Hemophilia Gene Therapy Redux – The End of the Beginning?

Gene therapy for hemophilia A and B now exists as a licensed, prescribable treatment option for patients in certain countries; however, many questions and challenges remain. Senior advisor Dr. Donna DiMichele and patient-host Patrick James Lynch speak to global KOLs about the current state of hemophilia A and B gene therapies, both commercially and investigationally.

Contributors:

Lindsey A. George, MD

Margareth Ozelo, MD

Steven Pipe, MD

Senior Advisor: Donna DiMichele, MD

Hosted & Written by: Patrick James Lynch

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Notes and References:

Nathwani: Hematology Am Soc Hematol Educ Program . 2022 Dec 9;2022(1):569-578.

The current state of this exciting and rapidly evolving field, as well as the challenges that need to be overcome for the widespread adaptation of this new treatment paradigm, is the subject of this review.

Pipe: N Engl J Med. 2023 Feb 23;388(8):706-718

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.

Long-Term Effects of Hemophilia B Gene Therapy. Makris M.N Engl J Med. 2023 May 18;388(20):1918.

Long-Term Effects of Hemophilia B Gene Therapy. Reply. Pipe SW, Monahan PE.N Engl J Med. 2023 May 18;388(20):1918-1919

Mahlangu: N Engl J Med. 2023 Feb 23;388(8):694-705

Results: At week 104, a total of 132 participants, including 112 with data that were prospectively collected at baseline, remained in the study. The mean annualized treated bleeding rate decreased by 84.5% from baseline (P<0.001) among the participants. From week 76 onward, the trajectory of the transgene-derived factor VIII activity showed first-order elimination kinetics; the model-estimated typical half-life of the transgene-derived factor VIII production system was 123 weeks (95% confidence interval, 84 to 232). The risk of joint bleeding was estimated among the trial participants; at a transgene-derived factor VIII level of 5 IU per deciliter measured with chromogenic assay, we expected that participants would have 1.0 episode of joint bleeding per year. At 2 years post infusion, no new safety signals had emerged and no new serious adverse events related to treatment had occurred

Miesbach : Dtsch Arztebl Int. 2022 Dec 27;119(51-52):887-894.

Data from non-randomized phase 1 to phase 3 trials reveal an adequate expression of factors VIII and IX in patients with mostly severe hemophilia A or B. Even though they were no longer receiving prophylactic treatment, most patients experienced a considerable reduction, by 53% to 96%, in the number of bleedings compared to previous therapy. Persistently elevated factor levels have been described for up to six years in hemophilia A and up to eight years in hemophilia B. The most common side effect of gene therapy is an inflammatory response with elevated alanine aminotransferase levels (17% to 89%, depending on the study), which may be associated with a reduced clotting factor level and requires treatment with transient immunosuppression. Gene therapy for hemophilia holds out the prospect of freedom from hemorrhage without the need for regular treatment with drugs. The various steps that need to be carried out in gene therapy should be coordinated in a graded and partly overlapping integrated care model (a so-called hub-and-spoke model). Electronic platforms should be used for data acquisition and transmission.

Samuelson Jones & George: Annu Rev Med. 2023 Jan 27:74:231-247.

Importantly, despite repeated proof-of-concept success in current hemophilia gene therapy, stable, durable FVIII or FIX expression able to ameliorate bleeding in all patients is an unrealized hope. This defines the development goals of the next generation of gene-based therapies for hemophilia.

