Current animal models of hemophilia: the state of the art

A Novel Murine Model Enabling rAAV8-PC Gene Therapy for Severe Protein C Deficiency

Severe protein C deficiency (SPCD) is a rare inherited thrombotic disease associated with high morbidity and mortality. In the current study, we established a viable murine model of SPCD, enabling preclinical gene therapy studies. By creating SPCD mice with severe hemophilia A (PROC-/-/F8-), the multi-month survival of SPCD mice enabled the exploration of recombinant adeno-associated viral vector-PC (rAAV8-PC) gene therapy (GT). rAAV8- PC (1012 vg/kg of AAV8-PC) was injected via the tail vein into 6-8-week-old PROC-/-/F8- mice. Their plasma PC antigen levels (median of 714 ng/mL, range 166-2488 ng/mL) and activity (303.5 ± 59%) significantly increased to the normal range after GT compared to untreated control animals. PC's presence in the liver after GT was also confirmed by immunofluorescence staining. Our translational research results provide the first proof of concept that an infusion of rAAV8-PC increases PC antigen and activity in mice and may contribute to future GT in SPCD. Further basic research of SPCD mice with prolonged survival due to the rebalancing of this disorder using severe hemophilia A may provide essential data regarding PC's contribution to specific tissues' development, local PC generation, and its regulation in inflammatory conditions.

Recapitulating the immune system of hemophilia A patients with inhibitors using immunodeficient mice

BACKGROUND AND AIM

Treating hemophilia A patients who develop inhibitors remains a clinical challenge. A mouse model of hemophilia A can be used to test the efficacy of strategies for inhibitor suppression, but the differences in the immune systems of mice and humans limit its utility. To address this shortcoming, we established a humanized NOD/SCID-IL2rγnull hemophilia A (hu-NSG-HA) mouse model with a severely deficient mouse immune system presenting a patient's adapted immune cells.

METHODS AND RESULTS

Through intrasplenic injection with patient inhibitor-positive peripheral blood mononuclear cells (PBMCs), utilizing an adeno-associated viral delivery system expressing human BLyS, and regular FVIII challenge, human C19+ B cells were expanded in vivo to secrete anti-FVIII antibodies. Both the inhibitor and the human anti-FVIII IgG, including the predominant subclasses (IgG1 and IgG4) present in the majority of inhibitor patients, were detected in the mouse model. We further segregated and expanded the different clones of human anti-FVIII-secreting cells through subsequent transplantation of splenocytes derived from hu-NSG-HA mice into another NSG-HA mouse. By transplanting a patient's PBMCs into the NSG-HA mouse model, we demonstrated the success of reintroducing a strong anti-FVIII immune response for a short period in mice with the immune systems of inhibitor-positive patients.

CONCLUSION

Our results demonstrate a potential tool for directly obtaining functional human-derived antigen-specific antibodies and antibody-secreting cells, which may have therapeutic value for testing patient-specific immune responses to treatment options to assist in clinical decisions.

Generation of Mouse Model of Hemophilia A by Introducing Novel Mutations, Using CRISPR/Nickase Gene Targeting System

Developing mouse models of hemophilia A has been shown to facilitate in vivo studies to explore the probable mechanism(s) underlying the disease and to examine the efficiency of the relevant potential therapeutics. This study aimed to knockout (KO) the coagulation factor viii (fviii) gene in NMRI mice, using CRISPR/Cas9 (D10A/nickase) system, to generate a mouse model of hemophilia A. Two single guide RNAs (sgRNAs), designed from two distinct regions on NMRI mouse FVIII (mFVIII) exon 3, were designed and inserted in the pX335 vector, expressing both sgRNAs and nickase. The recombinant construct was delivered into mouse zygotes and implanted into the pseudopregnant female mice's uterus. Mutant mice were identified by genotyping, genomic sequencing, and mFVIII activity assessment. Two separate lines of hemophilia A were obtained through interbreeding the offspring of the female mice receiving potential CRISPR-Cas9-edited zygotes. Genomic DNA analysis revealed disruptions of the mfviii gene reading frame through a 22-bp deletion and a 23-bp insertion in two separate founder mice. The founder mice showed all the clinical signs of hemophilia A including; excessive bleeding after injuries, and spontaneous bleeding in joints and other organs. Coagulation test data showed that mFVIII coagulation activity was significantly diminished in the mFVIII knockout (FVIIIKO) mice compared to normal mice. The CRISPR/nickase system was successfully applied to generate mouse lines with the knockout fviii gene. The two novel FVIIIKO mice demonstrated all clinical symptoms of hemophilia A, which could be successfully inherited. Therefore, both of the developed FVIIIKO mouse lines are eligible for being considered as proper mouse models of hemophilia A for in vivo therapeutic studies.

