Comparative study of the sugar chains of factor VIII purified from human plasma and from the culture media of recombinant baby hamster kidney cells

Immunogenicity of Therapeutic Biological Modalities - Lessons from Hemophilia A Therapies

The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed.

Long-term immunogenicity, efficacy and tolerability of simoctocog alfa in patients with severe haemophilia A who had completed the NuProtect study in previously untreated patients

BACKGROUND

The NuProtect study reported data on the immunogenicity, efficacy and tolerability of simoctocog alfa (Nuwiq^® ) in 108 previously untreated patients with severe haemophilia A planned to be treated for ≥100 exposure days or up to 5 years. The NuProtect-Extension study collected long-term prophylaxis data in children with severe haemophilia A.

METHODS

Patients who completed the NuProtect study according to the protocol were eligible for the NuProtect-Extension study, a prospective, multinational, non-controlled, Phase 3b study.

RESULTS

Of 48 patients who entered the extension study, 47 (median age 2.8 years) received prophylaxis with simoctocog alfa for a median of 24 months, with 82%-88% on a twice-weekly or less regimen. No patient developed FVIII inhibitors during the extension study. The median (IQR) annualized bleeding rate (ABR) during prophylaxis was 0 (0-0.5) for spontaneous bleeding episodes (BEs) and 1.00 (0-1.95) for all BEs. ABRs estimated using a negative binomial model were .28 (95% CI: .15, .53) for spontaneous and 1.62 (95% CI: 1.09, 2.42) for all BEs. During the median follow-up of 24 months, 34 (72%) patients had zero spontaneous BEs and 46 (98%) had zero spontaneous joint BEs. Efficacy in treating BEs was excellent or good for 78.2% of rated BEs, and efficacy of surgical prophylaxis was excellent for two rated surgeries. No treatment-related adverse events were reported.

CONCLUSION

No FVIII inhibitors developed during long-term prophylaxis in the NuProtect-Extension study. Prophylaxis with simoctocog alfa was efficacious and well-tolerated, and is therefore an attractive long-term option for children with severe haemophilia A.

Plasma Clearance of Coagulation Factor VIII and Extension of Its Half-Life for the Therapy of Hemophilia A: A Critical Review of the Current State of Research and Practice

Factor VIII (FVIII) is an important component of blood coagulation as its congenital deficiency results in life-threatening bleeding. Current prophylactic therapy of the disease (hemophilia A) is based on 3-4 intravenous infusions of therapeutic FVIII per week. This poses a burden on patients, demanding reduction of infusion frequency by using FVIII with extended plasma half-life (EHL). Development of these products requires understanding FVIII plasma clearance mechanisms. This paper overviews (i) an up-to-date state of the research in this field and (ii) current EHL FVIII products, including recently approved efanesoctocog alfa, for which the plasma half-life exceeds a biochemical barrier posed by von Willebrand factor, complexed with FVIII in plasma, which results in ~1 per week infusion frequency. We focus on the EHL FVIII products' structure and function, in particular related to the known discrepancy in results of one-stage clotting (OC) and chromogenic substrate (CS) assays used to assign the products' potency, dosing, and for clinical monitoring in plasma. We suggest a possible root cause of these assays' discrepancy that is also pertinent to EHL factor IX variants used to treat hemophilia B. Finally, we discuss approaches in designing future EHL FVIII variants, including those to be used for hemophilia A gene therapy.

Site-specific glycosylation of proteoglycans: a revisited frontier in proteoglycan research

Proteoglycans (PGs), a class of carbohydrate-modified proteins, are present in essentially all metazoan organisms investigated to date. PGs are composed of glycosaminoglycan (GAG) chains attached to various core proteins and are important for embryogenesis and normal homeostasis. PGs exert many of their functions via their GAG chains and understanding the details of GAG-ligand interactions has been an essential part of PG research. Although PGs are also involved in many diseases, the number of GAG-related drugs used in the clinic is yet very limited, indicating a lack of detailed structure-function understanding. Structural analysis of PGs has traditionally been obtained by first separating the GAG chains from the core proteins, after which the two components are analyzed separately. While this strategy greatly facilitates the analysis, it precludes site-specific information and introduces either a "GAG" or a "core protein" perspective on the data interpretation. Mass-spectrometric (MS) glycoproteomic approaches have recently been introduced, providing site-specific information on PGs. Such methods have revealed a previously unknown structural complexity of the GAG linkage regions and resulted in identification of several novel CSPGs and HSPGs in humans and in model organisms, thereby expanding our view on PG complexity. In light of these findings, we discuss here if the use of such MS-based techniques, in combination with various functional assays, can also be used to expand our functional understanding of PGs. We have also summarized the site-specific information of all human PGs known to date, providing a theoretical framework for future studies on site-specific functional analysis of PGs in human pathophysiology.

Removal of single-site N-linked glycans on factor VIII alters binding of domain-specific monoclonal antibodies

BACKGROUND

A portion of individuals with hemophilia A develop neutralizing antibodies called inhibitors to glycoprotein factor VIII (FVIII). There are multiple risk factors that contribute to the risk of inhibitor formation. However, knowledge of the role of FVIII asparagine (N)-linked glycosylation in FVIII immunity is limited.

OBJECTIVE

To evaluate the effect of site-specific N-linked glycan removal on FVIII biochemical properties, endocytosis by murine bone marrow-derived dendritic cells (BMDCs), and antibody responses.

METHODS

Four recombinant B domain-deleted (BDD) FVIII variants with single-site amino acid substitutions to remove N-linked glycans were produced for experimental assays.

RESULTS

BDD FVIII-N41G, FVIII-N239A, FVIII-N1810A, and FVIII-N2118A with confirmed removal of N-linked glycans and similar glycosylation profiles to BDD FVIII were produced. There were no differences in thrombin activation or von Willebrand factor binding of FVIII variants compared with BDD FVIII; however, reduced FVIII expression, activity, and specific activity was observed with all variants. BDD FVIII-N41G and FVIII-N1810A had reduced uptake by BMDCs, but there were no differences in antibody development in immunized hemophilia A mice compared with BDD FVIII. Half of a repertoire of 12 domain-specific FVIII MAbs had significantly reduced binding to ≥1 FVIII variant with a 50% decrease in A1 domain MAb 2-116 binding to FVIII-N239A.

CONCLUSIONS

Modifications of FVIII N-linked glycans reduced FVIII endocytosis by BMDCs and binding of domain-specific FVIII MAbs, but did not alter de novo antibody production in hemophilia A mice, suggesting that N-glycans do not significantly contribute to inhibitor formation.

