The complex, confusing and poorly understood immune responses to AAV-mediated gene transfer in haemophilia-Is more or less immunosuppression required?

Attempts to achieve a functional cure or amelioration of the severe X linked bleeding disorders haemophilia A (factor VIII deficiency) and haemophilia B (factor IX deficiency) using AAV-based vectors have been frustrated by immune responses that limit efficacy and durability. The immune responses include adaptive and innate pathways as well as cytokine mediated inflammation, especially of the target organ cells-hepatocytes. Immune suppression has only been partly effective in clinical trials at ameliorating the immune response and the lack of good animal models has delayed progress in identifying mechanisms and developing more effective approaches to controlling these effects of AAV gene transfer. Here we discuss the arguments for and against more potent immunosuppression to improve factor expression after AAV-mediated gene therapy.

Mathematical models of coagulation-are we there yet?

BACKGROUND

Mathematical models of coagulation have been developed to mirror thrombin generation in plasma, with the aim of investigating how variation in coagulation factor levels regulates hemostasis. However, current models vary in the reactions they capture and the reaction rates used, and their validation is restricted by a lack of large coherent datasets, resulting in questioning of their utility.

OBJECTIVES

To address this debate, we systematically assessed current models against a large dataset, using plasma coagulation factor levels from 348 individuals with normal hemostasis to identify the causes of these variations.

METHODS

We compared model predictions with measured thrombin generation, quantifying and comparing the ability of each model to predict thrombin generation, the contributions of the individual reactions, and their dependence on reaction rates.

RESULTS

We found that no current model predicted the hemostatic response across the whole cohort and all produced thrombin generation curves that did not resemble those obtained experimentally. Our analysis has identified the key reactions that lead to differential model predictions, where experimental uncertainty leads to variability in predictions, and we determined reactions that have a high influence on measured thrombin generation, such as the contribution of factor XI.

CONCLUSION

This systematic assessment of models of coagulation, using large dataset inputs, points to ways in which these models can be improved. A model that accurately reflects the effects of the multiple subtle variations in an individual's hemostatic profile could be used for assessing antithrombotics or as a tool for precision medicine.

Haemophilia, the journey in search of a cure. 1960-2020

The single most important step on the path to our modern understanding of blood coagulation and haemophilia in the 20th century was taken by British pathologist Robert Gwyn Macfarlane with his 1964 publication 'An enzyme cascade in the blood clotting mechanism, and its function as a biochemical amplifier'. In the same year, Ratnoff and Davie in the USA reached the same conclusion. Macfarlane and Rosemary Biggs had previously, in 1952, discovered factor IX as the factor deficient in haemophilia B. In 1973, Arthur Bloom defined the distinct role of Factor VIII and von Willebrand factor in haemophilia A and von Willebrand's disease respectively. This inspired the efforts of Tuddenham and his group towards the purification of Factor VIII which reached homogeneity in 1982, leading to the cloning of the Factor VIII gene in 1984 in collaboration with US scientists at Genentech, which in turn enabled development of safe recombinant factor concentrates for patients with haemophilia. Brownlee cloned the factor IX gene in 1982 at the Sir William Dunn Institute of Pathology in Oxford. This led eventually to the first successful trial of gene therapy for haemophilia B in 2011 by the Nathwani group at UCL, which built on pioneering work of US groups and was partnered with St Jude in Memphis where Nathwani started the project. This trial has fuelled the current quest for a functional cure of haemophilia A and B. The UK has, therefore, made a rich contribution to advances in haemostasis over the last 60 years, often in partnership with other groups across the world.

Factor VIII: the protein, cloning its gene, synthetic factor and now - 35 years later - gene therapy; what happened in between?

The foundation of haemophilia A therapy in the last 35 years has been critically dependent on isolation of the Factor VIII (FVIII) protein and discovery of the cDNA sequence of the FVIII gene, published in 1984. Identification of the FVIII sequence resulted in a new era of recombinant concentrates and led to significant improvements in safety, set against the tragedy of widespread HIV and hepatitis infections in haemophilia patients from contaminated plasma-based products. We chronicle the scientific methods and race leading up to the publication of the FVIII DNA sequence and the legacy that follows through to revolutionary gene therapy treatment in clinical trials today.

Interaction Between the a3 Region of Factor VIII and the TIL'E' Domains of the von Willebrand Factor

The von Willebrand factor (VWF) and coagulation factor VIII (FVIII) are intricately involved in hemostasis. A tight, noncovalent complex between VWF and FVIII prolongs the half-life of FVIII in plasma, and failure to form this complex leads to rapid clearance of FVIII and bleeding diatheses such as hemophilia A and von Willebrand disease (VWD) type 2N. High-resolution insight into the complex between VWF and FVIII has so far been strikingly lacking. This is particularly the case for the flexible a3 region of FVIII, which is imperative for high-affinity binding. Here, a structural and biophysical characterization of the interaction between VWF and FVIII is presented with focus on two of the domains that have been proven pivotal for mediating the interaction, namely the a3 region of FVIII and the TIL'E' domains of VWF. Binding between the FVIII a3 region and VWF TIL'E' was here observed using NMR spectroscopy, where chemical shift changes were localized to two β-sheet regions on the edge of TIL'E' upon FVIII a3 region binding. Isothermal titration calorimetry and NMR spectroscopy were used to characterize the interaction between FVIII and TIL'E' as well as mutants of TIL'E', which further highlights the importance of the β-sheet region of TIL'E' for high-affinity binding. Overall, the results presented provide new insight into the role the FVIII a3 region plays for complex formation between VWF and FVIII and the β-sheet region of TIL'E' is shown to be important for FVIII binding. Thus, the results pave the way for further high-resolution insights into this imperative complex.

Factor VIII S373L: Mutation at P1’ Site Confers Thrombin Cleavage Resistance, Causing Mild Haemophilia A

A novel CRM+ mutation, factor VIII position 373 serine to leucine substitution (FVIII 373-Leu) was identified during a survey of Factor VIII (FVIII) mutations. We have purified the variant protein from the patient's plasma in order to allow further characterisation of the molecule. The CRM+ plasma contained 120% Factor VIII antigen (FVIILAg) and 6% Factor Vili coagulant activity (FVIILC). After purification the mutant FVIII was subjected to thrombin proteolysis, and was thereby activated 5.6-fold compared with 7-fold for wild type molecule. Subsequently, spontaneous inactivation of the mutant was much slower than noted for wild type FVIII. Western blot analysis using monoclonal antibodies demonstrated that thrombin cleavage of FVIII 373-Leu at positions 740 and 1689 were normal but that cleavage at position 372 was completely absent.

