Treosulfan-based conditioning regimens for hematopoietic stem cell transplantation in children with primary immunodeficiency: United Kingdom experience

Pharmacology of dimethanesulfonate alkylating agents: busulfan and treosulfan

INTRODUCTION

Among the dimethanesulfonates, busulfan, in combination with other alkylating agents or nucleoside analogues, is the cornerstone of high-dose chemotherapy. It is used, and followed hematopoietic stem cell transplantation, for the treatment of various hematologic malignancies and immunodeficiencies. Treosulfan, which is a hydrophilic analogue of busulfan, was the first dimethanesufonate registered for the treatment of ovarian cancer. Recently, treosulfan has been investigated for the treatment of hematologic malignancies in combination with the same second agents before hematopoietic stem cell transplantation.

AREAS COVERED

This work reviews the pharmacological data of these two dimethanesulfonates alkylating agents. Specifically, the article looks at their chemistry, metabolism, anticancer activity, and their pharmacokinetics and pharmacodynamics.

EXPERT OPINION

Busulfan has been investigated widely for more than three decades leading to a large and precise handling of this agent with numerous studies on activity and pharmacokinetics and pharmacodynamics. In contrast, the behavior of treosulfan is still under investigation and not fully described. The complexity of treosulfan's metabolism and mechanism of action gives rise to the need of a deeper understanding of its pharmacological activity in a context of high-dose chemotherapy. Specifically, there is a great need to better understand its pharmacokinetics/pharmacodynamics relationship.

Outcome of hematopoietic stem cell transplantation for adenosine deaminase–deficient severe combined immunodeficiency

Deficiency of the purine salvage enzyme adenosine deaminase leads to SCID (ADA-SCID). Hematopoietic cell transplantation (HCT) can lead to a permanent cure of SCID; however, little data are available on outcome of HCT for ADA-SCID in particular. In this multicenter retrospective study, we analyzed outcome of HCT in 106 patients with ADA-SCID who received a total of 119 transplants. HCT from matched sibling and family donors (MSDs, MFDs) had significantly better overall survival (86% and 81%) in comparison with HCT from matched unrelated (66%; P < .05) and haploidentical donors (43%; P < .001). Superior overall survival was also seen in patients who received unconditioned transplants in comparison with myeloablative procedures (81% vs 54%; P < .003), although in unconditioned haploidentical donor HCT, nonengraftment was a major problem. Long-term immune recovery showed that regardless of transplant type, overall T-cell numbers were similar, although a faster rate of T-cell recovery was observed after MSD/MFD HCT. Humoral immunity and donor B-cell engraftment was achieved in nearly all evaluable surviving patients and was seen even after unconditioned HCT. These data detail for the first time the outcomes of HCT for ADA-SCID and show that, if patients survive HCT, long-term cellular and humoral immune recovery is achieved.

Long-term follow-up of children conditioned with Treosulfan: German and Austrian experience

We report the long-term follow-up of children transplanted with Treosulfan (TREO)-based conditioning in Germany and Austria. Nine centres reported a total of 109 transplantations. Patients were stratified according to the paediatric TRM risk score derived from the paediatric BMT registry (PRST) and compared with the historical transplant population of this registry. Underlying diseases were malignancies, immunodeficiencies, and haematologic and metabolic disorders. TREO total dose ranged from 21-42 g/m(2). Additional conditioning drugs included fludarabine, thiotepa, melphalan, CY and/or TBI. EFS at 3 years for non-malignant and malignant diseases was 88% and 49%, respectively. Leukaemia patients in remission had a survival of 51% at 3 years; nonremission patients relapsed and died within 18 months. TRM and OS in the low-risk groups 0 and 1 were similar to PRST controls. TRM in the high-risk groups 2 and 3 was markedly lower (9% vs 28% and 13% vs 53%, respectively) than in the PRST group, but OS was similar. In conclusion, TREO-based conditioning regimens in children resulted in excellent engraftment and long-term survival in nonmalignant disease. In high-risk malignancy, low acute toxicity was followed by low TRM but it did not translate into increased survival.

