A putative inhibitory mechanism in the tenase complex responsible for loss of coagulation function in acquired haemophilia A patients with anti-C2 autoantibodies

Characterization and Usefulness of Clot-Fibrinolysis Waveform Analysis in Critical Care Patients with Enhanced or Suppressed Fibrinolysis

INTRODUCTION

 Recently, clot-fibrinolysis waveform analysis (CFWA), which is a coagulation and fibrinolysis global assay based on assessing the activated partial thromboplastin time with tissue-type plasminogen activator, was developed. This study aimed to investigate the characteristics of CFWA using plasma samples from patients in the critical care unit.

MATERIALS AND METHODS

 The fibrinolysis times using CFWA were measured in 298 plasma samples. These samples were divided into three groups based on the reference interval (RI) of fibrinolysis time using CFWA: shortened group, less than RI; within group, within RI; prolonged group, more than RI. The coagulation and fibrinolysis markers, including D-dimer, plasmin-α2 plasmin inhibitor complex (PIC), fibrin monomer complex (FMC), plasmin-α2 plasmin inhibitor (α2-PI), plasminogen (Plg), and fibrinogen (Fbg) were analyzed and compared among the three groups.

RESULTS

 The FMC level decreased in the order of shortened, within, and prolonged groups, and the decrease was statistically significant among all three group pairs. The opposite tendency was observed for Fbg and fibrinolysis-related markers of α2-PI and Plg, and significant differences were recognized in all pair comparisons except for between within and prolonged groups in Plg. The mean values of the fibrinolysis markers D-dimer and PIC in all three groups were higher than the cut-off values, and the PIC value differed significantly between the within and prolonged groups.

CONCLUSION

 The fibrinolysis reaction was detected in all three groups, but the status differed. CFWA has the potential to reflect the fibrinolysis status in one global assay.

Clot Waveform Analysis for Monitoring Hemostasis

Clot waveform analysis (CWA) is a recently developed global coagulation assessment, based on the continuous observation of changes in light transmittance, absorbance, or light scattering that occurs as fibrin formed in a plasma sample during routine clotting tests such as activated partial thromboplastin time (aPTT) and prothrombin time (PT). CWA can utilize qualitative waveform patterns as well as sensitive quantitative parameters and can be used as a simple method to assess global hemostasis, and can be applied to various challenging clinical situations. Although not all coagulation analyzers currently in use are able to provide CWA, the number of analyzers available to do so is increasing, as the usefulness of this process has become more widely recognized. CWA can be based on the coagulation mechanism of aPTT, an intrinsic trigger, and this has been reported in many studies, including diagnosis and treatment of patients with hemophilia, disseminated intravascular coagulation, and monitoring of anticoagulants and thrombosis. CWA using trace amounts of tissue factors also has the potential to expand the applications of this technology. Recently, there have been reports of the combined evaluation of fibrinolytic dynamics. Among the existing global coagulation assays, CWA may prove to be the easiest to standardize in clinical practice. However, more extensive testing using standardized methods in various clinical settings is needed to determine the true role of CWA in the evaluation of hemostasis and thrombosis in the future.

Acquired haemophilia A in southern Switzerland from 2013 to 2019: a case series

AIMS OF THE STUDY: Acquired haemophilia A is a rare disease with an annual incidence of 1.48 per million. Based on clinical observations, we suspect a higher incidence in southern Switzerland, and aimed at providing local epidemiological data, and clinical information regarding diagnosis, treatment and outcome in our region. METHODS: All adult patients with acquired haemophilia A treated between 2013 and 2019 in our facility were included in the present retrospective analysis. RESULTS: We treated 11 patients with acquired haemophilia A between 2013 and 2019, resulting in an annual incidence of 4.5 per million (95% confidence interval [CI] 0–9.0). Median delay from first symptoms to diagnosis was 4.5 days, and the median age at diagnosis was 79 years (range 23–87). Possible causative conditions were: pregnancy (n = 1), polyarteritis nodosa (n = 1), myelodysplastic syndrome (n = 1), chronic human immunodeficiency virus (HIV) (n = 1), and HIV postexposure prophylaxis (n = 1). In five patients no underlying or associated condition was identified. Median activated partial thromboplastin time (aPTT)) at baseline was 79 seconds (65–117; ref. value <38 sec), and FVIII:C 2.15% (<1–3.75%). A FVIII:C <1% was present in 4/10 patients. Median FVIII-inhibitor titre was 10.3 BU/ml (2.4–75.0 BU/ml). All patients had bleeding symptoms, 5/10 patients had major bleedings, and 7/10 patients were treated with bypassing agents. All patients received corticosteroids; 7/10 patients received immunosuppressive combination therapy. FVIII levels of ≥50% were achieved after a median of 40 days (8–62). One patient had a severe immunosuppressive therapy-related infection. An 87-years-old woman died for reasons not related to acquired haemophilia A or immunosuppressive therapy. CONCLUSIONS: Acquired haemophilia A is a rare disease, but manageable despite the advanced patient age and comorbidities. Its incidence in Southern Switzerland is higher than previously suspected.

Acquired Hemophilia A: A Retrospective Multicenter Analysis of 42 Patients

INTRODUCTION

Immunosuppressive therapy (IST) for acquired hemophilia A (AHA) results in remission within days to months in 60% to 80% of patients. However, little is known regarding the predictors of response.

AIM

This study aimed to identify the factors that influence response to treatment.

METHODS

The data of 42 patients with AHA from three hospitals were retrospectively analyzed.

