Hybrid human-porcine factor VIII proteins partially escape the inhibitory effects of anti-factor VIII inhibitor alloantibodies having A2 or C2 domain specificity

INTRODUCTION

Porcine factor (pF)VIII has low cross-reactivity with anti-human (h)FVIII inhibitor alloantibodies. Clinical trials of pFVIII in congenital haemophilia A patients with inhibitor (PwHA-I) are in progress. Most polyclonal anti-hFVIII inhibitors recognize its A2 and/or C2 domain(s), and recombinant human-porcine hybrid (hp)FVIII proteins may escape neutralization by these inhibitors.

AIM

To evaluate the ability of hpFVIII to limit the anti-FVIII activity of inhibitor alloantibodies.

METHODS

Three hybrid proteins were created by substituting the hFVIII A2, C2 domain or both with the corresponding domains of pFVIII [termed hp(A2), hp(C2) and hp(A2/C2), respectively]. The reactivity of these hybrids was assessed by one-stage clotting assays (OSA), thrombin generation assays (TGA) and rotational thromboelastometry (ROTEM) by adding them to FVIII-deficient samples.

RESULTS

OSA demonstrated that the hybrid proteins avoided neutralization by anti-FVIII A2 or C2 monoclonal antibodies (mAb) and polyclonal inhibitor-antibodies (polyAb) from PwHA-I. In TGA, thrombin generation with hp(A2) and hp(A2/C2) was not attenuated in the presence of patient IgG recognizing anti-A2 domain. In contrast, that with hFVIII and hp(C2) was suppressed by this IgG to levels equivalent to those of FVIII-deficient plasma. With anti-A2/C2 polyAb, the activity of hp(A2/C2) was unaffected. ROTEM demonstrated that the addition of hp(A2) or hp(A2/C2) to anti-A2 polyAb shortened clot times/clot formation times, whilst hFVIII or hp(C2) were ineffective. Similarly with anti-A2/C2 polyAb, hp(A2/C2) restored coagulation potential to a greater extent than hp(A2) and hp(C2).

CONCLUSION

Hybrid FVIII proteins containing porcine FVIII A2 and/or C2 domain(s) could support effective therapy in PwHA-I by avoiding neutralization.

Longitudinal dynamic changes in factor VIII inhibitor titers in patients with hemophilia A and inhibitors receiving emicizumab prophylaxis

Emicizumab prophylaxis dramatically reduces bleeding events in patients with hemophilia A (PwHA) with or without factor VIII (FVIII) inhibitors. However, long-term dynamic changes in FVIII inhibitor titers during emicizumab prophylaxis remain to be investigated. We conducted a retrospective follow-up study of FVIII inhibitor titers after initiation of emicizumab prophylaxis in 25 PwHA carrying current or historical FVIII inhibitors. Nineteen PwHA had FVIII inhibitors at initiation of emicizumab prophylaxis (age: median 22 [range 4-60] years and inhibitor titer: 30 [1.0-1450] BU/mL). In 17 of the 19 patients, the inhibitor titers markedly decreased to a median of 1.2 (< 0.6-58) BU/mL at a median follow-up of 71 (38-111) months. In two patients, titers were slightly elevated after initiation of emicizumab but decreased in the long term. The remaining six patients had negative inhibitor status (< 0.6 BU/mL) when switched to emicizumab from FVIII prophylaxis. Five patients maintained negative titers. One patient had inhibitor recurrence, with a peak titer of 1.6 BU/mL that decreased to 0.9 BU/mL. In most cases, FVIII inhibitor titers can be expected to decrease spontaneously during emicizumab prophylaxis, but regular follow-up is necessary to manage breakthrough bleeds.

Coagulant potentials of emicizumab in the plasmas from infant and toddler patients with hemophilia A

BACKGROUND

Emicizumab significantly reduces bleedings in patients with hemophilia A (PwHA). A clinical study (HAVEN 7; NCT04431726) for PwHA aged less than or equal to 12 months is ongoing, but emicizumab-driven coagulation potential in PwHA in early childhood remains to be clarified.

AIM

To investigate the in vitro or in vivo coagulation potential of emicizumab in plasmas obtained from infant and toddler PwHA.

METHODS

Twenty-seven plasma samples from 14 infant/toddler PwHA (aged 0-42 months, median 19 months) who received emicizumab (n = 9), factor (F)VIII products (n = 8), or no treatment (n = 10) were obtained. FVIII activity in FVIII-treated plasmas was cancelled by the addition of anti-FVIII monoclonal antibody (mAb). Emicizumab-treated plasmas (in vivo) and emicizumab-spiked plasmas (in vitro) were analyzed. Emicizumab-untreated plasma or emicizumab-treated plasma supplemented with two anti-emicizumab mAbs were used as references. Adjusted maximum coagulation velocity (Ad|min1|) by clot waveform analysis and peak thrombin (Peak-Th) by thrombin generation assay was assessed.

RESULTS

Ad|min1| values in 24 samples were improved by the presence of emicizumab. Values did not improve in the three remaining samples (aged 1, 23, and 31 months). Although the presence of emicizumab showed an age-dependent increase in Peak-Th in 20 samples, this increase was not observed in seven samples (aged 0, 1, 1, 2, 8, 19, and 36 months). Emicizumab-dependent increases in both Ad|min1| and Peak-Th were shown in 18 samples, and increases in either parameter were shown in eight samples. One sample (from patient aged 1 month) showed no increase in both, however.

CONCLUSION

Emicizumab could improve coagulant potential in plasmas from infant/toddler patients with hemophilia A.

Factor VIII A3 domain residues 1793-1795 represent a factor IXa-interactive site in the tenase complex

BACKGROUND

Factor (F)VIII functions as a cofactor in the tenase complex responsible for conversion of FX to FXa by FIXa. Earlier studies indicated that one of the FIXa-binding sites is located in residues 1811-1818 (crucially F1816) of the FVIII A3 domain. A putative, three-dimensional structure model of the FVIIIa molecule suggested that residues 1790-1798 form a V-shaped loop, and juxtapose residues 1811-1818 on the extended surface of FVIIIa.

