Hydroxyurea-Increased Fetal Hemoglobin Is Associated with Less Organ Damage and Longer Survival in Adults with Sickle Cell Anemia

End Organ Affection in Sickle Cell Disease

Sickle cell disease is an orphan disease affecting ethnic minorities and characterized by profound systemic manifestations. Although around 100,000 individuals with SCD are living in the US, the exact number of individuals is unknown, and it is considered an orphan disease. This single-gene disorder leads to red blood cell sickling and the deoxygenation of hemoglobin, resulting in hemolysis. SCD is associated with acute complications such as vaso-occlusive crisis, infections, and chronic target organ complications such as pulmonary disease and renal failure. While genetic therapy holds promise to alter the fundamental disease process, the major challenge in the field remains the target end organ damage and ways to mitigate or reverse it. Here, we provide an overview of the clinical manifestations and pathogenesis with a focus on end-organ damage and current therapeutic options, including recent FDA-approved stem cell and gene editing therapies.

Empirically derived profiles of neurocognitive functioning in youth and young adults with sickle cell disease

OBJECTIVE

Sickle cell disease (SCD) is an inherited blood disorder associated with neurocognitive deficits. In contrast to variable-centered approaches, no known research has utilized person-centered strategies to identify multidimensional patterns of neurocognitive functioning of an individual with SCD. The purpose of the present study was to create empirically derived profiles and identify predictors of neurocognitive functioning subgroups among youth and young adults with SCD.

METHODS

Individuals with SCD (N = 393, mean age 14.05 years, age range 8-24, 50.4% female/49.6% male) completed neurocognitive assessments. Latent profile analysis derived subgroups/classes of neurocognitive functioning and determined relations with demographic and medical variables.

RESULTS

Three latent classes emerged: average functioning (n = 102, 27%), low average functioning (n = 225, 60%), and exceptionally low functioning (n = 46, 12%). Older age was associated with membership in the low average and exceptionally low functioning groups (relative to the average group). Being prescribed hydroxyurea was associated with membership in the average functioning group (relative to the low average group) and absence of hydroxyurea use was associated with membership in the exceptionally low group (relative to the low average group). Lower social vulnerability was associated with membership in the average functioning group compared to the low average and exceptionally low groups.

CONCLUSIONS

Clinicians can help reduce disparities in cognitive development for individuals with SCD by promoting early treatment with hydroxyurea and implementing methods to reduce social vulnerabilities that can interfere with access to evidence-based care.

A multilevel mHealth intervention boosts adherence to hydroxyurea in individuals with sickle cell disease

Hydroxyurea reduces sickle cell disease (SCD) complications, but medication adherence is low. We tested 2 mobile health (mHealth) interventions targeting determinants of low adherence among patients (InCharge Health) and low prescribing among providers (HU Toolbox) in a multi-center, non-randomized trial of individuals with SCD ages 15-45. We compared the percentage of days covered (PDC), labs, healthcare utilization, and self-reported pain over 24 weeks of intervention and 12 weeks post-study with a 24-week preintervention interval. We enrolled 293 patients (51% male; median age 27.5 years, 86.8% HbSS/HbSβ0-thalassemia). The mean change in PDC among 235 evaluable subjects increased (39.7% to 56.0%; P < 0.001) and sustained (39.7% to 51.4%, P < 0.001). Mean HbF increased (10.95% to 12.78%; P = 0.03). Self-reported pain frequency reduced (3.54 to 3.35 events/year; P = 0.041). InCharge Health was used ≥1 day by 199 of 235 participants (84.7% implementation; median usage: 17% study days; IQR: 4.8-45.8%). For individuals with ≥1 baseline admission for pain, admissions per 24 weeks declined from baseline through 24 weeks (1.97 to 1.48 events/patient, P = 0.0045) and weeks 25-36 (1.25 events/patient, P = 0.0015). PDC increased with app use (P < 0.001), with the greatest effect in those with private insurance (P = 0.0078), older subjects (P = 0.033), and those with lower pain interference (P = 0.0012). Of the 89 providers (49 hematologists, 36 advanced care providers, 4 unreported), only 11.2% used HU Toolbox ≥1/month on average. This use did not affect change in PDC. Tailoring mHealth solutions to address barriers to hydroxyurea adherence can potentially improve adherence and provide clinical benefits. A definitive randomized study is warranted. This trial was registered at www.clinicaltrials.gov as #NCT04080167.

Creating an automated contemporaneous cohort in sickle cell anemia to predict survival after disease-modifying therapy

The Food and Drug Administration requires contemporaneous controls to compare clinical outcomes for participants receiving experimental gene therapy or gene editing clinical trials. However, developing a contemporaneous cohort of rare diseases requires multiple person-hours. In a single referral center for sickle cell disease, we tested the hypothesis that we could create an automated contemporaneous cohort of children and adults with sickle cell anemia (SCA) to predict mortality. Data were obtained between 1 January 2004 and 30 April 2021. We identified 419 individuals with SCA with consistent medical care defined as followed continuously for >0.5 years with no visit gaps >3.0 years. The median age was 10.2 years (IQR, 1-24 years), with a median follow-up of 7.4 years (IQR, 3.6-13.5 years) and 47 deaths. A total of 98% (274 of 277) of the children remained alive at 18 years of age, and 34.3% (94 of 274) of those children were followed into adulthood. For adults, the median age of survival was 49.3 years. Treatment groups were mutually exclusive and in a hierarchical order: hematopoietic stem cell transplant (n = 22)>regular blood transfusion for at least 2 years (n = 56)>hydroxyurea for at least 1 year (n = 243)>no disease-modifying therapy (n = 98). Compared to those receiving no disease-modifying treatment, those treated with hydroxyurea therapy had a significantly lower hazard of mortality (hazard ratio = 0.38; P = 0.016), but no statistical difference for those receiving regular blood transfusions compared to no disease-modifying therapy (hazard ratio = 0.71; P = 0.440). An automated contemporaneous SCA cohort can be generated to estimate mortality in children and adults with SCA.

