Multicentre pharmacokinetic evaluation of rFVIII‐Fc (efmoroctocog alfa) in a real life and comparison with non‐extended half‐life FVIII concentrates

The use of enhanced half‐life (EHL) FVIII has improved the quality of prophylaxis in haemophilia A, but with a benefit that may vary from one patient to another. We analysed the pharmacokinetic data obtained with efmoroctocog alfa (rFVIII‐Fc) in 114 patients and, in 47 cases, compared them to those previously measured with non‐EHL FVIII. The in vivo recovery (IVR) of rFVIII‐Fc measured with one stage clotting assay (OSA) and chromogenic assay (CSA) was 2.2 and 2.8 IU/mL per IU/kg, respectively. The median half‐life (T_1/2) of rFVIII‐Fc was 14.5 hours whatever the FVIII:C assay used, but variable and correlated with preinfusion VWF:Ag levels (r = .76). Both IVR and T_1/2 were lower in patients under 12 years old (2.4 IU/mL per IU/kg and 11.1 hours, respectively; CSA). PK study of rFVIII‐Fc vs non‐EHL FVIII showed a T_1/2 ratio of 1.4 in favour of rFVIII‐Fc, regardless of the patient's age. However the relative increase in T_1/2 with rFVIII‐Fc was lower than 30% in one‐third of patients evaluated, particularly when the previous FVIII administered was a BHK‐derived product. This study therefore suggests that analysis of individual PK profile in response to a specific FVIII concentrate is potentially useful before a switch in haemophilia A patients.     

Parameters influencing FVIII pharmacokinetics in patients with severe and moderate haemophilia A

In haemophilia A patients factor VIII (FVIII) recovery and half‐life can vary substantially. There are parameters known to modulate FVIII pharmacokinetics (PK), but they explain only about 34% of the variability. The aim of this study was to identify new parameters that influence FVIII PK and thus to expand the current knowledge. FVIII PK were determined in 42 haemophilia A patients (37 severe, 5 moderate) without inhibitor. Patients' characteristics and laboratory parameters were evaluated for an association with FVIII PK. We analysed plasma levels of low‐density lipoprotein receptor‐related protein 1 (LRP1) and protein C (PC) activity, which had been hypothesized to influence FVIII activity. Furthermore, four variations in intron 6 of the LRP1 gene, which had been shown to influence LRP1, were investigated. FVIII half‐life differed widely from 6.2 to 20.7 h, with a median of 10.0 h. Patients with blood group O had shorter FVIII half‐life compared to patients with non‐O blood group (median FVIII half‐life 9.0 h vs. 10.4 h, P = 0.018). Age was significantly associated with FVIII half‐life (r = 0.32, P = 0.035). Besides age, also VWF antigen (r = 0.52, P < 0.001) and blood group (r = ?0.37, P = 0.015) was associated with FVIII half‐life. No correlation was found with FVIII‐ or LRP1‐genotype, LRP1 or PC concentrations. Our data showed large differences in FVIII PK between individual patients and revealed age, blood group and VWF levels as important determining factors for FVIII half‐life. FVIII genotype or levels of LRP1 or PC had no influence on FVIII PK.     

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 (r² = 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.     

Pharmacokinetic study of minipooled solvent/detergent‐filtered cryoprecipitate factor VIII

