Etranacogene dezaparvovec gene therapy for haemophilia B (HOPE-B): 24-month post-hoc efficacy and safety data from a single-arm, multicentre, phase 3 trial

BACKGROUND

Etranacogene dezaparvovec, the first gene therapy approved for haemophilia B treatment, was shown to be superior to treatment with continuous prophylactic factor IX in terms of bleeding protection 18 months after gene therapy in a phase 3 trial. We report post-hoc 24-month efficacy and safety data from this trial to evaluate the longer-term effects of etranacogene dezaparvovec in individuals with haemophilia B.

METHODS

The phase 3 HOPE-B trial enrolled males aged 18 years or older with inherited haemophilia B, classified as severe (plasma factor IX activity level <1%) or moderately severe (plasma factor IX activity level ≥1% and ≤2%), with a severe bleeding phenotype and who were on stable continuous factor IX prophylaxis. Participants were treated with a single infusion of etranacogene dezaparvovec (2 × 1013 genome copies per kg of bodyweight). The primary endpoint, reported previously, was non-inferiority of the annualised bleeding rate (ABR) during the 52 weeks following stable factor IX expression (defined as months 7-18 after treatment) versus an at least 6-month lead-in period in which participants received their usual continuous factor IX prophylaxis, and is updated here up to month 24. Additional, post-hoc efficacy analyses, including adjusted ABR, factor IX activity, participants within factor IX ranges, and factor IX use, and safety analyses were performed at 24 months after gene therapy. Data were analysed in the full analysis set, which comprised the 54 patients who received at least a partial dose of gene therapy. The trial is ongoing and is registered with ClinicalTrials.gov, number NCT03569891.

FINDINGS

The study began on June 27, 2018, and participants were treated between January, 2019, and March, 2020; the date of data cutoff was April 21, 2022. 54 adult males (40 White, two Asian, one Black or African American, 11 other or missing) received a single intravenous infusion of etranacogene dezaparvovec and were followed for a median of 26·51 months (IQR 24·54-27·99), after a lead-in period of 7·13 months (6·51-7·82). In the updated analysis comparing months 7-24 after gene therapy to the lead-in period, mean adjusted ABR significantly reduced from 4·18 to 1·51 (p=0·0002) for all bleeds and from 3·65 to 0·99 (p=0·0001) for factor IX-treated bleeds. During each 6-month period after gene therapy, at least 67% of participants experienced no bleeding (36 of 54 during months 0-6 and stable thereafter), compared with 14 (26%) of 54 during the lead-in period. 24 months after gene therapy, 1 (2%) participant had one-stage factor IX activity less than 5%, whereas 18 (33%) had factor IX activity more than 40% (non-haemophilia range), with mean factor IX activity stable and sustained at 36·7% (SD 19·0%). 52 (96%) of 54 participants expressed endogenous factor IX, remaining free of factor IX prophylaxis at month 24. No new safety concerns were identified and no treatment-related serious adverse events or treatment-related deaths occurred. The most common treatment-related adverse events were an increase in alanine aminotransferase (nine [17%] of 54 patients), headache (eight [15%]), influenza-like illness (seven [13%]), and an increase in aspartate aminotransferase (five [9%]).

INTERPRETATION

By providing durable disease correction throughout the 24 months after gene therapy, etranacogene dezaparvovec provides a safe and effective therapeutic option for patients with severe or moderately severe haemophilia B.

FUNDING

uniQure and CSL Behring.

Effect of etranacogene dezaparvovec on quality of life for severe and moderately severe haemophilia B participants: Results from the phase III HOPE-B trial 2 years after gene therapy

INTRODUCTION

For people with haemophilia B (PwHB), bleeding may occur despite prophylaxis, negatively affecting health-related quality of life (HRQoL). The pivotal phase 3 HOPE-B trial investigating the adeno-associated virus gene transfer product, etranacogene dezaparvovec (EDZ), demonstrated sustained factor IX (FIX) activity and bleed protection in PwHB with baseline FIX levels ≤2%.

AIM

Assess how EDZ affects HRQoL in HOPE-B trial participants.

METHODS

HRQoL was evaluated using generic and disease-specific patient reported outcomes (PROs) including the EQ-5D-5L and the Hem-A-QoL questionnaires. Mean domain and total scores were compared 6 months pre- and the first 2 years post-EDZ administration using repeated measures linear mixed models. The percentage of participants with minimal clinically important improvements in HRQoL was also evaluated.

RESULTS

Two years post-EDZ, there were nominally significant increases in the least squares (LS) mean score for the EQ-5D-5L Index Value (.04; p = .0129), reflecting better HRQoL. Nominally significant decreases in the LS mean scores, reflecting better HRQoL, were also found for the Hem-A-QoL total score (-6.0; p < .0001) and the Treatment (-13.94; p < .0001), Feelings (-9.01; p < .0001), Future (-6.45; p = .0004) and Work/School (-5.21; p = .0098) domains. The percentage of participants with ≥15-point improvement ranged from 45.83% (95% CI: 31.37%, 60.83%) for Treatment to 13.89% (95% CI: 4.67%, 29.50%) for Family Planning. Results were similar for Year 1.

CONCLUSION

In conclusion, gene therapy with EDZ improved HRQoL in the first and second years in several Hem-A-QoL domains, including Treatment, Feelings, Work/School and Future domains, whereas improvement in other aspects of HRQoL were not demonstrated.

Indirect treatment comparisons of the gene therapy etranacogene dezaparvovec versus extended half-life factor IX therapies for severe or moderately severe haemophilia B

INTRODUCTION

Etranacogene dezaparvovec gene therapy for haemophilia B demonstrated superior efficacy at 24 months in reducing bleeds versus a ≥6-month lead-in period of prophylaxis with FIX products in the phase 3 trial, HOPE-B. In the absence of head-to-head comparisons of etranacogene dezaparvovec versus FIX products, indirect treatment comparisons (ITC) can be used.

AIM

To compare the efficacy of etranacogene dezaparvovec versus rIX-FP, rFIXFc and N9-GP using ITC, and support HOPE-B results.

METHODS

Data were leveraged from Phase 3 pivotal trials: HOPE-B, PROLONG-9FP, B-LONG and Paradigm 2. Annualised bleeding rates (ABR), spontaneous (AsBR) and joint (AjBR) bleeding rates, percentage of patients with no bleeds, and FIX consumption were assessed using inverse probability of treatment weighting and matching adjusted indirect comparisons.

RESULTS

Etranacogene dezaparvovec demonstrated statistically significantly lower bleeding rates versus all comparators. Rate ratios for ABR, AsBR and AjBR versus rIX-FP were 0.19 (p < .0001), 0.08 (p < .0001) and 0.09 (p < .0001), respectively. Rate ratios for ABR, AsBR and AjBR versus rFIXFc were 0.14 (p < .0001), 0.13 (p = .0083) and 0.15 (p = .0111), respectively. Rate ratios for ABR and AsBR, versus N9-GP were 0.24 (p = .0231) and 0.13 (p = .0071), respectively. Etranacogene dezaparvovec demonstrated significantly higher percentage of patients with no bleeds versus rIX-FP and rFIXFc; odds ratios: 17.60 (p < .0001) and 5.65 (p = .0037), respectively. Etranacogene dezaparvovec resulted in significantly lower FIX consumption than all comparators.

CONCLUSIONS

ITC suggests that etranacogene dezaparvovec offers patients with haemophilia B (≤2% of normal FIX expression) a single dose treatment that can significantly reduce bleeding rates and eliminate routine infusions associated with FIX therapies.