The Asialoglycoprotein Receptor Minor Subunit Gene Contributes to Pharmacokinetics of Factor VIII Concentrates in Hemophilia A

BACKGROUND

 The asialoglycoprotein receptor (ASGPR) binds with high affinity factor VIII (FVIII) through its N-linked oligosaccharides. However, its contribution to the wide inter-individual variation of infused FVIII pharmacokinetics (PK) in hemophilia A (HA) is unknown.

OBJECTIVE

 To investigate the variability in FVIII PK outcomes in relation to genetic variation in the ASGR2, encoding the ASGPR2 subunit.

METHODS

 Thirty-two HA patients with FVIII:C ≤2 IU/dL underwent 66 single-dose FVIII PK studies. PK parameters were evaluated in relation to ASGR2 5' untranslated region (5'UTR) polymorphisms, which were investigated by recombinant and white blood cell reverse transcription-polymerase chain reaction approaches.

RESULTS

 The 5'UTR polymorphisms determine a frequent and conserved haplotype (HT1) in a regulatory region. The HT1 homozygotes may differ in the amounts of alternatively spliced mRNA transcripts and thus ASGPR2 isoforms. Compared with the other ASGR2 genotypes, the c.-95TT homozygotes (n = 9), showed threefold longer Alpha HL (3.60 hours, 95% confidence interval: 1.44-5.76, p = 0.006), and the c.-95TC heterozygotes (n = 17) showed 25% shorter mean residence time (MRT; 18.5 hours, 15.0-22.0, p = 0.038) and 32% shorter Beta HL (13.5 hours, 10.9-16.0, p = 0.016). These differences were confirmed in patients (n = 27) undergoing PK studies (n = 54) with full-length FVIII only. In different linear regression models, the contribution of the ASGR2 genotypes remained significant after adjustment by ABO genotypes and von Willebrand factor (VWF) antigen levels, and explained 14% (MRT), 15 to 18% (Beta HL), and 22% (Alpha HL) of parameter variability.

CONCLUSIONS

 Infused FVIII distribution was modulated by frequent ASGR2 genotypes, independently from and together with ABO and VWF antigen levels, which has potential implications for genetically tailored substitutive treatment in HA.

Non-Human Glycans Can Regulate Anti-FVIII Antibody Formation in Mice

Recombinant Factor VIII (FVIII) products represent a life-saving intervention for patients with hemophilia A. However, patients can develop antibodies against FVIII that prevent FVIII function and directly increase morbidity and mortality. The development of anti-FVIII antibodies varies depending on the type of recombinant product employed, with previous studies suggesting that 2nd generation baby hamster kidney (BHK)-derived FVIII products display greater immunogenicity than 3rd generation Chinese hamster ovary (CHO)-derived FVIII. However, the underlying mechanisms responsible for these differences remain incompletely understood. Our results demonstrate that BHK cells express higher levels of the non-human carbohydrate a1-3 galactose (aGal) than CHO cells, suggesting that aGal incorporation onto FVIII may result in anti-aGal antibody recognition that could positively influence the development of anti-FVIII antibodies. Consistent with this, BHK-derived FVIII exhibits increased levels of aGal, which corresponds to increased reactivity with anti-aGal antibodies. Infusion of BHK-derived, but not CHO-derived, FVIII into aGal knock out mice, which spontaneously generate anti-aGal antibodies, results in significantly higher anti-FVIII antibody formation, suggesting that the increased levels of aGal on BHK-derived FVIII can influence immunogenicity. These results suggest that post-translational modifications of recombinant FVIII products with non-human carbohydrates may influence the development of anti-FVIII antibodies.

Immune Responses to Plasma-Derived Versus Recombinant FVIII Products

The most severe side effect of hemophilia treatment is the inhibitor development occurring in 30% of patients, during the earliest stages of treatment with factor (F)VIII concentrates. These catastrophic immune responses rapidly inactivate the infused FVIII, rendering the treatment ineffective. This complication is associated with a substantial morbidity and mortality. The risk factors involved in the onset of the inhibitors are both genetic and environmental. The source of FVIII products, i.e. plasma-derived or recombinant FVIII products, is considered one of the most relevant factors for inhibitor development. Numerous studies in the literature report conflicting data on the different immunogenicity of the products. The SIPPET randomized trial showed an increased in the inhibitor rate in patients using recombinant FVIII products than those receiving plasma-derived products in the first exposure days. The SIPPET randomized trial showed an increase in the inhibitor rate in patients using recombinant FVIII products compared to those treated with plasma-derived products in the first days of exposure. The potential increase in the immunogenicity of recombinant products can be attributed to several factors such as: the different post-translational modification in different cell lines, the presence of protein aggregates, and the role played by the chaperon protein of FVIII, the von Willebrand factor, which modulates the uptake of FVIII by antigen presenting cells (APCs). Furthermore, the presence of non-neutralizing antibodies against FVIII has shown to be in increased inhibitor development as demonstrated in a sub-analysis of the SIPPET study. In addition, the presence of the specific subclasses of the immunoglobulins may also be an important biomarker to indicate whether the inhibitor will evolve into a persistent neutralizing antibody or a transient one that would disappear without any specific treatment. Recently, the availability of novel non-replacement therapies as well as emicizumab, administered by weekly subcutaneous infusion, have significantly changed the quality of life of patients with inhibitors showing a considerable reduction of the annual bleeding rate and in most patients the absence of bleeding. Although, these novel drugs improve patients' quality of life, they do not abolish the need to infuse FVIII during acute bleeding or surgery. Therefore, the issue of immunogenicity against FVIII still remains an important side effect of hemophilia treatment.

Comparative glycosylation mapping of plasma-derived and recombinant human factor VIII

Human coagulation factor VIII (FVIII) is a key co-factor in the clotting cascade, the deficiency of which leads to Hemophilia A. Human plasma-derived (pdFVIII) and recombinant FVIII (rFVIII) had been used as effective products to prevent and treat bleeding episodes. Both FVIII products share identical amino acid sequences and appear to be equivalent as of clinical efficiency. However, systemic reviews found an increased risk of neutralizing antibody (or inhibitor) development with recombinant products. FVIII is a highly glycosylated protein, and its glycosylation pattern is specific to host cells and environments. The roles of glycosylation in immune responses toward pdFVIII and rFVIII are yet to be defined. Herein, we systemically profiled N- and O-glycomes of pdFVIII and rFVIII using a mass spectrometry-based glycoproteomic strategy. A total of 110 site-specific N-glycopeptides consisting of 61 N-glycoforms were identified quantitatively from rFVIII and pdFVIII. Additionally, 31 O-glycoforms were identified on 23 peptides from rFVIII and pdFVIII. A comprehensive comparison of their site-specific glycan profiles revealed distinct differences between the glycosylation of pdFVIII and rFVIII.

