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Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is associated with thrombotic complications in adults, but the incidence of COVID-19-related thrombosis in children and adolescents is unclear. Most children with acute COVID-19 have mild disease, but coagulopathy has been associated with multisystem inflammatory syndrome in children (MIS-C), a postinfectious complication. We conducted a multicenter retrospective cohort study to determine the incidence of thrombosis in children hospitalized with COVID-19 or MIS-C and evaluate associated risk factors. We classified patients into 1 of 3 groups for analysis: COVID-19, MIS-C, or asymptomatic SARS-CoV-2. Among a total of 853 admissions (COVID-19, n = 426; MIS-C, n = 138; and asymptomatic SARS-CoV-2, n = 289) in 814 patients, there were 20 patients with thrombotic events (TEs; including 1 stroke). Patients with MIS-C had the highest incidence (9 [6.5%] of 138) vs COVID-19 (9 [2.1%] of 426) or asymptomatic SARS-CoV-2 (2 [0.7%] of 289). In patients with COVID-19 or MIS-C, a majority of TEs (89%) occurred in patients age ≥12 years. Patients age ≥12 years with MIS-C had the highest rate of thrombosis at 19% (9 of 48). Notably, 71% of TEs that were not present on admission occurred despite thromboprophylaxis. Multivariable analysis identified the following as significantly associated with thrombosis: age ≥12 years, cancer, presence of a central venous catheter, and MIS-C. In patients with COVID-19 or MIS-C, hospital mortality was 2.3% (13 of 564), but it was 28% (5 of 18) in patients with TEs. Our findings may help inform pediatric thromboprophylaxis strategies.

Although survival outcomes have significantly improved, up to 40% of patients die within 1 year of HLA-matched unrelated-donor blood and marrow transplantation (BMT). To identify non-HLA genetic contributors to mortality after BMT, we performed the first exome-wide association study in the DISCOVeRY-BMT cohorts using the Illumina HumanExome BeadChip. This study includes 2473 patients with acute myeloid leukemia, acute lymphoblastic leukemia, or myelodysplastic syndrome and 2221 10/10 HLA-matched donors treated from 2000 to 2011. Single-variant and gene-level analyses were performed on overall survival (OS), transplantation-related mortality (TRM), and disease-related mortality (DRM). Genotype mismatches between recipients and donors in a rare nonsynonymous variant of testis-expressed gene TEX38 significantly increased risk of TRM, which was more dramatic when either the recipient or donor was female. Using the SKAT-O test to evaluate gene-level effects, variant genotypes of OR51D1 in recipients were significantly associated with OS and TRM. In donors, 4 (ALPP, EMID1, SLC44A5, LRP1), 1 (HHAT), and 2 genes (LYZL4, NT5E) were significantly associated with OS, TRM, and DRM, respectively. Inspection of NT5E crystal structures showed 4 of the associated variants affected the enzyme structure and likely decreased the catalytic efficiency of the enzyme. Further confirmation of these findings and additional functional studies may provide individualized risk prediction and prognosis, as well as alternative donor selection strategies.

Background: Vaso-occlusive crises (VOC) are the most common acute complication of sickle cell disease (SCD). Crizanlizumab, an anti-P-selectin monoclonal antibody, is an FDA-approved disease-modifying therapy (DMT) for SCD patients (pts) aged ≥16 yrs to reduce the frequency of VOC. To better understand its use and impact, the National Alliance for Sickle Cell Centers (NASCC) conducted a retrospective study of pts prescribed crizanlizumab from 11/2019-6/30/2021. NASCC is a non-profit organization formed to support SCD centers in delivering quality comprehensive care by setting and adopting specific standards and advocating for improved health outcomes in SCD. This study describes the largest real-world cohort of pts treated with crizanlizumab. Methods: This is a two-part study. Part 1 was to evaluate NASCC center crizanlizumab practice and to summarize data on insurance approval and the frequency of drug discontinuation. Part 2 includes pt level data to evaluate reasons for discontinuation and acute care utilization pre and post therapy. Acute care use includes day hospital/infusion, emergency department visits, and hospitalizations for VOC (excluding COVID-19). The index date for each pt is defined as the 1st crizanlizumab infusion date. Chart review (electronic health records) was used to identify all acute care visits 12 months pre-index and ≤12 months post index. Acute care data will be analyzed in aggregate. Evaluation of center-specific use of crizanlizumab, time to initial site level formulary approval and drug discontinuation were analyzed. Pt level data collection is ongoing to include sufficient time post index date. VOC characteristics will be summarized using medians, median differences (pre/post treatment), and 95% confidence intervals. Additional evaluation of effectiveness of crizanlizumab will include analysis based on number of doses received, pre-treatment VOC burden, concomitant hydroxyurea (HU) use and genotype. Results: Data includes pts prescribed crizanlizumab at 11 NASCC centers. Site- formulary approvals to use crizanlizumab varied from 12/2019-12/2020. As a result, the 1st pt to receive treatment at each site varied from 1/15/2020-1/20/2021. Mean time from site-level approval to first infusion was 77 days (range: 0-394). Over 50% of sites received insurance denials mainly due to "insufficient medical necessity" or "medication not covered by the prescription plan." Sites were able to successfully appeal denials for 71% of pts (Table 1). Treatment Delivery: Each site gives infusions over 30 minutes and the majority (64%) do not use pre-medication unless pts had reactions. Some sites use diphenhydramine/acetaminophen (3) or normal saline and ketorolac (1). All sites prescribe crizanlizumab to pts of all SCD genotypes. Pts Treated: 297 pts were prescribed crizanlizumab of whom 238 received ≥ 1 infusion. There was variation in number of pts/site (range 6-73, mean 21) due to time to site-level approval, insurance and pt population. Of these 238, 75 pts (32%) discontinued treatment (0-17 pts/site). Sites reported pts perceived lack of improvement or feeling their overall pain was increased, transportation issues and infusion related reactions (IRRs) characterized by pain as some of the reasons for discontinuation. Evaluation of real-world efficacy measured by changes in acute care utilization, including sub-analysis by genotype, pre-treatment VOC burden and concomitant HU use, are pending sample size dependent feasibility. Discussion: This is the first multi-center real-world analysis of crizanlizumab. Findings demonstrate some insurance barriers to therapy. The majority of pts who initiated crizanlizumab have remained on therapy; however, 1/3 of pts had lack of effect or barriers to care. Pt level data will include characteristics related to treatment failure or IRR. Improving the understanding of phenotype-specific response to novel therapies is essential in SCD. Conclusion: Post-approval therapies for rare diseases must undergo real-world evaluation to ensure study results translate to the community. NASCC uses defined criteria for multidisciplinary care for Alliance inclusion and findings reflect the use of DMT in such centers. This is the first NASCC study of DMT in SCD. Part 2 of the study will give early insights into the effectiveness of crizanlizumab; long term follow-up is needed for a full understanding of its utility in SCD. Figure 1 Figure 1. Disclosures Kanter: Fulcrum Therapeutics, Inc.: Consultancy; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Forma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees; Beam: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Graphite Bio: Consultancy; GuidePoint Global: Honoraria; Fulcrum Tx: Consultancy. Manwani: Novartis: Consultancy. Idowu: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Forma Therapeutics, Inc.: Research Funding; Ironwood: Research Funding. Treadwell: National Alliance of Sickle Cell Centers: Other: Early Evaluation of the Use of Crizanlizumab in Sickle Cell Disease. Clay: GBT: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria. Little: Hemex Health, Inc.: Patents & Royalties; Biochip Labs: Patents & Royalties. Desai: Global Blood Therapeutics: Honoraria, Research Funding; Novartis: Research Funding, Speakers Bureau; Pfizer: Other: Publication Fee, Research Funding; Forma: Consultancy; Foundation for Sickle Cell Research: Honoraria. Lanzkron: Shire: Research Funding; Pfizer: Current holder of individual stocks in a privately-held company; Bluebird Bio: Consultancy; Teva: Current holder of individual stocks in a privately-held company; Novo Nordisk: Consultancy; GBT: Research Funding; Imara: Research Funding; CSL Behring: Research Funding; Novartis: Research Funding.