AIM

To examine FIXa molecular interactions in the clustered acidic sites of FVIII including residues 1790-1798.

METHODS AND RESULTS

Specific ELISA's demonstrated that the synthetic peptides, encompassing residues 1790-1798 and 1811-1818, competitively inhibited the binding of FVIII light chain to active-site-blocked Glu-Gly-Arg-FIXa (EGR-FIXa) (IC50; 19.2 and 42.9 μM, respectively), in keeping with a possible role for the 1790-1798 in FIXa interactions. Surface plasmon resonance-based analyses demonstrated that variants of FVIII, in which the clustered acidic residues (E1793/E1794/D1793) or F1816 contained substituted alanine, bound to immobilized biotin labeled-Phe-Pro-Arg-FIXa (bFPR-FIXa) with a 1.5-2.2-fold greater KD compared to wild-type FVIII (WT). Similarly, FXa generation assays indicated that E1793A/E1794A/D1795A and F1816A mutants increased the Km by 1.6-2.8-fold relative to WT. Furthermore, E1793A/E1794A/D1795A/F1816A mutant showed that the Km was increased by 3.4-fold and the Vmax was decreased by 0.75-fold, compared to WT. Molecular dynamics simulation analyses revealed the subtle changes between WT and E1793A/E1794A/D1795A mutant, supportive of the contribution of these residues for FIXa interaction.

CONCLUSION

The 1790-1798 region in the A3 domain, especially clustered acidic residues E1793/E1794/D1795, contains a FIXa-interactive site.

Study protocol for assessment of the coagulation potential of concomitantly used factor VIII concentrates in patients with haemophilia A with emicizumab prophylaxis (CAGUYAMA Study): a multicentre open-label non-randomised clinical trial

INTRODUCTION

Emicizumab prophylaxis substantially reduces bleeding episodes in patients with haemophilia A (HA). The haemostatic efficacy of emicizumab in patients with HA is estimated as approximately 15% based on mimic activity of factor (F) VIII. Although it has been proven effective in preventing bleeding, its haemostatic effect during breakthrough bleeding or surgery is considered insufficient. Therefore, haemostatic management of emicizumab-treated patients with HA without inhibitors frequently requires FVIII replacement therapy. In haemostatic management of emicizumab-treated patients with HA, conventional FVIII dosage calculations are used in clinical practice without considering the coagulant effects of emicizumab.

METHODS AND ANALYSIS

In the CAGUYAMA study, 100 patients with HA without inhibitors will be enrolled for a maximum duration of 1 year, and samples of 30 events following the concomitant use of FVIII concentrates (30±5 U/kg) with emicizumab will be collected. An 'event' is defined as obtaining blood samples at preadministration and postadministration of FVIII concentrates during a breakthrough bleeding or a surgical procedure. Global coagulation assays will be used to measure the coagulation potential of the obtained samples. Clot waveform analysis (CWA) is used to identify the primary end-point, that is, the degree of improvement in the maximum coagulation rate at preadministration and post-administration of fixed-dose FVIII concentrations. The parameter obtained from CWA, which is triggered by an optimally diluted mixture of prothrombin time reagent and activated partial thromboplastin time reagent, is reported to be an excellent marker for assessing the degree of improvement of the coagulation potential in emicizumab-treated plasmas.

ETHICS AND DISSEMINATION

The CAGUYAMA study was approved by the Japan-Certified Review Board of Nara Medical University (Approval ID; nara0031). The study results will be communicated through publication in international scientific journals and presentations at (inter)national conferences.

TRIAL REGISTRATION NUMBER

jRCTs051210137.

Impaired factor V-related anticoagulant mechanisms and deep vein thrombosis associated with A2086D and W1920R mutations

Factor V (FV) plays pivotal roles in both procoagulant and anticoagulant mechanisms. Genetic mutations, FV-W1920R (FVNara) and FV-A2086D (FVBesançon), in the C1 and C2 domains of FV light chain, respectively, seem to be associated with deep vein thrombosis. However, the detailed mechanism(s) through which these mutations are linked to thrombophilia remains to be fully explored. The aim of this study was to clarify thrombotic mechanism(s) in the presence of these FV abnormalities. Full-length wild-type (WT) and mutated FV were prepared using stable, human cell lines (HEK293T) and the piggyBac transposon system. Susceptibility of FVa-A2086D to activated protein C (APC) was reduced, resulting in significant inhibition of APC-catalyzed inactivation with limited cleavage at Arg306 and delayed cleavage at Arg506. Furthermore, APC cofactor activity of FV-A2086D in APC-catalyzed inactivation of FVIIIa through cleavage at Arg336 was impaired. Surface plasmon resonance-based assays demonstrated that FV-A2086D bound to Glu-Gly-Arg-chloromethylketone active site-blocked APC and protein S (P) with similar affinities to that of FV-WT. However, weakened interaction between FVa-A2086D and phospholipid membranes was evident through the prothrombinase assay. Moreover, addition of FVa-A2086D to plasma failed to inhibit tissue factor (TF)-induced thrombin generation and reduce prothrombin times. This inhibitory effect was independent of PC, PS, and antithrombin. The coagulant and anticoagulant characteristics of FV(a)-W1920R were similar to those of FV(a)-A2086D. FV-A2086D presented defects in the APC mechanisms associated with FVa inactivation and FV cofactor activity, similar to FV-W1920R. Moreover, both FV proteins that were mutated in the light chain impaired inhibition of TF-induced coagulation reactions. These defects were consistent with congenital thrombophilia.