*Valentino et al: J Thromb Haemost. 2023 Sep;21(9):2354-2361

In 2022, the National Hemophilia Foundation submitted a citizen petition (docket number FDA-2022-P-1444-0001) to the FDA requesting that a risk evaluation and mitigation strategy (REMS) be required as a condition of approval for both valoctocogene roxaparvovec and etranacogene dezaparvovec. Other organizations including the World Federation of Hemophilia, Hemophilia Federation of America, and the European Haemophilia Consortium joined this effort submitting separate but supportive statements to the FDA. However, the FDA reasoned that the requirements for the REMS for etranacogene dezaparvovec were not met, and it has received marketing authorization from the FDA without the requirement for the REMS. While this may be the case for people living with hemophilia B, for whom the benefit to risk equation for gene therapy is generally favorable [[58]], it may not be the same for people with hemophilia A when considering gene therapy. Standard and extended half-life products for the prevention of bleeding for people living with either hemophilia A and B may provide very good outcomes but at a substantial burden of treatment and also fail to prevent all bleeding.

Another approach is a restrictive introduction, such as a conditional marketing authorization in which a medicine fulfills an unmet medical need but there is still a need for comprehensive safety, efficacy, and quality data generation after approval [[62]]. Such approvals are granted for 1 year but can be renewed annually. Compliance with specific obligations with defined timelines is a necessary prerequisite for continued authorization [

[63]]. This mechanism was utilized in the case of onasemnogene abeparvovec, an AAV9 gene therapy for spinal muscular atrophy [[64]].

Here, we recommend that the following steps be taken by the hemophilia community to ensure the safety and optimal outcomes for PwH who choose to receive a gene therapy product:

1.Training and education must be provided for physicians and HCPs on gene therapy and the management of PwH who receive a gene therapy product

2.Training and education on shared decision making must be provided for physicians and HCPs who will evaluate, administer, and follow PwH who are candidates to receive a gene therapy product [

3.Facilities administering valoctocogene roxaparvovec and etranacogene dezaparvovec must receive adequate training and instruction on all aspects of gene therapy [

4.Valoctocogene roxaparvovec and etranacogene dezaparvovec must only be administered at or in conjunction with a hemophilia treatment center with knowledge and expertise in evaluating, administering, and managing PwH who have received investigational gene therapy products [

5.Individuals receiving valoctocogene roxaparvovec and etranacogene dezaparvovec must be enrolled in the global gene therapy registry initiated by the World Federation of Hemophilia in order to collect robust data, including adverse events of special interest [

6.Educational support should be developed in a transparent and unbiased way to facilitate learning by PwH so that they may participate in shared decision making

7.Formal collaboration between the relevant national hemophilia patient organizations and the centers administering gene therapy on the provision of education and information should be ensured so that the PwH is ready to fully participate in a shared and informed decision-making process.

8.Work to ensure that postmarket studies, registries, and future registrational studies take into consideration principles of health equity in their design.

*Baas: J Thromb Haemost. 2023 Mar;21(3):413-420. (Ethics)

Based on our analysis of the literature, we identified 3 ethical themes. The theme Living up to expectations describes the existing hopes for gene therapy and the unlikelihood of the currently approved product becoming a permanent cure. In the theme Psychosocial impacts, we discuss the fear that gene therapy will impact the identity of people with hemophilia and their need for psychosocial support. The theme Costs and access discusses the expected cost-effectiveness of gene therapy and its implications on accessibility worldwide. We conclude that it may be necessary to change the narratives surrounding gene therapy, from describing it as a cure to describing it as one of the many treatments that temporarily relieve symptoms and that there is a need to reevaluate the desirability of gene therapy for hemophilia, given the availability of other treatments.

*Kumar: J Thromb Haemost. 2024 Jan;22(1):23-34

Of note, multiple preclinical studies using platelet-specific lentiviral gene delivery to hematopoietic stem cells in hemophilia have demonstrated promising results with therapeutic levels of neo-protein that rescue the hemorrhagic bleeding phenotype and induce antigen-specific immune tolerance. Further studies using ovalbumin as a surrogate protein for platelet gene therapy have shown robust antigen-specific immune tolerance induced via peripheral clonal deletions of antigen-specific CD4- and CD8-T effector cells and induction of antigen-specific regulatory T (Treg) cells. This review discusses platelet-targeted gene therapy, focusing on immune tolerance induction.