RESULTS

All 42 AHA patients received IST; complete treatment data were available for 34 patients. The response rate was 60% among the 5/34 (14.7%) patients who received steroids alone, 70.8% among the 24/34 (70.6%) patients who received steroids plus cyclophosphamide, and 80% among the 5/34 (14.7%) patients who received steroids plus cyclophosphamide and rituximab. Overall, 29/34 (85.3%) patients achieved CR; 4/34 (13.8%) of them relapsed after a median time of 410 (21-1279) days. Adverse events occurred in 14/34 (41.2%) patients: 13/34 (38.2%) had infections and 1/34 (2.9%) developed pancytopenia. In univariate and multivariate Cox regression analyses, FVIII inhibitor titer ≥20 BU/mL was the only significant prognostic factor affecting time to CR. No variable had significant effect on OS.

CONCLUSION

FVIII inhibitory antibody titer ≥20 BU/mL appears to be an important predictor of time to complete response in patients with acquired hemophilia A treated with immunosuppressive therapy.

Comprehensive blood coagulation potential in patients with acquired hemophilia A: retrospective analyses of plasma samples obtained from nationwide centers across Japan

Global coagulation potential was assessed in 59 patients with acquired hemophilia A (PwAHA) by clot waveform analysis (CWA) and/or thrombin and plasmin generation assay. Relationships between factor VIII activity (FVIII:C) and the parameters from CWA and T/P-GA in patients with congenital HA were compared by grading coagulation potential related to FVIII:C: T1 (FVIII:C < 1 IU/dL), T2 (1 ≤ , ≤ 5 IU/dL), T3 (5 < , 12 ≤ IU/dL), and T4 (12 < , ≤ 50 IU/dL). The median FVIII:C and inhibitor titers in PwAHA on admission were 3.3 IU/dL and 63.0 BU/mL, respectively, but global coagulation parameters corresponded to T1 or less. Median FVIII:C levels during follow-up in PwAHA were 1.7-9.6-6.7-40.0-21.7 IU/dL on days 0-14-28-56-93, respectively. CWA-based data corresponded to less than T2 until day 28, but more closely reflected FVIII:C after day 56. Peak thrombin was severely low (near T1) until day 28 and improved modestly after day 56 but remained less than T2. Peak plasmin was lower than T1 until day 56, and returned to T4 on day 93. In conclusion, global coagulation function in PwAHA was impaired to a greater extent than could be anticipated from assays of FVIII:C, until approximately 1 month after immunosuppression and treatment with FVIII-bypassing agents.

Single centre experience on Acquired Haemophilia A patients: Diagnosis, clinical management and analysis of factors predictive of response and outcome

BACKGROUND

Acquired Haemophilia A (AHA) patients show a high response rate to immunosuppressive therapy (IST) but few information about predictors of response and outcome are reported.

AIMS

We describe a large single-centre AHA cohort, investigating prognostic variables for the 'best response' (BR), time to BR (TTBR) and overall survival (OS).

METHODS

A total of 61 patients were included, collecting data from clinical charts.

RESULTS

A progressive increase in diagnoses, from 1978 to 2019, was observed. Fifty/56 patients (89%) underwent haemostatic therapy (rFVIIa 46%, aPCC 34%) with no significant differences in the response (rFVIIa 92.3% vs aPCC 100%) and no thromboembolic events. Sixty/61 patients underwent first-line IST with an initial response rate of 58.4%. The 12-months OS was 85%, the bleeding associated mortality rate 3% (2/61). The response rates at last observation were: CR 64%, PR 8%. We evaluated the influence of age, gender, associated conditions, IST, haemoglobin levels, FVIII:C, inhibitor titre on BR, TTBR and OS: post-partum AHA achieved the BR after a longer time than AHA related to other aetiologies or idiopathic (p = .05); in univariate analysis female sex (p = .03) and the achievement of BR (p = .001) had a positive impact on the OS while AHA secondary to neoplasms showed a shorter survival (p = .04); only the BR achievement remained significant in multivariate analysis (p = .02).

CONCLUSIONS

Our data on response and survival confirmed those from the main registries. Post-partum AHA and BR achievement were significantly associated to a longer TTBR and a longer OS, respectively. Other predictors of outcome deserve to be explored in prospective studies.

Ex Vivo Prediction of Comprehensive Coagulation Potential Using Simulated Blood Concentrations of Emicizumab in Patients with Acquired Hemophilia A

INTRODUCTION

 Emicizumab prophylaxis improves coagulation function in congenital hemophilia A, regardless of inhibitor presence. We recently reported that emicizumab enhanced the coagulant potentials, ex vivo, in plasmas from patients with acquired hemophilia A (PwAHAs) at diagnosis. However, coagulant effects of emicizumab in PwAHAs during the clinical course remain unclear.

AIM

 To assess ex vivo coagulant effects of emicizumab in PwAHAs during the clinical course.

METHODS/RESULTS

 Blood samples were obtained from 14 PwAHAs on (median) days 0 and 6 during a severe-bleeding phase, and days 27 and 59 during a reduced-bleeding phase with elevated endogenous factor VIII (FVIII) and decreased inhibitor titers. If administered a single dose of 3 or 6 mg/kg, or two doses at 6 mg/kg followed by 3 mg/kg, estimated plasma emicizumab concentrations (10/5/2.5, 20/10/5, and 30/15/7.5 µg/mL on days 0-7/30/60, respectively) could be used to represent potential changes, based on the half-life (T _1/2: ∼30 days). Emicizumab concentrations that covered maximum plasma concentrations of each dosage were used for spiking on day 0. Ex vivo addition of estimated emicizumab to PwAHA's plasma containing endogenous FVIII and/or inhibitor, without and with recombinant (r)FVIIa administration during immunosuppressive therapy, increased the calculated Ad|min1| values, assessed by clot waveform analysis, and their coagulant potentials were below normal levels. Rotational thromboelastometry revealed that ex vivo emicizumab addition resulted in the further improvement of coagulant potentials in whole bloods when combined with rFVIIa administration.

CONCLUSION

 Based on ex vivo and in vitro data, emicizumab has the potential to be effective in clinical situations for PwAHAs.