Stable and durable factor IX levels in patients with hemophilia B over 3 years after etranacogene dezaparvovec gene therapy

Etranacogene dezaparvovec (AMT-061) is a recombinant adeno-associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) transgene with a liver-specific promoter. Here, we report 3-year outcomes from a phase 2b, open-label, single-dose, single-arm, multicenter trial conducted among adults with severe or moderately severe hemophilia B (FIX ≤2%). All participants (n = 3) received a single intravenous dose (2 × 1013 gene copies per kg) and will be followed up for 5 years. The primary end point of FIX activity ≥5% at 6 weeks was met. Secondary end points included bleed frequency, FIX concentrate use, joint health, and adverse events (AEs). All participants required routine FIX prophylaxis and had neutralizing antibodies to AAV5 before etranacogene dezaparvovec treatment. After administration, FIX activity rose to a mean of 40.8% in year 1 and was sustained in year 3 at 36.9%. All participants discontinued FIX prophylaxis. Bleeding was completely eliminated in 2 out of 3 participants. One participant required on-demand FIX replacement therapy per protocol because of elective surgical procedures, for 2 reported bleeding episodes, and twice for a single self-administered infusion because of an unreported reason. One participant experienced 2 mild, self-limiting AEs shortly after dosing. During the 3-year study period, there were no clinically significant elevations in liver enzymes, no requirement for steroids, no FIX inhibitor development, and no late-emergent safety events in any participant. Etranacogene dezaparvovec was safe and effective in adults with hemophilia B over 3 years after administration. This trial was registered at www.clinicaltrials.gov as #NCT03489291.

Gene Therapy with Etranacogene Dezaparvovec for Hemophilia B

BACKGROUND

Moderate-to-severe hemophilia B is treated with lifelong, continuous coagulation factor IX replacement to prevent bleeding. Gene therapy for hemophilia B aims to establish sustained factor IX activity, thereby protecting against bleeding without burdensome factor IX replacement.

METHODS

In this open-label, phase 3 study, after a lead-in period (≥6 months) of factor IX prophylaxis, we administered one infusion of adeno-associated virus 5 (AAV5) vector expressing the Padua factor IX variant (etranacogene dezaparvovec; 2×10¹³ genome copies per kilogram of body weight) to 54 men with hemophilia B (factor IX activity ≤2% of the normal value) regardless of preexisting AAV5 neutralizing antibodies. The primary end point was the annualized bleeding rate, evaluated in a noninferiority analysis comparing the rate during months 7 through 18 after etranacogene dezaparvovec treatment with the rate during the lead-in period. Noninferiority of etranacogene dezaparvovec was defined as an upper limit of the two-sided 95% Wald confidence interval of the annualized bleeding rate ratio that was less than the noninferiority margin of 1.8. Superiority, additional efficacy measures, and safety were also assessed.

RESULTS

The annualized bleeding rate decreased from 4.19 (95% confidence interval [CI], 3.22 to 5.45) during the lead-in period to 1.51 (95% CI, 0.81 to 2.82) during months 7 through 18 after treatment, for a rate ratio of 0.36 (95% Wald CI, 0.20 to 0.64; P<0.001), demonstrating noninferiority and superiority of etranacogene dezaparvovec as compared with factor IX prophylaxis. Factor IX activity had increased from baseline by a least-squares mean of 36.2 percentage points (95% CI, 31.4 to 41.0) at 6 months and 34.3 percentage points (95% CI, 29.5 to 39.1) at 18 months after treatment, and usage of factor IX concentrate decreased by a mean of 248,825 IU per year per participant in the post-treatment period (P<0.001 for all three comparisons). Benefits and safety were observed in participants with predose AAV5 neutralizing antibody titers of less than 700. No treatment-related serious adverse events occurred.

CONCLUSIONS

Etranacogene dezaparvovec gene therapy was superior to prophylactic factor IX with respect to the annualized bleeding rate, and it had a favorable safety profile. (Funded by uniQure and CSL Behring; HOPE-B ClinicalTrials.gov number, NCT03569891.).

Comprehensive analysis and prediction of long-term durability of factor IX activity following etranacogene dezaparvovec gene therapy in the treatment of hemophilia B

OBJECTIVE

Congenital hemophilia B is a rare bleeding disorder caused by defects in the gene encoding factor IX (FIX) leading to coagulation deficiency. Recurrent bleeds may cause chronic pain, disability, and reduced quality of life. Phase 2 b and 3 single-arm, open-label, single-dose trials assessing etranacogene dezaparvovec gene therapy for hemophilia B have demonstrated sustained FIX activity levels over observed periods, but long-term durability of the treatment effect has not been established. Using statistical modeling, we estimate long-term durability of FIX activity levels after receiving etranacogene dezaparvovec.

METHODS

Participants from Phase 2 b (N = 3; NCT03489291) and 3 studies (N = 52; NCT03569891) were included. Two participants who did not respond to treatment were excluded. FIX activity was assessed by one-stage activated partial thromboplastin time assay. FIX activity levels at Month 6 post-treatment were considered baseline. Bayesian and Frequentist linear mixed models predicted FIX activity levels up to 25.5 years at an individual and population level with pre-treatment adeno-associated virus 5 (AAV5) neutralizing antibody (NAb) status as primary covariate.

RESULTS

Bayesian and Frequentist linear mixed models predicted no more than 6/55 (10.91%) observed participants would have FIX activity levels <2% up to 25.5 years post-infusion. Bayesian model-based predictions of future participants suggest >80% would be free from prophylactic FIX replacement products 25.5 years post-infusion. Both models predicted FIX activity levels were not significantly influenced by pre-treatment AAV5 NAb status.

CONCLUSIONS

People with hemophilia B receiving etranacogene dezaparvovec would likely achieve durable FIX activity levels and remain free of prophylactic FIX replacement products for up to 25.5 years following single administration. The long-term factor IX durability predictions are based on statistical methods and results in vivo may differ.

Multiyear Factor VIII Expression after AAV Gene Transfer for Hemophilia A

BACKGROUND

The goal of gene therapy for patients with hemophilia A is to safely impart long-term stable factor VIII expression that predictably ameliorates bleeding with the use of the lowest possible vector dose.

METHODS

In this phase 1-2 trial, we infused an investigational adeno-associated viral (AAV) vector (SPK-8011) for hepatocyte expression of factor VIII in 18 men with hemophilia A. Four dose cohorts were enrolled; the lowest-dose cohort received a dose of 5  × 10¹¹ vector genomes (vg) per kilogram of body weight, and the highest-dose cohort received 2 × 10¹² vg per kilogram. Some participants received glucocorticoids within 52 weeks after vector administration either to prevent or to treat a presumed AAV capsid immune response. Trial objectives included evaluation of the safety and preliminary efficacy of SPK-8011 and of the expression and durability of factor VIII.

RESULTS

The median safety observation period was 36.6 months (range, 5.5 to 50.3). A total of 33 treatment-related adverse events occurred in 8 participants; 17 events were vector-related, including 1 serious adverse event, and 16 were glucocorticoid-related. Two participants lost all factor VIII expression because of an anti-AAV capsid cellular immune response that was not sensitive to immune suppression. In the remaining 16 participants, factor VIII expression was maintained; 12 of these participants were followed for more than 2 years, and a one-stage factor VIII assay showed no apparent decrease in factor VIII activity over time (mean [±SD] factor VIII activity, 12.9±6.9% of the normal value at 26 to 52 weeks when the participants were not receiving glucocorticoids vs. 12.0±7.1% of the normal value at >52 weeks after vector administration; 95% confidence interval [CI], -2.4 to 0.6 for the difference between matched pairs). The participants had a 91.5% reduction (95% CI, 88.8 to 94.1) in the annualized bleeding rate (median rate, 8.5 events per year [range, 0 to 43.0] before vector administration vs. 0.3 events per year [range, 0 to 6.5] after vector administration).

CONCLUSIONS

Sustained factor VIII expression in 16 of 18 participants who received SPK-8011 permitted discontinuation of prophylaxis and a reduction in bleeding episodes. No major safety concerns were reported. (Funded by Spark Therapeutics and the National Heart, Lung, and Blood Institute; ClinicalTrials.gov numbers, NCT03003533 and NCT03432520.).

