Stem-cell transplantation for sickle cell disease

Neurocognitive outcome in children with sickle cell disease after myeloimmunoablative conditioning and haploidentical hematopoietic stem cell transplantation: a non-randomized clinical trial

Background

Due to the risk of cerebral vascular injury, children and adolescents with high-risk sickle cell disease (SCD) experience neurocognitive decline over time. Haploidentical stem cell transplantation (HISCT) from human leukocyte antigen-matched sibling donors may slow or stop progression of neurocognitive changes.

Objectives

The study is to determine if HISCT can ameliorate SCD-associated neurocognitive changes and prevent neurocognitive progression, determine which specific areas of neurocognitive functioning are particularly vulnerable to SCD, and determine if there are age-related differences in neurocognitive functioning over time.

Methods

We performed neurocognitive and neuroimaging in SCD recipients following HISCT. Children and adolescents with high-risk SCD who received parental HISCT utilizing CD34+ enrichment and mononuclear cell (T-cell) addback following myeloimmunoablative conditioning received cognitive evaluations and neuroimaging at three time points: pre-transplant, 1 and 2 years post-transplant.

Results

Nineteen participants (13.1 ± 1.2 years [3.3-20.0]) received HISCT. At 2 years post-transplant, neuroimaging and cognitive function were stable. Regarding age-related differences pre-transplantation, older children (≥13 years) had already experienced significant decreases in language functioning (p < 0.023), verbal intelligence quotient (p < 0.05), non-verbal intelligence quotient (p < 0.006), and processing speed (p < 0.05), but normalized post-HISCT in all categories.

Conclusion

Thus, HISCT has the potential to ameliorate SCD-associated neurocognitive changes and prevent neurocognitive progression. Further studies are required to determine if neurocognitive performance remains stable beyond 2 years post-HISCT.Clinical trial registration: The study was conducted under an investigator IND (14359) (MSC) and registered at clinicaltrials.gov (NCT01461837).

Status quo of allogeneic stem cell transplantation for patients with sickle cell disease using matched unrelated donors

This mini review is based on an oral presentation reflecting the current status quo of allogeneic hematopoietic stem cell transplantation (HSCT) for patients with sickle cell disease (SCD) using matched unrelated donors (MUDs) presented at the EBMT Sickle Disease Meeting held in Regensburg, Germany, in May 2019. Although the clinical trial landscape for MUD HSCT in patients with SCD is limited to date, some attempts to improve patient outcome in terms of overall survival and event-free survival have been made recently, including optimization of conditioning regimens and prevention of engraftment failure as well as graft-versus-host disease. The results achieved by these approaches are summarized in this review and are still unsatisfactory. Whether new haploidentical transplantation protocols will achieve superior results and are able to replace MUD HSCT for patients with SCD remains to be elucidated.

Gene Therapy for Sickle Cell Disease: A Lentiviral Vector Comparison Study

Sickle cell disease (SCD) is an inherited blood disorder caused by a single amino acid substitution in the β-globin chain of hemoglobin. Gene therapy is a promising therapeutic alternative, particularly in patients lacking an allogeneic bone marrow (BM) donor. One of the major challenges for an effective gene therapy approach is the design of an efficient vector that combines high-level and long-term β-globin expression with high infectivity in primary CD34+ cells. Two lentiviral vectors carrying an anti-sickling β-globin transgene (AS3) were directly compared: the Lenti/βAS3-FB, and Globe-AS3 with and without the FB insulator. The comparison was performed initially in human BM CD34+ cells derived from SCD patients in an in vitro model of erythroid differentiation. Additionally, the comparison was carried out in two in vivo models: First, an NOD SCID gamma mouse model was used to compare transduction efficiency and β-globin expression in human BM CD34+ cells after transplant. Second, a sickle mouse model was used to analyze β-globin expression produced from the vectors tested, as well as hematologic correction of the sickle phenotype. While minor differences were found in the vectors in the in vitro study (2.4-fold higher vector copy number in CD34+ cells when using Globe-AS3), no differences were noted in the overall correction of the SCD phenotype in the in vivo mouse model. This study provides a comprehensive in vitro and in vivo analysis of two globin lentiviral vectors, which is useful for determining the optimal candidate for SCD gene therapy.

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.

Fertility preservation in patients with haematological disorders: a retrospective cohort study

This study investigated the factors associated with utilization of fertility preservation and the differences in treatments and outcomes by prior chemotherapy exposure in patients with haematological diseases. This study included all 67 women with haematological diseases seen for fertility preservation consultation at two university hospitals between 2006 and 2011. Of the total, 49% had lymphoma, 33% had leukaemia, 7% had myelodysplastic syndrome and 4% had aplastic anaemia; 46% had prior chemotherapy; and 33% were planning for bone marrow transplantation, 33% pursued ovarian stimulation and 7% used ovarian tissue banking; and 48% of patients did not pursue fertility preservation treatment. All five cycle cancellations were in the post-chemotherapy group: three patients with leukaemia and two with lymphoma. Patients with prior chemotherapy had lower baseline antral follicle count (10 versus 22) and received more gonadotrophins to achieve similar peak oestradiol concentrations, with no difference in oocyte yield (10.5 versus 10) after adjustment for age. Embryo yield was similar between those who had prior chemotherapy and those who had not. Half of the patients with haematological diseases who present for fertility preservation have been exposed to chemotherapy. While ovarian reserve is likely impaired in this group, oocyte yield may be acceptable.

