Evidence-based focused review of the status of hematopoietic stem cell transplantation as treatment of sickle cell disease and thalassemia

Chronic automated red cell exchange therapy for sickle cell disease

BACKGROUND

The data to support chronic automated red cell exchange (RCE) in sickle cell disease (SCD) outside of stroke prevention, is limited, especially in adults.

STUDY DESIGN AND METHODS

A retrospective analysis was conducted of patients with SCD who were referred for chronic RCE at our institution over a 10-year period. Data that were evaluated included patient demographics, referral indications, and procedural details (e.g., vascular access, adverse events, etc.). In a subanalysis, the number of annual acute care encounters during 3 years of chronic RCE was compared with that in the year preceding the first RCE.

RESULTS

A total of 164 patients were referred for chronic RCE: median age was 28 years (interquartile range [IQR] = 22-36) at referral and 60% were female. Seventy (42.6%) were naïve to chronic transfusion (simple or RCE) prior to referral. The leading indications for referral were refractory pain (73/164, 44.5%) and iron overload (57/164, 34.7%). A total of 5090 procedures occurred during the study period (median = 19, IQR = 5-45). Of the 138 patients who had central vascular access, 8 (6%) and 16 (12%) had ≥1 central-line-related thrombosis and/or infection, respectively. Of those who were not RBC alloimmunized at initiation of RCE, 12/105 (11.4%) developed new antibodies during chronic RCE. In those 30 patients who were adherent to therapy for 3 years, there was no significant difference in acute care encounters following initiation of RCE.

CONCLUSION

Prospective clinical trials are needed to determine which patients are most likely to benefit from chronic RCE and refine selection accordingly.

Organ function indications and potential improvements following curative therapy for sickle cell disease

Curative therapies for sickle cell disease include allogeneic hematopoietic stem cell transplantation (HSCT) and gene-modified autologous stem cell transplantation. HSCT has been used for 30 years with success measured by engraftment, symptom control, graft-vs-host disease (GVHD) risk, organ toxicity, and immune reconstitution. While human leukocyte antigen-matched sibling donor (MSD) transplants have excellent outcomes, alternate donor transplants (unrelated/haploidentical) are just beginning to overcome GVHD and engraftment hurdles to match MSD. Gene therapy, a newly developed treatment, is undergoing careful evaluation in many trials with varying approaches. The risk/benefit ratio to the patient in relation to outcomes, toxicities, and mortality risk drives eligibility for curative interventions. Consequently, eligibility criteria for MSD transplants can be less stringent, especially in the young. Posttransplant outcome analysis after the "cure" with respect to organ function recovery is essential. While established damage such as stroke is irreversible, transplant can help stabilize (pulmonary function), prevent further deterioration (stroke), improve (neurocognition), and protect unaffected organs. Tracking organ functions postintervention uniformly between clinical trials and for adequate duration is essential to answer safety and efficacy questions related to curative therapies. Age-appropriate application/outcome analyses of such therapies will be the ultimate goal in overcoming this disease.

Decision making for hematopoietic stem cell transplantation in pediatric, adolescent, and young adult patients with a hemoglobinopathy-Shared or not?

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) offers an established curative option for sickle cell disease (SCD) and thalassemia patients but is associated with significant risks. Decision making is a complex process and shared decision making (SDM) could be a fitting approach in case of such preference-sensitive decisions. This study investigated what level of SDM is used in conversations with hemoglobinopathy patients and/or their caregivers considering HSCT as a curative treatment option.

METHODS

Longitudinal, descriptive study using the Observing-Patient-Involvement-in-Decision-Making scale (OPTION⁵ ) scale to determine the level of SDM in conversations with 26 hemoglobinopathy patients and/or their caregivers.

RESULTS

The total mean OPTION⁵ score was 43%, which is a moderate SDM approach. There was no difference between conversations with thalassemia patients and SCD patients. Conversations needing an interpreter scored worse than nontranslated conversations. The best scoring OPTION⁵ item was item 3: "informing about the various treatment options" (mean score 2.3 on scale 0-4). For OPTION⁵ item 4: "eliciting patients' preferences" a more skilled effort was measured for SCD patients compared to thalassemia patients.

CONCLUSIONS

The mean OPTION⁵ score of "moderate" was achieved mainly by giving information on available options, which is primarily a one-way communication. The SDM process can be improved by actively inviting patients to deliberate about options and including their elicited preferences in decision making.

Navigating decisional conflict as a family when facing the decision of stem cell transplant for a child or adolescent with sickle cell disease

OBJECTIVE

Patients with sickle cell disease (SCD) face unpredictable disease, with stem cell transplant being a curative treatment option with risks. The aim of this study was to describe the level and source of decisional conflict in families of children/adolescents with SCD facing a transplant decision.

METHODS

A multiple-case study approach described decisional conflict in various SCD severity/donor risk decisional contexts. Cases included parents, child/adolescent with SCD, and sibling donor. The level and source of conflict was measured via O'Connor's Decisional Conflict Scale and analyzed using pattern-matching and cross-case synthesis. In-depth descriptions of conflict sources were obtained through thematic analysis of observation and interview data.

RESULTS

Among 11 participants in four cases (i.e. family units) decisional conflict was not unique not to the decisional context. Conflict levels represented a level that can be linked with feeling unsure and decisional delay. The theme, 'navigating decisional conflict together', described how family units discussed uncertainties.

CONCLUSION

Varying levels and sources of decisional conflict exist in pediatric patients with SCD and their families considering transplant.

PRACTICE IMPLICATIONS

In our cases, decisional conflict and the transplant decision occurred at the family-level. Clinicians should encourage all family members to participate in discussions concerning transplant.

