Unrelated Umbilical Cord Blood Transplantation for Sickle Cell Disease Following Reduced-Intensity Conditioning: Results of a Phase I Trial

An update review of new therapies in sickle cell disease: the prospects for drug combinations

INTRODUCTION

Sickle cell disease (SCD) is an inherited disorder characterised by polymerisation of deoxygenated haemoglobin S and microvascular obstruction. The cardinal feature is generalised pain referred to as vaso-occlusive crises (VOC), multi-organ damage and premature death. SCD is the most prevalent inherited life-threatening disorders in the world and over 85% of world's 400,000 annual births occur low-and-middle-income countries. Hydroxyurea remained the only approved disease modifying therapy (1998) until the FDA approved L-glutamine (2017), Crizanlizumab and Voxelotor (2019) and gene therapies (Exa-cel and Lovo-cel, 2023).

AREAS COVERED

Clinical trials performed in the last 10 years (November 2013 - November 2023) were selected for the review. They were divided according to the mechanisms of drug action. The following pubmed central search terms [sickle cell disease] or [sickle cell anaemia] Hydroxycarbamide/ Hydroxyurea, L-Glutamine, Voxelotor, Crizanlizumab, Mitapivat, Etavopivat, gene therapy, haematopoietic stem cell transplantation, and combination therapy.

EXPERT OPINION

We recommend future trials of combination therapies for specific complications such as VOCs, chronic pain and renal impairment as well as personalised medicine approach based on phenotype and patient characteristics. Following recent approval of gene therapy for SCD, the challenge is addressing the role of shared decision-making with families, global access and affordability.

Mixed donor chimerism following stem cell transplantation for sickle cell disease

Sickle cell disease is a debilitating hemoglobinopathy with high morbidity and mortality. Hematopoietic stem cell transplantation (HCT) is curative, but the presence of mixed donor/recipient chimerism post-HCT raises concerns about disease control long-term. Mixed donor/recipient chimerism is reported in significant numbers even after aggressive HCT conditioning regimens. Post-HCT, adequacy of donor erythropoiesis is crucial for disease control. This review explores the relationship between mixed donor/recipient chimerism and outcomes post-HCT. Serial chimerism analysis in lineage specific manner in erythroid or myeloid cells post-HCT predicts for disease control and HCT success. Adequate and stable donor-derived erythropoiesis is essential for reversing SCD manifestations. Myeloid lineage chimerism mirrors erythropoiesis is commercially available, and a reliable indicator of adequacy. Using this tool, the minimum threshold of donor chimerism is required to prevent SCD-related complications and maintain sickle hemoglobin less than 50% is approximately 20-25% even when a donor has Hb S trait. Curative interventions should, at a minimum, meet this goal long-term. Achieving a balance between successful engraftment while minimizing toxicity is important in patients vulnerable because of age or preexisting morbidity and is the objective of recent clinical trials. As HCT and gene therapies evolve, efficient long-term follow-up that includes durability assessment of mixed donor/recipient chimerism will be crucial.

Outcomes and long-term effects of hematopoietic stem cell transplant in sickle cell disease

INTRODUCTION

Hematopoietic stem cell transplant (HSCT) is the only readily available curative option for sickle cell disease (SCD). Cure rates following human leukocyte antigen (HLA)-matched related donor HSCT with myeloablative or non-myeloablative conditioning are >90%. Alternative donor sources, including haploidentical donor and autologous with gene therapy, expand donor options but are limited by inferior outcomes, limited data, and/or shorter follow-up and therefore remain experimental.

AREAS COVERED

Outcomes are improving with time, with donor type and conditioning regimens having the greatest impact on long-term complications. Patients with stable donor engraftment do not experience SCD-related symptoms and have stabilization or improvement of end-organ pathology; however, the long-term effects of curative strategies remain to be fully established and have significant implications in a patient's decision to seek therapy. This review covers currently published literature on HSCT outcomes, including organ-specific outcomes implicated in SCD, as well as long-term effects.

EXPERT OPINION

HSCT, both allogeneic and autologous gene therapy, in the SCD population reverses the sickle phenotype, prevents further organ damage, can resolve prior organ dysfunction in both pediatric and adult patients. Data support greater success with HSCT at a younger age, thus, curative therapies should be discussed early in the patient's life.

Sickle cell disease and acute leukemia: one case report and an extensive review

Population-based studies and case reports suggest that there may be an increased risk of acute leukemia associated with sickle cell disease (SCD). Following the description of a new case report, an extensive review of the literature identified 51 previously described cases. Most cases study showed myelodysplastic features confirmed, when available, by genetic markers such as chromosome 5 and/or chromosome 7 abnormalities and TP53 gene mutations. The increased risk of leukemogenesis is certainly multifactorial and related to the pathophysiologic mechanisms of the clinical manifestations of SCD. Chronic hemolysis and secondary hemochromatosis may cause increased chronic inflammation, resulting in persistent marrow stress, which could potentially compromise the genomic stability of the hematopoietic stem cells generating genomic damage and somatic mutations over the course of SCD and its treatment, resulting in a clone that led to acute myeloid leukemia.

Reduction in vaso-occlusive events following stem cell transplantation in patients with sickle cell disease

Hematopoietic stem cell transplantation (HSCT) is potentially curative for patients with sickle cell disease (SCD). Patients with stable donor engraftment after allogeneic HSCT generally do not experience SCD-related complications; however, there are no published data specifically reporting the change in vaso-occlusive events (VOE) after HSCT. Data regarding the number of VOEs requiring medical attention in the 2 years before allogeneic HSCT were compared with the number of VOEs in the 2 years (0-12 months and 12-24 months) after allogeneic HSCT in patients with SCD. One-hundred sixty-three patients with SCD underwent allogeneic HSCT between 2005 and 2019. The average age at the time of HSCT was 21 years (range, 7 months - 64 years). Most patients underwent nonmyeloablative conditioning (75% [N = 123]) and had a matched sibling donor (72% [N = 118]). The mean number of VOEs was reduced from 5.6 (range, 0-52) in the 2 years before HSCT to 0.9 (range, 0-12) in the 2 years after HSCT (P < .001). Among the post-HSCT events, VOE was more frequent during the first 12 months (0.8 [range, 0-12]) than at 12 to 24 months after HSCT (0.1 [range, 0-8) (P < .001)). In patients who had graft rejection (12%, N = 20), VOEs were reduced from 6.6 (range, 0-24) before HSCT to 1.1 (range, 0-6) and 0.8 (range, 0-8) at 0 to 12 months and 12 to 24 months after HSCT, respectively (P < .001). VOEs requiring medical care were significantly reduced after allogeneic HSCT for patients with SCD. These data will inform the development of novel autologous HSCT gene therapy approaches.

