Kurzfassung: Introduction: Among the most challenging complications of hemophilia A is inhibitor formation. A T-cell dependent B-cell response to exogenous factor VIII (FVIII), inhibitors result in a high burden of disease, with poorly controlled bleeding, twice the hospitalizations, 10-fold the cost, and 3.5-fold the mortality of non-inhibitor patients. Thus, a major goal of hemophilia management is to prevent and eradicate inhibitors. With the availability of novel therapies, including eloctate, a recombinant Fc-fusion protein (rFVIII-Fc) which induces regulatory T cells to promote FVIII tolerance, and emicizumab, a bispecific monoclonal FVIII mimetic, we designed the INHIBIT Clinical Trials Platform (X01HL143024), Fig.1. The platform is composed of two linked randomized phase III trials, the Inhibitor Prevention Trial (NCT04303559), comparing rFVIII-Fc vs emicizumab prophylaxis to prevent inhibitors, and the Inhibitor Eradication Trial (NCT04303572), comparing rFVIII-Fc immune tolerance induction (ITI) plus emicizumab vs rFVIII-Fc ITI alone to eradicate inhibitors. The platform uses adaptive design to incorporate historical data (Bayesian priors) on inhibitor formation to increase power and promote efficient use of rare data. Yet, there is equipoise regarding the optimal approach to inhibitor prevention and eradication, and, as clinical practice is changing, we aimed to test the feasibility of the INHIBIT trial design. Methods: To establish design feasibility, we conducted interviews with 30 hemophilia treatment center (HTC) physicians participating in the INHIBIT trials, to determine prophylaxis and tolerance regimens they prescribe and perceived barriers to the INHIBIT trials design. A 4-question survey was subsequently emailed to these physicians to ascertain the initial prophylaxis regimens they prescribe in previously untreated patients (PUPs) with severe hemophilia A, and the initial immune tolerance induction (ITI) they prescribe in high-responding inhibitor patients with severe hemophilia A; if new inhibitors had been observed during emicizumab prophylaxis, and willingness to participate in post-trial surveillance. Results: In interviews, HTC physicians indicated the issues that influenced choice of prophylaxis/ ITI regimen were patient preference, family history of inhibitors, infusion frequency, IV access, port requirement, and family fatigue. In the absence of clinical trials data in PUPs, there was general agreement that emicizumab prophylaxis, with it simpler subcutaneous (SQ) administration, might delay or potentially prevent inhibitors. Survey findings in Table 1 indicated 75% of physicians prescribe extended half-life (EHL) FVIII in a once-weekly prophylaxis regimen, as planned in the Prevention Trial, despite the persistent 27% inhibitor rate (ALong PUPs Trial, Königs et al, ISTH 2020) and potential risks with port use. There was support for the 1:3 preferential randomization to emicizumab in the Prevention Trial due to the simpler SQ route, despite concern it might delay rather than prevent inhibitor formation, although no inhibitors were reported by physician survey with emicizumab use alone. There was also concern that breakthrough bleeds requiring FVIII during emicizumab prophylaxis, might lead to immune activation and inhibitor formation. There was strong agreement, however, in 29 (97%) of physicians to participate in post-trial surveillance for long-term inhibitor outcomes. FVIII ITI was considered essential to eradicate inhibitors, despite the intensity of the infusion regimen. Notably, 60% prescribe emicizumab with FVIII ITI, as planned in the Eradicate Trial, although the every-other-day infusion was considered a potential barrier to participation. Omitting FVIII ITI was not favored due to the risk of inhibitor anamnesis if FVIII treatment was subsequently required for surgery or acute hemorrhages. Despite these concerns, there was agreement to participate in the trials. Discussion: Physician interviews and surveys confirm there is heterogeneity in current hemophilia clinical practice, specifically in initial prophylaxis regimens and in initial immune tolerance regimens, including agent choice and duration. However, there is physician consensus with the INHIBIT trial aims and with the proposed INHIBIT trial regimens to prevent