Exagamglogene Autotemcel for Transfusion-Dependent ß-Thalassemia.

BACKGROUND: Exagamglogene autotemcel (exa-cel) is a nonviral cell therapy designed to reactivate fetal hemoglobin synthesis through ex vivo clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing of the erythroid-specific enhancer region of BCL11A in autologous CD34+ hematopoietic stem and progenitor cells (HSPCs). METHODS: We conducted an open-label, single-group, phase 3 study of exa-cel in patients 12 to 35 years of age with transfusion-dependent ß-thalassemia and a ß0/ß0, ß0/ß0-like, or non-ß0/ß0-like genotype. CD34+ HSPCs were edited by means of CRISPR-Cas9 with a guide mRNA. Before the exa-cel infusion, patients underwent myeloablative conditioning with pharmacokinetically dose-adjusted busulfan. The primary end point was transfusion independence, defined as a weighted average hemoglobin level of 9 g per deciliter or higher without red-cell transfusion for at least 12 consecutive months. Total and fetal hemoglobin concentrations and safety were also assessed. RESULTS: A total of 52 patients with transfusion-dependent ß-thalassemia received exa-cel and were included in this prespecified interim analysis; the median follow-up was 20.4 months (range, 2.1 to 48.1). Neutrophils and platelets engrafted in each patient. Among the 35 patients with sufficient follow-up data for evaluation, transfusion independence occurred in 32 (91%; 95% confidence interval, 77 to 98; P<0.001 against the null hypothesis of a 50% response). During transfusion independence, the mean total hemoglobin level was 13.1 g per deciliter and the mean fetal hemoglobin level was 11.9 g per deciliter, and fetal hemoglobin had a pancellular distribution (≥94% of red cells). The safety profile of exa-cel was generally consistent with that of myeloablative busulfan conditioning and autologous HSPC transplantation. No deaths or cancers occurred. CONCLUSIONS: Treatment with exa-cel, preceded by myeloablation, resulted in transfusion independence in 91% of patients with transfusion-dependent ß-thalassemia. (Supported by Vertex Pharmaceuticals and CRISPR Therapeutics; CLIMB THAL-111 ClinicalTrials.gov number, NCT03655678.).

Real-world evidence: Long-term safety of deferiprone in a large cohort of patients with sickle cell disease enrolled in a registry for up to 10 years.

Patients with sickle cell disease (SCD) and other anemias who receive blood transfusions are at risk of organ damage due to transfusional iron overload. Deferiprone is an iron chelator with a well-established safety and efficacy profile that is indicated for the treatment of transfusional iron overload. Here, we report safety data from the large-scale, retrospective Ferriprox® Total Care Registry, which involved all patients with SCD taking deferiprone following the 2011 approval of deferiprone in the United States through August 2020. A total of 634 patients who had initiated deferiprone treatment were included. The mean (SD) duration of deferiprone exposure in the registry was 1.6 (1.6) years (range 0 to 9.7 years). In the overall patient population (N = 634), 64.7% (n = 410) of patients reported a total of 1885 adverse events (AEs). In subgroup analyses, 54.6% (n = 71) of pediatric patients and 67.3% (n = 339) of adult patients reported AEs. The most common AEs reported in patients receiving deferiprone were sickle cell crisis (22.7%), nausea (12.1%), vomiting (8.7%), abdominal discomfort (5.4%), and fatigue (5.4%). Neutropenia was reported in four (0.6%) patients and severe neutropenia/agranulocytosis (defined as absolute neutrophil count <0.5 × 109/L) was reported in two (0.3%) patients. Of patients with evaluable data, all cases of neutropenia and severe neutropenia/agranulocytosis resolved with deferiprone discontinuation. Results from the nearly 10 years of real-world data collected in the Ferriprox® Total Care Registry demonstrate that deferiprone is safe and well tolerated in patients with SCD or other anemias who have transfusional iron overload.

Diagnosis and management of pyruvate kinase deficiency: international expert guidelines.

