Engineering Factor Viii for Hemophilia Gene Therapy

Advances in biopharmaceutical products for hemophilia

Hemophilia is caused by the deficiency of clotting factors due to a single genetic abnormality. Replacement therapies have evolved from plasma-derived to recombinant coagulation factor concentrates but continue to have certain limitations. Monoclonal antibodies are clinical prophylactic treatment options unaffected by inhibitors and have better compliance than coagulation factor concentrates for patients with hemophilia. Gene therapy is a breakthrough in hemophilia treatment, as it drives the hepatic expression of factor VIII or factor IX and requires only a single administration to enable long-term replacement treatment in adult patients. Furthermore, biopharmaceutical products that target new pathways unaffected by inhibitors, including tissue factor pathway inhibitors, activated protein C, and antithrombin, as well as pharmaceutical technology advances to reduce dosing frequency, have demonstrated promising clinical results. This review provides a comprehensive overview of these biopharmaceutical products and explores the future of hemophilia treatment.

Evaluating Gene Therapy as a Potential Paradigm Shift in Treating Severe Hemophilia

Hemophilia is characterized by a deficiency in coagulation factors VIII or IX. The general standard of care for severe hemophilia is frequent intravenous recombinant or plasma-derived factor replacement to prevent bleeding. While this treatment is effective in preventing bleeding, frequent infusions are burdensome for patients. Nonadherence to the therapeutic regimen leaves people with hemophilia at risk for spontaneous and traumatic bleeds into joints as well as life-threatening bleeds such as intracranial hemorrhage. The chronicity of the disorder often leads to the formation of target joints, causing long-term pain and impairing mobility. As a monogenic disorder with well-understood genetics, hemophilia is an ideal disorder for implementing innovations in gene therapies. Indeed, recent approvals of two gene therapy products have the potential to shift the hemophilia treatment paradigm. Valoctocogene roxaparvovec and etranacogene dezaparvovec-drlb are gene therapies for hemophilia A and B, respectively. These therapies, given as a single intravenous infusion, may improve patients' quality of life, decreasing treatment burden and resulting in factor expression that virtually eliminates the need for factor replacement. Since both treatments involve viral vectors targeted to the liver, short- and long-term safety and efficacy monitoring involves monitoring liver enzymes to track liver health. Long-term monitoring of efficacy, durability of gene expression, and safety are ongoing. Gene therapy presents a promising new therapeutic option for patients with hemophilia and warrants continued innovation and investigation.

Development of an AAV DNA-based synthetic vector for the potential gene therapy of hemophilia in children

Recombinant AAV serotype vectors and their variants have been or are currently being used for gene therapy for hemophilia in several phase I/II/III clinical trials in humans. However, none of these trials have included children with hemophilia since the traditional liver-directed AAV gene therapy will not work in these patients because of the following reasons: (i) Up until age 10–12, the liver is still growing and dividing, and with every cell division, the AAV vector genomes will be diluted out due to their episomal nature; and (ii) Repeated gene delivery will be needed, but repeat dosing, even with an ideal AAV vector is not an option because of pre-existing antibodies to AAV vectors following the first administration. Here we describe the development of an optimized human Factor IX (hF.IX) gene expression cassette under the control of a human liver-specific transthyretin promoter covalently flanked by AAV inverted terminal repeats (ITRs) with no open ends (optNE-TTR-hF.IX), which mediated ~sixfold higher hF.IX levels than that from a linear TTR-hF.IX DNA construct in human hepatoma cells up to four-weeks post-transfection. In future studies, encapsidation of the optNE-TTR-hF.IX DNA in liver-targeted synthetic liposomes, may provide a viable approach for the potential gene therapy for hemophilia in children.

Minimal Essential Human Factor VIII Alterations Enhance Secretion and Gene Therapy Efficiency

One important limitation for achieving therapeutic expression of human factor VIII (FVIII) in hemophilia A gene therapy is inefficient secretion of the FVIII protein. Substitution of five amino acids in the A1 domain of human FVIII with the corresponding porcine FVIII residues generated a secretion-enhanced human FVIII variant termed B-domain-deleted (BDD)-FVIII-X5 that resulted in 8-fold higher FVIII activity levels in the supernatant of an in vitro cell-based assay system than seen with unmodified human BDD-FVIII. Analysis of purified recombinant BDD-FVIII-X5 and BDD-FVIII revealed similar specific activities for both proteins, indicating that the effect of the X5 alteration is confined to increased FVIII secretion. Intravenous delivery in FVIII-deficient mice of liver-targeted adeno-associated virus (AAV) vectors designed to express BDD-FVIII-X5 or BDD-FVIII achieved substantially higher plasma FVIII activity levels for BDD-FVIII-X5, even when highly efficient codon-optimized F8 nucleotide sequences were employed. A comprehensive immunogenicity assessment using in vitro stimulation assays and various in vivo preclinical models of hemophilia A demonstrated that the BDD-FVIII-X5 variant does not exhibit an increased immunogenicity risk compared to BDD-FVIII. In conclusion, BDD-FVIII-X5 is an effective FVIII variant molecule that can be further developed for use in gene- and protein-based therapeutics for patients with hemophilia A.

