The Impacts of G4S Mutation on N-glycosylation and conformation of the Human Coagulation Factor IX GLA domain: In silico and In vitro Analysis

Missense mutations are the most prevalent form of mutation in hemophilia B patients. These alterations may result in the creation of novel and non-native N-glycosylation sites (Asn-X-Ser/Thr) through single amino acid substitutions. The pathogenic mechanisms of N-glycosylation mutations in hemophilia B patients have not been extensively studied yet. By survey among known missense mutations, we found only one N-glycosylation mutation in the γ-carboxyglutamic-rich (GLA) domain of the human coagulation factor IX (hFIX). This mutation that was reported in patients with mild and moderate hemophilia B, is caused by G4S amino acid substitution. To investigate the possibility of glycan attachment to the novel N-glycosylation site in G4S-mutant hFIX and the occurrence of hyperglycosylation, site-directed mutagenesis was applied to introduce the selected mutation into the coding sequence of the hFIX. The nucleotide sequences of the both native and G4S-mutant hFIX were separately cloned into the pcDNA3.1 expression plasmid and transiently expressed in HEK293T cells. Our results from gradient SDS-PAGE and western blotting analysis of the both recombinant native and mutant hFIX demonstrated no glycan attachment to the new N-glycosylation site in the G4S-mutant hFIX. Molecular dynamics (MD) simulation was also conducted to provide atomistic insights into structure and behavior of the native and G4S-mutant GLA domains in the both free and membrane-bound states. The results revealed that the mutation slightly affected the dynamic behavior of the mutant GLA domain. The conformational analysis proved that the native GLA domain had less fluctuation and more stability than the mutant GLA domain. The slight conformational changes may influence the binding capacity and interaction of the mutant GLA domain to phospholipid bilayer which is necessary for coagulation activity of the hFIX. These findings were in accordance with the nature of the G4S mutation which causes mild hemophilia B.

Bleeding Data across Baseline FIX Expression Levels in People with Hemophilia B: An Analysis Using the 'Factor Expression Study'

Introduction Complications such as spontaneous and trauma-related bleeding events typically experienced by people with hemophilia B (PWHB) are associated with long-term joint damage and chronic pain, and burdensome treatment with intravenous factor IX administration. Gene therapy, designed to enable the endogenous production of the missing clotting factor, has potential for curative benefit in PWHB (Dolan et al, 2018). Due to its link to risk for bleeding episodes, factor expression level (FEL) is commonly used as an endpoint in hemophilia gene therapy trials. However, little data currently exist linking FEL to bleeding risk in PWHB, most notably within the mild range. As such, the aim of this analysis was to examine the relationship between annual bleed rate (ABR) data across baseline FEL in PWHB. Methods Data from adult non-inhibitor PWHB, across Europe and the United States (US) who received clotting factor on-demand (OD), were drawn from the 'Cost of HaEmophilia in adults: a Socioeconomic Survey' (CHESS) studies. The CHESS studies are retrospective, burden-of-illness studies in people with hemophilia A or B, capturing the economic and humanistic burden associated with living with hemophilia. Additional data were collected to supplement the existing CHESS studies, particularly in people with exogenous FEL in the mild and moderate range. ABR was defined as the physician-reported number of bleed events experienced by the patient in the 12 months to study capture. A generalized linear model (GLM) was used to analyze variation in ABR data across FEL, adjusting for covariates age, body mass index (BMI), and blood-borne viruses. Following this, a multivariable restricted cubic spline (RCS) GLM regression was performed to create, model, and test for the potential non-linear relationship between FEL and ABR. The RCS regression employed 3 knots, located at baseline FEL values of 1, 5, and 10, and controlled once again for age, BMI, and blood-borne viruses. Results A total of 407 adult non-inhibitor PWHB, receiving an OD therapy regimen and with information on ABR, were profiled. The GLM provided adequate fit for the modeling of bleed data; the average marginal effect at the mean was computed from the GLM regression outputs. After controlling for the effects of all other model covariates, the regression analysis showed a significant association between FEL and ABR; for every 1% increase in FEL, the average ABR decreased by 0.08 units (p<0.001). The results of the RCS regression found a significant non-linear relationship between FEL and ABR, ceteris paribus (p<0.001). Conclusions The results of this analysis found baseline FEL to be significantly associated with ABR in PWHB; as baseline FEL increased, ABR reduced. This highlights the clinical importance of new hemophilia gene therapies potentially increasing FEL to that of the mild or non-hemophilic range in terms of reducing patient burden through the better prevention of bleeding events in PWHB. Disclosures Ali: UniQure: Current Employment. Li: UniQure: Current Employment. Konkle: Pfizer, Sangamo, Sanofi, Sigilon, Spark, Takeda and Uniqure: Research Funding; BioMarin, Pfizer and Sigilon: Consultancy. O'Mahony: BioMarin Pharmaceutical Inc.: Consultancy; Freeline: Consultancy; Uniqure: Speakers Bureau. Pipe: Apcintex: Consultancy; ASC Therapeutics: Consultancy; Bayer: Consultancy; Biomarin: Consultancy, Other: Clinical trial investigator; Catalyst Biosciences: Consultancy; CSL Behring: Consultancy; HEMA Biologics: Consultancy; Freeline: Consultancy, Other: Clinical trial investigator; Novo Nordisk: Consultancy; Pfizer: Consultancy; Roche/Genentech: Consultancy, Other; Sangamo Therapeutics: Consultancy; Sanofi: Consultancy, Other; Takeda: Consultancy; Spark Therapeutics: Consultancy; uniQure: Consultancy, Other; Regeneron/ Intellia: Consultancy; Genventiv: Consultancy; Grifols: Consultancy; Octapharma: Consultancy; Shire: Consultancy.

