Reduced plasma factor X is associated with a lack of response to recombinant activated factor VII in patients with hemophilia A and inhibitor, but does not impair emicizumab-driven hemostasis in vitro.

BACKGROUND: The hemostatic effect of recombinant (r) factor (F)VIIa after repetitive intermittent administration may be attenuated in patients with hemophilia A (PwHA) with inhibitors (PwHAwI) creating a clinically unresponsive status, although mechanism(s) remain to be clarified. In patients receiving prophylaxis treatment with emicizumab, concomitant rFVIIa is sometimes utilized in multiple doses for surgical procedures or breakthrough bleeding. AIM AND METHODS: We identified 'unresponsiveness' to rFVIIa, based on global coagulation function monitored using rotational thromboelastometry (ROTEM) in 11 PwHAwI and 5 patients with acquired HA, and investigated possible mechanisms focusing on the association between plasma FX levels and rFVIIa-mediated interactions. RESULTS: Our data demonstrated that FX antigen levels were lower in the rFVIIa-unresponsive group than in the rFVIIa-responsive group (0.46 ± 0.14 IU/mL vs. 0.87 ± 0.15 IU/mL, p < 0.01). This relationship was further examined by thrombin generation assays using a FX-deficient PwHAwI plasma model. The addition of FX with rFVIIa was associated with increased peak thrombin (PeakTh) generation. At low levels of FX (<0.5 IU/mL), rFVIIa failed to increase PeakTh to the normal range, consistent with clinical rFVIIa-unresponsiveness. In the presence of emicizumab (50 µg/mL), PeakTh was increased maximally to 80 % of normal, even at low levels of FX (0.28 IU/mL). CONCLUSIONS: Unresponsiveness to rFVIIa was associated with reduced levels of FX in PwHAwI. Emicizumab exhibited in vitro coagulation potential in the presence of FX at concentrations that appeared to limit the clinical response to rFVIIa therapy.

Force-sensing treadmill gait analysis system can detect gait abnormalities in haemophilia patients without arthropathy.

BACKGROUND: Joint damage in patients with haemophilia (PwH) is commonly assessed by imaging, but few reports have described how structural changes in joints, for example, haemophilic arthropathy (HA)-affect gait ability. OBJECTIVES: We evaluated gait function among PwH with HA, PwH without HA, and people without haemophilia (non-PwH) using a Zebris FDM-T treadmill (FDM-T), an easy-to-use gait assessment instrument with a force sensor matrix. METHODS: The following gait parameters were collected: centre of pressure trajectory intersection (COPi) anterior/posterior variability, COPi lateral variability, COPi anterior/posterior symmetry, COPi lateral symmetry, single-limb support line (SLSL) length, and SLSL variability. Participants walked at their typical gait speed. The physical function of the PwH was assessed by the Hemophilia Joint Health Score (HJHS). Parameters were compared among the three groups. RESULTS: Twelve PwH with HA, 28 PwH without HA, and 12 non-PwH were enrolled. Gait speed significantly differed between groups (non-PwH, 3.1 ± 0.7; PwH without HA, 2.0 ± 0.7; PwH with HA; 1.5 ± 0.4). The COPi anterior/posterior variability, COPi lateral variability, SLSL length, and SLSL variability were greater in the PwH groups than in the non-PwH group. The COPi lateral symmetry differed between PwH with HA and the other groups. The HJHS was not correlated with gait parameters among PwH with HA. CONCLUSIONS: Gait parameters and speed were abnormal in both PwH with HA and PwH without HA. The FDM-T can be used to identify early stages of physical dysfunction that cannot be detected by conventional functional assessments such as the HJHS.

Anticoagulant effects of protein C, protein S, and antithrombin levels on the protein C pathway in young children.

The protein C (PC) pathway involves physiological anticoagulant factors (PC, protein S [PS], and factor V) and performs major anticoagulant functions in adults. Variations in overall PC pathway function due to dynamic changes in PC and PS in early childhood are poorly understood. We aimed to evaluate the contributions of PC pathway function during early childhood by measuring changes in plasma thrombin generation (TG) after administration of the PC activator protac. We evaluated correlations between anticoagulant factors and percentage of protac-induced coagulation inhibition (PiCi%). Before protac addition, TG in newborns (n = 35), infants (n = 42), young children (n = 35), and adults (n = 20) were 525 ± 74, 720 ± 96, 785 ± 53, and 802 ± 64 mOD/min, and PiCi% were 42.1 ± 9.9, 69.8 ± 11.0, 82.9 ± 4.4, and 86.9 ± 3.4%, respectively. The distribution of PiCi% on the two axes of TG (with or without protac) changed continuously with age and differed from that of warfarin-treated plasma and adult PC- or PS-deficient plasma. PiCi% increased dynamically during infancy and correlated with PS levels in newborns and PC levels in young children. Addition of PC or fresh frozen plasma equivalent to approximately 25% PC to PC-deficient plasma improved PiCi%. This automatic measurement requires only a small sample volume and is useful for analysis of developmental hemostasis.