Summary. Eighteen cryoprecipitate minipools, each made of 30 units of low volume, concentrated cryoprecipitate, have been treated by solvent‐detergent and filtration (S/D‐F) in a single‐use CE‐marked bag system. The S/D‐F cryoprecipitate contained a mean of 10.5 IU mL⁻¹ factor VIII (FVIII), 17 mg mL⁻¹ clottable fibrinogen, and >10 IU mL⁻¹ von Willebrand factor ristocetin co‐factor, and anti‐A and anti‐B isoagglutinins were undetectable. The products have been infused in 11 severe (FVIII <1%) haemophilia A patients (mean age: 17.4 years; mean weight: 57.6 kg) at a dose close to 40 IU kg⁻¹. Patients were hospitalized for at least 36 h to determine FVIII recovery, half‐life and clearance. They were also closely monitored for possible adverse events. None of the infused patients demonstrated reactions or adverse events even though they did not receive anti‐allergic drugs or corticosteroids prior to infusion. The mean recovery of FVIII 10 min postinfusion was 69.7%. Mean FVIII half‐life was 14.2 h and clearance was 2.6 mL h⁻¹ kg⁻¹. All patients had a bleeding‐free interval of 8–10 days postS/D‐F cryoprecipitate infusion. The data show that S/D‐F cryoprecipitate FVIII presents a normal pharmacokinetics profile, and support that it could be safely used for the control of acute and chronic bleeding episodes in haemophilia A patients.     

Allergic reaction in a cohort of haemophilia A patients using plasma‐derived factor VIII (FVIII) concentrate is rare and not necessarily triggered by FVIII

In contrast to haemophilia B, allergic manifestations are rare complications in haemophilia A (HA) patients treated with factor VIII (FVIII) concentrates. Nevertheless, it can be serious and hamper replacement therapy in these cases. The aims of this study were to evaluate the frequency of allergic reaction in a cohort of HA patients treated only with plasma‐derived FVIII (pdFVIII) concentrates, and assess the possible immune mechanisms involved. History of allergic reaction was retrospectively assessed. Patients with allergic manifestations were followed, and had plasma samples collected in different timepoints in relation to the allergic episode. These samples were analysed for the presence of inhibitor and anti‐FVIII immunoglobulins subclasses. Three of 322 HA patients (0.9%) developed allergic reaction after exposure to pdFVIII products during the last 15 years in our centre. The first patient, with severe HA, without inhibitor, had anti‐pdFVIII IgE and IgG4, but no anti‐recombinant FVIII (rFVIII) IgE. The second patient, with severe HA, and high‐responding inhibitor, presented allergic manifestation with both, pdFVIII concentrate and activated prothrombin complex concentrate. Although anti‐pdFVIII and anti‐rFVIII IgG4 were detected, no anti‐FVIII IgE was present. The third patient, with moderate HA without inhibitor, atopic, had no anti‐FVIII immunoglobulin detected, and allergic symptoms disappeared after switching to rFVIII concentrate. This study corroborates the low incidence of allergic reactions in HA patients. In the three cases presented, the anti‐FVIII immunoglobulin profile demonstrated that the allergic manifestation was triggered by other proteins contained in pdFVIII products, and not directed to FVIII.     

Real‐world comparative analysis of bleeding complications and health‐related quality of life in patients with haemophilia A and haemophilia B

Introduction

Clinical severity and impact of haemophilia on quality of life have been generally considered to be lower for haemophilia B (HB) compared with haemophilia A (HA) patients.

Aims

To compare annual bleeding rate (ABR), target joint development and health‐related quality of life (HRQoL) between adult (≥18 years) severe HA and HB patients using recent data from the Cost of Haemophilia in Europe: a Socioeconomic Survey (CHESS) study.

Methods

Multivariate generalized linear models (GLM) were constructed to assess the relationship between haemophilia type, ABR, HRQoL (derived from EQ‐5D index scores) and the presence of target joints while controlling for covariates.

Results

Of the 1225 patients included, 77% (n = 949) had HA and 23% (n = 278) had HB. Of the 514 patients who completed the EQ‐5D, 78% (n = 405) had HA, and 22% (n = 110) had HB. Unadjusted mean ABR was 3.79 in HA and 4.60 in HB. The presence of ≥1 target joint was reported in 59% and 54% of patients with HA and HB, respectively. Unadjusted mean EQ‐5D index score was 0.78 in HA and 0.76 in HB. Haemophilia type was not a significant predictor of ABR, target joints or HRQoL when adjusted for confounding factors such as BMI, age and replacement therapy regimen.