Factor VIII mutated with Lys1813Ala within the factor IXa-binding region enhances intrinsic coagulation potential

Factor VIII (FVIII) functions as a cofactor of FIXa for FX activation in the intrinsic tenase complex. The 1811-1818 region in the FVIII A3 domain was observed to contribute to FIXa binding, and the K1813A/K1818A mutant increased the binding affinity for FIXa. The current study aims to identify mutated FVIII protein(s) that increase FVIIIa cofactor activity in the 1811-1818 region. FVIII mutants with K1813A, K1818A, and K1813A/K1818A were expressed in baby hamster kidney cells and were followed by assessments using purified and global coagulation assays for mouse models with hemophilia A (HA). A surface plasmon resonance-based assay revealed that the Kd value of FVIII-K1813A for FIXa interaction was lower than that of the wild-type (WT) (3.9±0.7/6.3±0.3 nM). However, the Km value of FVIII-K1813A for FIXa on tenase activity was comparable with that of the WT, whereas the kcat of this mutant was significantly greater than that of the WT. Thrombin-catalyzed FVIII-K1813A activation was ∼1.3-fold more enhanced than that of the WT, and the spontaneous decay of activated FVIII-K1813A was ∼2.5-fold slower than that of WT. The heat stability assay revealed that the decay rate of FVIII-K1813A was ∼2.5-fold slower than that of WT. Thrombin generation assay and rotational thromboelastometry using blood samples from patients with HA demonstrated that the addition of FVIII-K1813A (0.5 nM) exhibited a coagulation potential compatible with that of WT (1 nM). In the tail clip assay of HA mice, FVIII-K1813A showed a two- to fourfold higher hemostatic potential than that of the WT. FVIII-K1813A, with higher a FIXa binding affinity, enhances the global coagulation potential because of the stability of FVIII/FVIIIa molecules.

Decrease in in vivo coagulant potential of emicizumab in a patient with hemophilia A and inhibitor complicated with infectious mononucleosis

Emicizumab prophylaxis significantly reduces bleeding episodes in patients with hemophilia A (PwHA). There is little information on coagulant potentials in emicizumab-treated PwHA with infection, however. We encountered an emicizumab-treated PwHA with inhibitor, complicated with Epstein-Barr virus-associated infectious mononucleosis (IM) in phase 1/2 study (ACE001JP/ACE002JP). Although it was a typical clinical course of IM, activated partial thromboplastin time was mildly prolonged but rotational thromboelastometry revealed severely impaired coagulant potential. The blood concentration of emicizumab decreased moderately in the low concentration range, resulting in an increased risk of bleeding and possibly leading to severe ileocecal bleeds requiring coil embolization. The blood concentrations of factors IX/X little decreased and antiemicizumab antibodies did not develop, however. After the influence by IM resolved, his coagulant potentials gradually recovered with the recovery of emicizumab concentration, and parameters by global coagulation assays improved. An IM case for emicizumab-treated PwHA may need to monitor using global coagulation assays.

Late-onset and congenital hearing loss detected using AABR due to congenital cytomegalovirus infection that improved with valganciclovir

Congenital cytomegalovirus (cCMV) infection is the most common congenital viral infection and is the leading non-genetic cause of sensorineural hearing loss and an important cause of neurodevelopmental disabilities. Auto auditory brainstem response (AABR) is a simple hearing test and used for the purpose of neonatal hearing screening, but can use it for early detection hard of hearing within the study age of the model. We experienced two case of asymptomatic CMV infection in which congenital and late-onset hearing loss were diagnosed early with AABR, and hearing loss improved with valganciclovir.

Acute-type acquired hemophilia A after COVID-19 mRNA vaccine administration: A new disease entity?

Acquired hemophilia A (AHA) is a rare autoimmune bleeding disorder. Various autoimmune diseases, including AHA, have been reported to occur after the administration of mRNA COVID-19 vaccines. However, the characteristics of these AHA cases remain unclear. We report a case in which AHA arose in a young patient after the administration of an mRNA COVID-19 vaccine, but improved rapidly. The patient's factor VIII (FVIII) inhibitor titer spontaneously decreased to less than half of that seen at diagnosis. One week after the initial immunosuppressive therapy, the FVIII inhibitor had disappeared. Our case suggests that AHA that arises in young patients after COVID-19 vaccination may resolve spontaneously, and the levels of FVIII inhibitors may decrease more rapidly in such cases than in idiopathic AHA. Unlike for immune thrombocytopenic purpura (ITP), no acute type of AHA has been recognized. This case suggests that just as there is an acute type of ITP that develops in children/after vaccination, there may be an acute type of AHA that arises in young patients that receive mRNA COVID-19 vaccines.

Activated partial thromboplastin time-based clot waveform analysis enables measurement of very low levels of factor IX activity in patients with severe hemophilia B

The precise measurement of very low levels of factor IX activity (FIX:C < 1 IU/dL) is essential for understanding clinical severity and risk of inhibitor development in patients with severe hemophilia B (Pw-SHB). However, such measurement sensitivity has not yet been achieved. We aimed to establish a measurement method using clot waveform analysis (CWA). Residual FIX:C by adding anti-FIX monoclonal antibody, FIX:C by adding recombinant (r)FIX to the commercial Pw-SHB plasmas, and FIX:C in our Pw-SHB were determined by CS-2000i^™/CS-2400^™, followed by analysis of CWA parameters. The presence of anti-FIX antibody in the commercial Pw-SHB plasmas significantly decreased coagulation potential compared to its absence. The addition of rFIX to these innate plasma samples produced significant changes in three parameters upon adding FIX:C at 0.1-1 IU/dL, supporting the presence of trace FIX:C in Pw-SHB. Therefore, appropriate FIX-depleted plasma containing minimum residual FIX:C was chosen from reference curves of FIX:C (0.01-1 IU/dL). Among patients with untreated Pw-SHB, two had FIX:C 0.6-0.7 IU/dL and two had lower than detectable levels using FIX-depleted plasma. One of the latter had detectable trough levels post-rFIX administration. In conclusion, CWA enabled measurement of very low levels of FIX:C using appropriate FIX-deficient plasma.

Heterogeneous coagulant potential of emicizumab in neonatal factor VIII-deficient plasma

BACKGROUND

Emicizumab prophylaxis reduces bleeding in hemophilia A (HA) patients. However, there are few data on emicizumab treatment in neonates with HA (neonate-HA), and the procoagulant effects of emicizumab in these patients are unknown.

AIM

To investigate the coagulation activity of emicizumab in vitro in a plasma model of neonate-HA.