Pyruvate kinase (PK) deficiency is the most common cause of chronic congenital non-spherocytic haemolytic anaemia worldwide, with an estimated prevalence of one in 100 000 to one in 300 000 people. PK deficiency results in chronic haemolytic anaemia, with wide ranging and serious consequences affecting health, quality of life, and mortality. The goal of the International Guidelines for the Diagnosis and Management of Pyruvate Kinase Deficiency was to develop evidence-based guidelines for the clinical care of patients with PK deficiency. These clinical guidelines were developed by use of GRADE methodology and the AGREE II framework. Experts were invited after consideration of area of expertise, scholarly contributions in PK deficiency, and country of practice for global representation. The expert panel included 29 expert physicians (including adult and paediatric haematologists and other subspecialists), geneticists, laboratory specialists, nurses, a guidelines methodologist, patients with PK deficiency, and caregivers from ten countries. Five key topic areas were identified, the panel prioritised key questions, and a systematic literature search was done to generate evidence summaries that were used in the development of draft recommendations. The expert panel then met in person to finalise and vote on recommendations according to a structured consensus procedure. Agreement of greater than or equal to 67% among the expert panel was required for inclusion of a recommendation in the final guideline. The expert panel agreed on 31 total recommendations across five key topics: diagnosis and genetics, monitoring and management of chronic complications, standard management of anaemia, targeted and advanced therapies, and special populations. These new guidelines should facilitate best practices and evidence-based PK deficiency care into clinical practice.

Evaluation of a Balloon Implant for Simultaneous Magnetic Nanoparticle Hyperthermia and High-Dose-Rate Brachytherapy of Brain Tumor Resection Cavities.

Previous work has reported the design of a novel thermobrachytherapy (TBT) balloon implant to deliver magnetic nanoparticle (MNP) hyperthermia and high-dose-rate (HDR) brachytherapy simultaneously after brain tumor resection, thereby maximizing their synergistic effect. This paper presents an evaluation of the robustness of the balloon device, compatibility of its heat and radiation delivery components, as well as thermal and radiation dosimetry of the TBT balloon. TBT balloon devices with 1 and 3 cm diameter were evaluated when placed in an external magnetic field with a maximal strength of 8.1 kA/m at 133 kHz. The MNP solution (nanofluid) in the balloon absorbs energy, thereby generating heat, while an HDR source travels to the center of the balloon via a catheter to deliver the radiation dose. A 3D-printed human skull model was filled with brain-tissue-equivalent gel for in-phantom heating and radiation measurements around four 3 cm balloons. For the in vivo experiments, a 1 cm diameter balloon was surgically implanted in the brains of three living pigs (40-50 kg). The durability and robustness of TBT balloon implants, as well as the compatibility of their heat and radiation delivery components, were demonstrated in laboratory studies. The presence of the nanofluid, magnetic field, and heating up to 77 °C did not affect the radiation dose significantly. Thermal mapping and 2D infrared images demonstrated spherically symmetric heating in phantom as well as in brain tissue. In vivo pig experiments showed the ability to heat well-perfused brain tissue to hyperthermic levels (≥40 °C) at a 5 mm distance from the 60 °C balloon surface.

Gene addition for beta thalassemia.

Individuals with transfusion-dependent beta thalassemia require a high burden of care and experience significant morbidity from the underlying disease and its treatment, which negatively impact the quality of life. Allogeneic hematopoietic stem cell transplantation offers the chance for a cure, but donor availability and transplant-related risks, especially in older patients, limit its use. Gene addition utilizing autologous CD34+ cells is an alternative, potentially curative, treatment option. Several clinical trials have investigated the use of lentiviral vectors containing a functional beta globin gene, including Lentiglobin BB305, GLOBE, and TNS9.3.55. The efficacy and safety data from these ongoing trials are discussed in this review.

Neonatal Thrombocytopenia as a Presenting Finding in de novo Pyruvate Kinase Deficiency.

Thrombocytopenia is a common laboratory abnormality encountered in critically ill neonates. The broad differential for thrombocytopenia, and its association with potentially severe neonatal pathology, often presents a diagnostic dilemma prompting extensive evaluation. Hemolysis due to red cell enzymopathies is a rare cause of neonatal thrombocytopenia that is typically brief and self-limiting. Here, we present a case of thrombocytopenia, refractory to transfusion, associated with anemia and hyperbilirubinemia in a neonate with pyruvate kinase deficiency (PKD) arising from compound heterozygous PKLR mutations. The nature of the thrombocytopenia in this patient created considerable diagnostic uncertainty, which was ultimately resolved by whole-exome sequencing. This case emphasizes that inherited red cell defects, such as PKD, are important to consider in cases of neonatal thrombocytopenia.