Shah: Curr Med Res Opin. 2023 Feb;39(2):227-237

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.

Miesbach: J Thromb Haemost. 2023 Feb;21(2):200-203

It is therefore important that hemophilia treaters and hepatologists collaborate at all stages of gene therapy to assess potential safety issues and ensure the long-term success of gene therapy. Special attention should be given to patients with not well-defined conditions, e.g. patients with some degree of liver fibrosis or fatty liver disease, patients with a history of hepatitis C and hepatitis B infection, patients with HIV infection, and patients taking medications that may affect liver function.

Rasul: J Patient Exp. 2023; 10: 23743735231193573.

Hemophilia is a bleeding disorder caused by a single absent/defective gene and characterized by a lack of functional clotting factors. People with hemophilia may experience joint damage, pain, and psychological impairments, all of which could contribute to reduced health-related quality of life (HRQoL). The current standard of care is clotting factor replacement, which is associated with regular infusions; therefore, alternative treatments such as gene therapy (GT) are in development. GT involves the delivery of a functional copy of the clotting factor 8/9 gene by a single infusion into the patient's cells, enabling them to produce their own clotting factor VIII/IX. The impact of treatment on patients’ HRQoL can be assessed using hemophilia-specific patient-reported outcome (PRO) measures. Since these measures were designed before the advent of GT, there is a need for updated individualized PRO measures. Patient groups and regulatory authorities emphasize the need for increased patient engagement when considering clinical trial design. Here, we provide patients’ perspective on undergoing GT and discuss how to capture the patient voice when measuring the therapy's transformative impact

Valentino: J Thromb Haemost. 2023 Nov;21(11):3033-3044

The therapeutic landscape for people living with hemophilia A (PwHA) has changed dramatically in recent years, but many clinical challenges remain, including the development of inhibitory antibodies directed against factor VIII (FVIII) that occur in approximately 30% of people with severe hemophilia A. Emicizumab, an FVIII mimetic bispecific monoclonal antibody, provides safe and effective bleeding prophylaxis for many PwHA, but clinicians still explore therapeutic strategies that result in immunologic tolerance to FVIII to enable effective treatment with FVIII for problematic bleeding events. This immune tolerance induction (ITI) to FVIII is typically accomplished through repeated long-term exposure to FVIII using a variety of protocols. Meanwhile, gene therapy has recently emerged as a novel ITI option that provides an intrinsic, consistent source of FVIII. As gene therapy and other therapies now expand therapeutic options for PwHA, we review the persistent unmet medical needs with respect to FVIII inhibitors and effective ITI in PwHA, the immunology of FVIII tolerization, the latest research on tolerization strategies, and the role of liver-directed gene therapy to mediate FVIII ITI.

Limjoco: Patient Prefer Adherence. 2023 Apr 19:17:1093-1105

These data highlight the utility of a SDM tool for hemophilia gene therapy and key information needs. Data including comparison to other treatments should be provided along with patient testimonials in a transparent format. Patients will engage the Hemophilia Treatment Center, family, and community members in the decision-making process.

Miesbach: Hamostaseologie. 2023 Jun;43(3):196-207

Gene therapy has recently become a realistic treatment perspective for patients with hemophilia. Reviewing the literature and our personal experience from clinical trials, we discuss key aspects of hemophilia A and B gene therapy with vectors derived from adeno-associated virus, including predictable results, risks, adverse events, and patient-reported outcomes. Patient selection, informed consent, administration, and monitoring of gene therapy as well as data collection are explained. We also discuss the need for interdisciplinary cooperation with hepatology and other specialties. We emphasize structural and organizational requirements for treatment centers according to the hub-and-spoke model and recommend the use of electronic diaries to ensure safe and timely collection and exchange of data. Electronic diaries will play a key role as a primary source of data for pharmacovigilance, post-marketing clinical studies, national and international registries, as well as health technology and benefit assessment. Reimbursement aspects and the future of gene therapy in adolescents and children are also considered. In a rapidly evolving scientific environment, these recommendations aim to support treatment providers and payers to prepare for the implementation of gene therapy following marketing authorization