METHODS

Plasmas from 84 neonates with non-HA were enrolled. However, due to the limited plasma volumes in some cases, 50 plasmas were assigned to two different assay groups. To prepare the neonate-HA model, plasma was first preincubated with an antifactor (F) VIII A2 monoclonal antibody (mAb). After further incubation with emicizumab, global coagulation activity was measured: adjusted maximum coagulation velocity (Ad|min1|) in clot waveform analysis (CWA) and peak thrombin in thrombin generation assay (TGA).

RESULTS

Because the addition of anti-FVIII mAb to 22 of 43 samples showed little decrease in Ad|min1|, the remaining 21 samples were analyzed by CWA. The addition of emicizumab increased Ad|min1| in 18 of the 19 cases (effective group) but not in the remaining 3 cases (noneffective group). Similarly, TGA found that emicizumab (effective group) improved peak thrombin in seven of the nine samples tested, but two cases did not respond (noneffective group). Although the effective group had lower levels of FX, there was no significant difference between the effective and noneffective groups in terms of FIX, protein S, protein C, antithrombin, and fibrinogen.

CONCLUSIONS

The in vitro coagulant potentials of emicizumab in the neonate-HA model were more heterogeneous than those recorded in the adult-HA model.

Screening of the protein C pathway abnormality-related thrombophilia by using thrombomodulin-mediated tissue factor-triggered clot waveform analysis

OBJECTIVES

Absolute or relative protein (P)C pathway abnormalities (PC deficiency, PS deficiency, antiphospholipid syndrome (APS), factor (F)V-abnormality, and high FVIII level) cause thrombophilia. Although screening assays for these thrombophilias are available, one utilizing clot waveform analysis (CWA) remains unknown. We aimed to establish a CWA-based screening assay to distinguish PC pathway abnormality-related thrombophilia.

METHODS

Samples were reacted with tissue factor (TF)/phospholipids and recombinant thrombomodulin (rTM; optimal 20 nM), followed by CWA measurement. The peak ratio (with/without rTM) of the first derivative curve of clot waveform was calculated.

RESULTS

The peak ratio in healthy plasmas (n = 35) was 0.36 ± 0.13; hence, the cutoff value was set to 0.49. The peak ratios in plasmas with PC deficiency, PS deficiency, high-FVIII (spiked 300 IU/dl), and APS were higher than the cutoff values (0.79/0.97/0.50/0.93, respectively). PC-deficient plasma or PS-deficient plasma mixed with normal plasma (25%/50%/75%/100% PC or PS level) showed dose-dependent decreases in the peak ratios (PC deficient: 0.85/0.64/0.44/0.28; PS deficient: 0.69/0.53/0.40/0.25), suggesting that the peak ratio at ≤50% of PC or PS level exceeded the cutoff value. The peak ratio in FV deficiency with FV ≤25% was higher than the cutoff value. FV-deficient plasma spiked with 40 IU/dl rFV-R506Q (FV_Leiden ) or rFV-W1920R (FV_Nara ) showed >90% peak ratios.

CONCLUSIONS

rTM-mediated TF-triggered CWA might be useful for screening PC pathway abnormality-related thrombophilia.

Use of thromboelastography before the administration of hemostatic agents to safely taper recombinant activated factor VII in acquired hemophilia A: a report of three cases

Background

Acquired hemophilia A (AHA) is a rare autoimmune disease characterized by bleeding events. Recombinant activated factor VII (rFVIIa) is a first-line bypassing agent, which is effective against clinically significant bleeding. However, there is no standard way of tapering and discontinuing rFVIIa, mainly because there is no established method for monitoring rFVIIa therapy for AHA.

Case presentation

Here, we report three AHA cases, in which we adjusted the rFVIIa dosing interval based on the results of thromboelastography (TEG) performed just before the administration of the next dose of rFVIIa. The dosing interval of rFVIIa was prolonged based on the reaction rate time (R) according to TEG, which is correlated with coagulation factor activity. The R-value reference range reported by the manufacturer of the TEG system was used as a threshold for making decisions. In these three cases, there was no rebleeding, and the patients’ ability to perform activities of daily living did not decline.

Conclusion

Our cases suggest that conducting TEG-based monitoring just before the administration of the next dose of rFVIIa may be useful for guiding increases in the rFVIIa dosing interval without causing rebleeding events. Further investigations are warranted to examine how TEG could be used to determine the most appropriate rFVIIa dosing interval, e.g., through regular TEG-based monitoring, and the optimal TEG-derived threshold for indicating changes to the rFVIIa dosing interval.

The balance of comprehensive coagulation and fibrinolytic potential is disrupted in patients with moderate to severe COVID-19

Coagulation and fibrinolytic mechanisms are enhanced in patients with coronavirus (COVID-19), but disturbances in the balance of both functions in COVID-19 patients remain unclear. We assessed global coagulation and fibrinolysis in plasma from 167 COVID-19 patients (mild/moderate/severe: 62/88/17, respectively) on admission using clot-fibrinolysis waveform analysis (CFWA). Maximum coagulation velocity (|min1|) and maximum fibrinolysis velocity (|FL-min1|) were expressed as ratios relative to normal plasma. Ten patients (6.0%) developed thrombosis, 5 (3.0%) had bleeding tendency, and 13 (7.8%) died during admission. FDP levels increased with severity of COVID-19 symptoms (mild/moderate/severe; median 2.7/4.9/9.9 μg/mL, respectively). The |min1| ratios were elevated in all categories (1.27/1.61/1.58) in keeping with enhanced coagulation potential, with significant differences between mild cases and moderate to severe cases. The |FL-min1| ratios were also elevated in all groups (1.19/1.39/1.40), reflecting enhanced fibrinolytic potential. These data identified coagulation dominance in moderate to severe cases, but balanced coagulation and fibrinolysis in mild cases. There were significant differences in FDP and TAT, but no significant differences in |min1| or |FL-min1| ratios, between patients with and without thrombosis. CFWA monitoring of coagulation and fibrinolysis dynamics could provide valuable data for understanding hemostatic changes and disease status in COVID-19 patients.

