T-cell deplete versus T-cell replete haploidentical hematopoietic stem cell transplantation for sickle cell disease: where are we?

Allogeneic hematopoietic stem cell transplantation to cure sickle cell disease: A review

Sickle cell disease (SCD) had first been mentioned in the literature a century ago. Advancement in the molecular basis of the pathophysiology of the disease opens the door for various therapeutic options. Though life-extending treatments are available for treating patients with SCD, allogeneic hematopoietic stem cell transplantation (HSCT) is the only option as of yet. A major obstacle before HSCT to cure patients with SCD is the availability of donors. Matched sibling donors are available only for a small percentage of patients. To expand the donor pool, different contrasting approaches of allogeneic HSCT like T-cell replete and deplete have been tested. None of those tested approaches have been without the risk of GvHD and graft rejection. Other limitations such as transplantation-related infections and organ dysfunction caused by the harsh conditioning regimen need to be addressed on a priority basis. In this review, we will discuss available allogeneic HSCT approaches to cure SCD, as well as recent advancements to make the approach safer. The center of interest is using megadose T-cell-depleted bone marrow in conjugation with donor-derived CD8 veto T cells to achieve engraftment and tolerance across MHC barriers, under reduced intensity conditioning (RIC). This approach is in phase I/II clinical trial at the MD Anderson Cancer Centre and is open to patients with hemoglobinopathies.

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.

KIR in Allogeneic Hematopoietic Stem Cell Transplantation: Need for a Unified Paradigm for Donor Selection

Allogeneic hematopoietic stem cell transplantation (aHSCT) is a lifesaving therapy for hematological malignancies. For years, a fully matched HLA donor was a requisite for the procedure. However, new immunosuppressive strategies have enabled the recruitment of viable alternative donors, particularly haploidentical donors. Over 95% of patients have at least two potential haploidentical donors available to them. To identify the best haploidentical donor, the assessment of new immunogenetic criteria could help. To this end, the clinical benefit of KIR genotyping in aHSCT has been widely studied but remains contentious. This review aims to evaluate the importance of KIR-driven NK cell alloreactivity in the context of aHSCT and explain potential reasons for the discrepancies in the literature. Here, through a non-systematic review, we highlight how the studies in this field and their respective predictive models or scoring strategies could be conceptually opposed, explaining why the role of NK cells remains unclear in aHCST outcomes. We evaluate the limitations of each published prediction model and describe how every scoring strategy to date only partly delivers the requirements for optimally effective NK cells in aHSCT. Finally, we propose approaches toward finding the optimal use of KIR genotyping in aHSCT for a unified criterion for donor selection.

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.

Evolution of the role of haploidentical stem cell transplantation: past, present, and future

INTRODUCTION

The accessibility to haplo-donors has led to an increase in the number of haplo-HSCT worldwide. A systematic search of the PubMed database between 2000 to present was performed.

AREAS COVERED

In this review, the authors discussed the most used approaches to perform haplo-HSCT and its results: T-cell depletion (TCD, including Perugia platform and its modifications) and T-cell repleted haplo (TCR, including the high-dose post-transplant cyclophosphamide strategy (Baltimore protocol) and the Beijing protocol). The improvements and modifications made to the different strategies have increased the indications of haplo-HSCT, including both malignant and nonmalignant disorders. Focusing on the Baltimore protocol, the authors review the results of the retrospective studies that have compared it to other donor transplants. The limitations of this strategy in terms of toxicity, graft complications, and GVHD are also discussed in detail. Finally, possible approaches to improve the outcomes of TCR haplo-HSCT are presented.

EXPERT OPINION

The recent advances in the field of haplo-HSCT have allowed a large number of patients with incurable diseases to benefit from this procedure despite not having a matched donor. With all available strategies, virtually no patient who needs an allogeneic transplant should be excluded by the absence of a donor.

Haploidentical bone marrow transplant with posttransplant cyclophosphamide for sickle cell disease: An update

Hematopoietic cell transplant (HCT) can cure both children and adults with sickle cell disease. Outcomes have historically been poor for the vast majority of patients who lack a matched sibling donor. However, the development of haploidentical HCT (haplo-HCT) with high doses of posttransplant cyclophosphamide (PTCy) has allowed for curative long-term potential with favorable transplant-related outcomes, though this has not obviated the potential for graft rejection from human leukocyte antigen mismatch and repeated red blood cell transfusions. Accordingly, multiple strategies have been developed to improve outcomes, the majority of which are based on the Johns Hopkins platform from 2012. Presently, we aim to discuss results from pertinent studies and compare outcomes with the two most recent approaches involving either thiotepa plus 200-cGy total body irradiation or 400-cGy total body irradiation. Direct comparisons are required to determine the optimized curative potential. Transplant-eligible patients must be referred to tertiary medical centers for consideration of haplo-HCT.