and eradicate inhibitors. Disclosures Ragni: Bioverativ: Membership on an entity's Board of Directors or advisory committees, Research Funding; Alnylam/Sanofi: Membership on an entity's Board of Directors or advisory committees, Research Funding; BioMarin: Membership on an entity's Board of Directors or advisory committees, Research Funding; ATHN: Research Funding; Sangamo: Research Funding. Seaman:Bayer: Consultancy; Genentech: Consultancy; Spark Therapeutics: Consultancy; Takeda: Consultancy. Acharya:Novonordisk: Membership on an entity's Board of Directors or advisory committees; BPL: Membership on an entity's Board of Directors or advisory committees; Bayer Pharma Inc.: Research Funding. Wheeler:Novo Nordisk: Membership on an entity's Board of Directors or advisory committees; Biomarin: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; UniQure: Membership on an entity's Board of Directors or advisory committees. Tarango:Takeda/Shire: Honoraria, Other; Bayer: Consultancy, Other; Sanofi: Honoraria, Other. Dunn:ATHN: Research Funding; Spire: Honoraria; Medscape: Honoraria; World Federation of Hemophilia USA: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; BioMarin: Research Funding; uniQure: Consultancy; Genentech, Inc.: Consultancy; Nationwide Children's Hospital: Current Employment. Kulkarni:Sanofi/ Bioverativ, Bayer, Biomarin, Shire/Takeda, Novo Nordisk, Freeline: Other: clinical trial research grants ; Bioverativ/Sanofi, BPL, Genentech, Kedrion, Novo Nordisk, Octapharma, Pfizer, Takeda, Catalyst Bioscience Bayer: Membership on an entity's Board of Directors or advisory committees. Ahuja:Genentech: Consultancy, Honoraria; Sanofi Genzyme: Consultancy, Honoraria; XaTek, Inc.: Consultancy, Patents & Royalties, Research Funding. Chitlur:Takeda: Honoraria; Biovertiv: Honoraria; Agios Pharmaceuticals: Research Funding; Pfizer: Honoraria; Novo Nordisk: Consultancy, Honoraria. Pipe:Apcintex, Bayer, BioMarin, Catalyst Biosciences, CSL Behring, HEMA Biologics, Freeline, Novo Nordisk, Pfizer, F. Hoffmann-La Roche Ltd/Genentech, Inc., Sangamo Therapeutics, Sanofi, Takeda, Spark Therapeutics, uniQure: Consultancy; Siemens: Research Funding; Medical and Scientific Advisory Council to the National Hemophilia Foundation; Medical Advisory Board to World Federation of Hemophilia: Membership on an entity's Board of Directors or advisory committees. Malec:Sanofi Genzyme: Consultancy, Research Funding, Speakers Bureau; CSL: Consultancy; Takeda: Consultancy; Bayer: Consultancy; SOBI: Consultancy. Leissinger:Bayer: Consultancy; Kedrion: Consultancy; CSL Behring: Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy; HEMA Biologics: Consultancy; Takeda: Consultancy; Uniqure: Consultancy; Spark: Consultancy. Carpenter:Hemostasis & Thrombosis Research Society: Membership on an entity's Board of Directors or advisory committees; American Academy of Pediatrics: Other: PREP Heme/Onc editorial board; Kedrion: Honoraria; Novo Nordisk: Honoraria; Genentech, Inc.: Honoraria; American Thrombosis and Hemostasis Network: Membership on an entity's Board of Directors or advisory committees; CSL Behring: Research Funding; Shire: Research Funding. Knoll:NovoNordisk: Membership on an entity's Board of Directors or advisory committees. Wang:Bioverativ Inc: Honoraria; Bayer: Honoraria; CSL Behring: Honoraria; Biomarin: Honoraria; Genentech: Honoraria; Takeda: Honoraria. Young:Genentech/Roche, Grifols, and Takeda: Research Funding; Bayer, CSL Behring, Freeline, UniQure: Consultancy; BioMarin, Freeline, Genentech/Roche, Grifols, Kedrion, Novo Nordisk, Sanofi Genzyme, Spark, Takeda, and UniQure: Honoraria. Thornburg:Genentech: Speakers Bureau; Spark Therapeutics: Consultancy; Bluebird Bio: Consultancy; Ironwood Pharmaceuticals: Consultancy, Other: Data Safety Monitoring Board; American Thrombosis and Hemostasis Network: Research Funding; Sanofi Genzyme: Consultancy, Other: Data Safety Monitoring Board, Research Funding; NovoNordisk: Research Funding; Biomarin: Consultancy, Speakers Bureau; Bayer Pharmaceuticals: Research Funding; National Hemophilia Foundation: Membership on an entity's Board of Directors or advisory committees, Research Funding. Lucas:CRISPR Therapeutics: Membership on an entity's Board of Directors or advisory committees. Hwang:Shire: Honoraria; Takeda: Honoraria.