Donor chimerism and immune reconstitution following haploidentical transplantation in sickle cell disease

Introduction

We previously reported the initial results of a phase II multicenter transplant trial using haploidentical parental donors for children and aolescents with high-risk sickle cell disease achieving excellent survival with exceptionally low rates of graft-versus-host disease and resolution of sickle cell disease symptoms. To investigate human leukocyte antigen (HLA) sensitization, graft characteristics, donor chimerism, and immune reconstitution in these recipients.

Methods

CD34 cells were enriched using the CliniMACS^® system with a target dose of 10 x 10⁶ CD34⁺ cells/kg with a peripheral blood mononuclear cell (PBMNC) addback dose of 2x10⁵ CD3/kg in the final product. Pre-transplant HLA antibodies were characterized. Donor chimerism was monitored 1-24 months post-transplant. Comprehensive assessment of immune reconstitution included lymphocyte subsets, plasma cytokines, complement levels, anti-viral T-cell responses, activation markers, and cytokine production. Infections were monitored.

Results

HLA antibodies were detected in 7 of 11 (64%) evaluable patients but rarely were against donor antigens. Myeloid engraftment was rapid (100%) at a median of 9 days. At 30 days, donor chimerism was 93-99% and natural killer cell levels were restored. By 60 days, CD19 B cells were normal. CD8 and CD4 T-cells levels were normal by 279 and 365 days, respectively. Activated CD4 and CD8 T-cells were elevated at 100-365 days post-transplant while naïve cells remained below baseline. Tregs were elevated at 100-270 days post-transplant, returning to baseline levels at one year. At one year, C3 and C4 levels were above baseline and CH50 levels were near baseline. At one year, cytokine levels were not significantly different from baseline.

Discussion

These results suggest that haploidentical transplantation with CD34-enriched cells and peripheral blood mononuclear cell addback results in rapid engraftment, sustained donor chimerism and broad-based immune reconstitution.

Effective therapies for sickle cell disease: are we there yet?

Sickle cell disease (SCD) is a common genetic blood disorder associated with acute and chronic pain, progressive multiorgan damage, and early mortality. Recent advances in technologies to manipulate the human genome, a century of research and the development of techniques enabling the isolation, efficient genetic modification, and reimplantation of autologous patient hematopoietic stem cells (HSCs), mean that curing most patients with SCD could soon be a reality in wealthy countries. In parallel, ongoing research is pursuing more facile treatments, such as in-vivo-delivered genetic therapies and new drugs that can eventually be administered in low- and middle-income countries where most SCD patients reside.

Development of curative therapies for sickle cell disease

Recent advances in managing Sickle Cell Disease (SCD) significantly improved patient survival and quality of life. Disease-modifying drug therapies such as hydroxyurea, L-glutamine, voxelotor, and crizanlizumab reduce pain crises and severe complications. Allogeneic hematopoietic stem cell transplantation using matched-sibling donors is currently the only standard curative option; however, only a small proportion of patients have such donors. Cord blood and haploidentical transplantation with a modified conditioning regimen have expanded the allogeneic donor pool, making the therapy available to more patients. Gene therapy is a promising cure that is currently undergoing clinical trials and different approaches have demonstrated efficacy. Multidisciplinary expertise is needed in developing the best treatment strategy for patients with SCD.

The effect of intensity of conditioning regimen on the outcome of HSCT in children with sickle cell disease

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) provides a cure for patients with sickle cell disease (SCD). This study describes the effect of conditioning regimen intensity on HSCT outcomes among children younger than 14 years with SCD.

METHODS

Transplants from HLA-matched related donors (MRD) and unrelated donors (MUD) using either myeloablative conditioning (MAC) regimens or reduced intensity conditioning (RIC) regimens were considered. Event-free survival (EFS) was the primary endpoint. Secondary endpoints included overall survival (OS) and occurrence of GVHD.

RESULTS

48 SCD patients underwent HSCT, 45 (93.8%) patients had MRD, 1 (2.1%) had 9/10 related donor, and 2 (4.1%) had MUD. The median age at transplant was 8.6 years (range, 3.1-13.8). Conditioning regimens were myeloablative (MAC) in 41 (85.4%) patients and of reduced intensity in 7 (14.6%) patients. EFS at 2 years was 100% among MAC group compared to 29% in the RIC group (p < .001). The median follow-up was 43.4 months (range 26.8-134). All events in the RIC group were secondary graft failure. However, OS was 100% in both groups at 2 years. Acute GVHD II-IV was diagnosed in 2 (4.1%) patients. Chronic GVHD occurred in 2 (4.1%) patients. GVHD did not occur in patients who underwent MUD HSCT.

CONCLUSIONS

MAC in children with SCD is well tolerated and associated with an excellent outcome for HLA-matched HSCT in SCD. There was a high rate of secondary graft failure with the use of RIC. Future studies are needed to optimize RIC regimens in HSCT of children with SCD.

Debating the Future of Sickle Cell Disease Curative Therapy: Haploidentical Hematopoietic Stem Cell Transplantation vs. Gene Therapy

Hematopoietic stem cell transplantation (HSCT) is a well-established curative therapy for patients with sickle cell disease (SCD) when using a human leukocyte antigen (HLA)-matched sibling donor. Most patients with SCD do not have a matched sibling donor, thereby significantly limiting the accessibility of this curative option to most patients. HLA-haploidentical HSCT with post-transplant cyclophosphamide expands the donor pool, with current approaches now demonstrating high overall survival, reduced toxicity, and an effective reduction in acute and chronic graft-vs.-host disease (GvHD). Alternatively, autologous genetic therapies appear promising and have the potential to overcome significant barriers associated with allogeneic HSCT, such as donor availability and GvHD. Here the authors each take a viewpoint and discuss what will be the future of curative options for patients with SCD outside of a matched sibling transplantation, specifically haploidentical HSCT vs. gene therapy.