Background: "Education and Mentoring to Bring Access to Care for SCD (EMBRACE SCD)"--U1EMC31108-- is a multicenter study sponsored by HRSA in the US southeastern region, which focuses on extending knowledge about sickle cell disease (SCD) to hematology and primary care providers and to improve the care of children and adults with SCD. In Florida we aimed to improve access by increasing prescription (RX) rates of hydroxyurea (HU), by at least 10% from baseline in patients with sickle cell anemia. Methods: Three SCD centers, assisted by three community-based organizations and with the support of two pediatricians with expertise in quality improvement (QI), were engaged in this QI project. The SCD centers are the University of Miami (UM), Salah Foundation at Broward Health and Johns Hopkins All Children's Hospital (JH). Data were abstracted locally and entered into REDCap by a central data manager. Run charts were created to assess data improvement. UM also assessed barriers using a parent/caregiver questionnaire administered at least 6 months after offering HU with the purpose of improving patient education and desire to take HU. Results: Beginning in June 2019 until June 2021, center clinicians concentrated in identifying all patients who were eligible for HU (namely, children 9 months and older with hemoglobin SS and hemoglobin SB 0thalassemia who were not on chronic transfusions). As a group, 50.2% (N=263) of patients were on hydroxyurea at entry (range 35.4-62.4 % among the sites) from a total of 524 eligible patients. The main organizing activities which allowed for higher percent were having a center patient database (done March 2019), educating all providers in the centers about the importance of HU as disease-modifying therapy, having a unified protocol for the education of parents and/or patients about HU benefits, and using visual aids (pictures) of erythrocytes pre and post HU treatment. The QI consultants met virtually with the Florida EMBRACE team monthly beginning June 2020 to increase engagement and interest in participating in this QI activity. We implemented a data collection sheet to track medical records every month to determine whether we were capturing all eligible patients. As depicted in the run chart, we surpassed the QI goal by ending with 64.8% (N=343) prescription rate (range 48.0-85.0 %) from a total of 529 eligible patients. From the 76 barrier assessment questionnaires given at UM, we identified 12 (15.8%) refusals. Seven of 12 refused because of fear of taking "chemotherapy", one because of fear of side effects, and four because their children's disease was considered mild. With further education, we decreased the refusals from 12 to 9. Conclusion: A unified approach to a QI project was successful among several centers in Florida, increasing the prescription rate of hydroxyurea by 14.6% among patients with sickle cell anemia. Acknowledgment: We acknowledge HRSA and region principal investigators for EMBRACE SCD Drs. Ify Osunkwo, Julie Kanter and John J. Strouse for their support in this work. Figure 1 Figure 1. Disclosures Alvarez: Forma Therapeutics: Membership on an entity's Board of Directors or advisory committees; GBT: Membership on an entity's Board of Directors or advisory committees. Clay: Novartis: Honoraria; GBT: Membership on an entity's Board of Directors or advisory committees.

MYC is over-expressed by many cancers, yet its oncogenic mechanisms are incompletely understood. MYC is central to acute lymphoblastic leukemia (ALL) - the most common and second most lethal pediatric malignancy, and ALL afflicts even more adults. Much of MYC's oncogenic function is attributed to its role as a transcription factor, but MYC has been shown to deregulate DNA replication independent of transcription. As master regulator of transcriptomes and epigenomes, we predict that MYC impacts both biologic features in both ALL types, B- and T-ALL. We hypothesize that MYC alters both RNA expression and DNA replication (the ordered spatio-temporal process where genomic domains replicate in either early or late S-phase) in B- and T-ALL, and that these perturbations-some shared, others unique to one ALL type-drive leukemogenesis. Our project utilizes a unique double-transgenic rag2:hMYC, lck:GFP zebrafish ALL model that we established, which is the only animal model that develops both highly penetrant B- and T-ALL. In this model, B- and T-ALL are induced by human MYC (hMYC) that is regulated by a zebrafish (Danio rerio) rag2 promoter. Because B and T lymphoblasts each express rag2, both lineages over-express MYC, inducing B- and T-ALL. The differential activity of the D. rerio lck promoter (regulating GFP) causes B cells to fluoresce dimly and T cells to fluoresce brightly, permitting identification of B- vs. T-ALL by fluorescent microscopy and FACS-purification. Thus, we can compare B- and T-ALL in an isogenic background. We have collected 30 ALL samples (18 T-ALL, 12 B-ALL) and completed two types of analyses on 12 T-ALL and 3 B-ALL. Using RNA-seq, we established gene expression profiles (GEP) for both ALL types; principal component analysis and other clustering algorithms demonstrate B- and T-ALL are distinct. Although we analyze the entire transcriptome, we prioritize genes conserved in humans to focus on translatable targets. To assess DNA replication, we generated Replication Timing (RT) profiles by first FAC-sorting ALL cells based on cell cycle phase (G1, S, G2; defined by DNA content) and then performing whole-genome sequencing to generate RT profiles for the same ALL analyzed by RNA-seq. We identified differentially replicating regions by comparing RT of B-vs. T-ALL, revealing many loci where replication reproducibly shifts from early-to-late, or late-to-early, based on ALL type. Overall, despite their shared genetic driver (MYC) , we found RT differences that distinguish B- vs. T-ALL in ~30% of the genome. Most differences occur in large chromosomal domains, suggesting abnormal chromatin structure in ALL. An additional unexpected result was that many ALL G1 samples had read count differences across large chromosomal regions, indicating the presence of aneuploidies/large CNAs. Several were recurrent and lineage-specific (i.e., exclusive to B- or T-ALL). Together, our data demonstrate differences in RNA transcription, DNA replication, and regions of genomic instability that are lineage-specific, despite a shared MYC oncogene that drives both B- and T-ALL. We will next determine which deranged loci are also perturbed in human ALL, with an overarching goal of finding prognostic biomarkers and therapeutic targets. MYC hyper-activity occurs in ~70% of human malignancies. Thus, MYC is crucial to virtually all cancer biology, making our findings likely to inform not only the mechanisms that drive ALL, but also other cancers where MYC is oncogenic. Disclosures No relevant conflicts of interest to declare.