Crystallographic coordinates of the active site of thrombin complexed to fibrinopeptide A were used to explore possible mechanistic reasons for the failure of thrombin to cleave the mutant FVIII at position 372. Steric hindrance between the mutant side chain and the side chain of the PI residue was apparent. We conclude that the functional defect of FVIII 373-Leu results from the inability of thrombin to cleave the mutant at position 372-373, and propose that this is due to steric hindrance by the side chain of leucine 373, preventing correct formation of the enzyme substrate complex.

A Two-Site, Monoclonal Antibody-Based Immunoassay for von Willebrand Factor -Demonstration that vWF Function Resides in a Conformational Epitope

Two monoclonal antibodies (RFF-VIII: R/l and RFF-VIII:R/ 2) which recognise the same epitope on von Willebrand factor (vWF) have been used in a simple, two-site, solid-phase immunoradiometric (IRMA) or enzyme-linked assay (ELISA) to analyse vWF in plasma from normal individuals and from patients with von Willebrand’s disease (vWD). Results obtained confirm our previous findings (using RFF-VIII :R/2 in a one-site, fluid-phase IRMA) that the MAbs detect the presence of an epitope on the vWF molecule that reflects its function. This epitope is involved in vWF binding to the GPIb protein on platelets. It is reduced in all types of vWD, including type II (or variant) vWD. It is present in normal plasma, in vWF released from normal platelets and from cultured umbilical cord vein endothelial cells. The epitope is, however, found to be reduced in serum. Studies on SDS-treated vWF prove that this GPIb-binding site is dependent on the conformation of the vWF multimers.

Relationships of Plasma Viscosity, Coagulation and Fibrinolysis to Coronary Risk Factors and Angina

Plasma viscosity, molecular markers of activated coagulation and fibrinolysis (fibrinopeptides A and Bβ15-42), coagulation factors (fibrinogen and factor VII) and antiplasmins were measured in 529 men aged 35-54 years and related to new angina pectoris (n = 117) and to coronary risk factors in controls without angina (n = 412). Five major risk factors (cigarette-smoking, blood pressure, cholesterol, triglyceride and body mass index) were each associated with increases in plasma viscosity, coagulation factors, and imbalance of coagulation over fibrinolysis (increased ratio of fibrinopeptide A/fibrinopeptide Bβ15-42). Increased viscosity and fibrinogen in smokers were partly reversed in exsmokers, but the imbalance of coagulation and fibrinolysis persisted. Cholesterol and triglyceride were also associated with increased antiplasmin activity. In men with angina, only fibrinogen was elevated compared to controls. We suggest that increased plasma viscosity and an imbalance of coagulation over fibrinolysis may be mechanisms by which known risk factors promote arterial thrombosis, but are not present in stable angina.

Disappearance of Antibodies to Factor VIII in a Patient with Acquired Haemophilia and Carcinoma of the Pancreas During Cytotoxic Therapy with Fluorouracil and CCNU

An inhibitor to clotting factor VIII (anti-VIII: C) developed in a 70 year old woman with carcinoma of the pancreas three months after palliative by-pass surgery. A life-threatening sublingual haemorrhage was controlled by infusion of human factor VIII concentrate in high dosage. With the objective of reducing pancreatic tumour size, combination cytotoxic therapy with fluorouracil and CCNU was given. Reduction in the size of the tumour was associated with disappearance of anti-VIII:C, reappearance of normal quantities of clotting factor VIII (VIII: C) in the plasma and resolution of the bleeding tendency. The anti-VIII: C was characterised as being predominantly of the IgG4 sub-class with k light chains. In vitro and in vivo studies showed the inactivation of VIII: C by anti-VIII: C was markedly non-linear. Normal quantities of factor VIII coagulant antigen (VIII: CAg) were detected in the patient’s plasma when VIII: C levels were negligible.

Studies on the Action of Ethamsylate (Dicynene) on Haemostasis

Twelve healthy subjects received ethamsylate or a placebo by mouth over a 48 h period in a randomized double-blind trial. The template bleeding time (including estimation of amount of blood loss), platelet aggregation studies, and plasma levels of plasminogen, alpha2-antiplasmin and fibronectin were carried out before and during treatment. The effect of a single dose (600 mg) of aspirin, given 24 h after commencement of treatment, was also determined.

Neither ethamsylate nor placebo caused a significant change in the basal values of any of the variables monitored but both the prolongation of the bleeding time and the amount of blood loss induced by aspirin were significantly less during ethamsylate treatment than with placebo. Ethamsylate failed to prevent the aspirin-induced elimination of the secondary wave of platelet aggregation.

We conclude that ethamsylate may reduce the haemorrhagic symptoms associated with mild functional platelet defects.

Human Tissue Factor Pathway Inhibitor Fused to CD4 Binds both FXa and TF/FVIIa at the Cell Surface

Tissue factor pathway inhibitor (TFPI) is one of the main regulators of the tissue factor (TF) pathway of coagulation. To tether human TFPI to the cell surface, full length or truncated TFPI lacking the third Kunitz domain were fused with domains three and four and the carboxy-termi- nal sequence of human CD4. Constructs were transfected into a mouse fibroblast cell line and individual clones were checked for expression using monoclonal antibodies directed against the first two TFPI Kunitz domains and against CD4. Specific human FXa binding was detected by flow cytometry using an anti-FX polyclonal antibody, and inhibition of FXa proteolytic activity was verified by chromogenic substrate assay using S-2765. In addition, TFPI-CD4-expressing cells, preincubated with FXa, specifically bound human TF-FVIIa complexes as revealed with an anti-human TF polyclonal antibody. No functional difference was observed between full length or truncated TFPI-CD4. These results demonstrate that functionally intact TFPI can be tethered to the cell surface. Genetic manipulation of, for example, endothelial cells leading to the stable expression of TFPI may inhibit the development of coronary artery heart disease following cardiac allotransplantation, and may inhibit thrombosis in the context of xenotransplantation.