Editing the core region in HPFH deletions alters fetal and adult globin expression for treatment of β-hemoglobinopathies

Reactivation of fetal hemoglobin (HbF) is a commonly adapted strategy to ameliorate β-hemoglobinopathies. However, the continued production of defective adult hemoglobin (HbA) limits HbF tetramer production affecting the therapeutic benefits. Here, we evaluated deletional hereditary persistence of fetal hemoglobin (HPFH) mutations and identified an 11-kb sequence, encompassing putative repressor region (PRR) to β-globin exon-1 (βE1), as the core deletion that ablates HbA and exhibits superior HbF production compared with HPFH or other well-established targets. PRR-βE1-edited hematopoietic stem and progenitor cells (HSPCs) retained their genome integrity and their engraftment potential to repopulate for long-term hematopoiesis in immunocompromised mice producing HbF positive cells in vivo. Furthermore, PRR-βE1 gene editing is feasible without ex vivo HSPC culture. Importantly, the editing induced therapeutically significant levels of HbF to reverse the phenotypes of both sickle cell disease and β-thalassemia major. These findings imply that PRR-βE1 gene editing of patient HSPCs could lead to improved therapeutic outcomes for β-hemoglobinopathy gene therapy.

An Overview of Solid Organ Transplantation in Patients With Sickle Cell Disease

Sickle cell disease is a common genetic disorder affecting >300 000 people across the world. The vast majority of patients cared for in high-resource settings live well into adulthood, but many develop a high burden of disease complications. Good standard of care including disease-modifying agents and transfusion programs limits the number of patients who develop end-stage organ disease, but for those that do, the prognosis can be very poor. Solid organ transplantation is a well-established mode of treatment for patients with sickle cell disease and kidney or liver failure, but appropriate patient selection and perioperative management are important for achieving good outcomes. Hematopoietic stem cell transplantation and gene therapy may offer novel treatment options for adult patients with chronic organ damage in the future, but these are not yet widely available. For now, good, holistic care and early intervention of end-organ complications can minimize the number of patients requiring solid organ transplantation later in life.

Impact of Hydroxyurea Starting Dose on Pain Outcomes in Patients with Sickle Cell Disease

In patients with sickle cell disease, hydroxyurea decreases the number of pain crises experienced. This study aimed to evaluate the difference in pain outcomes between patients started on a guideline concordant, weight-based starting dose of at least 15 mg/kg/day of hydroxyurea and those not. The first prescription of hydroxyurea was the baseline date, follow-up was a visit 60-120 days after baseline. The primary outcome was the change in opioid prescribing between baseline and follow-up. 138 patients met inclusion criteria; of these, 55 were started on a guideline concordant dose of hydroxyurea. Greater white blood cell count (9.5 vs 12.0; p < 0.01) was statistically associated with subtherapeutic dosing. Greater actual body weight (68.0 vs 72.1 kg; p = 0.16) also appeared higher in the non-guideline concordant group. No statistically significant difference in opioid prescribing was observed between those started on a guideline concordant dose of hydroxyurea and those who were not. In the guideline concordant starting dose group, 42% had a reduction in pain scores at first follow up, compared to 35% with a non-guideline recommended starting dose. (p = 0.41). While this difference is in the direction that would be expected based on the guidelines, the difference does not appear to be clinically meaningful.

Single Nucleotide Polymorphisms in XMN1-HBG2, HBS1L-MYB, and BCL11A and Their Relation to High Fetal Hemoglobin Levels That Alleviate Anemia

Anemia is a condition in which red blood cells and/or hemoglobin (Hb) concentrations are decreased below the normal range, resulting in a lack of oxygen being transported to tissues and organs. Those afflicted with this condition may feel lethargic and weak, which reduces their quality of life. The condition may be manifested in inherited blood disorders, such as thalassemia and sickle cell disease, whereas acquired disorders include aplastic anemia, chronic disease, drug toxicity, pregnancy, and nutritional deficiency. The augmentation of fetal hemoglobin (HbF) results in the reduction in clinical symptoms in beta-hemoglobinopathies. Several transcription factors as well as medications such as hydroxyurea may help red blood cells produce more HbF. HbF expression increases with the downregulation of three main quantitative trait loci, namely, the XMN1-HBG2, HBS1L-MYB, and BCL11A genes. These genes contain single nucleotide polymorphisms (SNPs) that modulate the expression of HbF differently in various populations. Allele discrimination is important in SNP genotyping and is widely applied in many assays. In conclusion, the expression of HbF with a genetic modifier is crucial in determining the severity of anemic diseases, and genetic modification of HbF expression may offer clinical benefits in diagnosis and disease management.

Long-Term Health Effects of Curative Therapies on Heart, Lungs, and Kidneys for Individuals with Sickle Cell Disease Compared to Those with Hematologic Malignancies

The goal of curing children and adults with sickle cell disease (SCD) is to maximize benefits and minimize intermediate and long-term adverse outcomes so that individuals can live an average life span with a high quality of life. While greater than 2000 individuals with SCD have been treated with curative therapy, systematic studies have not been performed to evaluate the long-term health effects of hematopoietic stem cell transplant (HSCT) in this population. Individuals with SCD suffer progressive heart, lung, and kidney disease prior to curative therapy. In adults, these sequalae are associated with earlier death. In comparison, individuals who undergo HSCT for cancer are heavily pretreated with chemotherapy, resulting in potential acute and chronic heart, lung, and kidney disease. The long-term health effects on the heart, lung, and kidney for children and adults undergoing HSCT for cancer have been extensively investigated. These studies provide the best available data to extrapolate the possible late health effects after curative therapy for SCD. Future research is needed to evaluate whether HSCT abates, stabilizes, or exacerbates heart, lung, kidney, and other diseases in children and adults with SCD receiving myeloablative and non-myeloablative conditioning regimens for curative therapy.