Sickle Cell Transplantation Evaluation of Long-term and Late Effects Registry (STELLAR) to Compare Long-term Outcomes After Hematopoietic Cell Transplantation to Those in Siblings Without Sickle Cell Disease and in Nontransplanted Individuals With Sickle Cell Disease: Design and Feasibility Study

BACKGROUND

There are sparse data on the long-term and late effects of hematopoietic cell transplantation (HCT) for sickle cell disease (SCD).

OBJECTIVE

This study aims to establish an international registry of long-term outcomes post-HCT for SCD and demonstrate the feasibility of recruitment at a single site in the United States.

METHODS

The Sickle Cell Transplantation Evaluation of Long-Term and Late Effects Registry (STELLAR) was designed to enroll patients with SCD ≥1 year post-HCT, their siblings without SCD, and nontransplanted controls with SCD to collect web-based participant self-reports of health status and practices by using the Bone Marrow Transplant Survivor Study (BMTSS) surveys, health-related quality of life (HRQOL) using the Patient-Reported Outcomes Measurement Information System (PROMIS) Pediatric Profile-25 or Pediatric Profile-29 survey, chronic graft-versus-host disease (cGVHD) using the symptom scale survey, daily pain using an electronic pain diary, the economic impact of HCT using the financial hardship survey, sexual function using the PROMIS Sexual Function SexFSv2.0 survey, and economic productivity using the American Time Use Survey (ATUS). We also piloted retrieval of clinical data previously submitted to the Center for International Blood and Marrow Transplant Research (CIBMTR); recorded demographics, height, weight, blood pressure, waist and hip circumferences, timed up and go (TUG) test, and handgrip test; and obtained blood for metabolic screening, gonadal function, fertility potential, and biorepository of plasma, serum, RNA, and DNA.

RESULTS

Of 100 eligible post-HCT patients, we enrolled 72 (72%) participants aged 9-38 (median 17) years. We also enrolled 19 siblings aged 5-32 (median 10) years and 28 nontransplanted controls with SCD aged 4-46 (median 22) years. Of the total 119 participants, 73 (61%) completed 85 sets of surveys and 41 (35%) contributed samples to the biorepository. We completed ATUS interviews of 28 (24%) participants. We successfully piloted retrieval of data submitted to the CIBMTR and expanded recruitment to multiple sites in the United States, Canada, the United Kingdom, and Nigeria.

CONCLUSIONS

It is feasible to recruit subjects and conduct study procedures for STELLAR in order to determine the long-term and late effects of HCT for SCD.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/36780.

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.

Emerging approaches to improve allogeneic hematopoietic cell transplantation outcomes for nonmalignant diseases

Many congenital or acquired nonmalignant diseases (NMDs) of the hematopoietic system can be potentially cured by allogeneic hematopoietic cell transplantation (HCT) with varying types of donor grafts, degrees of HLA matching, and intensity of conditioning regimens. Unique features that distinguish the use of allogeneic HCT in this population include higher rates of graft failure, immune-mediated cytopenias, and the potential to achieve long-term disease-free survival in a mixed chimerism state. Additionally, in contrast to patients with hematologic malignancies, a priority is to completely avoid graft-versus-host disease in patients with NMD because there is no theoretical beneficial graft-versus-leukemia effect that can accompany graft-versus-host responses. In this review, we discuss the current approach to each of these clinical issues and how emerging novel therapeutics hold promise to advance transplant care for patients with NMDs.

Hematopoietic Stem Cell Gene-Addition/Editing Therapy in Sickle Cell Disease

Autologous hematopoietic stem cell (HSC)-targeted gene therapy provides a one-time cure for various genetic diseases including sickle cell disease (SCD) and β-thalassemia. SCD is caused by a point mutation (20A > T) in the β-globin gene. Since SCD is the most common single-gene disorder, curing SCD is a primary goal in HSC gene therapy. β-thalassemia results from either the absence or the reduction of β-globin expression, and it can be cured using similar strategies. In HSC gene-addition therapy, patient CD34+ HSCs are genetically modified by adding a therapeutic β-globin gene with lentiviral transduction, followed by autologous transplantation. Alternatively, novel gene-editing therapies allow for the correction of the mutated β-globin gene, instead of addition. Furthermore, these diseases can be cured by γ-globin induction based on gene addition/editing in HSCs. In this review, we discuss HSC-targeted gene therapy in SCD with gene addition as well as gene editing.

Strategies for Success With Umbilical Cord Haematopoietic Stem Cell Transplantation in Children With Malignant and Non-Malignant Disease Indications

Umbilical Cord blood is an intuitively attractive stem cell source, but its use has declined since it is associated with an increased procedure-related morbidity and transplant related mortality. Some of this reflects that cord blood transplants are more often HLA-mismatched compared to other unrelated donor transplants. The ability to transplant in such a setting, indeed without high rates of chronic Graft versus Host Disease (GVHD), constitutes an advantage compared to other unrelated donor cell sources and there are other advantages specifically associated with cord blood as a donor cell source. These advantages must be weighed against its disadvantage, and we have utilised cord blood preferentially as a donor cell source in certain clinical situations in paediatric medicine. In non-malignant diseases, outcomes in metabolic disease are critically dependent on age at transplant and the enzyme delivered by that transplant, and in cord blood transplantation then the time to transplant can be minimised and the engrafted recipients have higher chimerism that delivers higher enzyme levels. In malignant diseases, studies have described reduced relapse rate and better GVHD-free survival, and so we have prioritised cord as a donor cell source where the risk of relapse is highest, and the effects of higher transplant related mortality is most clearly offset by the reduced relapse rates.