Factor VIII Ise (R2159C) in a Patient with Mild Hemophilia A, an Abnormal Factor VIII with Retention of Function but Modification of C2 Epitopes

We found a patient with mild hemophilia A who had no detectable factor VIII antigen (FVIII:Ag), as shown by two-site ELISA using inhibitor alloantibodies (TK). We then analyzed A2, A2/B, and C2 antigen of the patient's DDAVP-induced FVIII using several anti-FVIII monoclonal antibodies. Factor VIII activity (FVIII : C) was increased from 12 to 42 Uldl by the administration of DDAVP. The DDAVPinduced increases in the A2 and A2/B antigens were 40 and 36 Uldl, respectively. However, the increase in the C2 antigen was only 7.5 Uldl. SSCP analysis and subsequent sequencing demonstrated an Arg to Cys transition at codon 2159. The anti-FVII1:C titer of monoclonal antibody, NMC-VIII15 which recognized the C2 domain, against normal plasma was 450 Bethesda Ulmg of IgG. However, the titer against DDAVP-treated patient's plasma was only 15 Bethesda Ulmg. We also tested DDAVP-induced increase in the FVIII : Ag in another mild hemophilia A patient with the same mutation at Arg2159. Increase in his C2 antigen levels was only 19% of those in the A2 and A2/B antigen. We designate this abnormal FVIII as FVIII Ise. Our results show that a missense mutation at Arg2159 to Cys modifies the antigenicity of the C2 domain.

High Prevalence of Elevated Factor VIII Levels in Patients Referred for Thrombophilia Screening: Role of Increased Synthesis and Relationship to the Acute Phase Reaction

A recent report from the Leiden Thrombophilia Survey identified high factor VIII activity levels as an independent risk factor for venous thromboembolism in a population survey. As the study measure for factor VIII was a one-stage coagulation assay, and since markers for the acute phase reaction were not assessed, it remained uncertain whether the increase was due to a constitutional increased rate of synthesis, to circulating activated factor VIII, or to an acute phase response.

We added factor VIII activity assay (FVIII:C), factor VIII antigen (FVIILAg), vWF antigen (vWF:Ag), ABO blood group, fibrinogen and C-reactive protein to our routine thrombophilia screen of patients referred because of unexplained thromboembolism.

Elevated FVIILC (>1.5 iu/ml) emerged as the single commonest abnormality detected in 25.4% of a group of 260 such patients.

FVIILC and FVIILAg were highly correlated (p = 0.003), showing that this represented a true increase in FVIII. In 4 of 46 patients this was clearly attributable to an acute phase reaction. Eleven others showed minor elevation of ESR and one of CRP. Neither FVIILC or FVIII:Ag showed significant correlation with fibrinogen, ESR or C-reactive protein by non parametric analysis.

Although there was an excess of patients with B blood group (known to be associated with FVIILC levels which are -15% higher than those in blood group 0), this could not account for the marked elevation of factor VIII observed in these patients.

We conclude that factor VIII activity assay should be a routine part of thrombophilia screening. We are investigating the cause of the increased synthesis, initially by means of family studies and linkage analysis with polymorphic markers of the FVIII locus. We postulate that it may be constitutive in some cases and in others an abnormal or exaggerated response to inflammatory stimuli.

Haemophilia A: Mutation Type Determines Risk of Inhibitor Formation

The formation of factor VIII antibodies is a major problem for replacement therapy of haemophilia A patients. Antibodies occur in 5-30% of patients with severe haemophilia A. The reason for antibody formation is still unknown. In this study we correlate for the first time different factor VIII gene mutations, stop- and missense mutations, large and small deletions and intrachromosomal intron 22 recombinations to antibody formation. A total of 364 patients with known inhibitor status of our institute, of the database, and of 3 studies representing intron-22-inversion data are included. The results show that the risk for developing factor VIII antibodies is strongly related to stop mutations, large deletions and intrachromosomal recombinations. A probable explanation could be the complete lack of endogenous circulating factor VIII protein in these cases. Other factors that might be important for the pathogenesis of inhibitor formation, e. g. the antenatal period, as well as possible therapeutic effects, are discussed.

HLA Genotype of Patients with Severe Haemophilia A due to Intron 22 Inversion with and without Inhibitors of Factor VIII

Molecular genetic studies have shown that development of antibodies to factor VIII (inhibitors) occurs most frequently in patients with severe haemophilia due to major gene lesions including inversions, stop codons and large deletions. Previous studies of HLA type were performed on inhibitor and non-inhibitor patients with diverse uncharacterised mutations which may have confounded detection of significant associations. We therefore selected a group of patients with a single mutation type, the prevalent intron 22 inversion, with or without inhibitors, to determine HLA genotype. Seventy-one such patients, 42 without and 29 with inhibitors (13 high, 9 low and 7 transient responders) were genotyped for MHC Class I HLA-A, -B, -C and Class II HLA-DQA, -DQB and -DRB loci. No strong correlation of any HLA-allele to inhibitor or non-inhibitor status was found. However, alleles of the haplotype HLA-A3, HLA-B7, HLA-C7, HLA-DQA0102, HLA-DQB0602, HLA-DR15 occurred more often in inhibitor patients. Since the alleles of this extended haplotype are common in the North European population only a very strong association would achieve statistical significance. Further studies of groups of patients similar to those studied here will be needed to confirm or exclude this association.

Definition of the Bleeding Tendency in Factor XI-Deficient Kindreds–A Clinical and Laboratory Study

Individuals with severe factor XI deficiency are prone to excessive bleeding after injury or surgery, but the existence of a haemorrhagic tendency in partial factor XI deficiency is controversial. In this study, 172 members of 30 kindreds (20 non-Jewish) transmitting factor XI deficiency in North West England were interviewed and a bleeding history questionnaire completed. Blood was taken for coagulation assays. The questionnaires were categorised independently by two assessors to determine presence or absence of a bleeding tendency, in the absence of information about the factor XI level or family history. Analysis shows that 48% of heterozygotes have a bleeding tendency. Eighteen (60%) families came to attention because of bleeding problems in heterozygotes. Comparison of histories between partially deficient and non-deficient individuals demonstrated a higher incidence of menstrual problems, an increase in significant bruising, and an increased likelihood of excessive bleeding after tonsillectomy and dental extractions.

