Alternative donor allogeneic hematopoietic cell transplantation for hemoglobinopathies

Management of transfusion-dependent β-thalassemia (TDT): Expert insights and practical overview from the Middle East

β-Thalassemia is one of the most common monogenetic diseases worldwide, with a particularly high prevalence in the Middle East region. As such, we have developed long-standing experience with disease management and devising solutions to address challenges attributed to resource limitations. The region has also participated in the majority of clinical trials and development programs of iron chelators and more novel ineffective erythropoiesis-targeted therapy. In this review, we provide a practical overview of management for patients with transfusion-dependent β-thalassemia, primarily driven by such experiences, with the aim of transferring knowledge to colleagues in other regions facing similar challenges.

Gene modification therapies for hereditary diseases in the fetus

Proof-of-principle disease models have demonstrated the feasibility of an intrauterine gene modification therapy (in utero gene therapy (IUGT)) approach to hereditary diseases as diverse as coagulation disorders, haemoglobinopathies, neurogenetic disorders, congenital metabolic, and pulmonary diseases. Gene addition, which requires the delivery of an integrating or episomal transgene to the target cell nucleus to be transcribed, and gene editing, where the mutation is corrected within the gene of origin, have both been used successfully to increase normal protein production in a bid to reverse or arrest pathology in utero. While most experimental models have employed lentiviral, adenoviral, and adeno-associated viral vectors engineered to efficiently enter target cells, newer models have also demonstrated the applicability of non-viral lipid nanoparticles. Amelioration of pathology is dependent primarily on achieving sustained therapeutic transgene expression, silencing of transgene expression, production of neutralising antibodies, the dilutional effect of the recipient's growth on the mass of transduced cells, and the degree of pre-existing cellular damage. Safety assessment of any IUGT strategy will require long-term postnatal surveillance of both the fetal recipient and the maternal bystander for cell and genome toxicity, oncogenic potential, immune-responsiveness, and germline mutation. In this review, we discuss advances in the field and the push toward clinical translation of IUGT.

Across the Myeloablative Spectrum: Hematopoietic Cell Transplant Conditioning Regimens for Pediatric Patients with Sickle Cell Disease

One out of every five hundred African American children in the United States has sickle cell disease (SCD). While multiple disease-modifying therapies are available, hematopoietic cell transplantation (HCT) remains the only curative option for children with SCD. HLA-matched sibling HCT has demonstrated excellent efficacy, but its availability remains limited; alternative donor strategies are increasingly explored. While Busulfan-Cyclophosphamide has become the most widespread conditioning regimen employed in HCT for pediatric SCD, many other regimens have been examined. This review explores different conditioning regimens across the intensity spectrum: from myeloablative to non-myeloablative. We describe survival and organ function outcomes in pediatric SCD patients who have received HCT and discuss the strengths and weaknesses of the various conditioning intensities. Finally, we posit novel directions in allogeneic HCT for SCD.

Parent and Guardian Knowledge of Hematopoietic Cell Transplantation as a Treatment Option for Sickle Cell Disease

Beginning early in childhood, patients with sickle cell disease (SCD) are at risk of life-threatening and debilitating health events. Despite the high morbidity and mortality of this disease, hematopoietic cell transplantation (HCT), a curative treatment for SCD, remains underutilized. In the literature there is a paucity of data concerning medical decision maker (MDM) awareness of HCT as a treatment option for SCD. The objective of this study was to estimate the proportion of parents/guardians of children with SCD who are aware of HCT as a treatment option, and to identify the demographic factors associated with knowledge of this therapy's curative potential. Between November 2015 and December 2016, 327 parents/guardians were surveyed across 4 clinical sites in 3 Midwestern US cities. Although 82% of parents/guardians had heard of HCT in the past and 78% were aware of the therapy's curative potential, nearly half indicated that they did not know whether HCT could specifically cure their child of the disease. Respondents who had discussed HCT with their child's physician had 5 times higher odds of being aware of HCT's curative potential than those who had not. These findings suggest that additional efforts to enhance MDM knowledge of HCT as well as shared decision making in the use of this therapy, is warranted.

Haploidentical haematopoietic stem cell transplantation for thalassaemia major based on an FBCA conditioning regimen

Allogeneic haematopoietic stem cell transplantation (HSCT) is the only available curative therapy for patients with thalassaemia major. With the progress in human leucocyte antigen (HLA) antigen typing technology and supportive care, the outcomes of thalassaemia major have greatly improved in recent years, even in high‐risk patients. However, the problem of finding a suitable donor is still a major obstacle to curing these patients. In recent decades, the lack of available HSCT donors has led to the increased use of haploidentical donors (HDs) for HSCT in haematological malignancies. Recently, we explored the effect of HD HSCT to eight children with thalassaemia major based on the FBCA conditioning regimen (fludarabine, busulphan, cyclophosphamide, antithymocyte globulin), which is usually used in leukaemia patients receiving haploidentical HSCT in our centre. So far, all of the transplanted patients have a stable engraftment and are transfusion independent in daily life. This encouraging result has revised our previous conception about haploidentical HCST for thalassaemia major and strongly suggests that HD HSCT is a feasible and safe method for thalassaemia major patients.

Long-Term Engraftment and Fetal Globin Induction upon BCL11A Gene Editing in Bone-Marrow-Derived CD34+ Hematopoietic Stem and Progenitor Cells

To develop an effective and sustainable cell therapy for sickle cell disease (SCD), we investigated the feasibility of targeted disruption of the BCL11A gene, either within exon 2 or at the GATAA motif in the intronic erythroid-specific enhancer, using zinc finger nucleases in human bone marrow (BM) CD34⁺ hematopoietic stem and progenitor cells (HSPCs). Both targeting strategies upregulated fetal globin expression in erythroid cells to levels predicted to inhibit hemoglobin S polymerization. However, complete inactivation of BCL11A resulting from bi-allelic frameshift mutations in BCL11A exon 2 adversely affected erythroid enucleation. In contrast, bi-allelic disruption of the GATAA motif in the erythroid enhancer of BCL11A did not negatively impact enucleation. Furthermore, BCL11A exon 2-edited BM-CD34⁺ cells demonstrated a significantly reduced engraftment potential in immunodeficient mice. Such an adverse effect on HSPC function was not observed upon BCL11A erythroid-enhancer GATAA motif editing, because enhancer-edited CD34⁺ cells achieved robust long-term engraftment and gave rise to erythroid cells with elevated levels of fetal globin expression when chimeric BM was cultured ex vivo. Altogether, our results support further clinical development of the BCL11A erythroid-specific enhancer editing in BM-CD34⁺ HSPCs as an autologous stem cell therapy in SCD patients.