Gene Therapy Approaches for the Treatment of Hemophilia B

In contrast to the standard enzyme-replacement therapy, administered from once per 7-14 days to 2-3 times a week in patients with severe hemophilia B, as a result of a single injection, gene therapy can restore F9 gene expression and maintain it for a prolonged time. In clinical research, the approach of delivering a functional copy of a gene using adeno-associated viral (AAV) vectors is widely used. The scientific community is actively researching possible modifications to improve delivery efficiency and expression. In preclinical studies, the possibility of genome editing using CRISPR/Cas9 technology for the treatment of hemophilia B is also being actively studied.

Gene therapy in haemophilia: literature review and regional perspectives for Turkey

Haemophilia is an X-linked lifelong congenital bleeding disorder that is caused by insufficient levels of factor VIII (FVIII; haemophilia A) or factor IX (FIX; haemophilia B) and characterized by spontaneous and trauma-related bleeding episodes. The cornerstone of the treatment, factor replacement, constitutes several difficulties, including frequent injections due to the short half-life of recombinant factors, intravenous administration and the risk of inhibitor development. While extended half-life factors and subcutaneous novel molecules enhanced the quality of life, initial successes with gene therapy offer a significant hope for cure. Although adeno-associated viral (AAV)-based gene therapy is one of the most emerging approaches for treatment of haemophilia, there are still challenges in vector immunogenicity, potency and efficacy, genotoxicity and persistence. As the approval for the first gene therapy product is coming closer, eligibility criteria for patient selection, multidisciplinary approach for optimal delivery and follow-up and development of new pricing policies and reimbursement models should be concerned. Therefore, this review addresses the unmet needs of current haemophilia treatment and explains the rationale and principles of gene therapy. Limitations and challenges are discussed from a global and national perspective and recommendations are provided to adopt the gene therapies faster and more sufficient for the haemophilia patients in developing countries like Turkey.

Using analogue data to substantiate long-term durability of gene therapies: a narrative review

The number of gene therapies in clinical trials and moving toward licensure is increasing. Most gene therapies are designed to achieve long-term effects, but at licensure the data to support claims of long-term durability are often limited, as long-term monitoring studies are often part of post-approval commitments by companies. Health technology assessors must therefore assess the potential for the long-term durability of a product and the potential cost-effectiveness based on the data available. The authors explored the benefit of strengthening the ability to infer durability of effect using analogue category data. Different analogue categories were assessed for the potential to substantiate claims of sustainability of effect for gene therapies by leveraging biological plausibility arguments. The authors propose a pathway for identifying potential analogues. Such a pathway should help establish plausible or theoretical long-term outcomes that can be considered in value assessments of gene therapies.