A Novel Assessment of Factor VIII Activity by Template Matching Utilizing Weighted Average Parameters from Comprehensive Clot Waveform Analysis

BACKGROUND

 Activated partial thromboplastin time (aPTT)-based clot waveform analysis is used to evaluate the comprehensive dynamics of fibrin clot formation. In addition, the technique can be usefully utilized for the rapid assessment of factor (F)VIII procoagulant activity in various clinical settings in patients with hemophilia A (HA). We defined a novel algorithm based on the weighted average parameters from aPTT-based waveforms to devise a template-matching procedure for assessing FVIII activity (FVIII:C).

METHODS

 The first derivatives of original clot waveforms triggered by the aPTT reagent (Coagpia APTT-N) were used to determine weighted averages of areas surrounded by the waveform at different percentages of maximum height in various clotting factor-deficient plasmas. Prepared templates based on 50 weighted average-related parameters were compared with 78 aPTT-prolonged plasmas.

RESULTS

 Original nonsmoothed waveforms of the various clotting factor-deficient plasmas with prolonged aPTTs demonstrated a variety of shapes. The weighted averages were calculated after adjustments for different baselines, and the patterns seemed to be governed by the specific clotting factor deficiency. The weighted average-related parameters including baseline wedge (r ² = 0.998) and aspect ratio (r ² = 0.998) were highly correlated with FVIII:C levels. Template-matching analyses based on weighted average-related waveform parameters obtained from 158 samples demonstrated that the sensitivity was 97.2% and specificity was 83.3% in aPTT-prolonged plasmas (n = 78).

CONCLUSION

 This novel algorithm based on weighted averages of aPTT-based waveforms together with template-matching may support clinical usefulness for judging of HA and may aid clinical management in the patients in the absence of specific clotting factor assays.

Acquired Haemophilia A: An Intriguing Disease

Abstract. Acquired Haemophilia A is a rare acquired bleeding disorder caused by Factor VIII autoantibodies, which neutralise FVIII activity. These inhibitors differ from alloantibodies against FVIII, which can occur in congenital Haemophilia A after repeated exposures to plasma-derived or recombinant FVIII products. In most cases, the disease occurs suddenly in subjects without a personal or familiar history of bleedings, with symptoms that may be mild, moderate, or severe. However, only laboratory alterations are present in ~ 30% of patients. The incidence varies from 1 to 4 cases per million/year; more than 80% of patients are elderly, males and females are similarly affected. There is a small peak of incidence related to pregnancy in young women aged 20–40 years. The disease may be underdiagnosed in the elderly. The diagnostic algorithm is based on an isolated prolonged activated partial thromboplastin time, normal thrombin time, absence of Lupus Anticoagulant, and a mixing test that reveals the presence of an inhibitor: the finding of reduced FVIII activity and the detection of neutralising autoantibodies against FVIII lead to the diagnosis. The disease is idiopathic in 44%–63% of cases, while in the others etiological factors are present. Bleeding prevention and treatment are based on therapeutic tools as by-passing agents, recombinant porcine FVIII concentrate or, in a limited number of cases, FVIII concentrates and desmopressin. As soon as the diagnosis has been made, immunosuppressive therapy must be started to eradicate the inhibitor. Better knowledge of the disease, optimal management of bleeding and eradication of the inhibitor have significantly reduced morbidity and mortality in most patients.

An anti-factor IXa/factor X bispecific antibody, emicizumab, improves ex vivo coagulant potentials in plasma from patients with acquired hemophilia A

INTRODUCTION

Acquired hemophilia A (AHA) is caused by autoantibodies against factor (F)VIII, and is characterized by severe, spontaneous bleeding, which can be life-threatening. Emicizumab, an anti-FIXa/FX bispecific antibody, significantly reduces bleeding events in congenital hemophilia A (HA) with and without inhibitors. The known pathophysiological mechanisms and current preclinical data in HA suggest that emicizumab could provide effective treatment for AHA, but the coagulation activities of emicizumab in these patients remain unknown.

AIM

To evaluate the coagulant effects of emicizumab in plasma from AHA patients.

METHODS AND RESULTS

Tissue factor-triggered thrombin generation assays using normal plasma preincubated with anti-FVIII monoclonal antibodies recognizing different epitopes demonstrated that 20 µg/mL emicizumab recovered the depressed peak levels of thrombin generation to 46% to 72%. Further studies were devised, therefore, to simulate the clinical course in AHA patients, including during the acute phase for severe bleeding requiring FVIII-bypassing therapy, and during the subacute/chronic phase with less bleeding. Various concentrations of emicizumab were used to represent the potential changes in plasma levels based on the half-life of the antibody (~30 days). The ex vivo addition of emicizumab to plasma samples from AHA patients (n = 16) increased peak thrombin in all cases, irrespective of the inhibitor epitope specificity. Thrombin generation at 20 and 100 µg/mL emicizumab was restored to (median) 43.9% and 92.2%, respectively. Differences were evident in some cases, however, and recovery rates appeared likely to be greater in patients with type 2 inhibitor than those with type 1.

CONCLUSION

Emicizumab improved ex vivo coagulation potential in plasma from AHA patients.