Universal Gene Correction Approaches for β-hemoglobinopathies Using CRISPR-Cas9 and Adeno-Associated Virus Serotype 6 Donor Templates

Mutations in the human β-globin gene are the cause of β-hemoglobinopathies, one of the most common inherited single-gene blood disorders in the world. Novel therapeutic approaches are based on lentiviral vectors (LVs) or CRISPR-Cas9-mediated gene disruption to express adult hemoglobin (HbA), or to reactivate the completely functional fetal hemoglobin, respectively. Nonetheless, LVs present a risk of insertional mutagenesis, while gene-disrupting transcription factors (BCL11A, KLF1) involved in the fetal-to-adult hemoglobin switch might generate dysregulation of other cellular processes. Therefore, universal gene addition/correction approaches combining CRISPR-Cas9 and homology directed repair (HDR) by delivering a DNA repair template through adeno-associated virus could mitigate the limitations of both lentiviral gene transfer and gene disruption strategies, ensuring targeted integration and controlled transgene expression. In this study, we attained high rates of gene addition (up to 12%) and gene correction (up to 38%) in hematopoietic stem and progenitor cells from healthy donors without any cell sorting/enrichment or the application of HDR enhancers. Furthermore, these approaches were tested in heterozygous (β⁰/β⁺) and homozygous (β⁰/β⁰, β⁺/β⁺) β-thalassemia patients, achieving a significant increase in HbA and demonstrating the universal therapeutic potential of this study for the treatment of β-hemoglobinopathies.

How to Facilitate Decision-Making for Hematopoietic Stem Cell Transplantation in Patients With Hemoglobinopathies. The Perspectives of Healthcare Professionals

Hematopoietic stem cell transplantation decision-making for hemoglobinopathy patients is a complex process, and it remains difficult for health care professionals to decide whether and when a hematopoietic stem cell transplantation should be offered. Gaining insight into health care professionals' considerations is required to understand and optimize this decision-making process. A qualitative interview study using semi-structured interviews with eighteen health care professionals. Data were thematically analyzed. Two main themes emerged from the data: (1) Experiencing the influence of a frame of reference and (2) Feeling responsible for a guided decision-making. The frame of reference, meaning the health care professionals' knowledge and experiences regarding hematopoietic stem cell transplantation, influenced the guided decision-making process. Subsequently, three subthemes evolved from the second theme: (a) weighing up disease severity against possible complications, (b) making an effort to inform, and (c) supporting the best fitting decision for the individual patient. The health care professionals' frame of reference determined the hematopoietic stem cell transplantation decision-making process. This demands reflection on the health care professionals' own frame of reference and its influence on decision-making. Furthermore, reflection on the frame of reference is needed by exchange of knowledge and experiences between referring and referred-to healthcare professionals in an open and two-way direction. The transplantation teams have a responsibility of keeping the frame of reference of their referring colleagues up to date and referring health care professionals should share their feelings regarding hematopoietic stem cell transplantation. To guide patients, a shared decision-making approach is supportive, in which eliciting the patients' preferences is highly important. Health care professionals can refine the decision-making process by guiding patients in eliciting their preferences and including these in the decision.

Discovery of Novel Fetal Hemoglobin Inducers through Small Chemical Library Screening

The screening of chemical libraries based on cellular biosensors is a useful approach to identify new hits for novel therapeutic targets involved in rare genetic pathologies, such as β-thalassemia and sickle cell disease. In particular, pharmacologically mediated stimulation of human γ-globin gene expression, and increase of fetal hemoglobin (HbF) production, have been suggested as potential therapeutic strategies for these hemoglobinopathies. In this article, we screened a small chemical library, constituted of 150 compounds, using the cellular biosensor K562.GR, carrying enhanced green fluorescence protein (EGFP) and red fluorescence protein (RFP) genes under the control of the human γ-globin and β-globin gene promoters, respectively. Then the identified compounds were analyzed as HbF inducers on primary cell cultures, obtained from β-thalassemia patients, confirming their activity as HbF inducers, and suggesting these molecules as lead compounds for further chemical and biological investigations.

Supramolecular nanosubstrate-mediated delivery system enables CRISPR-Cas9 knockin of hemoglobin beta gene for hemoglobinopathies

Leveraging the endogenous homology-directed repair (HDR) pathway, the CRISPR-Cas9 gene-editing system can be applied to knock in a therapeutic gene at a designated site in the genome, offering a general therapeutic solution for treating genetic diseases such as hemoglobinopathies. Here, a combined supramolecular nanoparticle (SMNP)/supramolecular nanosubstrate-mediated delivery (SNSMD) strategy is used to facilitate CRISPR-Cas9 knockin of the hemoglobin beta (HBB) gene into the adeno-associated virus integration site 1 (AAVS1) safe-harbor site of an engineered K562 3.21 cell line harboring the sickle cell disease mutation. Through stepwise treatments of the two SMNP vectors encapsulating a Cas9•single-guide RNA (sgRNA) complex and an HBB/green fluorescent protein (GFP)-encoding plasmid, CRISPR-Cas9 knockin was successfully achieved via HDR. Last, the HBB/GFP-knockin K562 3.21 cells were introduced into mice via intraperitoneal injection to show their in vivo proliferative potential. This proof-of-concept demonstration paves the way for general gene therapeutic solutions for treating hemoglobinopathies.

Comparative analysis of lentiviral gene transfer approaches designed to promote fetal hemoglobin production for the treatment of β-hemoglobinopathies

β-Hemoglobinopathies are among the most common single-gene disorders and are caused by different mutations in the β-globin gene. Recent curative therapeutic approaches for these disorders utilize lentiviral vectors (LVs) to introduce a functional copy of the β-globin gene into the patient's hematopoietic stem cells. Alternatively, fetal hemoglobin (HbF) can reduce or even prevent the symptoms of disease when expressed in adults. Thus, induction of HbF by means of LVs and other molecular approaches has become an alternative treatment of β-hemoglobinopathies. Here, we performed a head-to-head comparative analysis of HbF-inducing LVs encoding for: 1) IGF2BP1, 2) miRNA-embedded shRNA (shmiR) sequences specific for the γ-globin repressor protein BCL11A, and 3) γ-globin gene. Furthermore, two novel baboon envelope proteins (BaEV)-LVs were compared to the commonly used vesicular-stomatitis-virus glycoprotein (VSV-G)-LVs. Therapeutic levels of HbF were achieved for all VSV-G-LV approaches, from a therapeutic level of 20% using γ-globin LVs to 50% for both IGF2BP1 and BCL11A-shmiR LVs. Contrarily, BaEV-LVs conferred lower HbF expression with a peak level of 13%, however, this could still ameliorate symptoms of disease. From this thorough comparative analysis of independent HbF-inducing LV strategies, we conclude that HbF-inducing VSV-G-LVs represent a promising alternative to β-globin gene addition for patients with β-hemoglobinopathies.

