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1.  O-phospho-L-serine, multi-functional excipient for B domain deleted recombinant factor VIII 
The AAPS Journal  2007;9(2):E251-E259.
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, ∼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 bindinding 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.
doi:10.1208/aapsj0902028
PMCID: PMC2573386  PMID: 17907766
B domain deleted recombinant factor VIII; O-phospho-L-serine; protein formulation; excipient; physical stability; immunogenicity; inhibitor development
2.  Phosphatidylserine Containing Liposomes Reduce Immunogenicity of Recombinant Human Factor VIII (rFVIII) in a Murine Model of Hemophilia A 
Journal of pharmaceutical sciences  2008;97(4):1386-1398.
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.
doi:10.1002/jps.21102
PMCID: PMC2574438  PMID: 17705286
hemophilia A; recombinant FVIII; immunogenicity; inhibitor antibodies; phosphatidylserine liposomes; protein delivery; protein formulation; lipids; immunology
3.  Phosphatidylinositol Containing Lipidic Particles Reduces Immunogenicity and Catabolism of Factor VIII in Hemophilia A Mice 
The AAPS Journal  2010;12(3):473-481.
Factor VIII (FVIII) is an important cofactor in blood coagulation cascade. It is a multidomain protein that consists of six domains, NH2-A1-A2-B-A3-C1-C2-COOH. The deficiency or dysfunction of FVIII causes hemophilia A, a life-threatening bleeding disorder. Replacement therapy using recombinant FVIII (rFVIII) is the first line of therapy, but a major clinical complication is the development of inhibitory antibodies that abrogate the pharmacological activity of the administered protein. FVIII binds to anionic phospholipids (PL), such as phosphatidylinositol (PI), via lipid binding region within the C2 domain of FVIII. This lipid binding site not only consists of immunodominant epitopes but is also involved in von Willebrand factor binding that protects FVIII from degradation in vivo. Thus, we hypothesize that FVIII–PL complex will influence immunogenicity and catabolism of FVIII. The biophysical studies showed that PI binding did not alter conformation of the protein but improved intrinsic stability as measured by thermal denaturation studies. ELISA studies confirmed the involvement of the C2 domain in binding to PI containing lipid particles. PI binding prolonged the in vivo circulation time and reduced catabolism of FVIII in hemophilia A mice. FVIII–PI complex reduced inhibitor development in hemophilia A mice following intravenous and subcutaneous administration. The data suggest that PI binding reduces catabolism and immunogenicity of FVIII and has potential to be a useful therapeutic approach for hemophilia A.
doi:10.1208/s12248-010-9207-z
PMCID: PMC2895449  PMID: 20517659
factor VIII; hemophilia A; inhibitor development; immunogenicity; phosphatidylinositol
4.  Interaction of Dicaproyl Phosphatidylserine With Recombinant Factor VIII and Its Impact on Immunogenicity 
The AAPS journal  2006;8(2):E362-E370.
Replacement therapy with exogenous recombinant factor VIII (rFVIII) to control bleeding episodes results in the development of inhibitory antibodies in 15% to 30% of hemophilia A patients. The inhibitory antibodies are mainly directed against specific and universal immunodominant epitopes located in the C2 domain. Previously we have shown that complexation of O-phospho-L-serine (phosphatidylserine head group) with the phospholipid binding region of the C2 domain can lead to an overall reduction in the immunogenicity of rFVIII. Here, we have investigated the hypothesis that dicaproyl phosphatidylserine, a short-chain water-soluble phospholipid, can reduce the immunogenicity of rFVIII. Circular dichroism and fluorescence spectroscopy studies suggest that dicaproyl phosphatidyl-serine interacts with rFVIII, causing subtle changes in the tertiary and secondary structure of the protein. Sandwich enzyme-linked immunosorbent assay studies indicate that dicaproyl phosphatidylserine probably interacts with the phospholipid binding region of the C2 domain. The immunogenicity of FVIII-dicaproyl phosphatidylserine complexes prepared at concentrations above and below the critical micellar concentrations of the lipid were evaluated in hemophilia A mice. Our results suggest that micellar dicaproyl phosphatidylserine may be useful to reduce the immunogenicity of rFVIII preparations.
doi:10.1208/aapsj080241
PMCID: PMC2574005  PMID: 16796387
Hemophilia A; inhibitor development; aggregation; recombinant human factor VIII; protein folding; factor VIII-DCPS complex
5.  Interaction of dicaproyl phosphatidylserine with recombinant factor VIII and its impact on immunogenicity 
The AAPS Journal  2006;8(2):E362-E370.