Fetal hemoglobin modulates neurocognitive performance in sickle cell anemia✰,✰✰

PURPOSE OF THE STUDY

Fetal hemoglobin (HbF) is a modifier of the clinical and hematologic phenotype of sickle cell anemia (SCA). Three quantitative trait loci (QTL) modulate HbF expression. The neurocognitive effects of variants in these QTL have yet to be explored. We evaluated the relation between 11 SNPs in the three HbF QTL: BCL11A, MYB, the HBB gene cluster, and full-scale intelligence (IQ) in SCA.

PATIENTS AND METHODS

The prospective longitudinal cohort study, Sickle Cell Clinical Research and Intervention Program, was used as a discovery cohort (n = 166). The genotypes for 11 SNPs were extracted through whole genome sequencing and were analyzed using an additive model. A polygenic score for HbF (PGS^HbF) integrating the numbers of low HbF alleles from 11 SNPs was analyzed as a continuous variable. The Cooperative Study of Sickle Cell Disease (n = 156) and the Silent Cerebral Infarction Transfusion (n = 114) Trial were used as two independent replication cohorts. Benjamini and Hochberg approach was used to calculate false discovery rate adjusted p-value (pFDR).

RESULTS

HbF was positively associated with IQ (minimum raw p = 0·0018) at pFDR<0·05. HbF mediated the relationship between two BCL11A SNPs, rs1427407 and rs7606173, HBS1L-MYB: rs9494142, and PGS^HbF with IQ (minimum raw p = 0·0035) at pFDR<0·05.

CONCLUSION

As the major modulator of the severity of SCA, HbF also influences neurocognition, which is done through mediation of its QTL. These findings have implications for early identification of neurocognitive risk and targeted intervention.

Real-world effectiveness of voxelotor for treating sickle cell disease in the US: a large claims data analysis

BACKGROUND

Sickle cell disease (SCD) is a genetic disease that impacts patients' quality of life, healthcare costs, and life expectancy. Elevated sickle hemoglobin (HbS), which readily polymerizes, causes red blood cell sickling, leading to chronic hemolytic anemia and complications often requiring hospitalization and transfusions. In 2019, voxelotor, which inhibits HbS polymerization, was approved for SCD treatment.

OBJECTIVES

This study uses real-world evidence to assess voxelotor's effectiveness in SCD patients in typical clinical practice from 2019 to 2021 using a national medical claims database (N = 3128).

RESULTS

After initiating voxelotor, 60.8% of patients with available hemoglobin (Hb) laboratory data (n = 74) showed a Hb increase >1 g/dL. Mean transfusion rate per patient-year dropped 52% in patients with ≥1 transfusion before treatment (n = 190). In patients with ≥1 of the corresponding events (n = 1065), decreases were observed in mean vaso-occlusive crisis (VOC) frequency (-23%); mean VOC-related hospitalizations and length of stay (LOS) time (-34% and -30%, respectively); mean all-cause hospitalization and LOS time (-37% and -23%, respectively); outpatient visits (-10%); iron chelation use (-46%); and prescribed opioids (-13%).

CONCLUSION

These data align with randomized controlled trial results showing voxelotor improvements and support that voxelotor may lower transfusion and VOC rates in clinical practice.

Hydroxyurea treatment and neurocognitive functioning in sickle cell disease from school age to young adulthood

Neurocognitive impairment is common in sickle cell disease (SCD) and is associated with significant functional limitations. In a cross-sectional analysis, we examined the association between hydroxyurea (HU) treatment and neurocognitive functioning from school-age to young adulthood in individuals with SCD. A total of 215 patients with HbSS/HbSβ⁰ -thalassaemia (71% HU treated) and 149 patients with HbSC/HbSβ⁺ -thalassaemia (20% HU treated) completed neurocognitive measures at one of four developmental stages: school-age (age 8-9 years), early adolescence (age 12-13 years), late adolescence (age 16-17 years) and young adulthood (ages 19-24 years). For participants with multiple assessments, only the most recent evaluation was included. In multivariable analysis adjusted for social vulnerability, HU treatment and sex, older age was associated with a reduction in overall intelligence quotient (IQ) of 0·55 points per year of life [standard error (SE) = 0·18, false discovery rate adjusted P value (PFDR) = 0.01] for patients with HbSS/HbSβ⁰ -thalassaemia. Earlier initiation of HU (n = 152) in HbSS/HbSβ⁰ -thalassaemia was associated with higher scores on neurocognitive measures across most domains, including IQ [estimate (SE) 0·77 (0·25)/year, PFDR = 0·01], after adjusting for social vulnerability, sex and treatment duration. These results support the early use of HU to limit the detrimental neurocognitive effects of SCD, while highlighting the need for additional measures to further mitigate neurocognitive deterioration.

Sickle Cell Disease

Sickle cell disease is an umbrella term for a group of hemoglobinopathies characterized by the presence of 2 β-globin gene mutations or deletions, at least 1 of which is the point mutation that leads to the production of hemoglobin S. Sickle cell disease is associated with hemolytic anemia, significant chronic end-organ damage, and early death. In high-income countries, at least 95% of children with the disease survive into adulthood, resulting in a growing population of affected adults with significant comorbidities, complex medical issues, and not enough specialists to provide care. Hydroxyurea is the primary therapy, and recent advances in understanding disease pathophysiology have led to new therapies; progress in bone marrow transplant and gene editing has resulted in cure in some patients. The purpose of this review is to provide an overview of the diagnosis, common acute and chronic clinical manifestations, and best practices for management of sickle cell disease.