Anti-Glycan Autoantibodies Induced by Helicobacter pylori as a Potential Risk Factor for Myocardial Infarction

A number of epidemiological studies have evaluated the potential association between H. pylori and cardiovascular disease, but with contrasting results. We have previously shown that Helicobacter pylori infection is able to induce in mice and humans autoantibodies cross-reacting with histo–blood group Lewis antigens, expressed in different organs and in plasma glycoproteins and glycolipids. The aim of this study was to assess whether immunization of animals with H. pylori might induce myocardial histopathological changes. We have retrospectively examined, in detail, the histology of archived organs from mice and rabbits immunized with H. pylori in our previous studies. Human sera and cross-reacting monoclonal antibodies were also tested against bacterial preparations and tissue sections. Areas of myocardial necrosis, associated with coronary thrombotic occlusion, were found in 5 of 20 mice and 2 of 5 rabbits previously immunized with suspensions of H. pylori. No similar lesions were found in control animals, suggesting a causal link with H. pylori immunization. The animals bearing myocardial lesions had not been infected but only immunized months earlier with parenteral injections of dead H. pylori cells. This strongly suggests that immunization, by itself, might play a causative role. We propose that the cross-reactive autoimmune response induced by H. pylori could promote thrombotic occlusion through direct endothelial damage or by perturbing the coagulation process.

Efficacy and safety of simoctocog alfa (Nuwiq®) in patients with severe hemophilia A: a review of clinical trial data from the GENA program

Simoctocog alfa (human-cl rhFVIII, Nuwiq®) is a 4th generation recombinant FVIII (rFVIII), without chemical modification or fusion with any other protein/fragment. Nuwiq® is produced in a human embryonic kidney cell line (HEK293F), which ensures human-specific post-translational protein processing. Nuwiq® was evaluated in seven prospective clinical studies in 201 adult and pediatric previously treated patients (PTPs) with severe hemophilia A. The NuProtect study in 110 previously untreated patients (PUPs) is ongoing. The mean half-life of Nuwiq® was 15.1–17.1 h in PTP studies with adults and adolescents, and 12.5 h in children aged 2–12 years. Clinical trials in PTPs demonstrated the efficacy and safety of Nuwiq® in the prevention and treatment of bleeds and as surgical prophylaxis. In the NuPreviq study of pharmacokinetic (PK)-guided personalized prophylaxis in 66 adult PTPs, 83% of patients had no spontaneous bleeds during 6 months of personalized prophylaxis and 57% were treated ⩽2 per week. No FVIII inhibitors were detected in PTPs after treatment with 43,267 injections and >80 million IU of Nuwiq®. Interim data for 66 PUPs with ⩾20 exposure days to Nuwiq® in NuProtect demonstrated a low cumulative high-titer inhibitor rate of 12.8% [actual incidence 12.1% (8/66)] and convincing efficacy and safety.

The endothelial lectin clearance receptor CLEC4M binds and internalizes factor VIII in a VWF-dependent and independent manner

Essentials CLEC4M is an endocytic receptor for factor FVIII. CLEC4M interacts with FVIII in a VWF-dependent and independent manner. CLEC4M binds to mannose-containing glycans on FVIII. CLEC4M internalization of FVIII involves clathrin coated pits. SUMMARY: Background von Willebrand factor (VWF) and factor VIII (FVIII) circulate in the plasma as a non-covalent complex, and the majority of FVIII is likely to be cleared by VWF-dependent pathways. Clearance of VWF-free FVIII is rapid and underlies the pathological basis of some quantitative FVIII deficiencies. The receptor pathways that regulate the clearance of VWF-bound and VWF-free FVIII are incompletely uncharacterized. The human liver-expressed endothelial lectin CLEC4M has been previously characterized as a clearance receptor for VWF, although its influence on FVIII is unknown. Objective The interaction between FVIII and CLEC4M was characterized in the presence or absence of VWF. Methods FVIII interactions with CLEC4M were evaluated by in vitro cell-based and solid phase binding assays. Interactions between FVIII and CLEC4M or liver sinusoidal endothelial cells were evaluated in vivo by immunohistochemistry. Results CLEC4M-expressing HEK 293 cells bound and internalized recombinant and plasma-derived FVIII through VWF-dependent and independent mechanisms. CLEC4M binding to recombinant FVIII was dependent on mannose-exposed N-linked glycans. CLEC4M mediated FVIII internalization via a clathrin-coated pit-dependent mechanism, resulting in transport of FVIII from early and late endosomes for catabolism by lysosomes. In vivo hepatic expression of CLEC4M after hydrodynamic liver transfer was associated with a decrease in plasma levels of endogenous murine FVIII:C in normal mice, whereas infused recombinant human FVIII was associated with sinusoidal endothelial cells in the presence or absence of VWF. Conclusions These findings suggest that CLEC4M is a novel clearance receptor that interacts with mannose-exposed glycans on FVIII in the presence or absence of VWF.

Analysis of the Glycosylation Profile of Disease-Associated Water-Soluble Prion Protein Using Lectins

The disease-associated water-soluble form of hamster prion protein (ws-PrP^Sc) has recently been found to be less stable than classical PrP^Sc. Since the stability of PrP to degradation correlates with its glycosylation level, the aim of this study was to investigate whether there are differences between the glycosylation of ws-PrP^Sc and classical PrP^Sc of hamster which might account for the ws-PrP^Sc minor stability compared with that of the classical PrP^Sc. Thus, ws-PrP and classical PrP were captured from noninfected or scrapie-infected hamster brain homogenate [high-speed supernatant (S^HS) and high-speed pellet (P^HS)] and blood plasma by anti-PrP antibodies (3F4 and 6H4) and subjected to screening for glycans by lectins under denaturing or nondenaturing procedures in a sandwich lectin-ELISA. Glycans have been found in minor quantities and differently exposed on ws-PrP^Sc from S^HS and plasma compared with classical PrP^Sc from P^HS. These differences have been shown to be potentially responsible for the instability of ws-PrP^Sc. Treatment of infected blood with GdnHCl significantly (P<0.01) increased the detection of ws-PrP^Sc in ELISA, reflecting an increase in its stability, and showed efficacy in removing high-abundance proteins in silver-stained gels. This increase in ws-PrP^Sc stability is due to an interaction of GdnHCl not only with high-abundance proteins but also with the ws-PrP^Sc glycosylation with particular regard to the mannose sugar. Analysis of lectins immunoreactivity toward total proteins from plasma collected before and at different time points after infection revealed that mannose might exert a stabilizing effect toward all of hamster blood glycoproteins, regardless of scrapie infection. Since low levels of ws-PrP^Sc/soluble-infectivity have been estimated both in blood and brain of hamster, this glycosylation-related instability may have negatively influenced the propensity of ws-PrP^C to convert to ws-PrP^Sc both in blood and the brain. Therefore, PrP^C glycosylation characteristics may provide a tool for the determination risk of prion transmissibility.