Replacement therapy with exogenous recombinant factor VIII (rFVIII) to control bleeding episodes results in the development of inhibitory antibodies in 15% to 30% of hemophilia A patients. The inhibitory antibodies are mainly directed against specific and universal immunodominant epitopes located in the C2 domain. Previously we have shown that complexation of O-phospho-L-serine (phosphatidylserine head group) with the phospholipid binding region of the C2 domain can lead to an overall reduction in the immunogenicity of rFVIII. Here, we have investigated the hypothesis that dicaproyl phosphatidylserine, a short-chain water-soluble phospholipid, can reduce the immunogenicity of rFVIII. Circular dichroism and fluorescence spectroscopy studies suggest that dicaproyl phosphatidyl-serine interacts with rFVIII, causing subtle changes in the tertiary and secondary structure of the protein. Sandwich enzyme-linked immunosorbent assay studies indicate that dicaproyl phosphatidylserine probably interacts with the phospholipid binding region of the C2 domain. The immunogenicity of FVIII-dicaproyl phosphatidylserine complexes prepared at concentrations above and below the critical micellar concentrations of the lipid were evaluated in hemophilia A mice. Our results suggest that micellar dicaproyl phosphatidylserine may be useful to reduce the immunogenicity of rFVIII preparations.
doi:10.1007/BF02854907
PMCID: PMC2574005  PMID: 16796387
Hemophilia A; inhibitor development; aggregation; recombinant human factor VIII; protein folding; factor VIII-DCPS complex
6.  Development and Characterization of Recombinant Ovine Coagulation Factor VIII 
PLoS ONE  2012;7(11):e49481.
Animal models of the bleeding disorder, hemophilia A, have been an integral component of the biopharmaceutical development process and have facilitated the development of recombinant coagulation factor VIII (fVIII) products capable of restoring median survival of persons with hemophilia A to that of the general population. However, there remain several limitations to recombinant fVIII as a biotherapeutic, including invasiveness of intravenous infusion, short half-life, immunogenicity, and lack of availability to the majority of the world's population. The recently described ovine model of hemophilia A is the largest and most accurate phenocopy. Affected sheep die prematurely due to bleeding-related pathogenesis and display robust adaptive humoral immunity to non-ovine fVIII. Herein, we describe the development and characterization of recombinant ovine fVIII (ofVIII) to support further the utility of the ovine hemophilia A model. Full-length and B-domain deleted (BDD) ofVIII cDNAs were generated and demonstrated to facilitate greater biosynthetic rates than their human fVIII counterparts while both BDD constructs showed greater expression rates than the same-species full-length versions. A top recombinant BDD ofVIII producing baby hamster kidney clone was identified and used to biosynthesize raw material for purification and biochemical characterization. Highly purified recombinant BDD ofVIII preparations possess a specific activity nearly 2-fold higher than recombinant BDD human fVIII and display a differential glycosylation pattern. However, binding to the carrier protein, von Willebrand factor, which is critical for stability of fVIII in circulation, is indistinguishable. Decay of thrombin-activated ofVIIIa is 2-fold slower than human fVIII indicating greater intrinsic stability. Furthermore, intravenous administration of ofVIII effectively reverses the bleeding phenotype in the murine model of hemophilia A. Recombinant ofVIII should facilitate the maintenance of the ovine hemophilia A herd and their utilization as a relevant large animal model for the research and development of novel nucleic acid and protein-based therapies for hemophilia A.
doi:10.1371/journal.pone.0049481
PMCID: PMC3494657  PMID: 23152911
7.  Role of Glycosylation in Conformational Stability, Activity, Macromolecular Interaction and Immunogenicity of Recombinant Human Factor VIII 
The AAPS Journal  2009;11(3):424-431.
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.
doi:10.1208/s12248-009-9119-y
PMCID: PMC2758112  PMID: 19499345
factor VIII; glycosylation; hemophilia A; immunogenicity; inhibitor development
8.  Potentiation of Thrombin Generation in Hemophilia A Plasma by Coagulation Factor VIII and Characterization of Antibody-Specific Inhibition 
PLoS ONE  2012;7(10):e48172.
Development of inhibitory antibodies to coagulation factor VIII (fVIII) is the primary obstacle to the treatment of hemophilia A in the developed world. This adverse reaction occurs in 20–30% of persons with severe hemophilia A treated with fVIII-replacement products and is characterized by the development of a humoral and neutralizing immune response to fVIII. Patients with inhibitory anti-fVIII antibodies are treated with bypassing agents including recombinant factor VIIa (rfVIIa). However, some patients display poor hemostatic response to bypass therapy and improved treatment options are needed. Recently, we demonstrated that fVIII inhibitors display widely variable kinetics of inhibition that correlate with their respective target epitopes. Thus, it was hypothesized that for antibodies that display slow rates of inhibition, supplementation of rfVIIa with fVIII would result in improved thrombin generation and be predictive of clinical responses to this novel treatment regimen. In order to test this hypothesis, 10 murine monoclonal antibodies (MAbs) with non-overlapping epitopes spanning fVIII, differential inhibition titers, and inhibition kinetics were studied using a thrombin generation assay. Of the 3 MAbs with high inhibitory titers, only the one with fast and complete (classically defined as “type I”) kinetics displayed significant inhibition of thrombin generation with no improvement upon supplementation of rfVIIa with fVIII. The other two MAbs that displayed incomplete (classically defined as “type II”) inhibition did not suppress the potentiation of thrombin generation by fVIII. All antibodies that did not completely inhibit fVIII activity demonstrated potentiation of thrombin generation by the addition of fVIII as compared to rfVIIa alone. In conclusion, fVIII alone or in combination with rfVIIa corrects the thrombin generation defect produced by the majority of anti-fVIII MAbs better than single agent rfVIIa. Therefore, combined fVIII/rfVIIa therapy may provide better hemostatic control than current therapy in some patients with anti-fVIII inhibitors.