Highly efficient editing of the β-globin gene in patient-derived hematopoietic stem and progenitor cells to treat sickle cell disease

Sickle cell disease (SCD) is a monogenic disorder that affects millions worldwide. Allogeneic hematopoietic stem cell transplantation is the only available cure. Here, we demonstrate the use of CRISPR/Cas9 and a short single-stranded oligonucleotide template to correct the sickle mutation in the β-globin gene in hematopoietic stem and progenitor cells (HSPCs) from peripheral blood or bone marrow of patients with SCD, with 24.5 ± 7.6% efficiency without selection. Erythrocytes derived from gene-edited cells showed a marked reduction of sickle cells, with the level of normal hemoglobin (HbA) increased to 25.3 ± 13.9%. Gene-corrected SCD HSPCs retained the ability to engraft when transplanted into non-obese diabetic (NOD)-SCID-gamma (NSG) mice with detectable levels of gene correction 16-19 weeks post-transplantation. We show that, by using a high-fidelity SpyCas9 that maintained the same level of on-target gene modification, the off-target effects including chromosomal rearrangements were significantly reduced. Taken together, our results demonstrate efficient gene correction of the sickle mutation in both peripheral blood and bone marrow-derived SCD HSPCs, a significant reduction in sickling of red blood cells, engraftment of gene-edited SCD HSPCs in vivo and the importance of reducing off-target effects; all are essential for moving genome editing based SCD treatment into clinical practice.

Sickle cell retinopathy. A focused review

PURPOSE

To provide a focused review of sickle cell retinopathy in the light of recent advances in the pathogenesis, multimodal retinal imaging, management of the condition, and migration trends, which may lead to increased prevalence of the condition in the Western world.

METHODS

Non-systematic focused literature review.

RESULTS

Sickle retinopathy results from aggregation of abnormal hemoglobin in the red blood cells in the retinal microcirculation, leading to reduced deformability of the red blood cells, stagnant blood flow in the retinal precapillary arterioles, thrombosis, and ischemia. This may be precipitated by hypoxia, acidosis, and hyperosmolarity. Sickle retinopathy may result in sight threatening complications, such as paracentral middle maculopathy or sequelae of proliferative retinopathy, such as vitreous hemorrhage and retinal detachment. New imaging modalities, such as wide-field imaging and optical coherence tomography angiography, have revealed the microstructural features of sickle retinopathy, enabling earlier diagnosis. The vascular growth factor ANGPTL-4 has recently been identified as a potential mediator of progression to proliferative retinopathy and may represent a possible therapeutic target. Laser therapy should be considered for proliferative retinopathy in order to prevent visual loss; however, the evidence is not very strong. With recent development of wide-field imaging, targeted laser to ischemic retina may prove to be beneficial. Exact control of intraoperative intraocular pressure, including valved trocar vitrectomy systems, may improve the outcomes of vitreoretinal surgery for complications, such as vitreous hemorrhage and retinal detachment. Stem cell transplantation and gene therapy are potentially curative treatments, which may prevent retinopathy.

CONCLUSIONS

There is lack of evidence regarding the optimal management of sickle retinopathy. Further study is needed to determine if recent progress in the understanding of the pathophysiology and diagnosis of sickle retinopathy may translate into improved management and outcome.

Hydroxyurea Treated β-Thalassemia Children Demonstrate a Shift in Metabolism Towards Healthy Pattern

Augmentation of fetal hemoglobin (HbF) production has been an enduring therapeutic objective in β-thalassemia patients for which hydroxyurea (HU) has largely been the drug of choice and the most cost-effective approach. A serum metabolomics study on 40 patients with β-thalassemia prior to and after administration of HU was done along with healthy controls. Treated patients were divided further into non-responders (NR), partial (PR) and good (GR) per their response. 25 metabolites that were altered before HU therapy at p ≤ 0.05 and fold change >2.0 in β-thalassemia patients; started reverting towards healthy group after HU treatment. A prediction model based on another set of 70 HU treated patients showed a good separation of GR from untreated β-thalassemia patients with an overall accuracy of 76.37%. Metabolic pathway analysis revealed that various important pathways that were disturbed in β-thalassemia were reverted after treatment with HU and among them linoleic acid pathway was most impactfully improved in HU treated patients which is a precursor of important signaling molecules. In conclusion, this study indicates that HU is a good treatment option for β-thalassemia patients because in addition to reducing blood transfusion burden it also ameliorates disease complications by shifting body metabolism towards normal.

Access to hematopoietic stem cell transplant for patients with sickle cell anemia

Hematopoietic stem cell transplantation (HSCT) is a curative therapy for patients with phenotypically severe sickle cell anemia, and survival rates following matched-sibling HSCT are very high. However, despite cure rates much higher than HSCT for malignant diseases, the field has been slow to adopt this treatment modality for sickle cell anemia. This article explores some of the social forces that may contribute to this dichotomy.

On the Value of the Umbilical Cord Blood Supply

BACKGROUND

Several public cord blood banks are struggling financially, and the question remains as to whether additional allocations of funds to them are justified.

OBJECTIVES

To estimate the social benefits of public cord blood bank inventory net of cord blood banks' operational costs.

