Molecular characterization of the immune response to factor VIII

First observation of inhibitor development against efmoroctocog alfa in France

In patients with severe haemophilia receiving clotting factor concentrates, the risk of immunisation against their usual treatment is still patent and feared. New haemophilia drug treatments with an extended half-life have become available over the past few years. The risk of inhibitor development to these new treatments is unclear. We report the case of a 51-year-old man with severe haemophilia A, who was previously treated with no history of inhibitor development. Soon after a switch in his treatment to efmoroctocog alfa he developed an inhibitor against this recombinant Fc fusion extended half-life FVIII (rFc-FVIII) product. The patient was on an on-demand treatment regimen and was treated for mucosal bleeding. The inhibitor was characterised as type I, with classical epitope mapping. The spontaneous evolution of this inhibitor was favourable, but an anamnestic response led to a switch in his treatment to emicizumab.

A close insight to factor VIII inhibitor in the congenital hemophilia A

INTRODUCTION

Hemophilia A (HA) has an X-linked pattern of inheritance and is the most common of the hemorrhagic disorders. HA is caused by a decreased or deficiency of the functional clotting factor VIII (FVIII) and effects 1 in 5000-10,000 male births. The common treatment for hemophilia is replacement therapy by plasma-derived or recombinant FVIII. Approximately 20-30% of people with a severe type of HA develop an inhibitor and this phenomenon is the main challenge in the management of these patients. Genetic factors and environmental determinants contribute to inhibitor development. Here, the roles of various genetic and environmental factors such as the type of FVIII concentrate used, the number of exposure days, and peak treatment time will be discussed in detail. It seems this information is helpful for hematologists.

AREAS COVERED

A literature review was done in January 2016 on PubMed and Scopus using the following keywords:' h(a)emophilia A & factor VIII inhibitor', 'h(a)emophilia A & factor VIII alloantibody', 'h(a)emophilia A & inhibitor'. There was no time limitation; however, there was an English language limitation placed on the articles selected. Expert commentary: Influential genetic and environmental factors in developing inhibitors have been discussed. Most of the risk factors are related to previously untreated patients with hemophili.

Non-clinical pharmacokinetics and pharmacodynamics of rVIII-SingleChain, a novel recombinant single-chain factor VIII

INTRODUCTION

rVIII-SingleChain (CSL627), a novel recombinant coagulation factor VIII (FVIII), is under investigation in a phase I/III clinical programme (AFFINITY) for the treatment of haemophilia A. Non-clinical studies were conducted to investigate the pharmacokinetic/pharmacodynamic profile of rVIII-SingleChain in comparison with full-length recombinant FVIII.

MATERIALS AND METHODS

Binding affinity of rVIII-SingleChain for von Willebrand factor was investigated by surface plasmon resonance analysis. The pharmacokinetic profile of rVIII-SingleChain was compared with a marketed full-length recombinant FVIII concentrate (Advate(®)) in haemophilia A mice, von Willebrand factor knock-out mice, Crl:CD (SD) rats, rabbits and cynomolgus monkeys. Systemic FVIII activity or antigen levels were recorded. Procoagulant activity was measured in an FeCl3-induced arterial occlusion model and by recording thrombin generation activity (ex vivo) after administration of 200-250 IU/kg rVIII-SingleChain or full-length FVIII to haemophilia A mice.

RESULTS

rVIII-SingleChain displayed a high affinity for von Willebrand factor (KD=44 pM vs. 139 pM for full-length recombinant FVIII). In all animal species tested, rVIII-SingleChain had more favourable pharmacokinetic properties than full-length recombinant FVIII: clearance was decreased and area under the curve and terminal half-life were enhanced vs. full-length recombinant FVIII, while in vivo recovery and volume of distribution were equivalent. rVIII-SingleChain showed a prolonged thrombin generation potential and prolonged procoagulant activity vs. full-length recombinant FVIII in an FeCl3-induced arterial occlusion model.

CONCLUSIONS

rVIII-SingleChain had a higher affinity for von Willebrand factor than full-length recombinant FVIII and displayed favourable pharmacokinetic/pharmacodynamic properties in non-clinical models.