FVIII at the crossroad of coagulation, bone and immune biology: Emerging evidence of biological activities beyond hemostasis

Hemophilia A is an X-linked hereditary disorder that results from deficient coagulation factor VIII (FVIII) activity, leading to spontaneous bleeding episodes, particularly in joints and muscles. FVIII deficiency has been associated with altered bone remodeling, dysregulated macrophage polarization, and inflammatory processes that are associated with the neoformation of abnormal blood vessels. Treatment based on FVIII replacement can lead to the development of inhibitors that render FVIII concentrate infusion ineffective. In this context, hemophilia has entered a new therapeutic era with the development of new drugs, such as emicizumab, that seek to restore the hemostatic balance by bypassing pathologically acquired antibodies. We discuss the potential extrahemostatic functions of FVIII that may be crucial for defining future therapies in hemophilia.

Exploring the Potential Feasibility of Intra-Articular Adeno-Associated Virus-Mediated Gene Therapy for Hemophilia Arthropathy

Hemophilia arthropathy (HA) represents the majority of morbidity in severe hemophilia patients, especially in resource-limited countries. Adeno-associated virus (AAV)-mediated gene therapy is showing promise for managing hemophilia. However, patients with neutralizing antibodies (NAbs) against AAV, and inhibitors to clotting factors, are excluded from such therapy. This study explored the feasibility of AAV-mediated local gene therapy for HA. Factor VIII knockout (FVIII^-/-) mice, with or without a FVIII inhibitor, were subjected to hemarthrosis induction and treated with either intravenous (IV) or intraarticular (IA) recombinant human factor VIII (rhFVIII). To investigate whether rhFVIII carried the risk to develop a FVIII inhibitor, FVIII^-/- mice were treated with three doses of IV or IA rhFVIII and inhibitor development was measured. In patients with established HA requiring synovial fluid aspiration, plasma, and synovial fluid were collected and measured for anti-AAV capsid IgG (serotypes 1-9 and 843) and NAbs for AAV843. IA rhFVIII provided better protection from synovitis compared with IV rhFVIII, with or without the FVIII inhibitor. While IV rhFVIII led to all FVIII^-/- mice developing an FVIII inhibitor (n = 31, median 4.9 Bethesda units [BU]/mL), only 50% of the mice developed a FVIII inhibitor by IA administration, and at a lower titer (median 0.55 BU/mL). In hemophilia patients, total anti-AAV IgG was lowest for AAV4 and AAV5, both in plasma and synovial fluid. Anti-AAV IgGs in synovial fluid for most samples were lower or similar to the plasma levels. These results show that direct IA rhFVIII administration yields better protection against bleeding-induced joint damage, even in the presence of an inhibitor antibody. IA rhFVIII delivery carried a lower risk of FVIII inhibitor formation compared with IV FVIII. The anti-AAV antibody level in synovial fluid was similar or lower than the plasma level, supporting the feasibility of local gene therapy for managing HA.

Hemophilia A and B mice, but not VWF-/-mice, display bone defects in congenital development and remodeling after injury

While joint damage is the primary co-morbidity of hemophilia, osteoporosis and osteopenia are also observed. Coagulation factor VIII deficient (FVIII^−/−) mice develop an osteoporotic phenotype in the absence of induced hemarthrosis that is exacerbated two weeks after an induced joint injury. Here we have compared comprehensively the bone health of clotting factor VIII, factor IX, and Von Willebrand Factor knockout (FVIII^−/−, FIX^−/−, and VWF^−/− respectively) mice both in the absence of joint hemorrhage and following induced joint injury. We found FVIII^−/− and FIX^−/− mice, but not VWF^−/− mice, developmentally have an osteoporotic phenotype. Unilateral induced hemarthrosis causes further bone damage in both FVIII^−/− and FIX^−/− mice, but has little effect on VWF^−/− bone health, indicating that the FVIII.VWF complex is not required for normal bone remodeling in vivo. To further investigate the bone healing following hemarthrosis in hemophilia we examined a two week time course using microCT, serum chemistry, and histological analysis. Elevated ratio of osteoprotegerin (OPG)/receptor activator of nuclear factor-kappa B ligand (RANKL), increased osterix⁺ osteoblastic cells, and decreased smoothness of the cortical bone surface were evident within several days of injury, indicative of acute heterotopic mineralization along the cortical surface. This was closely followed by increased interleukin-6 (IL-6) levels, increased osteoclast numbers, and significant trabecular bone loss. Uncoupled and disorganized bone formation and resorption continued for the duration of the study resulting in significant deterioration of the joint. Further elucidation of the shared mechanisms underlying abnormal bone homeostasis in the absence of FVIII or FIX is needed to guide evidence-based approaches to the screening and treatment of the prevalent bone defects in hemophilia A and B.

Autologous and Heterologous Cell Therapy for Hemophilia B toward Functional Restoration of Factor IX

Hemophilia B is an ideal target for gene- and cell-based therapies because of its monogenic nature and broad therapeutic index. Here, we demonstrate the use of cell therapy as a potential long-term cure for hemophilia B in our FIX-deficient mouse model. We show that transplanted, cryopreserved, cadaveric human hepatocytes remain functional for more than a year and secrete FIX at therapeutic levels. Hepatocytes from different sources (companies and donors) perform comparably in curing the bleeding defect. We also generated induced pluripotent stem cells (iPSCs) from two hemophilia B patients and corrected the disease-causing mutations in them by two different approaches (mutation specific and universal). These corrected iPSCs were differentiated into hepatocyte- like cells (HLCs) and transplanted into hemophilic mice. We demonstrate these iPSC-HLCs to be viable and functional in mouse models for 9–12 months. This study aims to establish the use of cells from autologous and heterologous sources to treat hemophilia B.

Prophylactic administration of glycoPEGylated factor IX provides protection and joint outcome superior to recombinant factor IX after induced joint bleeding

BACKGROUND

Following induced joint hemorrhage, hemophilia B results in the abnormal persistence of iron deposition, inflammation, and neovascularity of the synovial tissue, as well as deterioration of the bone articular surface and strength. Previously, we demonstrated that a factor IX (FIX) replacement protein with extended circulating FIX activity, glycoPEGylated FIX nonacog beta pegol (N9-GP), could improve synovial and osteochondral parameters in F9 knockout mice when administered after joint injury.

OBJECTIVE

We explored the use of N9-GP prior to unilateral joint hemorrhage and compared to unmodified recombinant FIX (rFIX).

METHODS

Pharmacodynamics, histology, and microcomputed tomography were used to assess the effects of prophylactic administration of glycoPEGylated FIX.

RESULTS

In comparison to rFIX, N9-GP significantly improved soft tissue histological parameters, as well as bone outcome at 2 weeks post injury, while performing equally in reduction of blood present in the joint space assessed 1 day after injury.

CONCLUSIONS

These results indicate that, in comparison to rFIX, the prophylactic use of extended half-life FIX provides superior protection from bleeding-induced joint damage, manifested by improved correction of histologic parameters.

An Observational Study from Long-Term AAV Re-administration in Two Hemophilia Dogs

Adeno-associated virus (AAV) vectors have been successfully applied in hemophilia clinical trials. However, this approach is limited to patients without AAV-neutralizing antibodies (NAbs). In this study, we explored the feasibility of AAV re-administration in hemophilia A dogs treated initially 8 years ago with AAV8.canine FVIII. After the re-administration in two NAb-negative dogs with AAV8 vectors carrying human factor VIII (hFVIII), along with the proteasome inhibitor bortezomib, we observed a phenotypic improvement in both dogs that persisted in one dog. Phenotypic improvement disappeared at 59 days after re-administration in the other dog, and specific cytotoxic T lymphocytes (CTLs) to the capsid were detected at day 17, but not to hFVIII. hFVIII inhibitors were observed at day 59 and gradually increased. Mechanistic studies demonstrated an increase in pro-inflammatory cytokines, a decrease in immunomodulatory cytokines, as well as lower Tregs after re-administration. These results suggest that hFVIII inhibitor development may contribute to the therapeutic failure via immune response activation. Interestingly, it takes about 30–50 days for AAV NAb titers to decrease by half. Collectively, this study suggests that re-administration of the same AAV serotype after long-term follow-up is feasible and that the study of AAV NAb kinetics will provide important information for predicating the efficacy of re-administration.

