Innovative Curative Treatment of Beta Thalassemia: Cost-Efficacy Analysis of Gene Therapy Versus Allogenic Hematopoietic Stem-Cell Transplantation

Effects of an indole derivative on cell proliferation, transfection, and alternative splicing in production of lentiviral vectors by transient co-transfection

Lentiviral vectors derived from human immunodeficiency virus type I are widely used to deliver functional gene copies to mammalian cells for research and gene therapies. Post-transcriptional splicing of lentiviral vector transgene in transduced host and transfected producer cells presents barriers to widespread application of lentiviral vector-based therapies. The present study examined effects of indole derivative compound IDC16 on splicing of lentiviral vector transcripts in producer cells and corresponding yield of infectious lentiviral vectors. Indole IDC16 was shown previously to modify alternative splicing in human immunodeficiency virus type I. Human embryonic kidney 293T cells were transiently transfected by 3rd generation backbone and packaging plasmids using polyethyleneimine. Reverse transcription-quantitative polymerase chain reaction of the fraction of unspliced genomes in human embryonic kidney 293T cells increased up to 31% upon the indole's treatment at 2.5 uM. Corresponding yield of infectious lentiviral vectors decreased up to 4.5-fold in a cell transduction assay. Adjusting timing and duration of IDC16 treatment indicated that the indole's disruption of early stages of transfection and cell cycle had a greater effect on exponential time course of lentiviral vector production than its reduction of post-transcriptional splicing. Decrease in transfected human embryonic kidney 293T proliferation by IDC16 became significant at 10 uM. These findings indicated contributions by early-stage transfection, cell proliferation, and post-transcriptional splicing in transient transfection of human embryonic kidney 293T cells for lentiviral vector production.

Gene therapy for sickle cell disease

Sickle cell disease (SCD) is potentially curable after allogeneic hematopoietic stem cell transplantation (HSCT) or autologous HSCT after ex vivo genetic modification. Autologous HSCT with gene therapy has the potential to overcome many of the limitations of allogeneic HSCT that include the lack of suitable donors, graft-versus-host disease, the need for immune suppression, and the potential for graft rejection. Significant progress in gene therapy for SCD has been made over the past several decades, now with a growing number of clinical trials investigating various gene addition and gene editing strategies. Available results from a small number of patients, some with relatively short follow-up, are promising as a potentially curative strategy, with current efforts focused on continuing to improve the efficacy, durability, and safety of gene therapies for the cure of SCD.

Sickle Cell Disease: From Genetics to Curative Approaches

Sickle cell disease (SCD) is a monogenic blood disease caused by a point mutation in the gene coding for β-globin. The abnormal hemoglobin [sickle hemoglobin (HbS)] polymerizes under low-oxygen conditions and causes red blood cells to sickle. The clinical presentation varies from very severe (with acute pain, chronic pain, and early mortality) to normal (few complications and a normal life span). The variability of SCD might be due (in part) to various genetic modulators. First, we review the main genetic factors, polymorphisms, and modifier genes that influence the expression of globin or otherwise modulate the severity of SCD. Considering SCD as a complex, multifactorial disorder is important for the development of appropriate pharmacological and genetic treatments. Second, we review the characteristics, advantages, and disadvantages of the latest advances in gene therapy for SCD, from lentiviral-vector-based approaches to gene-editing strategies.

Gene modification therapies for hereditary diseases in the fetus

Proof-of-principle disease models have demonstrated the feasibility of an intrauterine gene modification therapy (in utero gene therapy (IUGT)) approach to hereditary diseases as diverse as coagulation disorders, haemoglobinopathies, neurogenetic disorders, congenital metabolic, and pulmonary diseases. Gene addition, which requires the delivery of an integrating or episomal transgene to the target cell nucleus to be transcribed, and gene editing, where the mutation is corrected within the gene of origin, have both been used successfully to increase normal protein production in a bid to reverse or arrest pathology in utero. While most experimental models have employed lentiviral, adenoviral, and adeno-associated viral vectors engineered to efficiently enter target cells, newer models have also demonstrated the applicability of non-viral lipid nanoparticles. Amelioration of pathology is dependent primarily on achieving sustained therapeutic transgene expression, silencing of transgene expression, production of neutralising antibodies, the dilutional effect of the recipient's growth on the mass of transduced cells, and the degree of pre-existing cellular damage. Safety assessment of any IUGT strategy will require long-term postnatal surveillance of both the fetal recipient and the maternal bystander for cell and genome toxicity, oncogenic potential, immune-responsiveness, and germline mutation. In this review, we discuss advances in the field and the push toward clinical translation of IUGT.