Engineering Factor Viii for Hemophilia Gene Therapy

Current treatment of hemophilia A by intravenous infusion of factor VIII (fVIII) concentrates is very costly and has a potential adverse effect of developing inhibitors. Gene therapy, on the other hand, can potentially overcome these limitations associated with fVIII replacement therapy. Although hemophilia B gene therapy has achieved promising outcomes in human clinical trials, hemophilia A gene therapy lags far behind. Compared to factor IX, fVIII is a large protein which is difficult to express at sustaining therapeutic levels when delivered by either viral or non-viral vectors. To improve fVIII gene delivery, numerous strategies have been exploited to engineer the fVIII molecule and overcome the hurdles preventing long term and high level expression. Here we reviewed these strategies, and discussed their pros and cons in human gene therapy of hemophilia A.

Animal models of hemophilia

The X-linked bleeding disorder hemophilia is caused by mutations in coagulation factor VIII (hemophilia A) or factor IX (hemophilia B). Unless prophylactic treatment is provided, patients with severe disease (less than 1% clotting activity) typically experience frequent spontaneous bleeds. Current treatment is largely based on intravenous infusion of recombinant or plasma-derived coagulation factor concentrate. More effective factor products are being developed. Moreover, gene therapies for sustained correction of hemophilia are showing much promise in preclinical studies and in clinical trials. These advances in molecular medicine heavily depend on availability of well-characterized small and large animal models of hemophilia, primarily hemophilia mice and dogs. Experiments in these animals represent important early and intermediate steps of translational research aimed at development of better and safer treatments for hemophilia, such a protein and gene therapies or immune tolerance protocols. While murine models are excellent for studies of large groups of animals using genetically defined strains, canine models are important for testing scale-up and for long-term follow-up as well as for studies that require larger blood volumes.

Downregulation of CD40 signal and induction of TGF-β by phosphatidylinositol mediates reduction in immunogenicity against recombinant human Factor VIII

Factor VIII (FVIII) is an important coagulation cofactor and its deficiency causes Hemophilia A, a bleeding disorder. Replacement therapy using recombinant FVIII is currently the first line of therapy for Hemophilia A, but the development of neutralizing antibody is a major clinical complication for this therapy. Recently, it has been shown that FVIII associated with phosphatidylinositol (PI)-containing lipidic nanoparticles reduced development of neutralizing antibodies in Hemophilia A mice (Peng A, Straubinger RM, Balu-Iyer SV. 2010. AAPS J 12(3):473-481). Here, we investigated the underlying mechanism of this reduction in antibody response in culturing conditions. In vitro, PI interfered with the processing of FVIII by cultured dendritic cells (DC), resulting in a reduction in the upregulation of phenotypic costimulatory signal CD40. Furthermore, PI increased secretion of regulatory cytokines Transforming Growth Factor β1 and Interleukin 10 (IL-10) but reduced the secretion of proinflammatory cytokines IL-6 and IL-17. The data suggest that PI reduces immunogenicity of FVIII by modulating DC maturation and inducing secretion of regulatory cytokines.

Role of glycosylation in conformational stability, activity, macromolecular interaction and immunogenicity of recombinant human factor VIII

Factor VIII (FVIII) is a multi-domain glycoprotein that is an essential cofactor in the blood coagulation cascade. Its deficiency or dysfunction causes hemophilia A, a bleeding disorder. Replacement using exogenous recombinant human factor VIII (rFVIII) is the first line of therapy for hemophilia A. The role of glycosylation on the activity, stability, protein-lipid interaction, and immunogenicity of FVIII is not known. In order to investigate the role of glycosylation, a deglycosylated form of FVIII was generated by enzymatic cleavage of carbohydrate chains. The biochemical properties of fully glycosylated and completely deglycosylated forms of rFVIII (degly rFVIII) were compared using enzyme-linked immunosorbent assay, size exclusion chromatography, and clotting activity studies. The biological activity of degly FVIII decreased in comparison to the fully glycosylated protein. The ability of degly rFVIII to interact with phosphatidylserine containing membranes was partly impaired. Data suggested that glycosylation significantly influences the stability and the biologically relevant macromolecular interactions of FVIII. The effect of glycosylation on immunogenicity was investigated in a murine model of hemophilia A. Studies showed that deletion of glycosylation did not increase immunogenicity.

