Safety of stem cell mobilization in donors with sickle cell trait

Favorable outcome of non-myeloablative allogeneic transplantation in adult patients with severe sickle cell disease: A single center experience of 200 patients

Allogeneic hematopoietic stem cell transplant (HSCT) for adults with severe sickle cell disease (SCD) is potentially curative but not commonly utilized therapy due to complications such as graft failure (GF) and organ toxicity. Herein, we are reporting our long-term outcome data of non-myeloablative (NMA) HSCT in adults with severe SCD with emphasis on factors predicting event free survival (EFS). Adults with severe SCD undergoing NMA match-related donor allogeneic HSCT from 2015 to 2021 with at least 12 months of follow-up were included. A total of 200 patients were included with a median age of 26 years (14-43) and 56% were male. The median infused CD34 dose was 13.7 (5.07-25.8), respectively. Median absolute neutrophil count engraftment was 19 (13-39) days with 51% of patients receiving GCSF to expedite recovery. A total of 17 patients experienced GF; 3 as primary and 14 as secondary within a median time of 204 days (40-905). A 76% successfully discontinued sirolimus at the last follow-up. Median follow-up for the cohort is 29.2 (2.1-71.4) months. Estimated 3-year EFS and OS were 88.2% (81.9-92.5) and 94.6% (89.2-97.3). At multivariable analysis, minor ABC incompatibility hazard ratio (HR) 4 (1.3-12.1; 0.014) and allo-antibody against non-ABO donor antigens HR 4.3 (1.3-14.1; 0.016) were significant for EFS. No clonal evolution or myeloid malignancies were seen. This largest single-center report of NMA HSCT in adults with severe SCD further delineated its feasibility, potential toxicities, and fertility outcomes. GF remains a major impediment and appears dependent on ABO matching and non-ABO antibodies.

Feasibility of peripheral blood stem cell collection from sickle cell trait donors with an intensified G-CSF regimen

OBJECTIVES

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment for SCD and bone marrow from an HLA-matched sibling is currently the standard of care. Haploidentical HSCT from a family donor with a TCR αβ/CD19 depleted graft (T-haplo) is an increasingly successful alternative, which requires the generation of G-CSF stimulated peripheral stem cell (PBSC) from haploidentical relatives. These sickle cell trait (SCT) donors reported to develop SCD-related complications in conditions of severe stress.

METHODS

In this retrospective analysis, we compared the safety and efficacy of PBSC mobilization with a G-CSF intensified mobilization regimen in SCT donors with a conventional G-CSF mobilization regimen in healthy donors.

RESULTS

The reported adverse events were similar during intensified G-CSF mobilization, apheresis, and shortly after stem cell apheresis in SCT and control donors. In SCT and control donors, we were able to mobilize high yields of CD34+ stem cells and the harvested CD34+ cell count was comparable with control donors.

CONCLUSIONS

Peripheral stem cell mobilization using an intensified G-CSF regimen is safe, and well tolerated among SCT donors. SCT donors are a valid alternative for collection of peripheral CD34+ stem cells for T-cell-depleted haploidentical stem cell transplantation.

Management of the Sickle Cell Trait: An Opinion by Expert Panel Members

The number of individuals with the sickle cell trait exceeds 300 million worldwide, making sickle cell disease one of the most common monogenetic diseases globally. Because of the high frequency of sickle cell disease, reproductive counseling is of crucial importance. In addition, unlike other carrier states, Sickle Cell Trait (SCT) seems to be a risk factor for several clinical complications, such as extreme exertional injury, chronic kidney disease, and complications during pregnancy and surgery. This expert panel believes that increasing knowledge about these clinical manifestations and their prevention and management can be a useful tool for all healthcare providers involved in this issue.

Gene therapy for sickle cell disease: where we are now?

The landscape of sickle cell disease (SCD) treatment continues to evolve rapidly, with new disease-modifying therapies in development and potentially curative options on the horizon. Until recently, allogeneic stem cell transplant has been the only proven cure for SCD. Gene therapy is rising to the forefront of the discussion as a potentially curative or highly disease- modifying option for abating the complications of the disease. Understanding the different types of gene therapy in use, the differences in their end points, and their potential risks and benefits will be key to optimizing the long-term use of this therapy.

