Tissue factor pathway inhibitor in activated prothrombin complex concentrates (aPCC) moderates the effectiveness of therapy in some severe hemophilia A patients with inhibitor

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.

Predicted coagulation potential using an in vitro simulated model of emicizumab prophylaxis and immune tolerance induction therapy in hemophilia A patients with inhibitor

Emicizumab reduces bleeding in hemophilia A patients with inhibitor (HA-inh). A combination of immune tolerance induction therapy (ITI) and emicizumab prophylaxis may provide additional benefits, but coagulation potential during this treatment remains unknown. We assessed coagulation potentials in simulated ITI models in vitro using modified-clot waveform analysis. Factor (F)VIII-deficient plasma preincubated with anti-A2 and anti-C2 monoclonal antibodies was reacted with emicizumab (50 µg/mL) (emicizumab-HA-plasma), then spiking bypassing agents (BPAs): activated prothrombin complex concentrates (aPCC 1.3 IU/mL; 50 IU/kg), recombinant factor (rF)VIIa (2.2 µg/mL; 90 µg/kg), and FVIIa/FX (1.5 µg/mL; 60 µg/kg), and/or FVIII (100, 200 IU/dL). Coagulation potentials in emicizumab-HA-plasma (10 BU/mL) remained within the normal range when BPA and FVIII were both present. In emicizumab-HA-plasma (1 BU/mL) with BPA and FVIII (200 IU/dL), they were near or beyond the normal range, but those with a half concentration of rFVIIa based on the half-life in blood were within the normal range. In samples without inhibitor, coagulation potentials with combined BPA and FVIII were far beyond the normal range but with FVIII (100 IU/dL) and rFVIIa at half concentration they remained within the normal range. These results may provide information on the feasibility of concurrent ITI under emicizumab prophylaxis.

Clot waveform analysis for perioperative hemostatic monitoring of arthroscopic synovectomy in a pediatric patient with hemophilia A and inhibitor receiving emicizumab prophylaxis

Emicizumab reduces bleeding in patients with hemophilia A and inhibitors (PwHA-I). Coagulation potential during the perioperative period in emicizumab-treated PwHA-I undergoing surgery remains to be evaluated. We describe a 14-year-old boy with HA-I receiving emicizumab prophylaxis who experienced arthroscopic synovectomy. He was treated with a bolus infusion of recombinant factor VIIa (rFVIIa; 80 μg/kg) immediately before surgery, and treatment continued at the same dose every 3 h on day 1, every 4 h on day 2, and every 6 h on day 3. Treatment with rFVIIa was discontinued on day 4. No perioperative bleeding or thrombotic events were observed. Coagulation potential throughout the perioperative period was retrospectively assessed with an easy-to-use clot waveform analysis (CWA). Measurements from CWA returned to within or near the normal range, suggesting successful hemostatic management. Coagulation potentials assessed by CWA showed a significant correspondence with those from a thrombin generation assay (TGA) that is already in use. CWA and TGA could both provide useful data for assessing coagulation potential in the perioperative hemostatic management of emicizumab-treated PwHA-I.

Emicizumab Augments Thrombus Formation in Whole Blood from Patients with Hemophilia A under High Shear Flow Conditions

BACKGROUND

 Emicizumab is a bispecific antibody to factor (F) IXa and FX that mimics the FVIIIa cofactor function. Emicizumab prophylaxis markedly decreases bleeding episodes in patients with hemophilia A (PwHAs), irrespective of the presence of FVIII inhibitors. However, thrombotic microangiopathy (TMA) was reported when repeated high doses of activated prothrombin complex concentrates (aPCC) were concomitantly used with emicizumab. Although bypassing agents (BPAs) are vital in the hemostatic treatment for PwHAs with inhibitors, the mechanism of emicizumab-related TMA remains unclear.

AIM

 To assess the risk of excessive thrombus formation associated with BPAs and emicizumab under high shear conditions.

METHODS

 Perfusion flow-chamber experiments under high shear conditions were performed using whole blood from PwHAs in the presence of emicizumab without or together with FVIII or BPAs ex vivo.

RESULTS

 Emicizumab (100 μg/mL) added ex vivo to whole blood from PwHAs improved defective thrombus formation in a similar manner to that observed with the addition of recombinant FVIII at the early phase, while FVIII continued to be important at the later stages. aPCC (1.2 U/mL equivalent to 100 U/kg) or recombinant FVIIa (1.1 µg/mL; equivalent to 90 µg/kg) together with emicizumab further promoted platelet interactions and fibrin formation ex vivo but did not induce excessive thrombus formation.