Granulocyte Colony-Stimulating Factor is Safe and Well Tolerated following Allogeneic Transplantation in Patients with Sickle Cell Disease

Granulocyte colony-stimulating factor (G-CSF) used after hematopoietic stem cell transplantation (HSCT) can enhance neutrophil recovery in patients rendered neutropenic by the preparative regimen. G-CSF is contraindicated in patients with sickle cell disease (SCD) as life-threatening complications can ensue in the presence of sickle vasculopathy. However, the safety profile of G-CSF after HSCT for SCD has not been previously described. We report clinical outcomes in the first 100 days post-HSCT in patients supported with G-CSF until neutrophil recovery on a clinical trial of reduced intensity transplantation for SCD. Patients (n=62) received G-CSF for a median of 9 days (range, 5-33) following transplant from the best available stem cell source. Preparation for transplant included a target hemoglobin S level of ≤45%. Neutrophil engraftment (ANC >0.5 × 10³/mL) was achieved at a median of 13 days (range,10-34) and platelet engraftment (>50 × 10³/mL) at a median of 19 days (range, 12-71). The median duration of inpatient hospitalization following stem cell infusion (day 0) was 21.5 days (range 11-33). No patient developed SCD related complications following G-CSF use. The most common organ toxicities encountered between G-CSF commencement (on day +7) and day +100 were anorexia (14), hypertension (11) and electrolyte imbalance requiring correction (9). Central nervous system related events were noted in 5 patients, all with pre-existing cerebral vasculopathy/moyamoya disease and attributed to reversible posterior leukoencephalopathy syndrome (RPLS) in the presence of calcineurin inhibitor therapy and hypertension. We conclude that G-CSF does not adversely impact SCD transplant recipients and can be safely used post-HSCT to enhance neutrophil recovery.

Hematopoietic cell transplantation for sickle cell disease: updates and future directions

Excellent outcomes in hematopoietic cell transplantation (HCT) from HLA-identical siblings, improvements in conditioning regimens, novel graft-versus-host disease prophylaxis, and the availability of alternative donors have all contributed to the increased applicability and acceptability of HCT for sickle cell disease (SCD). In young children with symptomatic SCD with an available HLA-identical related donor, HCT should be carefully considered. HCT from alternative donors is typically undertaken only in patients with severe symptoms, causing or likely to cause organ damage, and in the context of clinical trials. Patients undergoing HCT for SCD require careful counseling and preparation. They require careful monitoring of unique organ toxicities and complications during HCT. Patients must be prospectively followed for a prolonged time to determine the long-term outcomes and late effects of HCT for SCD. Thus, there is a need for a universal, longitudinal clinical registry to follow patients after HCT for SCD in conjunction with individuals who do not receive HCT to compare outcomes. Antibody-based conditioning and ex-vivo umbilical cord blood expansion are likely to improve the availability and acceptability of HCT. In addition, new disease-modifying drugs and the emerging option of the autologous transplantation of gene-modified hematopoietic progenitor cells are likely to expand the available therapeutic options and make decision-making by patients, physicians, and caregivers even more complicated. Future efforts must also focus on determining the impact of socioeconomic status on access to and outcomes of HCT and the long-term impact of HCT on patients, families, and society.

Curative therapy for hemoglobinopathies: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee review comparing outcomes, accessibility and cost of ex vivo stem cell gene therapy versus allogeneic hematopoietic stem cell transplantation

Thalassemia and sickle cell disease (SCD) are the most common monogenic diseases in the world and represent a growing global health burden. Management is limited by a paucity of disease-modifying therapies; however, allogeneic hematopoietic stem cell transplantation (HSCT) and autologous HSCT after genetic modification offer patients a curative option. Allogeneic HSCT is limited by donor selection, morbidity and mortality from transplant conditioning, graft-versus-host disease and graft rejection, whereas significant concerns regarding long-term safety, efficacy and cost limit the broad applicability of gene therapy. Here the authors review current outcomes in allogeneic and autologous HSCT for transfusion-dependent thalassemia and SCD and provide our perspective on issues surrounding accessibility and costs as barriers to offering curative therapy to patients with hereditary hemoglobinopathies.

American Society of Hematology 2021 guidelines for sickle cell disease: stem cell transplantation

BACKGROUND

Sickle cell disease (SCD) is a life-limiting inherited hemoglobinopathy that results in significant complications and affects quality of life. Hematopoietic stem cell transplantation (HSCT) is currently the only curative intervention for SCD; however, guidelines are needed to inform how to apply HSCT in clinical practice.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians, and health professionals in their decisions about HSCT for SCD.

METHODS

The multidisciplinary guideline panel formed by ASH included 2 patient representatives and was balanced to minimize potential bias from conflicts of interest. The Mayo Evidence-Based Practice Research Program supported the guideline development process, including performing systematic evidence reviews (through 2019). The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including GRADE Evidence-to-Decision frameworks, to assess evidence and make recommendations, which were subject to public comment.

RESULTS

The panel agreed on 8 recommendations to help patients and providers assess how individuals with SCD should consider the timing and type of HSCT.

CONCLUSIONS

The evidence review yielded no randomized controlled clinical trials for HSCT in SCD; therefore, all recommendations are based on very low certainty in the evidence. Key recommendations include considering HSCT for those with neurologic injury or recurrent acute chest syndrome at an early age and to improve nonmyeloablative regimens. Future research should include the development of a robust SCD registry to serve as a comparator for HSCT studies.

Stable to improved cardiac and pulmonary function in children with high-risk sickle cell disease following haploidentical stem cell transplantation

Children with sickle cell disease (SCD) are at high-risk of progressive, chronic pulmonary and cardiac dysfunction. In this prospective multicenter Phase II trial of myeloimmunoablative conditioning followed by haploidentical stem cell transplantation in children with high-risk SCD, 19 patients, 2.0-21.0 years of age, were enrolled with one or more of the following: history of (1) overt stroke; (2) silent stroke; (3) elevated transcranial Doppler velocity; (4) multiple vaso-occlusive crises; and/or (5) two or more acute chest syndromes and received haploidentical transplants from 18 parental donors. Cardiac and pulmonary centralized cores were established. Pulmonary function results were expressed as percent of the median of healthy reference cohorts, matched for age, sex, height and race. At 2 years, pulmonary functions including forced expiratory volume (FEV), FEV₁/ forced vital capacity (FVC), total lung capacity (TLC), diffusing capacity of lung for carbon monoxide (DLCO) were stable to improved compared to baseline values. Importantly, specific airway conductance was significantly improved at 2 years (p < 0.004). Left ventricular systolic function (fractional shortening) and tricuspid regurgitant velocity were stable at 2 years. These results demonstrate that haploidentical stem cell transplantation can stabilize or improve cardiopulmonary function in patients with SCD.