doi:10.1371/journal.pone.0048172
PMCID: PMC3483154  PMID: 23144741
9.  Influence of Aggregation on Immunogenicity of Recombinant Human Factor VIII in Hemophilia A Mice 
Recombinant human factor VIII (rFVIII), a multidomain glycoprotein is used in replacement therapy for treatment of hemophilia A. Unfortunately, 15%–30% of the treated patients develop inhibitory antibodies. The pathogenesis of antibody development is not completely understood. The presence of aggregated protein in formulations is generally believed to enhance the immune response. rFVIII has a tendency to aggregate but the effect of such aggregation on the immunogenicity of rFVIII is not known. We have, therefore, characterized aggregated rFVIII produced by thermal stress and evaluated its effect on the immunogenicity of rFVIII in hemophilia A mice. Aggregated rFVIII alone and mixtures of rFVIII with aggregated rFVIII were less immunogenic than native rFVIII. In vitro Th-cell proliferation studies and cytokine analyses conducted on splenocytes obtained from immunized animals suggest that aggregated rFVIII behaves as a unique antigen compared to native monomeric rFVIII. The antigenic properties of the aggregated and native rFVIII were compared using ELISAs (epitope availability) and cathepsin-B (an antigen processing enzyme) digestion. The data suggest significant differences in the antigenic properties of rFVIII and aggregated rFVIII. Overall it appears that aggregated rFVIII does not enhance the immunogenicity (inhibitor development) of rFVIII in hemophilia A mice but rather acts as a distinct antigen.
doi:10.1002/jps.20529
PMCID: PMC2574426  PMID: 16372314
circular dichroism; fluorescence spectroscopy; hemophilia A; inhibitor development; protein aggregation; protein structure; recombinant human Factor VIII; immunogenicity; immunology
10.  The Comparative Immunogenicity of Human and Porcine Factor VIII in Hemophilia A Mice 
Thrombosis and haemostasis  2009;102(1):35-41.
Summary
Inhibitory antibodies to factor VIII (fVIII inhibitors) are the most significant complication in the management of hemophilia A. The immunogenicity of fVIII may be driven in part by structural determinants within the fVIII molecule itself. Regions of non-identity between human and porcine fVIII possibly could drive differential immune responses. The goal of this study was to compare the overall antibody response and levels of antibodies to the individual fVIII domains in naïve hemophilia A mice immunized with human or porcine fVIII. Hemophilia A mice were immunized with human or porcine fVIII using a protocol that mimics human clinical use. Inhibitor and total anti-fVIII antibody titers were measured and the domain-specificity of antibodies from 1759 anti-fVIII hybridomas was determined. The overall immunogenicity of human and porcine fVIII was similar but significant differences in domain recognition were discovered. Anti-A2 and anti-C2 antibodies constituted the majority of inhibitors in both the human and porcine fVIII groups, similar to inhibitors that develop in humans. The proportions of anti-A2 or anti-C2 antibodies were not significantly different between the two groups. However, the specific inhibitory activity of anti-A2 antibodies was higher in the human fVIII group. Additionally, proportion of anti-C1 antibodies was significantly higher in the human fVIII group. In contrast, anti-A3 antibodies were more common in the porcine fVIII group. The differential immune response to human and porcine fVIII suggests that it may be possible to reduce the immunogenicity of fVIII by mutagenesis of the A2, A3 and C1 domains.
doi:10.1160/TH08-12-0818
PMCID: PMC3071503  PMID: 19572065
Factor VIII; hemophilia therapy; coagulation inhibitors
11.  Correction of Murine Hemophilia A by Hematopoietic Stem Cell Gene Therapy 
A serious complication of current protein replacement therapy for hemophilia A patients with coagulation factor VIII (FVIII) deficiency is the frequent development of anti-FVIII inhibitor antibodies that preclude therapeutic benefit from further treatment. Induction of tolerance by persistent high-level FVIII synthesis following transplantation with hematopoietic stem cells expressing a retrovirally-delivered FVIII transgene offers the possibility to permanently correct the disease. Here, we transplanted bone marrow cells transduced with an optimized MSCV-based FVIII oncoretroviral vector into immunocompetent hemophilia A mice that had been conditioned with a potentially lethal dose of irradiation (800 cGy), a sublethal dose of irradiation (550 cGy) or a nonmyelablative preparative regimen involving busulfan. Therapeutic levels of FVIII (42%, 18% and 11% of normal, respectively) were detected in the plasma of the transplant recipients for the duration of the study (over 6 months). Moreover, subsequent challenge with recombinant FVIII elicited at most a minor anti-FVIII inhibitor antibody response in any of the experimental animals in contrast to the vigorous neutralizing humoral reaction to FVIII that was stimulated in naive hemophilia A mice. These findings represent an encouraging advance toward potential clinical application and long-term amelioration or cure of this progressively debilitating, life-threatening bleeding disorder.