Juggling between the Cost and Value of New Therapies: Does Science Still Serve Patient Needs?

Thalassaemia International Federation (TIF), representing the united voice of people with thalassaemia and their families globally, has been striving for more than three decades to empower research, by academic communities and industry, to focus on developing a safe and effective curative approach for thalassaemia. Such a cure would lead to new lives with equal opportunities and challenges, as for every other person not suffering from a severe chronic disease. A gene therapy product was finally authorised in May 2019 by the European Medicinal Agency, thus marking a milestone in the history of the disease. However, after this conditional authorization, everyone focused on numbers and opted for cost of illness and cost-effectiveness studies, inadmissibly ignoring patients’ voices and needs. The product was finally withdrawn from Europe, despite the fact that all implicated stakeholders, including governments, academia and industry always knew that an innovative and complex therapy would be expensive but always supported and fought for its development. In this article, TIF expresses its view on this issue, including some thoughts on how to address the high cost of innovative therapies.

Clinical genome editing to treat sickle cell disease-A brief update

Sickle cell disease (SCD) is one of the most common hemoglobinopathies. Due to its high prevalence, with about 20 million affected individuals worldwide, the development of novel effective treatments is highly warranted. While transplantation of allogeneic hematopoietic stem cells (HSC) is the standard curative treatment approach, a variety of gene transfer and genome editing strategies have demonstrated their potential to provide a prospective cure for SCD patients. Several stratagems employing CRISPR-Cas nucleases or base editors aim at reactivation of γ-globin expression to replace the faulty β-globin chain. The fetal hemoglobin (HbF), consisting of two α-globin and two γ-globin chains, can compensate for defective adult hemoglobin (HbA) and reverse the sickling of hemoglobin-S (HbS). Both disruption of cis-regulatory elements that are involved in inhibiting γ-globin expression, such as BCL11A or LRF binding sites in the γ-globin gene promoters (HBG1/2), or the lineage-specific disruption of BCL11A to reduce its expression in human erythroblasts, have been demonstrated to reestablish HbF expression. Alternatively, the point mutation in the HBB gene has been corrected using homology-directed repair (HDR)-based methodologies. In general, genome editing has shown promising results not only in preclinical animal models but also in clinical trials, both in terms of efficacy and safety. This review provides a brief update on the recent clinical advances in the genome editing space to offer cure for SCD patients, discusses open questions with regard to off-target effects induced by the employed genome editors, and gives an outlook of forthcoming developments.

Challenges for Economic Evaluations of Advanced Therapy Medicinal Products: A Systematic Review

OBJECTIVES

Advanced therapy medicinal products (ATMPs) are drugs for human use for the treatment of chronic, degenerative, or life-threatening diseases that are based on genes, tissues, or cells. This article aimed to identify and critically review published economic analyses of ATMPs.

METHODS

A systematic review of economic analyses of ATMPs was undertaken. Study characteristics, design, sources of data, resources and unit costs, modeling and extrapolation methods, study results, and sensitivity analyses were assessed.

RESULTS

A total of 46 economic analyses of ATMP (from 45 articles) were included; 4 were cell therapy medicinal products, 33 gene therapy medicinal products, and 9 tissue-engineered products. 30 therapies had commercial marketing approval; 39 studies were cost-utility analysis, 5 were cost-effectiveness analysis, and 2 were cost only studies. Four studies predicted that the ATMP offered a step change in the management of the condition and 10 studies estimated that the ATMP would offer a lower mean cost.

CONCLUSIONS

Comparison with historical controls, pooling of data, and use of techniques such as mixture cure fraction models should be used cautiously. Sensitivity analyses should be used across a plausible range of prices. Clinical studies need to be designed to align with health technology assessment requirements, including generic quality of life, and payers should aim for clarity of criteria. Regulators and national payers should aim for compatibility of registers to allow interchange of data. Given the increasing reliance on industry-funded economic analyses, careful critical review is recommended.