Follow-up of More Than 5 Years in a Cohort of Patients with Hemophilia B Treated with Fidanacogene Elaparvovec Adeno-Associated Virus Gene Therapy

Fifteen patients with moderately severe to severe hemophilia B (factor IX [FIX] activity ≤2%) were treated with fidanacogene elaparvovec at a dose of 5e11 vg/kg as part of a phase 1/2a study. The study was 52 weeks in duration, after which patients were eligible to enroll in the long-term follow-up (LTFU) study of up to 5 years. All 15 patients completed the phase 1/2a study, and 14 patients were subsequently enrolled in the LTFU study. At the time of the data cut (December 2020), 13 patients were enrolled in the LTFU study, with follow-up ranging from >2.5 years to >5 years following vector administration. Over this period of time, fidanacogene elaparvovec remained generally well tolerated. As reported previously, 3 patients were treated with corticosteroids within the first 6 months of the phase 1/2a study. No patients have required treatment or re-treatment with corticosteroids in the LTFU study. There were no serious adverse events (SAEs) in the phase 1/2a study, and 3 patients reported SAEs in the LTFU study, none of which were considered treatment related. No patient developed an inhibitor or had a thrombotic event. No patients have developed hepatic masses or significant elevations in alpha-fetoprotein (AFP). Annual liver ultrasounds revealed only hepatic steatosis in one patient. Mean FIX activity levels by year remain in the mild hemophilia severity range: 22.8%, year 1 (n=15); 25.4%, year 2 (n=14); 22.9%, year 3 (n=14); 24.9%, year 4 (n=9); and 19.8%, year 5 (n=7) when evaluated centrally using the ACTIN/FSL one-stage assay. These levels have been associated with mean annualized bleeding rates ranging from 0-0.9 over the course of follow-up, and no patients have resumed FIX prophylaxis. Four patients have undergone 6 surgical procedures during the LTFU study, 4 elective and 2 emergent. There were no bleeding complications with these procedures, and the 2 emergent procedures (appendectomy and lumbar discectomy) were performed without the need of additional FIX. Overall, this represents the largest cohort of hemophilia B patients with a duration of follow-up up to 5 years following treatment with an adeno-associated virus gene therapy expressing a highly active variant of FIX. Fidanacogene elaparvovec remains generally well tolerated over a period up to 5 years postinfusion. While encouraging, more long-term data in a larger cohort of patients are needed to further characterize the safety and durability of fidanacogene elaparvovec, which is under way in an ongoing phase 3 study. Disclosures Samelson-Jones: Pfizer: Consultancy, Research Funding; Spark: Research Funding. Sullivan: Genentech: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Pfizer Inc.: Membership on an entity's Board of Directors or advisory committees; Biomarin: Membership on an entity's Board of Directors or advisory committees; Octapharma: Membership on an entity's Board of Directors or advisory committees. Rasko: Imago: Consultancy; Cynata: Honoraria, Speakers Bureau; Gene Technology Technical Advisory Board: Membership on an entity's Board of Directors or advisory committees; NHMRC Mitochondrial Donation Expert Working Committee: Membership on an entity's Board of Directors or advisory committees; Australian Cancer Research: Membership on an entity's Board of Directors or advisory committees; Cure the Future Foundation: Membership on an entity's Board of Directors or advisory committees; FSHD Global Research Foundation: Membership on an entity's Board of Directors or advisory committees; Australian Government: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Pfizer Inc: Honoraria, Speakers Bureau; Glaxo-Smith-Kline: Honoraria, Speakers Bureau; Spark: Honoraria, Speakers Bureau; Takeda: Honoraria, Speakers Bureau; bluebird bio: Honoraria, Speakers Bureau; Genea: Current equity holder in publicly-traded company; Celgene: Honoraria, Speakers Bureau. Giermasz: BioMarin: Consultancy, Research Funding; Genentech/Roche: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy; Bayer: Consultancy; ATHN: Consultancy; NovoNordisk: Consultancy; UniQure: Consultancy, Research Funding; Sanofi Genzyme: Consultancy; Bioverativ/Sanofi: Consultancy, Research Funding, Speakers Bureau; Sangamo Therapeutics,: Research Funding. George: CSL Behring: Consultancy; Bayer: Consultancy; Avrobio: Other: Data Safety Monitoring Committee . Ducore: Octapharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Shire: Consultancy, Honoraria; Bayer: Consultancy, Honoraria, Speakers Bureau; HEMA Biologics: Consultancy, Honoraria. Teitel: Pfizer: Consultancy, Research Funding; Spark: Research Funding; Bayer: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Novo Nordisk: Consultancy; Octapharma: Consultancy; CSL Behring: Consultancy. McGuinn: Biogen: Research Funding; Roche/Genentech: Research Funding; Shire/Baxalta: Consultancy, Research Funding; Spark: Research Funding. O'Brien: Pfizer Inc.: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Winburn: Pfizer Inc.: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Smith: Pfizer Inc.: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Chhabra: Pfizer Inc.: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Rupon: Pfizer Inc.: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company.