doi:10.1016/j.ymthe.2005.09.007
PMCID: PMC2387180  PMID: 16226058
hemophilia A; factor VIII gene therapy; oncoretroviral vector; hematopoietic stem cells; bone marrow transplantation; transgene-specific tolerance induction
12.  Long-Term Expression of Human Coagulation Factor VIII in a Tolerant Mouse Model Using the φC31 Integrase System 
Human Gene Therapy  2011;23(4):390-398.
Abstract
We generated a mouse model for hemophilia A that combines a homozygous knockout for murine factor VIII (FVIII) and a homozygous addition of a mutant human FVIII (hFVIII). The resulting mouse, having no detectable FVIII protein or activity and tolerant to hFVIII, is useful for evaluating FVIII gene-therapy protocols. This model was used to develop an effective gene-therapy strategy using the φC31 integrase to mediate permanent genomic integration of an hFVIII cDNA deleted for the B-domain. Various plasmids encoding φC31 integrase and hFVIII were delivered to the livers of these mice by using hydrodynamic tail-vein injection. Long-term expression of therapeutic levels of hFVIII was observed over a 6-month time course when an intron was included in the hFVIII expression cassette and wild-type φC31 integrase was used. A second dose of the hFVIII and integrase plasmids resulted in higher long-term hFVIII levels, indicating that incremental doses were beneficial and that a second dose of φC31 integrase was tolerated. We observed a significant decrease in the bleeding time after a tail-clip challenge in mice treated with plasmids expressing hFVIII and φC31 integrase. Genomic integration of the hFVIII expression plasmid was demonstrated by junction PCR at a known hotspot for integration in mouse liver. The φC31 integrase system provided a nonviral method to achieve long-term FVIII gene therapy in a relevant mouse model of hemophilia A.
Chavez and colleagues report on a gene therapy strategy wherein the uC31 integrase is used to mediate permanent genomic integration of human coagulation factor VIII (hFVIII) cDNA. Plasmids encoding uC31 and hFVIII were administered intravenously to mice defective in murine factor VIII and tolerant to hFVIII. Long-term expression of therapeutic hFVIII levels was observed over 6 months, and bleeding time after tail-clip challenge was significantly decreased.
doi:10.1089/hum.2011.110
PMCID: PMC3327602  PMID: 22077817
13.  Limited Promiscuity of HLA-DRB1 Presented Peptides Derived of Blood Coagulation Factor VIII  
PLoS ONE  2013;8(11):e80239.
The formation of inhibitory antibodies directed against coagulation factor VIII (FVIII) is a severe complication in the treatment of hemophilia A patients. The induction of anti-FVIII antibodies is a CD4+ T cell-dependent process. Activation of FVIII-specific CD4+ T cells is dependent on the presentation of FVIII-derived peptides on MHC class II by antigen-presenting cells. Previously, we have shown that FVIII-pulsed human monocyte-derived dendritic cells can present peptides from several FVIII domains. In this study we show that FVIII peptides are presented on immature as well as mature dendritic cells. In immature dendritic cells half of the FVIII-loaded MHC class II molecules are retained within the cell, whereas in LPS-matured dendritic cells the majority of MHC class II/peptide complexes is present on the plasma membrane. Time-course studies revealed that presentation of FVIII-derived peptides was optimal between 12 and 24 hours after maturation but persisted for at least 96 hours. We also show that macrophages are able to internalize FVIII as efficiently as dendritic cells, however FVIII was presented on MHC class II with a lower efficiency and with different epitopes compared to dendritic cells. In total, 48 FVIII core-peptides were identified using a DCs derived of 8 different donors. Five HLA-promiscuous FVIII peptide regions were found – these were presented by at least 4 out of 8 donors. The remaining 42 peptide core regions in FVIII were presented by DCs derived from a single (30 peptides) or two to three donors (12 peptides). Overall, our findings show that a broad repertoire of FVIII peptides can be presented on HLA-DR.
doi:10.1371/journal.pone.0080239
PMCID: PMC3828219  PMID: 24244658
14.  Development and characterization of lipidic cochleate containing recombinant factor VIII 
Biochimica et biophysica acta  2007;1768(11):2890-2898.