Conclusion

Data suggest comparable ABR, incidence of target joints and HRQoL between patients with HB and HA indicating comparable clinical severity and disease impact on patient quality of life.     

In silico calculated affinity of FVIII‐derived peptides for HLA class II alleles predicts inhibitor development in haemophilia A patients with missense mutations in the F8 gene

Forty per cent of haemophilia A (HA) patients have missense mutations in the F8 gene. Yet, all patients with identical mutations are not at the same risk of developing factor VIII (FVIII) inhibitors. In severe HA patients, human leucocyte antigen (HLA) haplotype was identified as a risk factor for onset of FVIII inhibitors. We hypothesized that missense mutations in endogenous FVIII alter the affinity of the mutated peptides for HLA class II, thus skewing FVIII‐specific T‐cell tolerance and increasing the risk that the corresponding wild‐type FVIII‐derived peptides induce an anti‐FVIII immune response during replacement therapy. Here, we investigated whether affinity for HLA class II of wild‐type FVIII‐derived peptides that correspond to missense mutations described in the Haemophilia A Mutation, Structure, Test and Resource database is associated with inhibitor development. We predicted the mean affinity for 10 major HLA class II alleles of wild‐type FVIII‐derived peptides that corresponded to 1456 reported cases of missense mutations. Linear regression analysis confirmed a significant association between the predicted mean peptide affinity and the mutation inhibitory status (P = 0.006). Significance was lost after adjustment on mutation position on FVIII domains. Although analysis of the A1‐A2‐A3‐C1 domains yielded a positive correlation between predicted HLA‐binding affinity and inhibitory status (OR = 0.29 [95% CI: 0.14–0.60] for the high affinity tertile, P = 0.002), the C2 domain‐restricted analysis indicated an inverse correlation (OR = 3.56 [1.10–11.52], P = 0.03). Our data validate the importance of the affinity of FVIII peptides for HLA alleles to the immunogenicity of therapeutic FVIII in patients with missense mutations.     

Long‐term anti‐FVIII antibody response in Bethesda‐negative haemophilia A patients receiving continuous replacement therapy

It has previously been shown that patients with haemophilia A may develop non‐neutralizing anti‐factor VIII (FVIII) antibodies (NNA) that escape detection by the Bethesda assay, but are detected using immune‐based assays. We and others found NNAs to be directed not only towards non‐functional parts of the protein, but towards all regions of the FVIII protein. We also showed a heterogeneous antibody response towards different FVIII products. However, the clinical relevance and the natural history of NNA remain unclear. Therefore, we followed a cohort of unrelated subjects with haemophilia A for 4 years with the goal of exploring the long‐term development of NNA using an enzyme‐linked immunosorbent assay (ELISA). Ten of 78 subjects (12·8%) exhibited an immune response that was transient and heterogeneous, and none of the subjects developed an FVIII inhibitor. The result of the ELISA was examined in relation to clinical variables and no significant associations between a positive ELISA and age, F8 mutation, port‐à‐cath implantation and HCV infection were shown. Interestingly, patients with NNA had significantly fewer bleeding episodes (P = 0·048) compared with NNA‐negative subjects. The results indicate that the immune response to FVIII products within an individual may vary over time. However, the clinical impact of NNA remains unclear.     

Thrombin generation as objective parameter of treatment response in patients with severe haemophilia A and high‐titre inhibitors