In-depth comparison of N-glycosylation of human plasma-derived factor VIII and different recombinant products: from structure to clinical implications

Essentials Glycosylation heterogeneity of recombinant proteins affects pharmacokinetics and immunogenicity. N-glycomics/glycoproteomics of plasma-derived Factor VIII and 6 recombinant FVIIIs were compared. Depending on cell line, significant differences to plasma-derived FVIII were observed. Recombinant FVIIIs expressed distinct and immunologically relevant epitopes.

SUMMARY

Background/Objective Human factor VIII (FVIII) is a plasma glycoprotein, defects of which result in hemophilia A. Current substitution therapy uses FVIII products purified from human plasma or from various cell lines (recombinant FVIII) with different levels of B-domain deletion. Glycosylation is a post-translational protein modification in FVIII that has a substantial influence on its physical, functional and antigenic properties. Variation in glycosylation is likely to be the reason that FVIII products differ in their pharmacokinetics, pharmacodynamics and immunogenicity. However, the literature on FVIII glycosylation is inconsistent, preventing assembly into a coherent model. Seeking to better understand the glycosylation mechanisms underlying FVIII biology, we studied the N-glycosylation of human plasma-derived (pd)FVIII and six rFVIII products expressed in CHO, BHK or HEK cell lines. Methods FVIII samples were subjected to head-to-head detailed glycomic and glycoproteomic characterization using a combination of MALDI-MS and MS/MS, GC-MS and UPLC-UV-MSE technologies. Results/Conclusion The results of our study detail the N-glycan repertoire of pdFVIII to an unprecedented level, and for the first time, provide evidence of N-glycolylneuraminic acid (NeuGc) found on pdFVIII. Although site-specific glycosylation of rFVIII proved consistent with pdFVIII regardless of the expression system, the entire N-glycan content of each sample appeared significantly different. Although the proportion of biologically important epitopes common to all samples (i.e. sialylation and high-mannose) varied between samples, some recombinant products expressed distinct and immunologically relevant epitopes, such as LacdiNAc (LDN), fucosylated LacdiNAc (FucLDN), NeuGc, LewisX/Y and Galα1,3 Gal epitopes. rFVIII expressed in HEK cells showed the greatest glycomic differences to human pdFVIII.

Long-term tolerability, immunogenicity and efficacy of Nuwiq® (human-cl rhFVIII) in children with severe haemophilia A

INTRODUCTION

Nuwiq^® (human-cl rhFVIII, simoctocog alfa) is a 4th generation recombinant human FVIII, without chemical modification or fusion with any other protein, produced in a human cell line.

AIM/METHODS

This study (GENA-13) was an extension of the GENA-03 study in which previously treated children aged 2-12 years with severe haemophilia A received Nuwiq^® prophylaxis for ≥6 months. GENA-13 examined long-term tolerability, immunogenicity and efficacy of Nuwiq^® prophylaxis in children.

RESULTS

Of 59 patients enrolled in GENA-03, 49 continued Nuwiq^® prophylaxis in GENA-13 for a median (range) of 30.0 (9.5-52.0) months. No patient withdrew due to drug-related adverse events or developed inhibitors. Only 2 of 20 518 infusions were associated with possibly related adverse events (dyspnoea, fever). The estimated annualized bleeding rate (ABR) was 0.67 (95% CI: 0.44, 1.02) for spontaneous and 2.88 (95% CI: 1.86, 4.46) for all bleeds. Younger children (2-5 years) had lower ABRs than children aged 6-12 years. Annualized bleeding rates were reduced in GENA-13 vs GENA-03, especially for spontaneous bleeds in younger children (71% reduction; ABR ratio 0.29 [95% CI: 0.11, 0.74]). Nuwiq^® efficacy was rated as excellent/good in the treatment of 83.0% of 305 evaluated breakthrough bleeds. Surgical prophylaxis with Nuwiq^® was rated as excellent for all 17 assessed procedures.

CONCLUSION

Long-term treatment with Nuwiq^® for the prevention of bleeds in children with severe haemophilia A was well tolerated, effective and reduced spontaneous bleeding by up to 70% compared with GENA-03.

Early cellular interactions and immune transcriptome profiles in human factor VIII-exposed hemophilia A mice

Essentials Initial immune cell interactions leading to factor (F) VIII immunity are not well characterized. We assessed cellular interactions and expression profiles in hemophilia A mice. MARCO+, followed by SIGLEC1+ and SIGNR1+ macrophages co-localize most with human FVIII. The splenic transcriptome highlights potential therapeutic targets to prevent inhibitors.

SUMMARY

Background Developing factor VIII (FVIII) inhibitory antibodies is the most serious complication in hemophilia A treatment, representing a significant health and economic burden. A better understanding of the early events in an immune response leading to this outcome may provide insight into inhibitor development. Objective To identify early mediators of FVIII immunity and to detail immune expression profiles in the spleen and liver. Methods C57Bl/6 F8 E16 knockout mice were infused with 5-20 μg (2000-8000 IU kg-1 ) of recombinant FVIII. Spleens were frozen at various time-points post-infusion and stained for FVIII and cellular markers. Splenic and liver RNA expression analysis was performed 3 h post-infusion of 0.6 μg (240 IU kg-1 ) FVIII by nCounter technology using a 561-gene immunology panel. Results FVIII localization in the spleen did not change over 2.5 h. We observed significantly higher co-localization of FVIII with MARCO+ cells compared with SIGLEC1+ and SIGNR1+ in the splenic marginal zone. FVIII exhibited little co-localization with CD11c+ dendritic cells and the macrophage mannose receptor, CD206. Following FVIII infusion, the splenic mRNA profiling identified genes such as Tnfaip6 and Il23r, which are implicated in chemotaxis and a proinflammatory Th17 response, respectively. In contrast, an upregulation of Gfi1 in the liver suggests an anti-inflammatory environment. Conclusions FVIII co-localizes predominantly with marginal zone macrophages (MARCO+ ) in the murine spleen following intravenous infusion. Targeting pathways that are implicated in the early FVIII innate immune response in the spleen may lead to therapeutic interventions to prevent inhibitor formation.

Timing and severity of inhibitor development in recombinant versus plasma-derived factor VIII concentrates: a SIPPET analysis

Essentials Recombinant factor VIII (rFVIII) was contrasted with plasma-derived FVIII (pdFVIII). In previously untreated patients with hemophilia A, rFVIII led to more inhibitors than pdFVIII. Inhibitors with rFVIII developed earlier, and the peak rate was higher than with pdFVIII. Inhibitors with rFVIII were more severe (higher titre) than with pdFVIII.