Hemophilia A, a life threatening bleeding disorder is caused by deficiency of Factor VIII (FVIII). Replacement therapy using rFVIII is the first line therapy for hemophilia A. However, 15-30% of patients develop neutralizing antibody, mainly against the C2, A3 and A2 domains. It has been reported that PS-FVIII complex reduced total and neutralizing anti-rFVIII antibody titers in hemophilia A murine models. Here, we developed FVIII – containing cochleate cylinders, utilizing PS-Ca2+ interactions and characterized these particles for optimal in vivo properties using biophysical and biochemical techniques. Approximately 75% of the protein was associated with cochleate cylinders. Sandwich ELISA, acrylamide quenching and enzymatic digestion studies established that rFVIII was shielded from the bulk aqueous phase by the lipidic structures, possibly leading to improved in vivo stability. Freeze – thawing and rate limiting diffusion studies revealed that small cochleate cylinders with a particles size of 500 nm or less could be generated. The release kinetics and in vivo experiments suggested that there is slow and sustained release of FVIII from the complex upon systemic exposure. In vivo studies using tail clip method indicated that FVIII-cochleate complex is effective and protects hemophilic mice from bleeding. Based on these studies, we speculate that the molecular interaction between FVIII and PS may provide a basis for the design of novel FVIII lipidic structures for delivery applications.
doi:10.1016/j.bbamem.2007.08.001
PMCID: PMC2137893  PMID: 17936245
cochleate cylinders; B Domain Deleted recombinant factor VIII; epitope shielding; Laurdan; protein formulation; acrylamide quenching
15.  Healthy subjects produce both anti-factor VIII and specific anti-idiotypic antibodies. 
Journal of Clinical Investigation  1994;94(4):1496-1505.
Anti-Factor VIII (FVIII) antibodies were prepared by a combination of salt precipitation, gel filtration chromatography, and specific adsorption over insolubilized FVIII from the serum of 10 healthy subjects with normal levels of FVIII. Antibody specificity was confirmed by the capacity to recognize soluble and insolubilized FVIII and to neutralize FVIII cofactor activity in FX activation. Epitope mapping was carried out using a competition ELISA in which affinity-purified human antibodies inhibited the binding of labeled monoclonal antibodies. In most cases, a single region of the A3 domain of the FVIII light chain was recognized by the antibodies, while the reactivity toward heavy chain epitopes differed from one antibody preparation to the other. Sera or IgG fractions of the serum before immunoadsorption over insolubilized FVIII did not bind to FVIII. The IgG fraction that was not retained on the FVIII immunosorbent contained IgG that bound to the variable part of anti-FVIII mouse monoclonal antibodies and inhibited the binding of labeled FVIII; in addition, the IgG fraction inhibited the binding of affinity-purified human antibodies to FVIII, thereby strongly suggesting the presence of anti-idiotypic antibodies. These findings indicate that the presence of anti-FVIII antibodies is a more universal phenomenon than previously thought and that anti-idiotypic antibodies capable of inhibiting the binding of anti-FVIII antibodies to FVIII are produced spontaneously.
PMCID: PMC295292  PMID: 7523452
16.  Biochemical and functional characterization of a recombinant monomeric factor VIII–Fc fusion protein 
Background: Hemophilia A results from a deficiency in factor VIII activity. Current treatment regimens require frequent dosing, owing to the short half-life of FVIII. A recombinant FVIII–Fc fusion protein (rFVIIIFc) was molecularly engineered to increase the half-life of FVIII, by 1.5–2-fold, in several preclinical animal models and humans. Objective: To perform a biochemical and functional in vitro characterization of rFVIIIFc, with existing FVIII products as comparators.Methods: rFVIIIFc was examined by utilizing a series of structural and analytic assays, including mass spectrometry following lysyl endopeptidase or thrombin digestion. rFVIIIFc activity was determined in both one-stage clotting (activated partial thromboplastin time) and chromogenic activity assays, in the context of the FXase complex with purified components, and in both in vitro and ex vivo rotational thromboelastometry (ROTEM) assays performed in whole blood. Results: rFVIIIFc contained the predicted primary structure and post-translational modifications, with an FVIII moiety that was similar to other recombinant FVIII products. The von Willebrand factor-binding and specific activity of rFVIIIFc were also found to be similar to those of other recombinant FVIII molecules. Both chromogenic and one-stage assays of rFVIIIFc gave similar results. Ex vivo ROTEM studies demonstrated that circulating rFVIIIFc activity was prolonged in mice with hemophilia A in comparison with B-domain-deleted or full-length FVIII. Clot parameters at early time points were similar to those for FVIII, whereas rFVIIIFc showed prolonged improvement of clot formation. Conclusions: rFVIIIFc maintains normal FVIII interactions with other proteins necessary for its activity, with prolonged in vivo activity, owing to fusion with the Fc region of IgG1.
doi:10.1111/jth.12076
PMCID: PMC3588154  PMID: 23205847
Factor VIII; Fc fusion; hemophilia A; long-acting; rFVIIIFc
17.  Comparison of Factor VIII Transgenes Bioengineered for Improved Expression in Gene Therapy of Hemophilia A 
Human Gene Therapy  2009;20(5):465-478.