O-Fucose and Fringe-modified NOTCH1 extracellular domain fragments as decoys to release niche-lodged hematopoietic progenitor cells

Successful hematopoietic progenitor cell (HPC) transplant therapy is improved by mobilizing HPCs from the bone marrow niche in donors. Notch receptor-ligand interactions are known to retain HPCs in the bone marrow, and neutralizing antibodies against Notch ligands, Jagged-1 or Delta-like ligand (DLL4), or NOTCH2 receptor potentiates HPC mobilization. Notch-ligand interactions are dependent on posttranslational modification of Notch receptors with O-fucose and are modulated by Fringe-mediated extension of O-fucose moieties. We previously reported that O-fucosylglycans on Notch are required for Notch receptor-ligand engagement controlling hematopoietic stem cell quiescence and retention in the marrow niche. Here, we generated recombinant fragments of NOTCH1 or NOTCH2 extracellular domain carrying the core ligand-binding regions (EGF11-13) either as unmodified forms or as O-fucosylglycan-modified forms. We found that the addition of O-fucose monosaccharide or the Fringe-extended forms of O-fucose to EGF11-13 showed substantial increases in binding to DLL4. Furthermore, the O-fucose and Fringe-extended NOTCH1 EGF11-13 protein displayed much stronger binding to DLL4 than the NOTCH2 counterpart. When assessed in an in vitro 3D osteoblastic niche model, we showed that the Fringe-extended NOTCH1 EGF11-13 fragment effectively released lodged HPC cells with a higher potency than the NOTCH2 blocking antibody. We concluded that O-fucose and Fringe-modified NOTCH1 EGF11-13 protein can be utilized as effective decoys for stem cell niche localized ligands to potentiate HPC egress and improve HPC collection for hematopoietic cell therapy.

Toward dual hematopoietic stem-cell transplantation and solid-organ transplantation for sickle-cell disease

Sickle-cell disease (SCD) leads to recurrent vaso-occlusive crises, chronic end-organ damage, and resultant physical, psychological, and social disabilities. Although hematopoietic stem-cell transplantation (HSCT) is potentially curative for SCD, this procedure is associated with well-recognized morbidity and mortality and thus is ideally offered only to patients at high risk of significant complications. However, it is difficult to identify patients at high risk before significant complications have occurred, and once patients experience significant organ damage, they are considered poor candidates for HSCT. In turn, patients who have experienced long-term organ toxicity from SCD such as renal or liver failure may be candidates for solid-organ transplantation (SOT); however, the transplanted organs are at risk of damage by the original disease. Thus, dual HSCT and organ transplantation could simultaneously replace the failing organ and eliminate the underlying disease process. Advances in HSCT conditioning such as reduced-intensity regimens and alternative donor selection may expand both the feasibility of and potential donor pool for transplantation. This review summarizes the current state of HSCT and organ transplantation in SCD and discusses future directions and the clinical feasibility of dual HSCT/SOT.

Haploidentical Bone Marrow Transplantation with Post-Transplantation Cyclophosphamide Plus Thiotepa Improves Donor Engraftment in Patients with Sickle Cell Anemia: Results of an International Learning Collaborative

Curative therapy for individuals with severe sickle cell disease (SCD) who lack an HLA-identical sibling donor has been frustratingly elusive. In with the goal of improving engraftment while minimizing transplantation-related morbidity, a multi-institutional learning collaborative was developed in the context of a Phase II clinical trial of nonmyeloablative, related HLA-haploidentical (haplo) bone marrow transplantation (BMT) with post-transplantation cyclophosphamide. All eligible participants had hemoglobin SS, and 89% (16 of 18) had an identifiable donor. The median patient age was 20.9 years (IQR, 12.1 to 26.0 years), and the most common indication for transplantation was overt stroke (in 69%; 11 of 16). In the first 3 patients, the conditioning regimen consisted of antithymocyte globulin, fludarabine, cyclophosphamide, and low-dose total body irradiation. Graft-versus-host disease (GVHD) prophylaxis included post-transplantation cyclophosphamide, mycophenolate mofetil, and sirolimus. Primary graft rejection occurred in 2 of the 3 patients (67%), which triggered the study-stopping rule. To reduce graft rejection risk, thiotepa was added to the conditioning regimen, and then 15 patients (including 2 with previous graft rejection) underwent haplo-BMT with this thiotepa-augmented conditioning regimen. At a median follow-up of 13.3 months (interquartile range [IQR], 3.8 to 23.1 months), 93% (14 of 15) had >95% stable donor engraftment at 6 months, with 100% overall survival. The median time to neutrophil engraftment (>500) was 22 days (IQR, 19 to 27 days), and that for platelet engraftment (>50 x 10^9/L) was 28 days (IQR, 27 days to not reached). Two patients had grade III-IV acute GVHD, 1 patient had mild chronic GVHD, and 86% of patients (6 of 7) were off immunosuppression therapy by 1-year post-transplantation. Our data suggest that haplo-BMT with post-transplantation cyclophosphamide and thiotepa improves donor engraftment without significantly increasing morbidity or mortality and could dramatically expand curative options for individuals with SCD.