INTRODUCTION Diffuse large B-cell lymphoma (DLBCL) represents several distinct clinical pathologic entities recently identified by molecular profiling. Treatment with anti-CD19 chimeric antigen receptor (CAR) T-cell therapies is now standard for many patients with relapsed/refractory (R/R) disease. Although antigen loss of CD19 represents a known cause of late relapses, the majority of CAR-T cell treatment failure occurs very soon after treatment at which time the impact of molecular subtype and other somatic mutations of DLBCL is undefined. We sought to determine impact of molecular features of DLBCL tumors on clinical outcomes in a cohort of patients with R/R disease who were treated with axicabtagene ciloleucel (axi-cel) or tisagenlecleucel (tisa-cel) in order to provide insight into the mechanism of response or resistance to CAR-T cell therapy. METHODS We collected clinical data and formalin-fixed, paraffin embedded (FFPE) biopsy specimens from 121 DLBCL patients at the time of R/R disease after prior treatment with standard chemoimmunotherapy across 12 US academic medical centers who subsequently received commercial CAR-T cell treatment. Whole exome and transcriptome sequencing was performed on all cases to measure gene expression and gene copy number alterations. Genetic analysis was done on 96 patients with pre-treatment biopsies that passed sequencing quality filters, and expression analysis on 93 patients. Progression-free and overall survival (PFS, OS) measured from the day of CAR-T cell infusion were estimated using the Kaplan-Meier method and compared with the log-rank test. RESULTS Baseline demographics and treatment details of the patient population are shown in the Table (Panel A). Best overall response was CR in 43% of patients and PR in 10% patients. PFS and OS were significantly different based on best response to treatment (P CONCLUSIONS DLBCL patients whose tumors have molecular features that are predictive of inferior response to standard frontline treatment including the high-risk subgroups (C2/A53) and (C5/MCD) have favorable treatment outcomes with CAR-T cell therapy. In contrast, individual driver mutations including MYC and BCL2, CDKN2A, and KLHL6 are associated with inferior PFS with CAR-T cell therapy, while mutations in BTG2, MYD88, and CD79B are associated with a favorable PFS. In addition, gene expression analysis implicates a potential role for the microenvironment in modulating responses to CAR-T therapy. These findings suggest that predictive biomarkers for response to traditional chemoimmunotherapy and cellular immunotherapy are distinct. Our results provide insight into potentially targetable pathways for the development of rational treatment strategies that may augment response CAR-T cell therapy. Figure 1 Figure 1. Disclosures Hill: Celgene (BMS): Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria; Gentenech: Consultancy, Honoraria, Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Other: Travel Support, Research Funding; Beigene: Consultancy, Honoraria, Research Funding; AstraZenica: Consultancy, Honoraria; Epizyme: Consultancy, Honoraria; Incyte/Morphysis: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding. McKinney: Novartis: Research Funding; Nordic Nanovector: Research Funding; Molecular Templates: Consultancy, Research Funding; Kite/Gilead: Honoraria, Speakers Bureau; Incyte: Research Funding; Genetech: Consultancy, Honoraria, Research Funding; Epizyme: Consultancy; Celgene: Consultancy, Research Funding; BTG: Consultancy; Beigene: Research Funding; ADC Therapeutics: Consultancy, Speakers Bureau; Pharmacyclics: Consultancy; Verastem: Consultancy. Neff: Spring Discovery: Consultancy, Ended employment in the past 24 months; EUSA Pharma: Speakers Bureau; Enzyvant: Consultancy. Reshef: BMS, Regeneron, TScan, Synthekine, Atara, Jasper, Bayer: Consultancy; ilead, BMS, Precision, Immatics, Atara, Takeda, Shire, Pharmacyclics, Incyte: Research Funding; Bayer: Consultancy; Gilead and Novartis: Honoraria. Oluwole: Janssen: Consultancy; Pfizer: Consultancy; Curio Science: Consultancy; Kite, a Gilead Company: Consultancy, Research Funding. Ghosh: Incyte: Consultancy, Honoraria; Pharmacyclics LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Speakers Bureau; TG Therapeutics: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Genmab: Consultancy, Honoraria; Epizyme: Honoraria, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; ADC Therapeutics: Consultancy, Honoraria; Adaptive Biotech: Consultancy, Honoraria; AbbVie: Honoraria, Speakers Bureau; Karyopharma: Consultancy, Honoraria; Genentech: Research Funding. Chen: Actinium Pharmaceuticals: Other: Principal Investigator, SIERRA Trial, Actinium. Hernandez-Ilizaliturri: AbbVie: Other: Advisory Boards; Incyte: Other: Advisory Boards; Celgene: Other: Advisory Boards; BMS: Other: Advisory Boards; Pharmacyclics: Other: Advisory Boards; Amgen: Other: Advisory Boards; Kite: Other: Advisory Boards; Gilead: Other: Advisory Boards; Epyzime: Other: Advisory Boards. Shah: Lily: Consultancy, Honoraria, Research Funding; Miltenyi Biotec: Consultancy, Honoraria, Research Funding; Kite: Consultancy; Epizyme: Consultancy; Legend: Consultancy; Incyte: Consultancy; Umoja: Consultancy. Stephens: Epizyme: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Innate Pharma: Membership on an entity's Board of Directors or advisory committees; Beigene: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Adaptive: Membership on an entity's Board of Directors or advisory committees; JUNO: Research Funding; Novartis: Research Funding; Abbvie: Consultancy; AstraZeneca: Consultancy; CSL Behring: Consultancy; Celgene: Consultancy; Mingsight: Research Funding; Arqule: Research Funding. Patel: Janssen: Consultancy; Kite Pharma: Consultancy, Speakers Bureau; TG Therapeutics: Consultancy, Speakers Bureau; MEI Pharma: Consultancy; Abbvie: Consultancy; Genentech: Consultancy; Bristol Myers Squibb: Consultancy, Speakers Bureau; BeiGene: Consultancy; Morphosys: Consultancy; Pharmacyclics: Consultancy; AstraZeneca: Consultancy, Research Funding, Speakers Bureau; ADC Therapeutics: Consultancy; Lilly: Consultancy. Pagel: Gilead: Consultancy; Actinium Pharmaceuticals: Consultancy; Kite, a Gilead Company: Consultancy; Incyte/MorphoSys: Consultancy; AstraZeneca: Consultancy; Pharmacyclics/AbbVie: Consultancy; Epizyme: Consultancy; BeiGene: Consultancy; MEI Pharma: Consultancy. Hsi: AbbVie Inc, Eli Lilly: Research Funding. Goy: Genentech/Hoffman la Roche: Research Funding; AbbVie/Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta: Consultancy, Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Medscape: Consultancy; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Physicians' Education Resource: Consultancy, Other: Meeting/travel support; Xcenda: Consultancy, Honoraria; Genomic Testing Cooperative: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; LLC(Targeted Oncology): Consultancy; Hoffman la Roche: Consultancy; Vincerx: Honoraria, Membership on an entity's Board of Directors or advisory committees; Rosewell Park: Consultancy; Infinity/Verastem: Research Funding; MorphoSys: Honoraria, Other; Elsevier PracticeUpdate: Oncology: Consultancy, Honoraria; Xcenda: Consultancy; Bristol Meyers Squibb: Membership on an entity's Board of Directors or advisory committees; Vincerx pharma: Membership on an entity's Board of Directors or advisory committees; OncLive Peer Exchange: Honoraria; COTA (Cancer Outcome Tracking Analysis): Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Elsevier's Practice Update Oncology, Intellisphere, LLC(Targeted Oncology): Consultancy; Incyte: Honoraria; AbbVie/Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Michael J Hennessey Associates INC: Consultancy; Novartis: Consultancy, Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Janssen: Research Funding; Karyopharm: Research Funding; Bristol Meyers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Phamacyclics: Research Funding; Constellation: Research Funding; Hackensack Meridian Health, Regional Cancer Care Associates/OMI: Current Employment. Ohgami: Stemline Therapeutics: Research Funding. Andreadis: CRISPR Therapeutics: Research Funding; GenMAB: Research Funding; Novartis: Research Funding; Roche: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Epizyme: Honoraria; Incyte: Honoraria; TG Therapeutics: Honoraria; Kite: Honoraria; Karyopharm: Honoraria; Atara: Consultancy, Honoraria; BMS: Research Funding; Merck: Research Funding. Thacker: Data Driven Bioscience: Current Employment. Rozzi: Data Driven Bioscience: Current Employment. Parker: Data Driven Bioscience: Current Employment. Happ: Data Driven Bioscience: Current Employment. Dave: Data Driven Bioscience: Current equity holder in publicly-traded company.

Introduction: Sickle Cell Disease (SCD) is the most common inherited blood disorder, affecting over 100,000 people in the United States. The latest medical managements have yielded better outcomes in mortality and morbidity among people with SCD. Despite these advancements, emerging young adults have complications transitioning from pediatric care to adult care and remain with the highest mortality rate in the population. Got Transition is a federally funded national resource center that aims to support youth and young adults moving from pediatric to adult care by implementing the Six Core Elements of Transition. At our institution, we established a transition program aimed at improving clinical care, medical management, and improvement in the transition from pediatric to adult medical care. Our goal was to develop a standardized, age appropriate sickle cell education curriculum to implement at clinic visits for our patients aged 13 and older. Hypothesis: We hypothesize that with a structured transition curriculum, we would be able to improve patient knowledge in medical aspect of the disease, academic resources and a better understanding of their complex psychosocial needs. Methods: We developed a transition program called Adolescent and Young Adult Sickle Cell Uplift and Learn Program for Transition (AYA SCULPT) that would focus on patients starting at 13 years old with a multidisciplinary approach of care. We adopted the Got Transition model implementing the Six Core Elements of Transition. Our team not only wanted to address educational topics related to their medical care, but also psychosocial and academic topics. A transition education curriculum was created spanning three age groups on the three major topics and further broken up into three smaller sections for clinic use to accommodate for time restraints (Table 1). A pilot of the medical curriculum was started August 2019 addressing medical topics relating to better understanding of sickle cell disease. We then introduced our psychosocial curriculum in January 2021. A member of our comprehensive sickle cell team provides the four-question pre-test to the patient at the beginning of their regularly scheduled clinic appointment. At the end of the appointment the nurse or provider will grade the pre-test and provide verbal education as well as printed material on the topics for the day. Scoring and topics are tracked in the patient's note as well as in a transition education database. At the patient's next visit, the same test is administered as a post-test in order to determine knowledge acquired and retention of the materials. Post-test scores are also recorded in the patient note and transition education database. Once the patient finishes a module, we move to the next topic at the next regularly scheduled visit. Depending on the patient's genotype and medication management, post-tests can be given between two to six months after the pre-test. Results: Scores from pre-test were compared to those of post-test for patients that had the opportunity to complete the medical curriculum quizzes. One hundred and fifty six patients range from age 13-21 were included in this pilot study. Of patients aged 19-21, 69% have taken at least one pre-test and post-test for the medical education (63 total pre- and post-tests). Forty-three (78%) patients aged 16-18 have taken at least one pre-test and post-test (75 total pre- and post-tests). Thirty-three (67%) patients aged 13-15 have taken at least one pre-test and post-test (53 total pre- and post-tests). Results were categorized as score increased, score unchanged (pre-test score was not 100%), maintained 100% (unable to increase in score), and score decreased. In every age group, the category with the most results was "score increased." Shown in Table 2. Conclusion: Further extrapolation suggests that the medical curriculum provided in clinic improves the sickle cell knowledge in this adolescent and young adult population. Though all age groups improved, the biggest improvement was noted in knowledge with our 13-15 year olds. These results suggest that early transition education can be impactful even if started at the early phases of adolescence. Studies are still ongoing with our medical curriculum and early psychosocial data is beginning to support our previous findings. As part of transition health care, focusing on disease education can provide better knowledge and hopefully improve patient outcomes. Figure 1 Figure 1. Disclosures Clay: Novartis: Honoraria; GBT: Membership on an entity's Board of Directors or advisory committees.