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.

Emicizumab-mediated hemostatic function assessed by thrombin generation assay in an in vitro model of factor VIII-depleted thrombophilia plasma.

Patients with hemophilia A (PwHA) may have concurrent deficiency of representative anticoagulant proteins, protein (P)C, PS, and antithrombin (AT), which reduces bleeding frequency. However, emicizumab-driven hemostasis in PwHA with such thrombophilic potential remains unclarified. This study investigated the influence of natural anticoagulants on emicizumab-driven coagulation in HA model plasma. Various concentrations of PS and AT were added to PS-deficient plasma and AT-deficient plasma in the presence of anti-FVIII antibody (FVIIIAb; 10BU/mL). PC-deficient plasma was mixed with normal plasma at various concentrations in the presence of FVIIIAb. Emicizumab (50 µg/mL) was added to these thrombophilic HA model plasmas, prior to tissue factor/ellagic acid-triggered thrombin generation assays. Co-presence of emicizumab increased peak thrombin values (PeakTh) dependent on PS, AT, and PC concentrations. Maximum coagulation potentials in the PS-reduced HA model plasmas remained normal in the presence of emicizumab. PeakTh were close to normal in the presence of 50%AT irrespective of emicizumab, but were higher than normal in the presence of 25%AT. Addition of recombinant FVIIa (corresponding to an administered dose of 90 µg/kg) enhanced coagulation potential to normal levels. Our findings provide novel information on hemostatic regulation in emicizumab-treated PwHA with a possible thrombophilic disposition.

NXT007-mediated hemostatic potential is suppressed by activated protein C-catalyzed inactivation of activated factor V.

Background: Activated protein C (APC) inactivates activated factor (F) V (FVa) and FVIIIa. NXT007, an emicizumab-based engineered therapeutic bispecific antibody, enhances the coagulation potential of FVIII-deficient plasma (FVIIIdef-plasma) to near normal levels. However, little is known about the effect of APC-induced inactivation in NXT007-mediated hemostatic function. Objectives: To investigate the contribution of APC-mediated reactions to NXT007-driven hemostasis. Methods: In pooled normal plasma (PNP) or FVIIIdef-plasma spiked with NXT007 (10 µg/mL), effects of APC (0-16 nM) were measured using a thrombin generation assay (TGA). The direct effects of APC on cofactor activity of NXT007 or FVIIIa in a FXa generation assay were also measured. The FVdef-plasma and FV Leiden plasma (FVLeiden plasma) were preincubated with 2 anti-FVIII monoclonal antibodies (termed FVIII-depleted), and the APC effect in the presence of NXT007 in FVIII-depleted FVdef-plasma with the addition of exogenous FV (7.5-30 nM) or FVIII-depleted FVLeiden plasma was investigated. Results: The APC dose-dependent suppression effect in TGA of FVIIIdef-plasma spiked with NXT007 was similar to that of PNP. FXa generation with NXT007 was not impaired by the addition of APC, suggesting that the APC-induced reaction in TGA with NXT007 was attributed to the direct inactivation of FVa. The addition of APC to FVIII-depleted FVdef-plasma, along with NXT007 and various FV concentrations, showed a similar attenuation to PNP. The NXT007-driven thrombin generation in FVIII-depleted FVLeiden plasma was suppressed by APC, similar to the reaction in native FVLeiden plasma. Conclusion: NXT007 did not impair APC-mediated downregulation of FVa in FVIIIdef-plasmas, regardless of the presence of FV mutation with APC resistance.

Hemostatic potential of recombinant von Willebrand factor and standard or pegylated extended half-life recombinant factor VIII on thrombus formation under high shear flow.