In Mexico, 15% of haemophilia A (HA) patients develop inhibitory alloantibodies in response to replacement therapy with factor VIII (FVIII), requiring bypass therapy such as activated prothrombin complex concentrate (APCC). Because bypass therapy has not been broadly available in Mexico even in recent years, this study aimed to evaluate the thrombin generation assay (TGA) in assessing the response to FVIII or APCC treatment in patients with severe HA positive to inhibitors. We studied 189 patients with severe HA. Clinical severity was verified by one‐stage APTT‐based clotting assay. Inhibitors to FVIII were investigated by the Nijmegen–Bethesda (N–B) method, and type of inhibition was assessed through serial plasma dilutions. Thrombin generation was measured with the calibrated automated thrombogram in inhibitor‐positive plasmas previously spiked and incubated with FVIII or APCC. Data were analysed using anova , Student or Fisher's exact tests. We detected 47 (24.9%) subjects with high‐titre (5–1700 N–B U mL^?1) and 25 (13.2%) subjects with low‐titre inhibitor antibodies (0.6–4.7 N–B U mL^?1). We found an association between kinetic behaviour and clinical response to FVIII (P = 0.0049) or vs. FVIII response evaluated with TGA (P = 0.0007). Global concordance between clinical and in vitro response was 70%. By evaluating the capacity of thrombin formation in a plasma sample, TGA predicts the response to FVIII or APCC therapy and allows individual optimization of resources in patients with severe HA and high‐titre inhibitors. The inhibition pattern of the antibodies to FVIII:C correlated with the TGA parameters and showed an association with the clinical response to FVIII.     

Treatment burden,haemostatic strategies and real world inhibitor screening practice in non‐severe haemophilia A

Inhibitor formation in non‐severe haemophilia A is a life‐long risk and associated with morbidity and mortality. There is a paucity of data to understand real‐world inhibitor screening practice. We evaluated the treatment burden, haemostatic strategies, F8 genotyping and inhibitor screening practices in non‐severe haemophilia A in seven London haemophilia centres. In the 2‐year study period, 44% (377/853) patients received at least one haemostatic treatment. Seventy‐nine percent of those treated (296/377) received factor VIII (FVIII) concentrate. F8 genotype was known in 88% (331/377) of individuals. Eighteen per cent (58/331) had ‘high‐risk’ F8 genotypes. In patients with ‘standard‐risk’ F8 genotypes treated on‐demand with FVIII concentrate, 51·3% episodes (243/474) were screened within 1 year. However, poor screening compliance was observed after ‘high‐risk’ treatment episodes. In patients with ‘standard‐risk’ F8 genotypes, 12·3% (28/227) of treatment episodes were screened in the subsequent 6 weeks after surgery or a bleed requiring ≥5 exposure days. Similarly, in the context of ‘high‐risk’ F8 genotypes after any FVIII exposure, only 13·6% (12/88) of episodes were screened within 6 weeks. Further study is required to assess optimal practice of inhibitor screening in non‐severe haemophilia A to inform subsequent clinical decisions and provide more robust prevalence data to further understand the underlying immunological mechanism.     

Immunoglobulin isotypes and functional anti‐FVIII antibodies in response to FVIII treatment in Balb/c and C57BL/6 haemophilia A mice

Summary. Previous studies have demonstrated that genetic factors play an important role in determining the likelihood of formation of anti‐factor VIII (FVIII) antibodies in haemophilia A patients. We were interested in characterizing the spectrum of FVIII antibody formation and the primary and secondary immune responses after FVIII administration in two different exon 16‐disrupted haemophilia A mouse strains, Balb/c and C57BL/6. Balb/c and C57BL/6 E16 haemophilia A mice were used in all experiments. Total FVIII antibodies and FVIII inhibitors were measured using ELISA and Bethesda assays respectively. T‐ and B‐cell cytokines were quantified using ELISA and flow cytometry. FVIII antibodies, but not functional inhibitors were detectable 1 week after the first FVIII treatment in both strains. These antibodies mainly belonged to the IgM and IgA isotypes. After the fourth FVIII treatment, neutralizing anti‐FVIII antibodies were detected in both mouse strains: Balb/c (mean inhibitory titer 58 BU) and C57BL/6 (mean inhibitory titer 82 BU). IgG1 levels were similar in both strains but the IgG2A and IgG2B subclasses were higher in C57BL/6 mice. The results of intracellular cytokine staining of T cells indicated that the FVIII‐treated C57BL/6 mice produced more IL10 and Th1 cytokines than the FVIII‐treated Balb/c mice. These studies show that C57BL/6 mice develop a stronger immune response towards FVIII than Balb/c mice. We propose that the enhanced Th1 and IL10 cytokine micro‐environment induced in C57BL/6 mice is responsible for this difference. Therefore, genetic strain‐dependent differences must be considered when evaluating immunological outcomes in mouse models of haemophilia A.     