Estimating the Cost of Thalassemia Care across the World: A Thalassemia International Federation Model

Estimating the cost of thalassemia care is important for the optimization of care planning, resource allocation and the empowerment of patient advocacy. However, available evidence is heterogeneous, reflecting diverse healthcare systems and cost estimation methods. We sought to build a globally applicable cost model for thalassemia care. We followed a three-step approach, including (i) a targeted literature review to identify previous cost-of-illness studies on thalassemia; (ii) a generic model development based on the main determinants of cost in different countries emerged from a literature review and validated by a team of medical experts; (iii) a piloting of the model using data from two diverse countries. The literature review revealed studies focusing on the total costs of thalassemia care or the cost or cost-effectiveness of specific treatment or prevention modalities in high- and low-prevalence countries across the world. The resulting evidence was used to build a model that calculates total annual therapy cost based on entry of country-level and patient-level data, and data on healthcare modalities, indirect costs and prevention. Testing the model using published data from the UK, Iran, India and Malaysia, revealed an annual cost per patient of £81,796.00 for the UK, Iranian rial (IRR) 13,757.00 for Iran, Indian rupee (INR) 166,750.00 for India and Malyasian ringgit (or dollar) (MYR) 111,372.00 for Malaysia. A globally applicable model that calculates total annual cost of thalassemia care was built based on existing evidence. The model successfully predicted the annual cost of thalassemia care in the UK, Iran, India and Malaysia.

A landscape analysis and discussion of value of gene therapies for sickle cell disease

INTRODUCTION

Sickle cell disease (SCD) is a rare genetic disease with limited therapeutic options. Gene-based therapies are being investigated in clinical trials to evaluate their curative potential. The expected life-long benefits of one-time administration of genetically corrected stem cells present uncharted challenges in estimating value of these treatments. Our objective is to conduct a landscape analysis of clinical trials and prompt a discussion estimating the value of gene therapy as a therapeutic option for SCD.

AREAS COVERED

We searched Clinicaltrials.gov to identify and characterize clinical trials in gene therapies for SCD. We report available results and discuss current concerns and elements of value necessary to consider as these products come to market.

EXPERT OPINION

Gene therapies could represent a major advance in SCD treatment. Although clinical trials are ongoing, reports of serious adverse events have led to pause of these trials, emphasizing the need to prove long-term tolerability. Measured using the methods of health economic evaluation, we anticipate high up-front costs may be offset by potential life-long benefits of these treatments. During development and after treatment approval, attention should be focused on ensuring adequate availability and equitable access to emerging therapies in underserved areas and low-middle-income countries (LMIC).

Debating the Future of Sickle Cell Disease Curative Therapy: Haploidentical Hematopoietic Stem Cell Transplantation vs. Gene Therapy

Hematopoietic stem cell transplantation (HSCT) is a well-established curative therapy for patients with sickle cell disease (SCD) when using a human leukocyte antigen (HLA)-matched sibling donor. Most patients with SCD do not have a matched sibling donor, thereby significantly limiting the accessibility of this curative option to most patients. HLA-haploidentical HSCT with post-transplant cyclophosphamide expands the donor pool, with current approaches now demonstrating high overall survival, reduced toxicity, and an effective reduction in acute and chronic graft-vs.-host disease (GvHD). Alternatively, autologous genetic therapies appear promising and have the potential to overcome significant barriers associated with allogeneic HSCT, such as donor availability and GvHD. Here the authors each take a viewpoint and discuss what will be the future of curative options for patients with SCD outside of a matched sibling transplantation, specifically haploidentical HSCT vs. gene therapy.