SUMMARY

Background The development of neutralizing antibodies (inhibitors) against factor VIII (FVIII) is the most severe complication in the early phases of treatment of severe hemophilia A. Recently, a randomized trial, the Survey of Inhibitors in Plasma-Product Exposed Toddlers (SIPPET) demonstrated a 2-fold higher risk of inhibitor development in children treated with recombinant FVIII (rFVIII) products than with plasma-derived FVIII (pdFVIII) during the first 50 exposure days (EDs). Objective/Methods In this post-hoc SIPPET analysis we evaluated the rate of inhibitor incidence over time by every 5 EDs (from 0 to 50 EDs) in patients treated with different classes of FVIII product, made possible by a frequent testing regime. Results The highest rate of inhibitor development occurred in the first 10 EDs, with a large contrast between rFVIII and pdFVIII during the first 5 EDs: hazard ratio 3.14 (95% confidence interval [CI], 1.01-9.74) for all inhibitors and 4.19 (95% CI, 1.18-14.8) for high-titer inhibitors. For patients treated with pdFVIII, the peak of inhibitor development occurred later (6-10 EDs) and lasted for a shorter time. Conclusion These results emphasize the high immunologic vulnerability of patients during the earliest exposure to FVIII concentrates, with the strongest response to recombinant FVIII products.

To serve and protect: The modulatory role of von Willebrand factor on factor VIII immunogenicity

Hemophilia A is a bleeding disorder characterized by the absence or dysfunction of blood coagulation factor VIII (FVIII). Patients are treated with regular infusions of FVIII concentrate. In response to treatment, approximately 30% of patients with severe hemophilia A develop inhibitory antibodies targeting FVIII. Both patient and treatment related risk factors for inhibitor development have been described. Multiple studies comparing the immunogenicity of recombinant and plasma-derived FVIII have yielded conflicting results. The randomized controlled SIPPET (Survey of Inhibitors in Plasma-Product Exposed Toddlers) trial demonstrated an increased risk of inhibitor development of recombinant FVIII when compared to von Willebrand factor (VWF)-containing plasma-derived FVIII. Presently, it is unclear which mechanism underlies the reduced immunogenicity of plasma-derived FVIII. In this review we address the potential role of VWF on FVIII immunogenicity and we discuss how VWF affects the immune recognition, processing and presentation of FVIII. We also briefly discuss the potential impact of glycan-composition on FVIII immunogenicity. It is well established that VWF shields the uptake of FVIII by antigen presenting cells. We have recently shown that VWF binds to the surface of dendritic cells. Here, we present a novel model in which surface bound FVIII-VWF complexes regulate the internalization of FVIII. Binding of FVIII to VWF is critically dependent on sulfation of Tyr1699 (HVGS numbering) in the light chain of FVIII. Incomplete sulfation of Tyr1699 has been suggested to occur in several recombinant FVIII products resulting in a loss of VWF binding. We hypothesize that this results in alternative pathways of FVIII internalization by antigen presenting cells which are not regulated by VWF. This hypothetical mechanism may explain the reduced immunogenicity of VWF containing plasma-derived FVIII concentrates as found in the SIPPET study.

Biological considerations of plasma-derived and recombinant factor VIII immunogenicity

In hemophilia A, the most severe complication of factor VIII (FVIII) replacement therapy involves the formation of FVIII neutralizing antibodies, also known as inhibitors, in 25% to 30% of patients. This adverse event is associated with a significant increase in morbidity and economic burden, thus highlighting the need to identify methods to limit FVIII immunogenicity. Inhibitor development is regulated by a complex balance of genetic factors, such as FVIII genotype, and environmental variables, such as coexistent inflammation. One of the hypothesized risk factors of inhibitor development is the source of the FVIII concentrate, which could be either recombinant or plasma derived. Differential immunogenicity of these concentrates has been documented in several recent epidemiologic studies, thus generating significant debate within the hemophilia treatment community. To date, these discussions have been unable to reach a consensus regarding how these outcomes might be integrated into enhancing clinical care. Moreover, the biological mechanistic explanations for the observed differences are poorly understood. In this article, we complement the existing epidemiologic investigations with an overview of the range of possible biochemical and immunologic mechanisms that may contribute to the different immune outcomes observed with plasma-derived and recombinant FVIII products.

Missense mutations near the N-glycosylation site of the A2 domain lead to various intracellular trafficking defects in coagulation factor VIII

Missense mutation is the most common mutation type in hemophilia. However, the majority of missense mutations remain uncharacterized. Here we characterize how hemophilia mutations near the unused N-glycosylation site of the A2 domain (N582) of FVIII affect protein conformation and intracellular trafficking. N582 is located in the middle of a short 3₁₀-helical turn (D580-S584), in which most amino acids have multiple hemophilia mutations. All 14 missense mutations found in this 3₁₀-helix reduced secretion levels of the A2 domain and full-length FVIII. Secreted mutants have decreased activities relative to WT FVIII. Selected mutations also lead to partial glycosylation of N582, suggesting that rapid folding of local conformation prevents glycosylation of this site in wild-type FVIII. Protease sensitivity, stability and degradation of the A2 domain vary among mutants, and between non-glycosylated and glycosylated species of the same mutant. Most of the mutants interact with the ER chaperone BiP, while only mutants with aberrant glycosylation interact with calreticulin. Our results show that the short 3₁₀-helix from D580 to S584 is critical for proper biogenesis of the A2 domain and FVIII, and reveal a range of molecular mechanisms by which FVIII missense mutations lead to moderate to severe hemophilia A.

Baby hamster kidney cell-derived recombinant factor VIII: a quarter century of learning and clinical experience

INTRODUCTION

Management and care of individuals with hemophilia A advanced immensely with the introduction of recombinant factor VIII (rFVIII) replacement products. This review provides a historical overview of rFVIII development with a focus on Bayer's rFVIII (with albumin) and sucrose-formulated rFVIII (rFVIII-FS), the only rFVIII products cloned in baby hamster kidney (BHK) cells with >25 years of proven safety and efficacy. Areas covered: We review the advances in rFVIII technology and the efficacy and safety data for BHK-derived rFVIII/rFVIII-FS from clinical trials, investigator-initiated studies, and observational studies. Innovative products with new treatment potentials (eg, BAY 81-8973 and BAY 94-9027) built on this established safety and efficacy profile are also briefly discussed. The literature search strategy included targeted searches (PubMed) with manual article selection and other product-specific searches. Expert commentary: Development of rFVIII products and related improvements in viral safety and manufacturing efficiency have guaranteed an adequate supply of factor products worldwide and increased prophylaxis use. The net effects have been joint health preservation, reduction in morbidity and mortality, and quality-of-life enhancements. Current treatment challenges include lack of adherence to prophylaxis and inhibitor development; extended-half-life rFVIII products and non-FVIII replacement therapies in development may help overcome these challenges.