Gene Therapy for Sickle Cell Disease - Moving from the Bench to the Bedside

Gene therapy as a potential cure for sickle cell disease (SCD) has long been pursued given that this hemoglobin disorder results from a single point mutation. Advances in genomic sequencing, increased understanding of hemoglobin regulation and discoveries of molecular tools for genome modification of hematopoietic stem cells have made gene therapy for SCD possible. Gene addition strategies using gene transfer vectors have been optimized over the last few decades to enable expression of normal or anti-sickling globins as strategies to ameliorate SCD. Many hurdles had to be addressed prior to clinical translation including collection of sufficient stem cells for gene-modification, increasing expression of transferred genes to a therapeutic level and conditioning patients in a safe manner that enabled adequate engraftment of gene-modified cells. The discovery of genome editors that make precise modifications has further advanced the safety and efficacy of gene therapy and a rapid movement to clinical trial has undoubtedly been supported by lessons learned from optimizing gene addition strategies. Current gene therapies being tested in clinical trial require significant infrastructure and expertise given the needs to harvest cells from and administer chemotherapy to patients who often have significant organ dysfunction and that gene-modification takes place ex vivo in specialized facilities. For these therapies to realize their full potential they would need to be portable, safe and efficient making an in-vivo based approach attractive. Additionally, adequate resources for SCD screening and access to standardized care are critically important for gene therapy to be a viable treatment option for SCD.

Allogeneic stem cell transplantation with omidubicel in sickle cell disease

Many patients with sickle cell disease (SCD) do not have HLA-matched related donors for hematopoietic stem cell transplantation (HSCT). Unrelated cord blood (UCB) is an alternative graft option but is historically associated with high graft failure rates, with inadequate cell dose a major limitation. Omidubicel is a nicotinamide-based, ex vivo-expanded UCB product associated with rapid engraftment in adults with hematologic malignancies. We hypothesized that increasing the UCB cell dose with this strategy would lead to improved engraftment in pediatric patients undergoing myeloablative HSCT for SCD. We report the outcomes of a phase 1/2 study in 13 patients with severe SCD who received omidubicel in combination with an unmanipulated UCB graft and 3 who received a single omidubicel graft. Grafts were minimally matched with patients at 4 of 6 HLA alleles. Median age at transplant was 13 years. A median CD34+ expansion of ∼80-fold was observed in omidubicel and led to rapid neutrophil engraftment (median, 7 days). Long-term engraftment was derived from the unmanipulated graft in most of the double cord blood recipients. Two of the 3 single omidubicel recipients also had sustained engraftment. Incidence of acute graft-versus-host disease (GVHD) was high, but resolved in all surviving patients. Event-free survival in the double cord group was 85% (median follow-up 4 years). All 3 patients in the single cord group were alive at 1 year after transplantation. Ex vivo expansion of UCB with omidubicel supports engraftment in patients with SCD. This approach to decreasing the incidence of GVHD should be optimized for general use in patients with SCD. This study was registered at www.clinicaltrials.gov as #NCT01590628.

Stroke and stroke prevention in sickle cell anemia in developed and selected developing countries

This comprehensive review provides an insight into the pathophysiology, epidemiology, evaluation, and treatment of sickle cell anemia (SCA)-related stroke in developed and developing countries. Vascular injury, hypercoagulability and vaso-occlusion play a role in the pathophysiology of stroke in SCA. Transcranial Doppler ultrasound (TCD) has lowered the incidence of ischemic stroke from 11% to 1% as TCD identifies children who are at risk for stroke, providing opportunities for interventions to reduce this risk. Whereas blood exchange is indicated in acute stroke, chronic transfusions (either simple or exchange on a monthly basis) are used for primary as well as secondary stroke prevention in developed countries. Children with abnormally high TCD velocities (≥ 200 cm/s) are at high risk of stroke and might benefit from hydroxyurea or hydroxycarbamide (HU) after a period of a successful transition from chronic transfusions. Hematopoietic stem cell transplant presents a cure for SCA. Gene therapy is currently investigated and may be offered to patients with SCA who had a stroke or who are at high risk of stroke if proven efficacious and safe. However, gene therapy is not likely to be implemented in low-income countries due to cost. Alternatively, HU is utilized for primary and secondary stroke prevention in developing countries. Further expansion of TCD implementation should be a priority in those settings.

Gene therapy as the new frontier for Sickle Cell Disease

Sickle Cell Disease (SCD) is one of the most common monogenic disorders caused by a point mutation in the β-globin gene. This mutation results in polymerization of hemoglobin (Hb) under reduced oxygenation conditions, causing rigid sickle-shaped RBCs and hemolytic anemia. This clearly defined fundamental molecular mechanism makes SCD a prototypical target for precision therapy. Both the mutant β-globin protein and its downstream pathophysiology are pharmacological targets of intensive research. SCD also is a disease well-suited for biological interventions like gene therapy. Recent advances in hematopoietic stem cell (HSC) transplantation and gene therapy platforms, like Lentiviral vectors and gene editing strategies, expand the potentially curative options for patients with SCD. This review discusses the recent advances in precision therapy for SCD and the preclinical and clinical advances in autologous HSC gene therapy for SCD.

Abatacept is effective as GVHD prophylaxis in unrelated donor stem cell transplantation for children with severe sickle cell disease

We report results of a phase 1 multicenter stem cell transplantation (SCT) trial from HLA-matched (n = 7) or one-antigen-mismatched (n = 7) unrelated donors (URD) using bone marrow or cord blood as stem cell source, following reduced-intensity conditioning (RIC) in severe sickle cell disease (SCD). Conditioning included distal alemtuzumab, fludarabine, and melphalan (matched donors), with thiotepa (mismatched donors). Abatacept, a selective inhibitor of T cell costimulation, was added to tacrolimus and methotrexate as graft-versus-host disease (GVHD) prophylaxis to offset GVHD risks, and was administered for longer duration in bone marrow recipients than in cord blood recipients because of increased incidence of chronic GVHD with bone marrow. Median age at transplant was 13 years (range, 7-21 years). The incidence of grades II to IV and grades III to IV acute GVHD at day +100 was 28.6% and 7%, respectively. One-year incidence of chronic GVHD was 57% and mild/limited in all but 1 patient who received abatacept for a longer duration. Only 1 patient developed reversible posterior encephalopathy syndrome and recovered. With a median follow-up of 1.6 years (range, 1-5.5 years), the 2-year overall and disease-free survival was 100% and 92.9%, respectively. The encouraging results from the phase 1 portion of this RIC SCT trial, despite risk factors such as older age, URD, and HLA-mismatch, support further evaluation of URD SCT in clinical trial settings. The phase 2 portion of the trial is in progress. This trial was registered at www.clinicaltrials.gov as NCT03128996.