Factor IX Expression within the Normal Range Prevents Spontaneous Bleeds Requiring Treatment Following FLT180a Gene Therapy in Patients with Severe Hemophilia B: Long-Term Follow-up Study of the B-Amaze Program

Introduction: FLT180a (verbrinacogene setparvovec) is an investigational, liver-directed AAV gene therapy for the treatment of patients with hemophilia B (HB). FLT180a consists of a novel, potent, engineered capsid (AAVS3) containing an expression cassette encoding a Factor IX (FIX) gain-of-function protein variant ('Padua'; FIX-R338L). The B-AMAZE study was designed to identify a dose of FLT180a that maintains FIX activity within the normal range (50-150%) and thereby protect patients with severe HB from spontaneous and traumatic bleeds. Methods: B-AMAZE was a multicentre, open-label Phase 1/2 clinical trial (NCT03369444; sponsored by UCL) that evaluated FLT180a dose levels using an escalating/descending adaptive design in patients with severe (FIX activity <1%) or moderately severe (FIX activity 1-2%) HB who were negative for AAVS3 neutralizing antibodies. A novel regimen of prophylactic corticosteroids with/without tacrolimus was implemented to mitigate the impact of vector-related transaminitis on FIX expression. Patients who completed the 26-week B-AMAZE study were eligible for the ongoing long-term follow-up study (NCT03641703; sponsored by Freeline). Results: Ten HB patients received a single dose of FLT180a. Four FLT180a doses ranging from 3.84e11 vg/kg to 1.28e12 vg/kg were assessed. As of the data cut-off date, all patients have been followed for ≥16 months. FLT180a demonstrated a favorable safety profile, without evidence of inhibitors against FIX, infusion-related or allergic reactions. The most common treatment-related adverse event was transient elevation in alanine aminotransferase. An event of AV fistula thrombosis occurred in a 67-year-old patient who received the highest dose of 1.28e12 vg/kg (total dose of 1.15e14 vg) and had supranormal FIX levels; this patient was treated with anticoagulants. While these FIX levels demonstrate the potency of our proprietary AAVS3 capsid, this dose will not be used in future hemophilia studies. At Week 26 after FLT180a administration, a dose-response relationship was observed with mean FIX activity of 45.0%, 35.5%, 141.5%, and 175.5% for 3.84e11, 6.4e11, 8.32e11, and 1.28e12 vg/kg doses, respectively (Table); FIX activity levels ≥50% were achieved in 7 of 8 patients treated with the three highest doses. One patient (Patient 4) who received 6.4e11 vg/kg lost transgene expression early due to transaminitis and resumed routine factor prophylaxis. The 8.32e11 vg/kg cohort received an extended immune management regimen (9-18 weeks) with prophylactic tacrolimus in addition to prednisolone to prevent breakthrough vector-related transaminitis. However, after cessation of the immune management regimen, transaminitis with concomitant reductions in FIX activity was observed in all patients in the 8.32e11 vg/kg cohort. The combination of prophylactic tacrolimus and prednisolone appeared to have suppressed immune-mediated transaminitis while administered, but recurrence of transaminitis developed soon after cessation. This unique and previously unreported observation suggests that the longer-duration prophylactic immune management regimen may have prevented tolerization to the vector because this was not observed in earlier cohorts where a brief course of tacrolimus was given reactively for breakthrough transaminitis. All patients (including the 8.32e11 vg/kg cohort) have achieved steady state. Patients in the earliest cohort who received the lowest dose (3.84e11 vg/kg) have shown stable FIX activity for >3 years. There were no spontaneous bleeds that required FIX supplementation in patients who maintained FIX activity above 50%; Patient 4 in the 6.4e11 vg/kg cohort experienced two bleeds (cause unknown) after he lost transgene expression, which were treated with exogenous FIX. One patient received exogenous FIX for treatment of a traumatic bleed, but his FIX activity level was 57% at the time of the event. Additional efficacy and safety results with >3.5 years of follow-up will be presented. Conclusions: B-AMAZE is the first HB gene therapy study to achieve normal levels of FIX activity using relatively low vector doses. Results suggest that a dose of 7.7e11 vg/kg, coupled with a short course of prophylactic immune management, has the potential to achieve durable FIX activity in the normal range (50-150%) and thereby prevent spontaneous bleeds and normalize hemostasis in the event of traumatic bleeds. Figure 1 Figure 1. Disclosures Chowdary: Sanofi: Honoraria; Roche: Honoraria; CSL Behring: Honoraria, Research Funding; Freeline: Honoraria, Research Funding; Novo Nordisk: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; SOBI: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Boehringer Ingelheim: Honoraria; Chugai: Honoraria; Spark: Honoraria; Bayer: Honoraria, Research Funding. Shapiro: Roche: Honoraria; CSL Bering: Honoraria; Takeda: Honoraria, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau. Makris: Freeline: Consultancy. Dolan: Takeda: Speakers Bureau; Roche-Chugai: Speakers Bureau; Spark Therapeutics: Speakers Bureau; Octapharma: Speakers Bureau; CSL: Speakers Bureau; Biomarin: Speakers Bureau; Bayer: Research Funding, Speakers Bureau; Novo Nordisk: Research Funding, Speakers Bureau; Pfizer: Research Funding. Tuddenham: Freeline: Consultancy, Current holder of individual stocks in a privately-held company. Long: Freeline: Current Employment. Krop: Freeline: Current Employment. Nathwani: Freeline: Current holder of individual stocks in a privately-held company, Other: Board of directors.

Reduced Dosing Frequency Following a Switch to Rix-FP for the Treatment of Hemophilia B: Results from the Athn 2 Study

