Initial Results from Study Hgb-206: A Phase 1 Study Evaluating Gene Therapy By Transplantation of Autologous CD34+ Stem Cells Transduced Ex Vivo with the Lentiglobin BB305 Lentiviral Vector in Subjects with Severe Sickle Cell Disease

Abstract Background: Hematopoietic stem cell (HSC) gene transfer has the potential to reduce or eliminate the symptoms of severe sickle cell disease (SCD). Previously reported early results in a single subject with severe SCD from the ongoing study HGB-205 suggested that transplantation with autologous CD34+ cells transduced with a replication-defective, self-inactivating LentiGlobin BB305 lentiviral vector containing an engineered βA-T87Q -globin gene (LentiGlobin BB305 Drug Product) is well-tolerated and yields robust production of anti-sickling HbAT87Q at 6 months post-transplant. Here we provide initial data on subjects with severe SCD enrolled in the multi-center HGB-206 Study. Subjects and Methods: Subjects with severe SCD undergo HSC collection via bone marrow harvest. CD34+ cells are selected and transduced with LentiGlobin BB305 lentiviral vector. Subjects undergo myeloablation with intravenous busulfan, followed by infusion of LentiGlobin BB305 transduced cells. Subjects are monitored for hematologic engraftment, vector copy number (VCN), βA-T87Q -globinexpression and adverse events. Integration site analysis (ISA) and replication-competent lentivirus (RCL) assays are also performed. Prophylactic pRBC transfusions are continued in subjects with SCD who are on chronic transfusion pre-transplant to maintain HbS <30%, followed by gradual taper over time. Results: As of 31 July 2015, LentiGlobin BB305 drug product has been manufactured for 2 subjects with severe SCD, and 1 subject has been infused. Additional subjects are undergoing screening. Patient data are presented in Table 1. To date, the safety profile is consistent with autologous transplantation, without ≥ Grade 3 LentiGlobin BB305 Drug Product related adverse events.Follow-up of the infused subject and available data on additional subjects who may have undergone drug product infusion in the coming months will be presented. Conclusions: LentiGlobin BB305 transduced cells have been manufactured for 2 subjects with severe SCD, and 1 subject has been infused with the drug product. LentiGlobin BB305 gene therapy is a promising approach to decrease the HbS levels in patients with severe sickle cell disease. Table 1.Preliminary dosing parameters and transplantation outcomesSubjectAge (years)/ Sex (M/F)GenotypeVCN in Drug ProductaCD34+ cell dose (x106/kg)Day of Neutrophil EngraftmentDrug Product- related Adverse EventsLast Study Visit (Months Post-infusion)206-113-130125/FβS/βS0.5/0.62.7NANAPending infusion206-114-130342/MβS/βS1.32.9Day +16None1MAs of 31 July 2015.F=female; M= Male for gender, and months post-infusion for visit; NA, not applicable; VCN, vector copy number;aIf more than one drug product was manufactured, the VCN of each drug product lot is presented. Disclosures Walters: ViaCord and AllCells, Inc: Other: Medical director. Thompson:bluebird bio, Inc.: Consultancy, Research Funding. Kwiatkowski:ISIS: Membership on an entity's Board of Directors or advisory committees; Shire Pharmaceuticals and Sideris Pharmaceuticals: Consultancy; Sideris Pharmaceuticals: Consultancy; Novartis: Research Funding. von Kalle:bluebird bio, Inc.: Consultancy. Leboulch:bluebird bio: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Sandler:bluebird bio, Inc.: Employment, Equity Ownership. Soni:bluebird bio, Inc.: Employment, Equity Ownership.

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Validation of BCL11A As Therapeutic Target in Sickle Cell Disease: Results from the Adult Cohort of a Pilot/Feasibility Gene Therapy Trial Inducing Sustained Expression of Fetal Hemoglobin Using Post-Transcriptional Gene Silencing

Blood ◽

10.1182/blood-2019-132745 ◽

2019 ◽

Vol 134 (Supplement_2) ◽

pp. LBA-5-LBA-5 ◽

Cited By ~ 8

Author(s):

Erica B. Esrick ◽

Maureen Achebe ◽

Myriam Armant ◽

Pablo Bartolucci ◽

Marioara Felicia Ciuculescu ◽

...

Keyword(s):

