Snake Venom Proteomics, Immunoreactivity and Toxicity Neutralization Studies for the Asiatic Mountain Pit Vipers, Ovophis convictus, Ovophis tonkinensis, and Hime Habu, Ovophis okinavensis.

Snakebite envenomation is a serious neglected tropical disease, and its management is often complicated by the diversity of snake venoms. In Asia, pit vipers of the Ovophis species complex are medically important venomous snakes whose venom properties have not been investigated in depth. This study characterized the venom proteomes of Ovophis convictus (West Malaysia), Ovophis tonkinensis (northern Vietnam, southern China), and Ovophis okinavensis (Okinawa, Japan) by applying liquid chromatography-tandem mass spectrometry, which detected a high abundance of snake venom serine proteases (SVSP, constituting 40-60% of total venom proteins), followed by phospholipases A2, snake venom metalloproteinases of mainly P-III class, L-amino acid oxidases, and toxins from other protein families which were less abundant. The venoms exhibited different procoagulant activities in human plasma, with potency decreasing from O. tonkinensis > O. okinavensis > O. convictus. The procoagulant nature of venom confirms that consumptive coagulopathy underlies the pathophysiology of Ovophis pit viper envenomation. The hetero-specific antivenoms Gloydius brevicaudus monovalent antivenom (GbMAV) and Trimeresurus albolabris monovalent antivenom (TaMAV) were immunoreactive toward the venoms, and cross-neutralized their procoagulant activities, albeit at variably limited efficacy. In the absence of species-specific antivenom, these hetero-specific antivenoms may be useful in treating coagulotoxic envenomation caused by the different snakes in their respective regions.

Simoctocog Alfa (Nuwiq) in Previously Untreated Patients with Severe Haemophilia A: Final Results of the NuProtect Study.

INTRODUCTION: FVIII inhibitor development is the most serious contemporary treatment complication in haemophilia A, particularly in previously untreated patients (PUPs). No inhibitors developed in clinical trials in previously treated patients treated with simoctocog alfa (Nuwiq), a fourth-generation recombinant FVIII produced in a human cell line. METHODS: The NuProtect study investigated the immunogenicity of simoctocog alfa in PUPs. NuProtect was a prospective, multinational, open-label, non-controlled, phase III study. PUPs with severe haemophilia A (FVIII:C <1%) of any age and ethnicity were treated with simoctocog alfa for 100 exposure days or a maximum of 5 years. Patients were true PUPs without prior exposure to FVIII concentrates or blood components. Inhibitor titres were measured with the Nijmegen-modified Bethesda assay; cut-off for positivity was 0.6 BU mL-1 (≥0.6 to <5 low-titre, ≥5 high titre). RESULTS: A total of 108 PUPs with a median age at first treatment of 12.0 months (interquartile range: 8.0-23.5) were treated with simoctocog alfa. F8 mutation type was known for 102 patients (94.4%) of whom 90 (88.2%) had null F8 mutations and 12 (11.8%) had non-null mutations. Of 105 PUPs evaluable for inhibitor development, 28 (26.7%) developed inhibitors; 17 high titre (16.2%) and 11 low titre (10.5%). No PUPs with non-null F8 mutations developed inhibitors. CONCLUSION: In the NuProtect study, the rate of inhibitor development in PUPs with severe haemophilia A treated with simoctocog alfa was lower than the rate reported for hamster-cell-derived recombinant factor VIII products in other recent clinical trials. No inhibitors were reported in PUPs with non-null F8 mutations.

Calibration-free concentration analysis for quantification of anti-drug specific antibodies in polyclonal positive control antibodies and in clinical samples.