Standardization of Coagulation Factor V Reference Intervals, Prothrombin Time, and Activated Partial Thromboplastin Time in Mice for Use in Factor V Deficiency Pathological Models

Factor V together with activated factor X forms the prothrombinase complex, which transforms prothrombin into thrombin. The Mus musculus species is characterized by very high levels of this factor and short clotting times, which hinders accurate measurements. For that reason, a detailed characterization of such parameters is indispensable. A method was designed as part of this study to provide an accurate determination and standardization of factor V levels, prothrombin time and activated partial thromboplastin time in Mus musculus. Those parameters were evaluated in a sample of 66 healthy animals using a semi-automated coagulometer and human diagnostic reagents in an attempt to determine the most appropriate time of day for the extractions. A mouse-based protocol was designed, capable of making corrections to the samples at dilutions of 1:100 for factor V and at of 1:3 for prothrombin time. The goal was to smoothen the calibration curves, which often present with steep slopes and narrow measurement ranges between one calibration point and another. It was found that the most stable period for blood sample extraction was that comprised between the first 6 h of light. No clinical differences were observed between the sexes and reference intervals were established for factor V (95.80% ± 18.14; 25.21 s ± 1.34), prothrombin time (104.31% ± 14.52; 16.85 s ± 1.32) and activated partial thromboplastin time (32.86 s ± 3.01). The results obtained are applicable to human or veterinary biomedical research, to transfusional medicine or to pathological models for diseases such as factor V deficiency.

Development of alternative gene transfer techniques for ex vivo and in vivo gene therapy in a canine model

INTRODUCTION

Gene therapy have recently attracted much attention as a curative therapeutic option for inherited single gene disorders such as hemophilia. Hemophilia is a hereditary bleeding disorder caused by the deficiency of clotting activity of factor VIII (FVIII) or factor IX (FIX), and gene therapy for hemophilia using viral vector have been vigorously investigated worldwide. Toward further advancement of gene therapy for hemophilia, we have previously developed and validated the efficacy of novel two types of gene transfer technologies using a mouse model of hemophilia A. Here we investigated the efficacy and safety of the technologies in canine model. Especially, validations of technical procedures of the gene transfers for dogs were focused.

METHODS

Green fluorescence protein (GFP) gene were transduced into normal beagle dogs by ex vivo and in vivo gene transfer techniques. For ex vivo gene transfer, blood outgrowth endothelial cells (BOECs) derived from peripheral blood of normal dogs were transduced with GFP gene using lentivirus vector, propagated, fabricated as cell sheets, then implanted onto the omentum of the same dogs. For in vivo gene transfer, normal dogs were subjected to GFP gene transduction with non-viral piggyBac vector by liver-targeted hydrodynamic injections.

RESULTS

No major adverse events were observed during the gene transfers in both gene transfer systems. As for ex vivo gene transfer, histological findings from the omental biopsy performed 4 weeks after implantation revealed the tube formation by implanted GFP-positive BOECs in the sub-adipose tissue layer without any inflammatory findings, and the detected GFP signals were maintained over 6 months. Regarding in vivo gene transfer, analyses of liver biopsy samples revealed more than 90% of liver cells were positive for GFP signals in the injected liver lobes 1 week after gene transfers, then the signals gradually declined overtime.

CONCLUSIONS

Two types of gene transfer techniques were successfully applied to a canine model, and the transduced gene expressions persisted for a long term. Toward clinical application for hemophilia patients, practical assessments of therapeutic efficacy of these techniques will need to be performed using a dog model of hemophilia and FVIII (or FIX) gene.

Novel Severe Hemophilia A Mouse Model with Factor VIII Intron 22 Inversion

Simple Summary

Recently, innovative gene therapy has been developing toward functional restoration by gain of function or gene correction. Hemophilia is a representative genetic disorder with many human patients and is considered a candidate disease for gene therapy. The most frequent severe hemophilia A is caused by inversion mediated structural variation of the human F8 gene. Nevertheless, a mouse model with F8 intron 22 inversion is not developed yet. This study presents a novel hemophilia A mouse model with 319 kb inversion and severe coagulation disorder and could be utilized in future gene correction preclinical trials.