Factor IX: Insights from knock-out and genetically engineered mice

The study of coagulation factors has been rapidly advanced by studies performed in genetically engineered mouse strains. Investigation of factor IX (FIX) has benefited from excellent genedeleted mouse models that recapitulate many of the features of human haemophilia B. Moreover, advanced positional cloning techniques and availability of technology to allow not only knock-out mice, but also knock-in and knock-down mice, provide new opportunities to observe genotype-phenotype and structure-function correlations regarding FIX, as well as the interaction of FIX with inflammatory, immune, and tissue repair systems. In this paper, available FIX knock-out mice and additional haemophilia B mouse models are reviewed specifically in regards to observations these models have facilitated concerning: factor IX gene expression and factor IX protein pharmacokinetics; the role of FIX in haemostasis, thrombosis and wound healing; insights into coagulation FIX arising out of gene therapy applications in haemophilia mouse models; immunology of tolerance or loss of tolerance of FIX and inhibitor antibody formation.

Recombinant porcine factor VIII for high-risk surgery in paediatric congenital haemophilia A with high-titre inhibitor

INTRODUCTION

High-titre factor VIII (FVIII) inhibitors complicate peri-operative haemostasis. Recombinant porcine FVIII (r-pFVIII) may provide an alternative haemostatic agent for high-risk procedures and allow FVIII activity monitoring.

AIM

Devise an effective haemostatic plan for repair of a progressively symptomatic aortic coarctation in a 5-year-old male with immune tolerance induction (ITI) refractory high-titre FVIII inhibitors.

METHODS

Preprocedure human FVIII inhibitor titre was 58 Bethesda Units mL^-1 (BU) and cross-reacted to neutralize porcine FVIII at 30 BU. Daily ITI with plasma-derived FVIII concentrate was supplemented with anti-B-cell and anti-plasma cell immunotherapy to reduce FVIII inhibitor titres. Potential haemostatic agents were evaluated in comparative ex vivo thrombin generation assays (TGA).

RESULTS

Four weeks after immunosuppression, human and porcine inhibitor titres declined to 16 and 2 BU respectively. TGA with r-pFVIII was less robust than with activated prothrombin complex concentrate (aPCC); however, r-pFVIII was selected for cardiac surgery to secure the ability to assay FVIII levels throughout this high-bleeding risk procedure. Haemostasis with r-pFVIII was excellent; initial trough FVIII activity levels ranged from 0.81-1.17 IU mL^-1 . On postoperative day 3, peak and trough levels markedly declined suggesting a rising porcine inhibitor titre. Postprocedure prophylaxis was transitioned to aPCC, informed by TGA.

CONCLUSIONS

R-pFVIII provided effective peri-procedural haemostasis with no adverse events. Rapid neutralization of r-pFVIII after the first 60 hours, despite intensive immune suppression, accentuates the importance of careful monitoring. Use of TGA can support bypassing agent selection for convalescence. The comparative cost of r-pFVIII may limit its use to high morbidity clinical scenarios.

Inhibitor recurrence after immune tolerance induction: a multicenter retrospective cohort study

BACKGROUND

Immune tolerance induction (ITI) in patients with congenital hemophilia A is successful in up to 70%. Although there is growing understanding of predictors of response to ITI, the probability and predictors of inhibitor recurrence after successful ITI are not well understood.

OBJECTIVES

To determine the association of clinical characteristics, particularly adherence to factor VIII (FVIII) prophylaxis after ITI, with inhibitor recurrence in patients with hemophilia A who were considered tolerant after ITI.

METHODS

In this multicenter retrospective cohort study, 64 subjects with FVIII level < 2% who were considered successfully tolerant after ITI were analyzed to estimate the cumulative probability of inhibitor recurrence using the Kaplan-Meier method. The association of clinical characteristics with inhibitor recurrence was assessed using logistic regression.

RESULTS

A recurrent inhibitor titer ≥ 0.6 BU mL(-1) occurred at least once in 19 (29.7%) and more than once in 12 (18.8%). The probability of any recurrent inhibitor at 1 and 5 years was 12.8% and 32.5%, respectively. Having a recurrent inhibitor was associated with having received immune modulation during ITI (odds ratio [OR] 3.8, 95% confidence interval [CI] 1.2-22.4) and FVIII recovery of < 85% at the end of ITI (OR 2.6, 95% CI 1.3-5.9) but was not associated with adherence to post-ITI prophylactic FVIII infusion (OR 0.5, 95% CI 0.06-4.3).

CONCLUSIONS

The use of immune modulation therapy during ITI and lower FVIII recovery at the end of ITI appear to be associated with an increased risk of inhibitor recurrence after successful ITI. Adherence to post-ITI prophylactic FVIII infusions is not a major determinant of recurrence.

Gene therapy in an era of emerging treatment options for hemophilia B

Factor IX deficiency (hemophilia B) is less common than factor VIII deficiency (hemophilia A), and innovations in therapy for hemophilia B have generally lagged behind those for hemophilia A. Recently, the first sustained correction of the hemophilia bleeding phenotype by clotting factor gene therapy has been described using recombinant adeno-associated virus (AAV) to deliver factor IX. Despite this success, many individuals with hemophilia B, including children, men with active hepatitis, and individuals who have pre-existing natural immunity to AAV, are not eligible for the current iteration of hemophilia B gene therapy. In addition, recent advances in recombinant factor IX protein engineering have led some hemophilia treaters to reconsider the urgency of genetic cure. Current clinical and preclinical approaches to advancing AAV-based and alternative approaches to factor IX gene therapy are considered in the context of current demographics and treatment of the hemophilia B population.

Employing a gain-of-function factor IX variant R338L to advance the efficacy and safety of hemophilia B human gene therapy: preclinical evaluation supporting an ongoing adeno-associated virus clinical trial

Vector capsid dose-dependent inflammation of transduced liver has limited the ability of adeno-associated virus (AAV) factor IX (FIX) gene therapy vectors to reliably convert severe to mild hemophilia B in human clinical trials. These trials also identified the need to understand AAV neutralizing antibodies and empty AAV capsids regarding their impact on clinical success. To address these safety concerns, we have used a scalable manufacturing process to produce GMP-grade AAV8 expressing the FIXR338L gain-of-function variant with minimal (<10%) empty capsid and have performed comprehensive dose-response, biodistribution, and safety evaluations in clinically relevant hemophilia models. The scAAV8.FIXR338L vector produced greater than 6-fold increased FIX specific activity compared with wild-type FIX and demonstrated linear dose responses from doses that produced 2-500% FIX activity, associated with dose-dependent hemostasis in a tail transection bleeding challenge. More importantly, using a bleeding model that closely mimics the clinical morbidity of hemophilic arthropathy, mice that received the scAAV8.FIXR338L vector developed minimal histopathological findings of synovitis after hemarthrosis, when compared with mice that received identical doses of wild-type FIX vector. Hemostatically normal mice (n=20) and hemophilic mice (n=88) developed no FIX antibodies after peripheral intravenous vector delivery. No CD8(+) T cell liver infiltrates were observed, despite the marked tropism of scAAV8.FIXR338L for the liver in a comprehensive biodistribution evaluation (n=60 animals). With respect to the role of empty capsids, we demonstrated that in vivo FIXR338L expression was not influenced by the presence of empty AAV particles, either in the presence or absence of various titers of AAV8-neutralizing antibodies. Necropsy of FIX(-/-) mice 8-10 months after vector delivery revealed no microvascular or macrovascular thrombosis in mice expressing FIXR338L (plasma FIX activity, 100-500%). These preclinical studies demonstrate a safety:efficacy profile supporting an ongoing phase 1/2 human clinical trial of the scAAV8.FIXR338L vector (designated BAX335).