Fetal hemoglobin in sickle cell anemia

Fetal hemoglobin (HbF) can blunt the pathophysiology, temper the clinical course, and offer prospects for curative therapy of sickle cell disease. This review focuses on (1) HbF quantitative trait loci and the geography of β-globin gene haplotypes, especially those found in the Middle East; (2) how HbF might differentially impact the pathophysiology and many subphenotypes of sickle cell disease; (3) clinical implications of person-to-person variation in the distribution of HbF among HbF-containing erythrocytes; and (4) reactivation of HbF gene expression using both pharmacologic and cell-based therapeutic approaches. A confluence of detailed understanding of the molecular basis of HbF gene expression, coupled with the ability to precisely target by genomic editing most areas of the genome, is producing important preliminary therapeutic results that could provide new options for cell-based therapeutics with curative intent.

Association of Exon 14 of the SOX6 Gene Sequence Variations with Response to Hydroxyurea Therapy in Patients Carrying Non Transfusion-Dependent Thalassemia

Hydroxyurea (HU) activates the γ-globin gene, resulting in increased Hb F synthesis. The SOX6 gene is a member of the Sox (Sry-type HMG box) family of transcription factors, characterized by minor groove binding domain. The DNA binding domain of this gene is encoded by exon 14. We assessed the relationship between response to HU and exon 14 of the SOX6 gene sequence variations in patients with non transfusion-dependent thalassemia (NTDT). One hundred NTDT patients from southern Iran underwent HU therapy randomly participated in this cross-sectional study between February 2013 and October 2014. Based on response to HU therapy, the patients were divided into two groups: good and poor responder. Sequence variations of exon 14 of the SOX6 gene was assayed by the Sanger sequencing technique. From all evaluated single nucleotide polymorphisms (SNPs) as above, we found no significant association between sequence variations of exon 14 of the SOX6 gene and response to HU therapy (p > 0.05). It seems that no SNPs in exon 14 of the SOX6 gene is associated with response to HU in NTDT patients, but more studies are needed for further evaluation.

Computer Algorithm-Based Hydroxyurea Dosing Facilitates Titration to Maximum Tolerated Dose in Sickle Cell Anemia

Adults with sickle cell disease (SCD) experience acute and chronic complications and die prematurely. When taken at maximum tolerated dose (MTD), hydroxyurea prolongs survival; however, it has not consistently reversed organ dysfunction. Patients also frequently do not take hydroxyurea, at least in part because of physician discomfort with prescribing hydroxyurea. We sought to develop a computer program that could easily titrate hydroxyurea to MTD. This was a single-arm, open-label pilot study. Fifteen patients with homozygous SCD were enrolled in the protocol, and 10 patients were followed at baseline and then for 1 year after hydroxyurea initiation or dose titration. Fetal hemoglobin significantly increased in all 10 patients from 8.3% to 25.1% (P < .001). Nine patients were titrated to MTD in an average of 7.9 months, and the tenth patient's hydroxyurea dose was increased to 33 mg/kg/day. Computer program dosing recommendations were the same as manual dosing decisions made using the same algorithm for all patients and at all times. We also evaluated markers of cardiopulmonary, liver and renal damage. Although cardiopulmonary function did not significantly improve, direct bilirubin and alanine aminotransferase levels significantly decreased (P < .001 and P < .01, respectively). Last, although kidney function did not improve, degree of proteinuria was significantly reduced (P < .05). We have developed a computer program that reliably titrates hydroxyurea to MTD. A larger study is indicated to test the program either as a computer program or a downloadable application.

Inpatient Ordering of Home Hydroxyurea by Residents for Hospitalized Patients With Sickle Cell Disease

BACKGROUND

Hydroxyurea is a well-established disease-modifying medication for sickle cell disease (SCD). At some institutions, hydroxyurea can only be ordered by "chemotherapy-certified" providers which may not include pediatric resident physicians.

METHODS

We conducted a survey of 39 American pediatric hospitals regarding their policy on resident hydroxyurea ordering for SCD. Our institution changed its policy in June 2016 to allow residents to order hydroxyurea for hospitalized patients with SCD who were already on hydroxyurea at home. We conducted a retrospective review of the medical records of a random sample of patients with SCD on hydroxyurea admitted the year before and the year after this policy change.

RESULTS

In our national survey, 51% of surveyed hospitals allowed residents to order hydroxyurea, 19% required a second signature, and 30% did not allow residents to order hydroxyurea. In our institutional study, patients after the policy change were significantly more likely to have received their home hydroxyurea by hospital day 1: before 62/90 (69%) versus after 105/119 (88%), P=0.0005. The proportion of patients who inappropriately received hydroxyurea was very low in both groups: before 1/91 (1%) versus after 3/126 (2%), P=0.64, with no serious adverse clinical events due to inappropriate hydroxyurea administration.

CONCLUSIONS

Considerable national variation in practice currently exists in regards to resident hydroxyurea ordering hospital policies. A policy allowing residents to order hydroxyurea significantly increased the likelihood of a patient receiving hydroxyurea while hospitalized with no significant increase in inappropriate hydroxyurea administration. Resident hydroxyurea ordering seems safe and beneficial.