Association of Single Nucleotide Polymorphisms in the ST3GAL4 Gene with VWF Antigen and Factor VIII Activity

VWF is extensively glycosylated with biantennary core fucosylated glycans. Most N-linked and O-linked glycans on VWF are sialylated. FVIII is also glycosylated, with a glycan structure similar to that of VWF. ST3GAL sialyltransferases catalyze the transfer of sialic acids in the α2,3 linkage to termini of N- and O-glycans. This sialic acid modification is critical for VWF synthesis and activity. We analyzed genetic and phenotypic data from the Atherosclerosis Risk in Communities (ARIC) study for the association of single nucleotide polymorphisms (SNPs) in the ST3GAL4 gene with plasma VWF levels and FVIII activity in 12,117 subjects. We also analyzed ST3GAL4 SNPs found in 2,535 subjects of 26 ethnicities from the 1000 Genomes (1000G) project for ethnic diversity, SNP imputation, and ST3GAL4 haplotypes. We identified 14 and 1,714 ST3GAL4 variants in the ARIC GWAS and 1000G databases respectively, with 46% being ethnically diverse in their allele frequencies. Among the 14 ST3GAL4 SNPs found in ARIC GWAS, the intronic rs2186717, rs7928391, and rs11220465 were associated with VWF levels and with FVIII activity after adjustment for age, BMI, hypertension, diabetes, ever-smoking status, and ABO. This study illustrates the power of next-generation sequencing in the discovery of new genetic variants and a significant ethnic diversity in the ST3GAL4 gene. We discuss potential mechanisms through which these intronic SNPs regulate ST3GAL4 biosynthesis and the activity that affects VWF and FVIII.

Tailoring hemostatic therapies to lower inhibitor development in previously untreated patients with severe hemophilia A

After technological progress provided safer therapeutic products for patients with hemophilia A, the development of alloantibodies (inhibitors) neutralizing the coagulant activity of infused factor VIII (FVIII) remains the most serious complication of replacement therapy, predisposing patients to greater morbidity and causing higher treatment costs. The pathogenesis of inhibitors, which develop at a high rate in previously untreated children with severe hemophilia A, is multifactorial, resulting from complex interactions between genetic and environmental factors. Among non-genetic determinants, a key role is played by treatment-related factors, including the source of FVIII product (i.e., plasma derived or recombinant) and the mode of replacement therapy delivery (i.e., intensity, prophylaxis vs. on demand). We review the potential interventions on these modifiable factors that may help to lower the rate of inhibitor development. In addition, interest is currently directed toward the potential for lesser immunogenicity of novel hemostatic agents designed to decrease the dosing frequency or avoid/delay the need of FVIII replacement therapy.

Aging and ABO blood type influence von Willebrand factor and factor VIII levels through interrelated mechanisms

Essentials von Willebrand factor (VWF) and factor VIII (FVIII) levels are modulated by age and ABO status. The effect of aging and ABO blood type on VWF and FVIII was assessed in 207 normal individuals. Aging and ABO blood type showed combined and bidirectional influences on VWF and FVIII levels. Aging and ABO blood type influence VWF levels through both secretion and clearance mechanisms.

SUMMARY

Background The effect of aging and ABO blood type on plasma levels of von Willebrand factor (VWF) and factor VIII (FVIII) have been widely reported; however, a comprehensive analysis of their combined effect has not been performed and the mechanisms responsible for the age-related changes have not been determined. Objectives To assess the influence of aging and ABO blood type on VWF and FVIII levels, and to evaluate the contribution of VWF secretion and clearance to the age-related changes. Methods A cross-sectional observational study was performed in a cohort of 207 normal individuals, whose levels of VWF, FVIII, VWF propeptide (VWFpp), VWFpp/VWF:Ag ratio and blood type A antigen content on VWF (A-VWF) were quantified. Results Aging and ABO blood type exerted interrelated effects on VWF and FVIII plasma levels, because the age-related increase in both proteins was significantly higher in type non-O individuals (β = 0.011 vs. 0.005). This increase with age in non-O subjects drove the differences between blood types in VWF levels, as the mean difference increased from 0.13 U/mL in the young to 0.57 U/mL in the old. Moreover, A-VWF was associated with both VWF antigen (β = 0.29; 95% confidence interval [CI], 0.09, 0.50) and VWF clearance (β = -0.15; 95% CI, -0.25, -0.06). We also documented an effect of ABO blood type on VWF secretion with aging, as old individuals with blood type non-O showed higher levels of VWFpp (mean difference 0.29 U/mL). Conclusions Aging and ABO blood type have an interrelated effect on VWF and FVIII levels, where the effect of one is significantly influenced by the presence of the other.

Galectin-1 and Galectin-3 Constitute Novel-Binding Partners for Factor VIII

OBJECTIVE

Recent studies have demonstrated that galectin-1 (Gal-1) and galectin-3 (Gal-3) can bind von Willebrand factor and directly modulate von Willebrand factor-dependent early thrombus formation in vivo. Because the glycans expressed on human factor VIII (FVIII) are similar to those of von Willebrand factor, we investigated whether galectins might also bind and modulate the activity of FVIII.

APPROACH AND RESULTS

Immunosorbant assays and surface plasmon resonance analysis confirmed that Gal-1 and Gal-3 bound purified FVIII with high affinity. Exoglycosidase removal of FVIII N-linked glycans significantly reduced binding to both Gal-1 and Gal-3. Moreover, combined removal of both the N- and O-glycans of FVIII further attenuated Gal-3 binding. Notably, specific digestion of FVIII high-mannose glycans at N239 and N2118 significantly impaired FVIII affinity for Gal-1. Importantly Gal-1, but not Gal-3, bound to free FVIII in the plasma milieu, and significantly inhibited FVIII functional activity. Interestingly, commercial recombinant FVIII (rFVIII) concentrates are manufactured in different cell lines and differ in their glycosylation profiles. Although the biological mechanism has not been defined, recent studies in previously untreated patients with severe hemophilia A reported significant differences in inhibitor development associated with different rFVIII products. Interestingly, Gal-1 and Gal-3 both displayed enhanced affinity for BHK-rFVIII compared with CHO-rFVIII. Furthermore, binding of Gal-1 and Gal-3 to BDD-FVIII was markedly reduced compared with full-length rFVIII.

CONCLUSIONS

We have identified Gal-1 and Gal-3 as novel-binding partners for human FVIII and demonstrated that Gal-1 binding can influence the procoagulant activity of FVIII.