Emerging genetic and pharmacologic therapies for controlling hemostasis: beyond recombinant clotting factors

For more than 3 decades, the scientific community has pursued gene correction of hemophilia, with the goal that an individual with congenitally deficient factor VIII or factor IX might synthesize adequate endogenous clotting factor to be relieved of burdensome repeated clotting factor infusions, as well as the emotional weight of continuous hemorrhage risk. Recent reports of successful factor IX gene therapy and partial correction of the bleeding phenotype have raised the bar for success for a robust crop of new clinical gene therapy efforts for both hemophilia A and B. At the same time that gene therapy is gaining momentum, suggesting the possibility of relief from regular intravenous coagulation protein replacement, a number of innovative technologies that enhance hemostatic potential independently of replacement factor administration are demonstrating success in human clinical application. Human clinical trial progress is reviewed regarding a recombinant bispecific IgG antibody to factors IXa and X that mimics factor VIII cofactor activity, as well as monoclonal antibody and short interfering RNA strategies that demonstrate hemostatic efficacy via opposing inhibitors of coagulation. These strategies, associated with prolonged hemostatic potential following subcutaneous (ACE910, ALN-AT3, Concizumab) or single administration (eg, gene therapy) make it possible to imagine a day when recombinant clotting factor administration, rather than being a daily preoccupation, is relegated to an adjunctive role in supporting more novel standard of care therapies.

Joint bleeding in factor VIII deficient mice causes an acute loss of trabecular bone and calcification of joint soft tissues which is prevented with aggressive factor replacement

While chronic degenerative arthropathy is the main morbidity of haemophilia, a very high prevalence of low bone density is also seen in men and boys with haemophilia. This study investigates bone degradation in the knee joint of haemophilic mice resulting from haemarthrosis and the efficacy of aggressive treatment with factor VIII in the period surrounding injury to prevent bone pathology. Skeletally mature factor VIII knock-out mice were subjected to knee joint haemorrhage induced by puncture of the left knee joint capsule. Mice received either intravenous factor VIII treatment or placebo immediately prior to injury and at hours 4, 24, 48, 72 and 96 after haemorrhage. Mice were killed 2-weeks after injury and the joint morphology and loss of bone in the proximal tibia was assessed using microCT imaging. Quantitative microCT imaging of the knee joint found acute bone loss at the proximal tibia following injury including loss of trabecular bone volumetric density and bone mineral density, as well as trabecular connectivity density, number and thickness. Unexpectedly, joint injury also resulted in calcification of the joint soft tissues including the tendons, ligaments, menisci and cartilage. Treatment with factor VIII prevented this bone and soft tissue degeneration. Knee joint haemorrhage resulted in acute changes in adjacent bone including loss of bone density and mineralization of joint soft tissues. The rapid calcification and loss of bone has implications for the initiation and progression of osteoarthritic degradation following joint bleeding.

National surveillance for hemophilia inhibitors in the United States: Summary report of an expert meeting

On March 12, 2012, the Centers for Disease Control and Prevention (CDC) held a meeting of its partners in hemophilia treatment, community-based organizations, industry, and government to review data and discuss implementation issues relevant to planned United States (U.S.) national inhibitor surveillance. Issues discussed included the current status of inhibitor surveillance in the United Kingdom (UK) and the US, the results of a US inhibitor surveillance feasibility study, proposed national surveillance schemes, laboratory testing and reporting issues and potential opportunities for future inhibitor-related research. It was concluded that implementation of a national program of inhibitor surveillance using standardized testing through an established public health registry along with patient and care provider education and targeted research provide the best opportunity to inform efforts to develop and evaluate effective prevention strategies.

Integration-deficient lentiviral vectors expressing codon-optimized R338L human FIX restore normal hemostasis in Hemophilia B mice

Integration-deficient lentiviral vectors (IDLVs) have been shown to transduce a wide spectrum of target cells and organs in vitro and in vivo and to maintain long-term transgene expression in nondividing cells. However, epigenetic silencing of episomal vector genomes reduces IDLV transgene expression levels and renders these safe vectors less efficient. In this article, we describe for the first time a complete correction of factor IX (FIX) deficiency in hemophilia B mice by IDLVs carrying a novel, highly potent human FIX cDNA. A 50-fold increase in human FIX cDNA potency was achieved by combining two mechanistically independent yet synergistic strategies: (i) optimization of the human FIX cDNA codon usage to increase human FIX protein production per vector genome and (ii) generation of a highly catalytic mutant human FIX protein in which the arginine residue at position 338 was substituted with leucine. The enhanced human FIX activity was not associated with liver damage or with the formation of human FIX-directed inhibitory antibodies and rendered IDLV-treated FIX-knockout mice resistant to a challenging tail-clipping assay. A novel S1 nuclease-based B1-quantitative polymerase chain reaction assay showed low levels of IDLV integration in mouse liver. Overall, this study demonstrates that IDLVs carrying an improved human FIX cDNA safely and efficiently cure hemophilia B in a mouse model.

Prevalent inhibitors in haemophilia B subjects enrolled in the Universal Data Collection database

Several risk factors for inhibitors have recently been described for haemophilia A. It has been assumed that similar risk factors are also relevant for haemophilia B, but there is limited data to confirm this notion. The aim of this study was to determine the prevalence of and risk factors associated with inhibitors in haemophilia B. The database of the Universal Data Collection (UDC) project of the Centers for Disease Control for the years 1998-2011 was queried to determine the prevalence of inhibitors in haemophilia B subjects. In addition, disease severity, race/ethnicity, age, factor exposure and prophylaxis usage were evaluated to determine their impact on inhibitor prevalence. Of the 3785 male subjects with haemophilia B enrolled in the UDC database, 75 (2%) were determined to have an inhibitor at some point during the study period. Severe disease (OR 13.1, 95% CI 6.2-27.7), black race (OR 2.2, 95% CI 1.2-4.1), and age <11 years (OR 2.5, 95% CI 1.5-4.0) were found to be significantly associated with having an inhibitor. There was insufficient data to determine if type of factor used and prophylaxis were associated with inhibitors. Inhibitors in haemophilia B are much less prevalent than haemophilia A, especially in patients with mild disease. Similar factors associated with inhibitors in haemophilia A also seem to be present for haemophilia B. The information collected by this large surveillance project did not permit evaluation of potential risk factors related to treatment approaches and exposures, and additional studies will be required.

Evidence for the transmission of parvovirus B19 in patients with bleeding disorders treated with plasma-derived factor concentrates in the era of nucleic acid test screening

BACKGROUND

Parvovirus B19 (B19V) is a small, nonenveloped virus that typically causes a benign flu-like illness that occurs most frequently in childhood. The virus is resistant to current viral inactivation steps used in the manufacture of antihemophilic factor concentrates and B19V transmission through these products has been documented. Since 2000, B19V nucleic acid test (NAT) screening of plasma pools has been implemented to further decrease the viral burden in these products, but no study has examined populations using these products to assess the impact of the screening on B19V transmission.

STUDY DESIGN AND METHODS

Blood specimens obtained from participants of a surveillance system established in federally supported specialized bleeding disorders clinics were used in a B19V seroprevalence study.

RESULTS

A total of 1643 specimens from 1043 participants age 2 to 7 years born after B19V NAT screening was implemented were tested. Age-specific prevalence rates were generally higher for subjects exposed to either plasma-derived products alone or in combination with other products compared to subjects with no exposure to antihemophilic products. Overall, compared to participants unexposed to blood or blood products, those exposed to plasma-derived products alone were 1.7 times more likely to have antibodies to B19V (p = 0.002).

CONCLUSION

These results are consistent with continued B19V transmission through plasma-derived factor concentrates. Effective viral inactivation and detection processes are needed to protect users of these products from infection with B19V or other new or emerging viruses.