Abstract
Successful gene therapy of hemophilia A depends on the sustained expression of therapeutic levels of factor VIII (fVIII). Because of mRNA instability, interactions with resident endoplasmic reticulum (ER) chaperones, and the requirement for carbohydrate-facilitated transport from the ER to the Golgi apparatus, fVIII is expressed at much lower levels from mammalian cells than other proteins of similar size and complexity. A number of bioengineered forms of B domain-deleted (BDD) human fVIII have been generated and shown to have enhanced expression. Previously, we demonstrated that recombinant BDD porcine fVIII exhibits high-level expression due to specific sequence elements that increase biosynthesis via enhanced posttranslational transit through the secretory pathway. In the current study, high-expression recombinant fVIII constructs were compared directly in order to determine the relative expression of the various bioengineered fVIII transgenes. The data demonstrate that BDD porcine fVIII expression is superior to that of any of the human fVIII variant constructs tested. Mean fVIII expression of 18 units/106 cells/24 hr was observed from HEK-293 cells expressing a single copy of the porcine fVIII transgene, which was 36- to 225-fold greater than that of any human fVIII transgene tested. Furthermore, greater than 10-fold higher expression was observed in human cells transduced with BDD porcine fVIII versus BDD human fVIII-encoding lentiviral vectors, even at low proviral copy numbers, supporting its use over other human fVIII variants in future hemophilia A gene therapy clinical trials.
doi:10.1089/hum.2008.150
PMCID: PMC2828624  PMID: 19222367
18.  Delivery of Factor VIII Gene into Skeletal Muscle Cells Using Lentiviral Vector 
Yonsei Medical Journal  2009;51(1):52-57.
Purpose
This study was designed to investigate whether transduction of lentiviral vectors (LV) carrying human coagulation factor VIII (hFVIII) cDNA into skeletal muscle could increase circulating hFVIII concentrations.
Materials and Methods
A LV containing bacterial LacZ gene as a control or human FVIII gene was intramuscularly administered into the thigh muscle of 5 weeks old Sparague-Dawley rats. The plasma human FVIII concentration and neutralizing anti-FVIII antibodies were measured for up to 12 weeks in these experimental animals.
Results
The plasma human FVIII levels in the rats injected with LV carrying FVIII cDNA peaked at post-injection 1st week (5.19 ± 0.14 ng/mL vs. 0.21 ± 0.05 ng/mL in control rats , p < 0.05). Elevated hFVIII concentrations were maintained for 4 weeks (2.52 ± 0.83 ng/mL vs. 0.17 ± 0.08 ng/mL in control rats, p < 0.05) after a single intramuscular injection. In the Bethesda assay, neutralizing antibodies for FVIII protein were detected only in FVIII-LV injected rats by the 10th week, but not in control rats.
Conclusion
This study suggested that a single administration of an advanced generation LV carrying the human FVIII cDNA resulted in elevation of FVIII level in immune competent rats, and that this gene transfer approach to the skeletal muscle could be an effective tool in treatment of hemophilia A.
doi:10.3349/ymj.2010.51.1.52
PMCID: PMC2799978  PMID: 20046514
Gene therapy; human coagulation factor VIII; hemophilia A; lentiviral vector
19.  Stable Expression of Recombinant Factor VIII in CHO Cells Using Methotrexate-Driven Transgene Amplification 
Acta Naturae  2012;4(1):93-100.
Prophylaxis and treatment of inherited clotting disorder hemophilia A requires regular administration of factor VIII. Recombinant factor VIII, which is produced in CHO or BHK cells, is equivalent to the plasma-derived one and is prevalent in current clinical practice in developed countries. Development of a biosimilar recombinant FVIII requires the creation of a highly productive clonal cell line and generation of monoclonal antibodies suitable for affinity purification of the product. Methotrexate-driven transgene amplification of genetic cassettes that code full-length and truncated variants of FVIII under the control of the CMV promoter was studied. It was shown that the expression level of the truncated variant of FVIII is 6.5 times higher than that of the full-length molecule. The transgene amplification procedure was sufficient for a twofold increase of the expression level in the transfected cells pool and subsequent selection of the clonal line, stably producing truncated FVIII at the level of 0.52 IU/ml during cultivation in a chemically defined protein-free culture medium. Four generated mouse monoclonal antibodies toward the heavy chain of FVIII were found suitable for binding the truncated variant of FVIII directly from the conditioned medium and elution of the FVIII with a more than 85% yield and normal pro-coagulant activity. The producer cell line and monoclonal antibodies obtained are sufficient for the development of upstream and downstream processes of biosimilar FVIII production. Generation of more productive cell lines by the use of stronger, nonviral promoters and shorter cDNA of FVIII will be the subject of further studies.