Conditioning Regimens in Patients with β-Thalassemia Who Underwent Hematopoietic Stem Cell Transplantation: A Scoping Review

The success of transplant procedures in patients with beta-thalassemia major (β-thalassemia) goes hand-in-hand with improvements in disease knowledge, better supportive care, discoveries in immunogenetics, increase in stem cell sources, and enhancement of conditioning regimens. The aim of this scoping review was to report the evolution of conditioning regimes for β-thalassemia hematopoietic stem cell transplantation. We performed a systematic search for all relevant articles published before July 2021, using the following Medical Subject Headings: "bone marrow transplantation", "stem cell transplantation", "allogeneic", "thalassemia", "β-thalassemia", and "thalassemia major". The final analysis included 52 studies, published between 1988 and 2021, out of 3877 records. The most common conditioning regimen was a combination of busulfan and cyclophosphamide, with successive dose adjustments or remodulation based on patient characteristics. Pre-transplant treatments, reductions in cyclophosphamide dosage, or the adoption of novel agents such as treosulphan all improved overall survival and thalassemia-free survival in transplant-related mortality high-risk patients. Conditioning regimes were modulated for those without a suitable fully matched sibling or unrelated donor, with encouraging results. Hematopoietic stem cell transplantation with haploidentical donors is currently available to virtually all patients with β-thalassemia. However, disparities in outcome are still present around the world. In developing and limited-resource countries, where most diagnoses are focused, transplants are not always available. Therefore, more efforts are needed to close this treatment gap.

Current approaches in CRISPR-Cas9 mediated gene editing for biomedical and therapeutic applications

A single gene mutation can cause a number of human diseases that affect quality of life. Until the development of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein (Cas) systems, it was challenging to correct a gene mutation to avoid disease by reverting phenotypes. The advent of CRISPR technology has changed the field of gene editing, given its simplicity and intrinsic programmability, surpassing the limitations of both zinc-finger nuclease and transcription activator-like effector nuclease and becoming the method of choice for therapeutic gene editing by overcoming the bottlenecks of conventional gene-editing techniques. Currently, there is no commercially available medicinal cure to correct a gene mutation that corrects and reverses the abnormality of a gene's function. Devising reprogramming strategies for faithful recapitulation of normal phenotypes is a crucial aspect for directing the reprogrammed cells toward clinical trials. The CRISPR-Cas9 system has been promising as a tool for correcting gene mutations in maladies including blood disorders and muscular degeneration as well as neurological, cardiovascular, renal, genetic, stem cell, and optical diseases. In this review, we highlight recent developments and utilization of the CRISPR-Cas9 system in correcting or generating gene mutations to create model organisms to develop deeper insights into diseases, rescue normal gene functionality, and curb the progression of a disease.

OUP accepted manuscript

Beta-thalassemia is one of the most common monogenic disorders. Standard treatment of the most severe forms, i.e., transfusion-dependent thalassemia (TDT) with long-term transfusion and iron chelation, represents a considerable medical, psychological, and economic burden. Allogeneic hematopoietic stem cell transplantation from an HLA-identical donor is a curative treatment with excellent results in children. Recently, several gene therapy approaches were evaluated in academia or industry-sponsored clinical trials as alternative curative options for children and young adults without an HLA-identical donor. Gene therapy by addition of a functional beta-globin gene using self-inactivating lentiviral vectors in autologous stem cells resulted in transfusion independence for a majority of TDT patients across different age groups and genotypes, with a current follow-up of multiple years. More recently, promising results were reported in TDT patients treated with autologous hematopoietic stem cells edited with the clustered regularly interspaced short palindromic repeats-Cas9 technology targeting erythroid BCL11A expression, a key regulator of the normal switch from fetal to adult globin production. Patients achieved high levels of fetal hemoglobin allowing for discontinuation of transfusions. Despite remarkable clinical efficacy, 2 major hurdles to gene therapy access for TDT patients materialized in 2021: (1) a risk of secondary hematological malignancies that is complex and multifactorial in origin and not limited to the risk of insertional mutagenesis, (2) the cost—even in high-income countries—is leading to the arrest of commercialization in Europe of the first gene therapy medicinal product indicated for TDT despite conditional approval by the European Medicines Agency.

Curative therapy for hemoglobinopathies: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee review comparing outcomes, accessibility and cost of ex vivo stem cell gene therapy versus allogeneic hematopoietic stem cell transplantation

Thalassemia and sickle cell disease (SCD) are the most common monogenic diseases in the world and represent a growing global health burden. Management is limited by a paucity of disease-modifying therapies; however, allogeneic hematopoietic stem cell transplantation (HSCT) and autologous HSCT after genetic modification offer patients a curative option. Allogeneic HSCT is limited by donor selection, morbidity and mortality from transplant conditioning, graft-versus-host disease and graft rejection, whereas significant concerns regarding long-term safety, efficacy and cost limit the broad applicability of gene therapy. Here the authors review current outcomes in allogeneic and autologous HSCT for transfusion-dependent thalassemia and SCD and provide our perspective on issues surrounding accessibility and costs as barriers to offering curative therapy to patients with hereditary hemoglobinopathies.