Gene Therapy ◽

Sickle Cell Disease ◽

Board Of Directors ◽

Research Funding ◽

Lentiviral Vector ◽

Cell Disease ◽

Advisory Committees ◽

Cd34 Cells ◽

F Cells ◽

Post Infusion

BCL11A regulates the fetal-adult hemoglobin switch by repressing expression at the gamma (γ)-globin locus (Sankaran et al., Science, 2008), and thus it represents an appealing therapeutic target for sickle cell disease (SCD). BCH-BB694 is a lentiviral vector (LVV) encoding a shRNA targeting BCL11A embedded in a microRNA scaffold (shmiR) allowing erythroid-specific knockdown to induce γ-globin expression and concomitantly and coordinately repress β-sickle globin expression (Brendel et al. JCI, 2016). In a pilot and feasibility gene therapy study we are evaluating the safety of infusion of BCH-BB694-transduced autologous CD34+ cells in patients with severe SCD. The study is an IND enabled and IRB approved open label, non-randomized, single center trial (NCT 03282656). We report here data from the full adult cohort which has completed enrollment with > 6 months of follow up in all patients. The adult cohort included three patients >/= 18 years old. Autologous CD34+ cells were collected by plerixafor mobilization and then transduced ex vivo with the BCH-BB694 shmiR lentiviral vector. Cell doses and vector copy number (VCN) are shown in the Table. After testing and release, gene modified cells were infused into subjects who had received busulfan conditioning. There were no Grade 3 or 4 AEs associated with mobilization, collection or infusion. All three adults (age 21-26 years old) demonstrated neutrophil engraftment on day +22 with adverse events consistent with busulfan conditioning. These patients are now 7, 9, and 17 months post infusion. One subject resumed red cell transfusions at 3 months due to pre-existing moyamoya using a pre-defined conservative trigger value of 40% sickle Hb in whole blood and will be detailed separately. There have been no adverse events related to the gene therapy product. VCN has been stable in bone marrow (BM) and peripheral blood (PB) in all cell lineages during the length of the study, with the latest time point studied at 15 months (BCL002) and ranged from 0.45-2.85 copies per cell in erythroid progenitor cells. BCL11A protein levels evaluated by immunoblot in subject BCL002 at 30 days (PB) and 6 months (BM) post-infusion showed highly effective and selective knockdown of BCL11A in erythroid progenitors with no reduction in BCL11A expression in B lymphoid cells. The number of HbF-containing cells (F cells) was assessed by flow cytometry and the kinetics of F cell production was remarkably similar in all subjects. The two untransfused subjects (BCL002 and BCL004) produced 70% F-cells in PB at 3 and 5 months, which has remained stable until the last point assayed (15 months and 7.5 months, respectively) (table). Calculated average HbF per F cell was >10pg in all subjects (table) and quantitative single cell HbF flow analysis showed the majority of F cells had >4pg F/cell, a level that is believed to prevent sickling under physiological oxygen saturation (Rakotoson et al., ASH 2017). In both untransfused subjects, total Hb remained stable with evidence of reduced hemolysis by reticulocyte count (slightly elevated) and LDH (normal in one subject, slightly elevated in the other). At the 3-month timepoint before re-starting transfusions, the subject with moyamoya (BCL003) had a pre-transfusion Hb of 11 g/dL with 76% of non-transfused cells containing on average 17pg F/F cell. For all subjects, we estimated the fraction of RBCs containing significant Hb sickle polymers and the amount of polymer in each sickled RBC at physiologic oxygen tension (where 50% of monomeric hemoglobin was oxygen saturated, or the P50) (Di Caprio et al. PNAS 2019, in press). The results for all 3 subjects in this adult cohort showed fewer RBCs with significant Hb polymer than two hydroxyurea-responsive treated comparators and significantly less Hb polymer per sickled RBC than a third highly responsive hydroxyurea-treated comparator. In conclusion, these data demonstrate successful and sustained engraftment in three adult patients treated with LVV-delivered shmiR technology targeting BCL11A. Early results suggest an acceptable safety profile, validation of BCL11A as effective target for HbF induction in humans with high numbers of F cells in circulation containing high levels of HbF per F cell, and mitigation of cellular pathology of SCD. Disclosures Achebe: Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pharmacosmos: Membership on an entity's Board of Directors or advisory committees; Fulcrum Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees. Bartolucci:Novartis: Membership on an entity's Board of Directors or advisory committees; AddMedica: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; HEMANEXT: 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; Agios: Membership on an entity's Board of Directors or advisory committees. Heeney:AstraZeneca: Research Funding; Micelle Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; Novartis: Consultancy, Research Funding; Ironwood / Cyclerion: Research Funding; Vertex / Crisper Therapeutics: Other: Data Safety Monitoring Board. Higgins:Sanofi: Consultancy, Research Funding. Nikiforow:Kite/Gilead: Honoraria; Novartis: Honoraria; NKarta: Honoraria. Wood:Sanofi: Consultancy, Research Funding. Williams:Alerion Biosciences: Other: Co-founder; Novartis: Membership on an entity's Board of Directors or advisory committees; Orchard Therapeutics: Membership on an entity's Board of Directors or advisory committees, Other: Co-founder, Patents & Royalties: Potential for future royalty/milestone income, X-SCID., Research Funding; bluebird bio: Patents & Royalties: Licensed certain IP relevant to hemoglobinopathies to bluebird bio. Received payment in the past bluebird bio through a BCH institutional licensing agreement and there is a potential for future royalty/milestone income from this agreement., Research Funding.

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Successful Plerixafor-Mediated Mobilization, Apheresis, and Lentiviral Vector Transduction of Hematopoietic Stem Cells in Patients with Severe Sickle Cell Disease

Blood ◽

10.1182/blood.v130.suppl_1.990.990 ◽

2017 ◽

Vol 130 (Suppl_1) ◽

pp. 990-990

Author(s):

John F Tisdale ◽

Francis J. Pierciey ◽

Rammurti Kamble ◽

Julie Kanter ◽

Lakshmanan Krishnamurti ◽

...

Keyword(s):