Highly sensitive assays for anti-drug antibodies (ADAs) are both a regulatory requirement and requisite for proper evaluation of the effects of immunogenicity on clinical efficacy and safety. Determination of ADA assay sensitivity depends on positive control antibodies to represent naturally occurring or treatment-induced ADA responses. An accurate determination of the proportion of drug-specific antibodies in these polyclonal positive control batches is critical for correct evaluation of assay sensitivity. Target purification of positive control antibodies is commonly applied but infers the risk to lose a proportion of the antibodies. This may lead to an incorrect estimate of the ADA assay sensitivity, especially if high-affinity antibodies are lost that may be representative of natural ADAs with clinical implication. The Surface Plasmon Resonance platform on the Biacore™ systems offers methods for real-time analysis of biomolecular interactions without introducing any modifications to the analysed material. Calibration-free concentration analysis (CFCA) is such an application for determination of the proportion of drug-specific antibodies, which allows direct determination of active antibody concentrations, as defined by the ligand, in a flow-based system. Here, we present a novel CFCA method for ADA quantification developed and validated using polyclonal positive control antibodies against endogenous human insulin, insulin degludec (Tresiba®) and turoctocog alfa (NovoEight®). We find that CFCA precisely and accurately measures concentrations of drug-specific IgG antibodies with a precision of ±10% and 90%-112% recovery of expected values of monoclonal positive control antibodies. Additionally, we have achieved a more accurate measure of the sensitivity of a cell-based bioassay for in vitro neutralising ADAs using the specific concentration determined with CFCA. Moreover, we effectively quantified serum anti-insulin antibodies in high-titre clinical samples from individuals with diabetes mellitus. This application extends the relevance of the CFCA technology to analysis of immunogenicity for accurate quantification of ADAs in both the polyclonal positive control and in clinical samples.

A previously treated severe haemophilia A patient developed high-titre inhibitor after vaccinations.

The factor VIII (FVIII)-neutralizing antibody (inhibitor) seen in 25%-30% of patients with severe haemophilia A (SHA). Vaccination is a non-genetic risk factor of inhibitor development as 'danger signal' which may provide a pro-inflammatory microenvironment to increase FVIII immunogenicity. We reported a previously treated SHA patient postponed the first vaccination to 15-month age received diphtheria-pertussis-tetanus intramuscularly. At 18-month age, the patient received Hepatitis A intramuscularly and Varicella Zoster Virus subcutaneously with 2 weeks interval and FVIII infusion was given <24 h prior for each. Successive bleedings occurred 1 week later with inefficacy of FVIII replacement. High-titre inhibitor was tested at 117 exposure days. This case suggested that continuous vaccinations in close proximity to FVIII could induce inhibitor. The relationship between vaccination and FVIII immunogenicity still needs to be revealed by further study.

Economic impact model of delayed inhibitor development in patients with hemophilia a receiving emicizumab for the prevention of bleeding events.

Aims: Cumulative exogenous factor VIII (FVIII) exposure is an important predictor of developing neutralizing antibodies (inhibitors) to FVIII in patients with persons with hemophilia A (PwHA). The aim of this study was to model the costs of emicizumab versus FVIII prophylaxis and total treatment costs for patients with severe HA.Materials and Methods: An Excel-based decision model was developed to calculate cumulative costs in PwHA over a 20-year time horizon from the US payer perspective. The model considered persons with severe HA beginning at age 12 months with no prior FVIII exposure and initiating prophylaxis with emicizumab or FVIII. PwHA could develop inhibitors on accumulation of 20 FVIII exposure days. PwHA with inhibitors replaced FVIII with bypassing agents until inhibitors resolved spontaneously, following immune tolerance induction (ITI), or at the end of the time horizon. The primary model outcome was the difference in emicizumab versus FVIII treatment costs in 2019 USD. Sensitivity analyses were performed to test the robustness of results.Results: Total incremental cost over 20 years was -$1,945,480 (emicizumab arm, $4,919,058; FVIII arm, $6,864,538). Prophylaxis costs (emicizumab arm, $4,096,105; FVIII arm, $6,290,919) comprised the majority of costs in both groups, followed by breakthrough bleed treatment for the FVIII arm ($342,652) and ITI costs for the emicizumab arm ($733,671). Higher costs in the FVIII group reflected earlier inhibitor development (FVIII, 4 months; emicizumab, 162 months) and switch to bypassing agents.Limitations: The model design reflects a simplified treatment pathway for patients with severe HA who initiate FVIII or emicizumab prophylaxis. In the absence of clinical data, a key conservative assumption of the model is that patients receiving emicizumab and FVIII prophylaxis have the same risk of developing inhibitors.Conclusions: This study suggests that prophylaxis with emicizumab results in cost savings compared to FVIII prophylaxis in HA.

Comparative proteomes, immunoreactivities and neutralization of procoagulant activities of Calloselasma rhodostoma (Malayan pit viper) venoms from four regions in Southeast Asia.