PMCID: PMC3372988  PMID: 22708069
coagulation factor VIII; B-domain deleted factor VIII; hemophilia A;  heterologous protein expression systems
20.  Product-dependent anti-factor VIII antibodies 
Introduction
The development of anti-factor (F)VIII antibodies in hemophilia A (HA) subjects undergoing replacement therapy has been well-documented. The correlation between antibody development and the FVIII product used for replacement therapy remains a subject of discussion.
Aim
To evaluate the presence of anti-FVIII antibodies toward three commercial rFVIII products in 34 HA subjects’ plasmas.
Methods
Antibodies were quantitated by a Multiplex Fluorescence Immunoassay.
Results
All plasmas contained anti-FVIII antibodies at variable concentrations ranging from 50 nM to 570 μM. Eleven of 20 HA subjects treated with one (r)FVIII product contained inhibitory anti-FVIII antibodies (0.8–3584 BU). The inhibitory antibody titer and the molar concentrations of total antibody were mildly correlated (r2=0.6). Pronounced differences in antibody recognition with the three rFVIII products were observed. For the group treated with Product “A”, the titer toward this product was 2.4-fold higher than that observed with another full-length rFVIII-containing product (Product “B”) and almost 4-fold higher than that measured with a B domain-less rFVIII product (Product “C”). For the group of 14 HA subjects treated with FVIII other than Product “A”, only one showed higher antibody titer when measured with this product.
Conclusions
Our data suggest that the development of anti-FVIII antibodies is biased toward the product used for treatment and that a significant fraction of antibodies bind to the B domain of FVIII.
doi:10.1111/hae.12127
PMCID: PMC3688703  PMID: 23557464
Hemophilia A; Anti-factor VIII antibodies; Immunoassay; Factor VIII products; Bethesda assay; Factor VIII inhibitors
21.  PEGylation of a Factor VIII–Phosphatidylinositol Complex: Pharmacokinetics and Immunogenicity in Hemophilia A Mice 
The AAPS Journal  2011;14(1):35-42.
Hemophilia A is an X-linked bleeding disorder caused by the deficiency of factor VIII (FVIII). Exogenous FVIII is administered therapeutically, and due to a short half-life, frequent infusions are often required. Fifteen to thirty-five percent of severe hemophilia A patients develop inhibitory antibodies toward FVIII that complicate clinical management of the disease. Previously, we used phosphatidylinositol (PI) containing lipidic nanoparticles to improve the therapeutic efficacy of recombinant FVIII by reducing immunogenicity and prolonging the circulating half-life. The objective of this study is to investigate further improvements in the FVIII–PI formulation resulting from the addition of polyethylene glycol (PEG) to the particle. PEGylation was achieved by passive transfer of PEG conjugated lipid into the FVIII–PI complex. PEGylated FVIII–PI (FVIII–PI/PEG) was generated with high association efficiency. Reduced activity in vitro and improved retention of activity in the presence of antibodies suggested strong shielding of FVIII by the particle; thus, in vivo studies were conducted in hemophilia A mice. Following intravenous administration, the apparent terminal half-life was improved versus both free FVIII and FVIII–PI, but exposure determined by area under the curve was reduced. The formation of inhibitory antibodies after subcutaneous immunization with FVIII–PI/PEG was lower than free FVIII but resulted in a significant increase in inhibitors following intravenous administration. Passive transfer of PEG onto the FVIII–PI complex does not provide any therapeutic benefit.
doi:10.1208/s12248-011-9309-2
PMCID: PMC3291190  PMID: 22173945
factor VIII; hemophilia A; immunogenicity; inhibitor development; PEGylation
22.  Identification and Multidimensional Optimization of an Asymmetric Bispecific IgG Antibody Mimicking the Function of Factor VIII Cofactor Activity 
PLoS ONE  2013;8(2):e57479.
In hemophilia A, routine prophylaxis with exogenous factor VIII (FVIII) requires frequent intravenous injections and can lead to the development of anti-FVIII alloantibodies (FVIII inhibitors). To overcome these drawbacks, we screened asymmetric bispecific IgG antibodies to factor IXa (FIXa) and factor X (FX), mimicking the FVIII cofactor function. Since the therapeutic potential of the lead bispecific antibody was marginal, FVIII-mimetic activity was improved by modifying its binding properties to FIXa and FX, and the pharmacokinetics was improved by engineering the charge properties of the variable region. Difficulties in manufacturing the bispecific antibody were overcome by identifying a common light chain for the anti-FIXa and anti-FX heavy chains through framework/complementarity determining region shuffling, and by pI engineering of the two heavy chains to facilitate ion exchange chromatographic purification of the bispecific antibody from the mixture of byproducts. Engineering to overcome low solubility and deamidation was also performed. The multidimensionally optimized bispecific antibody hBS910 exhibited potent FVIII-mimetic activity in human FVIII-deficient plasma, and had a half-life of 3 weeks and high subcutaneous bioavailability in cynomolgus monkeys. Importantly, the activity of hBS910 was not affected by FVIII inhibitors, while anti-hBS910 antibodies did not inhibit FVIII activity, allowing the use of hBS910 without considering the development or presence of FVIII inhibitors. Furthermore, hBS910 could be purified on a large manufacturing scale and formulated into a subcutaneously injectable liquid formulation for clinical use. These features of hBS910 enable routine prophylaxis by subcutaneous delivery at a long dosing interval without considering the development or presence of FVIII inhibitors. We expect that hBS910 (investigational drug name: ACE910) will provide significant benefit for severe hemophilia A patients.