Genome-based therapeutic interventions for β-type hemoglobinopathies

For decades, various strategies have been proposed to solve the enigma of hemoglobinopathies, especially severe cases. However, most of them seem to be lagging in terms of effectiveness and safety. So far, the most prevalent and promising treatment options for patients with β-types hemoglobinopathies, among others, predominantly include drug treatment and gene therapy. Despite the significant improvements of such interventions to the patient's quality of life, a variable response has been demonstrated among different groups of patients and populations. This is essentially due to the complexity of the disease and other genetic factors. In recent years, a more in-depth understanding of the molecular basis of the β-type hemoglobinopathies has led to significant upgrades to the current technologies, as well as the addition of new ones attempting to elucidate these barriers. Therefore, the purpose of this article is to shed light on pharmacogenomics, gene addition, and genome editing technologies, and consequently, their potential use as direct and indirect genome-based interventions, in different strategies, referring to drug and gene therapy. Furthermore, all the latest progress, updates, and scientific achievements for patients with β-type hemoglobinopathies will be described in detail.

Novel therapies in β-thalassaemia

Beta-thalassaemia is one of the most significant haemoglobinopathies worldwide resulting in the synthesis of little or no β-globin chains. Without treatment, β-thalassaemia major is lethal within the first decade of life due to the complex pathophysiology, which leads to wide clinical manifestations. Current clinical management for these patients depends on repeated transfusions followed by iron-chelating therapy. Several novel approaches to correct the resulting α/β-globin chain imbalance, treat ineffective erythropoiesis and improve iron overload are currently being developed. Up to now, the only curative treatment for β-thalassemia is haematopoietic stem-cell transplantation, but this is a risky and costly procedure. Gene therapy, gene editing and base editing are emerging as a powerful approach to treat this disease. In β-thalassaemia, gene therapy involves the insertion of a vector containing the normal β-globin or γ-globin gene into haematopoietic stem cells to permanently produce normal red blood cells. Gene editing and base editing involves the use of zinc finger nucleases, transcription activator-like nucleases and clustered regularly interspaced short palindromic repeats/Cas9 to either correct the causative mutation or else insert a single nucleotide variant that will increase foetal haemoglobin. In this review, we will examine the current management strategies used to treat β-thalassaemia and focus on the novel therapies targeting ineffective erythropoiesis, improving iron overload and correction of the globin chain imbalance.

Hematopoietic stem cell transplantation for people with β-thalassaemia

BACKGROUND

Thalassaemia is an autosomal recessive blood disorder, caused by mutations in globin genes or their regulatory regions, resulting in a reduced rate of synthesis of one of the globin chains that make up haemoglobin. In β-thalassaemia there is an underproduction of β-globin chains combined with excess of free α-globin chains. The excess free α-globin chains precipitate in red blood cells, leading to their increased destruction (haemolysis) and ineffective erythropoiesis. The conventional treatment is based on the correction of haemoglobin through regular red blood cell transfusions and treating the iron overload that develops subsequently with iron chelation therapy. Although, early detection and initiations of such supportive treatment has improved the quality of life for people with transfusion-dependent thalassaemia, allogeneic hematopoietic stem cell transplantation is the only widely available therapy with a curative potential. Gene therapy for β-thalassaemia has recently received conditional authorisation for marketing in Europe, and may soon become widely available as another alternative therapy with curative potential for people with transfusion-dependent thalassaemia. This is an update of a previously published Cochrane Review.

OBJECTIVES

To evaluate the effectiveness and safety of different types of hematopoietic stem cell transplantation, in people with transfusion-dependent β-thalassaemia.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Haemoglobinopathies Trials Register comprising references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. We also searched online trial registries. Date of the most recent search: 07 April 2021.

SELECTION CRITERIA

Randomised controlled trials and quasi-randomised controlled trials comparing hematopoietic stem cell transplantation with each other or with standard therapy (regular transfusion and chelation regimen).