Clinical Challenges with Iron Chelation in Beta Thalassemia.

Conventional therapy for severe thalassemia includes regular red cell transfusions and iron chelation therapy to prevent and treat complications of iron overload. Iron chelation is very effective when appropriately used, but inadequate iron chelation therapy continues to contribute to preventable morbidity and mortality in transfusion-dependent thalassemia. Factors that contribute to suboptimal iron chelation include poor adherence, variable pharmacokinetics, chelator adverse effects, and difficulties with precise monitoring of response. The regular assessment of adherence, adverse effects, and iron burden with appropriate treatment adjustments is necessary to optimize patient outcomes.

Deferiprone for transfusional iron overload in sickle cell disease and other anemias: open-label study of up to 3 years.

Long-term safety and efficacy data on the iron chelator deferiprone in sickle cell disease (SCD) and other anemias are limited. FIRST-EXT was a 2-year extension study of FIRST (Ferriprox in Patients With Iron Overload in Sickle Cell Disease Trial), a 1-year, randomized noninferiority study of deferiprone vs deferoxamine in these populations. Patients who entered FIRST-EXT continued to receive, or were switched to, deferiprone. Altogether, 134 patients were enrolled in FIRST-EXT (mean age: 16.2 years), with mean (SD) exposure to deferiprone of 2.1 (0.8) years over the 2 studies. The primary end point was safety. Secondary end points were change in liver iron concentration (LIC), cardiac T2∗, serum ferritin (SF), and the proportion of responders (≥20% improvement in efficacy measure). The most common adverse events considered at least possibly related to deferiprone were neutropenia (9.0%) and abdominal pain (7.5%). LIC (mg/g dry weight) decreased over time, with mean (SD) changes from baseline at each time point (year 1, -2.64 [4.64]; year 2, -3.91 [6.38]; year 3, -6.64 [7.72], all P < .0001). Mean SF levels (µg/L) decreased significantly after year 2 (-771, P = .0008) and year 3 (-1016, P = .0420). Responder rates for LIC and SF increased each year (LIC: year 1, 46.5%; year 2, 57.1%; year 3, 66.1%; SF: year 1, 35.2%; year 2, 55.2%; year 3, 70.9%). Cardiac T2∗ remained normal in all patients. In conclusion, long-term therapy with deferiprone was not associated with new safety concerns and led to continued and progressive reduction in iron load in individuals with SCD or other anemias. The trial was registered at www.clinicaltrials.gov as #NCT02443545.

Hemorrhagic Stroke in Children and Adults With Sickle Cell Anemia: The Post-STOP Cohort.

BACKGROUND: Hemorrhagic stroke in young patients with sickle cell anemia remains poorly characterized. METHODS: The Post-STOP (Stroke Prevention Trial in Sickle Cell Anemia) retrospective study collected follow-up data on STOP and STOP II clinical trial cohorts. From January 2012 to May 2014, a team of analysts abstracted data from medical records of prior participants (all with sickle cell anemia). Two vascular neurologists reviewed data to confirm hemorrhagic strokes defined as spontaneous intracerebral, subarachnoid, or intraventricular hemorrhage. Incidence rates were calculated using survival analysis techniques Results: Follow-up data were collected from 2850 of 3835 STOP or STOP II participants. Patients (51% male) were a median of 19.1 (interquartile range, 16.6-22.6) years old at the time of last known status. The overall hemorrhagic stroke incidence rate was 63 per 100 000 person-years (95% CI, 45-87). Stratified by age, the incidence rate per 100 000 person-years was 50 (95% CI, 34-75) for children and 134 (95% CI, 74-243) for adults >18 years. Vascular abnormalities (moyamoya arteriopathy, aneurysm or cavernous malformation) were identified in 18 of 35 patients with hemorrhagic stroke. CONCLUSIONS: The incidence rate of hemorrhagic stroke in patients with sickle cell anemia increases with age. Structural vascular abnormalities such as moyamoya arteriopathy and aneurysms are common etiologies for hemorrhage and screening may be warranted.

Thalassaemia.