Kurzfassung: Evidence regarding the safety and efficacy of anticoagulant thromboprophylaxis among pediatric patients hospitalized for coronavirus disease 2019 (COVID-19) is limited. We sought to evaluate safety, dose-finding, and preliminary efficacy of twice-daily enoxaparin as primary thromboprophylaxis among children hospitalized for symptomatic COVID-19, including primary respiratory infection and multisystem inflammatory syndrome in children (MISC). METHODS We performed a phase 2, multicenter, prospective, open-label, single-arm clinical trial of twice-daily enoxaparin (initial dose: 0.5mg/kg per dose; max: 60mg; target anti-Xa activity: 0.20–0.49IU/mL) as primary thromboprophylaxis for children & lt;18 years of age hospitalized for symptomatic COVID-19. Study endpoints included: cumulative incidence of International Society of Thrombosis and Haemostasis-defined clinically relevant bleeding; enoxaparin dose-requirements; and cumulative incidence of venous thromboembolism within 30-days of hospital discharge. Descriptive statistics summarized endpoint estimates that were further evaluated by participant age (±12 years) and clinical presentation. RESULTS Forty children were enrolled and 38 met analyses criteria. None experienced clinically relevant bleeding. Median (interquartile range) dose to achieve target anti-Xa levels was 0.5 mg/kg (0.48–0.54). Dose-requirement did not differ by age (0.5 [0.46–0.52] mg/kg for age ≥12 years versus 0.52 [0.49–0.55] mg/kg for age & lt;12 years, P = .51) but was greater for participants with MISC (0.52 [0.5–0.61] mg/kg) as compared with primary COVID-19 (0.48 [0.39–0.51] mg/kg, P = .010). Two children (5.3%) developed central-venous catheter-related venous thromboembolism. No serious adverse events were related to trial intervention. CONCLUSIONS Among children hospitalized for COVID-19, thromboprophylaxis with twice-daily enoxaparin appears safe and warrants further investigation to assess efficacy.

Kurzfassung: Introduction: ATHN 8: U.S. Cohort Study of Previously Untreated Patients (PUPs) with Congenital Hemophilia is sponsored by the American Thrombosis and Hemostasis Network (ATHN) and is being conducted at ATHN-affiliated sites in the United States. The ATHN 8: PUPs Study collects detailed demographic, diagnosis, treatment, bleed, and inhibitor data on children with moderate and severe hemophilia born on or after January 1, 2010 and followed at an ATHN-affiliated hemophilia treatment center (HTC). The endpoint for the overall study is inhibitor development or achieving 50 exposure days. A confirmed inhibitor is defined as two consecutive positive inhibitor titers ( & gt;0.5 Nijmegen Bethesda Units (BU) for hemophilia A and & gt;0.3 Nijmegen BU for hemophilia B) which results in change in treatment. Available family history is also collected. For this interim analysis, we hypothesized that children with severe hemophilia A (HA) and a family history (FH) of hemophilia would have earlier age of diagnosis. Methods: Available data through April 30, 2020 were analyzed for participants with severe HA (factor VIII & lt;1%) born between January 1, 2010 and December 31, 2019. Diagnostic history, circumcision, and bleeding and treatment within the first 30 days of life were compared between participants with and without a known FH. Results: Twenty-six HTCs have enrolled 112 male participants with severe HA. FH regarding hemophilia is known in 94 (84%) and positive in 60 (64%). Patients with a positive FH compared to patients without a positive FH were diagnosed significantly earlier and were less likely to have circumcision (Table 1). Bleeding rate and factor exposure rate was similar within the first 30 days of life. Among 46 subjects who bled within the first 30 days of life, 6 (13.0%) bled due to circumcision (2 have a positive family history, and 4 have a negative family history); 34/46 (74%) had other bleeding events within the first 30 days. Conclusions: The interim analysis of PUPs born with severe HA between 2010-2019 demonstrates a majority have a FH of HA which is associated with an earlier age at diagnosis compared to those without a FH. Those without a FH of HA have higher rates of circumcision. Earlier identification of hemophilia could result in perinatal management strategies and avoidance of procedures such as circumcision that could result in bleeding. Disclosures Thornburg: NovoNordisk: Research Funding; Genentech: Speakers Bureau; American