Passive transfer of polyethylene glycol to liposomal-recombinant human FVIII enhances its efficacy in a murine model for hemophilia A

The replacement therapy using recombinant human FVIII (rFVIII) is the first line of therapy for hemophilia A. Approximately 15-30% of the patients develop inhibitory antibodies. Recently, we reported that liposomes composed of phosphatidylserine (PS) could reduce the immunogenicity of rFVIII. However, PS containing liposomal-rFVIII is likely to reduce the systemic exposure and efficacy of FVIII due to rapid uptake of the PS containing liposomes by the reticuloendothelial system (RES). Here, we investigated whether phosphatidylserine (PS) liposomes containing Polyethylene glycol (PEG) (PEGylated), could reduce the immunogenicity of rFVIII and reverse the reduction in systemic exposure of rFVIII. Animals given PEGylated liposomal-rFVIII had lower total and inhibitory anti-rFVIII antibody titers, compared to animals treated with rFVIII alone. The mean stimulation index of CD4+ T-cells from animals given PEGylated liposomal-rFVIII also was lower than for animals that were given rFVIII alone. Pharmacokinetic studies following intravenous dosing indicated that the systemic exposure (area under the activity curve, AUAC(0-24h)) of PEGylated liposomal-rFVIII was approximately 59 IU/mL x h and significantly higher than that of non-PEGylated liposomal-rFVIII (AUAC(0-24h) approximately 36 IU/mL x h). Based on these studies, we speculate that PEGylated PS-containing liposomal rFVIII may improve efficacy of rFVIII.

Phosphatidylserine containing liposomes reduce immunogenicity of recombinant human factor VIII (rFVIII) in a murine model of hemophilia A

Factor VIII (FVIII) is a multidomain protein that is deficient in hemophilia A, a clinically important bleeding disorder. Replacement therapy using recombinant human FVIII (rFVIII) is the main therapy. However, approximately 15-30% of patients develop inhibitory antibodies that neutralize rFVIII activity. Antibodies to epitopes in C2 domain, which is involved in FVIII binding to phospholipids, are highly prevalent. Here, we investigated the effect of phosphatidylserine (PS)-containing liposomes, which bind to C2 domain with high affinity and specificity, upon the immunogenicity of rFVIII. Circular dichroism studies showed that PS-containing liposomes interfered with aggregation of rFVIII. Immunogenicity of free- versus liposomal-rFVIII was evaluated in a murine model of hemophilia A. Animals treated with s.c. injections of liposomal-rFVIII had lower total- and inhibitory titers, compared to animals treated with rFVIII alone. Antigen processing by proteolytic enzymes was reduced in the presence of liposomes. Animals treated with s.c. injections of liposomal-rFVIII showed a significant increase in rFVIII plasma concentration compared to animals that received rFVIII alone. Based on these studies, we hypothesize that specific molecular interactions between PS-containing bilayers and rFVIII may provide a basis for designing lipidic complexes that improve the stability, reduce the immunogenicity of rFVIII formulations, and permit administration by s.c. route.

O-phospho-L-serine, multi-functional excipient for B domain deleted recombinant factor VIII

Factor VIII (FVIII) is an important cofactor in the blood coagulation cascade. A deficiency or dysfunction of FVIII causes hemophilia A, a life-threatening bleeding disorder. FVIII circulates in plasma as a heterodimer comprising 6 domains (heavy chain, A1-A2-B and light chain, A3-C1-C2). Replacement therapy using FVIII is the leading therapy in the management of hemophilia A. However, approximately 15% to 30% of patients develop inhibitory antibodies that neutralize the activity of the protein. Neutralizing antibodies to epitopes in the lipid binding region of FVIII are commonly identified in patients' plasma. In this report, we investigated the effect of O-phospho-L-serine (OPLS), which binds to the lipid binding region, on the immunogenicity of B domain deleted recombinant factor VIII (BDDrFVIII). Sandwich enzyme-linked immunosorbent assay (ELISA) studies showed that OPLS specifically bind to the lipid binding region, localized in the C2 domain of the coagulation factor. Size exclusion chromatography and fluorescence anisotropy studies showed that OPLS interfered with the aggregation of BDDrFVIII. Immunogenicity of free- vs BDDrFVIII-OPLS complex was evaluated in a murine model of hemophilia A. Animals administered subcutaneous (sc) injections of BDDrFVIII-OPLS had lower neutralizing titers compared with animals treated with BDDrFVIII alone. Based on these studies, we hypothesize that specific molecular interactions between OPLS and BDDrFVIII may improve the stability and reduce the immunogenicity of BDDrFVIII formulations.