Sickle Cell Disease ◽

Board Of Directors ◽

Sickle Cell ◽

Research Funding ◽

Ex Vivo ◽

Cell Disease ◽

Employment Equity ◽

Advisory Committees ◽

Cd34 Cells ◽

Equity Ownership

Abstract Background Patients with severe sickle cell disease (SCD) may benefit from β-globin gene transfer into autologous hematopoietic stem cells (HSC). Successful HBB gene transfer requires vector-mediated transduction of primitive HSCs. Steady-state bone marrow (BM) is the default HSC source in patients with SCD. Normal human BM contains up to 30% CD34+CD19+ pro-B cells and other lineage-committed cell types (CD34dim) that will not contribute to improved long-term erythropoiesis via gene therapy; these cells mobilize at low rates. CD34+ cell yields from BM harvest (BMH) are typically lower than those after mobilization and peripheral blood (PB) apheresis; multiple rounds of BMH may be required to obtain adequate cell doses for autologous gene therapy (GT) protocols. As G-CSF can cause life-threatening SCD complications and is contraindicated, plerixafor, a CXCR4 receptor antagonist, may accomplish HSC mobilization without the neutrophil or endothelial activation that elicit vaso-occlusion. We modified the protocol for the HGB-206 phase 1 study of LentiGlobin GT in severe SCD (NCT02140554) to assess HSC mobilization with plerixafor alone, followed by apheresis and transduction of mobilized cells. We also characterized BM-derived and plerixafor-mobilized HSC populations from patients with SCD. Methods HGB-206 is a phase 1 study of LentiGlobin Drug Product (DP), which contains autologous HSCs transduced ex vivo with the betibeglogene darolentivec (BB305) lentiviral vector, in patients with severe SCD (defined as a history of recurrent vaso-occlusive crisis [VOC], acute chest syndrome, stroke, or tricuspid regurgitant jet velocity of >2.5 m/s). Patients in group B receive 240 µg/kg plerixafor followed 4-6 hours later by apheresis, processing ~3 total blood volumes to collect backup HSCs. If < 1.5 x 106 CD34+ cells are collected, patients undergo a second day of apheresis. Cells collected in excess of those required for backup in case of graft failure are transduced with BB305 lentiviral vector for exploratory analyses. Group B patients then proceed to BMH to obtain cells for clinical DP manufacture. Group C will receive DP manufactured from mobilized PB. Mass cytometry (CyTOF) was used to analyze ex vivo cultured CD34+ cells with over 35 cell surface markers. Results To date, 3 patients have undergone plerixafor mobilization. Patients had a transient 1.5- to 3-fold increase in peak white blood cell and absolute neutrophil levels after plerixafor. Peak absolute CD34+ cell counts in PB were 170, 58, and 160 x 106 CD34+ cells/liter. A total of 15.3, 5.6, and 9.0 x 106 CD34+ cells/kg were collected in a single day of apheresis, and no subsequent apheresis or mobilization was required. In the same study, a mean of 5.0 (range 0.3-10.8) x 106 CD34+ cells/kg were collected per BMH (N=21). The mobilization and apheresis procedures had an acceptable toxicity profile. No dose-limiting toxicities were observed after plerixafor dosing. One patient had a single VOC approximately 48 hours after receiving plerixafor; this patient also experienced VOCs of similar severity after BMH. In contrast, after 21 BMHs in 9 patients, 18 ≥ grade 3 AEs were reported in 6 patients, primarily pain. Ex vivo cultured CD34+ cells isolated from BMH consisted of an average of 41.0% (17.3%-50.7%) CD34dim cells, with 16%-50% of the CD34dim cells expressing lymphoid markers. In contrast, ex vivo cultured CD34+ cells isolated from plerixafor mobilized PB contained an average of 8.2% (1.5-19.5%) CD34dim cells. Similar drug product vector copy numbers were obtained after research-scale transduction of CD34+ cells from marrow and PB from the same patient. Conclusion Initial results suggest that obtaining adequate doses of CD34+ cells from plerixafor-mobilized PB of patients with SCD may be safe and feasible, without the life-threatening complications associated with G-CSF, and with fewer, less invasive procedures compared with BMH. PB-derived CD34+ cells may contain lower proportions of lineage-committed CD34+ cells than BM-derived cells from patients with SCD. Cells collected by BMH and PB mobilization/apheresis appear to have an equivalent transduction efficiency. Together these results indicate that it may be possible to use plerixafor-only mobilization in clinical studies of autologous HSC GT in SCD. Results of mobilization, apheresis, and DP manufacturing at clinical scale for additional patients will be available for presentation. Disclosures Pierciey: bluebird bio: Employment. Kanter: American Society of Hematology (Sickle Cell Disease Guideline Panel): Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; MUSC: Other: The site PI for sponsored research conducted at MUSC who receives funds from: Novartis, bluebird bio, GBT, Sancillo, Apopharma, Pfizer; NHLBI (sickle cell disease research advisory committee): Membership on an entity's Board of Directors or advisory committees, Research Funding; Sancillo: Research Funding; Apopharma: Research Funding; Pfizer: Research Funding; GBT: Research Funding; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees, Research Funding. Kwiatkowski: Novartis: Research Funding; Bluebird Bio: Research Funding; Apopharma: Research Funding; Agios: Consultancy, Honoraria; Ionis: Consultancy, Honoraria. Thompson: Novartis: Consultancy, Research Funding; bluebird bio: Consultancy, Research Funding; Baxalta: Research Funding; Celgene: Consultancy, Research Funding. Shestopalov: bluebird bio: Employment, Equity Ownership. Bonner: bluebird bio: Employment, Equity Ownership. Joseney-Antoine: bluebird bio: Employment, Equity Ownership. Asmal: bluebird bio: Employment, Equity Ownership. Walters: bluebird bio: Research Funding; ViaCord Processing Lab: Other: Medical Director; Sangamo Therapeutics: Consultancy; AllCells, Inc: Other: Medical Director.

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Edx-17: A Novel, Safe and Efficacious Treatment for Sickle Cell Disease

Blood ◽

10.1182/blood.v124.21.1357.1357 ◽

2014 ◽

Vol 124 (21) ◽

pp. 1357-1357

Author(s):

Robert H. Broyles ◽

Sunil K. Joshi ◽

Carol D. Curtis ◽

Austin C. Roth ◽

Patrick A. Floyd ◽

...

Keyword(s):

Sickle Cell Disease ◽

Board Of Directors ◽

Sickle Cell ◽

Research Funding ◽

Cell Disease ◽

Employment Equity ◽

Advisory Committees ◽

Erythroid Precursor ◽

Gamma Globin ◽

Equity Ownership

Abstract Gene regulation of developmental hemoglobin switching holds the potential for therapeutic relief from all symptoms associated with Sickle Cell Disease (SCD). Reactivation of fetal gamma-globin expression (HbF) can replace mutant betaS-globin (HbS) to produce functional hemoglobin tetramers and eliminate the hemoglobin polymerization that is characteristic of sickled red blood cells. We have discovered a protein that regulates this developmental switch, and have identified a compound that stimulates expression of this protein. EdX-17 promotes expression of the anti-stress factor ferritin heavy chain (FtH), which enters the nucleus of erythroid precursor cells and activates expression of fetal gamma-globin, producing HbF (PNAS 98:9145-50, 2001; Blood 108:790a, 2006). Mononuclear cells were isolated from SCD patient blood and matured in vitro to the advanced erythroblast stage using a 28-day, 2-phase culture system (Methods in Molecular Biology 482:127-40, 2009; Blood 119:6296-306, 2012). Treatment with EdX-17 for 24h resulted in a dose-responsive induction of gamma-globin gene expression and a concomitant dose-responsive increase in HbF was observed after 28 days in culture. These studies demonstrate that EdX-17 doses in the picomolar range are sufficient to significantly enhance HbF. Furthermore, EdX-17 treatment reconstitutes fetal hemoglobin (HbF) in transgenic betaYAC mice to levels above 25-30% - the range thought to be sufficient to ameliorate symptoms of SCD – with no detectable ill effects. In fact, mice treated with EdX-17 tend to have shinier coats, are more alert and stronger than age-matched, untreated mice. Development of this novel therapeutic is expected to ameliorate SCD symptoms, decrease pain and morbidity, increase life-span, greatly improve patient quality of life, and significantly reduce treatment costs. Supported in part by The Sickle Cell Cure Foundation, Inc., the Bill & Melinda Gates Foundation, and EpimedX, LLC. Disclosures Broyles: EpimedX, LLC: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding. Curtis:EpimedX, LLC: Employment, Equity Ownership, Research Funding. Roth:EpimedX, LLC: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding. Floyd:EpimedX, LLC: Employment, Equity Ownership, Research Funding. Belegu:EpimedX, LLC: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding. Floyd:EpimedX, LLC: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding.

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Chronic Kidney Disease Is Under-Screened in SCD and Mild Albuminuria Is Associated with a Drop in Hemoglobin: A Report from the Grndad Sickle Cell Registry

Blood ◽

10.1182/blood-2019-124933 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 2284-2284

Author(s):

Elizabeth Williams ◽

Elizabeth Brown ◽

Deepa Manwani ◽

Payal Desai ◽

Joshua J. Field ◽

...