Abstract

Hemophilia A (HA) is an X-linked recessive blood coagulation disorder, and approximately 50% of severe HA patients are caused by F8 intron 22 inversion (F8I22I). However, the F8I22I mouse model has not been developed despite being a necessary model to challenge pre-clinical study. A mouse model similar to human F8I22I was developed through consequent inversion by CRISPR/Cas9-based dual double-stranded breakage (DSB) formation, and clinical symptoms of severe hemophilia were confirmed. The F8I22I mouse showed inversion of a 391 kb segment and truncation of mRNA transcription at the F8 gene. Furthermore, the F8I22I mouse showed a deficiency of FVIII activity (10.9 vs. 0 ng/mL in WT and F8I22I, p < 0.0001) and severe coagulation disorder phenotype in the activated partial thromboplastin time (38 vs. 480 s, p < 0.0001), in vivo bleeding test (blood loss/body weight; 0.4 vs. 2.1%, p < 0.0001), and calibrated automated thrombogram assays (Thrombin generation peak, 183 vs. 21.5 nM, p = 0.0012). Moreover, histological changes related to spontaneous bleeding were observed in the liver, spleen, and lungs. We present a novel HA mouse model mimicking human F8I22I. With a structural similarity with human F8I22I, the F8I22I mouse model will be applicable to the evaluation of general hemophilia drugs and the development of gene-editing-based therapy research.

Significant differences in single-platelet biophysics exist across species but attenuate during clot formation

Human, canine, ovine, and porcine platelets exhibit disparate biophysical signatures, whereas human and murine platelets are similar. Multiple biophysical parameters integrate during clot formation, measured by bulk clot contraction, and attenuate biophysical differences.

Characterisation and application of recombinant FVIII-neutralising antibodies from haemophilia A inhibitor patients

The development of anti-drug antibodies (ADAs) is a serious outcome of treatment strategies involving biological medicines. Coagulation factor VIII (FVIII) is used to treat haemophilia A patients, but its immunogenicity precludes a third of severe haemophiliac patients from receiving this treatment. The availability of patient-derived anti-drug antibodies can help us better understand drug immunogenicity and identify ways to overcome it. Thus, there were two aims to this work: (i) to develop and characterise a panel of recombinant, patient-derived, monoclonal antibodies covering a range of FVIII epitopes with varying potencies, kinetics and mechanism of action, and (ii) to demonstrate their applicability to assay development, evaluation of FVIII molecules and basic research. For the first objective we used recombinant antibodies to develop a rapid, sensitive, flexible and reproducible ex vivo assay that recapitulates inhibitor patient blood using blood from healthy volunteers. We also demonstrate how the panel can provide important information about the efficacy of FVIII products and reagents without the need for patient or animal material. These materials can be used as experimental exemplars or controls, as well as tools for rational, hypothesis-driven research and assay development in relation to FVIII immunogenicity and FVIII-related products.

Preclinical evaluation of a next-generation, subcutaneously administered, coagulation factor IX variant, dalcinonacog alfa

Introduction

The rapid clearance of factor IX necessitates frequent intravenous administrations to achieve effective prophylaxis for patients with hemophilia B. Subcutaneous administration has historically been limited by low bioavailability and potency. Dalcinonacog alfa was developed using a rational design approach to be a subcutaneously administered, next-generation coagulation prophylactic factor IX therapy.

Aim

This study aimed to investigate the pharmacokinetic, pharmacodynamic, and safety profile of dalcinonacog alfa administered subcutaneously in hemophilia B dogs.

Methods

Two hemophilia B dogs received single-dose daily subcutaneous dalcinonacog alfa injections for six days. Factor IX antigen and activity, whole blood clotting time, and activated partial thromboplastin time were measured at various time points. Additionally, safety assessments for clinical adverse events and evaluations of laboratory test results were conducted.

Results

There was an increase in plasma factor IX antigen with daily subcutaneous dalcinonacog alfa. Bioavailability of subcutaneous dalcinonacog alfa was 10.3% in hemophilia B dogs. Daily subcutaneous dosing of dalcinonacog alfa demonstrated the effects of bioavailability, time to maximal concentration, and half-life by reaching a steady-state activity sufficient to correct severe hemophilia to normal, after four days.

Conclusion

The increased potency of dalcinonacog alfa facilitated the initiation and completion of the Phase 1/2 subcutaneous dosing study in individuals with hemophilia B.