Thrombosis and Hemostasis Network: Research Funding; National Hemophilia Foundation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer Pharmaceuticals: Research Funding; Spark Therapeutics: Consultancy; Sanofi Genzyme: Consultancy, Other: Data Safety Monitoring Board, Research Funding; Bluebird Bio: Consultancy; Ironwood Pharmaceuticals: Consultancy, Other: Data Safety Monitoring Board; Biomarin: Consultancy, Speakers Bureau. Friedman:Alexion: Speakers Bureau; Instrumentation Laboratories: Consultancy; Alexion: Consultancy; Bayer: Consultancy. Guerrera:NovoNordisk: Consultancy, Speakers Bureau; Kedrion: Consultancy; Biomarin: Speakers Bureau; Sanofi Genzyme: Speakers Bureau; Takeda: Consultancy. Malec:SOBI: Consultancy; Bayer: Consultancy; CSL: Consultancy; Takeda: Consultancy; Sanofi Genzyme: Consultancy, Research Funding, Speakers Bureau. Simpson:HEMA Biologics: Consultancy, Honoraria; Octapharma: Consultancy, Honoraria, Research Funding; Bayer: Consultancy, Honoraria, Speakers Bureau; CSL Behring: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Novo Nordisk: Consultancy, Honoraria, Speakers Bureau; Bioverativ/Sanofi: Research Funding. Tarantino:Spark: Membership on an entity's Board of Directors or advisory committees; HRSA: Membership on an entity's Board of Directors or advisory committees; CDC: Membership on an entity's Board of Directors or advisory committees; Dova: Membership on an entity's Board of Directors or advisory committees; Pfizer: Other; NovoNordisk: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Research Funding; Octapharma: Membership on an entity's Board of Directors or advisory committees; Grifols: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Genentech: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Sobi: Membership on an entity's Board of Directors or advisory committees; Biomarin: Membership on an entity's Board of Directors or advisory committees. Carpenter:Novo Nordisk: Honoraria; Shire: Research Funding; Genentech, Inc.: Honoraria; Kedrion: Honoraria; CSL Behring: Research Funding; Hemostasis & Thrombosis Research Society: Membership on an entity's Board of Directors or advisory committees; American Academy of Pediatrics: Other: PREP Heme/Onc editorial board; American Thrombosis and Hemostasis Network: Membership on an entity's Board of Directors or advisory committees.

Kurzfassung: This is the first published report of a young girl with co-inherited sickle cell-β + thalassemia and cystic fibrosis. Although a small subset of patients with co-inherited cystic fibrosis and other hemoglobinopathies have been reported, this patient developed early hematologic and pulmonary complications that were more severe than the previous cases. To assess pulmonary co-morbidities, we used infant pulmonary function testing through the raised volume rapid thoracoabdominal compression technique as both an established study of early cystic fibrosis and also as a newer study of mechanism for early sickle cell lung disease. This further serves as the first report of the raised volume rapid thoracoabdominal compression technique to determine raised volume forced expiratory flows and fractional lung volumes in a patient with a hemoglobinopathy. Case presentation A 2-year-old African-American girl with co-inherited cystic fibrosis and sickle cell-β + thalassemia developed severe hematologic complications (recurrent vaso-occlusive events, hepatic sequestration, and acute chest syndrome) during periods of cystic fibrosis pulmonary exacerbations and weight loss. Because cystic fibrosis and sickle cell-β + thalassemia both confer distinct patterns of pulmonary disease, infant pulmonary function testing with the raised volume rapid thoracoabdominal compression technique was used to define respiratory pathophysiology and guide treatment options. Infant pulmonary function testing data demonstrated moderate-to-severe lower airways obstruction, moderate air trapping, and no evidence of restrictive lung disease. Conclusions Infant pulmonary function testing with the raised volume rapid thoracoabdominal compression technique guided therapy in this patient with cystic fibrosis and sickle cell-β + thalassemia. Although this is an original case report on a unique patient, this case highlights the need to evaluate early respiratory pathophysiology in a broader population of young patients with hemoglobinopathies and screen those at risk for early pulmonary co-morbidities.