Introduction: Ibr and ven are 1 st generation BTK and BCL2 inhibitors respectively that are approved for use in patients with CLL. They are both oral agents that have been shown to work synergistically together with no unexpected toxicities beyond what is already known about each of them. Their combination is very effective in the frontline treatment of CLL including fixed duration therapy for 15 cycles which produces high complete remissions (CR) and undetectable minimal residual disease (uMRD) rates as well as high progression free survival (PFS) and overall survival (OS) independent of high-risk features [Allen JH, et al. EHA virtual annual meeting 2021; Jain N, et al N Engl J Med 2019]. There is also data to support the use of this combination in the rel/ref setting [Hillmen P, et al. J Clin Oncol 2019] and here we present results of a phase 2 trial of fixed duration therapy with ibr+ven in rel/ref CLL (NCT03045328). Methods: Patients with rel/ref CLL with indications for treatment were enrolled at Stanford Cancer Institute and City of Hope National Medical Center. Treatment was initiated with ibr monotherapy (420mg daily) for 8 weeks after which ven ramp up was introduced. Ven was escalated to full dose (400mg daily) over 5 weeks and the combination of ibr+ven was then continued for a total of 2 years. Treatment was stopped in all patients at week 118 and all patients were evaluated 30 days later to complete study follow up. The primary endpoint was the assessment of CR rate at week 62. Secondary endpoints included overall response rate (ORR), duration of response (DOR), PFS, OS, evaluation of adverse events (AEs), as well as rate of uMRD in the bone marrow at week 62 and week 117 of treatment by flow cytometry (10 -4 sensitivity [uMRD4]) and Clonoseq sequencing (10 -6 sensitivity [uMRD6]). Results: A total of 22 patients were enrolled. Median age of the patients was 68 (range 39-82 years). Median prior treatment regimens were 1 (range 1-3). Eleven patients received prior FCR as 1 st line therapy, 9 received BR, 1 received FR, and 1 had received rituximab alone. None had prior BTK inhibitor or ven. Baseline characteristics are shown in Table 1. Twenty-one patients initiated ven. One patient withdrew consent prior to the start of ven. Eighteen patients completed full trial treatment. Three patients discontinued treatment for these reasons: Hodgkin's transformation, kidney failure, need for a coronary stent. Five patients interrupted dosing due to toxicity and five patients had dose reductions. Three patients reduced ibrutinib, 2 due to rash and 1 due to recurrent atrial fibrillation, and 5 patients reduced ven due to fatigue, neutropenia (2), or diarrhea (2). CR rate (intention to treat [n=22]) at week 62 was 55% while the ORR was 91%. PFS and OS were 95% and 100% at 2 years. After 1 year of combination therapy, 13 of 20 (65%) evaluable patients had achieved bone marrow uMRD4 (5 positive and 2 not done) and 4 of 20 (20%) achieved bone marrow uMRD6. After 2 years, 2 additional patients achieved bone marrow uMRD4 (15 of 20 [75%]). Bone marrow flow and Clonoseq MRD data were available in 13 patients at the end of study. Eight were undetectable by flow and Clonoseq (uMRD6), 3 by flow only (uMRD4), and 2 were positive with both (MRD+). Seven patients experienced 11 serious AEs attributed to treatment: 3 with sepsis, 3 pneumonia, 2 atrial fibrillation, and 1 each diarrhea, dehydration, and pulmonary embolism. AEs ≥ Grade 3 are shown in Table 2. There were no TLS events. Conclusions: Ibr+ven combination for a fixed duration of 2 years after initial ibrutinib lead in is a well-tolerated, effective, oral, targeted therapy regimen for patients with rel/ref CLL. Most patients achieve an uMRD4 response in the bone marrow. The effect of poor risk features of disease and dose interruptions on depth of response will be reported. Figure 1 Figure 1. Disclosures Siddiqi: Janssen: Speakers Bureau; Oncternal: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Kite Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; BeiGene: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; TG Therapeutics: Research Funding. Coutre: Acerta: Other: Data Safety Monitoring Committee, Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Beigene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Data Safety Monitoring Committee, Research Funding; AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Background: Coronavirus disease-19 (COVID-19) is an acute respiratory illness caused by the SARS-COV-2 virus. Patients with COVID-19 infection can present with thrombosis in the setting of inflammation (thromboinflammation), presumably from endothelial dysfunction, or "endotheliopathy". Yu et al demonstrated in vitro that the spike protein subunit of SARS-COV2 acts as a potent activator of the alternative complement pathway (AP), one of three complement pathways within the innate immune system. Satyam et alreported the deposition of complement components on lung tissue of patients who succumbed to COVID-19, consistent with activation of classical and alternate pathways. These studies suggest complement dysregulation potentially causing endotheliopathy in COVID-19 patients. Thrombomodulin (TM) is an endothelial glycoprotein that plays two crucial roles in maintaining a healthy endothelium - as a natural anticoagulant and a negative regulator of complement. TM shed into the circulation due to endothelial injury can be measured in the plasma as soluble TM (sTM). Goshua et al showed elevated sTM in an adult cohort of patients with COVID-19. However, it is yet to be demonstrated if there is any correlation between endothelial injury and AP activation in COVID-19, or if either play a role in clinical outcome in the pediatric population. Objective: To 1) assess endothelial injury and AP activation in a cohort of critically ill pediatric patients with COVID-19 by measuring sTM and Ba (an AP activation product); 2) determine the correlation between endothelial injury and AP activation; and 3) analyze the utility of sTM and Ba in predicting pediatric clinical outcomes. Methods: We collected plasma samples of patients admitted to the Pediatric Intensive Care Unit and found to be positive for SARS-CoV-2 between Dec 2, 2020 and Jan 22, 2021 at Texas Children's Hospital. For controls, we collected plasma samples from pediatric patients undergoing preoperative clearance, all at their baseline state of health. sTM levels and Ba levels were measured in plasma samples using commercially available TM and Ba ELISA kits. sTM greater than 7.6 ng/ml (based on the assay range in adults) and Ba greater than 1080 ng/ml (based on data from adult healthy controls) were considered elevated. Data regarding demographics, length of ICU stay, clinical indicators of end organ damage- mechanical ventilation, dialysis, use of vasopressors, ECMO, mortality were obtained retrospectively via chart review. Inclusion criteria included all patients with a positive SARS-COV2 PCR admitted to the ICU. Exclusion criteria was age greater than 21 years, pregnant female, patients with known inflammatory or complement-mediated disorders. Statistical analysis: For sTM and Ba levels between control and COVID-19 patients, mean +/- standard deviation was calculated and significance determined with an unpaired t-test. Fischer exact test, Wilcoxon rank sum and Pearson product-moment correlation tests were used for statistical analysis of clinical outcomes as appropriate. A p-value Results: A total of 38 control patients and 33 COVID-19 patients were enrolled. Ba and sTM levels were both significantly higher in the COVID-19 pediatric patients compared to the controls (Fig. 1). Within the COVID-19 patient cohort, 61% (n=20) had elevated sTM and 42% (n=14) had elevated Ba levels. There was a moderately positive correlation between sTM and plasma Ba levels in the COVID-19 cohort (Fig. 2). Within the COVID-19 patients' cohort, though higher Ba levels were not associated with an increased rate of intubation, they were associated with an increased duration of mechanical ventilation (p=.039) for those intubated (Table 1). Elevated sTM was associated with increased vasopressor use (p=.011). Although other clinical outcome variables did not reach statistical significance likely owing to small numbers, overall trend indicated worse outcomes in patients with elevated sTM. Conclusions: Our findings are consistent with the hypothesis that SARS-COV-2 activates AP and causes endothelial injury in children. The positive correlation between sTM and Ba suggest interplay between inflammation, coagulation and endotheliopathy supporting thromboinflammation in COVID-19. Higher sTM and Ba levels indicated worse clinical outcomes in children, but larger studies are needed to confirm our findings. Figure 1 Figure 1. Disclosures Sartain: Alexon Pharamaceuticals: Membership on an entity's Board of Directors or advisory committees.