Inhibitors in haemophilia A: a perspective on clotting factor products as a potential contributing factor

INTRODUCTION

The occurrence of a neutralizing antibody in previously untreated patients (PUPs) with haemophilia A appears to be the result of an intricate interplay of both genetic and environmental factors. Recently, the type of factor VIII (FVIII) product used in the PUPs population has been implicated as a risk factor for inhibitor development.

AIM

The aim of this review was to explore in a systematic manner potential hypotheses for the product-related findings in these studies (i.e. differences in the expression system of the cell lines used to produce recombinant FVIII [rFVIII], differences in the administered antigen load or changes in clinical practice over time).

RESULTS

Review of the available clinical studies illustrates the high degree of variability for the risk of inhibitor development for the same products across different studies. Differences in cell lines or antigen load were not found to provide a reasonable explanation.

CONCLUSION

The possibility of changes in clinical practice over time and patient selection bias (i.e. the preferential use of one product over another in patients at higher risk for inhibitors) offers a potential explanation and should be carefully considered when evaluating the studies.

To clear or to fear: An innate perspective on factor VIII immunity

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FVIII inhibitor development involves a combination of innate immune modulators.

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Clearance and immunity is influenced at 3 levels: the protein, cell, and location.

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Cells associated with FVIII half-life may influence the immune response against FVIII.

The enigma that is factor VIII immunogenicity remains ever pertinent in the treatment of hemophilia A. Development of neutralizing antibodies against the therapeutic protein in 25–30% of patients likely depends on the appropriate activation of the innate immune response shortly following antigen encounter. Our understanding of this important immunological synapse remains ill-defined. In this review, we examine the three distinct factors contributing to the fate of factor VIII almost immediately after infusion: the characteristics of the protein, the cell, and the microenvironment. We propose a continuum between clearance and antigen presentation that facilitates removal of FVIII from circulation leading to either tolerance or immunity.

Thrombin Generating Capacity and Phenotypic Association in ABO Blood Groups

Individuals with blood group O have a higher bleeding risk than non-O blood groups. This could be explained by the lower levels of FVIII and von Willebrand Factor (VWF) levels in O individuals. We investigated the relationship between blood groups, thrombin generation (TG), prothrombin activation and thrombin inactivation. Plasma levels of VWF, FVIII, antithrombin, fibrinogen, prothrombin and α₂Macroglobulin (α₂M) levels were determined. TG was measured in platelet rich (PRP) and platelet poor plasma (PPP) of 217 healthy donors and prothrombin conversion and thrombin inactivation were calculated. VWF and FVIII levels were lower (75% and 78%) and α₂M levels were higher (125%) in the O group. TG is 10% lower in the O group in PPP and PRP. Less prothrombin was converted in the O group (86%) and the thrombin decay capacity was lower as well. In the O group, α₂M plays a significantly larger role in the inhibition of thrombin (126%). In conclusion, TG is lower in the O group due to lower prothrombin conversion, and a larger contribution of α₂M to thrombin inactivation. The former is unrelated to platelet function because it is similar in PRP and PPP, but can be explained by the lower levels of FVIII.

Differences in N-glycosylation of recombinant human coagulation factor VII derived from BHK, CHO, and HEK293 cells

BACKGROUND &

METHODS

Recombinant factor VII (rFVII), the precursor molecule for recombinant activated FVII (rFVIIa), is, due to its need for complex post translational modifications, produced in mammalian cells. To evaluate the suitability of a human cell line in order to produce rFVII with post-translational modifications as close as possible to pdFVII, we compared the biochemical properties of rFVII synthesized in human embryonic kidney-derived (HEK)293 cells (HEK293rFVII) with those of rFVII expressed in Chinese hamster ovary (CHO, CHOrFVII) and baby hamster kidney (BHK, BHKrFVII) cells, and also with those of plasma derived FVII (pdFVII), using various analytical methods. rFVII was purified from selected production clones derived from BHK, CHO, and HEK293 cells after stable transfection, and rFVII isolates were analyzed for protein activity, impurities and post-translational modifications. RESULTS &

DISCUSSION

The analytical results showed no apparent gross differences between the various FVII proteins, except in their N-linked glycosylation pattern. Most N-glycans found on rFVII produced in HEK293 cells were not detected on rFVII from CHO and BHK cells, or, somewhat unexpectedly, on pdFVII; all other protein features were similar. HEK293rFVII glycans were mainly characterized by a higher structural variety and a lower degree of terminal sialylation, and a high amount of terminal N-acetyl galactosamines (GalNAc). All HEK293rFVII oligosaccharides contained one or more fucoses (Fuc), as well as hybrid and high mannose (Man) structures.

CONCLUSIONS

From all rFVII isolates investigated, CHOrFVII contained the highest degree of sialylation and no terminal GalNAc, and CHO cells were therefore assumed to be the best option for the production of rFVII.

Novel investigations on the protective role of the FVIII/VWF complex in inhibitor development

Development of inhibitory antibodies to infused factor VIII (FVIII) concentrates is the most serious unresolved complication of haemophilia A treatment. Systematic reviews suggest a twofold higher incidence of inhibitors with recombinant (rFVIII) vs. plasma-derived (pdFVIII) FVIII products, but study methodologies vary widely. The lower immunogenicity of pdFVIII concentrates is believed to derive from the presence of von Willebrand factor (VWF) which acts as protector and chaperone for FVIII. Several novel investigations reinforce the protective role of the VWF/FVIII complex in inhibitor development. At the basic science level, numerous in vitro and in vivo experiments have demonstrated that VWF-containing pdFVIII concentrates (pdFVIII/VWF) provide better protection against inhibitor neutralization than rFVIII products. Conformational aspects of the binding between VWF and FVIII are thought to prevent the 'attack' on FVIII by inhibitory antibodies. VWF/FVIII binding is 100% in pdFVIII products but only 80% in recombinant products and this 'free' FVIII may be a target for inhibitory antibodies. At the clinical level, newer strategies to prevent inhibitor development in previously untreated patients with severe haemophilia are under investigation. The concept of early prophylaxis (before the onset of a bleed) is convincing from a theoretical point of view but requires further evaluation. The Study on Inhibitors in Plasma-Product Exposed Toddlers is specifically addressing the issue of relative immunogenicity between classes of FVIII product (recombinant vs. plasma-derived). Currently nearing its target enrolment of 300 patients, this international randomized controlled trial is expected to provide some definitive answers about this ever-present clinical dilemma.