DATA COLLECTION AND ANALYSIS

Two review authors independently screened trials and had planned to extract data and assess risk of bias using standard Cochrane methodologies and assess the quality using GRADE approach, but no trials were identified for inclusion in the current review.

MAIN RESULTS

No relevant trials were retrieved after a comprehensive search of the literature.

AUTHORS' CONCLUSIONS

We were unable to identify any randomised controlled trials or quasi-randomised controlled trials on the effectiveness and safety of different types of hematopoietic stem cell transplantation in people with transfusion-dependent β-thalassaemia. The absence of high-level evidence for the effectiveness of these interventions emphasises the need for well-designed, adequately-powered, randomised controlled clinical trials.

HIV-based lentiviral vectors: origin and sequence differences

Three gene therapy strategies have received US Food and Drug Administration (FDA) approval; one includes HIV-1-based lentiviral vectors. These vectors incorporate features to provide long-term gene transfer and expression while minimizing generation of a replication-competent virus or pathogenicity. Importantly, the coding regions of viral proteins were deleted, and the cis-acting regulatory elements were retained. With the use of representative vectors developed for clinical/commercial applications, we compared the vector backbone sequences to the initial sources of the HIV-1. All vectors included required elements: 5′ long terminal repeat (LTR) through the Ψ packaging signal, central polypurine tract/chain termination sequence (cPPT/CTS), Rev responsive element (RRE), and 3′ LTR, including a poly(A) signal. The Ψ signaling sequence demonstrated the greatest similarity between all vectors with only minor changes. The 3′ LTR was the most divergent sequence with a range of deletions. The RRE length varied between vectors. Phylogenetic analysis of the cPPT/CTS indicated multiple sources, perhaps because of its later inclusion into lentiviral vector systems, whereas other regions revealed node clusters around the HIV-1 reference genomes HXB2 and NL4-3. We examine the function of each region in a lentiviral vector, the molecular differences between vectors, and where optimization may guide development of the lentiviral delivery systems.

Genome editing approaches to β-hemoglobinopathies

β-hemoglobinopathies are the most common monogenic disorders worldwide and are caused by mutations in the β-globin locus altering the production of adult hemoglobin (HbA). Transplantation of autologous hematopoietic stem cells (HSCs) corrected by lentiviral vector-mediated addition of a functional β-like globin raised new hopes to treat sickle cell disease and β-thalassemia patients; however, the low expression of the therapeutic gene per vector copy is often not sufficient to fully correct the patients with a severe clinical phenotype. Recent advances in the genome editing field brought new possibilities to cure β-hemoglobinopathies by allowing the direct modification of specific endogenous loci. Double-strand breaks (DSBs)-inducing nucleases (i.e., ZFNs, TALENs and CRISPR-Cas9) or DSB-free tools (i.e., base and prime editing) have been used to directly correct the disease-causing mutations, restoring HbA expression, or to reactivate the expression of the fetal hemoglobin (HbF), which is known to alleviate clinical symptoms of β-hemoglobinopathy patients. Here, we describe the different genome editing tools, their application to develop therapeutic approaches to β-hemoglobinopathies and ongoing clinical trials using genome editing strategies.

Genome Editing for β-Hemoglobinopathies: Advances and Challenges

β-hemoglobinopathies are the most common genetic disorders worldwide and are caused by mutations affecting the production or the structure of adult hemoglobin. Patients affected by these diseases suffer from anemia, impaired oxygen delivery to tissues, and multi-organ damage. In the absence of a compatible donor for allogeneic bone marrow transplantation, the lifelong therapeutic options are symptomatic care, red blood cell transfusions and pharmacological treatments. The last decades of research established lentiviral-mediated gene therapy as an efficacious therapeutic strategy. However, this approach is highly expensive and associated with a variable outcome depending on the effectiveness of the viral vector and the quality of the cell product. In the last years, genome editing emerged as a valuable tool for the development of curative strategies for β-hemoglobinopathies. Moreover, due to the wide range of its applications, genome editing has been extensively used to study regulatory mechanisms underlying globin gene regulation allowing the identification of novel genetic and pharmacological targets. In this work, we review the current advances and challenges of genome editing approaches to β-hemoglobinopathies. Special focus has been directed towards strategies aimed at correcting the defective β-globin gene or at inducing fetal hemoglobin (HbF), which are in an advanced state of clinical development.