IL-6 receptor antagonist as adjunctive therapy with clotting factor replacement to protect against bleeding-induced arthropathy in hemophilia

BACKGROUND

The most common morbidity that results from hemophilia is bleeding-induced hemophilic arthropathy (HA), which once established may not be interrupted completely even by prophylactic clotting factor replacement. Specific therapies to oppose inflammatory cytokines, including Interleukin 6 (IL-6) receptor antagonists, have become important in the management of inflammatory arthritides.

OBJECTIVES

We investigated combining therapy using MR16-1, a rat IgG antibody directed against mouse IL-6 receptor (anti-IL-6R), with factor VIII (FVIII) replacement to protect against bleeding-induced arthropathy in hemophilia A mice.

METHODS

Three recurrent hemarthroses were induced in the knee joint capsule of FVIII knockout mice. Treatment at the time of each hemorrhage included either: no treatment; FVIII replacement given at the time of hemorrhage; FVIII replacement at hemorrhage plus anti-IL-6R as 4-weekly injections; FVIII replacement with non-specific control antibody (rat IgG); and anti-IL-6R alone without FVIII replacement. Six weeks following the first hemarthosis, joints were harvested and histopathology was scored for synovitis, for cartilage integrity and for macrophage infiltration.

RESULTS

Animals that received anti-IL-6R as an adjunct to FVIII replacement demonstrated the best survival and the least acute joint swelling and pathology on histologic examination of the synovium and cartilage (P < 0.05 for each parameter). All histopathologic parameters in the mice receiving FVIII+anti-IL-6R were limited and were comparable to findings in injured hemostatically normal mice. The major benefits of adjunctive anti-IL-6R were decreasing synovial hyperplasia, hemosiderin deposition and macrophage infiltration.

CONCLUSIONS

Short-course specific inhibition of inflammatory cytokines as an adjunct to replacement hemostasis may be an approach to minimize hemophilic joint degeneration.

Phase 1 gene therapy for Duchenne muscular dystrophy using a translational optimized AAV vector

Efficient and widespread gene transfer is required for successful treatment of Duchenne muscular dystrophy (DMD). Here, we performed the first clinical trial using a chimeric adeno-associated virus (AAV) capsid variant (designated AAV2.5) derived from a rational design strategy. AAV2.5 was generated from the AAV2 capsid with five mutations from AAV1. The novel chimeric vector combines the improved muscle transduction capacity of AAV1 with reduced antigenic crossreactivity against both parental serotypes, while keeping the AAV2 receptor binding. In a randomized double-blind placebo-controlled phase I clinical study in DMD boys, AAV2.5 vector was injected into the bicep muscle in one arm, with saline control in the contralateral arm. A subset of patients received AAV empty capsid instead of saline in an effort to distinguish an immune response to vector versus minidystrophin transgene. Recombinant AAV genomes were detected in all patients with up to 2.56 vector copies per diploid genome. There was no cellular immune response to AAV2.5 capsid. This trial established that rationally designed AAV2.5 vector was safe and well tolerated, lays the foundation of customizing AAV vectors that best suit the clinical objective (e.g., limb infusion gene delivery) and should usher in the next generation of viral delivery systems for human gene transfer.

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.

Physical functioning in boys with hemophilia in the U.S

BACKGROUND

Hemophilia is the most common inherited severe bleeding disorder. Although the most frequent complication of repeated hemorrhages is a crippling joint disease that begins in childhood, the extent of resultant joint functional impairment varies widely within the hemophilia population.

PURPOSE

The goal of this exploratory analysis was to examine a national database that collects information on boys with hemophilia, an X-linked severe congenital bleeding disorder, to determine characteristics associated with increased risk of developing limitations in physical functioning as an outcome of recurrent hemorrhages.

METHODS

A standard set of data is collected annually at ∼130 U.S. comprehensive hemophilia treatment centers (HTCs) in a voluntary surveillance program called the Universal Data Collection (UDC) program. Fifteen potential predictors for poor outcomes of physical functioning related to bleeding were examined for boys (aged ≤ 18 years) from 1998 to 2008. Bivariate and multivariate analyses of these predictors performed in 2009 examined associations with self-reported limitation of activities, absenteeism from work or school, and reliance on assistive devices for ambulation and mobility.

RESULTS

Multiple characteristics of underlying hemophilia severity and disease chronicity (in particular, increasing age, presence of joint bleeding, and inhibitor antibodies) were independently associated with increased risk of limitations of physical function. Nonwhite race/ethnicity was associated with each of the poorer functional outcomes in bivariate analyses. After controlling for the potential confounding effects of the multiple population characteristics on race, only African-American race was independently associated with activity restrictions, and African-American and Asian/Pacific Island ethnicity with absenteeism. With the exception of indicators of underlying disease severity, only obesity and medical insurance coverage with Medicaid rather than commercial insurance were independently associated with multiple poor outcomes.

CONCLUSIONS

Interventions focused on eliminating inhibitors, improving outcomes for African-American children with hemophilia, and maintaining healthy body weight are warranted. In addition, strategies are needed to assure adequate insurance coverage for all people with hemophilia to eliminate economic barriers to optimal functional outcomes.

Neutralizing antibodies against adeno-associated virus examined prospectively in pediatric patients with hemophilia

Recombinant adeno-associated virus (rAAV) is a promising gene delivery vector and has recently been used in patients with hemophilia. One limitation of AAV application is that most humans have experienced wild-type AAV serotype 2 exposure, which frequently generates neutralizing antibodies (NAbs) that may inhibit rAAV2 vector transduction. Employing alternative serotypes of rAAV vectors may circumvent this problem. We investigated the development of NAbs in early childhood by examining sera gathered prospectively from 62 children with hemophilia A, participating in a multi-institutional hemophilia clinical trial (the Joint Outcome Study). Clinical applications in hemophilia therapy have been suggested for serotypes AAV2, AAV5 and AAV8, therefore NAbs against these serotypes were serially assayed over a median follow-up of 4 years. NAbs prevalence increased during early childhood for all serotypes. NAbs against AAV2 (43.5%) were observed more frequently and at higher titers compared with both AAV5 (25.8%) and AAV8 (22.6%). NAbs against AAV5 or AAV8 were rarely observed in the absence of co-prevalent and higher titer AAV2 NAbs, suggesting that NAbs to AAV5 and AAV8 were detected following AAV2 exposure due to partial cross-reactivity of AAV2-directed NAbs. The results may guide rational design of clinical trials using alternative AAV serotypes and suggest that younger patients who are given AAV gene therapy will benefit from the lower prevalence of NAbs.

Long-term phenotypic correction in factor IX knockout mice by using ΦC31 integrase-mediated gene therapy

Hemophilia B, a hereditary bleeding disorder caused by a deficiency of coagulation factor IX (FIX), is an excellent candidate for gene therapy. However, to date, success in hemophilia gene therapy clinical trials has been limited due to failure to achieve or sustain therapeutic levels of factor expression. The ΦC31 integrase system efficiently integrates plasmid DNA carrying a transgene and an attB site into a limited number of endogenous pseudo attP sites in mammalian genomes, leading to robust, sustained transgene expression. A strategy utilizing plasmid DNA integrated with ΦC31 integrase may offer a facile and safe alternative for sustained human FIX (hFIX) expression. Hydrodynamic tail vein injection was used for delivery of plasmids encoding ΦC31 integrase and hFIX to the liver of FIX knockout mice. We demonstrated prolonged therapeutic levels of hFIX in this knockout mouse model of hemophilia B over a 6-month time course when ΦC31 integrase was used. Additionally, we observed sustained FIX activity in plasma and phenotypic correction of bleeding after tail clip in ΦC31-treated mice. In the livers that received integrase, we also demonstrated prolonged hFIX expression in hepatocytes by immunohistochemistry and documented sequence-specific genomic integration of the hFIX plasmid. These studies suggest the possibility that a similar approach in large animals and humans could lead to a simple and successful gene therapy for hemophilia.