A Foundational Study for Normal F8-Containing Mouse Models for the miRNA Regulation of Hemophilia A: Identification and Analysis of Mouse miRNAs that Downregulate the Murine F8 Gene

Hemophilia A (HA) is associated with defects in the F8 gene, encoding coagulation factor VIII (FVIII). Our previous studies show that F8-targeting micro RNAs (miRNAs), a group of small RNAs involved in gene regulation, can downregulate F8 expression causing HA in individuals with normal F8-genotypes and increased HA severity in patients with mutations in F8. Understanding the mechanistic underpinnings of human genetic diseases caused or modulated by miRNAs require a small animal model, such as a mouse model. Here, we report a foundational study to develop such a model system. We identified the mouse 3'untranslated region (3'UTR) on murine F8-mRNA (muF8-mRNA) that can bind to murine miRNAs. We then selected three miRNAs for evaluation: miR-208a, miR-351 and miR-125a. We first demonstrate that these three miRNAs directly target the 3'UTR of muF8-mRNA and reduce the expression of a reporter gene (luciferase) mRNA fused to the muF8-3' UTR in mammalian cells. Furthermore, in mouse cells that endogenously express the F8 gene and produce FVIII protein, the ectopic expression of these miRNAs downregulated F8-mRNA and FVIII protein. These results provide proof-of-concept and reagents as a foundation for using a normal F8-containing mouse as a model for the miRNA regulation of normal F8 in causing or aggravating the genetic disease HA.

Mouse models of hemostasis

Hemostasis is the normal process that produces a blood clot at a site of vascular injury. Mice are widely used to study hemostasis and abnormalities of blood coagulation because their hemostatic system is similar in most respects to that of humans, and their genomes can be easily manipulated to create models of inherited human coagulation disorders. Two of the most widely used techniques for assessing hemostasis in mice are the tail bleeding time (TBT) and saphenous vein bleeding (SVB) models. Here we discuss the use of these methods in the evaluation of hemostasis, and the advantages and limits of using mice as surrogates for studying hemostasis in humans.

The Immune Response to the fVIII Gene Therapy in Preclinical Models

Neutralizing antibodies to factor VIII (fVIII), referred to as "inhibitors," remain the most challenging complication post-fVIII replacement therapy. Preclinical development of novel fVIII products involves studies incorporating hemophilia A (HA) and wild-type animal models. Though immunogenicity is a critical aspect of preclinical pharmacology studies, gene therapy studies tend to focus on fVIII expression levels without major consideration for immunogenicity. Therefore, little clarity exists on whether preclinical testing can be predictive of clinical immunogenicity risk. Despite this, but perhaps due to the potential for transformative benefits, clinical gene therapy trials have progressed rapidly. In more than two decades, no inhibitors have been observed. However, all trials are conducted in previously treated patients without a history of inhibitors. The current review thus focuses on our understanding of preclinical immunogenicity for HA gene therapy candidates and the potential indication for inhibitor treatment, with a focus on product- and platform-specific determinants, including fVIII transgene sequence composition and tissue/vector biodistribution. Currently, the two leading clinical gene therapy vectors are adeno-associated viral (AAV) and lentiviral (LV) vectors. For HA applications, AAV vectors are liver-tropic and employ synthetic, high-expressing, liver-specific promoters. Factors including vector serotype and biodistribution, transcriptional regulatory elements, transgene sequence, dosing, liver immunoprivilege, and host immune status may contribute to tipping the scale between immunogenicity and tolerance. Many of these factors can also be important in delivery of LV-fVIII gene therapy, especially when delivered intravenously for liver-directed fVIII expression. However, ex vivo LV-fVIII targeting and transplantation of hematopoietic stem and progenitor cells (HSPC) has been demonstrated to achieve durable and curative fVIII production without inhibitor development in preclinical models. A critical variable appears to be pre-transplantation conditioning regimens that suppress and/or ablate T cells. Additionally, we and others have demonstrated the potential of LV-fVIII HSPC and liver-directed AAV-fVIII gene therapy to eradicate pre-existing inhibitors in murine and canine models of HA, respectively. Future preclinical studies will be essential to elucidate immune mechanism(s) at play in the context of gene therapy for HA, as well as strategies for preventing adverse immune responses and promoting immune tolerance even in the setting of pre-existing inhibitors.