Keyword(s):

Chronic Kidney Disease ◽

Sickle Cell Disease ◽

Kidney Disease ◽

Board Of Directors ◽

Sickle Cell ◽

Research Funding ◽

Cell Disease ◽

Employment Equity ◽

Advisory Committees ◽

Equity Ownership

The Globin Research Network for Data and Discovery (GRNDaD) is a combined effort, from 6 US clinical sites (Baltimore, Cleveland, Columbus OH, Milwaukee, Oakland, and The Bronx) that care for people with sickle cell disease (SCD), to improve care through shared data collection and review and quality improvement. Using a single IRB-Reliant protocol, we have assembled harmonized baseline and annual data on 758 adults with sickle cell disease (41.7% male and 58.3% female, mean age 35.5), collected on a REDCap server housed at Johns Hopkins. For this study, we reviewed adherence to the 2014 NHLBI Guidelines on the management of SCD -- which recommends annual screening for chronic kidney disease (CKD) by testing for albuminuria or proteinuria in anyone over the age of 10 with sickle cell disease. To evaluate whether subjects had an annual visit in any given year we used the recording of a well visit hemoglobin. Of the 758 adults in the study 411 had at least one year of follow up data marked as completed. Among these 411 adults there were 826 distinct observations. Of these 826 observations, 137 observations among 85 subjects did not have any hemoglobin lab drawn, suggesting that they did not have a well outpatient visit during that year. Amongst the observation years, where a well hemoglobin was performed, yearly screening for albuminuria occurred in 37.4% (258/689) of annual observations. There was an association between having screening for CKD and site of care (p<.0001), with some sites having adhered to guidelines in 34.2% of observation years and others having adhered 75.9% of years. There was no association between adherence and genotype or sex. Albuminuria was associated with a clinical phenotype. A multi-variable linear mixed effects model controlling for age and gender with a randomly varying intercept based on the subject, excluding chronically transfused subjects, and stratified by sickle cell anemia (HbSS or HbSB0, SCA) or variant genotypes was used. There was a significant association in those with SCA between the presence of albuminuria between 30 and 300, level (A2) and hemoglobin. Hemoglobin levels were, on average, 0.79 g/dL lower in those with albuminuria between 30-300 when compared to those with no albuminuria (A1, P=0.005). For those with SCA and albuminuria greater than 300 (A3), the sample size was small (n=28) and hemoglobin levels were 0.61 g/dl lower compared to those without albuminuria but this was not statistically significant (p=0.12). For those with variant compound heterozygous SCD and A2 albuminuria, hemoglobin levels were not statistically significantly different from those without albuminuria. However, high-grade albuminuria (A3) was associated with hemoglobin levels which were, on average, 1.86 g/dL lower than those in group A1 (P=0.004). Interestingly, the association between reduced hemoglobin and albuminuria was seen in both variant and SCA genotypes in the context of a preserved creatinine (<1.0 mg/dL). Using a multisite registry we demonstrate the need to develop strategies to assist providers and patients with adherence to guideline based recommendations for routine screening for chronic kidney disease in adults with SCD. The early association of albuminuria with worsening anemia, even in the absence of elevated creatinine levels, suggests an added urgency to screening. The causality of the association remains unclear but emphasizes the need for longitudinally followed cohorts that might help us understand the relationship between anemia and the development of CKD. Figure Disclosures Manwani: Novartis: Consultancy; Pfizer: Consultancy; GBT: Consultancy, Research Funding. Desai:Novartis: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; University of Pittsburgh: Research Funding; Ironwood: Other: Adjudication Board; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Potomac: Speakers Bureau. Field:Ironwood: Consultancy, Research Funding; Rigel: Research Funding; Prolong: Research Funding; Incyte: Research Funding. Neumayr:La Jolla Pharmaceuticals: Research Funding; Pfizer: Consultancy, Research Funding; Bayer: Consultancy; CTD Holdings: Consultancy; CDC: Research Funding; Celgene: Research Funding; Imara: Research Funding; NHLBI: Research Funding; Sangamo: Research Funding; HRSA: Research Funding; GBT: Research Funding; Emmaus: Consultancy; Apopharma: Consultancy; Sancillo: Research Funding; Novartis: Research Funding; Bluebird Bio: Research Funding; Silarus: Research Funding; Terumo: Research Funding; PCORI: Research Funding; Doris Duke Foundation: Research Funding; Seattle Children's Research Grants: Research Funding. Clay:Novartis: Speakers Bureau. Cong:Global Blood Therapeutics: Employment, Equity Ownership. Agodoa:Global Blood Therapeutics: Employment, Equity Ownership. Hoppe:Global Blood Therapeutics: Employment, Equity Ownership. Lanzkron:PCORI: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Research Funding; Ironwood: Research Funding; HRSA: Research Funding; NIH: Research Funding. Little:Hemex Health, Inc.: Patents & Royalties; GBT: Research Funding.

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Clinical and Biomarker Predictors for Avascular Necrosis in Sickle Cell Disease

Blood ◽

10.1182/blood-2021-147829 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 3091-3091

Author(s):

Michael Rabaza ◽

Maria Armila Ruiz ◽

Liana Posch ◽

Faiz Ahmed Hussain ◽

Franklin Njoku ◽

...

Keyword(s):