Emicizumab, the bispecific antibody to factors IX/IXa and X/Xa, potentiates coagulation function in factor XI-deficient plasma in vitro

Essentials Emicizumab mimics factor (F)VIIIa cofactor function, augments the intrinsic tenase activity. We assessed the emicizumab-driven hemostatic function in FXI-deficient plasmas. Emicizumab improved the coagulation potentials in severe FXI-deficient plasma. Emicizumab may provide a possibility for clinical application in patients with FXI deficiency. SUMMARY: Background Patients with factor (F)XI deficiency commonly present with markedly prolonged activated partial thromboplastin times (APTT), although bleeding phenotypes are heterogeneous. Emicizumab, a bispecific monoclonal antibody to FIX/FIXa and FX/FXa, mimics FVIIIa cofactor function on phospholipid (PL) surfaces. Antibody reactions were designed, therefore, to augment mechanisms during the propagation phase of blood coagulation. Aim To assess emicizumab-driven hemostatic function in FXI-deficient plasmas. Methods and Results Standard ellagic acid (Elg)/PL-based APTTs of different FXI-deficient plasmas (n = 13; FXI activity, < 1 IU dl-1 ) were markedly shortened dose dependently by the presence of emicizumab. To further analyze the effects of emicizumab, clot waveform analysis (CWA) in FXI-deficient plasmas with emicizumab, triggered by tissue factor (TF)/Elg demonstrated improvements in both clot times, reflecting the initiation phase, and coagulation velocity, which represents the propagation phase. Emicizumab also enhanced the TF/Elg-triggered thrombin generation in FXI-deficient plasmas dose-dependently although the degree of enhancement varied in individual cases. Thrombin generation with either FVII-deficient plasma or FIX-deficient plasma treated with anti-FXI antibody showed little or no increase by the co-presence of emicizumab, suggesting that the accelerated thrombin generation in FXI-deficient plasmas by emicizumab should depend on the FIXa-involved coagulation propagation initially triggered by FVIIa/TF. The ex vivo addition of emicizumab to whole blood from three patients with severe FXI deficiency demonstrated modest, dose-dependent improvements in Ca2+ -triggered thromboelastograms (NATEM mode). Conclusion Emicizumab appeared to improve coagulation function in severe FXI-deficient plasma, and might provide possibilities for clinical application in patients with FXI deficiency.

[A Pediatric Case of Acquired Hemophilia A: The Usefulness of the Activated Partial Thromboplastin Time (APTT) Cross-Mixing Test for Early Diagnosis]

Acquired hemophilia A (AHA), a bleeding disorder caused by autoantibodies against FVIII, has the potential for life-threatening bleeding. The annual onset rate is said to be one in 4 million people, but diagnosis examples increase in adults because a disorder concept penetrated. AHA is quite rare in children, with an incidence rate of 0.045 per 1 million, but early detection is crucial because serious bleeding can happen, as in adults. We report a pediatric case who received an early diagnosis of AHA by an activated partial thromboplastin time (APTT) cross-mixing test. The 12-year-old girl had neither a past history nor a family history of bleeding episodes. She presented with intramuscular bleeding and epistaxis without trauma or medication. At diagnosis, her blood test showed prolonged APTT. Other hemostatic tests, such as the platelet count, prothrombin time and fibrinogen concentration, were within the normal range. We administered an APTT cross-mixing test that detected an inhibitor pattern and inhibitory antibodies against factors VIII. As a result, we administered prednisolone and the inhibitor disappeared after 1.5 months. In conclusion, AHA is a bleeding disorder which should be considered even in children due to the potential for life-threatening bleeding. Furthermore, the APTT cross-mixing test is useful for screening coagulation factor deficiencies and inhibitors.

Assessment of in vitro effects of direct thrombin inhibitors and activated factor X inhibitors through clot waveform analysis

Aims

Clot waveform analysis (CWA) has been reported to extend the interpretation of clotting time measurement. The parameters obtained from successive derivatives of the clotting reaction curves reflect the rates of activation of individual coagulation factors, theoretically dissecting the cascade pathway. This study aims to assess the in vitro effects of direct thrombin inhibitors (DTIs) and activated factor X (FXa) inhibitors.

Methods

CWA was applied to the activated partial thromboplastin time (APTT) assay of plasma samples spiked with each drug. For CWA of APTT measurement curves (APTT-CWA), the positive mode of clotting reaction curves was defined as the direction towards fibrin generation.

Results

All the maximum positive values in the successive derivatives were decreased dependently on the concentrations of each drug. Moreover, the negative values in the second and third derivatives appeared putatively due to consumption of thrombin and factor FXa, respectively, to form complexes with plasma serine protease inhibitors. The decrease of the maximum negative values observed dependently on the concentrations of each drug appeared to be consistent with the decreased generation of thrombin and factor FXa. The analysis of Hill coefficients of each drug in the dose–response of changes in the APTT-CWA parameters revealed a difference in anticoagulant cooperativity between DTIs versus FXa inhibitors.

Conclusions

The APTT-CWA demonstrated evidence for the blockade of thrombin-positive feedback by DTIs and FXa inhibitors and that for the differences in anticoagulant cooperativity between them. The results demonstrate the usability of CWA for assessment of anticoagulation and provide insights into direct anticoagulants.

Increased factor VIII plays a significant role in plasma hypercoagulability phenotype of patients with cirrhosis

Essentials The role of increased factor VIII in cirrhosis-induced hypercoagulability has never been demonstrated. Factor VIII and protein C effects were characterized by thrombin generation with thrombomodulin. Factor VIII elevation plays a significant role in cirrhosis-induced plasma hypercoagulability. Only protein C and factor VIII normalization led to thrombin generation similar to controls.