Introduction: The approval of extended half-life recombinant factor IX (rFIX) replacement products has expanded the range of therapeutic options available for the treatment of hemophilia B. Compared with standard half-life FIX, these products allow for extended dosing intervals while maintaining appropriate bleed control. One such extended half-life product is rIX-FP (IDELVION; CSL Behring), a recombinant fusion protein linking rFIX with recombinant albumin, offering the possibility of dosing up to every 21 days in adults. The ATHN 2: Factor Switching Study provides information on patient outcomes following a switch from a previous FIX product to rIX-FP. Methods: ATHN 2 was a factor-switching study sponsored by the American Thrombosis and Hemostasis Network (ATHN) conducted in participants across the US hemophilia treatment center (HTC) network. This was a multi-center, longitudinal, observational study with two arms: a prospective arm following participants for up to one year after switching factor replacement product, and a retrospective arm including participants who have switched products within the 50 weeks prior to enrollment with retrospective and/or prospective assessment for up to one year. Male and female children and adults (≥2 years) with FIX clotting activity ≤5% of normal who had previously been treated with plasma-derived or recombinant FIX for at least 50 exposure days were eligible for inclusion. Treatment was administered at the discretion of the participant's hemophilia caregiver. Data was collected at study/clinic visits, or via a telephone interview conducted every three months. Baseline demographic data was collected for all participants. The prescribed dosing frequency for each participant was collected before and after the switch to rIX-FP, including dosing frequency taken from the first and last treatment records taken during the study following the switch. Participants were also asked to rank their satisfaction with rIX-FP upon the completion or early termination of the study. Results: A total of 41 participants were included in this analysis; 27 in the prospective arm and 14 in the retrospective arm. The mean (SD) age across all participants was 22.5 (17.1) years, ranging from 2 to 71 years. The median age was 18 years old and most participants had severe hemophilia B (FIX activity <1%; n=26, 63%). Prior to the switch to rIX-FP, 76% (n=31) of participants were receiving prophylaxis and 24% (n=10) received episodic treatment. The majority of participants (62%) receiving prophylaxis were treated twice a week (Table 1). Following the treatment switch, 93% of participants were initially assigned to a once-weekly or less frequent dosing regimen. This proportion remained stable over the course of the study, with 89% of participants on once-weekly or less frequent prophylaxis by the time of the last record taken. Among 23 participants with complete data on their prophylaxis dose interval before and after treatment switch, 70% of the participants were able to extend their dose frequency and maintain the extended dose frequency through the study. Thirty-seven participants responded to the