Genetic therapies for the first molecular disease

Sickle cell disease (SCD) is a monogenic disorder characterized by recurrent episodes of severe bone pain, multi-organ failure, and early mortality. Although medical progress over the past several decades has improved clinical outcomes and offered cures for many affected individuals living in high-income countries, most SCD patients still experience substantial morbidity and premature death. Emerging technologies to manipulate somatic cell genomes and insights into the mechanisms of developmental globin gene regulation are generating potentially transformative approaches to cure SCD by autologous hematopoietic stem cell (HSC) transplantation. Key components of current approaches include ethical informed consent, isolation of patient HSCs, in vitro genetic modification of HSCs to correct the SCD mutation or circumvent its damaging effects, and reinfusion of the modified HSCs following myelotoxic bone marrow conditioning. Successful integration of these components into effective therapies requires interdisciplinary collaborations between laboratory researchers, clinical caregivers, and patients. Here we summarize current knowledge and research challenges for each key component, emphasizing that the best approaches have yet to be developed.

Allogeneic hematopoietic stem cell transplantation from sibling and unrelated donors in pediatric patients with sickle cell disease-A single center experience

HSCT is curative in SCD. Patients with HLA-identical sibling donor have an excellent outcome ranging from 90%-100% overall and event-free survival. However, due to the lack of matched sibling donors this option is out of reach for 70% of patients with SCD. The pool of potential donors needs to be extended. Transplantations from HLA-matched unrelated donors were reported to be less successful with shorter event-free survival and higher incidences of complications including graft-vs-host disease, especially in patients with advanced stage SCD. Here we report transplantation outcomes for 25 children with SCD transplanted using HLA-matched grafts from related or unrelated donors. Overall survival was 100% with no severe (grade III-IV) graft-vs-host disease and a 12% rejection rate. Mixed donor chimerisms only occurred in transplantations from siblings, while transplantations from unrelated donors resulted in either complete donor chimerism or rejection. Despite the small patient number, overall and disease-free survival for unrelated donor transplantations is excellent in this cohort. The advanced disease state, higher alloreactive effect and stronger immunosuppression in unrelated donor transplantations raises patient risk, for which possible solutions could be found in optimization of transplant preparation, graft manipulation or haploidentical transplantation using T cell receptor α/β-depleted grafts.

Allogenic hematopoietic stem cell transplantation in sickle cell disease

Sickle cell disease (SCD) is one of the most common monogenic disorders worldwide and affects approximately 100,000 people in the United States alone. SCD can cause numerous complications, including anemia, pain, stroke, and organ failure, which can lead to death. Although there are a few disease-modifying treatments available to patients with SCD, the only current curative option is a hematopoietic stem cell transplant (HSCT). In this review, we will discuss the different approaches to allogeneic HSCT in the treatment of SCD and the outcomes of these approaches.

Hematopoietic Cell Transplantation for Sickle Cell Disease

Sickle cell disease (SCD) is a severe autosomal recessively inherited disorder of the red blood cell characterized by erythrocyte deformation caused by the polymerization of the abnormal hemoglobin, which leads to erythrocyte deformation and triggers downstream pathological changes. These include abnormal rheology, vaso-occlusion, ischemic tissue damage, and hemolysis-associated endothelial dysfunction. These acute and chronic physiologic disturbances contribute to morbidity, organ dysfunction, and diminished survival. Hematopoietic cell transplantation (HCT) from HLA-matched or unrelated donors or haploidentical related donors or genetically modified autologous hematopoietic progenitor cells is performed with the intent of cure or long-term amelioration of disease manifestations. Excellent outcomes have been observed following HLA-identical matched related donor HCT. The majority of SCD patients do not have an available HLA-identical sibling donor. Increasingly, however, they have the option of undergoing HCT from unrelated HLA matched or related haploidentical donors. The preliminary results of transplantation of autologous hematopoietic progenitor cells genetically modified by adding a non-sickling gene or by genomic editing to increase expression of fetal hemoglobin are encouraging. These approaches are being evaluated in early-phase clinical trials. In performing HCT in patients with SCD, careful consideration must be given to patient and donor selection, conditioning and graft-vs.-host disease regimen, and pre-HCT evaluation and management during and after HCT. Sociodemographic factors may also impact awareness of and access to HCT. Further, there is a substantial decisional dilemma in HCT with complex tradeoffs between the possibility of amelioration of disease manifestations and early or late complications of HCT. The performance of HCT for SCD requires careful multidisciplinary collaboration and shared decision making between the physician and informed patients and caregivers.

Matched sibling donor stem cell transplantation for sickle cell disease: Results from the Spanish group for bone marrow transplantation in children

OBJECTIVES

The prevalence of sickle cell disease (SCD) in Spain is markedly inferior compared with other European and Mediterranean countries. However, the diagnosis of new patients with SCD is expected to increase. In this multicenter retrospective study, we analyze the hematopoietic stem cell transplantation (HSCT) results obtained in Spain.

METHODS

Forty-five patients who underwent a matched sibling donor (MSD) HSCT between 1999 and 2018 were included. Primary endpoint was event-free survival (EFS), and secondary endpoints included acute and chronic graft-versus-host disease (GvHD) and overall survival (OS).

RESULTS

Bone marrow was the most frequent stem cell source (93.3%). Most patients received a conditioning regimen based on busulfan and cyclophosphamide (69%). Cumulative incidence of grade III-IV acute GvHD and chronic GvHD was 6.8% (95% CI: 2.3%-20.1%) and 5.4% (95% CI: 1.38%-19.9%), respectively. EFS and overall survival (OS) at 3 years post-HSCT were 89.4% (95% CI: 73.9%-95.9%) and 92.1% (95% CI: 77.2%-97.4%), respectively. All patients aged ≤ 5 presented 100% EFS and OS.