Comparisons of global coagulation potential and bleeding episodes in emicizumab-treated hemophilia A patients and mild hemophilia A patients

Emicizumab reduces bleeding events in patients with severe hemophilia A (HA). The coagulation potential of emicizumab at a clinical dose appears to correspond to about 15 IU/dL of factor VIII activity (FVIII:C), the equivalent of converting from a severe to mild phenotype. However, the clinical and laboratory characteristics of HA patients receiving emicizumab (Emi-PwHA) compared with patients with mild HA (PwMHA) remain to be determined. We reviewed clinical data from Emi-PwHA (n = 63) and PwMHA (n = 15) and evaluated comprehensive coagulation function using Ca²⁺-triggered rotational thromboelastometry (ROTEM) and ellagic acid/tissue factor-triggered clot waveform analysis (modified CWA). The median FVIII:C in PwMHA was 13.0 (IQR 8.5-17.0) IU/dL. Bleeding patterns in both groups were similar and classified into three categories: (1) spontaneous bleeding, post-traumatic, (2) bleeding within 1-2 days, and (3) delayed bleeding after 1-2 weeks. The coagulation potential in Emi-PwHA with and without breakthrough bleeds was comparable. Furthermore, coagulation function in Emi-PwHA was equivalent to PwMHA, although time between treatment and hospitalization for breakthrough bleeds in PwMHA appeared to be longer than those in Emi-PwHA. The coagulation potential and bleeding patterns appeared to be similar in Emi-PwHA and PwMHA, indicating that emicizumab-driven coagulation potential reflected mild HA.

A survey of healthcare workers’ recommendations about human papillomavirus vaccination

Purpose

The human papillomavirus (HPV) vaccine is safe and effective for preventing HPV-related diseases. However, HPV vaccination rates in Japan are low because the “Ministry of Health, Labour and Welfare” had stopped recommending vaccination. We assessed healthcare workers’ (HCWs) current recommendations regarding the HPV vaccine and how the provision of information about HPV vaccination affected their recommendations.

Materials and Methods

A survey was conducted among nurses and physicians in Nara prefecture from March 2021 to July 2021. The questionnaire asked about their understanding, recommendations, and opinions regarding HPV vaccination. Before answering the last two questions (optional), the HCWs read evidence-based information quantifying the risks and benefits of HPV vaccination.

Results

A total of 441 HCWs completed the questionnaire. Only 19% of HCWs always recommended HPV vaccination for girls aged 12–16 years. The evidence-based information significantly improved the percentage of HCWs who would “always recommend” vaccination.

Conclusion

This study showed that the proportion of HCWs who recommend HPV vaccination to adolescent girls remains low in Japan. However, we found that evidence-based information describing the causal relationship between adverse events and vaccination, quantifying the risks and benefits, noting the importance of HCW communications with families, and reporting the recommendations of national societies, might increase HCWs’ recommendations for HPV vaccination.

Travelers' vaccines and their adverse events in Nara, Japan

Background:

It is important to analyze the types of vaccines in travel clinics to determine the focus points in future practice.

Methods

We retrospectively reviewed the electronic medical records of all patients who visited the travel clinic of Nara Medical University between June 2013 and December 2019 to determine their background and the vaccines administered. The information regarding adverse events of the unapproved vaccines in Japan (Havrix^®, Verorab^®, Boostrix^®, Priorix^®, Typhim Vi^®, and Mencevax^®) was also collected.

Results

Of 645 patients, 58.6% were men and the median age was 31 years. Business was the most common travel purpose (34.9%), and Southeast Asia was the most common destination (40.2%). More than 80% of travelers to low- and middle-income countries were vaccinated against hepatitis A, while the rabies vaccination rate was approximately 50%. Typhoid vaccination coverage among travelers to South Asia was approximately 50%. The incidence of adverse events requiring medical consultation, telephonic consultation, or prolonged stay in the examination room was less than 5% for all unapproved vaccines in Japan.

Conclusion

More patient education is needed to increase the vaccination rate of rabies and typhoid vaccines. Adverse events to unapproved vaccines in Japan were not high and were well-tolerated.

A Single-Year Cosmic Ray Event at 5410 BCE Registered in 14C of Tree Rings

The annual 14C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and ∼660 BCE. Here, we report another rapid increase of 14C concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These 14C data series show a significant increase of ∼6‰ in 5411-5410 BCE. The signature of 14C variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid 14C increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand 14C excursion during 5481-5471 BCE. The similarity of our 14C data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event.

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 Case of Pediatric Subcutaneous Abscess Caused by Mycobacterium mageritense Infection

Soft tissue infections with Mycobacterium mageritense are uncommon. We report the case of a 5-year-old girl who developed a subcutaneous abscess in her right ankle caused by M. mageritense. She had a history of acute encephalopathy and adrenal insufficiency and was hospitalized for acute pancreatitis. During hospitalization, the patient developed fever and tachycardia. Blood culture was positive for gram-positive bacilli. Although initial testing with matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) reported a different organism, a repeat test identified M. mageritense. One month after the positive blood culture, she developed redness and swelling in the right ankle. The pus from the subcutaneous abscess after drainage grew M. mageritense, which was further confirmed by the sequencing of housekeeping genes. Based on sensitivity testing, the patient was treated with tosufloxacin and linezolid. The local inflammatory signs gradually improved on starting the treatment. The antibiotics were administered for 6 months, and she experienced no relapse during the 8 months of follow-up after the completion of therapy. This is the first case report of a pediatric M. mageritense infection, which also highlights an important potential pitfall of MALDI-TOF MS. Further, we observe that the choice of antimicrobials for the treatment of M. mageritense is more limited in children than in adults.

Stability of Turoctocog Alfa, a Recombinant Factor VIII Product, during Continuous Infusion In Vitro

Objective  Turoctocog alfa is a recombinant factor VIII (rFVIII) for the prevention and treatment of bleeding in patients with hemophilia A, including those undergoing surgery and invasive medical procedures. This in vitro study evaluated the physical and chemical stability of turoctocog alfa during continuous infusion (CI) over 24 hours at 30°C.

Materials and Methods  The study was performed at 30°C ( ± 2°C). A CI system with pump speed set at either 0.6 or 1.5 mL/h was used to evaluate the stability of three turoctocog alfa strengths (500, 1,000, and 3,000 IU), equating to doses of 1.1 to 16.1 IU/h per kilogram of body weight. The following parameters were evaluated at selected time points between 0 and 24 hours: appearance of solution, clarity, pH, potency, purity, content, total high molecular weight proteins (HMWPs), and oxidized rFVIII.