The incidence of von Willebrand’s disease was not increased, but individuals with heterozygous factor XI deficiency who were bleeders tended to have lower levels of factor VIIIc and von Willebrand factor, and were more commonly of blood group 0. These features may contribute to the bleeding tendency. There was no evidence of alteration in factor VII activity (as defined by the ratio of activity to antigen) between the bleeders and non-bleeders.

This is convincing evidence for abnormal bleeding in factor XI deficiency which is not confined to severely deficient patients.

The Interaction of Botrocetin with Normal or Variant von Willebrand Factor (Types IIA and IIB) and Its Inhibition by Monoclonal Antibodies that Block Receptor Binding

We have recently shown the existence of two distinct forms of botrocetin (one-chain and two-chain), and demonstrated that the two-chain species is approximately 30 times more active than the one-chain in promoting von Willebrand factor (vWF) binding to platelet glycoprotein (GP) Ib. The N-terminal sequence of two-chain botrocetin is highly homologous to sea-urchin Echinoidin and other Ca2+-dependent lectins (Fujimura et al., Biochemistry 1991; 30: 1957–64).

Present data indicate that purified two-chain botrocetin binds to vWF from plasmas of patients with type IIA or IIB von Willebrand disease and its interaction is indistinguishable from that with vWF from normal individuals. However, an “activated complex” formed between botrocetin and IIB vWF expresses an enhanced biological activity for binding to GP Ib whereas the complex with IIA vWF has a decreased binding activity. Among several anti-vWF monoclonal antibodies (MoAbs) which inhibit ristocetin-induced platelet aggregation and/or vWF binding to GPIb, only two MoAbs (NMC-4 and RFF-VIII RAG:1) abolished direct binding between purified botrocetin and vWF. This suggests that they recognize an epitope(s) on the vWF molecule in close proximity to the botrocetin binding site.

Characterization of a Panel of Monoclonal Antibodies to Human Coagulation Factor XI and Detection of Factor XI in Hep G2 Cell Conditioned Medium

We have produced a panel of ten monoclonal antibodies specific to coagulation factor XI. Western blot analysis demonstrates that 9 of these antibodies react with the heavy chain of factor XI and one with the light chain. Seven of these antibodies inhibit factor XI and factor XIa activity.

We have used immobilised monoclonal antibody for the production of factor XI deficient plasma and to purify factor XI to homogeneity with high yield in a simple two-step procedure. These monoclonal antibodies were used to develop highly sensitive immunoassays capable of detecting less than 0.01 u factor XI antigen ml−1. A strong correlation was found between antigen and activity levels in 11 patients with hereditary deficiency indicating that none was cross-reacting material positive. Cultured Hep G2 cells were found to synthesize small amounts of factor XI antigen and this could also be detected by functional assay and by western blot analysis.

Characterisation of blood coagulation factor XIT475I

PCR-SSCP and DNA sequence analysis of a factor XI (FXI) deficient patient (FXI:C 39 U/dL; FXI:Ag 27 U/dL) identified a C to T transition in exon 12 of the FXI gene (F11 c.1521C>T) that predicts the substitution of Thr475 by Ile (FXIT475I) within the serine protease domain of FXI. This mutation destroys a consensus sequence for N-linked glycosylation, N473-Y-T475, known to be utilized in vivo. The FXIT475I variant was generated by site-directed mutagenesis, together with other variants that could help explain the phenotype, and recombinant FXI variants were expressed in Chinese hamster ovary cells. FXI:Ag expression was analysed by Western blot analysis, ELISA and immunocyto-chemical staining. Wild-type FXI:Ag was secreted at high levels, however the mutant (FXIT475I) was secreted very poorly. Substitution of Thr475 by Ala, Pro, Lys or Arg (all of which abolish the glycosylation consensus sequence) also severely reduced the level of secreted FXI:Ag suggesting that glycosylation at Asn473 is required for folding or secretion. Concordant with this hypothesis the conservative substitution of Thr475 by Ser (which preserves the glycosylation consensus sequence) had no effect on FXI secretion. Thr/Ser475 is highly conserved in serine protease domains but the glycosylation site (Asn473) is not. Surprisingly, substitution of Asn473 by Ala (which removes the N-linked glycosylation site) had no effect on the levels of FXI:Ag secreted. In conclusion, although the FXI-T475I mutation destroys an N-linked glycosylation consensus sequence, the cause of failure to secrete FXI is not the loss of a glycosylation site but rather a direct effect of the substitution of this highly conserved residue.

Live birth following the first mutation specific pre-implantation genetic diagnosis for haemophilia A

Haemophilia A is an X-linked, recessive, inherited bleeding disorder which affects 1 in 5000 males born worldwide. It is caused by mutations in the FactorVIII (F8) gene on chromosome Xq28. We describe for the first time two mutation specific, single cell protocols for pre-implantation genetic diagnosis (PGD) of haemophilia A that enable the selection of both male and female unaffected embryos. This approach offers an alternative to sexing, frequently used for X-linked disorders, that results in the discarding of all male embryos including the 50% that would have been normal. Two families witha history of severe haemophilia A requested carrier diagnosis and subsequently proceeded to PGD. The mutation in family1 isa single nucleotide substitution c. 5953C>T, R1966X in exon 18 and in family 2, c. 5122C>T, R1689C in exon 14 of the F8 gene. Amplification efficiency was compared between distilled water and SDS/proteinase K cell lysis (98.0%, 96/98 and 80%, 112/140 respectively) using 238 single lymphocytes. Blastomeres from spare IVF cleavage-stage embryos donated for research showed amplification efficiencies of 83.3% (45/54) for the R1966X and 92.9% (13/14) for the R1689C mutations. The rate of allele dropout (ADO) on heterozygous lymphocytes was 1.1% (1/93) for R1966X and 5.94% (6/101) for R1689C mutations. A single PGD treatment cycle for family1 resulted in two embryos for transfer but these failed to implant. However, with family 2, two embryos were transferred to the uterus on day 4 resulting in a successful singleton pregnancy and subsequent live birth of a normal non-carrier female.