Lack of recombinant factor VIII B‐domain induces phospholipid vesicle aggregation: implications for the immunogenicity of factor VIII

Factor VIII (FVIII) is a multidomain blood plasma glycoprotein. Activated FVIII acts as a cofactor to the serine protease factor IXa within the membrane‐bound tenase complex assembled on the activated platelet surface. Defect or deficiency in FVIII causes haemophilia A, a severe hereditary bleeding disorder. Intravenous administration of plasma‐derived FVIII or recombinant FVIII concentrates restores normal coagulation in haemophilia A patients and is used as an effective therapy. In this work, we studied the biophysical properties of clinically potent recombinant FVIII forms: human FVIII full‐length (FVIII‐FL), human FVIII B‐domain deleted (FVIII‐BDD) and porcine FVIII‐BDD bound to negatively charged phospholipid vesicles at near‐physiological conditions. We used cryo‐electron microscopy (Cryo‐EM) as a direct method to evaluate the homogeneity and micro‐organization of the protein‐vesicle suspensions, which are important for FVIII therapeutic properties. Applying concurrent Cryo‐EM, circular dichroism and dynamic light scattering studies to the three recombinant FVIII forms when bound to phospholipid vesicles revealed novel properties for their functional, membrane‐bound state. The three FVIII constructs have similar activity, secondary structure distribution and bind specifically to negatively charged phospholipid membranes. Human and porcine FVIII‐BDD induce strong aggregation of the vesicles, but the human FVIII‐FL form does not. The proposed methodology is effective in characterizing and identifying differences in therapeutic recombinant FVIII membrane‐bound forms near physiological conditions, because protein‐containing aggregates are considered to be a factor in increasing the immunogenicity of protein therapeutics. This will provide better characterization and development of safer and more effective FVIII products with implications for haemophilia A treatment.     

Postauthorization safety surveillance of ADVATE [antihaemophilic factor (recombinant), plasma/albumin‐free method] demonstrates efficacy,safety and low‐risk for immunogenicity in routine clinical practice

Summary. Postauthorization safety surveillance of factor VIII (FVIII) concentrates is essential for assessing rare adverse event incidence. We determined safety and efficacy of ADVATE [antihaemophilic factor (recombinant), plasma/albumin‐free method, (rAHF‐PFM)] during routine clinical practice. Subjects with differing haemophilia A severities and medical histories were monitored during 12 months of prophylactic and/or on‐demand therapy. Among 408 evaluable subjects, 386 (95%) received excellent/good efficacy ratings for all on‐demand assessments; the corresponding number for subjects with previous FVIII inhibitors was 36/41 (88%). Among 276 evaluable subjects receiving prophylaxis continuously in the study, 255 (92%) had excellent/good ratings for all prophylactic assessments; the corresponding number for subjects with previous FVIII inhibitors was 41/46 (89%). Efficacy of surgical prophylaxis was excellent/good in 16/16 evaluable procedures. Among previously treated patients (PTPs) with >50 exposure days (EDs) and FVIII ≤2%, three (0.75%) developed low‐titre inhibitors. Two of these subjects had a positive inhibitor history; thus, the incidence of de novo inhibitor formation in PTPs with FVIII ≤2% and no inhibitor history was 1/348 (0.29%; 95% CI, 0.01–1.59%). A PTP with moderate haemophilia developed a low‐titre inhibitor. High‐titre inhibitors were reported in a PTP with mild disease (following surgery), a previously untreated patient (PUP) with moderate disease (following surgery) and a PUP with severe disease. The favourable benefit/risk profile of rAHF‐PFM previously documented in prospective clinical trials has been extended to include a broader range of haemophilia patients, many of whom would have been ineligible for registration studies.     