Unique strategies for therapeutic gene transfer in haemophilia A and haemophilia BWFH State-of-the-Art Session on Therapeutic Gene Transfer Buenos Aires, Argentina

SUMMARY

Gene therapy of haemophilia has been initiated through a number of approaches including expression in muscle, liver and omental implanted fibroblasts, or i.v. injection of an expression construct under the control of a ubiquitous promoter. In all these approaches, the goal was to have factor VIII (FVIII) or factor IX (FIX) synthesized so that it restored the levels of the missing protein in blood. The three talks in this session are totally, or at least in part, directed at strategies that may be clinically effective even in the absence of correction of the missing plasma clotting factor, although the haematopoietic stem cell or blood outgrowth endothelial cell therapy could achieve plasma correction as well. Two of the approaches achieve localized coagulation factor expression without necessarily correcting the systemic defect--one is with synthesis of FVIII or FIX within the joint space and the other is with the local release of FVIII (or FIX) by platelets at the site of vascular injury. All of the three approaches have demonstrated efficacy in small animal models and are now the subject of larger animal studies. None has yet to progress to human trials.

Hemophilic synovitis: factor VII and the potential role of extravascular factor VIIa

The initiation of coagulation via tissue factor/factor VIIa is relatively weak in normal synovium and joint tissues, so that hemophilic patients with additional deficiency of the intrinsic pathway of coagulation are especially at risk for joint bleeding and the development of hemophilic synovitis. The inflamed joint that results from recurrent bleeding-induced injury, however, may be an environment in which pharmacologic doses of factor VIIa have potentially greater procoagulant action than in the uninjured joint. There is accumulating evidence suggesting that coagulation factors in the extravascular space, and not only circulating plasma factors, have the potential to contribute to hemostatic protection of joints. The potential role of extravascular factor VIIa is considered.

Proteasome inhibitors enhance gene delivery by AAV virus vectors expressing large genomes in hemophilia mouse and dog models: a strategy for broad clinical application

Delivery of genes that are larger than the wild-type adeno-associated virus (AAV) 4,681 nucleotide genome is inefficient using AAV vectors. We previously demonstrated in vitro that concurrent proteasome inhibitor (PI) treatment improves transduction by AAV vectors encoding oversized transgenes. In this study, an AAV vector with a 5.6 kilobase (kb) factor VIII expression cassette was used to test the effect of an US Food and Drug Administration-approved PI (bortezomib) treatment concurrent with vector delivery in vivo. Intrahepatic vector delivery resulted in factor VIII expression that persisted for >1 year in hemophilia mice. Single-dose bortezomib given with AAV2 or AAV8 factor VIII vector enhanced expression on average ~600 and ~300%, respectively. Moreover, coadministration of AAV8.canineFVIII (1 × 10(13) vg/kg) and bortezomib in hemophilia A dogs (n = 4) resulted in normalization of the whole blood clotting time (WBCT) and 90% reduction in hemorrhages for >32 months compared to untreated hemophilia A dogs (n = 3) or dogs administered vector alone (n = 3). Demonstration of long-term phenotypic correction of hemophilia A dogs with combination adjuvant bortezomib and AAV vector expressing the oversized transgene establishes preclinical studies that support testing in humans and provides a working paradigm to facilitate a significant expansion of therapeutic targets for human gene therapy.

Safety and efficacy of investigator-prescribed BeneFIX prophylaxis in children less than 6 years of age with severe haemophilia B

Prophylaxis is increasingly prescribed in treatment of haemophilia and its benefit is believed to be most significant for the youngest patients as haemophilic arthropathy may be prevented if prophylaxis is initiated prior to recurrent haemarthroses. While clinical prophylaxis data are readily available for haemophilia A, analogous data for haemophilia B are relatively limited. A prospective clinical study of recombinant factor IX (BeneFIX; rFIX), designed to allow investigator prescribed prophylaxis according to customary practices, was conducted in children <6 years old with severe haemophilia B. Nearly all children were prescribed prophylaxis (22/25; 88%) for all or part of their study participation. Favourable efficacy and safety profiles were reported. Routine prophylaxis with 1 or 2 rFIX infusions per week over an average of greater than 6 months of therapy resulted in near complete prevention of spontaneous breakthrough haemorrhages (<1 per year), with most children (77%) having none, including seven patients (32%) who had no bleeding episodes at all. Haemorrhages in joints were less common than those outside joints (27% vs. 73% of haemorrhages). In a patient population that included children with multiple prior haemarthroses, 68% of children had no joint bleeding. Breakthrough haemorrhages resolved with 1 or 2 infusions in 89% of episodes. The absence of changes in prophylaxis infusion schedules suggests that 1 or 2 rFIX infusion(s) per week were well-tolerated by these young patients, including those with (41%) and without (59%) central venous access devices. Safety was established by the low incidence of treatment-related adverse events.

Abnormal hemostasis in a knock-in mouse carrying a variant of factor IX with impaired binding to collagen type IV

BACKGROUND

Factor IX binds to collagen type IV, but this binding has no known consequence.

OBJECTIVES

To determine the effect of reduced binding of FIX to collagen IV.

METHODS

We constructed and characterized 'knock-in' mice containing the mutation lysine 5 to alanine (K5A) in the Gla domain of their FIX. The K5A mutation dramatically reduced the affinity of FIX for collagen type IV, but had no measurable effect on platelet binding, phospholipid binding, or in vitro clotting activity. However, K5AFIX mice had a mild bleeding tendency, despite their in vitro clotting activity being normal. Hemostatic protection from delayed rebleeding was intermediate between wild-type and hemophilia B mice (which had no detectable clotting activity); moreover, survival of K5A FIX mice after nascent clot removal was dramatically improved as compared with hemophilia B mice. Importantly, there was no detectable difference between K5AFIX and wild-type mice in either a laser-induced thrombosis model or the chromogenic FIX activity assay. In contrast, after ferric chloride injury, which exposes collagen IV as well as other basement membrane proteins, intravital microscopy revealed that vessel occlusion was significantly slower in K5AFIX mice than in wild-type mice.

CONCLUSIONS

Our results indicate that the FIX molecule with decreased affinity for collagen IV has altered hemostatic properties in vivo and that the binding of FIX to collagen IV probably plays a significant functional role in hemostasis.

Familial deficiency of vitamin K-dependent clotting factors

Combined deficiency of vitamin K-dependent clotting factors II, VII, IX and X (and proteins C, S, and Z) is usually an acquired clinical problem, often resulting from liver disease, malabsorption, or warfarin overdose. A rare inherited form of defective gamma-carboxylation resulting in early onset of bleeding was first described by McMillan and Roberts in 1966 and subsequently has been termed 'vitamin K-dependent clotting factor deficiency' (VKCFD). Biochemical and molecular studies identify two variants of this autosomal recessive disorder: VKCFD1, which is associated with point mutations in the gamma-glutamylcarboxylase gene (GGCX), and VKCFD2, which results from point mutations in the vitamin K epoxide reductase gene (VKOR). Bleeding ranges in severity from mild to severe. Therapy includes high oral doses of vitamin K for prophylaxis, usually resulting in partial correction of factor deficiency, and episodic use of plasma infusions or prothrombin complex concentrate. Recent molecular studies have the potential to further our understanding of vitamin K metabolism, gamma-carboxylation, and the functional role this post-translational modification has for other proteins. The results may also provide potential targets for molecular therapeutics and pharmacogenetics.

Factor IX: Insights from knock-out and genetically engineered mice

The study of coagulation factors has been rapidly advanced by studies performed in genetically engineered mouse strains. Investigation of factor IX (FIX) has benefited from excellent gene-deleted mouse models that recapitulate many of the features of human haemophilia B. Moreover, advanced positional cloning techniques and availability of technology to allow not only knock-out mice, but also knock-in and knock-down mice, provide new opportunities to observe genotype-phenotype and structure-function correlations regarding FIX, as well as the interaction of FIX with inflammatory, immune, and tissue repair systems. In this paper, available FIX knock-out mice and additional haemophilia B mouse models are reviewed specifically in regards to observations these models have facilitated concerning:factor IX gene expression and factor IX protein pharmacokinetics; the role of FIX in haemostasis, thrombosis and wound healing; insights into coagulation FIX arising out of gene therapy applications in haemophilia mouse models; immunology of tolerance or loss of tolerance of FIX and inhibitor antibody formation.