Gene Therapy for Hemophilia

The best currently available treatments for hemophilia A and B (factor VIII or factor IX deficiency, respectively) require frequent intravenous infusion of highly expensive proteins that have short half-lives. Factor levels follow a saw-tooth pattern that is seldom in the normal range and falls so low that breakthrough bleeding occurs. Most hemophiliacs worldwide do not have access to even this level of care. In stark contrast, gene therapy holds out the hope of a cure by inducing continuous endogenous expression of factor VIII or factor IX following transfer of a functional gene to replace the hemophilic patient's own defective gene.

Long-term safety and efficacy of factor IX gene therapy in hemophilia B

BACKGROUND

In patients with severe hemophilia B, gene therapy that is mediated by a novel self-complementary adeno-associated virus serotype 8 (AAV8) vector has been shown to raise factor IX levels for periods of up to 16 months. We wanted to determine the durability of transgene expression, the vector dose-response relationship, and the level of persistent or late toxicity.

METHODS

We evaluated the stability of transgene expression and long-term safety in 10 patients with severe hemophilia B: 6 patients who had been enrolled in an initial phase 1 dose-escalation trial, with 2 patients each receiving a low, intermediate, or high dose, and 4 additional patients who received the high dose (2×10(12) vector genomes per kilogram of body weight). The patients subsequently underwent extensive clinical and laboratory monitoring.

RESULTS

A single intravenous infusion of vector in all 10 patients with severe hemophilia B resulted in a dose-dependent increase in circulating factor IX to a level that was 1 to 6% of the normal value over a median period of 3.2 years, with observation ongoing. In the high-dose group, a consistent increase in the factor IX level to a mean (±SD) of 5.1±1.7% was observed in all 6 patients, which resulted in a reduction of more than 90% in both bleeding episodes and the use of prophylactic factor IX concentrate. A transient increase in the mean alanine aminotransferase level to 86 IU per liter (range, 36 to 202) occurred between week 7 and week 10 in 4 of the 6 patients in the high-dose group but resolved over a median of 5 days (range, 2 to 35) after prednisolone treatment.

CONCLUSIONS

In 10 patients with severe hemophilia B, the infusion of a single dose of AAV8 vector resulted in long-term therapeutic factor IX expression associated with clinical improvement. With a follow-up period of up to 3 years, no late toxic effects from the therapy were reported. (Funded by the National Heart, Lung, and Blood Institute and others; ClinicalTrials.gov number, NCT00979238.).

Adenovirus-associated virus vector-mediated gene transfer in hemophilia B

BACKGROUND

Hemophilia B, an X-linked disorder, is ideally suited for gene therapy. We investigated the use of a new gene therapy in patients with the disorder.

METHODS

We infused a single dose of a serotype-8-pseudotyped, self-complementary adenovirus-associated virus (AAV) vector expressing a codon-optimized human factor IX (FIX) transgene (scAAV2/8-LP1-hFIXco) in a peripheral vein in six patients with severe hemophilia B (FIX activity, <1% of normal values). Study participants were enrolled sequentially in one of three cohorts (given a high, intermediate, or low dose of vector), with two participants in each group. Vector was administered without immunosuppressive therapy, and participants were followed for 6 to 16 months.

RESULTS

AAV-mediated expression of FIX at 2 to 11% of normal levels was observed in all participants. Four of the six discontinued FIX prophylaxis and remained free of spontaneous hemorrhage; in the other two, the interval between prophylactic injections was increased. Of the two participants who received the high dose of vector, one had a transient, asymptomatic elevation of serum aminotransferase levels, which was associated with the detection of AAV8-capsid-specific T cells in the peripheral blood; the other had a slight increase in liver-enzyme levels, the cause of which was less clear. Each of these two participants received a short course of glucocorticoid therapy, which rapidly normalized aminotransferase levels and maintained FIX levels in the range of 3 to 11% of normal values.

CONCLUSIONS

Peripheral-vein infusion of scAAV2/8-LP1-hFIXco resulted in FIX transgene expression at levels sufficient to improve the bleeding phenotype, with few side effects. Although immune-mediated clearance of AAV-transduced hepatocytes remains a concern, this process may be controlled with a short course of glucocorticoids without loss of transgene expression. (Funded by the Medical Research Council and others; ClinicalTrials.gov number, NCT00979238.).

Human congenital diseases with mixed modes of inheritance have a shortage of recessive disease. A demographic scenario?

An archive of congenital human diseases is presented, aiming to contain all those where recessive (biallelic) can be compared with X-linked and/or dominant (monoallelic) inheritance. A significant deficit of recessive inheritance is evident, both in disease inheritance and in contribution to inheritance per known disease gene. The deficit contrasts with expectation derived from the cell biology of mutation, and from the importance of recessive mutation in evolution and its preponderance in N-ethyl-N-nitrosourea (ENU) mutagenesis. The deficit fits well with the standard model of demographic change since the neolithic era, and may also reflect natural selection acting on heterozygotes.

Menorrhagia in adolescents with inherited bleeding disorders

STUDY OBJECTIVES

We reviewed the management and treatment outcomes of menorrhagia in adolescents with inherited bleeding disorders and assessed the impact of menorrhagia on their quality of life.

DESIGN

Retrospective review of case notes and a questionnaire study.

SETTING

Comprehensive-care hemophilia treatment center.

PARTICIPANTS

Adolescents with inherited bleeding disorders who had registered at the center and were attending the multidisciplinary hemophilia and gynecology clinic for management of menorrhagia.

INTERVENTIONS

Review of medical records and assessment of menstrual blood loss using the pictorial blood assessment chart and quality of life measurements during menstruation using a questionnaire.

MAIN OUTCOME MEASURES

Scores on pictorial blood assessment charts and quality of life measurements before and after treatment.

RESULTS

Of 153 girls aged 12 to 19 years who had registered at the center and had an inherited bleeding disorder, 42 (27%) attended the multidisciplinary clinic for management of menorrhagia. The majority (38/42; 90%) had experienced menorrhagia since menarche. Of the group, 5 (12%) required hospital admission for acute menorrhagia and severe anemia. Treatment options for menorrhagia included tranexamic acid, desmopressin, combined oral contraceptive pills, clotting factor concentrate, and the levonorgestrel intrauterine system. These treatment modalities, alone or in combination, were associated with a reduction in menstrual blood loss (median pre- and posttreatment pictorial blood assessment chart scores were 215 and 88, respectively) and improvement in quality of life scores (median pre- and posttreatment were 26 and 44, respectively).