Long-term survival and late deaths after hematopoietic cell transplantation for primary immunodeficiency diseases and inborn errors of metabolism

It is uncertain whether late mortality rates after hematopoietic cell transplantation for severe combined immunodeficiency (SCID), non-SCID primary immunodeficiency diseases (non-SCID PIDD), and inborn errors of metabolism (IEM) return to rates observed in the general population, matched for age, sex, and nationality. We studied patients with SCID (n = 201), non-SCID PIDD (n = 405), and IEM (n = 348) who survived for at least 2 years after transplantation with normal T cell function (SCID) or >95% donor chimerism (non-SCID PIDD and IEM). Importantly, mortality rate was significantly higher in these patients compared with the general population for several years after transplantation. The rate decreased toward the normal rate in patients with SCID and non-SCID PIDD beyond 6 years after transplantation, but not in patients with IEM. Active chronic graft-versus-host disease at 2 years was associated with increased risk of late mortality for all diseases (hazard ratio [HR], 1.87; P = .05). In addition, late mortality was higher in patients with non-SCID PIDD who received T cell-depleted grafts (HR 4.16; P = .007) and in patients with IEM who received unrelated donor grafts (HR, 2.72; P = .03) or mismatched related donor grafts (HR, 3.76; P = .01). The finding of higher mortality rates in these long-term survivors for many years after transplantation confirms the need for long-term surveillance.

Reduced-intensity conditioning for allogeneic stem cell transplant in primary immune deficiencies

Conventional myeloablative conditioning regimens prior to hematopoietic cell transplantation (HCT) are associated with significant transplant-related morbidity and mortality in children affected by primary immunodeficiency disorders. Reduced-intensity conditioning regimens have been extensively used without severe acute toxicity in patients with pre-HCT comorbidities, with the additional advantage of reducing or avoiding long-term sequelae such as infertility and growth retardation. Compared with myeloablative HCT, reduced-intensity conditioning regimens are associated with an increased incidence of mixed donor chimerism and graft rejection. While mixed donor engraftment is likely to correct the phenotypic expression of most children with primary immunodeficiency disorders, the use of donor lymphocyte infusion to increase donor chimerism or second HCT procedures may be required in some cases. Here we discuss the most recent data on the use of different reduced-intensity conditioning protocols in children with primary immunodeficiency disorders, highlighting significant clinical lessons and areas that need additional study.

Allogeneic hematopoietic stem cell transplantation in thalassemia major: results of a reduced-toxicity conditioning regimen based on the use of treosulfan

Sixty thalassemia patients (median age, 7 years; range, 1-37) underwent allogeneic hematopoietic stem cell transplantation (HSCT) after a preparation combining thiotepa, treosulfan, and fludarabine. Before HSCT, 27 children were assigned to risk class 1 of the Pesaro classification, 17 to class 2, and 4 to class 3; 12 patients were adults. Twenty patients were transplanted from an HLA-identical sibling and 40 from an unrelated donor. The cumulative incidence of graft failure and transplantation-related mortality was 9% and 7%, respectively. Eight patients experienced grade II-IV acute GVHD, the cumulative incidence being 14%. Among 56 patients at risk, 1 developed limited chronic GVHD. With a median follow-up of 36 months (range, 4-72), the 5-year probability of survival and thalassemia-free survival are 93% and 84%, respectively. Neither the class of risk nor the donor used influenced outcome. This treosulfan-based preparation proved to be safe and effective for thalassemia patients given allogeneic HSCT.