Identification of Key Coagulation Activity Determining Elements in Canine Factor VIII

It is well known that canine factor VIII (cFVIII) has a higher specific activity than does human FVIII (hFVIII), and it has been previously demonstrated that cFVIII light chain is able to enhance hFVIII activity. The goal of this study was to first determine which amino acids in cFVIII light chain were responsible for enhancing hFVIII activity, and second to use these amino acids to develop a hFVIII variant with enhanced functional activity. We systemically screened segments of cFVIII light chain by testing an array of human-canine light chain hybrids and found that canine amino acids 1857-2147 were key to this enhancement. Each canine amino acid within this span was screened individually using a negative selection method, which led to the identification of 12 aa (JF12) in the FVIII light chain that could enhance activity. Substitution of the corresponding 12 aa into hFVIII (hFVIIIJF12BDD) elevated the specific activity profile in vitro. Furthermore, hFVIIIJF12BDD expressed an in vivo-displayed increased coagulation activity compared to wild-type, while maintaining normal secretion efficiency. In conclusion, we identified the amino acids in cFVIII that are the key determinants for higher specific activity and may be the basis for future development of therapeutic treatments for hemophilia A.

Plant cell-made protein antigens for induction of Oral tolerance

The gut associated lymphoid tissue has effective mechanisms in place to maintain tolerance to food antigens. These can be exploited to induce antigen-specific tolerance for the prevention and treatment of autoimmune diseases and severe allergies and to prevent serious immune responses in protein replacement therapies for genetic diseases. An oral tolerance approach for the prevention of peanut allergy in infants proved highly efficacious and advances in treatment of peanut allergy have brought forth an oral immunotherapy drug that is currently awaiting FDA approval. Several other protein antigens made in plant cells are in clinical development. Plant cell-made proteins are protected in the stomach from acids and enzymes after their oral delivery because of bioencapsulation within plant cell wall, but are released to the immune system upon digestion by gut microbes. Utilization of fusion protein technologies facilitates their delivery to the immune system, oral tolerance induction at low antigen doses, resulting in efficient induction of FoxP3⁺ and latency-associated peptide (LAP)⁺ regulatory T cells that express immune suppressive cytokines such as IL-10. LAP and IL-10 expression represent potential biomarkers for plant-based oral tolerance. Efficacy studies in hemophilia dogs support clinical development of oral delivery of bioencapsulated antigens to prevent anti-drug antibody formation. Production of clinical grade materials in cGMP facilities, stability of antigens in lyophilized plant cells for several years when stored at ambient temperature, efficacy of oral delivery of human doses in large animal models and lack of toxicity augur well for clinical advancement of this novel drug delivery concept.

CRISPR therapeutic tools for complex genetic disorders and cancer (Review)

One of the fundamental discoveries in the field of biology is the ability to modulate the genome and to monitor the functional outputs derived from genomic alterations. In order to unravel new therapeutic options, scientists had initially focused on inducing genetic alterations in primary cells, in established cancer cell lines and mouse models using either RNA interference or cDNA overexpression or various programmable nucleases [zinc finger nucleases (ZNF), transcription activator-like effector nucleases (TALEN)]. Even though a huge volume of data was produced, its use was neither cheap nor accurate. Therefore, the clustered regularly interspaced short palindromic repeats (CRISPR) system was evidenced to be the next step in genome engineering tools. CRISPR-associated protein 9 (Cas9)-mediated genetic perturbation is simple, precise and highly efficient, empowering researchers to apply this method to immortalized cancerous cell lines, primary cells derived from mouse and human origins, xenografts, induced pluripotent stem cells, organoid cultures, as well as the generation of genetically engineered animal models. In this review, we assess the development of the CRISPR system and its therapeutic applications to a wide range of complex diseases (particularly distinct tumors), aiming at personalized therapy. Special emphasis is given to organoids and CRISPR screens in the design of innovative therapeutic approaches. Overall, the CRISPR system is regarded as an eminent genome engineering tool in therapeutics. We envision a new era in cancer biology during which the CRISPR-based genome engineering toolbox will serve as the fundamental conduit between the bench and the bedside; nonetheless, certain obstacles need to be addressed, such as the eradication of side-effects, maximization of efficiency, the assurance of delivery and the elimination of immunogenicity.