CONCLUSIONS

Menorrhagia is a common symptom in adolescents with inherited bleeding disorders. It can present acutely, and it adversely affects quality of life. Treatment options include hemostatic and/or hormonal therapies and can improve the quality of life of affected girls.

Bernard Soulier syndrome in pregnancy: a systematic review

Bernard Soulier syndrome (BSS) is a rare disorder of platelets, inherited mainly as an autosomal recessive trait. It is characterised by qualitative and quantitative defects of the platelet membrane glycoprotein (GP) Ib-IX-V complex. The main clinical characteristics are thrombocytopenia, prolonged bleeding time and the presence of giant platelets. Data on the clinical course and outcome of pregnancy in women with Bernard Soulier syndrome is scattered in individual case reports. In this paper, we performed a systematic review of literature and identified 16 relevant articles; all case reports that included 30 pregnancies among 18 women. Primary postpartum haemorrhage was reported in 10 (33%) and secondary in 12 (40%) of pregnancies, requiring blood transfusion in 15 pregnancies. Two women had an emergency obstetric hysterectomy. Alloimmune thrombocytopenia was reported in 6 neonates, with one intrauterine death and one neonatal death. Bernard Soulier syndrome in pregnancy is associated with a high risk of serious bleeding for the mother and the neonate. A multidisciplinary team approach and individualised management plan for such women are required to minimise these risks. An international registry is recommended to obtain further knowledge in managing women with this rare disorder.

Alpha1-antitrypsin Pittsburgh in a family with bleeding tendency

We describe a 16-year-old girl and her 41-year-old father who both had a bleeding tendency, dramatic prolongation of all standard clotting assays, undetectable levels of plasma protein C activity, and low or borderline levels of factors X, XI and XII. Plasma and serum electrophoresis revealed a minor peak following the main alpha(1) globulin peak, of which the proportion was increased. Platelet aggregation by thrombin (final concentration 1 U/mL) was absent in both patients, but this inhibition can be overcome by increasing the concentration of thrombin (4 U/mL). The molecular defect responsible for these coagulation abnormalities was identified by genomic sequencing. Both patients are heterozygous for alpha(1)-antitrypsin Met 358 to Arg (alpha(1)-antitrypsin Pittsburgh). Seven other members of this pedigree had normal coagulation tests and do not carry the same genetic mutation. This unique family with alpha1-antitrypsin Pittsburgh sheds some light on the study of this extremely rare mutation and its inheritance.

Identification of factor IX mutations in Iranian haemophilia B patients by SSCP and sequencing

Different kinds of mutations, mostly point mutations, in the coagulation factor IX (FIX) gene F9 result in a recessive X-linked bleeding disorder known as haemophilia B. In this study, molecular analysis of 76 unrelated Iranian haemophilia B patients was performed by PCR, single strand conformational polymorphism (SSCP) on important functional regions of the F9 gene followed by sequencing on samples with different migration pattern. Using this approach we found mutation in 52 out of 76 patients. Our data showed that the pathologic mechanisms are heterogeneous as recorded for patients in haemophilia B mutation database and seven of the mutations are previously undescribed.

Safe and efficient transduction of the liver after peripheral vein infusion of self-complementary AAV vector results in stable therapeutic expression of human FIX in nonhuman primates

The safety and efficacy of peripheral venous administration of a self-complementary adeno-associated viral vector encoding the human FIX gene (scAAV-LP1-hFIXco) was evaluated in nonhuman primates for gene therapy of hemophilia B. Peripheral vein infusion of 1x10(12) vg/kg scAAV-LP1-hFIXco pseudotyped with serotype 8 capsid, in 3 macaques, resulted in stable therapeutic expression (more than 9 months) of human FIX (hFIX) at levels (1.1+/-0.5 microg/mL, or 22% of normal) that were comparable to those achieved after direct delivery of the same vector dose into the portal circulation (1.3+/-0.3 microg/mL, or 26% of normal). Importantly, the pattern of vector biodistribution after systemic and portal vein administration of scAAV-LP1-hFIXco was almost identical. Additionally, comparable levels of gene transfer were achieved in macaques with preexisting immunity to AAV8 following peripheral vein administration of 1x10(12) vg/kg AAV5-pseudotyped scAAV-LP1-hFIXco. This confirms that alternative serotypes can circumvent preexisting naturally acquired immunity to AAV. Thus, peripheral venous administration of AAV5 and AAV8 vectors is safe and as effective at transducing the liver in nonhuman primates as direct vector administration into the portal circulation. These results should make vector administration to patients, especially those with a severe bleeding diathesis, significantly easier and safer.

Postinjury vascular intimal hyperplasia in mice is completely inhibited by CD34+ bone marrow-derived progenitor cells expressing membrane-tethered anticoagulant fusion proteins

BACKGROUND

Coagulation proteins promote neointimal hyperplasia and vascular remodelling after vessel injury, but the precise mechanisms by which they act in vivo remain undetermined.

OBJECTIVES

This study, using an injury model in which the neointima is derived from bone marrow (BM)-derived cells, compared inhibition of tissue factor or thrombin on either BM-derived or existing vascular smooth muscle cells.

METHODS

Two transgenic (Tg) mouse strains expressing membrane-tethered tissue factor pathway inhibitor (TFPI) or hirudin (Hir) fusion proteins driven by an alpha smooth muscle actin (SMA) promoter were generated (alpha-TFPI-Tg and alpha-Hir-Tg) and the phenotype after wire-induced endovascular injury was compared with that in wild-type (WT) controls.

RESULTS

WT mice developed progressive neointimal expansion, whereas injury in either Tg was followed by repair back to a preinjured state. This was also seen when WT mice were reconstituted with BM from Tg mice but not when Tgs were reconstituted with WT BM, in which injury was followed by slowly progressive neointimal expansion. Injection of CD34+ cells from Tg mice into injured WT mice resulted in the accumulation of fusion protein-expressing cells from day 3 onwards and an absence of neointimal hyperplasia in those areas.

CONCLUSIONS

Neointimal development after wire-induced endovascular injury in mice was completely inhibited when BM-derived cells infiltrating the damaged artery expressed membrane tethered anticoagulant fusion proteins under an alpha-SMA promoter. These findings enhance our understanding of the pathological role that coagulation proteins play in vascular inflammation.