METHODS

We used publicly available data from the Health Resources and Service Administration on the number of annual cord blood transplants as well as the patient age distribution in 2010, and the survival estimates between 2008 and 2012 for the several diseases treated by cord blood transplantation. Data on aggregate annual costs to the cord blood industry for recruitment, processing, and storage were obtained from published work. We used estimated increases in life expectancy due to treatment using umbilical cord blood and value for life-years gained to estimate the social benefits of the public cord blood inventory annually.

RESULTS

We found that the annual social benefits of between $500 million and $1.5 billion outweigh the current operational annual costs of running cord blood banks of $60 to $70 million by a significant margin.

CONCLUSIONS

We estimated that the annual social benefit of having a cord blood system far outweighs its costs, by more than an order of magnitude. Thus, the social benefits of maintaining the US public cord blood banking system at the present time far outweigh the costs of collecting, storing, and distributing cord blood. This suggests that there is a potential justification for government intervention to align social benefits and costs. Nevertheless, simple fixes may produce unintended consequences, and so a careful design for subsidies is needed.

Rare single gene disorders: estimating baseline prevalence and outcomes worldwide

As child mortality rates overall are decreasing, non-communicable conditions, such as genetic disorders, constitute an increasing proportion of child mortality, morbidity and disability. To date, policy and public health programmes have focused on common genetic disorders. Rare single gene disorders are an important source of morbidity and premature mortality for affected families. When considered collectively, they account for an important public health burden, which is frequently under-recognised. To document the collective frequency and health burden of rare single gene disorders, it is necessary to aggregate them into large manageable groupings and take account of their family implications, effective interventions and service needs. Here, we present an approach to estimate the burden of these conditions up to 5 years of age in settings without empirical data. This approaches uses population-level demographic data, combined with assumptions based on empirical data from settings with data available, to provide population-level estimates which programmes and policy-makers when planning services can use.

Treatment Options for Sickle Cell Disease

Sickle cell disease (SCD) complications begin with the polymerization of sickle hemoglobin (HbS). Thus, SCD therapies are focused on preventing HbS production or reducing the circulating amount of HbS. Hydroxyurea treatment has become more widespread, whereas the number of evidence-based indications for erythrocyte transfusion is small. Hematopoietic stem cell transplant is a curative option for SCD but less than 25% of patients have a suitable donor. This article focuses on supportive and preventive care improvements and the benefits of hydroxyurea. Indications for erythrocyte transfusion, hematopoietic stem cell transplant, and gene therapy trials are also summarized.

Early Identification of Barriers and Facilitators to Self-Management Behaviors in Pediatric Patients With Sickle Cell Disease to Minimize Hematopoietic Cell Transplantation Complications

Hematopoietic cell transplantation (HCT) is an elective, curative treatment option for patients with sickle cell disease (SCD). Transplant requires extensive self-management behaviors to be successful. The purpose of this study was to describe potential barriers and facilitators to self-management in a group of pediatric patients with SCD prior to HCT and their medical outcomes post-HCT. A multiple case study approach was used to describe 4 pairs of transplant recipients grouped by age, donor type, and donor source. Each pair included a case with minimal and increased post-HCT complications. Complications included readmissions, graft-versus-host disease, systemic infections, and survival in the first year post-HCT. Variables were retrospectively collected and content analyzed to identify barriers and facilitators within and across pairs using existing self-management frameworks. While higher risk transplants experienced more complications, 3 of the 4 cases with increased complications had a larger number of modifiable barriers identified compared with those experiencing minimal complications. At least one modifiable barrier and multiple facilitators were identified in all cases. A standardized psychosocial assessment process with an established plan to mitigate barriers and promote facilitators to self-management is essential to optimize outcomes in patients with SCD undergoing elective HCT.

A Phase II, Multicenter, Single-Arm Study to Evaluate the Safety and Efficacy of Deferasirox after Hematopoietic Stem Cell Transplantation in Children with β-Thalassemia Major

We conducted a prospective, phase II, multicenter, single-arm study to evaluate the efficacy and safety of deferasirox in patients age >2 to <18 years with β-thalassemia major (TM) who underwent hematopoietic stem cell transplantation (HSCT) and had evidence of iron overload (serum ferritin >1000 µg/L; cardiac MRI T2* <20 ms, or liver iron concentration [LIC; by MRI R2]  ≥5 mg/g). Patients received deferasirox at an initial dose of 10 mg/kg/day, with up-titration to a maximum of 20 mg/kg/day. The study continued for 52 weeks and included a total of 27 patients (mean age, 9.1 ± 3.8 years; 70.4% male). One patient (3.7%) was lost to follow-up. The majority of patients (n = 20; 74.1%) were able to achieve the intended dose of 20 mg/kg/day. No deaths occurred. A total of 134 adverse events (AEs) were reported in 25 patients (92.6%) during the study. The majority of patients had grade 1 or 2 AEs, with only 8 patients (29.6%) experiencing grade 3 AEs. Only 10 AEs occurring in 4 patients (14.8%) were suspected to be related to deferasirox (ALT/AST increase, n = 4; urinary tract infection, n = 1). The deferasirox dose had to be adjusted or interrupted for 6 AEs occurring in 4 patients (14.8%). A total of 6 serious AEs occurred in 3 patients (11.1%), none of which were suspected to be related to deferasirox. From baseline to week 52, there were decreases in median concentrations of alanine aminotransferase (ALT), from 30.0 to 17.0 IU/L, and aspartate aminotransferase (AST), from 35.5 to 26.0 IU/L. Median serum creatinine and cystatin C concentrations were similar at baseline and week 52. There was a continuous and significant decrease in median serum ferritin level from 1718.0 µg/L at baseline to 845.3 µg/L following 52 weeks of therapy (P < .001); 9 patients (33.3%) achieved a level of <500 µg/L. There was also a significant decrease in median LIC (from 8.6 to 4.1 mg/g; P < .001) and an increase in median cardiac T2* (from 26.0 to 28.0 ms; P = .520) from baseline to week 52. Our findings indicate that deferasirox treatment at doses up to 20 mg/kg/day reduces the iron burden in children with TM post-HSCT, with a manageable safety profile.