Optimization of self-complementary AAV vectors for liver-directed expression results in sustained correction of hemophilia B at low vector dose

Self-complementary adeno-associated virus (scAAV) vectors can significantly minimize the vector load required to achieve sustained transgene expression. In this study, transcriptional regulatory elements were systematically screened to produce constitutive and liver-specific scAAV factor IX (FIX) expression cassettes. In addition, optimization of GC content, cis- regulatory elements, and codon usage in the human FIX (hFIX) transgene increased expression 4-20-fold. A vector was developed that was capable of expressing high FIX levels in comparison with the single-stranded (ss) AAV vector used in a recent clinical trial. The ssAAV and scAAV vectors display different transgene expression and genome stability patterns in the liver, as determined by immunohistochemical staining, in situ messenger RNA (mRNA) hybridization and vector genome quantitation. The ssAAV2 vector promoted strong FIX expression in only a subset of hepatocytes. The scAAV2-hFIX vector showed widespread ( approximately 80% of hepatocytes), moderate FIX expression levels similar to normal livers with correction of coagulation function in FIX-deficient mice. The ability of low dose scAAV-FIX vectors to achieve near-physiological expression may circumvent inflammatory responses in the liver. In addition to providing an improved scAAV vector for potential application in future hemophilia B clinical trials and liver-directed gene delivery, these studies underscore the need for rigorous analysis and optimization of vector genome cassettes.

In vivo response to vascular injury in the absence of factor IX: Examination in factor IX knockout mice

INTRODUCTION

Recently, in vitro models of coagulation have called into question the traditional conception of Factor IX as an intrinsic pathway protein, essential to propagation of coagulation but not central to the initiation of hemostatic plug, which has been thought instead to involve TF/FVIIa interactions with factor X and platelets. We hypothesized that the activation of factor IX, and its role in a factor IXa/FVIIa "tenase" complex leading to thrombin generation, plays a more important role than that of TF/FVIIa complex activation of factor X in the early hemostatic response to vascular injury. In vivo modeling is possible because of the generation of factor IX(-/-) mice.

MATERIALS AND METHODS

We used two models of arterial vascular injury, histological examination following mechanical carotid artery disruption and intravital microscopy of a mesenteric arteriole subsequent to ferric chloride arteriolar injury to examine mice having complete deficiency of factor IX (FIX(-/-)).

RESULTS

Both injury models demonstrate that platelet rich thrombi /hemostatic plug in FIX(-/-) mice is dramatically reduced as compared to wild type mice under conditions of high shear; in fact, no platelet thrombi (>20 mum) were observed in the intravital experiments. Interestingly, the platelet defect is more striking than that described in mice lacking fibrinogen and/or von Willebrand factor.

CONCLUSIONS

The results suggest TF/FVIIa-->FX pathway is insufficient for effective platelet aggregation in the presence of high flow, requiring factor IX at the convergence of both intrinsic and extrinsic pathways. Following platelet adhesion, factor IX is required for normal platelet aggregation in vivo, as well as thrombin generation and propagation of occlusive thrombus at the site of vascular injury.

Transgene expression levels and kinetics determine risk of humoral immune response modeled in factor IX knockout and missense mutant mice

Immune responses leading to antibody-mediated elimination of the transgenic protein are a concern in gene replacement for congenital protein deficiencies, for which hemophilia is an important model. Although most hemophilia B patients have circulating non-functional but immunologically crossreactive factor IX (FIX) protein (CRM+ phenotype), inciting factors for FIX neutralizing antibody (inhibitor) development have been studied in crossreactive material-negative (CRM-) animal models. For this study, determinants of FIX inhibitor development were compared in hemophilia B mice, in which circulating FIX protein is absent (CRM- factor IX knockout (FIXKO) model) or present (CRM+ missense R333Q-hFIX model) modeling multiple potential therapies. The investigations compare for the first time different serotypes of adeno-associated virus (AAV) vectors (AAV2 and AAV1), each at multiple doses, in the setting of two different FIX mutations. The comparisons demonstrate in the FIXKO background (CRM- phenotype) that neither vector serotype nor vector particle number independently determine the inhibitor trigger, which is influenced primarily by the level and kinetics of transgene expression. In the CRM+ missense background, inhibitor development was never stimulated by AAV gene therapy or protein therapy, despite the persistence of lymphocytes capable of responding to FIX with non-inhibitory antibodies. This genotype/phenotype is strongly protective against antibody formation in response to FIX therapy.

Interval laparoscopic appendectomy for appendicitis complicated by pylephlebitis

BACKGROUND

Although rare, portal mesenteric venous thrombosis and pylephlebitis remain potential life-threatening sequelae of ruptured appendicitis in children. Treatment recommendations from recent reports have included urgent exploratory laparotomy with appendectomy, prolonged intravenous antibiotic therapy, and anticoagulation for up to a year.

METHODS

This report describes successful management of pylephlebitis and mesenteric venous thrombosis complicating ruptured appendicitis with intravenous antibiotics and anticoagulation followed by interval laparoscopic appendectomy.

RESULTS

A previously healthy 5-year-old girl was diagnosed with ruptured appendicitis complicated by pylephlebitis and mesenteric venous thrombosis at the time of presentation. She was treated with intravenous antibiotics and anticoagulated for 3 months. She subsequently underwent interval laparoscopic appendectomy. At 3-year follow-up, she is healthy without evidence of adverse sequelae.

DISCUSSION

This is the first reported case of successful, minimally invasive management of ruptured appendicitis complicated by mesenteric venous thrombosis and pylephlebitis.

CONCLUSION

Similar treatment of other children with this rare presentation seems reasonable.

Haemophilic factors produced by transgenic livestock: abundance that can enable alternative therapies worldwide

Haemophilia replacement factors, both plasma-derived and recombinant, are in relatively short supply and are high-cost products. This has stymied the study and development of alternative methods of administration of haemophilia therapy even in the most economically advanced countries, owing to the large amounts of material needed because bioabsorption and bioavailability of haemophilic factors can be less than 10% when using non-intravenous routes of delivery. There is therefore a need to increase access to therapy worldwide by decreasing the cost and increasing the abundance so that therapy can be achieved through simplified, alternative delivery methods. Transgenic livestock have been used to produce haemophilic factors in milk. Only the pig mammary gland has been shown to carry out the post-translational processing necessary to enable both the biological activity and long circulation half-life needed for therapeutic glycoproteins. Furthermore, the large amounts of recombinant protein that can be produced from pig milk make feasible the use of alternative delivery methods such as oral, intratracheal, subcutaneous, and intramuscular administration.

A classification system for cross-reactive material-negative factor XI deficiency

The bleeding disorder associated with factor XI (fXI) deficiency is typically inherited as an autosomal recessive trait. However, some fXI mutations may be associated with dominant disease transmission. FXI is a homodimer, a feature that could allow certain mutations to exert a dominant-negative effect on wild-type fXI secretion through heterodimer formation. We describe 2 novel fXI mutations (Ser225Phe and Cys398Tyr) that form intracellular dimers, are secreted poorly, and exhibit dominant-negative effects on wild-type fXI secretion in cotransfection experiments. Available data now suggest that mutations associated with crossreactive material-negative fXI deficiency fall into 1 of 3 mechanistic categories: (1) mutations that reduce or prevent polypeptide synthesis, (2) polypeptides that fail to form intracellular dimers and are retained in cells as monomers, and (3) polypeptides that form dimers that are not secreted. The latter category likely accounts for many cases of dominant disease transmission.