Background: Sickle cell disease (SCD) is an inherited systemic disorder in which sickle hemoglobin (HbS) polymerization triggers red blood cell sickling, chronic hemolytic anemia, and recurrent episodes of vaso-occlusion. SCD-related complications lead to acute and chronic life-threatening events, cumulative organ damage, disability, and early mortality. Voxelotor (Oxbryta ®) tablets are approved in the United States for treatment of SCD in adults and adolescents aged ≥12 years, based on the efficacy and safety data from the randomized, placebo-controlled, multicenter HOPE trial. Voxelotor is an oral, once-daily HbS-polymerization inhibitor that has been shown to increase hemoglobin (Hb) levels and reduce markers of hemolysis. The Retrospective Study to Evaluate Outcomes in Patients with Sickle Cell Disease Treated with Oxbryta (RETRO) is designed to collect, aggregate, and characterize real-world, retrospective laboratory and clinical data on adults and adolescents with SCD treated with voxelotor as part of their usual care at multiple clinical centers in the United States. Methods: RETRO is a multicenter, post-marketing, retrospective study of approximately 300 patients (aged ≥12 years) with SCD from 10 US study sites. Independent SCD expertise is provided by a steering committee to inform the design and conduct of the voxelotor registry. Clinical and laboratory data have been collected and aggregated 12 months before initiation of voxelotor treatment and compared with post-treatment data outcomes. Patients with documented SCD (all genotypes) who received voxelotor treatment for ≥2 consecutive weeks were included in this analysis. Only data available from patients' medical records (and other secondary data sources) 1 year before and up to 1 year after the first voxelotor dose were documented in de-identified case report forms via an electronic data capture system. Results: Forty-nine patients whose data were entered at 5 sites at the time of data cutoff (June 25, 2021) were included (mean age [SD]: 34.3 [12.91] years; 57.1% female; 85.7% HbSS and 6.1% HbSβ 0 genotype). Mean (SD) duration of voxelotor treatment was 48.1 (23.0) weeks. The initial prescribed voxelotor dose strengths (n, %) were 500 mg (4, 8.2%), 1000 mg (7, 14.3%), and 1500 mg (38, 77.6%). Rationale for prescription (n, %) included reduction of anemia (36, 73.5%), reduction in frequency of vaso-occlusive crises (23, 46.9%), reduction in pain (34, 69.4%), reduction in the need for blood transfusion (8, 16.3%) and other (5, 10.2%); more than 1 reason may have been selected. In 35 patients with recorded baseline and post-treatment Hb values, the peak observed post-treatment Hb (mean [SD]) was 9.4 (2.44) g/dL, an increase of 1.6 (1.5) g/dL from baseline (7.8 [2.02] g/dL). Fifty percent (11/22) of patients had a clinical response (Hb increase of >1.0 g/dL from baseline) within 12 months of voxelotor treatment. Per-patient peak changes in Hb during the study period showed that 62.9% of patients experienced a response at some time up to 12 months during treatment (Figure). Change in hemolytic markers was also evaluated. In patients with recorded baseline and post-treatment reticulocyte percentage (N=19) and indirect bilirubin (N=24), the mean (SD) absolute post-treatment value was 7.4% (4.65%) for reticulocyte percentage, a decrease of 4.9% (6.63%) compared with baseline (12.4% [8.32%]), and 1.9 (1.66) mg/dL for indirect bilirubin, a decrease of 17.7 (81.83) mg/dL compared with baseline (19.6 [81.82] mg/dL). The most common non-SCD-related treatment-emergent adverse events (AEs) were diarrhea, headache, and rash (Table); 19 (38.8%) patients reported ≥1 AE, and most non-SCD-related AEs were mild in severity. Conclusions: RETRO is the first multicenter, retrospective study to examine the real-world effectiveness of voxelotor and describe the observed changes in laboratory and clinical outcomes after ≥2 weeks of therapy. This study shows that voxelotor treatment was associated with increased Hb levels and decreased hemolytic markers. The safety data are consistent with those from the HOPE trial. Further evaluation is needed, with additional data from all 10 sites, and will be presented later. Funding: This study was supported by Global Blood Therapeutics. Figure 1 Figure 1. Disclosures Achebe: Fulcrum Therapeutics: Consultancy; Pharmacosmos: Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees. Clay: GBT: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria. Nero: Global Blood Therapeutics: Consultancy; Editas Medicine: Consultancy; bluebird bio: Consultancy; Novartis: Consultancy. Osunkwo: Terumo: Consultancy; Global Blood Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Acceleron: Consultancy; Forma Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Health and Services Administration: Research Funding; Patient Centered Outcomes Research Instituted: Research Funding; Micella Biopharma: Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Chiesi: Consultancy; Cyclerion: Consultancy; Emmaus: Consultancy. Idowu: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Ironwood: Research Funding; Forma Therapeutics, Inc.: Research Funding; Pfizer: Research Funding. Shah: Novartis: Research Funding, Speakers Bureau; Alexion: Speakers Bureau; Emmaus: Consultancy; GBT: Consultancy, Research Funding, Speakers Bureau; Guidepoint Global: Consultancy; CSL Behring: Consultancy; GLG: Consultancy; Bluebird Bio: Consultancy. Curtis: GBT: Consultancy. Minniti: Bluebird Bio: Other: Endpoint adjudicator ; F. Hoffmann-La Roche Ltd: Consultancy; Chiesi: Consultancy; Novo Nordisk: Consultancy; Forma: Consultancy; Novartis: Consultancy; GBT: Consultancy; CSL Behring: Other: Endpoint adjudicator .