Choice of Donor Source and Conditioning Regimen for Hematopoietic Stem Cell Transplantation in Sickle Cell Disease

In the United States, one out of every 500 African American children have sickle cell disease (SCD), and SCD affects approximately 100,000 Americans. Significant advances in the treatment of this monogenetic disorder have failed to substantially extend the life expectancy of adults with SCD over the past two decades. Hematopoietic stem cell transplantation (HSCT) remains the only curative option for patients with SCD. While human leukocyte antigen (HLA) matched sibling HSCT has been successful, its availability is extremely limited. This review summarizes various conditioning regimens that are currently available. We explore recent efforts to expand the availability of allogeneic HSCT, including matched unrelated, umbilical cord blood, and haploidentical stem cell sources. We consider the use of nonmyeloablative conditioning and haploidentical donor sources as emerging strategies to expand transplant availability, particularly for SCD patients with complications and comorbidities who can undergo neither matched related transplant nor myeloablative conditioning. Finally, we show that improved conditioning agents have improved success rates not only in the HLA-matched sibling setting but also alternative donor settings.

Innovations in Targeted Anti-Adhesion Treatment for Sickle Cell Disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy that leads to significant lifetime morbidity and early mortality. An enhanced understanding of the complex pathophysiology of the disease has elucidated novel therapeutic targets for which new therapies are in development. In order to increase the therapeutic landscape, it has been important to identify the blood vessel and more specifically the endothelium as the target organ in this complex disease. Through this lens, we present a review of new anti-adhesion therapies for SCD in development. The long-term promise of multimodal therapies for SCD is finally on the horizon.

Allogeneic Hematopoietic Stem Cell Transplantation for Adults with Sickle Cell Disease

Sickle cell disease (SCD) is an inherited red blood cell disorder that leads to substantial morbidity and early mortality. Acute and chronic SCD-related complications increase with older age, and therapies are urgently needed to treat adults. Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative therapy, but has been used less frequently in adults compared to children. This is, in part, due to (1) greater chronic organ damage, limiting tolerability to myeloablative conditioning regimens, (2) a higher rate of HSCT-related complications in adults versus children with SCD, and (3) limited coverage by public and private health insurance. Newer approaches using nonmyeloablative and reduced-intensity conditioning HSCT regimens have demonstrated better safety and tolerability, with high rates of stable engraftment in SCD adults. This review will focus on the impacts of HSCT, using more contemporary approaches to SCD-related complications in adults.

Why, Who, When, and How? Rationale for Considering Allogeneic Stem Cell Transplantation in Children with Sickle Cell Disease

Considering the progress made in the management of sickle cell disease during the past 30 years, along with the excellent results obtained with hematopoietic stem cell transplantation (SCT), it is important to reexamine why, who, when and how to recommend allogeneic SCT in children with sickle cell disease. While sickle cell disease has a low risk of death in children and a high risk for morbidity during aging, SCT carries an early risk of death, graft-vs-host disease and infertility. Nevertheless, SCT offers at least 95% chance of cure with low risk of chronic graft-vs-host disease when a matched-sibling donor is available and the risks of infertility can be reduced by ovarian, sperm or testis cryopreservation. Thus, all available therapies such as hydroxyurea, transfusions and SCT should be presented to the parents, providers, and affected children and discussed with them from infancy. Furthermore, the use of these therapies should be adjusted to the severity of the disease and to local availabilities in order to choose the treatment offering the best benefit/risk ratio.

Hydroxyurea: Pattern of Use, Patient Adherence, and Safety Profile in Patients with Sickle Cell Disease in Oman

OBJECTIVES

Many barriers contribute to the underutilization of hydroxyurea (HU) in the treatment of sickle cell disease (SCD), and adherence to its use is often reported to be suboptimal. It is important to have information on the safety of HU in patients with SCD. Our study assessed the pattern of use, patients' adherence to medication, discontinuation of use, and safety of HU in patients with SCD.

METHODS

This cross-sectional study was conducted in the department of medicine of a referral hospital in Oman over five months and included a review of patient files and patient interview. Approval was obtained from the Regional Research and Ethics Committee of the A'Dakhiliyah Governorate and the hospital administration. The parameters were compared between groups using the chi-square test.

RESULTS

Of 298 patients studied, 128 (43.0%) had used HU at some points. The difference in the prevalence of HU use was statistically significant based only on age (p = 0.014), with younger patients more likely to be currently using HU or used HU in the past. The majority of patients were adherent (82.5%) based on self-reported adherence. The prevalence of discontinuation (temporary or permanent) of HU use was high (57.0%), and suspected adverse drug reaction (ADR) was the most common reason. Among those who had never used HU, 33.7% of patients had an indication for the initiation of HU. A quarter of patients who used HU developed a suspected ADR, with blood abnormalities being the commonest. The duration of HU use influenced ADR prevalence (p = 0.015).

CONCLUSIONS

Among the current users of HU, the majority of the patients were adherent based on self-reported medication adherence. The prevalence of discontinuation of HU use and instances of non-initiation of HU among those indicated were high. A larger study, ideally of a prospective nature, in various governorates of Oman, would provide a wider picture at the national level.

Population Pharmacokinetic and Exposure-Response Analyses of Prasugrel in Pediatric Patients with Sickle Cell Anemia

BACKGROUND AND OBJECTIVE

Prasugrel, a P2Y₁₂ adenosine diphosphate (ADP) receptor antagonist, inhibits ADP-mediated platelet activation and aggregation in patients with sickle cell anemia (SCA). We developed a population pharmacokinetic (popPK) model in pediatric patients from 2 to <18 years of age with SCA, and performed exposure-response evaluations to characterize the effects of prasugrel in a subset of these patients who weighed 19 kg or more and experienced at least two episodes of vaso-occlusive crises (VOC) in the past year.