Thalassaemia is a diverse group of genetic disorders with a worldwide distribution affecting globin chain synthesis. The pathogenesis of thalassaemia lies in the unbalanced globin chain production, leading to ineffective erythropoiesis, increased haemolysis, and deranged iron homoeostasis. The clinical phenotype shows heterogeneity, ranging from close to normal without complications to severe requiring lifelong transfusion support. Conservative treatment with transfusion and iron chelation has transformed the natural history of thalassaemia major into a chronic disease with a prolonged life expectancy, albeit with co-morbidities and substantial disease burden. Curative therapy with allogeneic haematopoietic stem cell transplantation is advocated for suitable patients. The understanding of the pathogenesis of the disease is guiding therapeutic advances. Novel agents have shown efficacy in improving anaemia and transfusion burden, and initial results from gene therapy approaches are promising. Despite scientific developments, worldwide inequality in the access of health resources is a major concern, because most patients live in underserved areas.

Biologic and Clinical Efficacy of LentiGlobin for Sickle Cell Disease.

BACKGROUND: Sickle cell disease is characterized by the painful recurrence of vaso-occlusive events. Gene therapy with the use of LentiGlobin for sickle cell disease (bb1111; lovotibeglogene autotemcel) consists of autologous transplantation of hematopoietic stem and progenitor cells transduced with the BB305 lentiviral vector encoding a modified ß-globin gene, which produces an antisickling hemoglobin, HbAT87Q. METHODS: In this ongoing phase 1-2 study, we optimized the treatment process in the initial 7 patients in Group A and 2 patients in Group B with sickle cell disease. Group C was established for the pivotal evaluation of LentiGlobin for sickle cell disease, and we adopted a more stringent inclusion criterion that required a minimum of four severe vaso-occlusive events in the 24 months before enrollment. In this unprespecified interim analysis, we evaluated the safety and efficacy of LentiGlobin in 35 patients enrolled in Group C. Included in this analysis was the number of severe vaso-occlusive events after LentiGlobin infusion among patients with at least four vaso-occlusive events in the 24 months before enrollment and with at least 6 months of follow-up. RESULTS: As of February 2021, cell collection had been initiated in 43 patients in Group C; 35 received a LentiGlobin infusion, with a median follow-up of 17.3 months (range, 3.7 to 37.6). Engraftment occurred in all 35 patients. The median total hemoglobin level increased from 8.5 g per deciliter at baseline to 11 g or more per deciliter from 6 months through 36 months after infusion. HbAT87Q contributed at least 40% of total hemoglobin and was distributed across a mean (±SD) of 85±8% of red cells. Hemolysis markers were reduced. Among the 25 patients who could be evaluated, all had resolution of severe vaso-occlusive events, as compared with a median of 3.5 events per year (range, 2.0 to 13.5) in the 24 months before enrollment. Three patients had a nonserious adverse event related or possibly related to LentiGlobin that resolved within 1 week after onset. No cases of hematologic cancer were observed during up to 37.6 months of follow-up. CONCLUSIONS: One-time treatment with LentiGlobin resulted in sustained production of HbAT87Q in most red cells, leading to reduced hemolysis and complete resolution of severe vaso-occlusive events. (Funded by Bluebird Bio; HGB-206 ClinicalTrials.gov number, NCT02140554.).

Betibeglogene Autotemcel Gene Therapy for Non-ß0/ß0 Genotype ß-Thalassemia.

BACKGROUND: Betibeglogene autotemcel (beti-cel) gene therapy for transfusion-dependent ß-thalassemia contains autologous CD34+ hematopoietic stem cells and progenitor cells transduced with the BB305 lentiviral vector encoding the ß-globin (ßA-T87Q) gene. METHODS: In this open-label, phase 3 study, we evaluated the efficacy and safety of beti-cel in adult and pediatric patients with transfusion-dependent ß-thalassemia and a non-ß0/ß0 genotype. Patients underwent myeloablation with busulfan (with doses adjusted on the basis of pharmacokinetic analysis) and received beti-cel intravenously. The primary end point was transfusion independence (i.e., a weighted average hemoglobin level of ≥9 g per deciliter without red-cell transfusions for ≥12 months). RESULTS: A total of 23 patients were enrolled and received treatment, with a median follow-up of 29.5 months (range, 13.0 to 48.2). Transfusion independence occurred in 20 of 22 patients who could be evaluated (91%), including 6 of 7 patients (86%) who were younger than 12 years of age. The average hemoglobin level during transfusion independence was 11.7 g per deciliter (range, 9.5 to 12.8). Twelve months after beti-cel infusion, the median level of gene therapy-derived adult hemoglobin (HbA) with a T87Q amino acid substitution (HbAT87Q) was 8.7 g per deciliter (range, 5.2 to 10.6) in patients who had transfusion independence. The safety profile of beti-cel was consistent with that of busulfan-based myeloablation. Four patients had at least one adverse event that was considered by the investigators to be related or possibly related to beti-cel; all events were nonserious except for thrombocytopenia (in 1 patient). No cases of cancer were observed. CONCLUSIONS: Treatment with beti-cel resulted in a sustained HbAT87Q level and a total hemoglobin level that was high enough to enable transfusion independence in most patients with a non-ß0/ß0 genotype, including those younger than 12 years of age. (Funded by Bluebird Bio; HGB-207 ClinicalTrials.gov number, NCT02906202.).