Protected by nature? Effects of strenuous physical exercise on FVIII activity in moderate and mild haemophilia A patients: a pilot study

Increase of factor VIII activity (FVIII) after physical exercise has been reported in healthy subjects and small‐scale studies in patients with coagulopathies. The aim was to study whether moderate and mild haemophilia A patients are able to increase their endogenous FVIII activity levels by physical activity. We studied changes in FVIII activity levels after high‐intensity exercise in 15 haemophilia A patients, 20–39 years, eight with moderate, seven with mild haemophilia. Patients cycled until volitional exhaustion, blood samples were drawn before and 10 min after the exercise test. FVIII activity increased 2.5 times (range 1.8–7.0 times), for both severities. Absolute increases were markedly different: median 7 IU dL^?1 (range 3–9 IU dL^?1) in patients with moderate, compared to 15 IU dL^?1 (range 6–62 IU dL^?1) in mild haemophilia patients. VWF and VWFpp increased independently of severity; median 50% (range 8–123%) and median 165% (range 48–350%), respectively, reflecting acute release of VWF. These observations may be used to promote high‐intensity activities before participating in sports for moderate and mild haemophilia A patients, to reduce bleeding risk. Further studies are warranted to fully appreciate the clinical significance of exercise on different levels of intensity in patients with mild and moderate haemophilia A.     

BAY 94‐9027, a PEGylated recombinant factor VIII,exhibits a prolonged half‐life and higher area under the curve in patients with severe haemophilia A: Comprehensive pharmacokinetic assessment from clinical studies

Introduction

Recombinant factor VIII (rFVIII) products with extended half‐lives, such as BAY 94‐9027, can potentially maintain higher FVIII levels for longer periods of time, thus providing improved bleeding protection vs standard‐acting FVIII products.

Aim

To characterize the pharmacokinetic (PK) profile of BAY 94‐9027 from phase 1, phase 2/3 (PROTECT VIII) and phase 3 (PROTECT VIII Kids) clinical trials in adults, adolescents and children with severe haemophilia A

Methods

Patients with severe haemophilia A (FVIII <1%) with >50 FVIII exposure days (EDs) and no history of inhibitors were included in the phase 1 (18–65 years, ≥150 EDs), PROTECT VIII (12–65 years, ≥150 EDs) and PROTECT VIII Kids (<12 years, >50 EDs) trials. PK parameters were assessed following a 25‐IU/kg or 60‐IU/kg BAY 94‐9027 dose in the phase 1 study after the first and repeated infusion, in PROTECT VIII after the first and repeated 60‐IU/kg infusion and in PROTECT VIII Kids after a single 60‐IU/kg infusion. The chromogenic assay was used to assess FVIII activity.

Results

Compared with sucrose‐formulated rFVIII, BAY 94‐9027 had reduced clearance that resulted in a ~1.4‐fold increase in half‐life and dose‐normalized area under the curve (AUC). The BAY 94‐9027 PK profile was comparable after single‐ and repeated‐dose administrations. Dose‐proportional increases were observed between 25‐ and 60‐IU/kg administrations. BAY 94‐9027 PK characteristics were age dependent, consistent with other FVIII products.

Conclusions

BAY 94‐9027 shows an extended half‐life and increased AUC vs standard‐acting FVIII products. These PK characteristics will result in higher FVIII levels for longer duration.     