CONCLUSIONS

An early referral to HSCT centers should be proposed early in life, before severe complications occur. MSD HSCT should be considered a curative option for all patients aged ≤ 5 years and for older pediatric patients who present complications derived from the disease.

Chimerism in the Realm of Hematopoietic Stem Cell Transplantation for Non-malignant Disorders-A Perspective

Hematopoietic stem cell transplantation (HCT) is a curative intervention in non-malignant disorders (NMD) that benefit from donor-derived hematopoiesis, immunity, and establishment of vital cells or enzyme systems. Stability or reversal of disease symptoms depends on adequacy and long-term stability of donor cell engraftment in the compartment of interest. Unlike hematologic malignancies where complete replacement with donor derived hematopoiesis is desirable for a cure, NMD manifestations can often be controlled in the presence of mixed chimerism. This allows for exploration of reduced intensity conditioning regimens that can limit organ toxicity, late effects, and increase tolerability especially in young recipients or those with a large burden of disease related morbidity. However, the levels of donor chimerism conducive to disease control vary between NMD, need to focus on the hematopoietic lineage necessary to correct individual disorders, and need to be assessed for stability over time, i.e., a whole lifespan. An enhanced ability to reject grafts due to recipient immune competence, alloimmunization, and autoimmunity add to the complexity of this balance making NMD a highly diverse group of unrelated disorders. The addition of donor factors such as stem cell source and Human-Leukocyte-Antigen match extend the complexity such that 'one size does not fit all'. In this perspective, we will discuss current knowledge of the role of chimerism and goals, approach to HCT, and emerging methods of boosting engraftment and graft function, and monitoring recommendations. We draw attention to knowledge gaps and areas of necessity for further research and research support.

Curative options for sickle cell disease: haploidentical stem cell transplantation or gene therapy?

Haematopoietic stem cell transplantation (HSCT) is curative in sickle cell disease (SCD); however, the lack of available matched donors makes this therapy out of reach for the majority of patients with SCD. Alternative donor sources such as haploidentical HSCT expand the donor pool to nearly all patients with SCD, with recent data showing high overall survival, limited toxicities, and effective reduction in acute and chronic graft-versus-host disease (GVHD). Simultaneously, multiple gene therapy strategies are entering clinical trials with preliminary data showing their success, theoretically offering all patients yet another curative strategy without the morbidity and mortality of GVHD. As improvements are made for alternative donors in the allogeneic setting and as data emerge from gene therapy trials, the optimal curative strategy for any individual patient with SCD will be determined by many critical factors including efficacy, transplant morbidity and mortality, safety, patient disease status and preference, cost and applicability. Haploidentical may be the preferred choice now based mostly on availability of data; however, gene therapy is closing the gap and may ultimately prove to be the better option. Progress in both strategies, however, makes cure more attainable for the individual with SCD.

A single-center experience using alemtuzumab, fludarabine, melphalan, and thiotepa as conditioning for transplantation in pediatric patients with chronic granulomatous disease

Chronic granulomatous disease (CGD) is an immune deficiency characterized by defective neutrophil function and increased risk of life-threatening infections. Allogeneic hematopoietic cell transplantation is curative for CGD, and conditioning regimen impacts transplant-related outcomes. We report a single-center prospective study (NCT01821781) of four patients with CGD transplanted using a reduced-intensity conditioning regimen (RIC) containing alemtuzumab, fludarabine, melphalan, and thiotepa. Patients had early immune reconstitution with low incidence of infections. Disease-free survival was 75% at a median of five years after transplant. This RIC regimen presents an alternative approach for transplant of patients with CGD who may not tolerate busulfan-based conditioning.

How I treat sickle cell disease with hematopoietic cell transplantation

Sickle cell disease (SCD) leads to significant morbidity and early mortality, and hematopoietic cell transplantation (HCT) is the only widely available cure, with impacts seen on SCD-related organ dysfunction. Outcomes are excellent following matched-related donor (MRD) HCT, leading to significantly expanded application of this treatment over the past decade. The majority of SCD patients lack an MRD, but outcomes following alternative donor HCT continue to improve on clinical trials. Within this framework, we aim to provide our perspective on how to apply research findings to clinical practice, for an individual patient. We also emphasize that the preparation of SCD recipients for HCT and supporting them through HCT have special nuances that require awareness and close attention. Through the use of clinical vignettes, we provide our perpsective on the complex decision-making process in HCT for SCD as well as recommendations for the evaluation and support of these patients through HCT.

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.

Current status of umbilical cord blood transplantation in children

The first umbilical cord blood (UCB) transplantation was performed 30 years ago. UCB transplantation (UCBT) is now widely used in children with malignant and non-malignant disorders who lack a matched family donor. UCBT affords a lower incidence of graft-versus-host disease compared to alternative stem cell sources, but also presents a slower immune recovery and a high risk of infections if serotherapy is not omitted or targeted within the conditioning regimen. The selection of UCB units with high cell content and good human leucocyte antigen match is essential to improve the outcome. Techniques, such as double UCBT, ex vivo stem cell expansion and intra-bone injection of UCB, have improved cord blood engraftment, but clinical benefit remains to be demonstrated. Cell therapies derived from UCB are under evaluation as potential novel strategies to reduce relapse and viral infections following transplantation. In recent years, improvements within haploidentical transplantation have reduced the overall use of UCBT as an alternative stem cell source; however, each may have its relative merits and disadvantages and tailored use of these alternative stem cell sources may be the optimal approach.

Sickle cell disease: Clinical presentation and management of a global health challenge

Sickle cell disease is an autosomal recessive, multisystem disorder, characterised by chronic haemolytic anaemia, painful episodes of vaso-occlusion, progressive organ failure and a reduced life expectancy. Sickle cell disease is the most common monogenetic disease, with millions affected worldwide. In well-resourced countries, comprehensive care programs have increased life expectancy of sickle cell disease patients, with almost all infants surviving into adulthood. Therapeutic options for sickle cell disease patients are however, still scarce. Predictors of sickle cell disease severity and a better understanding of pathophysiology and (epi)genetic modifiers are warranted and could lead to more precise management and treatment. This review provides an extensive summary of the pathophysiology and management of sickle cell disease and encompasses the characteristics, complications and current and future treatment options of the disease.