Risk Factors ◽

Sickle Cell Disease ◽

Board Of Directors ◽

Avascular Necrosis ◽

Sickle Cell ◽

Research Funding ◽

Medical Attention ◽

Cell Disease ◽

Advisory Committees ◽

Early Management

Abstract Introduction Sickle cell disease (SCD) affects 1 in 365 African Americans and approximately 25 million people world-wide. A common skeletal system complication is avascular necrosis (AVN), which can cause substantial pain and a reduced quality of life. While early management of AVN is focused on increasing range of motion with physical therapy and pain relief, there are no clear predictors for who is more likely to develop AVN and earlier institution of these preventive measure could help decrease disease progression. Vascular endothelial growth factor (VEGF) is a biomarker of endothelial injury and may indicate reduced vascular supply to the femoral or humeral head. Here we describe potential risk factors and biologic pathways for AVN in SCD, as understanding these may lead to improvements in future monitoring, early detection, and early intervention practices. Methods We investigated clinical and laboratory risk factors associated with AVN in a cohort of 435 SCD patients from our center. Blood samples, clinical, and laboratory data were collected at the time of enrollment during a clinic visit. Genotyping for alpha thalassemia was performed by PCR and the serum concentration of VEGF was measured by ELISA. AVN status was confirmed by review of the medical record and available imaging. We conducted a cross-sectional analysis comparing categorical and linear variables by AVN status using the chi-square and Kruskal-Wallis test, respectively. The independent association of the clinical and laboratory variables with AVN status was determined by logistic regression analysis. The initial model included variables with a P-value < 0.1 on univariate analysis and the final model was ascertained by stepwise forward and backward selection. Median values and interquartile range (IQR) are provided. Results The median age of the cohort was 32 (IQR, 24 - 43) years, 57% (250/435) were female, and 46% (198/435) were on hydroxyurea. AVN was observed in 34% (149/435) of SCD patients. SCD patients with AVN were older, had more frequent vaso-occlusive crises requiring medical attention, and had a higher body mass index (Table I) (P ≤ 0.002). We measured VEGF in 241 of the SCD patients with serum samples available at the time of enrolment. Serum VEGF concentrations trended higher in SCD patients with versus without AVN (420 vs. 359 pg/mL, respectively; P = 0.078). In the multivariate analysis model, AVN was independently associated with increased number of vaso-occlusive crises (OR 1.1, 95% CI: 1.0 - 1.14; P = 0.02), AST concentration (natural log OR 0.5, 95% CI: 0.2 - 0.9; P = 0.03), VEGF concentration (natural log OR 1.4, 95% CI: 1.0 - 1.9; P = 0.047), and tobacco use (OR 1.9, 95% CI: 0.9 - 3.7; P = 0.078). Discussion In conclusion, we demonstrate a high prevalence of AVN in an adult cohort of SCD patients. The presence of AVN was independently associated with a greater frequency of vaso-occlusive pain episodes, which may demonstrate a shared pathophysiology between AVN and vaso-occlusion that merits further investigation. We demonstrate that serum VEGF concentrations are higher in SCD patients with AVN and may be a clinical tool to identify those at high-risk and for earlier intervention for this complication. Figure 1 Figure 1. Disclosures Gordeuk: Modus Therapeutics: Consultancy; Novartis: Research Funding; Incyte: Research Funding; Emmaus: Consultancy, Research Funding; Global Blood Therapeutics: Consultancy, Research Funding; CSL Behring: Consultancy. Saraf: Pfizer: Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding.

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A Phase 1 Study of Prasugrel in Subjects with Sickle Cell Disease: Effects on In Vivo Markers of Platelet Activation and of Coagulation

Blood ◽

10.1182/blood.v118.21.1049.1049 ◽

2011 ◽

Vol 118 (21) ◽

pp. 1049-1049

Author(s):

Joseph A. Jakubowski ◽

Chunmei Zhou ◽

David S. Small ◽

Kenneth J. Winters ◽

D. Richard Lachno ◽

...

Keyword(s):

Sickle Cell Disease ◽

Platelet Activation ◽

Sickle Cell ◽

Research Funding ◽

Blood Platelet ◽

Cell Disease ◽

Employment Equity ◽

Equity Ownership ◽

Adp Receptor

Abstract Abstract 1049 Introduction: Evidence suggests that platelets are activated in sickle cell disease (SCD) and this appears to increase further during painful crises caused by vascular occlusions from sickled red blood cells. Antiplatelet therapy may be useful in reducing the frequency and severity of acute pain episodes and reducing the risk of thrombotic complications. Prasugrel, an ADP receptor antagonist, irreversibly inhibits the P2Y12 ADP receptor, blocking ADP-stimulated platelet activation and aggregation and reducing downstream procoagulant activities. Here we present the first evaluation of prasugrel's effects on markers of in vivo platelet activation and of coagulation in subjects with SCD. Methods: Twenty-six adult subjects were enrolled and 25 completed the study: 12 with SCD and 13 well-matched healthy controls. Subjects were examined before and after 12±2 days of treatment with oral prasugrel (5.0 mg/day for subjects weighing <60 kg and 7.5 mg/day for subjects weighing ≥60 kg). Markers of platelet activation and coagulation included whole-blood platelet-monocyte and -neutrophil aggregates, and whole blood platelet-associated P-selectin and platelet CD40L, all measured by flow cytometry and presented as percent (%) of marker positive cells. Plasma soluble (s) P-selectin, CD40L, and plasma prothrombin fragment 1.2 (F1.2) were evaluated by ELISA. Results: Results from the biomarkers are presented in the table. Prior to prasugrel administration (baseline), subjects with SCD had significantly higher levels of the following biomarkers compared to healthy subjects: Platelet-monocyte aggregates, platelet-neutrophil aggregates, platelet CD40L, and plasma F1.2. In addition, subjects with SCD had numerically higher values of sCD40L, as well as platelet-associated and sP-selectin. Prasugrel treatment resulted in numerical decreases in levels of all biomarkers (with the exception of platelet-associated CD40L for control subjects), most notably in SCD subjects with elevated baseline levels. Prasugrel was safe and well tolerated with no serious adverse events observed during the study. No subject discontinued the study due to an adverse event (AE) and the majority of AEs were mild. No subjects with SCD reported any bleeding-related AEs. Conclusion: In this study, compared to healthy controls, baseline elevation of several platelet-activation and coagulation markers among adult subjects with SCD is consistent with that seen in previous studies of both children and adults with SCD. The decrease in platelet activation biomarkers following 12 days of prasugrel treatment in subjects with SCD suggests prasugrel interrupts SCD-related platelet activation in vivo and raises the possibility that prasugrel may modulate the frequency and/or severity of painful crises associated with SCD. These data support additional studies of the safety and efficacy of prasugrel in the treatment of vascular complications associated with SCD. Disclosures: Jakubowski: Eli Lilly and Company: Employment, Equity Ownership. Off Label Use: This abstract discusses prasugrel treatment in patients with sickle cell disease. Please see USPI for most up-to-date information. Zhou:Eli Lilly and Company: Employment, Equity Ownership. Small:Eli Lilly and Company: Employment, Equity Ownership. Winters:Eli Lilly and Company: Employment, Equity Ownership. Lachno:Eli Lilly and Company: Employment, Equity Ownership. Frelinger:Takeda: Research Funding; Daiichi Sankyo Company, Ltd. and Eli Lilly and Company: Consultancy, Research Funding; GLSynthesis: Research Funding. Howard:Daiichi Sankyo Company, Ltd. and Eli Lilly and Company: Research Funding. Payne:Eli Lilly and Compnay: Employment, Equity Ownership.

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Sex Based Differences in Sickle Cell Disease

Blood ◽

10.1182/blood-2020-140896 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 37-37

Author(s):

Rita V Masese ◽

Dominique Bulgin ◽

Mitchell Knisely ◽

Liliana Preiss ◽

Eleanor Stevenson ◽

...