Kurzfassung: The plasma glycoprotein von Willebrand factor (VWF) exhibits fivefold antigen level variation across the normal human population determined by both genetic and environmental factors. Low levels of VWF are associated with bleeding and elevated levels with increased risk for thrombosis, myocardial infarction, and stroke. To identify additional genetic determinants of VWF antigen levels and to minimize the impact of age and illness-related environmental factors, we performed genome-wide association analysis in two young and healthy cohorts ( n = 1,152 and n = 2,310) and identified signals at ABO ( P 〈 7.9E-139) and VWF ( P 〈 5.5E-16), consistent with previous reports. Additionally, linkage analysis based on sibling structure within the cohorts, identified significant signals at chromosome 2q12–2p13 (LOD score 5.3) and at the ABO locus on chromosome 9q34 (LOD score 2.9) that explained 19.2% and 24.5% of the variance in VWF levels, respectively. Given its strong effect, the linkage region on chromosome 2 could harbor a potentially important determinant of bleeding and thrombosis risk. The absence of a chromosome 2 association signal in this or previous association studies suggests a causative gene harboring many genetic variants that are individually rare, but in aggregate common. These results raise the possibility that similar loci could explain a significant portion of the “missing heritability” for other complex genetic traits.

Kurzfassung: Information on trends in venous thromboembolism (VTE) in US children is scant and inconsistent. We assessed national trends in VTE-associated pediatric hospitalizations. METHODS: All nonroutine newborn hospitalizations for children 0 to 17 years of age in the 1994–2009 Nationwide Inpatient Samples were included; routine newborn discharges were excluded. VTE diagnoses were identified by using the International Classification of Diseases, Ninth Revision, Clinical Modification codes. Variance weighted least square regression was used to assess trends in patient characteristics and rates of hospitalization per 100 000 population & lt;18 years of age. Multivariable logistic regression models were used to estimate the probability of VTE diagnosis over the study period. RESULTS: The rate of VTE-associated hospitalization increased for all age subgroups ( & lt;1, 1–5, 6–11, and 12–17 years), with the largest increase noted among children & lt;1 year of age (from 18.1 per 100 000 during 1994 to 49.6 per 100 000 during 2009). Compared with 1994–1997, the adjusted odds of hospitalization with a VTE diagnosis were 88% higher during 2006–2009 (adjusted odds ratio: 1.88 [95% confidence interval: 1.64–2.17]). Venous catheter use, mechanical ventilation, malignancy, hospitalization ≥5 days, and VTE-related medical conditions were associated with increased likelihood of VTE diagnosis. CONCLUSIONS: The rate of VTE-associated hospitalization among US children increased from 1994 through 2009. Increases in venous catheter procedures were associated with and may have contributed to the observed trends. The degree to which increased awareness of VTE influenced the temporal differences could not be determined.

Kurzfassung: Age-group analyses were conducted of patients in the prophylactic platelet dose trial (PLADO), which evaluated the relation between platelet dose per transfusion and bleeding. Hospitalized patients with treatment-induced hypoproliferative thrombocytopenia were randomly assigned to 1 of 3 platelet doses: 1.1 × 1011, 2.2 × 1011, or 4.4 × 1011 platelets/m2 per transfusion, given for morning counts of ≤ 10 000 platelets/μL. Daily hemostatic assessments were performed. The primary end point (percentage of patients who developed grade 2 or higher World Health Organization bleeding) was evaluated in 198 children (0-18 years) and 1044 adults. Although platelet dose did not predict bleeding for any age group, children overall had a significantly higher risk of grade 2 or higher bleeding than adults (86%, 88%, 77% vs 67% of patients aged 0-5 years, 6-12 years, 13-18 years, vs adults, respectively) and more days with grade 2 or higher bleeding (median, 3 days in each pediatric group vs 1 day in adults; P 〈 .001). The effect of age on bleeding differed by disease treatment category and was most pronounced among autologous transplant recipients. Pediatric subjects were at higher risk of bleeding over a wide range of platelet counts, indicating that their excess bleeding risk may be because of factors other than platelet counts. This trial was registered at www.clinicaltrials.gov as #NCT00128713.