A common ancestral glycoprotein (GP) 9 1828A>G (Asn45Ser) gene mutation occurring in European families from Australia and Northern Europe with Bernard-Soulier Syndrome (BSS)

Bernard-Soulier syndrome (BSS) is an extremely rare hereditary bleeding disorder, caused by mutations occurring in the Glycoprotein (GP) Ibalpha, GPIbbeta and GP9 genes that encode for the corresponding subunits of platelet GPIb-V-IX adhesion receptor complex. BSS has been reported in many populations, mostly behaving in an autosomal-recessive manner.While the great majority of BSS mutations are unique to a single individual or family, the GP9 1828A>G Asn45Ser mutation, which we have identified in an undocumented Australian Caucasian, has already been reported in multiple unrelated Caucasian families from various Northern and Central European countries. Haplotype analysis of 19 BSS patients from 15 unrelated Northern European families (including 2 compound heterozygote siblings from a British family previously published, and 17 1828A>G Asn45Ser homozygotes), showed that 14 of these BSS patients from 11 of the 1828A>G Asn45Ser homozygote families share a common haplotype at the chromosomal region 3' to the GP9 gene. Hence, the results suggest that the GP9 1828A>GAsn45Ser mutation in these families is ancient, and its frequent emergence in the European population is the result of a founder effect rather than recurrent mutational events. Association of the 1828A>G Asn45Ser mutation with variant haplotypes in 4 other Northern European BSS families raised the possibility of a second founder event, or rare recombinations in these families. Additional members from these 'atypical' lineages would need to be screened to resolve this question.

Self-complementary adeno-associated virus vectors containing a novel liver-specific human factor IX expression cassette enable highly efficient transduction of murine and nonhuman primate liver

Transduction with recombinant adeno-associated virus (AAV) vectors is limited by the need to convert its single-stranded (ss) genome to transcriptionally active double-stranded (ds) forms. For AAV-mediated hemophilia B (HB) gene therapy, we have overcome this obstacle by constructing a liver-restricted mini-human factor IX (hFIX) expression cassette that can be packaged as complementary dimers within individual AAV particles. Molecular analysis of murine liver transduced with these self-complementary (sc) vectors demonstrated rapid formation of active ds-linear genomes that persisted stably as concatamers or monomeric circles. This unique property resulted in a 20-fold improvement in hFIX expression in mice over comparable ssAAV vectors. Administration of only 1 x 10(10) scAAV particles led to expression of hFIX at supraphysiologic levels (8I U/mL) and correction of the bleeding diathesis in FIX knock-out mice. Of importance, therapeutic levels of hFIX (3%-30% of normal) were achieved in nonhuman primates using a significantly lower dose of scAAV than required with ssAAV. Furthermore, AAV5-pseudotyped scAAV vectors mediated successful transduction in macaques with pre-existing immunity to AAV8. Hence, this novel vector represents an important advance for hemophilia B gene therapy.

Combined deficiency of factor V and factor VIII is due to mutations in either LMAN1 or MCFD2

Mutations in LMAN1 (ERGIC-53) or MCFD2 cause combined deficiency of factor V and factor VIII (F5F8D). LMAN1 and MCFD2 form a protein complex that functions as a cargo receptor ferrying FV and FVIII from the endoplasmic reticulum to the Golgi. In this study, we analyzed 10 previously reported and 10 new F5F8D families. Mutations in the LMAN1 or MCFD2 genes accounted for 15 of these families, including 3 alleles resulting in no LMAN1 mRNA accumulation. Combined with our previous reports, we have identified LMAN1 or MCFD2 mutations as the causes of F5F8D in 71 of 76 families. Among the 5 families in which no mutations were identified, 3 were due to misdiagnosis, with the remaining 2 likely carrying LMAN1 or MCFD2 mutations that were missed by direct sequencing. Our results suggest that mutations in LMAN1 and MCFD2 may account for all cases of F5F8D. Immunoprecipitation and Western blot analysis detected a low level of LMAN1-MCFD2 complex in lymphoblasts derived from patients with missense mutations in LMAN1 (C475R) or MCFD2 (I136T), suggesting that complete loss of the complex may not be required for clinically significant reduction in FV and FVIII.

A novel missense mutation in ABCA1 results in altered protein trafficking and reduced phosphatidylserine translocation in a patient with Scott syndrome

Scott syndrome (SS) is a bleeding disorder characterized by a failure to expose phosphatidylserine (PS) to the outer leaflet of the platelet plasma membrane. Because the adenosine triphosphate (ATP)–binding cassette transporter A1 (ABCA1) is implicated in the exofacial translocation of PS, we assessed its role in the pathophysiology of a patient with SS. Substantially reduced levels of ABCA1 mRNA were found in the patient's leukocytes, compared with controls. The SS patient was heterozygous for a novel missense mutation c.6064G&gt;A (ABCA1 R1925Q), absent from unaffected family members and controls. Both mutant and wild-type alleles were reduced in mRNA expression, and no causative mutation for this phenomenon was identified in the ABCA1 gene or its proximal promoter, suggesting a putative second mutation in a trans-acting regulatory gene may also be involved in the disorder in this patient. In vitro expression studies showed impaired trafficking of ABCA1 R1925Q to the plasma membrane. Overexpression of wild-type ABCA1 in SS lymphocytes complemented the Ca2+-dependent PS exposure at the cell surface. These data identify a mutation in ABCA1 that contributes to the defective PS translocation phenotype in our patient with SS.