SUMMARY

Background In cirrhosis, thrombin generation (TG) studied in the presence of thrombomodulin (TM) indicates plasma hypercoagulability. Although the role of protein C (PC) deficiency has been investigated, the influence of an increase in the factor VIII level has never been addressed. Objectives We investigated the roles of high FVIII and low PC levels in increased TG in the presence of TM. Methods Blood samples were prospectively collected from 35 healthy controls and 93 patients with cirrhosis (Child-Turcotte-Pugh [CTP]-A, n = 61; CTP-B, n = 19; and CTP-C, n = 13) and FVIII levels > 150% (n = 48) and/or PC levels < 70% (n = 88). TG was performed with tissue factor (5 pm), phospholipids, and TM (4 nm). FVIII and PC levels were normalized by adding an inhibitory anti-FVIII antibody and exogenous PC, respectively. Results The endogenous thrombin potential (ETP) in the presence of TM was higher in patients than in controls. After FVIII normalization, the ETP (median) decreased from 929 nm min to 621 nm min (CTP-A), 1122 nm min to 1082 nm min (CTP-B), and 1221 nm min to 1143 nm min (CTP-C); after PC normalization, it decreased from 776 nm min to 566 nm min (CTP-A), 1120 nm min to 790 nm min (CTP-B), and 995 nm min to 790 nm min (CTP-C). The ETP was reduced by 17% and 30%, respectively, but normal TG was not restored. When both FVIII and PC levels were normalized, the ETP decreased from 929 nm min to 340 nm min (CTP-A), 1122 nm min to 506 nm min (CTP-B), and 1226 nm min to 586 nm min (CTP-C), becoming similar to control levels. Conclusion Cirrhosis-induced plasma hypercoagulability, as demonstrated in these experimental conditions, can be partly explained by opposite changes in two factors: PC level (decrease) and FVIII level (increase).

The mild phenotype in severe hemophilia A with Arg1781His mutation is associated with enhanced binding affinity of factor VIII for factor X

The clinical severity in some patients with haemophilia A appears to be unrelated to the levels of factor (F)VIII activity (FVIII:C), but mechanisms are poorly understood. We have investigated a patient with a FVIII gene mutation at Arg1781 to His (R1781H) presenting with a mild phenotype despite FVIII:C of 0.9 IU/dl. Rotational thromboelastometry using the patient’s whole blood demonstrated that the clot time and clot firmness were comparable to those usually observed at FVIII:C 5–10 IU/dl. Thrombin and FXa assays using plasma samples also showed that the peak levels of thrombin formation and the initial rate of FXa generation were comparable to those observed at FVIII:C 5–10 IU/dl. The results suggested a significantly greater haemostatic potential in this individual than in those with severe phenotype. The addition of incremental amounts of FX to control plasma with FVIII:C 0.9 IU/dl in clot waveform analyses suggested that the enhanced functional tenase assembly might have been related to changes in association between FVIII and FX. To further investigate this mechanism, we prepared a stably expressed, recombinant, B-domainless FVIII R1781H mutant. Thrombin generation assays using mixtures of control plasma and FVIII revealed that the coagulation function observed with the R1781H mutant (0.9 IU/dl) was comparable to that seen with wild-type FVIII:C at ∼5 IU/dl. In addition, the R1781H mutant demonstrated an ∼1.9-fold decrease in K m for FX compared to wild type. These results indicated that relatively enhanced binding affinity of FVIII R1781H for FX appeared to moderate the severity of the haemophilia A phenotype.

Note: An account of this work was presented, in part, at the 23rd Congress of the International Society of Thrombosis and Haemostasis, July 27, 2011, Kyoto, Japan.

First report of real-time monitoring of coagulation function potential and IgG subtype of anti-FVIII autoantibodies in a child with acquired hemophilia A associated with streptococcal infection and amoxicillin

We describe an 8-year-old boy with acquired hemophilia A (AHA) associated with streptococcal infection and amoxicillin. Laboratory data revealed low factor VIII activity (FVIII:C, 1.5 IU/dl), and FVIII inhibitor (15.9 BU/ml). Comprehensive coagulation function assays, including rotation thromboelastometry (ROTEM^®), revealed a markedly prolonged clotting time. Thrombin and plasmin generation (TG/PG) appeared to be moderately impaired. The inhibitor epitope of his anti-FVIII autoantibody recognized light and heavy chains. He was treated with Novoseven^® and prednisolone, resulting in rapid improvement. ROTEM showed the return of coagulation time to normal level on day 20, and TG gradually improved. PG was moderately reduced in the clinical early phase, but improved at day 20. The patient's IgG subtype was IgG₄ at onset. IgG₁ was transiently positive on day 20, but negative on day 46. FVIII inhibitor gradually decreased and was completely absent after day 46, along with the elevated FVIII:C. IgG4 was again elevated on day 83, followed by a rapid decrease, indicative of the presence of non-neutralizing antibody, which remains currently undetected. We for the first time report changes in comprehensive coagulation function and IgG subtype of anti-FVIII antibody in a rare pediatric case of AHA.

Frequency and epitope specificity of anti-factor VIII C1 domain antibodies in acquired and congenital hemophilia A

Several studies showed that neutralizing anti-factor VIII (anti-fVIII) antibodies (inhibitors) in patients with acquired hemophilia A (AHA) and congenital hemophilia A (HA) are primarily directed to the A2 and C2 domains. In this study, the frequency and epitope specificity of anti-C1 antibodies were analyzed in acquired and congenital hemophilia inhibitor patients (n = 178). The domain specificity of antibodies was studied by homolog-scanning mutagenesis (HSM) with single human domain human/porcine fVIII proteins and antibody binding to human A2, C1, and C2 domains presented as human serum albumin (HSA) fusion proteins. The analysis with HSA-fVIII domain proteins confirmed the results of the HSM approach but resulted in higher detection levels. The higher detection levels with HSA-fVIII domain proteins are a result of antibody cross-reactivity with human and porcine fVIII leading to false-negative HSM results. Overall, A2-, C1-, and C2-specific antibodies were detected in 23%, 78%, and 68% of patients with AHA (n = 115) and in 52%, 57%, and 81% of HA inhibitor patients (n = 63). Competitive binding of the human monoclonal antibody (mAb) LE2E9 revealed overlapping epitopes with murine C1-specific group A mAbs including 2A9. Mutational analyses identified distinct crucial binding residues for LE2E9 (E2066) and 2A9 (F2068) that are also recognized by anti-C1 antibodies present in patients with hemophilia. A strong contribution of LE2E9- and 2A9-like antibodies was particularly observed in patients with AHA. Overall, our study demonstrates that the C1 domain, in addition to the A2 and C2 domains, contributes significantly to the humoral anti-fVIII immune response in acquired and congenital hemophilia inhibitor patients.