Clonal mosaicism, detectable in peripheral blood, can be an important predictor of developing a hematological malignancy. We sought to determine if mosaic events, in addition to clinical and demographic variables, contributed independent information about acute lymphoblastic leukemia (ALL) patient survival and risk of relapse after allogeneic hematopoietic cell transplant (HCT). HumanOmniExpress-12v1_A BeadChip SNP array data were used to detect mosaicisms >=2Mb based on the log2 relative probe intensity ratio (LRR) and B allele frequency (BAF) for each SNP measured in 773 ALL patients from DISCOVeRY-BMT cohorts. DNA was extracted from recipient peripheral blood samples taken immediately prior to start of conditioning before allogeneic HCT for ALL (2000-2011). Mosaic events include copy-number gain (LRR >0), loss (LRR The impact of mosaicism on overall survival (OS) probability and cumulative incidence of relapse at 1-year post-HCT were calculated using the Kaplan-Meier estimator and cumulative incidence functions, respectively. The association of clonal mosaicism with OS was evaluated with multivariable Cox proportional hazard models. For disease relapse, competing risk models were used with transplant related mortality (TRM) treated as a competing event. Stratified survival analyses were performed by cytogenetic status at diagnosis. Statistical analyses were conducted using R 3.6.1. Thirty-four patients (4.4%) had 1 or more mosaicisms (82 total detected) with almost half having advanced disease (Table 1). The median proportion of affected cells was 61% (interquartile range = 39 - 93%). Copy-number losses on chromosomes 7 (13.4%) and 9 (8.54%) and 17 (6.10%) were the most frequently detected events (Figure 1). OS at 1-year post HCT in patients with and without a mosaic event was 26.5% and 60.1%, respectively, (P=8.2×10-8, Figure 2A) and normal cytogenetic patients with mosaicism had significantly lower survival compared to all other patients (OSnormal/mosaic+= 8.3% vs. OS= 60.6%, P=3.0×10-10, Figure 2B-C). ALL patients with a mosaic event also had an increased risk of disease relapse overall (Relapsemosaic+= 50% vs. Relapsemosaic-=26%, P=0.00067) and when stratified by cytogenetic abnormalities (P=0.015) and normal cytogenetics (P=0.041) (Figure 2D-F). Multivariable models of OS and relapse included age, race/ethnicity, complete remission or advanced disease status (Figure 3). Patients with a mosaic event had ~2.5 fold increase risk of death (P=2.5×10-5), independent from cytogenetics (P=8.6×10-5, Figure 3). OS associations are likely driven by the 2.8 fold increase risk of relapse (P= 5.9×10-5) which remains highly significant when stratified by cytogenetics (Figure 3). Almost half of the copy-number losses included well-known regions on chromosomes 7, 9 and 17 (Figure 1). Deletions of 7p have been shown to correlate with lower event-free survival in ALL pediatric patients. Our findings suggest mosaic loss of 7p might be an important indicator of poor OS across the lifespan, with 5/6 patients with 7p losses aged >18 years. Higher mortality was also associated with the loss of the chr9p21.3 locus, seen in all patients (N=5) with chromosome 9p losses. This region harbors tumor suppressor CDKN2A; inactivation of CDKN2A can lead to poor survival in both children and adults with ALL. Lastly, we found that all patients (N=4) with copy-number loss of 17p13.1, which contains tumor suppressor TP53 died within 1-year post-HCT. We identified detectable mosaicism prior to transplant in 4.4% of patients and showed that mosaicism was associated with lower survival and higher disease relapse at 1-year post-HCT. While mosaicism is more common in patients with advanced disease stage, mosaic events are an independent contributor to lower survival and higher relapse in the first year after transplant. This is the first study to show that mosaic events detectable in pre-transplant peripheral blood from ALL patients are correlated with poor survival. Future studies replicating these associations in different ethnicities and age groups and evaluating specific chromosomal regions could be informative in classifying patient risk post-HCT attributable to mosaic events. Disclosures McCarthy: Karyopharm: Consultancy, Honoraria; Magenta: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Genentech: Consultancy, Honoraria; Starton: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Juno Therapeutics, a Bristol-Myers Squibb Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board , Research Funding is to Roswell Park, Research Funding. Pasquini:Bristol Myers Squibb: Consultancy; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Other; Novartis: Research Funding; Kite: Research Funding. Lee:Pfizer: Consultancy, Research Funding; Novartis: Research Funding; Takeda: Research Funding; Amgen: Research Funding; Kadmon: Research Funding; Incyte: Consultancy, Research Funding; AstraZeneca: Research Funding; Syndax: Research Funding.

The first three authors contributed equally. The last three authors share senior authorship. Background: Although there has been an increased recognition of the contribution of germline variants to development of myeloid neoplasms, only two large-scale case-control genome-wide association studies (GWASs) have been conducted to identify variants that predispose to AML. Importantly, these studies were dedicated to AML predisposition in general, without investigation of molecularly distinct AML subtypes. Thus, we performed the first dedicated meta-analysis combining the two GWASs to investigate predisposing variants to cytogenetic AML subsets characterized by recurrent translocations and inversions. Methods: Two sets of adult de novo AML patients treated on Alliance for Clinical Trials in Oncology (Alliance) protocols, and two sets of adult de novo AML patients reported to CIBMTR (2000-11) from DISCOVeRY-BMT cohorts were compared with four sets of population-matched non-leukemic individuals of European ancestry. Illumina Infinium arrays were used for genotyping. The haplotype reference consortium was used for imputation and comparisons were performed using SNPtest and METAL with fixed-effects, for CBF-AML (n=251, including t(8;21), n=115; inv(16), n=136) and AML with 11q23/KMT2A translocations (n=177). Blood or bone marrow samples from subsets of these patients and additional AML patients with other cytogenetic abnormalities were used for total transcriptome RNA sequencing with Illumina instruments. Results: Two risk loci reached genome-wide significance in AML patients with 11q23/KMT2A translocations (Fig 1A). The most significant single nucleotide polymorphism (SNP) in the 4q21.3 risk locus, rs17668899[A] (P = 2.32 x 10-8, odds ratio [OR] = 3.92 [2.43-6.32]) is in intron 6 of the AFF1 gene (also called AF4) (Fig 1B), within an enhancer that interacts with the AFF1 transcription start site (Fig 1C, left). KMT2A-translocated AML patients with the risk allele had higher blast expression of AFF1 compared to those homozygous for the non-risk allele, although the trend did not reach significance (Fig 1D). Notably, AFF1 encodes a subunit of the super-elongation-complex (SEC) that acts as Pol II-associated master regulator of global transcription elongation. AFF1 is a common translocation partner of KMT2A in patients with acute lymphoblastic leukemia with t(4;11)(q21;q23), and is required for KMT2A-mediated leukemogenesis. We observed significantly higher AFF1 expression in both KMT2A-translocated AML and cytogenetically normal (CN) AML compared to CBF-AML (Fig 1E). The suggested role of AFF1/SEC is consistent with recent studies showing an important role for DOT1L, H3K79 methylation, and transcriptional elongation in NPM1-mutant AML (the most common subtype of CN-AML). Outcome analysis showed higher expression of AFF1 associated with shorter disease-free (DFS) in patients < 60 years treated on Alliance studies (hazard ratio [HR] = 1.36, P=0.04; Fig 1F). The second KMT2A-translocated AML risk locus was located at 22q13.31, and the most significant SNP was rs62231468[A] (P = 4.95 x 10-9, OR = 3.25). rs62231468 is immediately 5' of the LDOC1L gene (a retrotransposon GAG-related gene, also called RTL6), and analysis of expression quantitative trait loci (eQTL) showed association of rs62231468[A] with higher LDOC1L expression, consistent with its location in an active enhancer (Fig 1C, right). The association between rs62231468[A] and higher LDOC1L expression was validated in leukemic