Complication free survival long-term after hemopoietic cell transplantation in thalassemia

Targeting the Hematopoietic Stem Cell Niche in β-Thalassemia and Sickle Cell Disease

In the last decade, research on pathophysiology and therapeutic solutions for β-thalassemia (BThal) and sickle cell disease (SCD) has been mostly focused on the primary erythroid defect, thus neglecting the study of hematopoietic stem cells (HSCs) and bone marrow (BM) microenvironment. The quality and engraftment of HSCs depend on the BM microenvironment, influencing the outcome of HSC transplantation (HSCT) both in allogeneic and in autologous gene therapy settings. In BThal and SCD, the consequences of severe anemia alter erythropoiesis and cause chronic stress in different organs, including the BM. Here, we discuss the recent findings that highlighted multiple alterations of the BM niche in BThal and SCD. We point out the importance of improving our understanding of HSC biology, the status of the BM niche, and their functional crosstalk in these disorders towards the novel concept of combined therapies by not only targeting the genetic defect, but also key players of the HSC–niche interaction in order to improve the clinical outcomes of transplantation.

Thalassemia-free and graft-versus-host-free survival: outcomes of hematopoietic stem cell transplantation for thalassemia major, Turkish experience

We report the national data on the outcomes of hematopoietic stem cell transplantation (HSCT) for thalassemia major (TM) patients in Turkey on behalf of the Turkish Pediatric Stem Cell Transplantation Group. We retrospectively enrolled 1469 patients with TM who underwent their first HSCT between 1988 and 2020 in 25 pediatric centers in Turkey. The median follow-up duration and transplant ages were 62 months and 7 years, respectively; 113 patients had chronic graft versus host disease (cGVHD) and the cGVHD rate was 8.3% in surviving patients. Upon the last visit, 30 patients still had cGvHD (2.2%). The 5-year overall survival (OS), thalassemia-free survival (TFS) and thalassemia-GVHD-free survival (TGFS) rates were 92.3%, 82.1%, and 80.8%, respectively. cGVHD incidence was significantly lower in the mixed chimerism (MC) group compared to the complete chimerism (CC) group (p < 0.001). In survival analysis, OS, TFS, and TGFS rates were significantly higher for transplants after 2010. TFS and TGFS rates were better for patients under 7 years and at centers that had performed over 100 thalassemia transplants. Transplants from matched unrelated donors had significantly higher TFS rates. We recommend HSCT before 7 years old in thalassemia patients who have a matched donor for improved outcomes.

Efficacy and Safety of Iron Chelation Therapy After Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Thalassemia Patients: A Retrospective Observational Study

BACKGROUND

Studies on the increased body iron load in patients with thalassemia major have thoroughly demonstrated the problems caused by iron overload. In patients who undergo hematopoietic stem cell transplantation (HSCT) as curative therapy, iron overload continues long after transplantation. There are few pediatric studies on chelation therapy in the posttransplant period. In this study, we present the outcomes of our patients who received posttransplant oral chelation therapy.

PATIENTS AND METHODS

This retrospective observational study evaluated the outcomes of pediatric patients with thalassemia major who used oral chelation therapy after allogeneic HSCT at the Akdeniz University Pediatric Bone Marrow Unit between January 2008 and October 2019.

RESULTS

Deferasirox therapy was initiated in 58 pediatric patients who underwent HSCT for thalassemia. Pretreatment mean serum ferritin was 2166±1038 ng/mL. Treatment was initiated at a mean of 12±6.7 months after transplantation and continued for a mean of 15.7±11.5 months. At treatment discontinuation, the mean serum ferritin was 693±405 ng/mL and the mean reduction was -1472.75±1121.09 ng/mL (P<0.001 vs. posttreatment). Serum ferritin was below 500 ng/mL in 52% of the patients at treatment discontinuation. Manageable side effects such as nausea, vomiting, liver enzyme elevation, and proteinuria were observed in 17% of the patients, while one patient developed ototoxicity.

CONCLUSIONS

Deferasirox therapy effectively reduces iron overload in the posttransplant period. Studies evaluating the effects of early treatment on the graft may help to establish guidelines for posttransplant chelation therapy. Clear guidelines are needed regarding when to initiate and discontinue treatment.

HSCT remains the only cure for patients with transfusion-dependent thalassemia until gene therapy strategies are proven to be safe

Patients with β-thalassemia suffer from severe anemia, iron overload and multiple complications, that affect their quality of life and well-being. Allogeneic hematopoietic stem cell transplantation (HSCT) from an HLA-matched sibling donor, performed in childhood, has been the gold standard for thalassemic patients for decades. Unfortunately, siblings are available only for the minority of patients. Fully matched unrelated donors have been the second choice for cure, with equal results as far as overall survival is concerned, having though the cost of frequent and serious complications. On the other hand, haploidentical transplantation is performed more frequently during the last decade, with promising results. Gene therapy represents a novel therapeutic approach, with impressive results from clinical trials, both from gene addition strategies, as well as from the emerging gene editing tools. After reviewing current critical points of HSCT using alternative donors and assessing recently reported safety issues of gene therapy methods, we conclude that, although a breakthrough, the safety of gene therapy remains to be established.

Hematopoietic stem cell function in β-thalassemia is impaired and is rescued by targeting the bone marrow niche

Hematopoietic stem cells (HSCs) are regulated by signals from the bone marrow (BM) niche that tune hematopoiesis at steady state and in hematologic disorders. To understand HSC-niche interactions in altered nonmalignant homeostasis, we selected β-thalassemia, a hemoglobin disorder, as a paradigm. In this severe congenital anemia, alterations secondary to the primary hemoglobin defect have a potential impact on HSC-niche cross talk. We report that HSCs in thalassemic mice (th3) have an impaired function, caused by the interaction with an altered BM niche. The HSC self-renewal defect is rescued after cell transplantation into a normal microenvironment, thus proving the active role of the BM stroma. Consistent with the common finding of osteoporosis in patients, we found reduced bone deposition with decreased levels of parathyroid hormone (PTH), which is a key regulator of bone metabolism but also of HSC activity. In vivo activation of PTH signaling through the reestablished Jagged1 and osteopontin levels correlated with the rescue of the functional pool of th3 HSCs by correcting HSC-niche cross talk. Reduced HSC quiescence was confirmed in thalassemic patients, along with altered features of the BM stromal niche. Our findings reveal a defect in HSCs in β-thalassemia induced by an altered BM microenvironment and provide novel and relevant insight for improving transplantation and gene therapy approaches.

[Research advances in transplantation for thalassemia major]

Thalassemia is an inherited blood disorder caused by disordered globin chain synthesis due to mutations in the regulatory genes for hemoglobin. At present, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is recognized as the only curative method for treatment. Through the revolution of pretransplantation regimens and selection of donor and source of stem cells, patients' survival has been greatly improved. This article reviews the development of transplantation for thalassemia and related research advances, in order to provide suitable treatment options for clinical application.