A combined approach using global coagulation assays quickly differentiates coagulation disorders with prolonged aPTT and low levels of FVIII activity

Patients with mild/moderate hemophilia (H)A, acquired HA (AHA) and lupus anticoagulants (LA), have prolonged aPTTs with low levels of factor (F)VIII activity, but the differentiation of these disorders is complex and time consuming. We established an approach to quickly differentiate these disorders using comprehensive coagulation tests. Patients' plasmas with mild/moderate HA, AHA, LA without anti-phospholipid syndrome [LA-APS(-)], and LA with APS [LA-APS(+)] were examined using clot waveform analysis (CWA) and thrombin generation test (TGT). Activated protein C (APC) sensitivity was assessed by TGT. CWA revealed similarly prolonged clot times in all groups [NP/mild/moderate HA/AHA/LA-APS(-)/LA-APS(+); 33 ± 1/82 ± 12/116 ± 44/90 ± 29/96 ± 15 s] but significantly different decreased maximal coagulation velocity (3.1 ± 0.1/1.3 ± 0.3/0.9 ± 0.5/1.6 ± 0.3/2.2 ± 0.5). In TGT, AHA group demonstrated severely reduced peak-thrombin levels (362 ± 23/170 ± 27/49 ± 21/158 ± 75/158 ± 99 nM), whilst both LA groups markedly prolonged lag times (4.5 ± 0.3/5.0 ± 0.4/4.7 ± 0.8/12.5 ± 7.7/28.8 ± 11.8 min), suggesting that AHA could be readily identified, but the different LA sub-types failed to be classified. An APC sensitivity demonstrated that 'normalized' APC-induced levels of peak thrombin in LA-APS(+) were significantly lower relative to LA-APS(-) (normalized %inhibition; 5 ± 7/42 ± 39 %). Our studies confirmed that %inhibition by APC was significantly decreased in NP preincubated with purified IgGs from LA-APS(+) compared to LA-APS(-), facilitating differentiation between LA groups. A combined approach using CWA and TGT could be a useful means of differentiating coagulation disorders with prolonged aPTT.

Mild hemophilia A patient with novel Pro1809Leu mutation develops an anti-C2 antibody inhibiting allogeneic but not autologous factor VIII activity

BACKGROUND

In mild hemophilia A (MHA) patients, the risk of inhibitor development is generally low, but some factor VIII (FVIII) gene missense mutations are associated with a higher inhibitor incidence.

OBJECTIVE

To investigate the mechanism(s) of inhibitor development in MHA.

METHODS AND RESULTS

A patient, HA78, with MHA with a novel P1809L missense mutation in the A3 domain, exhibited significant residual FVIII activity (

FVIII

C ~10 IU dL(-1) ), despite the development of an inhibitor (5.6 BU mL(-1) ). Purified HA78-IgG significantly depressed

FVIII

C from normal plasma but not from patient's plasma without inhibitor, indicating that this IgG inhibited allogeneic but not autologous FVIII. The HA78-IgG blocked thrombin and FXa-catalyzed FVIII cleavage but had little effect on FVIII binding to von Willebrand factor and phospholipid. The IgG recognized a C2 epitope close or overlapping the previously described anti-C2 ESH8 epitope. Similarly, a recombinant FVIII-P1809L mutant was little inactivated by HA78-IgG. This mutant demonstrated ~3-fold lower binding affinities to von Willebrand factor and phospholipid compared with wild-type, while reactions with thrombin or FXa were not impaired. Reaction of FVIII-P1809L with the alternative anti-C2 ESH4 showed only an ~20% inhibition compared with wild-type FVIII but was similar to wild-type after incubation with ESH8. A surface plasmon resonance-based assay demonstrated that anti-C2 ESH4 bound to FVIII-P1809L with ~10(2) -fold lower affinity compared with ESH8.

CONCLUSION

These results indicated that the P1809L mutation in A3 induced the conformational change in the FVIII molecule that hampered antigenic determinant(s) located in the C2 domain and might result in the inhibitor development.

Biomimetic biosensor to distinguish between inhibitory and non-inhibitory factor VIII antibodies

Patients with hereditary or acquired haemophilia A may develop inhibitory factor VIII (FVIII) antibodies. These disrupt FVIII activity predominantly by preventing the formation of the tenase complex, leading to a serious bleeding disorder. Antibodies without inhibiting activity, however, can also be found when screening patients with haemophilia A under FVIII supplementation. Therefore, the detection of only these allo- or autoantibodies from plasma is not sufficient. Rather, the characterization of the antibody-induced effects on the coagulation cascade should be considered due to its great diagnostic importance. Currently, inhibitory activities are detected by the functional Bethesda assay, which directly measures the delay in clotting time by the patient plasma. However, this assay does not provide information on the cause of the inhibition. Here, we report the development of a surface plasmon resonance (SPR) biosensor that has the potential to integrate both quantitative and functional information on patient antibody characteristics in one measurement. Recombinant FVIII protein was immobilized on the sensor surface to detect antibodies from patient plasma. The interaction of the FIX- and FXa-clotting proteins with the formed anti-FVIII/FVIII complex could be detected subsequently within the same SPR measurement cycle. Inhibitory antibodies led to the prevention of these interactions. Thus, discrimination between the clinically relevant inhibitory and non-inhibitory antibodies was enabled. In a group of 16 patients with inhibitory antibodies (both ELISA- and Bethesda-positive), 5 patients with non-inhibitory antibodies (ELISA-positive but Bethesda-negative) and 12 healthy controls, diagnostic sensitivity and specificity data of 100% for the FIX interaction were achieved using this biomimetic biosensor approach. The new method allows for detection and quantification, as well as for evaluation of inhibitory activity of allo- and autoantibodies, using small sample volume and short analysis time.