Engineered U7 Small Nuclear RNA Restores Correct β-Globin Pre-mRNA Splicing in Mouse βIVS2-654-Thalassemic Erythroid Progenitor Cells

Restoration of correct splicing of β^IVS2-654-globin pre-mRNA was previously accomplished in erythroid cells from β-thalassemia/HbE patients by an engineered U7 small nuclear RNA (snRNA) that carried a sequence targeted to the cryptic branch point and an exonic splicing enhancer, U7.BP+623 snRNA. In this study, this approach was tested in thalassemic mice carrying the β^IVS2-654 mutation. While correction of β^IVS2-654 pre-mRNA splicing was achieved in erythroid progenitors transduced with a lentiviral vector carrying the U7.BP+623 snRNA, a high level of truncated U7.BP+623 snRNA was also observed. The discrepancy of processing of the modified U7 snRNA in human and mouse constructs hamper the evaluation of pathologic improvement in mouse model.

Hematopoietic Stem Cell Transplantation in Patients with Hemoglobinopathies

Hemoglobinopathies are the most common single-gene diseases and are estimated to affect millions of people worldwide. Thalassemia and sickle cell disease are the most prevalent diseases of this group. Today, despite the decreasing number of newborns diagnosed with a hemoglobinopathy, it remains an important health problem for many countries. Although regular red blood cell (RBC) transfusions, advanced iron chelation, and supportive therapy alternatives have improved life expectancy, allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative option for patients with hemoglobinopathies to prevent irreversible organ damage. Modern transplantation approaches and careful posttransplantation follow-up of patients have improved survival outcomes, and HSCT has now been performed in several patients with hemoglobinopathies worldwide. Considering current experiences, hematopoietic stem cell transplantation is recommended in cases of β-thalassemia (β-thal) in the presence of a matched family or unrelated donor, without secondary organ damage due to transfusion. In patients with sickle cell anemia, transplantation indications include transfusion dependence and cases of secondary organ damage. Recently, gene therapy as a possible treatment option has yielded promising results, though it is not in routine clinical use at its current stage.

Gene Therapy of the Hemoglobinopathies

Sickle cell disease and the ß-thalassemias are caused by mutations of the ß-globin gene and represent the most frequent single gene disorders worldwide. Even in European countries with a previous low frequency of these conditions the prevalence has substantially increased following large scale migration from Africa and the Middle East to Europe. The hemoglobin diseases severely limit both, life expectancy and quality of life and require either life-long supportive therapy if cure cannot be achieved by allogeneic stem cell transplantation. Strategies for ex vivo gene therapy aiming at either re-establishing normal ß-globin chain synthesis or at re-activating fetal γ-globin chain and HbF expression are currently in clinical development. The European Medicine Agency (EMA) conditionally licensed gene addition therapy based on lentiviral transduction of hematopoietic stem cells in 2019 for a selected group of patients with transfusion dependent non-ß° thalassemia major without a suitable stem cell donor. Gene therapy thus offers a relevant chance to this group of patients for whom cure has previously not been on the horizon. In this review, we discuss the potential and the challenges of gene addition and gene editing strategies for the hemoglobin diseases.

A Review of Methodological Considerations for Economic Evaluations of Gene Therapies and Their Application in Literature

OBJECTIVES

To identify methodological considerations discussed in literature addressing economic evaluations (EEs) of gene therapies (GTs). Additionally, we assessed if these considerations are applied in published GT EEs to increase understanding and explore impact.

METHODS

First a peer-reviewed literature review was performed to identify research addressing methodological considerations of GT EEs until August 2019. Identified considerations were grouped in themes using thematic content analysis. A second literature search was conducted in which we identified published evaluations. The EE quality of reporting was assessed using Consolidated Health Economic Evaluation Reporting Standards.