Keyword(s):

Sickle Cell Disease ◽

Board Of Directors ◽

Sickle Cell ◽

Research Funding ◽

Categorical Variables ◽

Continuous Variables ◽

Cell Disease ◽

Advisory Committees ◽

Blood Institute ◽

National Heart Lung

Introduction Sickle cell disease (SCD) is the most common inherited blood disorders in the United States. The disease predominantly affects African Americans with 1 out of every 365 individuals born with SCD. The disease is characterized by vascular inflammation and vaso-occlusion leading to numerous complications and multi-organ dysfunction. Previous studies have shown women with SCD tend to outlive their male counterparts. Other than the increased life expectancy, sex-based clinical outcome differences in SCD remain largely unknown. To better characterize sex-based differences in SCD, we assessed sociodemographic characteristics, pain, treatment characteristics, laboratory measures and complications among males and females currently enrolled in the Sickle Cell Disease Implementation Consortium (SCDIC) registry. Methods The SCDIC consists of eight academic and comprehensive SCD centers, and one data-coordinating center that received funding from the National Heart Lung and Blood Institute to improve outcomes for individuals with SCD. Participants were eligible for the enrollment in the SCDIC registry if they were 15 to 45 years of age and had a confirmed diagnosis of SCD. Participants were excluded if they had sickle cell trait or had a successful bone marrow transplant. Enrolled participants completed surveys. Data were also abstracted from the participants' medical records. Data were entered into a REDCap database and analyzed using SAS version 9.4 (SAS Institute; Cary, NC). Categorical variables were presented as frequencies and percentages, continuous variables were presented as medians and interquartile ranges (IQR) or means and standard deviations. Categorical variables were analyzed using Chi-Square or Fisher exact tests when appropriate. Continuous variables were compared using the Mann-Whitney U test or independent sample t-tests depending on the distribution. A two-sided p-value less than 0.05 was deemed significant. Results A total of 2,124 participants were included in the study. The mean (SD) age of our participants was 27.8 (7.9) years. Almost all (95.6%) were Africa American, female (56%) and had hemoglobin SS (68.2%) SCD genotype. More males (55.4 % vs. 44.6%, p <0.0001) were taking hydroxyurea. Females had significantly worse reports of pain frequency and severity (p=0.0002 and <0.0001 respectively), more vaso-occlusive episodes (p=0.01) and a higher occurrence of 3 or more hospital admissions in the past year (30.9 % vs. 25.5, p= 0.03). Males had significantly more skin ulcers and respiratory, musculoskeletal, genitourinary and cardiovascular complications while females had more anxiety, depression and autoimmune conditions. Males also had significantly higher creatinine, blood urea nitrogen, albumin and liver enzymes (alkaline phosphatase, aspartate and alanine aminotransferases). Females had higher fetal hemoglobin levels with and without hydroxyurea use. There were no statistical differences in ethnicity, marital and employment status. Conclusion Key differences in SCD presentation and occurrence of complications exist among males and females. Females had higher rates of depression and anxiety while males had more chronic end-organ complications that are life threatening. Our findings emphasize the need for stratification of data analysis by sex in future SCD studies. Disclosures Hankins: Global Blood Therapeutics: Consultancy, Research Funding; National Heart, Lung, and Blood Institute: Honoraria, Research Funding; LINKS Incorporate Foundation: Research Funding; American Society of Pediatric Hematology/Oncology: Honoraria; MJH Life Sciences: Consultancy, Patents & Royalties; UptoDate: Consultancy; Novartis: Research Funding. Treadwell:UpToDate: Honoraria; Global Blood Therapeutics: Consultancy. King:Tioma Therapuetics: Consultancy; WUGEN: Current equity holder in private company; RiverVest: Consultancy; Celgene: Consultancy; Cell Works: Consultancy; Incyte: Consultancy; Magenta Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bioline: Consultancy; Novimmune: Research Funding; Amphivena Therapeutics: Research Funding. Gordeuk:CSL Behring: Consultancy, Research Funding; Global Blood Therapeutics: Consultancy, Research Funding; Imara: Research Funding; Ironwood: Research Funding; Novartis: Consultancy. Kanter:bluebird bio, inc: Consultancy, Honoraria; SCDAA Medical and Research Advisory Board: Membership on an entity's Board of Directors or advisory committees; AGIOS: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Sanofi: Consultancy; Medscape: Honoraria; Guidepoint Global: Honoraria; GLG: Honoraria; Jeffries: Honoraria; Cowen: Honoraria; Wells Fargo: Honoraria; NHLBI Sickle Cell Advisory Board: Membership on an entity's Board of Directors or advisory committees; BEAM: Membership on an entity's Board of Directors or advisory committees. Glassberg:Eli Lilly and Company: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Consultancy. Shah:Bluebird Bio: Consultancy; Novartis: Consultancy, Research Funding, Speakers Bureau; Global Blood Therapeutics: Consultancy, Research Funding, Speakers Bureau; CSL Behring: Consultancy; Alexion: Speakers Bureau.

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Use of Thromboprophylaxis for Central Venous Access Devices in Patients with Sickle Cell Disease: A Survey of Canadian Providers

Blood ◽

10.1182/blood-2021-145889 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 4173-4173

Author(s):

Kristine Matusiak ◽

Stephanie Forte ◽

Jameel Abdulrehman ◽

Madeleine Verhovsek ◽

Kevin H.M. Kuo

Keyword(s):