doi:10.1371/journal.pone.0057479
PMCID: PMC3585358  PMID: 23468998
23.  Factor VIII-Pulsed Dendritic Cells Reduce Anti-F.VIII Antibody Formation in the Hemophilia A Mouse Model 
Experimental hematology  2009;37(6):744-754.
Objective
Hemophilia inhibitor formation is a T-cell dependent immune response to infused factor VIII (F.VIII). As immature dendritic cells (DCre) regulate immune response and promote tolerance, we evaluated F.VIII-pulsed DCre, propagated from bone marrow in the presence of GM-CSF and TGFβ, in achieving F.VIII tolerance.
Methods
The effects of intravenous F.VIII-pulsed DCre in C57BL/6 hemophilia A mice were determined by total F.VIII inhibitory antibodies, T cell proliferation, thymidine uptake, cytokine profile, and surface molecule expression.
Results
After tail vein injection of 2.5 U recombinant F.VIII (rF.VIII) on day 0, 2, and 4, anti-F.VIII antibody peaked on day 6, and increased further on day 17 following rF.VIII re-challenge on day 12, 14, and 16, with increased T cell proliferative response to in vitro F.VIII. When mice were pretreated with 2×106 F.VIII-pulsed immature DCre (deficient NF-kB nuclear protein binding, low CD80, low CD86, high IL-10 phenotype) 7 days before rF.VIII challenge, anti-F.VIII was reduced on day 6 and on day 8, 0.1±0.0 BU/ml (Bethesda units/ml) vs. control PBS-treated hemophilia A mice, 2.0±0.1 BU/ml, p<0.01. Re-challenge with rF.VIII on day 12 produced no increase in anti-F.VIII antibody response. This was associated with high serum IL-10 and low IL-2 levels by ELISA, and splenic T cell hyporesponsivess to F.VIII, with IL-10 production, high FoxP3 expression by qT-PCR, and T regulatory cell expansion, confirmed in OVA-TCR transgenic mice.
Conclusions
These findings suggest F.VIII-pulsed DCre reduce anti-F.VIII antibody formation in hemophilia A mice by induction of regulatory T cell-mediated hyporesponsiveness of T helper cells to F.VIII.
doi:10.1016/j.exphem.2009.02.011
PMCID: PMC2778316  PMID: 19463774
Hemophilia; anti-F.VIII antibody; dendritic cells; regulatory T cells
24.  Lipid Binding Region (2303–2332) Is Involved in Aggregation of Recombinant Human FVIII (rFVIII) 
Journal of pharmaceutical sciences  2005;94(6):1288-1299.
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.
doi:10.1002/jps.20340
PMCID: PMC2583467  PMID: 15858858
recombinant human FVIII (rFVIII); physical instability; multi-domain; lipid-binding region; hemophilia A; inhibitor development
25.  Immunogenicity and pharmacokinetic studies of recombinant Factor VIII containing lipid cochleates 
Drug delivery  2010;18(4):246-254.
Replacement therapy using recombinant factor VIII (rFVIII) is currently the most common therapy for hemophilia A, a bleeding disorder caused by the deficiency of FVIII. However, 15–30% of patients develop inhibitory antibodies against administered rFVIII which complicates the therapy. Encapsulation or association of protein with lipidic structures can reduce this immune response. Previously, we developed and characterized rFVIII-containing phosphatidylserine (PS) cochleate cylinders using biophysical techniques. We hypothesized that these structures may provide a reduction in immunogenicity while avoiding the rapid clearance by the reticuloendothelial system (RES) previously observed with liposomal vesicles of similar composition. We investigated in vivo behavior of the cochleates containing rFVIII including immunogenicity and pharmacokinetics in hemophilia A mice. The rFVIII-cochleate complex significantly reduced the level of inhibitory antibody developed against rFVIII following intravenous (i.v.) administration. Pharmacokinetic modeling allowed assessment of in vivo release kinetics. Cochleates acted as delayed release delivery vehicle with an input peak of rFVIII observed around 2 hrs post-injection. rFVIII associated with cochleates showed limited RES uptake and a similar disposition to the free protein upon release from the structure. Incomplete disassociation from the complex limits systemic availability of the protein. Further formulation efforts are warranted to regulate the rate and extent of release of rFVIII from cochleate complexes.
doi:10.3109/10717544.2010.536269
PMCID: PMC3068242  PMID: 21114461

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