BACKGROUND: Von Willebrand factor (VWF) and factor VIII (FVIII) complex play a pivotal role in hemostasis. A deficiency or defect of VWF causes von Willebrand disease (VWD). Recombinant (r)VWF product has proved to be effective for hemostatic treatment of VWD, but limited information is available on their role in moderating thrombus formation under flow condition. We aimed to assess thrombus formation in the presence of rVWF combined with rFVIII or pegylated-extended half-life rFVIII (peg-EHL-rFVIII) in VWD whole blood under high shear flow. METHODS: Perfusion chamber experiments under high shear (2,500 s- 1) combined with immunostaining were performed using patient's whole blood with type 1 VWD, mixed with rVWF (Vonvendi®; 1.6 IU/mL), rFVIII or peg-EHL-rFVIII (Advate® or Adynovate®; 1.0 IU/mL), or both. Similar experiments were also conducted with clinical medical devices (T-TAS®). RESULTS: The addition of rFVIII did not augment thrombus formation assessed by surface coverage (SC) and thrombus height (TH), whereas rVWF enhanced these parameters (SC 19.1 ± 1.1% vs. 30.1 ± 4.1%, TH 2.2 ± 0.14 µm vs. 3.6 ± 0.40 µm, respectively). The co-presence of rVWF/rFVIII was comparable to plasma-derived VWF/FVIII (Confact®, VWF:FVIII ratio = 1.6:1.0) for increasing thrombogenicity in SC (32.5 ± 4.3% vs. 38.7 ± 5.5%) and in TH (5.0 ± 0.60 µm vs. 5.5 ± 0.64 µm), respectively. The pre-incubation time with rVWF and rFVIII appeared to have a little effect on the size of thrombus. Peg-EHL-rFVIII mediated thrombus formation to similar extent as rFVIII in the co-presence of rVWF. Similar results were obtained even with T-TAS. Immunostaining demonstrated that rFVIII and peg-EHL-rFVIII were similarly co-localized with rVWF in formed thrombi, indicating that pegylation did not interfere with molecular complexes. CONCLUSION: The effects of high-level rVWF and peg-EHL-rFVIII on thrombus formation were comparable to conventional therapeutic products in a patient's whole blood with VWD under high shear flow.

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.

Pediatric mesangial proliferative glomerulonephritis has increased the platelet thrombus formation potentials under high-shear flow condition.

INTRODUCTION: Blood coagulation is associated with glomerulonephritis (GN) pathophysiology. Using whole-blood-based rotational thromboelastometry, we recently reported that the degree of hypercoagulability in pediatric patients with immunoglobulin A nephropathy (IgAN), a GN, might be associated with pathological severity. To further clarify the coagulation status of mesangial proliferative glomerulonephritis (MesPGN), we assessed the platelet thrombus formation (PTF) under high-shear flow using a microchip-based flow chamber system (T-TAS®). METHODS: Thirty-four pediatric patients definitively diagnosed with MesPGN by renal biopsy at Nara Medical University Hospital between 2015 and 2022 were enrolled, and 29 patients (case group; median age, 8.0 years) were assessed. Microchips coated with collagen (PL-chip) were used to assess PTF at high-shear in whole blood. The times to increase by 10 and 30 kPa (T10 and T30) from baseline were calculated and compared with those of the pediatric controls. Changes in the parameters during the treatment course and the relationship between pathological severity and the parameters were evaluated. RESULTS: T10 and T30 parameters in the PL-chip were significantly shorter and the area under the curves were greater in the case group than those in the control group (both p <0.05). Each parameter was enhanced during the 3-week treatment but improved after the end of treatment. No significant relationship was observed between pathological severity and these parameters. Little PTF difference was observed between IgAN and Henoch-Schönlein purpura nephritis. CONCLUSIONS: Pediatric MesPGN increased the potential for PTF under high-shear flow conditions.

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.

The spleen is the major site for the development and expansion of inhibitor producing-cells in hemophilia A mice upon FVIII infusion developing high-titer inhibitor.

BACKGROUND: Hemophilia A (HA) is a hereditary bleeding disorder caused by defects in endogenous factor (F)VIII. Approximately 30 % of patients with severe HA treated with FVIII develop neutralizing antibodies (inhibitors) against FVIII, which render the therapy ineffective. The managements of HA patients with high-titter inhibitors are especially challenging. Therefore, it is important to understand the mechanism(s) of high-titer inhibitor development and dynamics of FVIII-specific plasma cells (FVIII-PCs). AIMS: To identify the dynamics of FVIII-PCs and the lymphoid organs in which FVIII-PCs are localized during high-titer inhibitor formation. METHODS AND RESULTS: When FVIII-KO mice were intravenously injected with recombinant (r)FVIII in combination with lipopolysaccharide (LPS), a marked enhancement of anti-FVIII antibody induction was observed with increasing FVIII-PCs, especially in the spleen. When splenectomized or congenitally asplenic FVIII-KO mice were treated with LPS + rFVIII, the serum inhibitor levels decreased by approximately 80 %. Furthermore, when splenocytes or bone marrow (BM) cells from inhibitor+ FVIII-KO mice treated with LPS + rFVIII were grafted into immune-deficient mice, anti-FVIII IgG was detected only in the serum of splenocyte-administered mice and FVIII-PCs were detected in the spleen but not in the BM. In addition, when splenocytes from inhibitor+ FVIII-KO mice were grafted into splenectomized immuno-deficient mice, inhibitor levels were significantly reduced in the serum. CONCLUSION: The spleen is the major site responsible for the expansion and retention of FVIII-PCs in the presence of high-titer inhibitors.