CONCLUSION

 Emicizumab enhanced thrombin generation at local sites and improved defective hemostasis in whole blood from PwHAs under high shear conditions. Simple concomitant use of BPAs with emicizumab did not mediate excessive thrombus formation and remains an option for hemostatic management of emicizumab-treated PwHAs with inhibitors.

Prediction of the haemostatic effects of bypassing therapy using comprehensive coagulation assays in emicizumab prophylaxis-treated haemophilia A patients with inhibitors

In emicizumab prophylaxis, the concomitant therapy using bypassing agents (BPAs) is required for breakthrough bleeding and invasive procedures with attention to thrombotic complications. To predict coagulant effects of BPAs in emicizumab-treated patients with haemophilia A (PwHA) with inhibitor (PwHAwI), blood samples from emicizumab-treated PwHAwI (n = 8) and PwHA without inhibitor (n = 2) in phase 1/2 and HAVEN 1 study, spiked with activated prothrombin complex concentrates (aPCC) or recombinant factor VIIa (rFVIIa) ex vivo, and blood samples from emicizumab-treated PwHAwI-receiving BPAs were analysed by Ca²⁺ -triggered rotational thromboelastometry (ROTEM) and ellagic acid/tissue factor-triggered clot waveform analysis (CWA). Spiked aPCC, corresponded to 10-100 U/kg, markedly shortened ROTEM parameters beyond the normal range, while spiked rFVIIa, corresponded to 90-270 μg/kg, shortened them within near-normal range. Each of the spiked BPA-improved adjusted maximum coagulation velocity of CWA to within or near the normal range. In blood samples at post-infusion of aPCC (44-73 U/kg) or rFVIIa (79-93 μg/kg), the parameters of both assays improved to approximately the normal range. Taken together, ex vivo results of spiking tests in ROTEM and CWA, except aPCC spiking test in ROTEM, were relatively consistent with in vivo ones, and could usefully predict the coagulant effects of concomitant bypassing therapy for emicizumab-treated PwHAwI.

Perioperative safety and haematostatic efficacy of a new bypassing agent pd-FVIIa/FX (Byclot) in haemophilia patients with high-responding type inhibitors

: The novel agent pd-FVIIa/FX is a 1 : 10 protein weight mixture of activated factor VII (FVIIa) and factor X (FX) derived from donated blood plasma. A phase III clinical trial of pd-FVIIa/FX revealed high efficacy for bleeding episodes in haemophilia patients with inhibitors. However, up to now, only one case of this new agent being used for surgery had been reported. The objective of this study is to evaluate the perioperative haemostatic efficacy and safety of pd-FVIIa/FX in haemophilia patients with inhibitors. We retrospectively reviewed 25 operation charts from 14 haemophilia patients with high-responding inhibitors using pd-FVIIa/FX during the perioperative period. Efficacy was evaluated by attending physicians and results divided into four groups (excellent, good, fair, and poor). The operation chart was provided by nine Japanese medical institutes with expertise in haemophilia management. Out of the total of 25 surgical procedures, 44% (11/25) were classified as major surgery and the remainders were minor surgeries. In all of the surgeries but one, rFVIIa and/or APCC were administered in combination or sequential method. In all cases except one, the haemostatic efficiency rate was judged as excellent or good by treating physicians for an overall efficacy rate of 96%. No thrombotic adverse effects were reported. This study's results suggest that both combination and sequential therapy of pd-FVIIa/FX and other bypassing agents are well tolerated and effective for the control of perioperative bleeding in haemophilia patients with high-responding inhibitors.

New therapies using nonfactor products for patients with hemophilia and inhibitors