METHODS

A three-compartment popPK model adapted from that used in adults with acute coronary syndrome was used to describe the relationship between plasma concentrations of prasugrel's active metabolite (Pras-AM) and time using data from phase II and III clinical studies in children. A VOC event rate model was developed from the phase III study to explore the exposure-response relationship between Pras-AM exposure and VOC, and included evaluation of covariates.

RESULTS

The final popPK model for children with SCA provided a reasonable fit to Pras-AM plasma concentrations over time, with estimates of apparent clearance (CL/F) (172 L/h) and apparent volume of distribution (Vd/F) (51.7 L) that were comparable to previous studies in adults. The final model included weight as a covariate on both CL/F and Vd/F, and age as a covariate on CL/F. Analyses of safety (bleeding events requiring medical intervention) and efficacy (VOC event rate) variables showed no apparent relationship to model-predicted Pras-AM exposure quartiles, and no statistically significant effects of intrinsic or extrinsic factors on the VOC event rate were identified in the VOC event rate model. The effect of post hoc exposures on the VOC event rate did not reach statistical significance.

CONCLUSIONS

A popPK model was developed that provided reasonable parameter estimates, goodness-of-fit diagnostics, and visual predictive checks when applied to Pras-AM plasma concentrations in pediatric patients with SCA. Post hoc exposures obtained from this model did not correlate with measures of VOC or bleeding events in this population.

Risks associated with fertility preservation for women with sickle cell anemia

OBJECTIVE

To highlight the risk of complications among women with sickle cell anemia (SCA) receiving fertility preservation treatment (FPT) before hematopoietic stem cell transplant (HSCT).

DESIGN

Single-center case series.

SETTING

Academic fertility center.

PATIENT(S)

Women aged 15-32 years with SCA undergoing FPT before HSCT.

INTERVENTION(S)

Retrospective, systematic review.

MAIN OUTCOME MEASURE(S)

FPT modality, SCA complications during FPT.

RESULT(S)

Over an 8-year period (2009-2017), seven women with SCA ages 15-32 years (mean 28.5 years) underwent FPT with embryo cryopreservation (n = 1), oocyte cryopreservation (n = 4), and ovarian tissue cryopreservation (n = 2). The five women subjects who underwent oocyte or embryo cryopreservation were treated with an antagonist controlled ovarian hyperstimulation protocol and individualized gonadotropin dosing. The trigger medications included leuprolide acetate (n = 2), and human chorionic gonadotropin (n = 3). Most patients (n = 5) received a disease-modifying therapy for SCA (hydroxyurea or chronic transfusions) before FPT. Three patients experienced periprocedural SCA complications that included life-threatening respiratory failure, painful crisis requiring interruption of a stimulation cycle, and severe postharvest painful crisis.

CONCLUSION(S)

Women with SCA may choose to undergo diverse FPT strategies before HSCT and are at risk for serious SCA-related complications. Evidence-based strategies to mitigate SCA-related morbidity and to optimize fertility preservation outcomes are needed.

Intermittent or uneven daily administration of low-dose hydroxyurea is effective in treating children with sickle cell anemia in Angola

BACKGROUND

Although hydroxyurea is proven effective in treatment of sickle cell anemia (SCA) and is widely prescribed in high-income countries, due to questions about feasibility of treating large numbers of patients in resource-limited health systems, its use is limited in sub-Saharan Africa (SSA), where most children with SCA live. We assessed hematological response and toxicity of hydroxyurea treatment for SCA in Angola.

METHODS

Retrospective study of children with SCA (not selected for clinical severity) treated on a fixed dose of hydroxyurea for at least 6 months. Because only the 500 mg capsule was available, dose was averaged weekly. We evaluated toxicity events and magnitude of hydroxyurea-induced changes in blood counts and compared patients who received a uniform daily dose to those prescribed intermittent or uneven daily doses.

RESULTS

Only 13% of 303 patients received a uniform dose of hydroxyurea daily. Dose ranged from 16.5 to 22.8 mg/kg/day. Hydroxyurea increased HGB and mean cell volume values by 0.5 g/dL (P < 0.0001) and 8 fL (P < 0.0001), while ANC, PLT, and ARC decreased 1.1 × 10⁹ /L (P < 0.0001), 34 × 10⁹ /L (P = < 0.0001), and 19 × 10⁹ /L (P = 0.0008), respectively. There were no differences in magnitude of hydroxyurea-induced changes between patients prescribed intermittent or uneven doses and uniform daily doses, or between those treated in the lower and higher dose quartiles. Hematological toxicity events were mild and reversible.

CONCLUSION

Intermittent or uneven daily dosing of hydroxyurea is as effective as fixed daily doses in treating SCA. This strategy may enable treatment of additional children with SCA in SSA.

Targeted Hydroxyurea Education after an Emergency Department Visit Increases Hydroxyurea Use in Children with Sickle Cell Anemia

OBJECTIVE

To evaluate the impact of an initiative to increase hydroxyurea use among children with sickle cell anemia (SCA) who presented to the emergency department (ED).

STUDY DESIGN

This observational cohort study included children with SCA not taking hydroxyurea who presented to the ED with pain or acute chest syndrome and then attended a Quick-Start Hydroxyurea Initiation Project (Q-SHIP) session. A Q-SHIP session includes a hematologist-led discussion on hydroxyurea, a video of patients talking about hydroxyurea, and a direct offer to start hydroxyurea.