Coagulation function and mechanisms in various clinical phenotypes of patients with acquired factor V inhibitors

BACKGROUND

The clinical phenotype of individuals with acquired factor V (A-FV) inhibitors varies from asymptomatic (non-B group) to life-threatening bleeding (B group), but the mechanism(s) underlying this variation in hemorrhagic phenotype are poorly understood.

OBJECTIVE

To investigate coagulation mechanistically in a range of patients with A-FV antibodies.

METHODS AND RESULTS

Ten cases of A-FV inhibitors in the non-B (n = 5) and B groups (n = 5) were studied. Thrombin generation assays in these plasmas revealed little thrombin generation, despite similar FV activity levels in both groups. However, prothrombin time-based clot waveform analysis revealed that the clot times were significantly prolonged and the maximum velocity and acceleration of coagulation were lower in the B group than in the non-B group, suggesting that this technique might be useful for predicting and monitoring hemorrhagic symptoms. A-FV inhibitors from the non-B group recognized predominantly the FV heavy chain, whereas those from the B group recognized the light chain. Purified anti-FV autoantibodies (autoAbs) from the B group inhibited FV binding to phospholipid by 60-90%, whereas there was little effect on this reaction in the non-B group. In addition, anti-FV autoAbs from the non-B group impaired the activated protein C (APC) cofactor activity of FV in FVIIIa inactivation mechanisms, and delayed APC-catalyzed cleavage of FVa at Arg306, but not at Arg506, indicating the presence of APC resistance in the non-B group.

CONCLUSIONS

The results suggest that the different hemorrhagic phenotypes in A-FV inhibitors depend on the specific epitope of anti-FV autoAbs, and appear to be associated with an imbalance of procoagulant and anticoagulant function.

High-resolution mapping of epitopes on the C2 domain of factor VIII by analysis of point mutants using surface plasmon resonance

Neutralizing anti-factor VIII (FVIII) antibodies that develop in patients with hemophilia A and in murine hemophilia A models, clinically termed "inhibitors," bind to several distinct surfaces on the FVIII-C2 domain. To map these epitopes at high resolution, 60 recombinant FVIII-C2 proteins were generated, each having a single surface-exposed residue mutated to alanine or a conservative substitution. The binding kinetics of these muteins to 11 monoclonal, inhibitory anti-FVIII-C2 antibodies were evaluated by surface plasmon resonance and the results compared with those obtained for wild-type FVIII-C2. Clusters of residues with significantly altered binding kinetics identified "functional" B-cell epitopes, defined as those residues contributing appreciable antigen-antibody avidity. These antibodies were previously shown to neutralize FVIII activity by interfering with proteolytic activation of FVIII by thrombin or factor Xa, or with its binding to phospholipid surfaces, von Willebrand factor, or other components of the intrinsic tenase complex. Fine mapping of epitopes by surface plasmon resonance also indicated surfaces through which FVIII interacts with proteins and phospholipids as it participates in coagulation. Mutations that significantly altered the dissociation times/half-lives identified functionally important interactions within antigen-antibody interfaces and suggested specific sequence modifications to generate novel, less antigenic FVIII proteins with possible therapeutic potential for treatment of inhibitor patients.

Optimal monitoring of bypass therapy in hemophilia A patients with inhibitors by the use of clot waveform analysis

BACKGROUND

Assays to determine the optimal hemostatic effects of bypass therapy in hemophilia A (HA) patients with inhibitors are difficult to compare. Clot waveform analysis (CWA), based on the continuous monitoring of routine coagulation parameters (prothrombin time/activated partial thromboplastin time), offers a useful method for assessing global clotting function.

OBJECTIVES

To investigate the technique of CWA for the hemostatic monitoring of bypass therapy in HA patients with inhibitors.

METHODS AND RESULTS

Ellagic acid (Elg), tissue factor (TF) or both (Elg/TF) were used as trigger reagents in CWA. The standard parameters - clot time (CT), maximum coagulation velocity (|min1|), and acceleration (|min2|) - were recorded. Optimal monitoring was defined as: (i) a significant difference in these parameters between plasma from HA patients with inhibitors and normal plasmas; and (ii) a significant improvement in these indices in HA patients with inhibitors after bypass therapy. Experiments in vitro demonstrated that there were significant differences between plasma from HA patients with inhibitors and normal plasma with various triggers, in the order Elg > Elg/TF >> TF. Addition of therapeutically achievable concentrations of bypassing agents, however, showed significant improvements in the different parameters only with Elg/TF, suggesting that this reagent provided the most appropriate assay. A total of 20 plasmas from HA patients with inhibitors in which bypassing agents were infused were evaluated ex vivo by Elg/TF CWA. The postinfusion parameters CT and |min2| reflected clinical effects, and were close to normal levels. Furthermore, Elg/TF CWA facilitated quantitative evaluation of perioperative hemostatic management of bypass therapy in HA patients with inhibitors.

CONCLUSIONS

CWA is a promising method for the quantitative monitoring of bypass therapy during routine automated clotting assays with a modified trigger reagent comprising a well-balanced mixture of Elg and TF.