Cornerstones of CRISPR-Cas in drug discovery and therapy

The recent development of CRISPR-Cas systems as easily accessible and programmable tools for genome editing and regulation is spurring a revolution in biology. Paired with the rapid expansion of reference and personalized genomic sequence information, technologies based on CRISPR-Cas are enabling nearly unlimited genetic manipulation, even in previously difficult contexts, including human cells. Although much attention has focused on the potential of CRISPR-Cas to cure Mendelian diseases, the technology also holds promise to transform the development of therapies to treat complex heritable and somatic disorders. In this Review, we discuss how CRISPR-Cas can affect the next generation of drugs by accelerating the identification and validation of high-value targets, uncovering high-confidence biomarkers and developing differentiated breakthrough therapies. We focus on the promises, pitfalls and hurdles of this revolutionary gene-editing technology, discuss key aspects of different CRISPR-Cas screening platforms and offer our perspectives on the best practices in genome engineering.

mRNA-based therapeutics--developing a new class of drugs

In vitro transcribed (IVT) mRNA has recently come into focus as a potential new drug class to deliver genetic information. Such synthetic mRNA can be engineered to transiently express proteins by structurally resembling natural mRNA. Advances in addressing the inherent challenges of this drug class, particularly related to controlling the translational efficacy and immunogenicity of the IVTmRNA, provide the basis for a broad range of potential applications. mRNA-based cancer immunotherapies and infectious disease vaccines have entered clinical development. Meanwhile, emerging novel approaches include in vivo delivery of IVT mRNA to replace or supplement proteins, IVT mRNA-based generation of pluripotent stem cells and genome engineering using IVT mRNA-encoded designer nucleases. This Review provides a comprehensive overview of the current state of mRNA-based drug technologies and their applications, and discusses the key challenges and opportunities in developing these into a new class of drugs.

Suppression of inhibitor formation against FVIII in a murine model of hemophilia A by oral delivery of antigens bioencapsulated in plant cells

Hemophilia A is the X-linked bleeding disorder caused by deficiency of coagulation factor VIII (FVIII). To address serious complications of inhibitory antibody formation in current replacement therapy, we created tobacco transplastomic lines expressing FVIII antigens, heavy chain (HC) and C2, fused with the transmucosal carrier, cholera toxin B subunit. Cholera toxin B-HC and cholera toxin B-C2 fusion proteins expressed up to 80 or 370 µg/g in fresh leaves, assembled into pentameric forms, and bound to GM1 receptors. Protection of FVIII antigen through bioencapsulation in plant cells and oral delivery to the gut immune system was confirmed by immunostaining. Feeding of HC/C2 mixture substantially suppressed T helper cell responses and inhibitor formation against FVIII in mice of 2 different strain backgrounds with hemophilia A. Prolonged oral delivery was required to control inhibitor formation long-term. Substantial reduction of inhibitor titers in preimmune mice demonstrated that the protocol could also reverse inhibitor formation. Gene expression and flow cytometry analyses showed upregulation of immune suppressive cytokines (transforming growth factor β and interleukin 10). Adoptive transfer experiments confirmed an active suppression mechanism and revealed induction of CD4(+)CD25(+) and CD4(+)CD25(-) T cells that potently suppressed anti-FVIII formation. In sum, these data support plant cell-based oral tolerance for suppression of inhibitor formation against FVIII.

In vitro and In vivo Model Systems for Hemophilia A Gene Therapy

Hemophilia A is a hereditary disorder caused by various mutations in factor VIII gene resulting in either a severe deficit or total lack of the corresponding activity. Recent success in gene therapy of a related disease, hemophilia B, gives new hope that similar success can be achieved for hemophilia A as well. To develop a gene therapy strategy for the latter, a variety of model systems are needed to evaluate molecular engineering of the factor VIII gene, vector delivery efficacy and safety-related issues. Typically, a tissue culture cell line is the most convenient way to get a preliminary glimpse of the potential of a vector delivery strategy. It is then followed by extensive testing in hemophilia A mouse and dog models. Newly developed hemophilia A sheep may provide yet another tool for evaluation of factor VIII gene delivery vectors. Hemophilia models based on other species may also be developed since hemophiliac animals have been identified or generated in rat, pig, cattle and horse. Although a genetic nonhuman primate hemophilia A model has yet to be developed, the non-genetic hemophilia A model can also be used for special purposes when specific questions need to be addressed that cannot not be answered in other model systems. Hemophilia A is caused by a functional deficiency in the factor VIII gene. This X-linked, recessive bleeding disorder affects approximately 1 in 5000 males [1–3]. Clinically, it is characterized by frequent and spontaneous joint hemorrhages, easy bruising and prolonged bleeding time. The coagulation activity of FVIII dictates severity of the clinical symptoms. Approximately 50% of all cases are classified as severe with less than 1% of normal levels of factor VIII detected [4]. This deficiency may lead to spontaneous joint hemorrhages or life-threatening bleeding. In contrast, patients with 5–30% of normal factor VIII activity exhibit mild clinical manifestations.