Comparison of Outcomes in Patients Having Acute Myocardial Infarction With Versus Without Sickle-Cell Anemia

Sickle-cell disease (SCD) affects millions worldwide. Sickle-cell anemia (SCA), the most severe form of this disease, is the most common inherited blood disorder in the United States. There are limited data on the incidence, clinical characteristics, and outcomes of acute myocardial infarction (AMI) in these patients. Using data from the National Inpatient Sample database, we matched cases (AMI with SCA) with controls (AMI without SCA) in a 1:1 ratio for age, gender, race, and year of admission. We compared both groups in terms of clinical characteristics and inpatient outcomes and performed a logistic regression with mortality as the primary outcome. Using weighted samples, we also described trends of SCA in the general population of patients with AMI. Of the 2,386,657 admissions with AMI, SCA was reported in 501 (0.02%) patients, and 495 were successfully matched to controls. Patients with SCA were less likely to have risk factors for coronary artery disease than those without SCA. Patients with SCA were more likely to develop pneumonia, respiratory failure, and acute renal failure, and require mechanical ventilation, hemodialysis for acute renal failure and blood transfusion. In-hospital mortality was significantly higher in patients with SCA. In a multivariate analysis, SCA was an independent predictor of mortality (odds ratio 3.49; 95% confidence interval 1.99 to 6.12; p = < .001). In conclusion, myocardial infarction occurs in patients with SCA at a relatively early age. These patients do not typically have the traditional risk factors for the acute coronary syndrome. Mortality in these patients is significantly higher in age-, gender-, and race-matched controls.

Identification of Aptamers That Bind to Sickle Hemoglobin and Inhibit Its Polymerization

The pathophysiology of sickle cell disease (SCD) is dependent on the polymerization of deoxygenated sickle hemoglobin (HbS), leading to erythrocyte deformation (sickling) and vaso-occlusion within the microvasculature. Following deoxygenation, there is a delay time before polymerization is initiated, during which nucleation of HbS monomers occurs. An agent with the ability to extend this delay time or slow polymerization would therefore hold a therapeutic, possibly curative, potential. We used the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) method to screen for HbS-binding RNA aptamers modified with nuclease-resistant 2'-fluoropyrimidines. Polymerization assays were employed to identify aptamers with polymerization-inhibitory properties. Two noncompeting aptamers, DE3A and OX3B, were found to bind hemoglobin, significantly increase the delay time, and reduce the rate of polymerization of HbS. These modifiable, nuclease-resistant aptamers are potential new therapeutic agents for SCD.

Revisiting beta thalassemia intermedia: past, present, and future prospects

BACKGROUND

The spectrum of thalassemias is wide ranging from thalassemia minor, which consists of mild hypochromic microcytic anemia without obvious clinical manifestations, to thalassemia major (TM), which is characterized by severe anemia since the first years of life and is transfusion dependent. Thalassemia intermedia (TI) describes those patients with mild or moderate anemia.

OBJECTIVE

To describe the genetic features and major clinical complications of TI, and the therapeutic approaches available in the management of this disease.

METHODS

Publications from potentially relevant journals were searched on Medline.

RESULTS AND DISCUSSION

Over the past decade, the understanding of TI has increased with regard to pathophysiology and molecular studies. It is now clear that clinical presentation and specific complications make TI different from TM. It is associated with greater morbidity, a wider spectrum of organ dysfunction and more complications than previously thought.

CONCLUSION

TI is not a mild disease. The interplay of three hallmark pathophysiologic factors (ineffective erythropoiesis, chronic anemia, and iron overload) leads to the clinical presentations seen in TI. New treatment modalities are currently being investigated to broaden the options available for TI management.

Bidirectional immune tolerance in nonmyeloablative MHC-mismatched BMT for murine β-thalassemia

Nonmyeloablative conditioning using total lymphoid irradiation (TLI) and rabbit antithymocyte serum (ATS) (the murine preclinical equivalent of antithymocyte globulin [ATG]) facilitates immune tolerance after bone marrow transplantation (BMT) across major histocompatibility complex (MHC) disparities and may be a useful strategy for nonmalignant disorders. We previously reported that donor effector T-cell function and graft-versus-host disease (GVHD) are regulated via recipient invariant natural killer T-cell (iNKT) interleukin-4-driven expansion of donor Foxp3⁺ naturally occurring regulatory T cells (Tregs). This occurs via recipient iNKT- and STAT6-dependent expansion of recipient myeloid dendritic cells (MDCs) that induce contact-dependent expansion of donor Treg through PD-1/PD ligand signaling. After TLI/ATS + BMT, Gr-1^lowCD11c⁺ MDCs and Gr-1^highCD11c^neg myeloid-derived suppressor cells (MDSCs) were enriched in GVHD target organs. We now report that the recovery of both recipient MDSCs (P < .01) and MDCs (P < .01) is significantly increased when the alkylator cyclophosphamide (CTX) is added to TLI/ATS conditioning. In a BALB/c → B6 lethal GVHD model, adoptive transfer of MDSCs from TLI/ATS/CTX-conditioned recipients is associated with significantly improved GVHD colitis and survival (P < .001), conversion of MDSCs to PD ligand-expressing MDCs, and increased donor naturally occurring Treg recovery (P < .01) compared with control treatment. Using BALB/c donors and β-thalassemic HW-80 recipients, we found significantly improved rates of engraftment and GVHD following TLI/ATS/CTX compared with TLI/ATS, lethal or sublethal total body irradiation/ATS/CTX, or CTX/ATS conditioning. These data provide preclinical support for trials of TLI/ATG/alkylator regimens for MHC-mismatched BMT for hemoglobinopathies. The data also delineate innate immune mechanisms by which TLI/ATS/CTX conditioning may augment transplantation tolerance.