Investigation of hFVIII production in mammary glands of transgenic mice

Hemophilia A is an X-linked disorder affecting 1 in 10,000 males. The disease is caused by a defect or mutation of factor 8 or 9. Human factor 8 gene (hFVIII) is a relatively large gene consisting of 26 exons and approximately 2,351 amino acids with a length of 9 Kb mRNA. Expression of hFVIII in mammalian milk is becoming a widespread strategy for high-level production of hFVIII because of the most complex post-translational modifications. The aim of this study was the cloning and expression of hFVIII in mammary glands of two transgenic mice. To obtain a recombinant plasmid, first a plasmid carrying an FVIII gene fragment (pCMV6-hFVIII) was digested by EcoRI-SalI restriction enzymes and then the fragment was purified from agarose gel and inserted into a pUCWAP7 vector carrying a tissue-specific promoter (mWAP 4.1 kbp). After that, it was isolated by agarose gel and transferred into the murine zygotes by standard microinjection methods. Methods for expression of recombinant FVIII RT-PCR and ELISA were studied. The results show the successful expression of factor FVIII gene and its product in the mouse mammary glands.

Elucidating the role of carbohydrate determinants in regulating hemostasis: insights and opportunities

Recent improvement in modern analytical technologies has stimulated an explosive growth in the study of glycobiology. In turn, this has lead to a richer understanding of the crucial role of N- and O-linked carbohydrates in dictating the properties of the proteins to which they are attached and, in particular, their centrality in the control of protein synthesis, longevity, and activity. Given their importance, it is unsurprising that both gross and subtle defects in glycosylation often contribute to human disease pathology. In this review, we discuss the accumulating evidence for the significance of glycosylation in mediating the functions of the plasma glycoproteins involved in hemostasis and thrombosis. In particular, the role of naturally occurring coagulation protein glycoforms and inherited defects in carbohydrate attachment in modulating coagulation is considered. Finally, we describe the therapeutic opportunities presented by new insights into the role of attached carbohydrates in shaping coagulation protein function and the promise of carbohydrate modification in the delivery of novel therapeutic biologics with enhanced functional properties for the treatment of hemostatic disorders.

Factor VIII inhibitors in hemophilia A: rationale and latest evidence

Factor VIII (FVIII) replacement therapy is the foundation of treatment in hemophilia A and is effective unless a patient develops an alloantibody (inhibitor) against exogenous FVIII. Inhibitor development is currently the most significant treatment complication seen in patients with hemophilia and is associated with considerable morbidity and a decreased quality of life. The development of an inhibitor is the result of a complex interaction between a patient's immune system and genetic and environmental risk factors. The mainstay of treatment is the eradication of the inhibitor through immune tolerance. This review summarizes the current evidence regarding inhibitor risk factors, eradication, and hemostatic bypassing agents.

Product-dependent anti-factor VIII antibodies

The development of anti-factor (F)VIII antibodies in haemophilia 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. The aim of this study was to evaluate the presence of anti-FVIII antibodies towards three commercial rFVIII products in 34 HA subjects' plasmas. Antibodies were quantitated by a Multiplex Fluorescence Immunoassay. All plasmas contained anti-FVIII antibodies at variable concentrations ranging from 50 nm to 570 μm. Eleven of the 20 HA subjects treated with one (r)FVIII product contained inhibitory anti-FVIII antibodies (0.8-3584 BU). The inhibitory antibody titre and the molar concentrations of total antibody were mildly correlated (r(2) = 0.6). Pronounced differences in antibody recognition with the three rFVIII products were observed. For the group treated with Product 'A', the titre towards this product was 2.4-fold higher than that observed with another full-length rFVIII-containing product (Product 'B') and almost four-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 titre when measured with this product. Our data suggest that the development of anti-FVIII antibodies is biased towards the product used for treatment and that a significant fraction of antibodies bind to the B domain of FVIII.

The role of natural VWF/FVIII complex concentrates in contemporary haemophilia care: a guideline for the next decade

Current treatment for haemophilia provides excellent efficacy and safety albeit with a number of unresolved issues. The development of inhibitors following treatment with factor VIII (FVIII) is the most challenging complication of haemophilia and bears the highest economic burden for a chronic disease. Moreover, prophylactic therapy for haemophilia requires repeated infusions of FVIII, frequently as often as two or three times weekly, which can impact greatly on patients' daily lives. As considerable scope remains for further advancements in the management of this condition, the primary focus of this paper relates to issues regarding current treatment and strategies in place to resolve the various issues. For countries approaching access to replacement therapy, it is important to know whether or not plasma-derived and recombinant products are associated with different risks of inhibitor development in previously untreated patients with severe haemophilia. The ongoing international SIPPET study is expected to provide an answer to this clinical dilemma. Methods under investigation to prolong the half-life of factor concentrates offer new hope to reduce the burden of prophylaxis for patients with haemophilia, with early results suggesting greater benefits with FIX.

How we choose factor VIII to treat hemophilia

In high-income countries, the large availability of coagulation factors for replacement therapy of patients with hemophilia A has raised the life expectancy of these lifelong bleeders to that of males from the general population. The practicing clinician is offered a multitude of choices among several commercial brands of factor VIII extracted from human plasma or engineered from mammalian cell cultures by means of recombinant DNA technology. This article has the goal to offer our opinions on how to choose among the different products, that we consider interchangeable relevant to their clinical efficacy in the control of bleeding and safety from pathogen transmission. Hence, the main determinants of our choices are price and the risk of occurrence of factor VIII inhibitory alloantibodies. With this as background, we present the rationale underlying the choices for different categories of patients with severe hemophilia A: previously untreated patients, multiply treated patients, and patients undergoing immune tolerance induction with large doses of factor VIII to eradicate inhibitors. Mention is also made to the possible strategies that should be implemented to make available coagulation factors for replacement therapy in developing countries.

Factor VIII and von Willebrand factor--too sweet for their own good

SUMMARY

Although factor VIII (FVIII) and von Willebrand factor (VWF) are products of two distinct genes, they circulate in plasma as a tight non-covalent complex. Moreover, they both play a critical role in the haemostatic process, a fact that is illustrated by the severe bleeding tendency associated with the functional absence of either protein. FVIII is an essential cofactor for coagulation factor IX, while VWF is pertinent to the recruitment of platelets to the injured vessel wall under conditions of rapid flow. FVIII and VWF have in common that they are heavily glycosylated: full-length FVIII contains 20 N-linked and at least seven O-linked glycans, while VWF contains 12 N-linked and 10 O-linked glycans. Three decades of research have revealed that the carbohydrate structures of FVIII and VWF contribute to many of the steps that can be distinguished in the life-cycle of these proteins, including biosynthesis/secretion, function and clearance. In this review, several of these aspects will be discussed. In addition, the interaction of the FVIII/VWF complex with two families of carbohydrate-binding proteins, i.e. Galectins and Siglecs, and their potential physiological relevance will be discussed.