The intraspecific geographical venom variations of Calloselasma rhodostoma from Malaysia (CR-M), Indonesia (CR-I), Thailand (CR-T) and Vietnam (CR-V) were investigated through 1D SDS-PAGE and nano-ESI-LCMS/MS. The venom antigenicity, procoagulant activities and neutralization using Thai C. rhodostoma Monovalent Antivenom (CRMAV) were also investigated. SDS-PAGE patterns of the venoms were relatively similar with minor variations. Proteomic analysis revealed that snake venom metalloproteinases (SVMPs, particularly P-I class), serine proteases (SVSPs) and snaclecs dominated the venom protein composition (68.96-81.80%), followed by L-amino acid oxidase (LAAO) and phospholipase A2 (PLA2) (7.37-11.08% and 5.18-13.81%, respectively), corroborating C. rhodostoma envenoming effects (hemorrhage, consumptive coagulopathy, thrombocytopenia and local tissue necrosis). Other proteins of lower abundances (2.82-9.13%) identified include cysteine-rich secretory proteins (CRISP), phospholipase B, phosphodiesterase, nerve growth factor, 5'-nucleotidase, aminopeptidase and hyaluronidase. All four venoms exhibited strong procoagulant effects which were neutralized by CRMAV to different extents. CRMAV immunoreactivity was high toward venoms of CR-M, CR-I and CR-T but relatively low for CR-V venom. Among the venom samples from different locales, CR-V venom proteome has the smallest SVMP composition while SVSP, PLA2 and phosphodiesterase were more abundant in the venom. These variations in C. rhodostoma venom protein composition could partly explain the differences seen in immunoreactivity. (198 words).

New technologies in gene therapy for inducing immune tolerance in hemophilia A.

INTRODUCTION: Conventional hemophilia treatment is based on repeated infusion of the missing clotting factor. This therapy is lifelong, expensive and can result in the formation of neutralizing antibodies, thus causing failure of the treatment and requiring higher doses of the replacement drug. Areas covered: Gene and cell therapies offer the advantage of providing a definitive and long-lasting correction of the mutated gene, promoting its physiological expression and preventing neutralizing antibody development. This review focuses on the most recent approaches that have been shown to prevent and even eradicate immune response toward the replaced factor. Expert commentary: Despite the encouraging data demonstrated by ongoing clinical trials and pre-clinical studies, more extensive investigations are necessary to establish the long-term safety and efficacy of gene therapy treatments in maintaining immune tolerance.

Routine measurements of factor VIII activity and inhibitor titer in the presence of emicizumab utilizing anti-idiotype monoclonal antibodies.

Essentials Emicizumab (Emi) affects the APTT-based assays of factor (F)VIII activity and inhibitor titer. A mixture of two anti-Emi monoclonal antibodies (mAb) effectively neutralized the Emi activity. Anti-Emi mAbs completely eliminated the influence of Emi on FVIII activity and inhibitor titer. The inclusion of anti-Emi mAbs in routine FVIII assays would be useful for Emi-treated patients. SUMMARY: Background Emicizumab is an anti-factor (F)IXa/X bispecific monoclonal antibody (mAb), mimicking the factor (F)VIIIa cofactor activity. Emicizumab does not require activation by thrombin and its shortening effect on the activated partial prothrombin time (APTT) is more pronounced than that of factor (F)VIII. APTT-based FVIII activity (FVIII:C) and FVIII inhibiter titer measurements are influenced by the presence of emicizumab. Aim To establish a reliable APTT-based assay to measure FVIII in the presence of emicizumab. Methods Plasmas from hemophilia A (HA) patients without or with inhibitors were studied using one-stage FVIII:C and Bethesda inhibitor assays. Two recombinant anti-idiotype mAbs to emicizumab (anti-emicizumab mAbs) were prepared, rcAQ8 to anti-FIXa-Fab and rcAJ540 to anti-FX-Fab. Results The combined anti-idiotype mAbs (2000 nm each) eliminated the effects of emicizumab on APTTs of HA plasmas without or with inhibitor by competitive inhibition of antibody binding to FIX(a)/FX(a). Measurements of FVIII coagulation activity in HA plasmas without inhibitor were overestimated in the presence of emicizumab (1 µm = ~150 µg mL-1 ) at all reference levels of FVIII. The addition of anti-emicizumab mAbs to the assay mixtures completely neutralized the emicizumab and facilitated accurate determination of FVIII:C. Anti-FVIII inhibitor titers were undetectable in the presence of emicizumab in HA plasmas with inhibitor or normal plasmas mixed with anti-FVIII neutralizing antibodies. These effects of emicizumab were completely counteracted by the addition of the anti-idiotype mAbs, allowing accurate assessment of inhibitor titers. Conclusion The in vitro inclusion of anti-emicizumab mAbs in the standard one-stage coagulation assays prevented interference by emicizumab and enabled accurate measurements of FVIII:C and inhibitor titers.