Reduced-intensity conditioning for hematopoietic cell transplant for HLH and primary immune deficiencies

Allogeneic hematopoietic cell transplantation (HCT) with myeloablative conditioning for disorders associated with excessive inflammation such as hemophagocytic lymphohistiocytosis (HLH) is associated with early mortality. A multicenter prospective phase 2 trial of reduced-intensity conditioning with melphalan, fludarabine, and intermediate-timing alemtuzumab was conducted for HLA matched or single HLA locus mismatched related or unrelated donor HCT in a largely pediatric cohort. Graft-versus-host disease (GVHD) prophylaxis was cyclosporine with methylprednisolone. The primary end point was 1-year overall survival (OS). Thirty-four patients with HLH and 12 with other primary immune deficiencies were transplanted. With a median follow-up of 20 months, the 1-year OS for transplanted patients was 80.4% (90% confidence interval [CI], 68.6%-88.2%). Five additional deaths by 16 months yielded an 18-month OS probability of 66.7% (90% CI, 52.9%-77.3%). Two patients experienced primary graft failure, and 18 patients either experienced a secondary graft failure or required a second intervention (mostly donor lymphocyte infusion [DLI]). At 1 year, the proportion of patients alive with sustained engraftment without DLI or second HCT was 39.1% (95% CI, 25.2%-54.6%), and that of being alive and engrafted (with or without DLI) was 60.9% (95% CI, 45.4 %-74.9%). The day 100 incidence of grade II to IV acute GVHD was 17.4% (95% CI, 8.1%-29.7%), and 1-year incidence of chronic GVHD was 26.7% (95% CI, 14.6%-40.4%). Although the trial demonstrated low early mortality, the majority of surviving patients required DLI or second HCT. These results demonstrate a need for future approaches that maintain low early mortality with improved sustained engraftment. The trial was registered at Clinical Trials.gov (NCT 01998633).

Hematopoietic stem cell transplantation for sickle cell disease: Progress and challenges

Sickle cell disease (SCD) presents challenges to hematopoietic stem cell transplantation (HSCT), including donor availability and morbidity with age/disease severity. However, severe SCD causes irreversible organ damage that HSCT can mitigate. This benefit must be balanced against preparative regimen toxicity, graft-versus-host disease, and mortality risk. We review efforts to balance HSCT complications with the promise of cure, and knowledge gaps that warrant further investigation. We highlight the burden of SCD, HSCT risks and benefits, and SCD families' approach to this balance. We emphasize the necessity for information exchange to ensure a joint decision-making process between providers and patients.

Unrelated Donor Transplantation in Children with Thalassemia using Reduced-Intensity Conditioning: The URTH Trial

Allogeneic hematopoietic stem cell transplantation (HSCT) can cure transfusion-dependent thalassemia (TDT). In a multicenter trial we investigated the efficacy of reduced-intensity conditioning (RIC) before unrelated donor (URD) HSCT in children with TDT. Thirty-three children, ages 1 to 17 years, received bone marrow (BM) or umbilical cord blood (UCB) allografts. Median time to neutrophil engraftment was 13 days (range, 10 to 25) and 24 days (range, 18 to 49) and platelet engraftment 23 days (range, 12 to 46) and 50 days (range, 31 to 234) after BM and UCB allografts, respectively. With a median follow-up of 58 months (range, 7 to 79), overall and thalassemia-free survival was 82% (95% CI, .64% to .92%) and 79% (95% CI, .6% to .9%), respectively. The cumulative incidence of grades II to IV acute graft-versus-host disease (GVHD) after BM and UCB allografts was 24% and 44%; the 2-year cumulative incidence of chronic extensive GVHD was 29% and 21%, respectively; 71% of BM and 91% of UCB recipients discontinued systemic immunosuppression by 2 years. Six patients who had Pesaro risk class 2 (n = 5) and class 3 (n = 1) died of GVHD (n = 3), viral pneumonitis (n = 2) and pulmonary hemorrhage (n = 1). Outcomes after this RIC compared favorably with URD HSCT outcomes for TDT and supported engraftment in 32 of 33 patients. Efforts to reduce GVHD and infectious complications are being pursued further.

When there is no match, the game is not over: Alternative donor options for hematopoietic stem cell transplantation in sickle cell disease

Many patients with sickle cell disease experience severe morbidity and early mortality. The only curative option remains hematopoietic stem cell transplantation. Although HLA-matched sibling transplantation has been very successful for adults and children, the vast majority of patients with sickle cell disease do not have an HLA-matched sibling. Alternative donor options include haploidentical, unrelated umbilical cord blood, and matched unrelated donor transplantation. This report summarizes major alternative donor transplantation studies reported to date and ongoing and upcoming clinical trials. We conclude that when there is no HLA-match, all these approaches should be systematically considered before ruling out the option of hematopoietic stem cell transplantation.

Principles of alemtuzumab immunoablation in hematopoietic cell transplantation for non-malignant diseases in children: A review

Alemtuzumab is a humanized mAb targeted to CD52. Alemtuzumab is highly immunosuppressive with the ability to deplete T and B cells (in addition to other immune cell lines). A growing understanding of the PKs, dosing, and timing of administration of alemtuzumab has allowed for the study of its use as a conditioning agent for allogeneic HCT. The highly immunosuppressive properties of the drug are particularly appealing in the setting of non-malignant HCT, where GVHD provides no clinical benefit and relapse of malignancy is not applicable. In addition, the degree of immune suppression achieved with alemtuzumab has allowed for a reduction in the intensity of myeloablative cytotoxic agents included in some HCT conditioning regimens, allowing for fewer acute and late toxicities. This review paper will provide a comprehensive summary of the mechanism of action, PKs, dosing, and timing of alemtuzumab, a brief description of its use in various allogeneic HCT protocols for non-malignant conditions and a summary of the data regarding its use for GVHD therapy. The goal of this review was to provide an understanding as to how alemtuzumab might be safely incorporated into HCT conditioning regimens for children with non-malignant disease, allowing for expanded access to curative HCT therapy.