Sickle Cell Disease ◽

Sickle Cell ◽

Research Funding ◽

Central Venous Access ◽

Venous Access ◽

Cell Disease ◽

Central Venous ◽

Advisory Committees ◽

History Of

Abstract Background: Sickle cell disease (SCD) induces a chronic prothrombotic state, with a cumulative incidence of venous thromboembolism (VTE) reported to be 11% by age 40. Central venous access devices (CVAD) are commonly used for chronic transfusions and iron chelation in this patient population.The presence of a CVAD is an additional risk factor for venous thromboembolism (VTE), with a catheter related thrombosis rate of 24%. Despite this high risk of VTE, the role of thromboprophylaxis in this setting is uncertain due to a lack of high quality data. Methods: A survey was administered in March 2021 to physicians caring for adult sickle cell disease patients via the Canadian Haemoglobinopathy Association (CanHaem), covering nine SCD comprehensive care centers in Canada. One reminder email was distributed after 3 weeks to encourage participation. Questions were directed at characterizing the practice size, number of patients with CVADs, and the role of thromboprophylaxis for CVADs. Physicians were also surveyed about their willingness to enroll their SCD patients with CVADs in a randomized trial of thromboprophylaxis versus placebo. Items were generated and selected based on face and content validity. Results are reported in medians and percentages, where applicable. Results: Responses were collected from 14 physicians who care for a median of 100 (IQR 185) adult sickle cell disease patients in practices across Canada. Physicians reported approximately 5% of their patients currently require a CVAD, and physicians estimated no CVAD patients are lost to follow up. Respondents use a variety of CVADs, including port-a-caths (75%), followed by PICC lines (58%), tunneled (25%) and non-tunneled CVCs (25%) (Figure 1). Duration of venous access was reported to be <1 month (17%), 1-3 months (8%), 3-6 months (0%), 6-12 months (8%), and >12 months (67%). Fifty percent of respondents indicated they do not use thromboprophylaxis for CVADs. Responses varied with respect to choice and dose of antiplatelet or anticoagulant in cases where thromboprophylaxis is used (Figure 2). Forty-two percent of physicians indicated they were not very confident or not at all confident in choice of prophylaxis. Past history of VTE was the most cited factor influencing the choice to use thromboprophylaxis. Physicians were generally in favour of enrolling patients in an RCT using thromboprophylaxis for CVADs. The exception was that 69% answered "No" when asked about enrolling patients with a prior history of VTE who are not currently on anticoagulation. One-hundred percent of physicians agreed that an RCT would improve their confidence in decision-making around thromboprophylaxis in their patients with CVADs. Conclusions: While there is evidence for an increased risk of VTE for SCD patients with CVADs, our results suggest there remains clinical equipoise with respect to the use of thromboprophylaxis. Thromboprophylaxis options were variable when physicians chose to use them, as there is no evidence to support specific antithrombotic regimens. All physicians surveyed are supportive of an RCT to clarify this management approach, and many would enroll their patients. As a result of this survey, a Canadian multicenter pilot RCT addressing this question is currently underway. Figure 1 Figure 1. Disclosures Forte: Pfizer: Research Funding; Canadian Hematology Society: Research Funding; Novartis: Honoraria. Verhovsek: Vertex: Consultancy. Kuo: Alexion: Consultancy, Honoraria; Celgene: Consultancy; Bluebird Bio: Consultancy; Bioverativ: Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Research Funding; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria; Apellis: Consultancy. OffLabel Disclosure: This survey explored the use of LMWH, direct oral anticoagulants, warfarin and ASA for prophylaxis among patients with sickle cell disease using a central venous access device.

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Sickle-Cell Disease Patients' Attitudes Towards Their Treatment with Hydroxycarbamide

Blood ◽

10.1182/blood-2019-125673 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1013-1013

Author(s):

Frédéric Galactéros ◽

Ersi Voskaridou ◽

Anoosha Habibi ◽

Giovanna Cannas ◽

Laure Joseph ◽

...

Keyword(s):

Sickle Cell Disease ◽

Board Of Directors ◽

Sickle Cell ◽

Research Funding ◽

Fetal Hemoglobin ◽

Treatment Discontinuation ◽

Cell Disease ◽

Advisory Committees

Hydroxyurea (HU) is approved in the EU and USA for prevention of vaso-occlusive crises (VOC) including acute chest syndromes (ACS) in patients over 2 years with sickle-cell disease (SCD). The major benefits of HU in SCD are directly related to its abilities to increase HbF, decrease sickling of red blood cells and hemolysis, leading to reduction of vaso-occlusive episodes, need for blood transfusions and consequently reduction of morbidity and mortality. Adherence to the treatment is paramount for effectiveness, but in spite of proven benefits, barriers to adherence persist.[1] ESCORT-HU study (European Sickle Cell Disease COhoRT - HydroxyUrea), is a multicentric, prospective, non-interventional European study designed to evaluate the safety profile of HU in real life. Patients were enrolled from January 2009 to June 2017 with a follow-up of up to 10 years. All interruptions and resumptions of HU treatment exceeding 15 days were recorded in this study. We hereby present the analysis of the group of patients who self-discontinued HU at least once during the study before informing their caregiver, with a view to identify potential barriers to long-term adherence. In total, 1906 patients were enrolled in ESCORT-HU from 63 centers in France, Germany, Greece and Italy. Of these, 619 patients (32%) stopped HU for over 15 days at least once, and around a third (11% of all patients) were due to patient's will. The mean duration of HU treatment before the first discontinuation was 4.8 ± 5.1 years. Data are summarized in table 1. Compared to the rest of the cohort, the 'treatment discontinuation' group had similar distribution by gender and indication for HU prescription, but a higher proportion of adults stopped HU more than 15 days. It is notable that the proportion of patients with SC genotype was higher in the 'treatment discontinuation' group (4.5% vs 1.7%). The patients in the 'treatment discontinuation' group had more frequent SCD symptoms before enrolment in the study (table 2). Hematological and clinical improvement compared to the baseline was observed in both groups. However, average mean Corpuscular Volume (MCV) and Fetal Hemoglobin percentage (HbF%) were lower and mean percentages of patients with SCD symptoms were higher over the three years of follow-up in the 'treatment discontinuation' group, suggesting that HU daily dose was insufficient (table 2). Sixty patients have no treatment resumption date reported which suggest a permanent interruption of their treatment. Among them 32% preferred to switch to another HU medicinal product and 13% have safety issue (table 3). Understanding and managing self-discontinuation of HU before taking medical advice is challenging for the physician. It is tempting to speculate that it may be due, at least in part, to lack of effectiveness potentially due to an underdosage of the treatment. Resistance to the treatment may also be suggested based on past literature data revealing a great variability in the response (determined by HbF%) to HU therapy. There is evidence that genetic modifiers affect individual response to HU.[2],[3] Finally, weariness from long-term use may also explain the patient's wish to discontinue HU. But treatment at optimal effective should be the primary goal of caregivers. [1]Smaldone A., Manwani D., Green NS, Greater number of perceived barriers to hydroxyurea associated with poorer health-related quality of life in youth with sickle cell disease, Pediatr Blood Cancer. 2019 [2] Steinberg MH, Voskaridou E, Kutlar A, Loukopoulos D, Koshy M, et al. (2003). Concordant fetal hemoglobin response to hydroxyurea in siblings with sickle cell disease. Am J Hematol 72: 121-126 [3] Ware RE, Despotovic JM, Mortier NA, Flanagan JM, He J, et al. (2011) Pharmacokinetics, pharmacodynamics, and pharmacogenetics of hydroxyurea treatment for children with sickle cell anemia. Blood 118: 4985-4991 Disclosures Galactéros: Addmedica: Membership on an entity's Board of Directors or advisory committees. Voskaridou:Celgene Corporation: Consultancy, Research Funding; Protagonist: Research Funding; Genesis: Consultancy, Research Funding; Acceleron: Consultancy, Research Funding; Addmedica: Membership on an entity's Board of Directors or advisory committees. Cannas:Addmedica: Membership on an entity's Board of Directors or advisory committees.