Factor VIII products and inhibitor development in previously treated patients with severe or moderately severe hemophilia A: a systematic review.

Essentials Data on product-related immunogenicity in previously treated haemophilia A patients is scarce. A systematic review and meta-analysis of all currently available evidence was conducted. The overall incidence rate was 2.06 per 1000 person-years (95% confidence interval: 1.06-4.01). Some recombinant factor VIII products were associated with increased immunogenicity. SUMMARY: Background Patients with severe hemophilia A who have been treated extensively with factor VIII products have a low but potentially serious risk of inhibitor development. It is unknown why these patients develop inhibitors, and data on product-related immunogenicity are scarce. Aims To summarize the currently available evidence on the relationship between inhibitor development and recombinant FVIII product type in previously treated patients (PTPs) with severe hemophilia A. Methods Longitudinal studies were included that reported on de novo inhibitor formation in patients with baseline FVIII activity levels of < 0.02 IU mL-1 who had been treated with FVIII for at least 50 days. Pooled incidence rates of inhibitor development according to product types were calculated with a random intercept Poisson regression model. Results Forty-one independent cohorts were included; 39 patients developed de novo inhibitors during 19 157 person-years of observation. The overall incidence rate was 2.06 per 1000 person-years, with a 95% confidence interval (CI) of 1.06-4.01. According to product type, the pooled incidence rates were 0.99 (95% CI 0.37-2.70) per 1000 person-years for patients treated with Advate, 5.86 (95% CI 0.25-134.92) per 1000 person-years for those treated with Kogenate/Helixate, 1.35 (95% CI 0.66-2.77) per 1000 person-years for those treated with Kogenate FS/Helixate NexGen, 12.05 (95% CI 1.53-94.78) per 1000 person-years for those treated with Refacto, and 4.64 (95% CI 0.82-26.43) per 1000 person-years for those treated with Refacto AF. Conclusion These results suggest that some products may be associated with increased immunogenicity. However, the low incidence of inhibitors in PTPs and the differences in study design may cause significant variation in estimates of risk.

Factor Xa and VIIa inhibition by tissue factor pathway inhibitor is prevented by a monoclonal antibody to its Kunitz-1 domain.

Essentials Activated FVII (FVIIa) and FX (FXa) are inhibited by tissue factor pathway inhibitor (TFPI). A monoclonal antibody, mAb2F22, was raised against the N-terminal fragment of TFPI (1-79). mAb2F22 bound exclusively to the K1 domain of TFPI (KD ∼1 nm) and not to the K2 domain. mAb2F22 interfered with inhibition of both FVIIa and FXa activities and restored clot formation. SUMMARY: Background Initiation of coagulation is induced by binding of activated factor VII (FVIIa) to tissue factor (TF) and activation of factor X (FX) in a process regulated by tissue factor pathway inhibitor (TFPI). TFPI contains three Kunitz-type protease inhibitor domains (K1-K3), of which K1 and K2 block the active sites of FVIIa and FXa, respectively. Objective To produce a monoclonal antibody (mAb) directed towards K1, to characterize the binding epitope, and to study its effect on TFPI inhibition. Methods A monoclonal antibody, mAb2F22, was raised against the N-terminal TFPI(1-79) fragment. Binding data were obtained by surface plasmon resonance analysis. The Fab-fragment of mAb2F22, Fab2F22, was expressed and the structure of its complex with TFPI(1-79) determined by X-ray crystallography. Effects of mAb2F22 on TFPI inhibition were measured in buffer- and plasma-based systems. Results mAb2F22 bound exclusively to K1 of TFPI (KD ~1 nm) and not to K2. The crystal structure of Fab2F22/TFPI (1-79) mapped an epitope on K1 including seven residues upstream of the domain. TFPI inhibition of TF/FVIIa amidolytic activity was neutralized by mAb2F22, although the binding epitope on K1 did not include the P1 residue. Binding of mAb2F22 to K1 blocked TFPI inhibition of the FXa amidolytic activity and normalized hemostasis in hemophilia human A-like plasma and whole blood. Conclusion mAb2F22 blocked TFPI inhibition of both FVIIa and FXa activities and mapped a FXa exosite for binding to K1. It reversed TFPI feedback inhibition of TF/FVIIa-induced coagulation and restored clot formation in FVIII-neutralized human plasma and blood.