Results  The mean potency of turoctocog alfa was maintained within the predefined acceptance criteria during CI for both pump speeds with all three strengths at 6, 12, or 24 hours (500 IU: ≥484 IU/vial; 1,000 IU: ≥1,014 IU/vial; and 3,000 IU: ≥3,029 IU/vial). Furthermore, the appearance of solution, clarity, pH, purity, content of turoctocog alfa, total HMWP, and oxidized forms were also within the predefined limits, and comparable to the reference samples (time = 0 hours) for the pump speeds and product strengths assessed.

Conclusion  Physical and chemical stability of turoctocog alfa was maintained during CI over 24 hours. There was only minor degradation or changes in any of the parameters tested. Potency was within the prespecified acceptance limits throughout 24 hours of infusion. These findings confirm the suitability of turoctocog alfa for CI.

How to recover lost vaccine acceptance? A multi-center survey on HPV vaccine acceptance in Japan

BACKGROUND

The plummeting acceptance rate of the HPV vaccine in Japan is one of the most disappointing vaccine-related events in recent times. Since 2013, the national HPV vaccine coverage rate fell from more than 70% to less than 1%. This survey investigated parental HPV vaccine acceptance and the factors that influence it.

METHODS

A multi-center survey was conducted in eight hospitals in Nara prefecture, Japan, from July 2019 to March 2020. Parents were asked to answer a series of questions in a survey that included information on the HPV vaccine.

RESULTS

Among the 1884 parents who answered the questionnaire, 21.8% indicated that they had accepted the HPV vaccine even before reading the information provided in the questionnaire. The overall acceptance rate after everyone had read the information increased to 50.2% (p < 0.001). Among those who still did not accept the vaccine after reading the information (N = 925), 26.7% indicated that they might change their mind if more vaccine safety reports were to appear in the mass media; other potentially influencing factors were direct communication from health care providers (35.1%), a recommendation by government (19.5%), and peer behavior (16.8%).

CONCLUSION

The study showed that providing appropriate medical information significantly improves HPV vaccine acceptance. To reverse the loss of HPV vaccine acceptance in Japan, a multi-discipline approach that includes the mass media, health care providers, the government and the general population will be needed.

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.

Questionnaire survey on maternal pertussis vaccination for pregnant women and mothers in Nara prefecture, Japan

Background: Infantile pertussis is a major concern and causes a significant health burden worldwide. Maternal adult tetanus, diphtheria, and acellular pertussis (Tdap) vaccination is very effective way of preventing infantile pertussis. However, Tdap has not been approved by the Japanese government or been included in Japan's national immunization program (NIP). We carried out a questionnaire survey to investigate whether Japanese women would accept the Tdap vaccination if they were provided with appropriate information.Methods: The questionnaire survey was administered to pregnant women who visited the Obstetrics and Gynecology Department and mothers who visited the Pediatrics Department of Nara Medical University, Kashihara City, Japan, between October 2018 and May 2019. The questionnaire included information about pertussis infection and maternal vaccination, followed by seven questions.Results: A total of 943 participants answered the questionnaire (481 pregnant women and 462 mothers). Before reading the information, just 4.6% of participants knew that infantile pertussis can be prevented by maternal vaccination. After reading the information, 93.0% and 92.6% of participants thought that the maternal Tdap vaccine should be approved by the Japanese government and be included in the NIP, respectively. Although only 67.6% of participants wished to have the maternal Tdap vaccine without government financial support after reading the information, 92.5% said they would have the vaccine with government support (P < .001).Conclusion: Most Japanese mothers and pregnant women would like the maternal Tdap vaccine to be approved by the government and included in the NIP, once they have been provided with appropriate information.

Contribution of Factor VIII A2 Domain Residues 400–409 to a Factor X-Interactive Site in the Factor Xase Complex

The link between factor (F)VIII and FX is essential for optimum activity of the tenase complex. The interactive site(s) in FVIII for FX remains to be completely clarified, however. We investigated the FVIII A2 domain-FX association that was speculated from inhibitory mechanism(s) by an anti-A2 autoantibody. SDS-PAGE demonstrated that the purified inhibitor IgG recognizing residues 373–562 blocked FXa cleavage at Arg372 in FVIII, and surface-plasmon resonance (SPR)-based assays showed that intact A2 subunit directly bound to FX (K d; 63 nM). The FVIII structure model indicated possible FX-binding site(s) in residues 400–429 in A2. One peptide corresponding to residues 400–409 competitively inhibited both the A2–FX binding and FVIIIa/FIXa-dependent FXa generation. Covalent cross-linking was observed between this peptide and FX following reaction with EDC (1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide) using SDS-PAGE. K408 and S409 were not evident in N-terminal sequence analysis of the cross-linked product, suggesting that two residues participated in cross-link formation. SPR-based assays using recombinant FVIII mutants with one or both residues substituted to alanine demonstrated that K408A and K408A/S409A had approximately fourfold high K d values of wild-type (WT-)FVIII. FXa cleavages at Arg372 in both mutants were significantly delayed, suggesting a contribution of K408 for FXa cleavage at Arg372. Furthermore, FXa generation assays with these mutants demonstrated that the K m values were 1.4- to 1.7-fold greater, and overall catalytic efficiency (k cat/K m) was 0.49- to 0.89-fold lower than with WT-FVIII, suggesting a significant contribution of K408 for FVIII–FX interaction in tenase assembly. We concluded that the K408 in the A2 domain provided an interactive-site for FX.