Replacing the factor VIII C1 domain with a second C2 domain reduces factor VIII stability and affinity for factor IXa

Factor VIII (FVIII) consists of a heavy chain (A1(a1)A2(a2)B domains) and light chain ((a3)A3C1C2 domains). To gain insights into a role of the FVIII C domains, we eliminated the C1 domain by replacing it with the homologous C2 domain. FVIII stability of the mutant (FVIIIC2C2) as measured by thermal decay at 55 °C of FVIII activity was markedly reduced (~11-fold), whereas the decay rate of FVIIIa due to A2 subunit dissociation was similar to WT FVIIIa. The binding affinity of FVIIIC2C2 for phospholipid membranes as measured by fluorescence resonance energy transfer was modestly lower (~2.8-fold) than that for WT FVIII. Among several anti-FVIII antibodies tested (anti-C1 (GMA8011), anti-C2 (ESH4 and ESH8), and anti-A3 (2D2) antibody), only ESH4 inhibited membrane binding of both WT FVIII and FVIIIC2C2. FVIIIa cofactor activity measured in the presence of each of the above antibodies was examined by FXa generation assays. The activity of WT FVIIIa was inhibited by both GMA8011 and ESH4, whereas the activity of FVIIIC2C2 was inhibited by both the anti-C2 antibodies, ESH4 and ESH8. Interestingly, factor IXa (FIXa) binding affinity for WT FVIIIa was significantly reduced in the presence of GMA8011 (~10-fold), whereas the anti-C2 antibodies reduced FIXa binding affinity of FVIIIC2C2 variant (~4-fold). Together, the reduced stability plus impaired FIXa interaction of FVIIIC2C2 suggest that the C1 domain resides in close proximity to FIXa in the FXase complex and contributes a critical role to FVIII structure and function.

Simultaneous measurement of thrombin and plasmin generation to assess the interplay between coagulation and fibrinolysis

Normal haemostasis is maintained by a controlled balance between coagulation and fibrinolysis, involving thrombin and plasmin the respective key enzymes. Simultaneous evaluation of both enzymes facilitates, therefore, an overall understanding of normal and pathological haemostasis. Combined thrombin and plasmin generation (T/P-G) assays have been recently described, and we have adapted the technique to investigate the interplay between coagulation and fibrinolysis in patients with various haemostatic disorders. Our modified T/P-G was initiated by the addition of a mixture of optimised lower concentrations of tissue factor and tissue-type plasminogen activator. Thrombin generation (TG) and plasmin generation (PG) were monitored simultaneously using individual fluorescent substrates in separate microtitre wells. The relationship between coagulation and fibrinolysis was demonstrated by analysing the effects of thrombin inhibitors, activated protein C and thrombomodulin. The most evident impairments in TG were observed with plasma samples deficient of coagulation factors participating in the prothrombinase complex. Defects in PG were observed with deficiencies of factor (F)V, FX, fibrinogen, and plasminogen. TG appeared to be a prerequisite for the initiation of PG, and overall PG was governed by fibrinogen concentration. TG in patients with haemophilia A correlated with levels of FVIII activity, but there was no significant relationship between PG and FVIII:C, confirming that the abnormal haemostasis in haemophilia A results in a severe imbalance between coagulation and fibrinolysis. The findings demonstrate that global haemostasis depends on a sensitive balance between coagulation and fibrinolysis, and that the modified T/P-G assay could provide an enhanced understanding of haemorrhage and thrombosis in clinical practice.

Activated prothrombin complex concentrate (APCC)-mediated activation of factor (F)VIII in mixtures of FVIII and APCC enhances hemostatic effectiveness

BACKGROUND AND OBJECTIVES

Activated prothrombin complex concentrates (APCCs), utilized in bypassing therapy for hemophiliacs with inhibitor, contain factors (Fs) VII, FII, FIX and FX, and their active forms. A recent report has demonstrated that mixtures of APCC and FVIII potentiated thrombin generation, in vitro, in plasma from patients with severe hemophilia A, but the mechanism(s) involved remains unknown.

RESULTS

APCC (0.05 U mL(-1) ) increased FVIII activity ~ 4-fold within 1 min in one-stage clotting assays, followed by a return to initial levels within 10 min. This reaction was dependent on the presence of tissue factor and phospholipid. Thrombin generation produced from APCC was ~ 3.5-fold greater in the presence of FVIII than that in its absence. SDS-PAGE analysis revealed that APCC sequentially proteolyzed the heavy chain of FVIII at Arg(372) and Arg(740) , followed by cleavage at Arg(336) . Proteolysis was prevented by FVIIa inhibitor, but not by hirudin, supporting the concept that APCC itself possessed the potential to activate FVIII in early coagulation phases, and that FVIIa in APCC contributed mainly to this reaction. APCC-mediated FVIII activation was unaffected by the addition of anti-FVIII inhibitor antibodies, irrespective of epitope specificity. Anti-C2 type 1 inhibitors, however, diminished the inactivation phase of the APCC reaction by inhibiting cleavage at Arg(336) .

CONCLUSION

Small amounts of APCC, relative to the standard concentration used for clinical purposes, could activate FVIII directly, even in the presence of anti-FVIII antibodies. Combination therapy based on mixtures of APCC and FVIII could have significant beneficial implications for the treatment of hemophilia A patients with inhibitors.

Global haemostasis and point of care testing

The evaluation of the coagulation profile has used so far either clotting-based or chromogenic assays with different endpoints. Clotting-based techniques are the most used worldwide, and they certainly are useful for diagnosis of clotting factor deficiencies. However, the information provided is relatively limited, and therefore the individual profile of coagulation is poorly assessed. This is reflected by the weak correlation between the results of these assays and the clinical phenotype. Among the assays that benefited from technological advances, thrombin generation and thromboelastography are probably the most actively investigated, but they require specific instruments and are not fully automated. Their standardisation level is rapidly progressing, and they are progressively entering the clinical scene, with the attempt to provide additional information on the coagulation process and a meaningful clinical correlation. These inherited bleeding disorders frequently require replacement therapy using clotting factor concentrates that increase the plasma level of the missing clotting factor. The classical adjustment of the therapy is mainly based on the measurement of the plasma clotting activity of the protein administered. If one considers that a certain level of thrombin generated would predict clinical efficacy, monitoring of thrombin formation might offer new possibilities to individually predict the bleeding phenotype, select the most adapted therapeutic product and tailor the dose. The same holds true for thromboelastography/thromboelastometry which evaluate fibrin formation as well as clot resistance to fibrinolytic challenge, one step further down in the coagulation process. In this regard, these 2 assays could be seen as complementary in terms of information provided on the coagulation profile at the individual level.