Assessment of the thrombin generation assay in haemophilia: Comparative study between fresh and frozen platelet‐rich plasma

The severity of haemophilia A has traditionally been classified by the dosage of factor VIII (FVIII) by one‐step coagulation tests. However, an homogeneous group of patients with similar FVIII levels show clinical heterogeneity and 10–15% of the patients classified as severe haemophilia do not have a severe bleeding phenotype. Traditional tests used for measuring FVIII are not capable of detecting other prohaemorrhagic or prothrombotic factors. Global tests as the thrombin generation assay (TGA) may detect these haemostatic factors. So TGA may be an additional tool for classifying the actual severity of haemophilia. Our group is carrying out correlation tests between FVIII and TGA in platelet‐poor and ‐rich plasmas (PPP and PRP, respectively). PRP has the inconvenience that must be done freshly soon after blood extraction. Our aim is to study the differences between TGA performed with fresh and frozen PRP and PPP and its implementation in multicenter studies. We included 70 patients with severe haemophilia A in prophylactic treatment. Venous blood drawing was obtained prior to administration of FVIII, at the trough levels. FVIII measurement and TGA were performed in fresh and frozen PRP and PPP. The platelet absence caused a significant decrease in TGA although PPP and PRP correlated well. Frozen samples gave different results in PPP, but there were no significant differences between fresh and frozen PRP. This fact enables using frozen PRP in multicenter studies with a TGA‐specialized laboratory for reclassifying haemophilia severity and for pharmacokinetic studies with TGA.     

A longitudinal evaluation of anti‐FVIII antibodies demonstrated IgG4 subclass is mainly correlated with high‐titre inhibitor in haemophilia A patients

The development of inhibitory antibodies against factor VIII (FVIII) (inhibitor) is the major complication in haemophilia A patients. The FVIII‐binding antibodies development comprises a polyclonal immunoglobulin (Ig) G response. Recent studies showed strong correlation between the presence of neutralizing anti‐FVIII antibodies (inhibitors) and IgG4 subclass. The aim of this study was to evaluate anti‐FVIII IgG subclasses in haemophilia A patients with inhibitor both in a cross‐sectional and in a longitudinal analysis. Inhibitors were determined by Nijmegen–Bethesda assay. Anti‐FVIII IgG subclasses were performed by ELISA, and samples from 20 healthy individuals were used to validate the test. We studied 25 haemophilia A patients with inhibitor, previously treated exclusively with plasma‐derived FVIII concentrates or bypassing agents. The IgG subclasses distributions were evaluated in two groups of patients classified according to inhibitor response. IgG1 and IgG4 antibodies were most prominent in haemophilia A patients with inhibitors when compared with IgG2 and IgG3. This study reports for the first time the behaviour of FVIII‐binding IgG1 and IgG4 subclasses in a longitudinal analysis, in a clinical setting, of high‐response inhibitor haemophilia A patients, showing the correlation of IgG4 and the inhibitor titres. In spite of being considered a non‐pathologic antibody subclass with anti‐inflammatory properties in other situations, IgG4 is correlated with the presence of high‐titre inhibitor in the haemophilia setting. The comprehension of the IgG4 role in immune response may be crucial to establish the process for designing specific tolerance to FVIII.     

Break‐through bleeding in relation to pharmacokinetics of Factor VIII in paediatric patients with severe haemophilia A

Introduction

As the pharmacokinetics (PK) of factor VIII (FVIII) is individualized in children with haemophilia A (HA), PK parameters may be indicators of patients' bleeding phenotype and instruction for their personalized replacement program.

Aim

The aim of this study was to investigate the possible relationship between PK/FVIII level and bleeding frequency in Chinese paediatric patients with severe (HA).

Methods

A total of 24 patients were enrolled in Beijing Children's Hospital from February to October 2015, all of whom were given 50 IU/kg of FVIII concentrates after a 72‐hours washout period. Samples' activities (FVIII:C) were tested at 5 time points, using WinNonlin software for PK testing, and then the individual half‐life(t_1/2) and the time (h) of FVIII concentrations <1 IU/dL within a week during prophylaxis were calculated. Baseline and the annual bleeding rate (ABR), annual joint bleeding rate (AJBR) were recorded and analyzed.

Results

The mean t_1/2 of FVIII was 10.20 ± 2.72 hours and the mean time of FVIII <1 IU/dL in 1 week was 44.7 hours (?38.56 to 102.33 hours). A significant relationship between t_1/2 of FVIII and ABR₀/AJBR₀ (baseline bleeding) was found (R² = 0.75 and 0.62, P < .001). Besides, baseline and the annual bleeding rate during prophylactic treatment of haemophilia had a positive correlation with the time (hours) of FVIII <1 IU/dL in 1 week (R² = 0.67 and 0.52, P < .001).