Deferiprone vs deferoxamine for transfusional iron overload in SCD and other anemias: a randomized, open-label noninferiority study.

Many people with sickle cell disease (SCD) or other anemias require chronic blood transfusions, which often causes iron overload that requires chelation therapy. The iron chelator deferiprone is frequently used in individuals with thalassemia syndromes, but data in patients with SCD are limited. This open-label study assessed the efficacy and safety of deferiprone in patients with SCD or other anemias receiving chronic transfusion therapy. A total of 228 patients (mean age: 16.9 [range, 3-59] years; 46.9% female) were randomized to receive either oral deferiprone (n = 152) or subcutaneous deferoxamine (n = 76). The primary endpoint was change from baseline at 12 months in liver iron concentration (LIC), assessed by R2* magnetic resonance imaging (MRI). The least squares mean (standard error) change in LIC was -4.04 (0.48) mg/g dry weight for deferiprone vs -4.45 (0.57) mg/g dry weight for deferoxamine, with noninferiority of deferiprone to deferoxamine demonstrated by analysis of covariance (least squares mean difference 0.40 [0.56]; 96.01% confidence interval, -0.76 to 1.57). Noninferiority of deferiprone was also shown for both cardiac T2* MRI and serum ferritin. Rates of overall adverse events (AEs), treatment-related AEs, serious AEs, and AEs leading to withdrawal did not differ significantly between the groups. AEs related to deferiprone treatment included abdominal pain (17.1% of patients), vomiting (14.5%), pyrexia (9.2%), increased alanine transferase (9.2%) and aspartate transferase levels (9.2%), neutropenia (2.6%), and agranulocytosis (0.7%). The efficacy and safety profiles of deferiprone were acceptable and consistent with those seen in patients with transfusion-dependent thalassemia. This trial study was registered at www://clinicaltrials.gov as #NCT02041299.

Lentiviral vector ALS20 yields high hemoglobin levels with low genomic integrations for treatment of beta-globinopathies.

Ongoing clinical trials for treatment of beta-globinopathies by gene therapy involve the transfer of the beta-globin gene, which requires integration of three to four copies per genome in most target cells. This high proviral load may increase genome toxicity, potentially limiting the safety of this therapy and relegating its use to total body myeloablation. We hypothesized that introducing an additional hypersensitive site from the locus control region, the complete sequence of the second intron of the beta-globin gene, and the ankyrin insulator may enhance beta-globin expression. We identified a construct, ALS20, that synthesized significantly higher adult hemoglobin levels than those of other constructs currently used in clinical trials. These findings were confirmed in erythroblastic cell lines and in primary cells isolated from sickle cell disease patients. Bone marrow transplantation studies in beta-thalassemia mice revealed that ALS20 was curative at less than one copy per genome. Injection of human CD34+ cells transduced with ALS20 led to safe, long-term, and high polyclonal engraftment in xenograft experiments. Successful treatment of beta-globinopathies with ALS20 could potentially be achieved at less than two copies per genome, minimizing the risk of cytotoxic events and lowering the intensity of myeloablation.

The pyruvate kinase (PK) to hexokinase enzyme activity ratio and erythrocyte PK protein level in the diagnosis and phenotype of PK deficiency.