satisfaction survey, with the majority (n=33, 89%) being somewhat or very satisfied with rIX-FP treatment. Conclusions: Switching to rIX-FP allowed participants to extend their prophylaxis dosing interval and a majority of participants were able to maintain the extended dose interval through the study period. In addition, a majority of participants were satisfied with rIX-FP treatment, altogether suggesting that extended half-life factor replacement with rIX-FP offers a valuable treatment option for hemophilia B. Figure 1 Figure 1. Disclosures Journeycake: HEMA Biologics: Honoraria; LFB: Honoraria. Chrisentery-Singleton: Biomarin: Speakers Bureau; Kedrion: Consultancy; Takeda: Consultancy, Speakers Bureau; Spark: Consultancy, Research Funding; Sanofi: Consultancy; Pfizer: Consultancy, Research Funding, Speakers Bureau; Octapharma: Consultancy; Novo Nordisk: Consultancy, Speakers Bureau; Hema Biologics: Consultancy; Grifols: Consultancy; Genentech: Consultancy, Speakers Bureau; CSL Behring: Consultancy, Speakers Bureau. Desai: CSL Behring: Current Employment. von Drygalski: Pfizer: Research Funding; Novo Nordisk: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Hematherix, Inc: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: Super FVa; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CSL Behring: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Biomarin: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; uniQure: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Patel: CSL Behring: Current Employment. Raffini: CSL Behring: Consultancy; Genentech: Consultancy; HEMA Biologics: Consultancy; Bayer: Consultancy; XaTek: Consultancy. Recht: Foundation for Women and Girls with Blood Disorders, Partners in Bleeding Disorders: Speakers Bureau; uniQure: Consultancy; Takeda: Consultancy; Sanofi: Consultancy; Pfizer: Consultancy; Octapharma: Consultancy; Novo Nordisk: Consultancy; Kedrion: Consultancy; Hema Biologics: Consultancy; Genentech: Consultancy; CSL Behring: Consultancy; American Thrombosis and Hemostasis Network: Current Employment; Oregon Health & Science University: Current Employment; Catalyst Biosciences: Consultancy. Sidinio: Biomarin: Consultancy; Takeda: Consultancy, Research Funding; Pfizer: Consultancy; Novo Nordisk: Consultancy; Bayer: Consultancy; Guardian Therapeutics: Consultancy; Octapharma: Consultancy, Research Funding; Genentech/Roche: Consultancy, Research Funding; Catalyst: Consultancy. Wang: Bayer: Consultancy; Biomarin: Consultancy; CSL Behring: Consultancy; Genentech: Consultancy; Hema Biologics: Consultancy; Novo Nordisk: Consultancy; Sanofi: Consultancy; Takeda: Consultancy; uniQure: Consultancy. Zhang: CSL Behring: Current Employment, Current holder of individual stocks in a privately-held company. Neufeld: Pfizer: Consultancy; Chiesi: Consultancy; Bayer: Consultancy; Genentech: Consultancy; Octapharma: Consultancy, Research Funding; Acceleron Pharma: Consultancy; Baxter: Consultancy; Shire: Consultancy; Takeda: Consultancy; CSL: Consultancy; Biogen: Consultancy; Novo Nordisk: Consultancy; Bristol Myers-Squibb: Consultancy; ATHN: Research Funding; Celgene: Research Funding.