Hematopoietic stem cell transplantation for primary immunodeficiency diseases

Hematopoietic stem cell transplantation (HSCT) is now highly successfully curing a widening range of primary immunodeficiencies (PIDs). Better tissue typing, matching of donors, less toxic chemotherapy, better virus detection and treatment, improved supportive care, and graft-versus-host disease prophylaxis mean up to a 90% cure for severe combined immunodeficiency patients and a 70-80% cure for other PIDs given a matched unrelated donor, and rising to 95% for young patients with specific PIDs, such as Wiskott-Aldrich syndrome. Precise molecular diagnosis, detailed data on prognosis, and careful pre-HSCT assessment of infective lung and liver damage will ensure an informed benefit analysis of HSCT and the best outcome. It is now recognized that the best treatment option for chronic granulomatous disease is HSCT, which can also be curative for CD40 ligand deficiency and complex immune dysregulation disorders.

Reduced intensity transplantation for primary immunodeficiency disorders

Studies so far indicate that reduced intensity transplantation (RIT) may have an important role in treating patients with primary immunodeficiency disease (PID). Unlike more standard approaches, such regimens can be used without severe toxicity in patients with severe pulmonary or hepatic disease. RIT also offers the advantage that long-term sequelae such as infertility or growth retardation may be avoided or reduced. RIT appears to be most appropriate for those patients with significant co-morbidities (eg T cell deficiencies) and those undergoing unrelated donor haematopoietic cell transplantation. More studies are required using pharmacokinetic monitoring (eg busulphan, treosulfan and alemtuzumab) and varying stem cell sources to optimise graft vs marrow reactions and minimise graft vs host disease. In certain PID patients RIT will be the "first step" towards establishing donor cell engraftment; second infusions of donor stem cells, donor lymphocyte infusions, or a second myeloablative HCT, which appears to be well tolerated, may be required in some patients with low level donor chimerism or graft rejection.

Reduced-toxicity conditioning with treosulfan and fludarabine in allogeneic hematopoietic stem cell transplantation for myelodysplastic syndromes: final results of an international prospective phase II trial

BACKGROUND

An alternative reduced-toxicity conditioning regimen for allogeneic transplantation, based on treosulfan and fludarabine, has recently been identified. The rationale for this study was to investigate the efficacy and safety of this regimen prospectively in patients with a primary myelodysplastic syndrome.

DESIGN AND METHODS

A total of 45 patients with primary myelodysplastic syndromes were conditioned with 3×14 g/m(2) treosulfan and 5×30 mg/m(2) fludarabine followed by allogeneic hematopoietic stem cell transplantation. Subtypes of myelodysplastic syndromes were refractory anemia with excess blasts-2 (44%), refractory cytopenia with multilineage dysplasia (27%), refractory anemia (9%), refractory anemia with ringed sideroblasts (4%), refractory cytopenia with multilineage dysplasia and ringed sideroblasts (4%), refractory anemia with excess blasts-1 (2%), and myelodysplastic syndrome with isolated del (5q) (2%). The myelodysplastic syndrome was unclassified in 7% of the patients. Forty-seven percent of the patients had a favorable karyotype, 29% an unfavorable one, and 18% an intermediate karyotype. Patients were evaluated for engraftment, adverse events, graft-versus-host disease, non-relapse mortality, relapse incidence, overall survival and disease-free survival.

RESULTS

All but one patient showed primary engraftment of neutrophils after a median of 17 days. Non-hematologic adverse events of grade III-IV in severity included mainly infections and gastrointestinal symptoms (80% and 22% of the patients, respectively). Acute graft-versus-host disease grade II-IV developed in 24%, and extensive chronic graft-versus-host disease in 28% of the patients. After a median follow-up of 780 days, the 2-year overall and disease-free survival estimates were 71% and 67%, respectively. The 2-year cumulative incidences of non-relapse mortality and relapse were 17% and 16%, respectively.

CONCLUSIONS

Our safety and efficacy data suggest that treosulfan-based conditioning therapy is a promising treatment option for patients with myelodysplastic syndromes. clinicaltrials.gov identifier: NCT01062490.