Regular prophylaxis with factor VIII (FVIII) or FIX products to prevent bleeding in patients with severe hemophilia A (HA) and HB, respectively, results in marked suppression of the onset of arthropathy and contributes greatly to improvements in quality of life. Some issues remain with the use of clotting factor replacement therapy, however. The need for multiple IV infusions is associated with a substantial mental and physical burden, and the hemostatic effect of bypassing agents (BPAs) in patients with inhibitor is inconsistent. The development of subcutaneous products with prolonged hemostatic efficiency, irrespective of the presence of inhibitors, has been a longtime wish for patients. A new class of therapeutic agents that act by enhancing coagulation (emicizumab) and inhibiting anticoagulant pathways (fitusiran and concizumab) have been established, and clinical trials using these nonfactor products are ongoing. The current findings have demonstrated that prophylaxis by nonfactor products supports marked reductions of bleeding episodes in hemophilia patients with or without inhibitor. Emicizumab has already been approved for use internationally. Some concerns are evident, however. Thrombotic microangiopathy and thromboembolism have occurred in 5 emicizumab-treated patients receiving repeated infusions of activated prothrombin complex concentrates, and a sinus vein thrombosis has occurred in a fitusiran-treated patient receiving repeated infusions of FVIII product. Moreover, reliable techniques to monitor hemostatic function in patients receiving nonfactor products with concomitant BPA or FVIII/FIX therapies require further assessment. These novel therapeutic agents have promising hemostatic properties, although wider experience in hemophilia centers is warranted to establish appropriate therapeutic strategies.

The Potential Close Future of Hemophilia Treatment - Gene Therapy, TFPI Inhibition, Antithrombin Silencing, and Mimicking Factor VIII with an Engineered Antibody

Summary Hemophilia is one of the best researched monogenic diseases. Hemophilia A will affect approximately 1:5,000 male live births. In recent decades, great progress has been made with the introduction of recombinant proteins in the 1990s for therapy and prophylaxis, securing adequate availability and, with the introduction of the prophylaxis concept, reducing the negative impact of hemophilia on morbidity (especially arthropathy). Despite this progress, there are still challenges to overcome to secure adequate prophylaxis and treatment: for the time being, causal pharmacological hemophilia prophylaxis and therapy requires repeated i.v. application on a regular basis. Although this approach leads to a reduced comorbidity, it does not yet represent an optimized approach with continuous reversal of the hemophilic defect, which would be the ideal solution. This review summarizes the very new treatment strategies for the treatment of hemophilia A and B.

The utility of thromboelastography in inherited and acquired bleeding disorders

Thromboelastography (TEG) was first described by Hartert in 1948, and was designed to monitor viscoelastic clot strength in whole blood in real time. The current TEG method and Rotational Thromboelastometry (ROTEM) were subsequently developed from the original principles. Both of the modern methods provide data by measuring changes in the viscoelastic strength of a small sample of clotting blood in response to a constant rotational force. The important advantage of these techniques is to visually observe and quantify blood coagulation including the propagation, stabilization and dissolution phases of clot formation under low shear conditions. Analysis of the results provides detailed kinetic data on fibrin generation, clot strength and fibrinolysis. These TEG/ROTEM analyses therefore enable evaluation of global clotting function and the monitoring of haemostatic treatment in various clinical situations, not only in patients with genetic bleeding disorders, such as haemophilia, but also in patients undergoing cardiac surgery, liver transplantation or suffering from traumatic injury. Some evidence suggests that haemostatic management using TEG/ROTEM leads to a reduction in total transfusions of whole blood or clotting factors. Wider clinical application of this technology seems likely.

Systematic monitoring of hemostatic management in hemophilia A patients with inhibitor in the perioperative period using rotational thromboelastometry

BACKGROUND

The management of hemophilia A (HA) patients with inhibitors on bypassing therapy remains challenging. In particular, the monitoring of treatment is restricted by the limited reliability and lack of standardization of currently available methods to evaluate the physiological effects of various hemostatic agents. Accurate monitoring of these patients is particularly important in surgical situations. The recently developed comprehensive coagulation assays, including rotational thromboelastometry (ROTEM), may be useful in these circumstances.

OBJECTIVE

We have attempted to establish a systematic monitoring protocol using ROTEM (NATEM triggered by CaCl2 ) to evaluate the choice and effectiveness of different bypassing agents in the perioperative period.

METHODS AND RESULTS

The hemostatic effects of recombinant factor VIIa (rFVIIa) and activated prothrombin complex concentrates (aPCC) were determined using a three-step procedure (spike, preoperative and perioperative) in eight patients with HA inhibitor admitted for elective surgery and assessed for individually tailored therapy. The ROTEM parameters demonstrated similar improvement to approximately normal levels at each stage after treatment with rFVIIa. Results in the presence of aPCC showed a marked improvement in the spike data, although this appeared to be different from those in the preoperative and perioperative assessments. The information derived from the spike and preoperative findings provided a useful guide for establishing an effective dose of therapeutic material, and facilitated good hemostatic control during and after surgery in all cases.

CONCLUSION

The findings suggest that this systematic analysis using ROTEM could provide a promising strategy for the use of bypassing therapy in HA patients with inhibitor.