Timing and severity of inhibitor development in recombinant versus plasma-derived factor VIII concentrates: a SIPPET analysis.

Essentials Recombinant factor VIII (rFVIII) was contrasted with plasma-derived FVIII (pdFVIII). In previously untreated patients with hemophilia A, rFVIII led to more inhibitors than pdFVIII. Inhibitors with rFVIII developed earlier, and the peak rate was higher than with pdFVIII. Inhibitors with rFVIII were more severe (higher titre) than with pdFVIII. SUMMARY: Background The development of neutralizing antibodies (inhibitors) against factor VIII (FVIII) is the most severe complication in the early phases of treatment of severe hemophilia A. Recently, a randomized trial, the Survey of Inhibitors in Plasma-Product Exposed Toddlers (SIPPET) demonstrated a 2-fold higher risk of inhibitor development in children treated with recombinant FVIII (rFVIII) products than with plasma-derived FVIII (pdFVIII) during the first 50 exposure days (EDs). Objective/Methods In this post-hoc SIPPET analysis we evaluated the rate of inhibitor incidence over time by every 5 EDs (from 0 to 50 EDs) in patients treated with different classes of FVIII product, made possible by a frequent testing regime. Results The highest rate of inhibitor development occurred in the first 10 EDs, with a large contrast between rFVIII and pdFVIII during the first 5 EDs: hazard ratio 3.14 (95% confidence interval [CI], 1.01-9.74) for all inhibitors and 4.19 (95% CI, 1.18-14.8) for high-titer inhibitors. For patients treated with pdFVIII, the peak of inhibitor development occurred later (6-10 EDs) and lasted for a shorter time. Conclusion These results emphasize the high immunologic vulnerability of patients during the earliest exposure to FVIII concentrates, with the strongest response to recombinant FVIII products.

Combination of hemostatic therapies for treatment of patients with hemophilia A and inhibitors.

BACKGROUND: Therapy application and monitoring of patients with hemophilia A (HA) and inhibitors are challenging. In the current study, combined FVIII - bypass therapy was implemented for a cohort of severe HA patients with inhibitors. METHODS: Plasma of 15 HA patients with inhibitors was spiked ex vivo with FVIII, rFVIIa, FEIBA and their combinations and thrombin generation (TG) was studied. Some patients who experienced hemarthroses or required minor surgeries were treated by a combined concomitant administration of FVIII+FEIBA as IV bolus doses. RESULTS: TG spiking studies showed individual responses not correlated to inhibitor titer. Combinations of agents augmented TG as compared to any single agent, while combined FVIII+FEIBA yielded the highest TG, supporting it as a potential treatment. Following emergent successful surgery of child treated by concomitant FVIII+FEIBA, a total of 396 episodes in 7/15 patients were treated with concomitant FVIII+FEIBA. Five patients were treated for bleeding episodes only, whereas 2 were children undergoing immune tolerance induction (ITI) with FEIBA prophylaxis. Four minor surgeries were performed on FVIII+FEIBA repeated infusions. Neither thrombosis nor any other adverse events were documented. CONCLUSION: A combination of FVIII+FEIBA may be effective and safe as an alternative treatment option for some high-responding inhibitor patients.

CD32 inhibition and high dose of rhFVIII suppress murine FVIII-specific recall response by distinct mechanisms in vitro.