RESULTS

The first literature search yielded 13 articles discussing methodological considerations. The second search provided 12 EEs. Considerations identified were payment models, definition of perspectives, addressing uncertainty, data extrapolation, discount rates, novel value elements, and use of indirect and surrogate endpoints. All EEs scored satisfactory to good according to Consolidated Health Economic Evaluation Reporting Standards. Regarding methodological application, we found 1 methodological element (payment models) was applied in 2 base cases. Scenarios explored alternative perspectives, survival assumptions, and extrapolation methods in 10 EEs.

CONCLUSIONS

Although EE quality of reporting was considered good, their informativeness for health technology assessment and decision makers seemed limited owing to many uncertainties. We suggest accepted EE methods can broadly be applied to GTs, but few elements may need adjustment. Further research and multi-stakeholder consensus is needed to determine appropriateness and application of individual methodological considerations. For now, we recommend including scenario analyses to explore impact of methodological choices and (clinical) uncertainties. This study contributes to better understanding of perceived appropriate evaluation of GTs and informs best modeling practices.

Lentiviral and genome-editing strategies for the treatment of β-hemoglobinopathies

β-Thalassemia and sickle cell disease (SCD) are the most prevalent monogenic diseases. These disorders are caused by quantitative or qualitative defects in the production of adult hemoglobin. Gene therapy is a potential treatment option for patients lacking an allogenic compatible hematopoietic stem cell (HSC) donor. New-generation lentiviral vectors (LVs) carrying a β-globin-like gene have revolutionized this field by allowing effective HSC transduction, with no evidence of genotoxicity to date. Several clinical trials with different types of vector are underway worldwide; the initial results are encouraging with regard to the sustained production of therapeutic hemoglobin, improved biological parameters, a lower transfusion requirement, and better quality of life. Long-term follow-up studies will confirm the safety of LV-based gene therapy. The optimization of patient conditioning, HSC harvesting, and HSC transduction has further improved the therapeutic potential of this approach. Novel LV-based strategies for reactivating endogenous fetal hemoglobin (HbF) are also promising, because elevated HbF levels can reduce the severity of both β-thalassemia and SCD. Lastly, genome-editing approaches designed to correct the disease-causing mutation or reactivate HbF are currently under investigation. Here, we discuss the clinical outcomes of current LV-based gene addition trials and the promising advantages of novel alternative therapeutic strategies.

Editing a γ-globin repressor binding site restores fetal hemoglobin synthesis and corrects the sickle cell disease phenotype

Sickle cell disease (SCD) is caused by a single amino acid change in the adult hemoglobin (Hb) β chain that causes Hb polymerization and red blood cell (RBC) sickling. The co-inheritance of mutations causing fetal γ-globin production in adult life hereditary persistence of fetal Hb (HPFH) reduces the clinical severity of SCD. HPFH mutations in the HBG γ-globin promoters disrupt binding sites for the repressors BCL11A and LRF. We used CRISPR-Cas9 to mimic HPFH mutations in the HBG promoters by generating insertions and deletions, leading to disruption of known and putative repressor binding sites. Editing of the LRF-binding site in patient-derived hematopoietic stem/progenitor cells (HSPCs) resulted in γ-globin derepression and correction of the sickling phenotype. Xenotransplantation of HSPCs treated with gRNAs targeting the LRF-binding site showed a high editing efficiency in repopulating HSPCs. This study identifies the LRF-binding site as a potent target for genome-editing treatment of SCD.

In-Vivo Gene Therapy with Foamy Virus Vectors

Foamy viruses (FVs) are nonpathogenic retroviruses that infect various animals including bovines, felines, nonhuman primates (NHPs), and can be transmitted to humans through zoonotic infection. Due to their non-pathogenic nature, broad tissue tropism and relatively safe integration profile, FVs have been engineered as novel vectors (foamy virus vector, FVV) for stable gene transfer into different cells and tissues. FVVs have emerged as an alternative platform to contemporary viral vectors (e.g., adeno associated and lentiviral vectors) for experimental and therapeutic gene therapy of a variety of monogenetic diseases. Some of the important features of FVVs include the ability to efficiently transduce hematopoietic stem and progenitor cells (HSPCs) from humans, NHPs, canines and rodents. We have successfully used FVV for proof of concept studies to demonstrate safety and efficacy following in-vivo delivery in large animal models. In this review, we will comprehensively discuss FVV based in-vivo gene therapy approaches established in the X-linked severe combined immunodeficiency (SCID-X1) canine model.