Pharmacodynamic resistance to warfarin associated with a Val66Met substitution in vitamin K epoxide reductase complex subunit 1

The gene encoding vitamin K epoxide reductase complex subunit 1 (VKORC1), a component of the enzyme that is the therapeutic target site for warfarin, has recently been identified. In order to investigate the relationship betweenVKORC1 and warfarin dose response, we studied the VKORC1 gene (VKORC1) in patients with warfarin resistance. From a study group of 820 patients, we identified 4 individuals who required more than 25 mg of warfarin daily for therapeutic anticoagulation. Three of these had serum warfarin concentrations within the therapeutic range of 0.7-2.3 mg/l and showed wild-type VKORC1 sequence. The fourth warfarin resistant individual had consistently high (> or =5.7 mg/l) serum warfarin concentrations, yet had no clinically discernible cause for warfarin resistance. VKORC1 showed a heterozygous 196G-->A transition that predicted aVal66Met substitution in the VKORC1 polypeptide. This transition was also identified in 2 asymptomatic family members who had never received warfarin. These individuals had normal vitamin-K dependent coagulation factor activities and undetectable serum PIVKAII and vitamin K1 2,3 epoxide suggesting that their basal vitamin K epoxide reductase activity was not adversely affected by the VKORC1 Val66Met substitution. The association between a nucleotide transition in VKORC1 and pharmacodynamic warfarin resistance supports the hypothesis that VKORC1 is the site of action of warfarin and indicates thatVKORC1 sequence is an important determinant of the warfarin dose response.

Complete inhibition of acute humoral rejection using regulated expression of membrane-tethered anticoagulants on xenograft endothelium

Xenotransplantation promises an unlimited supply of organs for clinical transplantation. However, an aggressive humoral immune response continues to limit the survival of pig organs after transplantation into primates. Because intravascular thrombosis and systemic coagulopathy are prominent features of acute humoral xenograft rejection, we hypothesized that expression of anticoagulants on xenogeneic vascular endothelium might inhibit the process. Hearts from novel transgenic mice, expressing membrane-tethered fusion proteins based on human tissue factor pathway inhibitor and hirudin, respectively, were transplanted into rats. In contrast to control non-transgenic mouse hearts, which were all rejected within 3 days, 100% of the organs from both strains of transgenic mice were completely resistant to humoral rejection and survived for more than 100 days when T-cell-mediated rejection was inhibited by administration of ciclosporin A. These results demonstrate the critical role of coagulation in the pathophysiology of acute humoral rejection and the potential for inhibiting rejection by targeting the expression of anticoagulants to graft endothelial cells. This genetic strategy could be applied in a clinically relevant species such as the pig.

Permanent phenotypic correction of hemophilia B in immunocompetent mice by prenatal gene therapy

Hemophilia B, also known as Christmas disease, arises from mutations in the factor IX (F9) gene. Its treatment in humans, by recombinant protein substitution, is expensive, thus limiting its application to intermittent treatment in bleeding episodes and prophylaxis during surgery; development of inhibitory antibodies is an associated hazard. This study demonstrates permanent therapeutic correction of his disease without development of immune reactions by introduction of an HIV-based lentiviral vector encoding the human factor IX protein into the fetal circulation of immunocompetent hemophiliac and normal outbred mice. Plasma factor IX antigen remained at around 9%, 13%, and 16% of normal in the 3 hemophilia B mice, respectively, until the last measurement at 14 months. Substantial improvement in blood coagulability as measured by coagulation assay was seen in all 3 mice and they rapidly stopped bleeding after venipuncture. No humoral or cellular immunity against the protein, elevation of serum liver enzymes, or vector spread to the germline or maternal circulation were detected.

Prospects for gene therapy of haemophilia

That gene therapy offers the promise of a cure for haemophilia was apparent more than a decade ago. After years of failure, substantial progress in the efficiency of gene transfer technology has recently resulted in impressive success in animal models with haemophilia. However, fears of the risks intrinsic to such therapy have been raised by the fate of two children cured of immune deficiency by gene transfer who have, however, subsequently developed leukaemia as a result of insertional mutagenesis. The purpose of this review is to outline the current status of gene therapy in light of recent successes and tragedies and to consider the prospects for curing haemophilia in the short-to-medium term.

Two novel mutations in severe factor VII deficiency

We have characterized the molecular defect in two families with severe factor VII (FVII) deficiency. In family I, the proband was found to be homozygous for a novel 18 bp deletion in exon 8 (g.10896-10913del) resulting in the in-frame deletion of six amino acids in the serine protease domain. Molecular modelling suggests the deletion is likely to disrupt folding of the FVII molecule. The reduced FVII antigen (21 U/dl) and negligible activity (0.4 U/dl) in the patient's plasma indicated that the deletion affected both the secretion/stability and function of the mutant protein. In family II, the proband was found to be a compound heterozygote for a novel missense mutation (g.7884G>A; FVII G117R) in exon 5 encoding the EGF2 domain of FVII and a nonsense mutation (g.8960C>T; FVII R152X) in exon 6. Extensive sequence comparison in a wide evolutionary context suggested that the Gly117 residue is critical for structure of FVII. The grossly reduced FVII antigen (1.1 U/dl) and activity (0.4 U/dl) plasma values indicate the mutation primarily affected the folding/secretion or stability of the protein.

Functional characterization of factor V-Ile359Thr: a novel mutation associated with thrombosis

A missense mutation, FV-Ile359Thr (FV Liverpool), associated with thrombosis has recently been described. This mutation creates an additional potential N-linked glycosylation site (Asn-X-Ser/Thr) in factor V (FV) at Asn357 that could interfere with secretion and/or protein interactions. To investigate the molecular pathology of FV-Ile359Thr, the mutation was created by site-directed mutagenesis and expressed together with other mutations that could help explain the phenotype (FV-Arg306Gln/Ile359Thr/Arg679Gln, FV-Ile359Thr/Arg506Gln/Arg679Gln, and FV-Asn357Gln/Ile359Thr). The FV-Ile359Thr was secreted normally and had full procoagulant activity. Western blot analysis showed that FV-Ile359Thr migrated more slowly, while the FV-Asn357Gln/Ile359Thr was indistinguishable from FV-wild type (FV-WT), indicating that FV-Ile359Thr was expressed with an additional carbohydrate chain. Activated protein C (APC)-mediated inactivation in an FVa degradation assay showed that the Ile359Thr mutation significantly reduced the cleavage at Arg306 both in the presence and absence of protein S, whereas the cleavage at Arg506 was unaffected. When tested in an FVIIIa degradation assay, the FV-Ile359Thr variant exhibited equally low APC cofactor activity as FV Leiden (FVArg506Gln). In conclusion, the Ile359Thr mutation appears to affect anticoagulation by 2 mechanisms, impeding the APC-mediated down-regulation of the FVa molecule and additionally being a poor APC cofactor for the down-regulation of FVIIIa. These findings explain the association of the FV-Ile359Thr mutation with thrombosis.