Factor IX Delivery to the Skin Primes Inhibitor Formation and Sensitizes Hemophilia B Mice to Systemic Factor IX Administration

Inhibitor formation is the most serious complication of factor (F)IX replacement therapy for hemophilia B, exacerbated by anaphylactoid reactions occurring in up to 50% of inhibitor patients. Low success rates and a high burden of immune tolerance induction (ITI) therapy necessitate the search for novel immune tolerance therapies. Skin-associated lymphoid tissues (SALT) have been successfully targeted in allergen-specific immunotherapies. In this study, we aimed to develop a prophylactic immune tolerance protocol based on intradermal (ID) administration of rFIX. In a dose-finding experiment, hemophilia B mice on C3H/HeJ genetic background (C3H/HeJ-F9tm1Dws) received twice weekly ID injections of 0.01, 0.1 or 1 IU rFIX only for four weeks, followed by one intraperitoneal (IP) and four weekly intravenous (IV) injections of 1 IU FIX co-injected with anti-allergic agents (triprolidine and ABT-491). Control animals received the IP/IV doses only. One week after the last injection, plasma and/or lymph nodes (LNs) were collected for Bethesda assay, ELISA and flow cytometry analyses. Unexpectedly, all animals developed significantly (8.9-17.6-fold, p<0.05) higher FIX inhibitor titers than the control group (mean 4.4, 3.9, 8.5 and 0.6 BU/ml in the 0.01, 0.1, 1 IU and control group, respectively). Anti-FIX IgG1 antibody levels were also significantly higher (2.7-3.4-fold, p<0.001) in all ID treated groups (mean 54.8, 68.8, 69.3 and 20.1 µg/ml in the 0.01, 0.1, 1 IU and control group, respectively). This apparent enhancement of inhibitor formation prompted analyses of plasma samples collected after four weeks of ID FIX injections only to find out whether ID treatment alone could elicit FIX inhibitor formation. Two (0.1 and 1 IU) of the three evaluated ID FIX doses led to inhibitor formation of a similar magnitude to the full-length ID/IP/IV regimen. Although most (seven out of nine) mice treated with the lowest ID dose of FIX (0.01 IU) had no detectable inhibitors, the same dose, when followed by the IP/IV treatment, resulted in a similar inhibitor response to the two higher doses (0.1 and 1 IU), suggesting that the lowest dose primed the immune responses, which were further amplified by the IP/IV regimen. Also, all ID treated animals had readily detectable anti-FIX IgG1, but the levels were smaller than after the full-length treatment (mean 17.8, 35.6 and 33 µg/ml in the 0.01, 0.1 and 1 IU groups, respectively). This suggests that the IP/IV regimen following the ID treatment enhanced mainly the total anti-FIX IgG1 response, with a lesser impact on the neutralizing antibody development. Inhibitor formation following ID treatment seemed to be driven by T follicular helper (PD1 +CXCR5 +CD4 +) and Germinal Center B cell (GL7 +CD95 +CD19 +) responses in inguinal LNs, the frequencies of which were 1.75-fold and 4-fold (p<0.05) elevated in animals treated with 1 IU FIX ID compared to control mice that received PBS only. Notably, none of the ID treated mice died of anaphylaxis despite receiving eight ID injections of FIX without anti-allergic agents. IV administration of FIX alone in C3H/HeJ-F9tm1Dws hemophilia B mice results in fatal IgE-dependent anaphylaxis beginning after fourth injection with ~20% mortality and rising with subsequent injections in the surviving mice, which necessitates the use of anti-allergic agents. Interestingly, the ID treated mice had elevated levels of anti-FIX IgE antibodies. Animals that received ID injections only or followed by IP/IV treatment had 1.5- and 3.3-fold higher (p<0.01) anti-FIX IgE levels than mice that received the IP/IV treatment only. The absence of mortality in the ID treated animals suggested that ID FIX delivery might have a neutral or protective effect against anaphylaxis despite anti-FIX IgE development. To test this hypothesis, hemophilia B mice received eight twice weekly ID doses of 1 IU FIX followed by IV or IV only, with neither group receiving anti-allergic agents at any time (n=15/group). After the first IV injection, 33.3% and 0% animals died in the ID treated and the IV only group, respectively, prompting early termination of the experiment for humane reasons. In conclusion, ID administration of FIX primes or produces strong inhibitor responses in a wide range of doses and sensitizes hemophilia B mice to systemic delivery of FIX, suggesting that the skin-associated lymphoid tissue may not be amenable to FIX tolerance induction. Disclosures No relevant conflicts of interest to declare.