Butterfield: Cell Immunol. 2023 Sep-Oct:391-392:104742

Oral immunotherapies are being developed for various autoimmune diseases and allergies to suppress immune responses in an antigen-specific manner. Previous studies have shown that anti-drug antibody (inhibitor) formation in protein replacement therapy for the inherited bleeding disorder hemophilia can be prevented by repeated oral delivery of coagulation factor antigens bioencapsulated in transplastomic lettuce cells. Here, we find that this approach substantially reduces antibody development against factor VIII in hemophilia A mice treated with adeno-associated viral gene transfer. We propose that the concept of oral tolerance can be applied to prevent immune responses against therapeutic transgene products expressed in gene therapy

Nguyen: J Thromb Haemost. 2023 Aug;21(8):2101-2113.

The novel hFVIII-Δ3-SP/DE variant of the furin and a3 cleavage sites significantly improved secretion compared with hFVIII-BDD. This key feature of the Δ3-SP/DE variant provides a unique strategy that can be combined with other approaches to further improve factor VIII expression to achieve superior efficacy in AAV-based gene therapy for hemophilia A.

La Mura: Blood Adv. 2023 Oct 10;7(19):5817-5824

Overall, risk factors of chronic liver damage are frequent after HCV clearance, but changes in LSM and NITs after clearance may be inaccurate to rule out advanced fibrosis/cirrhosis. A specific diagnostic workup is warranted to evaluate liver health in PWH in the era of gene therapy.

Kashiwakura: Mol Ther Methods Clin Dev. 2023 Aug 22:30:502-514

Gene therapy using adeno-associated virus (AAV)-based vectors has become a realistic therapeutic option for hemophilia. We examined the potential of a novel engineered liver-tropic AAV3B-based vector, AAV.GT5, for hemophilia B gene therapy. In vitro transduction with AAV.GT5 in human hepatocytes was more than 100 times higher than with AAV-Spark100, another bioengineered vector used in a clinical trial. However, liver transduction following intravenous injection of these vectors was similar in mice with a humanized liver and in macaques. This discrepancy was due to the low recovery and short half-life of AAV.GT5 in blood, depending on the positive charge of the heparin-binding site in the capsid. Bypassing systemic clearance with the intra-hepatic vascular administration of AAV.GT5, but not AAV-Spark100, enhanced liver transduction in pigs and macaques. AAV.GT5 did not develop neutralizing antibodies (NAbs) in two of four animals, while AAV-Spark100 induced serotype-specific NAbs in all macaques tested (4 of 4). The NAbs produced after AAV-Spark100 administration were relatively serotype specific, and challenge with AAV.GT5 through the hepatic artery successfully boosted liver transduction in one animal previously administered AAV-Spark100. In summary, AAV.GT5 showed different vector kinetics and NAb induction compared with AAV-Spark100, and intra-hepatic vascular administration may minimize the vector dose required and vector dissemination.

Hermans: Ther Adv Hematol. 2023 Jan 12:14:20406207221145627.

First, awareness, communication, and education about the therapeutic potential and modalities of gene therapy must be further strengthened. To this end, objective, unbiased, transparent, and regularly updated information must be shared, in an appropriate way and understandable language with the support of patients' organizations. Second, healthcare providers should adopt a patient-centred approach, as the 'one size fits all' approach is inappropriate when considering gene therapy. Instead, a holistic patient view taking into account their physical and mental dimensions, along with unexpressed expectations and preferences, is mandatory. Third, the consent procedure must be improved, ensuring that patients' interests are maximally protected. Finally, gene therapy is likely to be first delivered in a few centres, with the highest expertise and experience in this domain. Thus, patients should be managed based on a hub-and-spoke model, taking into account that the key to gene therapy's success lies in an optimal communication and collaboration both within and between haemophilia centres sharing their experiences in the frame of international registries. This review describes recent progress and explains outstanding hurdles that must be tackled to ease the implementation of this paradigm-changing new therapy.