Escape or Fight: Inhibitors in Hemophilia A

Replacement therapy with coagulation factor VIII (FVIII) represents the current clinical treatment for patients affected by hemophilia A (HA). This treatment while effective is, however, hampered by the formation of antibodies which inhibit the activity of infused FVIII in up to 30% of treated patients. Immune tolerance induction (ITI) protocols, which envisage frequent infusions of high doses of FVIII to confront this side effect, dramatically increase the already high costs associated to a patient's therapy and are not always effective in all treated patients. Therefore, there are clear unmet needs that must be addressed in order to improve the outcome of these treatments for HA patients. Taking advantage of preclinical mouse models of hemophilia, several strategies have been proposed in recent years to prevent inhibitor formation and eradicate the pre-existing immunity to FVIII inhibitor positive patients. Herein, we will review some of the most promising strategies developed to avoid and eradicate inhibitors, including the use of immunomodulatory drugs or molecules, oral or transplacental delivery as well as cell and gene therapy approaches. The goal is to improve and potentiate the current ITI protocols and eventually make them obsolete.

Urinary Stem Cells as Tools to Study Genetic Disease: Overview of the Literature

Urine specimens represent a novel and non-invasive approach to isolate patient-specific stem cells by easy and low-cost procedures, replacing the traditional sources (muscle/skin biopsy/adipose tissue) obtained with invasive and time-consuming methods. Urine-derived stem cells (USCs) can be used in a broad field of applications, such as regenerative medicine, cell therapy, diagnostic testing, disease modelling and drug screening. USCs are a good source of cells for generating induced pluripotent stem cells (iPSCs) and importantly, they can also be directly converted into specific cell lines. In this review, we show the features of USCs and their use as a promising in vitro model to study genetic diseases.

CRISPR to fix bad blood: a new tool in basic and clinical hematology

Advances in genome engineering in the last decade, particularly in the development of programmable nucleases, have made it possible to edit the genomes of most cell types precisely and efficiently. Chief among these advances, the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system is a novel, versatile and easy-to-use tool to edit genomes irrespective of their complexity, with multiple and broad applications in biomedicine. In this review, we focus on the use of CRISPR/Cas9 genome editing in the context of hematologic diseases and appraise the major achievements and challenges in this rapidly moving field to gain a clearer perspective on the potential of this technology to move from the laboratory to the clinic. Accordingly, we discuss data from studies editing hematopoietic cells to understand and model blood diseases, and to develop novel therapies for hematologic malignancies. We provide an overview of the applications of gene editing in experimental, preclinical and clinical hematology including interrogation of gene function, target identification and drug discovery and chimeric antigen receptor T-cell engineering. We also highlight current limitations of CRISPR/Cas9 and the possible strategies to overcome them. Finally, we consider what advances in CRISPR/Cas9 are needed to move the hematology field forward.

Gene Therapy for Hemophilia

The X-linked bleeding disorder hemophilia causes frequent and exaggerated bleeding that can be life-threatening if untreated. Conventional therapy requires frequent intravenous infusions of the missing coagulation protein (factor VIII [FVIII] for hemophilia A and factor IX [FIX] for hemophilia B). However, a lasting cure through gene therapy has long been sought. After a series of successes in small and large animal models, this goal has finally been achieved in humans by in vivo gene transfer to the liver using adeno-associated viral (AAV) vectors. In fact, multiple recent clinical trials have shown therapeutic, and in some cases curative, expression. At the same time, cellular immune responses against the virus have emerged as an obstacle in humans, potentially resulting in loss of expression. Transient immune suppression protocols have been developed to blunt these responses. Here, we provide an overview of the clinical development of AAV gene transfer for hemophilia, as well as an outlook on future directions.