blast expression from a set of 449 AML patients of any cytogenetic subset (Fig 1G). Notably, higher LDOC1L expression was associated with shorter DFS and overall survival (OS) in Alliance patients < 60 years (DFS, HR = 1.25, P=0.03; OS, HR = 1.46, P Analysis of patients with CBF-AML identified rs71568004[C] as more common in CBF-AML patients compared to controls (P = 3.84 x 10-8 , OR = 3.05 [2.05-4.53]). This SNP is ~50kb 5' of the MARCKS gene located at 6q21, but genomic context analysis did not reveal any clear associations with MARCKS expression. Conclusions: Our first assessment of risk alleles for cytogenetic subsets of AML identified two novel independent risk loci associated with 11q23/KMT2A-translocated AML, and one risk locus associated with CBF-AML. These data suggest an important, subtype-specific role for transcriptional elongation in AML and that functional studies of retro transposition elements should be undertaken in leukemogenesis. Figure Disclosures Walker: Karyopharm: Current Employment, Current equity holder in publicly-traded company; Vigeo Therapeutics: Consultancy. Powell:Rafael Pharmaceuticals: Consultancy, Other: Advisor, Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Advisor, Research Funding; Genentech: Research Funding; Novartis: Research Funding; Pfizer: Research Funding. Kolitz:Pfizer: Membership on an entity's Board of Directors or advisory committees; Magellan: Membership on an entity's Board of Directors or advisory committees. Pasquini:Bristol Myers Squibb: Consultancy; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Other; Novartis: Research Funding; Kite: Research Funding. McCarthy:Karyopharm: Consultancy, Honoraria; Magenta: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Genentech: Consultancy, Honoraria; Starton: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Juno Therapeutics, a Bristol-Myers Squibb Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board , Research Funding is to Roswell Park, Research Funding. Stone:AbbVie: Consultancy, Research Funding; Actinium: Consultancy; Agios: Consultancy, Research Funding; Argenx: Consultancy, Other: Data and safety monitoring board; Arog: Research Funding; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Consultancy; Biolinerx: Consultancy; Celgene: Consultancy, Other: Data and safety monitoring board; Jazz: Consultancy; Novartis: Consultancy, Research Funding; Otsuka: Consultancy; Pfizer: Consultancy; Trovagene: Consultancy; Takeda: Consultancy; Daiichi-Sankyo: Consultancy; Elevate: Consultancy; Gemoab: Consultancy; Janssen: Consultancy; Macrogenics: Consultancy; Hoffman LaRoche: Consultancy; Stemline: Consultancy; Syndax: Consultancy; Syntrix: Consultancy; Syros: Consultancy. Byrd:Trillium: Research Funding; Novartis: Research Funding; Kartos Therapeutics: Research Funding; Syndax: Research Funding; Vincera: Research Funding; Acerta Pharma: Research Funding; Janssen: Consultancy; Leukemia and Lymphoma Society: Other; Pharmacyclics LLC, an AbbVie Company, Gilead, TG Therapeutics, BeiGene: Research Funding; Pharmacyclics LLC, an AbbVie Company, Janssen, Novartis, Gilead, TG Therapeutics: Other; Pharmacyclics LLC, an AbbVie Company, Gilead, TG Therapeutics, Novartis, Janssen: Speakers Bureau. Eisfeld:Karyopharm: Current Employment, Current equity holder in publicly-traded company; Vigeo Therapeutics: Consultancy.

Background: Sickle cell disease (SCD) comprises a group of inherited blood disorders, and is a complex, multi-system, disease. SCD is associated with a variety of clinical complications that affect multiple organ systems. These complications are driven primarily by vaso-occlusion and hemolytic anemia, and can result in end-organ damage and early death. Painful vaso-occlusive crises (VOCs) are a characteristic feature of SCD and can require healthcare intervention. Despite recent advances in the screening, management and treatment of SCD, gaps remain in our understanding of the disease in the real-world setting. These include how best to transition from pediatric to adult care and how to manage specific complications. Currently, most real-world evidence (RWE) is generated from information captured in payer databases, which is not as comprehensive as the information recorded in electronic medical records (EMRs). Despite being potentially valuable sources of real-world, clinical information, EMRs for individual patients in the USA are not centralized, often being held by multiple healthcare providers using different EMRs. This fragmented system prevents generation of clear, comprehensive RWE, both in general and for SCD specifically. Furthermore, there is a lack of harmonization between EMR companies/systems in the types of information included and how it's recorded. A separate approach that collates all available data from EMRs into a single, comprehensive record prior to RWE analysis would therefore greatly improve the accessibility of the available information and the quality of subsequent data analysis. Aims: In contrast to existing RWE, this study explores the value of collating EMRs for each patient into a single, consistently structured format, with the aim of developing richer RWE to complement existing data on SCD. It is hypothesized that the resulting longitudinal overview of each patient's care will contribute to an improved understanding of SCD in the real-world setting: firstly, by better capturing how many VOCs patients with SCD experience, with an indication of the proportion of VOCs that are being home-managed; secondly, by gaining deeper insights into the prevalence and progression of end-organ damage and any association with VOCs; and finally, by highlighting the type and site of care of SCD in the real world (eg medications, treating healthcare professional [HCP] specialties and the type of clinic visited). Study design: The study population will comprise 400 patients with SCD from the USA. Patient recruitment occurs directly via social media and indirectly through a variety of partnerships including HCPs and patient advocacy groups. To enroll, patients sign an informed consent form allowing their de-identified medical information to be shared with third-party organizations to advance SCD research. Enrolled patients gain access to their medical records via a dashboard. The key inclusion criteria are: a confirmed SCD diagnosis (irrespective of phenotype); aged ≥16 years at enrollment; and ≥1 inpatient admission for a VOC in the 12 months prior to enrollment. The key exclusion criterion is the absence of medical records. Components of EMRs collected include doctors' notes, laboratory and test results, clinical imaging and treatment records. Human-curated natural language processing and machine learning is used to extract, structure and code data from the structured sections and unstructured narrative text of the EMR. All medical records, from all visits, will be collected where possible and are expected to comprise ≥7 years of retrospective data for each patient. Results: Between 1 December 2019 and 24 June 2020, a total of 46 patients with a mean age of 36 years (SD 9.7) were enrolled. For each patient, a median of 6.8 years of data from a median of 32.5 providers were obtained. Conclusions: The evidence derived from this study aims to advance the understanding of real-world practices in the management of SCD. It may also provide further learnings regarding the prevalence of complications and any association between VOCs and end-organ damage. Generating a single, structured overview of all EMRs for each patient allows for richer insight generation and a more comprehensive analysis of RWE, compared with existing approaches. The insights gained from this RWE may inform future studies and clinical trials in SCD, with the ultimate aim of improving the quality of life of patients. Disclosures Clay: Novartis: Consultancy; GBT: Consultancy. Bailey:Novartis Pharmaceuticals Corporation: Current Employment. Drozd:F. Hoffmann-La Roche Ltd: Other: All authors received support for third party writing assistance, furnished by Scott Battle, PhD, provided by F. Hoffmann-La Roche, Basel, Switzerland.; PicnicHealth: Current Employment, Current equity holder in private company. Paulose:Novartis Pharma AG: Current Employment. Ramscar:Novartis Pharma AG: Current Employment. Mace:Roche/Genentech: Ended employment in the past 24 months; PicnicHealth: Current Employment. Wormser:Novartis Pharma AG: Current Employment, Current equity holder in publicly-traded company.