Castaman: Haemophilia. 2023 Mar;29(2):435-444

Use of the hub-and-spoke organisational model and multidisciplinary teams are expected to optimize patient selection for gene therapy, as well as the management of dosing and patient follow-up, patient engagement, laboratory surveillance, and patient expectations regarding outcomes. This approach should allow the benefits of AAV-based gene therapy for haemophilia A to be maximized.

Pipe: Haemophilia. 2023 Nov;29(6):1430-1441

The patient journey includes: information gathering; decision making; comprehensive patient assessment; preparation for the infusion itself; short- and long-term monitoring; lifestyle modifications; and the possible need for immunosuppressive treatment. Informed decision-making may require patient education with extensive discussions and an understanding that not all people with haemophilia will choose or be eligible for gene therapy, although eligibility criteria continue to evolve. The institutional journey includes: consideration of biosafety procedures; planning for product procurement, handling, storage, and administration; development of detailed protocols and guidance documents; contingency planning for immunosuppressive and haemostatic management; consideration of clinical capabilities and staff training needs; coordination of efforts by the full multidisciplinary team; and collaboration between referring, dosing, and follow-up treatment centres. Documented protocols and guidance documents are pivotal for this complex therapy to ensure safe handling, optimal delivery, and post-infusion management and follow-up.

Fletcher: Haemophilia. 2023 May;29(3):776-783

PwH have many expectations about the difference gene therapy can make to their lives. Studies show that these expectations may not be fully realised. For those who have either withdrawn or been withdrawn from gene therapy, any expectations they had may now be unachievable. The nature of these expectations and the loss expressed by the participants indicate that support needs to be provided to help them and their families manage it.

Chen: Mol Ther Nucleic Acids. 2023 Oct 5:34:102043

Development of factor VIII (FVIII) inhibitors is a serious complication in the treatment of hemophilia A (HemA) patients. In clinical trials, anti-CD3 antibody therapy effectively modulates the immune response of allograft rejection or autoimmune diseases without eliciting major adverse effects. In this study, we delivered mRNA-encapsulated lipid nanoparticles (LNPs) encoding therapeutic anti-CD3 antibody (αCD3 LNPs) to overcome the anti-FVIII immune responses in HemA mice. It was found that αCD3 LNPs encoding the single-chain antibodies (Fc-scFv) can efficiently deplete CD3+ and CD4+ effector T cells, whereas αCD3 LNPs encoding double-chain antibodies cannot. Concomitantly, mice treated with αCD3 (Fc-scFv) LNPs showed an increase in the CD4+CD25+Foxp3+ regulatory T cell percentages, which modulated the anti-FVIII immune responses. All T cells returned to normal levels within 2 months. HemA mice treated with αCD3 LNPs prior to hydrodynamic injection of liver-specific FVIII plasmids achieved persistent FVIII gene expression without formation of FVIII inhibitors. Furthermore, transgene expression was increased and persistent following secondary plasmid challenge, indicating induction of long-term tolerance to FVIII. Moreover, the treated mice maintained their immune competence against other antigens. In conclusion, our study established a potential new strategy to induce long-term antigen-specific tolerance using an αCD3 LNP formulation.

Ramamurthy: Front Immunol. 2022 Dec 15:13:954984

Although we did not achieve our primary objective, our results validate the utility of both PLCs and hLSECs as cell-based delivery vehicles for a fVIII transgene, and they highlight the hurdles that remain to be overcome before primary human cells can be gene-edited with sufficient efficiency for use in cell-based gene therapy to treat HA.