RESULTS

Over 64 weeks, 112 eligible patients presented to the ED and 59% (n = 66) participated in a Q-SHIP session a median of 6 days (IQR 2, 20 days) after ED or hospital discharge; 55% of participants (n = 36) started hydroxyurea. After a median follow-up of 49 weeks, 83% (n = 30) of these participants continued hydroxyurea. Laboratory markers of hydroxyurea adherence were significantly increased from baseline: median mean corpuscular volume +8.6 fL (IQR 5.0, 17.7, P < .0001) and median hemoglobin F +5.7% (IQR 2.5, 9.8, P = .0001). Comparing Q-SHIP participants to nonparticipants, 12 weeks after ED visit, participants were more likely to have started hydroxyurea than nonparticipants (53% vs 20%, P = .0004) and to be taking hydroxyurea at last follow-up (50% vs 20%, P = .001). Two years after the implementation of Q-SHIP the overall proportion of eligible patients on hydroxyurea presenting to our ED increased from 56% to 80%, P = .0069.

CONCLUSIONS

Participation in a clinic to specifically address starting hydroxyurea after a SCA complication increases hydroxyurea use.

Curative therapies: Allogeneic hematopoietic cell transplantation from matched related donors using myeloablative, reduced intensity, and nonmyeloablative conditioning in sickle cell disease

Sickle cell disease (SCD) chronically damages multiple organs over the lifetime of affected individuals. Allogeneic hematopoietic cell transplantation (allo-HCT) is the most studied curative intervention. Fully matched related marrow, peripheral blood derived, or cord blood HCT have the best transplant outcome for symptomatic patients with SCD. For patients with asymptomatic or milder disease who have this donor option available, risks and benefits of HCT should be discussed among the patient, family, treating hematologist, and transplant physician, and decision to proceed to HCT should be individualized. Myeloablative conditioning with busulfan, cyclophosphamide, and ATG has been a commonly employed regimen for children and young adults. Recently, low intensity conditioning with low dose total body irradiation and alemtuzumab is emerging as an efficacious and safe regimen for adults, young adults, and possibly children. Mixed donor chimerism (minimum ≥20% myeloid cells), from myeloablative or nonmyeloablative conditioning regimen, produces robust normal donor erythropoiesis and is sufficient to provide a clinical cure. The proportion of patients remaining on immunosuppression beyond 2 years post-HCT is likely <10% with either myeloablative or low intensity regimens. Late effects from myeloablative or reduced intensity conditioning, or from several more months of immunosuppression in low intensity conditioning may be less common than those observed in HCT for malignant indications. Nonmyeloablative approaches with low toxicities should be the focus of future research efforts. Prevention of GVHD is a shared goal in all approaches of allo-HCT in SCD.

The case for HLA-identical sibling hematopoietic stem cell transplantation in children with symptomatic sickle cell anemia

This article has a companion Counterpoint by DeBaun and Clayton.

An age dependent response to hydroxyurea in pediatric sickle cell anemia patients with alpha thalassemia trait

Hydroxyurea (HU) is a key drug therapy for individuals with sickle cell anemia (SCA), yet its clinical and hematologic responses can be variable. Various studies have reported the role of α-thalassemia as one of the most prevalent heritable traits that may modify HU response. We provide data from 62 pediatric and adolescent patients with SCA, 26 with co-inherited α-thalassemia trait. Our data suggest that altered hematologic and clinical responses to HU therapy are noted in adolescent SCA individuals with co-inherited α-thalassemia trait. Adolescent patients who co-inherited α-thalassemia trait had a greater reduction in vaso-occlusive episodes compared to those without α-thalassemia, despite a less robust fetal hemoglobin induction as well as a lower maximum HU dose. This clinical improvement was associated with a lower MCH and higher RBC count. Responses to HU in younger SCA children (ages 5-11years) with co-inherited α-thalassemia trait, compared to those without α-thalassemia trait, did not show any difference in number vaso-occlusive episodes, fetal hemoglobin induction and change in MCH and RBC count.

Cyclophosphamide improves engraftment in patients with SCD and severe organ damage who undergo haploidentical PBSCT

Peripheral blood stem cell transplantation (PBSCT) offers a curative option for sickle cell disease (SCD). Although HLA-matched sibling transplantation is promising, the vast majority of patients lack such a donor. We sought to develop a novel nonmyeloablative HLA-haploidentical PBSCT approach that could safely be used for patients with severe organ damage. Based on findings in our preclinical model, we developed a phase 1/2 trial using alemtuzumab, 400 cGy total body irradiation, and escalating doses of posttransplant cyclophosphamide (PT-Cy): 0 mg/kg in cohort 1, 50 mg/kg in cohort 2, and 100 mg/kg in cohort 3. A total of 21 patients with SCD and 2 with β-thalassemia received a transplant. The mean hematopoietic cell transplant-specific comorbidity index of 6 reflected patients with cirrhosis, heart failure, and end-stage renal disease. The engraftment rate improved from 1 (33%) of 3 in cohort 1 to 5 (63%) of 8 in cohort 2 and 10 (83%) of 12 in cohort 3. Percentage of donor myeloid and CD3 chimerism also improved with subsequent cohorts. There was no transplant-related mortality, and overall survival was 87%. At present, 0% in cohort 1, 25% in cohort 2, and 50% in cohort 3 remain free of their disease. There was no grade 2 to 4 acute or extensive chronic graft-versus-host disease (GVHD). Therefore, PT-Cy improves engraftment and successfully prevents severe GVHD after nonmyeloablative conditioning in patients with SCD who are at high risk for early mortality. Additional strategies are necessary to decrease the graft rejection rate and achieve a widely available cure for all patients with SCD. This trial was registered at www.clinicaltrials.gov as #NCT00977691.