Conclusion

t_1/2 was an important indicator to prevent bleeding in severe HA; the frequency of bleeding will be reduced with the increased of t_1/2 of FVIII. The data also demonstrates that increasing the time with a FVIII<1 IU/dL is associated with an increased rate of bleeding during prophylaxis.     

Retrospective analysis of differences in annual factor VIII utilization among haemophilia A patients

Finding differences in drug utilization patterns within rare patient populations is challenging without access to a large sample. Our objective was to identify patient and treatment-related factors associated with differences in annual recombinant factor VIII (rFVIII) utilization in a large cohort of haemophilia A patients. This retrospective analysis utilized a large, US specialty pharmacy dispensing database from January 2006 to September 2009. Differences in median annual FVIII utilization (IU kg(-1) year(-1)) by age, severity, treatment regimen, rFVIII product type and health insurance plan were tested using non-parametric statistics and regression analysis. A total of 1011 haemophilia A patients were included in the overall analysis. Severe haemophilia patients had higher median annual FVIII utilization than mild/moderate patients (P < 0.0001). Median annual FVIII utilization was also significantly different between treatment regimens (episodic = 1429 IU kg(-1) year(-1) vs. prophylaxis = 3993 IU kg(-1) year(-1) for severe patients, P < 0.0001). Children (0-12 years old), adolescents (13-18 years old) and adults (19+ years old) with severe haemophilia A receiving prophylaxis utilized 4588, 4082 and 3223 IU kg(-1) year(-1) (P < 0.0001). After controlling for age, severity, treatment regimen and insurance type, regression analysis revealed B domain-deleted recombinant FVIII (BDD-rFVIII) was associated with 33% higher FVIII consumption compared with full-length recombinant FVIII (FL-rFVIII) (P = 0.0172). Similar results were also seen when matching BDD-rFVIII and FL-rFVIII patients. Health insurance type was not associated with annual FVIII utilization. As expected, age, severity and treatment regimen were significantly associated with FVIII utilization. After controlling for confounders, patients receiving FL-rFVIII prophylactically were associated with lower annual FVIII utilization compared with patients receiving BDD-rFVIII prophylactically.     

Immune response against serial infusion of factor VIII antigen through an implantable venous-access device system in haemophilia A mice

Haemophilia A is a life long bleeding disorder caused by an inherited deficiency of factor VIII (FVIII). About 30% of haemophilia A patients develop neutralizing antibodies as a consequence of treatment with FVIII concentrates. Immune tolerance protocols for the eradication of inhibitors require daily delivery of intravenous FVIII. We evaluated the immune responses to serial intravenous administration of FVIII in preimmunized haemophilia A mice. We introduced an implantable venous-access device (iVAD) system into haemophilia A mice to facilitate sequential infusion of FVIII. After preimmunization with FVIII, the haemophilia A mice were subjected to serial intravenous administration of FVIII through the iVAD system. In all mice with serial infusion of FVIII, high titers of anti-FVIII inhibitory antibodies developed at 10 exposure days (EDs). However, the anti-FVIII IgG titers were decreased after 150 EDs of sequential low-dose infusion of FVIII [0.05 U g(-1) body weight (BW) five times per week]. Proliferative response to ex vivo FVIII stimulation was significantly suppressed in splenic CD4(+) T cells from mice with serial low-dose FVIII infusion compared with those from mice with high-dose FVIII infusion (0.5 U g(-1) BW five times per week) or preimmunized mice. Moreover, splenic CD4(+) T cells from mice with serial low-dose infusion of FVIII failed to produce interleukin-2 and interferon-γ. These data suggest that serial infusion of FVIII could induce T-cell anergy in haemophilia A mice with inhibitor antibodies.