Lipid binding region (2303-2332) is involved in aggregation of recombinant human FVIII (rFVIII)

Factor VIII (FVIII) is a multi-domain protein that is important in the clotting cascade. Its deficiency causes Hemophilia A, a bleeding disorder. The unfolding of protein domains can lead to physical instability such as aggregation, and hinder their use in replacement therapy. It has been shown that the aggregation of rFVIIII is initiated by small fluctuations in the protein's tertiary structure (Grillo et al., 2001, Biochemistry 40:586-595). We have investigated the domain(s) involved in the initiation of aggregation using circular dichroism (CD), size exclusion chromatography (SEC), fluorescence anisotropy, domain specific antibody binding, and clotting activity studies. The studies indicated that aggregation may be initiated as a result of conformational change in the C2 domain encompassing the lipid-binding region (2303-2332). The presence of O-phospho-L-Serine (OPLS), which binds to the lipid-binding region of FVIII, prevented aggregation of the protein.

Identification of a novel immunodominant cytotoxic T lymphocyte epitope derived from human factor VIII in a murine model of hemophilia A

Gene therapy of hemophilia A could be complicated by the development of immune responses against the vector as well as the Factor VIII (FVIII) transgene. Previous efforts have been focused on identifying FVIII inhibitor antibody epitopes, whereas the cytotoxic T lymphocyte (CTL) epitopes have not been characterized. CTL would kill cells expressing such epitopes and thus limit the efficacy of gene therapy. To investigate CTL responses against human FVIII in a mouse model of hemophilia A, a computer algorithm program (BIMAS) was employed to predict CTL epitopes of human FVIII. The potential binding of these predicted peptides to MHC class I K(b) was evaluated in a TAP-deficient cell line. When recombinant vaccinia virus expressing B domain-deleted human FVIII (vv-FVIII) was used to immunize E16 hemophilia A mice, a specific CTL response against FVIII152-159 was generated. In contrast, a CTL response to four other FVIII peptides was not detected. Therefore, FVIII152-159 represents a dominant CTL epitope. Identification of this epitope raises the possibility that CTL response to FVIII gene-transduced cells can be diminished by deliberatively mutating the dominant CTL epitope while retaining the biologic function of FVIII for hemophilia A gene therapy.

Immunoadsorption of factor VIII inhibitors

PURPOSE OF REVIEW

Extracorporeal immunoadsorption is being increasingly applied in a variety of disorders. This approach is particularly suited to removal of antibodies or inhibitors to coagulation factor VIII and may be particularly useful before the administration of large amounts of expensive replacement or bypass therapy for patients with hemophilia who are bleeding, or patients undergoing immune tolerance therapy.

RECENT FINDINGS

In patients with inhibitors to factor VIII, several types of immunoadsorption therapy have been used, although reports are mainly anecdotal, consisting of relatively small numbers of persons. Nonetheless, the findings suggest that immunoadsorption may be clinically effective and cost-effective and should be considered early in the treatment of appropriate patients. New immunoadsorption technologies are being described for a variety of disorders, including hemophilia, and a new synthetic matrix of polystyrene beads functionalized with sulfonate and tyrosyl methylester groups for immunoadsorption removal of factor VIII inhibitors is intriguing.

SUMMARY

Although immunoadsorption was shown to be clinically effective in patients with inhibitors to factor VIII more than two decades ago, recent papers have emphasized the desirability of early implementation of the modality in the treatment plan. Immunoadsorption is relatively easy to perform with few adverse effects, but specialized equipment is required, and it should be performed in an experienced setting. Although potentially less costly than other (bypass) therapies, immunoadsorption is itself not inexpensive, and its comparative effectiveness with plasmapheresis and other management options for the dangerously bleeding patient with antibodies to factor VIII should be determined by multicenter randomized controlled trials. Interesting recent novel technical developments in the field may facilitate increased use of the procedure.