Pregnancy Outcomes in Women with Bleeding Disorders: A Single Institutional Experience

Introduction Women with inherited bleeding disorders (IBD) are at increased risk of peripartum bleeding complications. The aim of our study was to assess our institutional outcomes of management of women with IBD during pregnancy and the peripartum period. Methods Eligible patients included women with IBD followed at the Mayo Clinic, Rochester Hemophilia Treatment Center and were followed at our institution for antenatal and peripartum care. Patients were excluded if detailed delivery outcomes were unavailable in the electronic medical record (EMR). If delivery was not in our institution but all records were available to review in EMR the pregnancy was included in analysis if our group was primarily involved in providing management recommendations. The EMR was retrospectively reviewed and details regarding factor usage, delivery method and outcome, analgesia, and post-partum hemorrhage (PPH) were recorded. Thrombotic complications 6 weeks post-partum was also recorded. Results 73 pregnancies in 46 unique patients met our inclusion criteria for this study. Distribution of underlying IBD in the 73 pregnancies was as follows: 50% type 1 VWD (n=37), 15% (n=11) hemophilia A carrier, baseline (bl) fVIII 46 (21-88)%.), and 13.7% (n=10) hemophilia B carrier (bl fIX 43 (23-69)% . In the remaining pregnancies, underlying IBD included type 2 VWD (n=6), type 3 VWD (n=1), VWF multimer abnormality (n=2) , factor XI deficiency (n=2, bl fXI: 44%), factor VII deficiency (n=2, bl fVII 37%) and factor V deficiency (n=2, bl fV 11%). Surprisingly, at the time of 24 deliveries, the patient's bleeding disorder (type 1 VWD, n=15) had not yet been diagnosed. In 56 % of pregnancies (n=41), a hematology delivery plan was in place prior to admission for delivery. Of 30 delivery inductions, 11 were performed due to IBD. There were 46 vaginal deliveries, 25 C-sections, and 2 dilation and curettage (D&C). Two C-sections were recommended due to IBD (hemophilia B and type 2 VWD). In 37/46 of vaginal deliveries neuraxial anesthesia was used with no complications noted. 26 deliveries were performed under the cover of hemostatic pharmacologic agents (Table one). Due to naturally increasing levels of VWF during the peripartum period, only 8/37 (21.6 %) pregnancies in those with type 1 VWD required hemostatic treatment. 61/73 pregnancies were at least at early term (>37 weeks) and all resulted in live birth. Of the remaining pregnancies (n=12), 5 resulted in a nonviable fetus. In one pregnancy, fetal demise was due to termination of pregnancy due to type III VWD and recent lymphoma in the mother. Pharmacologic hemostatic agents were used in 19 pregnancies in the post-partum period (Table 2). 10 pregnancies (6 vaginal), met American College of Gynecology criteria for early PPH. Underlying IBD for pregnancies with PPH included (type 1 VWD: n=7,hemophilia A carrier (n=1), type II VWD (n=1), factor VII deficiency (n=1). 4 of these had received pharmacologic hemostatic treatment prior to delivery. Primary management of PPH involved uterine intervention (ie. Massage and uterotonic agents). In three pregnancies, a D&C was required (one due to stillborn birth and two due to retained placenta). One case of PPH was due to placental abruption. Additional pharmacologic hemostatic management was utilized in 4 deliveries where PPH was noted. Red blood cell transfusions were needed in 3 pregnancies due to PPH. There were no thrombotic complication up to 6 weeks post-partum. Conclusion Though rates of early PPH were >10% in our cohort, most causes of PPH were unrelated to the underlying IBD. Although the current study is limited due to lack of many patients with type II and III VWD, results demonstrate that bleeding risk during delivery due to the IBD is low when patients are evaluated and managed with the use of a multidisciplinary care team. Figure 1 Figure 1. Disclosures Pruthi: CSL Behring: Honoraria; Merck: Honoraria; HEMA Biologics: Honoraria; Bayer Healthcare AG: Honoraria; Genentech: Honoraria; Instrumentation Laboratory: Honoraria.