Sickle cell disease: an international survey of results of HLA-identical sibling hematopoietic stem cell transplantation

Despite advances in supportive therapy to prevent complications of sickle cell disease (SCD), access to care is not universal. Hematopoietic cell transplantation is, to date, the only curative therapy for SCD, but its application is limited by availability of a suitable HLA-matched donor and lack of awareness of the benefits of transplant. Included in this study are 1000 recipients of HLA-identical sibling transplants performed between 1986 and 2013 and reported to the European Society for Blood and Marrow Transplantation, Eurocord, and the Center for International Blood and Marrow Transplant Research. The primary endpoint was event-free survival, defined as being alive without graft failure; risk factors were studied using a Cox regression models. The median age at transplantation was 9 years, and the median follow-up was longer than 5 years. Most patients received a myeloablative conditioning regimen (n = 873; 87%); the remainder received reduced-intensity conditioning regimens (n = 125; 13%). Bone marrow was the predominant stem cell source (n = 839; 84%); peripheral blood and cord blood progenitors were used in 73 (7%) and 88 (9%) patients, respectively. The 5-year event-free survival and overall survival were 91.4% (95% confidence interval, 89.6%-93.3%) and 92.9% (95% confidence interval, 91.1%-94.6%), respectively. Event-free survival was lower with increasing age at transplantation (hazard ratio [HR], 1.09; P < .001) and higher for transplantations performed after 2006 (HR, 0.95; P = .013). Twenty-three patients experienced graft failure, and 70 patients (7%) died, with the most common cause of death being infection. The excellent outcome of a cohort transplanted over the course of 3 decades confirms the role of HLA-identical sibling transplantation for children and adults with SCD.

Hematopoietic Stem Cell Transplantation in Adult Sickle Cell Disease: Problems and Solutions

Sickle cell disease-related organ injuries cannot be prevented despite hydroxyurea use, infection prophylaxis, and supportive therapies. As a consequence, disease-related mortality reaches 14% in adolescents and young adults. Hematopoietic stem cell transplantation is a unique curative therapeutic approach for sickle cell disease. Myeloablative allogeneic hematopoietic stem cell transplantation is curative for children with sickle cell disease. Current data indicate that long-term disease-free survival is about 90% and overall survival about 95% after transplantation. However, it is toxic in adults due to organ injuries. In addition, this curative treatment approach has several limitations, such as difficulties to find donors, transplant-related mortality, graft loss, graft-versus-host disease (GVHD), and infertility. Engraftment effectivity and toxicity for transplantations performed with nonmyeloablative reduced-intensity regimens in adults are being investigated in phase 1/2 trials at many centers. Preliminary data indicate that GVHD could be prevented with transplantations performed using reduced-intensity regimens. It is necessary to develop novel regimens to prevent graft loss and reduce the risk of GVHD.

Clinical Features of β-Thalassemia and Sickle Cell Disease

Sickle cell disease (SCD) and β-thalassemia are among the most common inherited diseases, affecting millions of persons globally. It is estimated that 5-7% of the world's population is a carrier of a significant hemoglobin variant. Without early diagnosis followed by initiation of preventative and therapeutic care, both SCD and β-thalassemia result in significant morbidity and early mortality. Despite great strides in the understanding of the molecular basis and pathophysiology of these conditions, the burden of disease remains high, particularly in limited resource settings. Current therapy relies heavily upon the availability and safety of erythrocyte transfusions to treat acute and chronic complications of these conditions, but frequent transfusions results in significant iron overload, as well as challenges from acquired infections and alloimmunization. Hydroxyurea is a highly effective treatment for SCD but less so for β-thalassemia, and does not represent curative therapy. As technology and use of cellular and gene therapies expand, SCD and thalassemia should be among the highest disease priorities.

Pediatric sickle cell disease: past successes and future challenges

Once a fatal disease of childhood, more than 95% of patients born today with sickle cell disease (SCD) in developed countries are expected to survive into adulthood, largely because of improvements in supportive and preventive care (newborn screening, penicillin prophylaxis, transcranial Doppler (TCD) screening). Hydroxyurea (HU) therapy, the only oral medication currently available to prevent SCD complications, has become more widespread over the past 20 y. The NHLBI recommends that HU be offered to all patients with HbSS beginning at 9 mo of age, and the recently published Abnormal TCD with Transfusions Changing to HU (TWiTCH) trial has shown HU as an acceptable alternative to transfusion therapy for patients at high risk of stroke. While hematopoietic stem cell transplant (HSCT) is a curative option for SCD, less than 25% of patients have a suitable donor. Alternative stem cell sources from unrelated donors and haplo-identical donors are currently under investigation as are gene therapy trials. This review will focus on early efforts to elucidate SCD pathophysiology as well as supportive and preventive care improvements. Findings from recent multi-center studies (Silent Infarct Transfusion (SIT) Trial and TWiTCH) will be summarized. Finally, HSCT trials and gene therapy will be reviewed.

CRISPR-Cas9 technology and its application in haematological disorders

The recent advent of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR associated protein 9 (Cas9) system for precise genome editing has revolutionized methodologies in haematology and oncology studies. CRISPR-Cas9 technology can be used to remove and correct genes or mutations, and to introduce site-specific therapeutic genes in human cells. Inherited haematological disorders represent ideal targets for CRISPR-Cas9-mediated gene therapy. Correcting disease-causing mutations could alleviate disease-related symptoms in the near future. The CRISPR-Cas9 system is also a useful tool for delineating molecular mechanisms involving haematological malignancies. Prior to the use of CRISPR-Cas9-mediated gene correction in humans, appropriate delivery systems with higher efficiency and specificity must be identified, and ethical guidelines for applying the technology with controllable safety must be established. Here, the latest applications of CRISPR-Cas9 technology in haematological disorders, current challenges and future directions are reviewed and discussed.