Characteristics of health problems in returned overseas travelers at a tertiary teaching hospital in a suburban area in Japan

Few studies have analyzed the characteristics of patients who develop physical disorders after overseas travel. We retrospectively reviewed the medical records of 183 patients who visited Nara Medical University Hospital from 2008 to 2016 because of physical problems after traveling abroad. The main travel destinations were Southeast Asia (n = 100), Africa (n = 27), and South Asia (n = 23). The main reasons for the travel were leisure (n = 96), business (n = 51), and volunteer work (n = 19). The most common final diagnosis was gastrointestinal disease (n = 72), followed by febrile disease (n = 59) and respiratory disease (n = 19). There were eight malaria cases, including one patient who was infected after <14 days of overseas travel. Additionally, 61 of 71 cases of travelers' diarrhea and 15 of 21 cases of dengue fever occurred after <14 days travel. 26 cases of vaccine preventable diseases, such as hepatitis A, typhoid fever, and influenza, were observed. Consequently, healthcare providers should notify Japanese overseas travelers that there is a non-negligible health risk inherent to short-term travel, while stressing on the importance of pre-travel medical consultation.

Determination of a factor VIII-interactive region within plasmin responsible for plasmin-catalysed activation and inactivation of factor VIII(a)

Plasmin, an active form of plasminogen, activates and inactivates factor VIII (FVIII) by limited proteolysis. We have previously identifiedly sine-binding site-independent plasmin-interactive sites on the FVIII A2 domain responsible for cleavages at Arg336 and Arg372, together with lysine-binding site-dependent plasmin sites on the light chain responsible for cleavage at Lys36. We have now characterised FVIII-interactive regions on plasmin. SDS-PAGE analysis demonstrated that a monoclon al antibody (mAb) against kringle (K)5-catalytic domain (K5-CD) of plasmin significantly blocked plasmin-catalysed cleavages at Arg336 and Arg372. K5-CD fragment and this mAb blocked plasmincatalysed activation and inactivation of FVIII(a). Anti-K1–2–3 and anti-K4 mAbs blocked plasmin-catalysed cleavages at Lys36, and K1–2–3 and K4 fragments inhibited plasmin-catalysed inactivation of A11–336 FVIIIa. The K5-CD preferentially bound to the A2 domain (Kd app ; 52 nM), whilst the K1–2–3 and K4 bound to the light chain (Kd app; 75 and 106 nM, respectively) in ELISA. Binding was attributed to the A2 484–509 region and A3 1690–1705/1804–1818 region, respectively. 6-aminohexanoic acid, a lysine analogue, significantly inhibited the light chain/K1–2–3 (and K4) binding by ∼90%, whilst A2/K5-CD binding was moderated by only ∼35%. Furthermore, an anti-CD antibody blocked plasmin-catalysed cleavage by inhibiting the A2/K5-CD interaction. These data demon strate that the K5-CD of plasmin (and plasminogen) interacts with the A2 domain independent of lysine-binding site, whilst interactions of K1–2–3 and K4 with the light chain are lysine-binding site-dependent. Interactions between the K5-CD and A2 likely constitute the major regulatory mechanism for activation and inactivation of FVIII(a) mediated by cleavage at Arg372 and Arg336.

Mechanisms of human neutrophil elastase-catalysed inactivation of factor VIII(a)

Mechanisms of inflammation and coagulation are linked through various pathways. Human neutrophil elastase (HNE), can bind to activated platelets, might be localised on platelet membranes that provide negatively-charged phospholipid essential for the optimum function of tenase complex. In this study, we examined the effect of HNE on factor (F)VIII. FVIII activity was rapidly diminished in the presence of HNE and was undetectable within 10 minutes. The inactivation rate waŝ8-fold greater than that of activated protein C (APC). This time-dependent inactivation was moderately affected by von Willebrand factor. HNE proteolysed the heavy chain (HCh) of FVIII into two terminal products, A11–358 and A2375–708, by limited proteolysis at Val358, Val374, and Val708. Cleavage at Val708 was much slower than that at Val358 in the >90-kDa A1-A2-B compared to the 90-kDa A1-A2. The 80-kDa light chain (LCh) was proteolysed to 75-kDa product by cleavage at Val1670. HNE-cata- lysed FVIIIa inactivation was markedly slower than that of native FVIII (by ~25-fold), due to delayed cleavage at Val708 in FVIIIa. The inactivation rate mediated by HNE was ~8-fold lower than that by APC. Cleavages at Val358 and Val708 were regulated by the presence of LCh and HCh, respectively. In conclusion, HNE-catalysed FVIII inactivation was associated with the limited-proteolysis that led to A11–358, A2375–708, and A3-C1-C21671–2332, and subsequently to critical cleavage at Val708. HNE-related FVIII(a) reaction might play a role in inactivation of HNE-induced coagulation process, and appeared to depend on the amounts of inactivated FVIII and active FVIIIa which is predominantly resistant to HNE inactivation.

Note: An account of this work was presented at the 51st annual meeting of the American Society of Hematology, December 10, 2009, New Orleans, LA, USA.

Identification of a protein S-interactive site within the A2 domain of the factor VIII heavy chain

We have recently demonstrated that protein S impairs the intrinsic tenase complex, independent of activated protein C, in competitive interactions between the A2 and A3 domains of factor VIIIa and factor IXa. In the present study, we have identified a protein S-interactive site in the A2 domain of factor VIIIa. Anti-A2 monoclonal antibody recognising a factor IXa-functional region (residues 484–509) on A2, and synthetic peptide inhibited the A2 binding to protein S by ∼60% and ∼70%, respectively, in solid-phase binding assays. The 484–509 peptide directly bound to protein S dose-dependently. Covalent cross-linking was observed between the 484–509 peptide and protein S following reaction with EDC (1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide). The cross-linked adduct was consistent with 1:1 stoichiometry of reactants. Cross-linking formation was blocked by addition of the 484–497 peptide, but not by the 498–509 peptide. Furthermore, N-terminal sequence analysis of the 484–509 peptide-protein S adduct showed that three sequential residues (S488, R489, and R490) in A2 were not identified, suggesting that these residues participate in cross-link formation. Mutant A2 molecules where these residues were converted to alanine were evaluated for the binding of protein S. The S488A, R489A, and R490A mutants demonstrated ∼four-fold lower affinity than wild-type A2.These results indicate that the 484–509 region in the A2 domain of factor VIIIa, in particular sequential residues at positions 488–490, contributes to a unique protein S-interactive site.

