFVIII levels correlated with the formation of cFVIII-neutralizing antibodies in these mice. Of importance, hemophilia A dogs that received AAV2-cFVIII, AAV6-cFVIII, and AAV8-cFVIII have persistently expressed therapeutic levels of FVIII, without antibody formation or other toxicities, for more than 3 years. However, liver transduction efficiencies are similar between AAV2, AAV6, and AAV8 serotypes in hemophilia A dogs, in contrast to mice. In summary, this is the first report demonstrating multiyear therapeutic efficacy and safety of multiple AAV-cFVIII vectors in hemophilia A dogs and provides the basis for human clinical studies.

Sustained FVIII expression and phenotypic correction of hemophilia A in neonatal mice using an endothelial-targeted sleeping beauty transposon

Hemophilia A, deficiency of coagulation factor VIII (FVIII), is an attractive candidate for gene therapy as expression of modest amounts of FVIII can provide therapeutic benefit. Most gene transfer approaches for hemophilia have focused on the liver, as this is the major source of endogenous FVIII; however, increasing evidence suggests that endothelial cells are capable of synthesis and release of FVIII. Here the Sleeping Beauty (SB) transposon is employed to target long-term expression of the human B-domain-depleted FVIII gene (approved gene symbol F8) within lung endothelia of hemophilic mice. As the formation of inhibitory antibodies to FVIII has been a significant impediment toward achieving therapeutic plasma levels after gene or protein therapy, we chose to perform gene transfer in neonatal mice, which are more likely to be immune tolerant. Using this approach, low therapeutic levels of FVIII ( approximately 10%), as well as phenotypic correction of the bleeding disorder, were achieved in all animals that received the FVIII transposon and functional transposase throughout the duration of the study (24 weeks). Rechallenge of these animals with additional gene transfer did not result in significant increases in FVIII levels, due mainly to increases in inhibitory antibodies. These studies demonstrate the feasibility of using endothelial-targeted SB transposons for the treatment of hemophilia A.

Expression of foreign genes in chicks by hydrodynamics-based naked plasmid transfer in vivo

The study of gene function in vivo is considered one of the top achievements of modern biology, inasmuch as it provides tools to study gene function in the context of the whole animal. In chickens, techniques of DNA-mediated gene transfer are less advanced than in other animal or livestock models, and remain a significant challenge. The study presented here is the first to show that a hydrodynamics-based gene-transfer technique, originally developed for naked DNA transfer in mice, can be applied to chickens. Rapid injection of naked plasmids containing expression cassettes into the jugular vein of 6- to 10-day-old chicks resulted in specific expression of the transgenes. A CMV promoter-driven luciferase reporter gene was expressed at significant levels in the liver during the first 3 days post-injection with lower levels also detected in the kidney. Significantly, all injected birds showed detectable levels of luciferase expression. Similarly, injection of a plasmid containing the secreted human coagulation factor IX (hFIX) gene under the control of human alpha-1-anti-trypsin promoter resulted in detectable levels of the hFIX in the plasma during the first 2 days post-injection. The method described herein has the potential for a quick and simple route for gain and loss-of function experiments in chicken liver and kidney, as well as for studying systemic effects of secreted proteins and hormones.

Correction of murine hemophilia A by hematopoietic stem cell gene therapy

A serious complication of current protein replacement therapy for hemophilia A patients with coagulation factor VIII (FVIII) deficiency is the frequent development of anti-FVIII inhibitor antibodies that preclude therapeutic benefit from further treatment. Induction of tolerance by persistent high-level FVIII synthesis following transplantation with hematopoietic stem cells expressing a retrovirally delivered FVIII transgene offers the possibility of permanently correcting the disease. Here, we transplanted bone marrow cells transduced with an optimized MSCV-based FVIII oncoretroviral vector into immunocompetent hemophilia A mice that had been conditioned with a potentially lethal dose of irradiation (800 cGy), a sublethal dose of irradiation (550 cGy), or a nonmyeloablative preparative regimen involving busulfan. Therapeutic levels of FVIII (42, 18, and 11% of normal, respectively) were detected in the plasma of the transplant recipients for the duration of the study (over 6 months). Moreover, subsequent challenge with recombinant FVIII elicited at most a minor anti-FVIII inhibitor antibody response in any of the experimental animals, in contrast to the vigorous neutralizing humoral reaction to FVIII that was stimulated in naive hemophilia A mice. These findings represent an encouraging advance toward potential clinical application and long-term amelioration or cure of this progressively debilitating, life-threatening bleeding disorder.

Single Hepatic Venous Injection of Liver-Specific Naked Plasmid Vector Expressing Human UGT1A1 Leads to Long-Term Correction of Hyperbilirubinemia and Prevention of Chronic Bilirubin Toxicity in Gunn Rats

Previously, we have demonstrated that hepatic venous injection of pcDNA3hUGT1A1 expressing human bilirubin glucuronosyl transferase 1A1 (hUGT1A1) under the control of the cytomegalovirus promoter results in excretion of bilirubin glucuronides in bile and significant decrease in serum bilirubin for at least 2 weeks in the Gunn rat, an animal model of Crigler-Najjar syndrome type I. In this study we compared repeat delivery of pcDNA3hUGT1A1 with single injection of pBShUGT1A1 expressing hUGT1A1 under liver-specific regulatory control, for treatment of hyperbilirubinemia in the Gunn rat. Although repeat injections of pcDNA3hUGT1A1 consistently reduced serum bilirubin levels, the effect did not exceed 2 weeks; hUGT1A1 was detectable in livers only for 2 weeks, despite the presence of vector and transcript for at least 1 month. In contrast, injection of pBShUGT1A1 resulted in persistence of vector, transcript, and recombinant protein and sustained correction of hyperbilirubinemia for at least 8 months; furthermore, renal tubular damage, the principal manifestation of chronic bilirubin toxicity in the Gunn rat, was prevented. Sera from animals treated with pBShUGT1A1 consistently contained anti-hUGT1A1 antibodies, but a significant increase in the number of hepatic CD4(+) and CD8(+) cells was seen only in the pcDNA3hUGT1A1 group; thus liver-specific expression of hUGT1A1 may attenuate immune response. Our results provide further evidence of the feasibility of long-term correction of hepatic enzyme deficiencies with plasmid vectors optimized for expression in the liver.