Development of neutralising antibodies (inhibitors) against factor VIII (FVIII) is a frequent and severe complication of replacement therapy in haemophilia A. Previous data from haemophilia A mouse model demonstrates that both CD32 inhibition and high doses of rhFVIII prevent the differentiation of FVIII-specific memory B cells (MBCs) into antibody secreting cells (ASCs). Here, cellular targets responsible for the suppression of ASC formation by means of CD32 inhibition and high dose of rhFVIII were analysed. We investigated apoptosis on FVIII-specific MBCs using a pan caspases inhibitor, and screened for defects in rhFVIII presentation by analysing T cell release of Th1- and Th2-cytokines in vitro. Although high dose of rhFVIII suppressed ASC formation, cytokine response was not affected. Upon re-stimulation of splenocytes with high dose of rhFVIII, prevention of apoptosis fully restored the FVIII-specific recall response. In contrast, genetic deletion or inhibition of CD32 significantly altered Th1- and Th2-response. CD32 blockade and inhibition of apoptosis resulted in a partial rescue of FVIII-specific ASCs. Normal cytokine secretion could not be restored. In conclusion, suppression of FVIII-specific recall response by CD32 and high doses of rhFVIII is mediated by distinct mechanisms. High dose of rhFVIII induces apoptosis in FVIII-specific MBCs but does not influence FVIII-specific T cell response. CD32 blockade, however, may suppress the FVIII-specific recall response by two ways: i) increasing apoptosis of FVIII-specific MBCs and ii) disturbing FVIII-specific T cell response by modulating presentation of rhFVIII to CD4+ T cells in vitro.

Large scale studies assessing anti-factor VIII antibody development in previously untreated haemophilia A: what has been learned, what to believe and how to learn more.

Minimizing the risk of inhibitor development by acting on modifiable risk factors remains a sensible goal for treatment optimization in haemophilia A. By critically appraising published studies assessing inhibitor development, this review addresses the role of studies in previously untreated patients (PUPs) for establishing the immunogenicity of new concentrates, suggest novel research design to be adopted in future studies and discuss clinical practice implications of the reported differential immunogenicity of Kogenate Bayer and Advate factor VIII concentrates. Three considerations are relevant here: (i) all of the existing concentrates, when tested following the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee recommendation, were shown to be safe; as a consequence, (ii) when considering using any newly introduced product, one should be aware that it could, in future, turn out to be as immunogenic as Kogenate Bayer, and (iii) at the population level, it might be wiser not to use Kogenate Bayer in PUPs, if the choice is against Advate. When presenting the risk of developing inhibitors to the individual patient (or their family), the message remains that the risk can be as high as 40%, without any efficient instrument to predict individual inhibitor risk. Patients should be invited to enrol into a randomized registry trial, including random assignment to trials with new investigational products.

Phase 1 dose-escalating study to evaluate the safety, pharmacokinetics, and pharmacodynamics of a recombinant factor Xa variant (FXaI16L ).

Essentials FXaI16L is a recombinant zymogen-like variant of activated coagulation factor X (FXa). A phase 1 dose escalation clinical trial of FXaI16L was conducted in healthy adults. FXaI16L was safe and tolerated at doses up to 5 µg/kg; no dose-limiting toxicity was observed. Data support further development of FXaI16L for patients with acute hemorrhagic conditions. SUMMARY: Background FXaI16L (PF-05230907) is a zymogen-like variant of activated factor X (FXa). It shows enhanced resistance to inactivation by endogenous inhibitors as compared with wild-type FXa, and restores hemostatic activity in non-clinical models of various bleeding conditions. Objectives To evaluate the safety, pharmacokinetics and pharmacodynamics of FXaI16L by performing a phase 1, first-in-human, dose-escalation clinical trial in healthy adult volunteers. Methods Participants were assigned to one of six ascending single-dose cohorts (0.1, 0.3, 1, 2, 3 or 5 µg kg-1 ), each planned to comprise six volunteers treated with FXaI16L and two treated with placebo. Assessments included safety monitoring, pharmacokinetic and pharmacodynamic (PD) analyses, and immunogenicity testing. Results The trial enrolled 49 male volunteers. Administration of a single intravenous bolus dose of FXaI16L was safe and tolerated at all dose levels tested, with no dose-limiting toxicity or serious adverse events. FXaI16L plasma levels appeared to increase dose-proportionally, with a half-life of ~ 4 min. Treatment-related PD changes were observed for activated partial thromboplastin time, thrombin generation assay, thrombin-antithrombin complexes, prothrombin fragment 1 + 2, and D-dimer. One volunteer had a weak and transient non-neutralizing antidrug antibody response, which did not cross-react with native FX or native FXa. Conclusions FXaI16L was safe and tolerated, and showed a pharmacologic effect in healthy adults when administered at doses up to 5 µg kg-1 . The safety profile, pharmacokinetics and pharmacodynamics observed in this clinical trial support the further development of FXaI16L for hemostatic treatment in individuals with acute hemorrhagic conditions.

Combination therapy for inhibitor reversal in haemophilia A using monoclonal anti-CD20 and rapamycin.