Characterisation of an antibody specific for coagulation factor VIII that enhances factor VIII activity

Many reports have identified factor (F)VIII inhibitory antibodies with epitopes located in all subunits of the FVIII molecule. Antibodies that promote FVIII activity do not appear to have been reported. We characterised, for the first time, a unique anti-FVIII monoclonal antibody, mAb216, that enhanced FVIII coagulant activity. The mAb216 shortened the activated partial thromboplastin time and specifically increased FVIII activity by ~1.5-fold dose-dependently. FXa generation and thrombin generation were similarly increased by ~1.4- and ~2.5-fold, respectively. An A2 epitope, not overlapping the common A2 epitope, was identified and the antibody was shown to enhance thrombin (and FXa)-catalysed activation of FVIII by modestly accelerating cleavage at Arg372. The presence of mAb216 mediated an ~1.5-fold decrease in Km for the FVIII-thrombin interaction. Enhanced FVIII activity was evident to an equal degree, even the presence of anti-FVIII neutralising antibodies with epitopes in each subunit. In addition, mAb216 depressed the rates of heat-denatured loss of FVIII activity and FVIIIa decay by 2 to ~2.5-fold. We have developed an anti-A2, FVIII mAb216 that augmented procoagulant activity. This enhancing effect could be attributed to an increase in thrombin-induced activation of FVIII, mediated by cleavage at Arg372 and a tighter interaction of thrombin with the A2 domain. The findings may cast new light on new principles for improving the treatment of haemophilia A patients.

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.

Assessing the clinical severity of type 1 von Willebrand disease patients with a microchip flow-chamber system

BACKGROUND

The clinical phenotype of von Willebrand disease (VWD) is heterogeneous, and von Willebrand factor ristocetin cofactor activity (VWF:RCo) does not always reflect clinical severity, especially in VWD type 1. We have reported the potential of a microchip flow-chamber system (Total-Thrombus Formation Analysis System [T-TAS®]) for assessing physiologic hemostasis in VWD. Aim To evaluate the relationship between T-TAS, bleeding score (BS) and laboratory test results in type 1 VWD patients.

METHODS

Microchips coated with collagen (platelet chip [PL-chip]) or collagen/thromboplastin (AR-chip) were used to assess platelet thrombus formation (PTF) at high shear rates or fibrin-rich PTF at low shear rates, respectively, in whole blood from 50 patients. The times needed for the flow pressure to increase by 10 kPa and 30 kPa (T10 and T30 ) from baseline were calculated from flow pressure curves. BS was determined by the use of a standardized questionnaire.

RESULTS

PL-T10 values correlated with BS (R(2) ~ 0.45) better than VWF:RCo (R(2) ~ 0.36), irrespective of the flow rate, whereas AR-T10 showed only a weak correlation with BS (R(2) ~ 0.18). Patients with PL-T10 > 10 min or AR-T10 > 30 min had lower VWF levels and higher BS than those with PL-T10 ≤ 10 min or AR-T10 ≤ 30 min, and the greatest differences were observed with PL-T10. Clinical severity appeared to correlate best with PL-T10 > 8 min. BS was significantly higher in patients with VWF:RCo of < 10 IU dL(-1) than in those with VWF:RCo of 10 IU dL(-1) to < 25 IU dL(-1) and 25-40 IU dL(-1). In patients with VWF:RCo of < 10 IU dL(-1) , BS was significantly higher in those with PL-T10 > 8 min than in those with PL-T10 ≤ 8 min.

CONCLUSION

T-TAS could be a useful technique for discriminating and predicting BS in VWD type 1 patients.

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.

Nuclear chemistry. Synthesis and detection of a seaborgium carbonyl complex

Experimental investigations of transactinoide elements provide benchmark results for chemical theory and probe the predictive power of trends in the periodic table. So far, in gas-phase chemical reactions, simple inorganic compounds with the transactinoide in its highest oxidation state have been synthesized. Single-atom production rates, short half-lives, and harsh experimental conditions limited the number of experimentally accessible compounds. We applied a gas-phase carbonylation technique previously tested on short-lived molybdenum (Mo) and tungsten (W) isotopes to the preparation of a carbonyl complex of seaborgium, the 106th element. The volatile seaborgium complex showed the same volatility and reactivity with a silicon dioxide surface as those of the hexacarbonyl complexes of the lighter homologs Mo and W. Comparison of the product's adsorption enthalpy with theoretical predictions and data for the lighter congeners supported a Sg(CO)6 formulation.

Variable contributions of basic residues forming an APC exosite in the binding and inactivation of factor VIIIa

Basic residues contained in the 39-, 60-, and 70-80-loops of activated protein C (APC) comprise an exosite that contributes to the binding and subsequent proteolytic inactivation of factor (F) VIIIa. Surface plasmon resonance (SPR) showed that WT APC bound to FVIII light chain (LC) and the FVIIIa A1/A3C1C2 dimer with equivalent affinity (Kd = 525 and 546 nM, respectively). These affinity values may reflect binding interactions to the acidic residue-rich a1 and a3 segments adjacent to A1 domain in the A1/A3C1C2 and A3 domain in LC, respectively. Results from SPR, using a panel of APC exosite variants where basic residues were mutated, in binding to immobilized FVIIIa A1/A3C1C2 or LC indicated ~4-10-fold increases in the Kd values relative to WT for several of the variants including Lys39Ala, Lys37-Lys38-Lys39/Pro-Gln-Glu, and Arg67Ala. On the other hand, a number of APC variants including Lys38Ala, Lys62Ala, and Lys78Ala showed little if any change in binding affinity to the FVIII substrates. FXa generation assays and Western blotting, used to monitor rates of FVIIIa inactivation and proteolysis at the primary cleavage site in the cofactor (Arg(336)), respectively, showed marked rate reductions relative to WT for the Lys39Ala, Lys37-Lys38-Lys39/Pro-Gln-Glu, Arg67Ala, and Arg74Ala variants. Furthermore, kinetic analysis monitoring FVIIIa inactivation by APC variants at varying FVIIIa substrate concentration showed ~2.6-4.4-fold increases in Km values relative to WT. These results show a variable contribution of basic residues comprising the APC exosite, with significant contributions from Lys39, Arg67, and Arg74 to forming a FVIIIa-interactive site.