Optimizing autologous cell grafts to improve stem cell gene therapy

Over the past decade, stem cell gene therapy has achieved unprecedented curative outcomes for several genetic disorders. Despite the unequivocal success, clinical gene therapy still faces challenges. Genetically engineered hematopoietic stem cells are particularly vulnerable to attenuation of their repopulating capacity once exposed to culture conditions, ultimately leading to low engraftment levels posttransplant. This becomes of particular importance when transduction rates are low or/and competitive transplant conditions are generated by reduced-intensity conditioning in the absence of a selective advantage of the transduced over the unmodified cells. These limitations could partially be overcome by introducing megadoses of genetically modified CD34(+) cells into conditioned patients or by transplanting hematopoietic stem cells hematopoietic stem cells with high engrafting and repopulating potential. On the basis of the lessons gained from cord blood transplantation, we summarize the most promising approaches to date of increasing either the numbers of hematopoietic stem cells for transplantation or/and their engraftability, as a platform toward the optimization of engineered stem cell grafts.

HLA-haploidentical blood or marrow transplantation with high-dose, post-transplantation cyclophosphamide

In the past, partially HLA-mismatched related donor, or HLA-haploidentical, blood or marrow transplantation (haploBMT), for hematologic malignancies has been complicated by unacceptably high incidences of graft rejection or GvHD resulting from intense bi-directional alloreactivity. Administration of high doses of cyclophosphamide early after haploBMT selectively kills proliferating, alloreactive T cells while sparing non-alloreactive T cells responsible for immune reconstitution and resistance to infection. In the clinic, haploBMT with high-dose, post-transplantation cyclophosphamide is associated with acceptably low incidences of fatal graft rejection, GvHD and non-relapse mortality, and provides an acceptable treatment option for hematologic malignancies patients lacking suitably HLA-matched donors. HaploBMT with PTCy is now being investigated as a treatment of hemoglobinopathy and as a method for inducing tolerance to solid organs transplanted from the same donor. Ongoing and future clinical trials will establish the hierarchy of donor preference for hematologic malignancy patients lacking an HLA-matched sibling.

The therapeutic potential of genome editing for β-thalassemia

The rapid advances in the field of genome editing using targeted endonucleases have called considerable attention to the potential of this technology for human gene therapy. Targeted correction of disease-causing mutations could ensure lifelong, tissue-specific expression of the relevant gene, thereby alleviating or resolving a specific disease phenotype. In this review, we aim to explore the potential of this technology for the therapy of β-thalassemia. This blood disorder is caused by mutations in the gene encoding the β-globin chain of hemoglobin, leading to severe anemia in affected patients. Curative allogeneic bone marrow transplantation is available only to a small subset of patients, leaving the majority of patients dependent on regular blood transfusions and iron chelation therapy. The transfer of gene-corrected autologous hematopoietic stem cells could provide a therapeutic alternative, as recent results from gene therapy trials using a lentiviral gene addition approach have demonstrated. Genome editing has the potential to further advance this approach as it eliminates the need for semi-randomly integrating viral vectors and their associated risk of insertional mutagenesis. In the following pages we will highlight the advantages and risks of genome editing compared to standard therapy for β-thalassemia and elaborate on lessons learned from recent gene therapy trials.

Modeling promising nonmyeloablative conditioning regimens in nonhuman primates

Minimal conditioning or even no conditioning would be the preferred preparation for most gene therapy applications for nonmalignant diseases. However, reduced intensity conditioning (RIC) regimens in patients with nonhematologic malignancies have not led to long-term engraftment unless a selective advantage was present for the transplanted donor cells. Similar findings have also been observed in a number of large animal studies. Inadequate myelosuppression levels were thought to be responsible for the outcomes. To address this issue several innovative protocols in small animals have been presented with selective hematopoietic myelosuppression and less systemic toxicity. Such protocols promised to curb the transplant-related morbidity and mortality in myeloablative conditioning and provide effective long-term engraftment, especially in patients with gene-corrected autografts. In the present study we have tested some of these promising RIC regimens in nonhuman primates, a clinically relevant large animal model. Our data suggest that transient myelosuppression induced by anti-c-Kit antibody in conjunction with low-dose irradiation may lead to long-term engraftment, albeit at low levels. The animals with busulfan conditioning with or without anti-c-Kit that received gene-modified autologous transplants with green fluorescent protein expression had similar myelosuppression, but failed long-term engraftment and despite immunosuppressive treatment had all the hallmarks seen previously in similar models without immunosuppression. Our preliminary data expand current knowledge of RIC and emphasize the need to explore whether specific and directed myelosuppression alone is adequate in the absence of microenvironmental modulation, or whether innovative combinations are necessary for safe and effective engraftment.

Current attitudes of parents and patients toward hematopoietic stem cell transplantation for sickle cell anemia

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only available cure for sickle cell anemia (SCA). HSCT-associated risks are one of many barriers to its widespread use for SCA. The study objective was to assess parent and patient perceptions of HSCT in the era of more widespread knowledge about HSCT for SCA.

PROCEDURE

We surveyed parents of children with SCA and adolescents with SCA using the standard reference gamble paradigm. Survey responses between Africans (A) and African Americans (AA) and between parents and adolescents were compared.

RESULTS

Seventy-two percent (64/89) of the respondents were willing to accept ≥ 5% risk of mortality, while 57% said they would accept a risk of ≥ 10% of graft versus host disease (GVHD). Twenty-two percent were unwilling to accept any risk of mortality or GVHD. Risk averseness did not differ between A or AA respondents. Fifty-six percent of respondents were willing to accept infertility post-HSCT.

CONCLUSIONS

These data suggest that the majority of parents and adolescents are willing to accept the current risks associated with matched sibling HSCT for SCA. However, there continue to be significant numbers of parents and adolescents who are unwilling to accept any risk of HSCT-associated mortality or GVHD.

Stem cell comparison: what can we learn clinically from unrelated cord blood transplantation as an alternative stem cell source?