Hematopoietic stem cell transplantation in SCD

Hematopoietic stem cell transplantation (HSCT) is the one and only curative therapy available for patient with severe sickle cell disease (SCD). Until today, several hundreds of patients have undergone geno-identical HSCT. More than 200 patients were transplanted in France. The first indication was cerebral vasculopathy. Among both malignant and non-malignant diseases treated with HSCT, the success rate obtained in SCD patients appears as the best one. From the year 2000, more than 95% of transplanted patients survived the HSCT procedure and more than 90% are completely cured and experience a very satisfying health condition post-transplantation. However, the current standard procedure includes a myeloablative conditioning regimen for warranting engraftment. Such regime is linked to severe long-term side effects such as hypofertility. Due to the excellent obtained results, we have to think about a possible widening of indications, a decrease of conditioning intensity and toxicity, and about HSCT from alternative stem cell sources, such as mismatch family donor, unrelated volunteer donor or unrelated cord blood.

Stem cell transplantation after reduced-intensity conditioning for sickle cell disease

Sickle cell disease (SCD) is still associated with substantial morbidity and reduced life expectancy. Disease-related mortality rises to 14% in adolescents and young adults. Overall and disease-free survival following haematopoietic stem cell transplantation (HSCT) is 90% and 95%, respectively. To reduce transplant-associated late effects, the feasibility of a highly immunosuppressive reduced-intensity conditioning (RIC) regimen was explored in children with SCD and a matched sibling donor. Eight patients (median age, 9 yr) and symptomatic SCD were included. The conditioning regimen consisted of fludarabine, melphalan and either thiotepa or total lymphoid irradiation plus antithymocyte globuline or alemtuzumab. The graft was bone marrow in seven and cord blood in one case. The conditioning regimen was well tolerated and no severe infectious complications occurred. All patients displayed mixed chimaerism on day +28. After a median follow-up of 4 yr, 3/8 patients have mixed leucocyte chimaerism and 8/8 patients have 100% donor erythropoiesis. HSCT from matched sibling donors following a RIC regimen was well tolerated and resulted in cure in all patients studied. If confirmed in larger patient cohorts, these observations will have important implications for the indications of HSCT in children with SCD.

Allogeneic transplantation strategies including haploidentical transplantation in sickle cell disease

Sickle cell disease (SCD) is the most common inherited hemoglobinopathy. Despite antenatal counseling and neonatal screening programs implemented in higher income countries, SCD is still associated with multiple morbidities and early mortality. To date, the only curative approach to SCD is hematopoietic stem cell transplantation, but this therapy is not yet established worldwide. The registries of the European Blood and Marrow Transplant (EBMT) and the Centre for International Blood and Marrow Transplant Research (CIBMTR) account, respectively, for 611 and 627 patients receiving transplantations for SCD. Most of these patients were transplanted with grafts from an HLA-identical sibling donor. The main obstacles to increasing the number of transplantations are a lack of awareness on the part of physicians and families, the absence of reliable prognostic factors for severity, and the perceived risk that transplantation complications may outweigh the benefits of early transplantation. Results show that more than 90% of patients having undergone an HLA-identical sibling transplantation after myeloablative conditioning are cured, with very limited complications. Major improvement is expected from the use of new reduced-toxicity conditioning regimens and the use of alternative donors, including unrelated cord blood transplantations and related haploidentical bone marrow or peripheral blood stem cell transplantations.

HLA-haploidentical bone marrow transplantation with posttransplant cyclophosphamide expands the donor pool for patients with sickle cell disease

Allogeneic marrow transplantation can cure sickle cell disease; however, HLA-matched donors are difficult to find, and the toxicities of myeloablative conditioning are prohibitive for most adults with this disease. We developed a nonmyeloablative bone marrow transplantation platform using related, including HLA-haploidentical, donors for patients with sickle cell disease. The regimen consisted of antithymocyte globulin, fludarabine, cyclophosphamide, and total body irradiation, and graft-versus-host disease prophylaxis with posttransplantation high-dose cyclophosphamide, mycophenolate mofetil, and tacrolimus or sirolimus. After screening 19 patients, we transplanted 17, 14 from HLA-haploidentical and 3 from HLA-matched related donors. Eleven patients engrafted durably. With a median follow-up of 711 days (minimal follow up 224 days), 10 patients are asymptomatic, and 6 patients are off immunosupression. Only 1 patient developed skin-only acute graft-versus-host disease that resolved without any therapy; no mortality was seen. Nonmyeloablative conditioning with posttransplantation high-dose cyclophosphamide expands the donor pool, making marrow transplantation feasible for most patients with sickle cell disease, and is associated with a low risk of complications, even with haploidentical related donors. Graft failure, 43% in haploidentical pairs, remains a major obstacle but may be acceptable in a fraction of patients if the majority can be cured without serious toxicities.