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Effects of BCL11A Shmir-Induced Post-Transcriptional Silencing on Distributions of HbF in Single-RBCs and Reticulocytes

Blood ◽

10.1182/blood-2021-150186 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 967-967

Author(s):

Nicolas Hebert ◽

Erica B. Esrick ◽

Myriam Armant ◽

Christian Brendel ◽

Marioara Felicia Ciuculescu ◽

...

Keyword(s):

Sickle Cell Disease ◽

Board Of Directors ◽

Sickle Cell ◽

Research Funding ◽

Insertion Site ◽

Fetal Hemoglobin ◽

Fold Increase ◽

Advisory Board ◽

Cell Disease ◽

Advisory Committees

Abstract NH and EE equally contributed. ADW and PB co-signed. The expression of fetal hemoglobin (HbF) is one of the main targets of sickle cell disease treatment, as it inhibits the polymerization of hemoglobin S. The hypothesis of an inhibitory threshold of HbF per red blood cell (RBC) has been suggested, 1 although not well defined, as the overall percentage of HbF does not reflect the heterogeneous distribution of HbF per cell. Likewise, the qualitative analysis of RBCs containing HbF, called F cells, is neither reproducible nor clinically interpretable, due to low expression. 2 We have developed a technique for measuring the amount of HbF per cell, to determine thresholds of HbF expression per RBC correlated with clinical and biological effects. 2 Among genes controlling its expression, BCL11A has a major repressive effect on the expression of gamma globin/HbF during the fetal to adult hemoglobin switch. Post-transcriptional silencing of BCL11A, using lentivirus expression of a shRNA embedded in a microRNA architecture (shmiR) to re-activate γ-globin expression, is safe and demonstrates high levels of %HbF in a pilot clinical study (NCT 03282656). 3 Here, we show the quantitative measurement of HbF per RBC and reticulocyte. Methods: During patient follow-up, HbF quantification per single cell RBC was performed using a fluorescent HbF antibody. 2 Addition of an anti-CD71 fluorescent antibody allowed selection of reticulocyte sub-populations for determining their HbF content. Fold-increase in percentage of RBC versus percentage of reticulocyte were calculated. Kinetics of HbF/RBC and HbF/Reticulocyte were modeled using mixed effects polynomial linear regression to account for the correlation between repeated data over time. Results: With a median follow-up of 15 months [12-20] after gene transfer, figure 1 shows the mathematical modeling of single-RBC HbF measurement representing RBC percentage containing at least 2, 4, 6, 8 and 10 pg of HbF. Percentage of RBC above each threshold was higher compared to 14 hydroxyurea treated patients for 6 months. Figure 2 shows fold increase between reticulocytes and RBCs with same thresholds of HbF/cell. For low thresholds, RBCs were found in same percentage as reticulocytes whereas RBCs containing increasing levels of HbF were found in higher percentage than reticulocytes, until 6pg/cell showing a clear selective advantage for red cells with a threshold ≥ 6pg/cell of HbF. Figure 3 shows different kinetics of HbF increase according to two different transduction strategies with 2 enhancers in patients 2-4 compared to one enhancer in patients 6-8. Conclusion: BCL11A down-regulation in six clinical trial subjects was associated with an in vivo selection process RBCs with ≥ 6pg HbF per cell attained with different engraftment kinetics, depending on transduction processes, and ultimately stable high level and broadly distributed HbF. 1 Steinberg MH, Chui DH, Dover GJ, Sebastiani P, Alsultan A. Fetal hemoglobin in sickle cell anemia: a glass half full? Blood. 2014 Jan 23;123(4):481-5. 2 Hebert N, Rakotoson MG, Bodivit G, et al. Individual red blood cell fetal hemoglobin quantification allows to determine protective thresholds in sickle cell disease. Am. J. Hematol. 3 Esrick EB, Lehmann LE, Biffi A, et al. Post-Transcriptional Genetic Silencing of BCL11A to Treat Sickle Cell Disease. N. Engl. J. Med. 2021;384(3):205-215. Figure 1 Figure 1. Disclosures Esrick: bluebird bio: Consultancy. Audureau: GBT: Honoraria. Higgins: Sebia, Inc.: Honoraria; Danaher Diagnostics: Consultancy. Williams: BioMarin: Membership on an entity's Board of Directors or advisory committees, Other: Insertion Site Advisory Board; Geneception: Membership on an entity's Board of Directors or advisory committees, Other: Scientific Advisory Board; Emerging Therapy Solutions: Membership on an entity's Board of Directors or advisory committees, Other: Chief Scientific Chair; Beam Therapeutics: Membership on an entity's Board of Directors or advisory committees, Other: Scientific Advisory Board; Alerion Biosciences: Other: Co-founder (now licensed to Avro Bio, potential for future milestones/royalties); Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Steering Committee, Novartis ETB115E2201 (eltrombopag in aplastic anemia). Advisory fees donated to NAPAAC.; Orchard Therapeutics: Membership on an entity's Board of Directors or advisory committees, Other: Membership on a safety advisory board (SAB): SAB position ended 05/20/2021. Co-founder , Patents & Royalties: Potential for future royalty/milestone income, X-SCID. Provided GMP vector for clinical trial, Research Funding; bluebird bio: Membership on an entity's Board of Directors or advisory committees, Other: Insertion Site Analysis Advisory Board, Patents & Royalties: BCH licensed certain IP relevant to hemoglobinopathies to bluebird bio. The current license includes the potential for future royalty/milestone income. Bluebird has indicated they will not pursue this as a clinical program and BCH is negotiating return of, Research Funding. Bartolucci: AGIOS: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Lecture fees, Steering committee, Research Funding; Jazz Pharma: Other: Lecture fees; Emmaus: Consultancy; Addmedica: Consultancy, Other: Lecture fees, Research Funding; INNOVHEM: Other: Co-founder; Hemanext: Consultancy; GBT: Consultancy; Bluebird: Consultancy, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy; Fabre Foundation: Research Funding.

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