Diagnosis of pyruvate kinase deficiency (PKD), the most common cause of hereditary non-spherocytic haemolytic anaemia, remains challenging in routine practice and no biomarkers for clinical severity have been characterised. This prospective study enrolled 41 patients with molecularly confirmed PKD from nine North American centres to evaluate the diagnostic sensitivity of pyruvate kinase (PK) enzyme activity and PK:hexokinase (HK) enzyme activity ratio, and evaluate the erythrocyte PK (PK-R) protein level and erythrocyte metabolites as biomarkers for clinical severity. In this population not transfused for ≥90 days before sampling, the diagnostic sensitivity of the PK enzyme assay was 90% [95% confidence interval (CI) 77-97%], whereas the PK:HK ratio sensitivity was 98% (95% CI 87-100%). There was no correlation between PK enzyme activity and clinical severity. Transfusion requirements correlated with normalised erythrocyte ATP levels (r = 0·527, P = 0·0016) and PK-R protein levels (r = -0·527, P = 0·0028). PK-R protein levels were significantly higher in the never transfused [median (range) 40·1 (9·8-73·9)%] versus ever transfused [median (range) 7·7 (0·4-15·1)%] patients (P = 0·0014). The PK:HK ratio had excellent sensitivity for PK diagnosis, superior to PKLR exon sequencing. Given that the number of PKLR variants and genotype combinations limits prognostication based on molecular findings, PK-R protein level may be a useful prognostic biomarker of disease severity and merits further study.

Genotype-phenotype correlation and molecular heterogeneity in pyruvate kinase deficiency.

Pyruvate kinase (PK) deficiency is a rare recessive congenital hemolytic anemia caused by mutations in the PKLR gene. This study reports the molecular features of 257 patients enrolled in the PKD Natural History Study. Of the 127 different pathogenic variants detected, 84 were missense and 43 non-missense, including 20 stop-gain, 11 affecting splicing, five large deletions, four in-frame indels, and three promoter variants. Within the 177 unrelated patients, 35 were homozygous and 142 compound heterozygous (77 for two missense, 48 for one missense and one non-missense, and 17 for two non-missense variants); the two most frequent mutations were p.R510Q in 23% and p.R486W in 9% of mutated alleles. Fifty-five (21%) patients were found to have at least one previously unreported variant with 45 newly described mutations. Patients with two non-missense mutations had lower hemoglobin levels, higher numbers of lifetime transfusions, and higher rates of complications including iron overload, extramedullary hematopoiesis, and pulmonary hypertension. Rare severe complications, including lower extremity ulcerations and hepatic failure, were seen more frequently in patients with non-missense mutations or with missense mutations characterized by severe protein instability. The PKLR genotype did not correlate with the frequency of complications in utero or in the newborn period. With ICCs ranging from 0.4 to 0.61, about the same degree of clinical similarity exists within siblings as it does between siblings, in terms of hemoglobin, total bilirubin, splenectomy status, and cholecystectomy status. Pregnancy outcomes were similar across genotypes in PK deficient women. This report confirms the wide genetic heterogeneity of PK deficiency.

American Society of Hematology 2020 guidelines for sickle cell disease: transfusion support.

BACKGROUND: Red cell transfusions remain a mainstay of therapy for patients with sickle cell disease (SCD), but pose significant clinical challenges. Guidance for specific indications and administration of transfusion, as well as screening, prevention, and management of alloimmunization, delayed hemolytic transfusion reactions (DHTRs), and iron overload may improve outcomes. OBJECTIVE: Our objective was to develop evidence-based guidelines to support patients, clinicians, and other healthcare professionals in their decisions about transfusion support for SCD and the management of transfusion-related complications. METHODS: The American Society of Hematology formed a multidisciplinary panel that was balanced to minimize bias from conflicts of interest and that included a patient representative. The panel prioritized clinical questions and outcomes. The Mayo Clinic Evidence-Based Practice Research Program supported the guideline development process. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to form recommendations, which were subject to public comment. RESULTS: The panel developed 10 recommendations focused on red cell antigen typing and matching, indications, and mode of administration (simple vs red cell exchange), as well as screening, prevention, and management of alloimmunization, DHTRs, and iron overload. CONCLUSIONS: The majority of panel recommendations were conditional due to the paucity of direct, high-certainty evidence for outcomes of interest. Research priorities were identified, including prospective studies to understand the role of serologic vs genotypic red cell matching, the mechanism of HTRs resulting from specific alloantigens to inform therapy, the role and timing of regular transfusions during pregnancy for women, and the optimal treatment of transfusional iron overload in SCD.