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.

High levels of factor VIII activity in patients with acquired hemophilia A in remission are associated with unusually low coagulation potentials.

BACKGROUND: Elevated factor VIII activity (FVIII:C) is often observed in patients with acquired hemophilia A (PwAHA) in remission. However, comprehensive coagulation potentials in this patient group remain to be investigated. AIM: To evaluate comprehensive coagulation potentials in PwAHA. METHODS: We investigated coagulation function in eleven PwAHA with high FVIII:C (> 150 IU/dL) using thrombin generation assay (TGA) and/or rotational thromboelastometry (ROTEM), and compared findings with results obtained from contrived samples generated by spiking recombinant FVIII. RESULTS: The median FVIII:C and FVIII inhibitor titers during remission in enrolled PwAHA were 206 IU/dL and 0.44 BU/mL, respectively. In all patients, lag time and time to peak were either prolonged or normal compared to contrived samples corresponding to their FVIII:C. However, higher values of peak thrombin and endogenous thrombin potentials compared to contrived samples were observed in two patients. ROTEM parameters were within normal ranges in all cases. One patient (FVIII:C 171 IU/dL) developed venous thrombosis and pulmonary embolism, but TGA parameters showed low or normal coagulation potential compared to contrived samples corresponding to his FVIII:C. CONCLUSION: PwAHA with high FVIII:C could exhibit lower coagulation potentials than those corresponding to their FVIII:C.

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.

Modified expi293 cell culture system using piggyBac transposon enables efficient production of human FVIII.

Human blood coagulation factor VIII (hFVIII) is used in hemostatic and prophylactic treatment of patients with hemophilia A. Biotechnological innovations have enabled purification of the culture medium of rodent or human cells harboring the hFVIII expression cassette. However, cell lines express hFVIII protein derived from an exogenous expression vector at a lower level than most other proteins. Here, we describe hFVIII production using piggyBac transposon and the human-derived expi293F cell line. Use of a drug selection protocol, rather than transient expression protocol, allowed cells harboring hFVIII expression cassettes to efficiently produce hFVIII. In heterogeneous drug-selected cells, the production level was maintained even after multiple passages. The specific activity of the produced hFVIII was comparable to that of the commercial product and hFVIII derived from baby hamster kidney cells. We also applied codon optimization to the hFVIII open reading frame sequences in the transgene, which increased production of full-length hFVIII, but decreased production of B-domain-deleted human FVIII (BDD-hFVIII). Low transcriptional abundance of the hF8 transgene was observed in cells harboring codon-optimized BDD-hFVIII expression cassettes, which might partially contribute to decreased hFVIII production. The mechanism underlying these distinct outcomes may offer clues to highly efficient hFVIII protein production.

Two pediatric cases of severe hemophilia A in which emicizumab prophylaxis failed to prevent traumatic extra-articular hemorrhage.

Emicizumab reduces bleeding episodes in patients with severe hemophilia A (PwHA). Little information is available on hemostatic management of severe traumatic hemorrhages in emicizumab-treated pediatric PwHA. We assessed therapeutic efficacy and global coagulation potentials in two pediatric cases of emicizumab-treated pediatric PwHA with intracranial or retroperitoneal/iliopsoas hemorrhage. A modified clot waveform analysis (CWA) triggered by mixtures of tissue factor and ellagic acid was used to assess coagulant potentials, and maximum coagulant velocity (Ad|min1|) was calculated. One patient with intracranial hemorrhage was treated with continuous infusions of recombinant factor VIII (rFVIII) at a dose of 4-4.6 IU/kg/hr for 9 days, followed by bolus infusion at 66 IU/kg/day for 2 days and 33 IU/kg/day for an additional 2 days. The Ad|min1| was increased from 5.5 (at baseline) to 7.0-8.1 under concomitant treatment and maintained within or near normal range (IQR; 6.9-7.7). The other patient with retroperitoneal/iliopsoas hemorrhage received bolus infusions of rFVIII at 50 IU/kg/day for 20 days and every-other-day infusion of rFVIII for 8 days. The Ad|min1| was increased from 5.2 (at baseline) to 5.8-6.8 under concomitant treatment and maintained within the normal range. We successfully managed a treatment plan for severe traumatic bleeding in emicizumab-treated pediatric PwHA using modified CWA.