Development of antibodies (inhibitors) against coagulation factor VIII (FVIII) is a major complication of intravenous replacement therapy in haemophilia A (HA). Current immune tolerance induction (ITI) regimens are not universally effective. Rituximab, a B cell-depleting antibody against CD20, has shown mixed results for inhibitor reversal in patients. This study aims to develop a combinatorial therapy for inhibitor reversal in HA, using anti-murine CD20 (anti-mCD20) antibody and rapamycin, which targets both B and T cell responses. Additionally, it extensively characterises the role of the IgG backbone in B cell depletion by anti-CD20 antibodies. For this, inhibitors were generated in BALB/c-HA mice by weekly IV injection of FVIII. Subsequently, anti-mCD20 (18B12) with IgG2a or IgG1 backbone was injected IV in two doses three weeks apart and B cell depletion and recovery was characterised. Rapamycin was administered orally 3x/week (for 1 month) while continuing FVIII injections. Altering the IgG backbone of anti-mCD20 from IgG2a to IgG1 reduced overall depletion of B cells (including memory B cells), and marginal zone, B-10, and B-1b cells were specifically unaffected. While neither antibody was effective alone, in combination with rapamycin, anti-mCD20 IgG2a but not IgG1 was able to reverse inhibitors in HA mice. This regimen was particularly effective for starting titres of ~10 BU. Although IgG1 anti-mCD20 spared potentially tolerogenic B cell subsets, IgG2a directed sustained hyporesponsiveness when administered in conjunction with rapamycin. This regimen represents a promising treatment for inhibitor reversal in HA, as both of these compounds have been extensively used in human patients.

Joint bleeds increase the inhibitor response to human factor VIII in a rat model of severe haemophilia A.

INTRODUCTION: The most serious complication in haemophilia A (HA) replacement therapy with coagulation factor VIII (FVIII) is neutralizing antibodies, i.e. inhibitors. It has been hypothesized that danger signals generated during a bleed might have an adjuvant effect on the immune response to FVIII in on-demand treatment, increasing the inhibitor risk. AIM: To compare the antibody response to treatment with recombinant human FVIII (rhFVIII) in relation to induced knee joint bleeds and treatment without concurrent bleeds in a HA rat model. METHOD: HA rats were divided into two groups: one group (n = 10) receiving three needle induced knee joint bleeds 14 days apart and a control group (n = 9) receiving three sham procedures. Three hours after each injury/sham 50 IU kg(-1) rhFVIII was administrated intravenously. Subsequently, both groups continued rhFVIII treatment for another 9 weeks. Binding antibodies were analysed using an enzyme-linked immunosorbent assay and neutralizing antibodies using a Bethesda-like assay. RESULTS: Rats in the knee-bleed group developed a significantly faster inhibitor response and reached significantly higher inhibitor levels. In the knee-bleed group, 80% developed inhibitors vs. 33% in the control group, demonstrating a 2.4 times higher inhibitor risk when treating concurrent with bleeds. CONCLUSION: FVIII treatment in relation to a bleed potentiates inhibitor development compared to FVIII treatment alone in this HA rat, indicating that bleeding is a potential danger signal. Our results support the theory that FVIII replacement therapy concurrent with a bleeding episode increases the inhibitor risk, which to the best of our knowledge, has not been confirmed in an animal model before.

Inhibitors in haemophilia A: a perspective on clotting factor products as a potential contributing factor.

INTRODUCTION: The occurrence of a neutralizing antibody in previously untreated patients (PUPs) with haemophilia A appears to be the result of an intricate interplay of both genetic and environmental factors. Recently, the type of factor VIII (FVIII) product used in the PUPs population has been implicated as a risk factor for inhibitor development. AIM: The aim of this review was to explore in a systematic manner potential hypotheses for the product-related findings in these studies (i.e. differences in the expression system of the cell lines used to produce recombinant FVIII [rFVIII], differences in the administered antigen load or changes in clinical practice over time). RESULTS: Review of the available clinical studies illustrates the high degree of variability for the risk of inhibitor development for the same products across different studies. Differences in cell lines or antigen load were not found to provide a reasonable explanation. CONCLUSION: The possibility of changes in clinical practice over time and patient selection bias (i.e. the preferential use of one product over another in patients at higher risk for inhibitors) offers a potential explanation and should be carefully considered when evaluating the studies.