Measurements of red cell deformability and hydration reflect HbF and HbA2 in blood from patients with sickle cell anemia

Decreased erythrocyte deformability, as measured by ektacytometry, may be associated with disease severity in sickle cell anemia (SCA). Heterogeneous populations of rigid and deformable cells in SCA blood result in distortions of diffraction pattern measurements that correlate with the concentration of hemoglobin S (HbS) and the percentage of irreversibly sickled cells. We hypothesize that red cell heterogeneity, as well as deformability, will also be influenced by the concentration of alternative hemoglobins such as fetal hemoglobin (HbF) and the adult variant, HbA₂. To test this hypothesis, we investigate the relationship between diffraction pattern distortion, osmotic gradient ektacytometry parameters, and the hemoglobin composition of SCA blood. We observe a correlation between the extent of diffraction pattern distortions and percentage of HbF and HbA₂. Osmotic gradient ektacytometry data indicate that minimum elongation in the hypotonic region is positively correlated with HbF, as is the osmolality at which it occurs. The osmolality at both minimum and maximum elongation is inversely correlated with HbS and HbA₂. These data suggest that HbF may effectively improve surface-to-volume ratio and osmotic fragility in SCA erythrocytes. HbA₂ may be relatively ineffective in improving these characteristics or cellular hydration at the levels found in this patient cohort.

Bone Marrow as a Hematopoietic Stem Cell Source for Gene Therapy in Sickle Cell Disease: Evidence from Rhesus and SCD Patients

Steady state bone marrow (BM) is the preferred hematopoietic stem cell (HSC) source for gene therapy in sickle cell disease (SCD) due to the recognized risk of vaso-occlusive crisis during granulocyte colony-stimulating factor mobilization. We previously established clinically relevant HSC gene transfer in the rhesus model following transplantation of mobilized peripheral blood (PB) CD34⁺ cells transduced with lentiviral vectors. In this study, we examined steady state bone marrow (BM) in the rhesus competitive repopulation model and demonstrate similar gene marking in vitro and in vivo, as compared with mobilized PB CD34⁺ cells. We then evaluated PB and steady state BM in subjects with SCD and observed a higher frequency of CD34⁺ cells when compared with controls, likely due to enhanced hematopoiesis. However, CD34⁺ cell counts were reduced in both the PB and BM in patients treated with hydroxyurea, and hydroxyurea treatment strongly inhibited iPS cell generation from SCD subjects. Our data support that steady state BM is a useful HSC source for SCD gene therapy with similar transduction. The lower CD34⁺ percentages observed with hydroxyurea treatment warrants withholding hydroxyurea temporarily prior to harvesting HSCs. Our results are important for the design of gene targeting strategies for SCD.

RNA Trans-Splicing Targeting Endogenous β-Globin Pre-Messenger RNA in Human Erythroid Cells

Sickle cell disease results from a point mutation in exon 1 of the β-globin gene (total 3 exons). Replacing sickle β-globin exon 1 (and exon 2) with a normal sequence by trans-splicing is a potential therapeutic strategy. Therefore, this study sought to develop trans-splicing targeting β-globin pre-messenger RNA among human erythroid cells. Binding domains from random β-globin sequences were comprehensively screened. Six candidates had optimal binding, and all targeted intron 2. Next, lentiviral vectors encoding RNA trans-splicing molecules were constructed incorporating a unique binding domain from these candidates, artificial 5' splice site, and γ-globin cDNA, and trans-splicing was evaluated in CD34⁺ cell-derived erythroid cells from healthy individuals. Lentiviral transduction was efficient, with vector copy numbers of 9.7 to 15.3. The intended trans-spliced RNA product, including exon 3 of endogenous β-globin and γ-globin, was detected at the molecular level. Trans-splicing efficiency was improved to 0.07-0.09% by longer binding domains, including the 5' splice site of intron 2. In summary, screening was performed to select efficient binding domains for trans-splicing. Detectable levels of trans-splicing were obtained for endogenous β-globin RNA in human erythroid cells. These methods provide the basis for future trans-splicing directed gene therapy.

Kinetic assay shows that increasing red cell volume could be a treatment for sickle cell disease

Although it has been known for more than 60 years that the cause of sickle cell disease is polymerization of a hemoglobin mutant, hydroxyurea is the only drug approved for treatment by the US Food and Drug Administration. This drug, however, is only partially successful, and the discovery of additional drugs that inhibit fiber formation has been hampered by the lack of a sensitive and quantitative cellular assay. Here, we describe such a method in a 96-well plate format that is based on laser-induced polymerization in sickle trait cells and robust, automated image analysis to detect the precise time at which fibers distort ("sickle") the cells. With this kinetic method, we show that small increases in cell volume to reduce the hemoglobin concentration can result in therapeutic increases in the delay time prior to fiber formation. We also show that, of the two drugs (AES103 and GBT440) in clinical trials that inhibit polymerization by increasing oxygen affinity, one of them (GBT440) also inhibits sickling in the absence of oxygen by two additional mechanisms.

Minireview: Prognostic factors and the response to hydroxurea treatment in sickle cell disease

This review describes current considerations in the use of hydroxyurea for the management of sickle cell disease in the context of clinical severity. Randomized trials of hydroxyurea have generally enrolled subjects with increased severity based on frequent vaso-occlusive events. An exception was the BABY HUG study in infants which documented substantial benefit even for asymptomatic subjects. Increasing data indicate that hydroxyurea has a substantial effect on reducing mortality in both adults and children-perhaps the most compelling reason for advocating the drug's widespread use. Although the efficacy of hydroxyurea is mediated primarily through increased erythrocyte fetal hemoglobin and much has been learned about the genomic influences on fetal hemoglobin levels in sickle cell disease, our ability to predict the fetal hemoglobin response to hydroxyurea remains limited; much more work in this area is indicated. The review is concluded with the recommendations of the 2014 NIH Evidence-Based Management of Sickle Cell Disease Expert Panel Report.