Allogeneic hematopoietic cell transplantation (HCT) is an important therapeutic option for a variety of malignant and non-malignant disorders (NMD). The use of umbilical cord blood transplantation (UCBT) has made HCT available to many more patients. The increased level of human leukocyte antigen disparity that can be tolerated makes UCBT a very attractive alternative source of hematopoietic stem cells; however, the increased risk of early death observed after UCBT remains an obstacle. Novel strategies such as ex vivo stem cell expansion are now becoming part of the standard clinical approach, and preliminary results are extremely encouraging with suggestion of reduction of early transplant-related mortality. Although there are no randomized studies that compare the risks and benefits of UCBT relative to those observed with related and unrelated donors both for malignant and NMD, several retrospective studies have compared outcomes between UCBT and other stem cell sources. In this review, we aim to describe and summarize the findings of the principal studies in this field. We hope that what we can learn from these studies and how we can use this information will improve the outcomes of HCT for patients with malignant and NMD.

Recent trends in the gene therapy of β-thalassemia

The β-thalassemias are a group of hereditary hematological diseases caused by over 300 mutations of the adult β-globin gene. Together with sickle cell anemia, thalassemia syndromes are among the most impactful diseases in developing countries, in which the lack of genetic counseling and prenatal diagnosis have contributed to the maintenance of a very high frequency of these genetic diseases in the population. Gene therapy for β-thalassemia has recently seen steadily accelerating progress and has reached a crossroads in its development. Presently, data from past and ongoing clinical trials guide the design of further clinical and preclinical studies based on gene augmentation, while fundamental insights into globin switching and new technology developments have inspired the investigation of novel gene-therapy approaches. Moreover, human erythropoietic stem cells from β-thalassemia patients have been the cellular targets of choice to date whereas future gene-therapy studies might increasingly draw on induced pluripotent stem cells. Herein, we summarize the most significant developments in β-thalassemia gene therapy over the last decade, with a strong emphasis on the most recent findings, for β-thalassemia model systems; for β-, γ-, and anti-sickling β-globin gene addition and combinatorial approaches including the latest results of clinical trials; and for novel approaches, such as transgene-mediated activation of γ-globin and genome editing using designer nucleases.

Advances in unrelated and alternative donor hematopoietic cell transplantation for nonmalignant disorders

PURPOSE OF REVIEW

The role of hematopoietic cell transplantation in non-malignant disorders has increased exponentially with the recognition that multiple diseases can be controlled or cured if engrafted with donor-derived cells. This review provides an overview of advances made in alternative donor transplants for nonmalignant disorders.

RECENT FINDINGS

Stem cell sources, novel transplant methods, and sophisticated supportive care have simultaneously made giant strides toward improving the safety and efficacy of hematopoietic cell transplantation. This has led to the utilization of marrow, cord, peripheral blood stem cell and haploidentical stem cell sources, and novel reduced toxicity or reduced intensity conditioning regimens to transplant non-malignant disorders such as immune dysfunctions, marrow failure syndromes, metabolic disorders and hemoglobinopathies. Transplant complications such as graft rejection, infections, and graft versus host disease are better combated in this modern era of medicine, achieving better survival with decreased late effects. These aspects of transplant for non-malignant disorders are discussed.

SUMMARY

This review presents the progress made in the realm of hematopoietic cell transplantation for non-malignant disorders. It advocates the consideration of alternative donor transplants in the absence of human leukocyte antigen matched siblings when indicated by disease severity. The ultimate goal is to provide curative transplant options for more patients that can benefit from this intervention, prior to detrimental outcomes.

Treatment of alpha(0)-thalassemia (--(SEA)/--(SEA)) via serial fetal and post-natal transfusions: Can early fetal intervention improve outcomes?

OBJECTIVE AND IMPORTANCE

Homozygous Southeast Asian alpha-thalassemia mutation (--(SEA)/--(SEA)) results in deletion of all alpha-globin genes (alpha(0)-thalassemia). Since all alpha-globin chains are absent, hemoglobin F cannot be synthesized, and hemoglobin Bart's becomes the dominant fetal hemoglobin. Hemoglobin Bart's is a γ tetramer with a very high oxygen affinity, thus oxygen delivery to the tissues is poor. Clinical manifestations include severe fetal anemia, hydrops fetalis, fetal demise, and high risk of neurodevelopmental impairment in the rare survivors.

CLINICAL PRESENTATION

A 39-year-old Vietnamese woman presented to our center at 28 0/7 weeks' gestation with fetal alpha(0)-thalassemia (--(SEA)/--(SEA) type deletion) and ultrasound markers suggestive of severe fetal anemia.

INTERVENTION

The fetus was treated with four intrauterine transfusions followed by post-natal chronic transfusions. Formal neurodevelopmental testing (Battelle Developmental Inventory, Second Edition) was performed at 18 months of age, and the developmental quotient was 93 (32nd percentile) with all subdomains noted within normal limits, indicating overall intact neurodevelopment.

CONCLUSION

We posit that earlier diagnosis and fetal treatment, prior to clinical findings suggestive of fetal anemia, may improve long-term outcomes by enhancing oxygen delivery to the tissues of the developing fetus.

The ethics of a proposed study of hematopoietic stem cell transplant for children with “less severe” sickle cell disease

Hematopoietic stem cell transplant (HSCT) is the only cure for sickle cell disease (SCD). HSCT using an HLA-identical sibling donor is currently an acceptable treatment option for children with severe SCD, with expected HSCT survival >95% and event-free survival >85%. HSCT for children with less severe SCD (children who have not yet suffered overt disease complications or only had mild problems) is controversial. It is important to consider the ethical issues of a proposed study comparing HLA-identical sibling HSCT to best supportive care for children with less severe SCD. In evaluating the principles of nonmaleficence, respect for individual autonomy, and justice, we conclude that a study of HLA-identical sibling HSCT for all children with SCD, particularly hemoglobin SS and Sβ0-thalassemia disease, is ethically sound. Future work should explore the implementation of a large trial to help determine whether HSCT is a beneficial treatment of children with less severe SCD.