Real-World Data of the Hemostatic Efficacy of Recombinant Human Factor VIIa Eptacog Beta for Acute Bleeding Events in Patients with Hemophilia a and B with Inhibitors

Introduction: Activated prothrombin complex concentrate (FEIBA, Takeda) and recombinant factor VIIa (rFVIIa, Novoseven, NovoNordisk) remain the primary bypassing agents (BPA) available for bleeding management in patients with hemophilia and inhibitors. Eptacog beta [rFVIIa-B, Coagulation factor VIIa (recombinant)-jncw, Sevenfact, HEMA Biologics & LFB] is a recombinant human FVIIa approved by the FDA in 2020 for the treatment of acute bleeding events in adult and adolescent patients ≥12 years old with hemophilia A or B with inhibitors. rFVIIa-B demonstrated hemostatic efficacy of 86% in a phase 3, randomized cross-over study of 465 mild/moderate bleeding events in 27 patients with hemophilia A and B with inhibitors. The purpose of this study is to report real-world data on the hemostatic efficacy of rFVIIa-B for acute bleeding management in patients with hemophilia A and B with inhibitors. Methods: This is a retrospective chart-review of individuals ≥12 years of age with severe hemophilia A (factor VIII <1%) or hemophilia B (factor IX <1%) with an active inhibitor from 3 U.S. hemophilia treatment centers who utilized rFVIIa-B for acute bleed management. Results: Seven bleeds were treated among the 3 patients identified. Patient characteristics and bleeding events are summarized in Table 1. The 3 patients were 12, 13, and 31 years of age. Two patients had hemophilia A and 1 patient had hemophilia B. The 2 patients with hemophilia A were on emicizumab prophylaxis per standard dosing regimens for bleeding prevention. The individual patient with hemophilia B had a history of anaphylaxis at inhibitor development and received on-demand BPA for acute bleeding events. All 7 bleeds consisted of hemarthroses with the knee being the primary site in 57% of the bleeds. Five of the 7 bleeds (71%) received a severe bleeding dose of 210-225 microgram per kilogram (mcg/kg) for the initial rFVIIa-B dose followed by 70-75 mcg/kg for subsequent doses. Final dosing regimens were dependent on available vial sizes. rFVIIa-B resulted in complete resolution of all bleeds (100%) at a median of 4 doses (range 1-8 doses) and a median of 24 hours (range 3-48 hours). There were no failures in bleeding resolution following treatment. No adverse events with infusions were reported including infusion-related reactions, hypersensitivity reactions, thrombosis, or thrombotic microangiopathy. Conclusions: Administration of rFVIIa-B in the real-world setting appears to demonstrate hemostatic efficacy in a cohort of pediatric and adult patients with hemophilia A and B with inhibitors and may serve as an alternative human rFVIIa therapy for the management of acute bleeds in this population. Further post-marketing studies are warranted to expand the indication to younger children (<12 years of age) and to continue to monitor drug efficacy and adverse events in a larger population of patients over time including individuals on non-factor therapies such as emicizumab. Figure 1 Figure 1. Disclosures Batsuli: Bio Product Laboratory: Honoraria; Kedrion: Honoraria. Tran: HEMA Biologics: Honoraria. Young: Apcintex, BioMarin, Genentech/Roche, Grifols, Novo Nordisk, Pfizer, Rani, Sanofi Genzyme, Spark, Takeda, and UniQure: Consultancy; Genentech/Roche, Grifols, and Takeda: Research Funding. Sidonio: Guardian Therapeutics: Consultancy; Octapharma: Consultancy, Research Funding; Catalyst: Consultancy; Pfizer: Consultancy; Takeda: Consultancy, Research Funding; Biomarin: Consultancy; Novo Nordisk: Consultancy; Bayer: Consultancy; Genentech: Consultancy, Research Funding.