Allogeneic hematopoietic SCT in patients with AML following treosulfan/fludarabine conditioning

Current status of conditioning regimens in haploidentical hematopoietic cell transplantation

The development of effective prophylaxis strategies against graft-versus-host disease (GVHD) has contributed to the widespread use of haploidentical related hematopoietic cell transplantation (Haplo-HCT). Currently, GVHD prophylaxis containing posttransplant cyclophosphamide (PTCY) is considered the standard of care in Haplo-HCT, and recent studies have shown comparable results for PTCY-based Haplo-HCT and HCT from other donor sources. The conditioning regimen plays an important role in eradicating tumor cells to prevent disease relapse and suppressing the recipient's immune system to facilitate engraftment. PTCY-based Haplo-HCT was initially developed using a nonmyeloablative conditioning regimen consisting of fludarabine, cyclophosphamide and low-dose total body irradiation, but high relapse rates reinforced the need to intensify the conditioning regimen. In this respect, various myeloablative and reduced-intensity conditioning regimens have been investigated. However, the optimal conditioning regimens for PTCY-based Haplo-HCT have not yet been established, and this issue needs to be addressed based on data from patients undergoing the procedure. In this article, we review the existing literature on conditioning regimens for PTCY-based Haplo-HCT and discuss future perspectives.

Treosulfan-Versus Melphalan-Based Reduced Intensity Conditioning in HLA-Haploidentical Transplantation for Patients ≥ 50 Years with Advanced MDS/AML

Relapse and regimen-related toxicities remain major challenges in achieving long-term survival, particularly among older patients with high-risk myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Previous studies have demonstrated the feasibility of treosulfan-based conditioning, noting stable engraftment and low non-relapse mortality (NRM) in patients undergoing HLA-matched allo-HSCT. However, data on treosulfan-based conditioning in the HLA-haploidentical transplantation (HaploT) setting are limited. We retrospectively compared conditioning with fludarabine-cyclophosphamide (FC)-melphalan (110 mg/m2) and FC-treosulfan (30 g/m2) prior to HaploT using post-transplantation cyclophosphamide (PTCy) in patients with high-risk MDS/AML patients ≥ 50 years, transplanted from 2009-2021 at our institution (n = 80). After balancing patient characteristics by a matched-pair analysis, we identified twenty-one matched pairs. Two-year OS and LFS were similar among the groups (OS 66% and LFS 66%, p = 0.8 and p = 0.57). However, FC-melphalan was associated with a significantly lower probability of relapse compared to FC-treosulfan (0% vs. 24%, p = 0.006), counterbalanced by a higher NRM (33% vs. 10%, p = 0.05). Time to engraftment and incidences of acute and chronic graft-versus-host disease (GvHD) did not differ significantly. In conclusion, HaploT using FC-treosulfan in combination with PTCy in patients aged ≥50 years with MDS/AML appears safe and effective, particularly in advanced disease stages. We confirm the favorable extramedullary toxicity profile, allowing for potential dose intensification to enhance antileukemic activity.

Fludarabine-treosulfan versus fludarabine-melphalan or busulfan-cyclophosphamide conditioning in older AML or MDS patients - A clinical trial to registry data comparison

A randomized study (acronym: MC-FludT.14/L Trial II) demonstrated that fludarabine plus treosulfan (30 g/m²) was an effective and well tolerated conditioning regimen for allogeneic hematopoietic cell transplantation (allo-HCT) in older patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). To further evaluate this regimen, all 252 study patients aged 50 to 70 years were compared with similar patients, who underwent allo-HCT after fludarabine/melphalan (140 mg/m²) (FluMel) or busulfan (12.8 mg/kg)/cyclophosphamide (120 mg/kg) (BuCy) regimens and whose data was provided by the European Society for Blood and Marrow Transplantation registry. In 1:1 propensity-score matched-paired analysis (PSA) of AML patients, there was no difference in 2-year-relapse-incidence after FluTreo compared with either FluMel (n = 110, p = 0.28) or BuCy (n = 78, p = 0.98). However, 2-year-non-relapse-mortality (NRM) was lower compared with FluMel (p = 0.019) and BuCy (p < 0.001). Consequently, 2-year-overall-survival (OS) after FluTreo was higher compared with FluMel (p = 0.04) and BuCy (p < 0.001). For MDS patients, no endpoint differences between FluTreo and FluMel (n = 30) were evident, whereas 2-year-OS after FluTreo was higher compared with BuCy (n = 25, p = 0.01) due to lower 2-year-NRM. Multivariate sensitivity analysis confirmed all significant results of PSA. Consequently, FluTreo (30 g/m²) seems to retain efficacy compared with FluMel and BuCy, but is better tolerated by older patients.

Treosulfan vs busulfan conditioning for allogeneic bmt in children with nonmalignant disease: a randomized phase 2 trial

Optimal conditioning prior to allogeneic hematopoietic stem cell transplantation for children with non-malignant diseases is subject of ongoing research. This prospective, randomized, phase 2 trial compared safety and efficacy of busulfan with treosulfan based preparative regimens. Children with non-malignant diseases received fludarabine and either intravenous (IV) busulfan (4.8 to 3.2 mg/kg/day) or IV treosulfan (10, 12, or 14 g/m2/day). Thiotepa administration (2 × 5 mg/kg) was at the investigator's discretion. Primary endpoint was freedom from transplantation (treatment)-related mortality (freedom from TRM), defined as death between Days -7 and +100. Overall, 101 patients (busulfan 50, treosulfan 51) with at least 12 months follow-up were analyzed. Freedom from TRM was 90.0% (95% CI: 78.2%, 96.7%) after busulfan and 100.0% (95% CI: 93.0%, 100.0%) after treosulfan. Secondary outcomes (transplantation-related mortality [12.0% versus 3.9%]) and overall survival (88.0% versus 96.1%) favored treosulfan. Graft failure was more common after treosulfan (n = 11), than after busulfan (n = 2) while all patients were rescued by second procedures except one busulfan patient. CTCAE Grade III adverse events were similar in both groups. This study confirmed treosulfan to be an excellent alternative to busulfan and can be safely used for conditioning treatment in children with non-malignant disease.

Dual-Activity Fluoroquinolone-Transportan 10 Conjugates Offer Alternative Leukemia Therapy during Hematopoietic Cell Transplantation

Hematopoietic cell transplantation (HCT) is often considered a last resort leukemia treatment, fraught with limited success due to microbial infections, a leading cause of mortality in leukemia patients. To address this critical issue, we explored a novel approach by synthesizing antileukemic agents containing antibacterial substances. This innovative strategy involves conjugating fluoroquinolone antibiotics, such as ciprofloxacin (CIP) or levofloxacin (LVX), with the cell-penetrating peptide transportan 10 (TP10). Here, we demonstrate that the resultant compounds display promising biologic activities in preclinical studies. These novel conjugates not only exhibit potent antimicrobial effects but are also selective against leukemia cells. The cytotoxic mechanism involves rapid disruption of cell membrane asymmetry leading to membrane damage. Importantly, these conjugates penetrated mammalian cells, accumulating within the nuclear membrane without significant effect on cellular architecture or mitochondrial function. Molecular simulations elucidated the aggregation tendencies of TP10 conjugates within lipid bilayers, resulting in membrane disruption and permeabilization. Moreover, mass spectrometry analysis confirmed efficient reduction of disulfide bonds within TP10 conjugates, facilitating release and activation of the fluoroquinolone derivatives. Intriguingly, these compounds inhibited human topoisomerases, setting them apart from traditional fluoroquinolones. Remarkably, TP10 conjugates generated lower intracellular levels of reactive oxygen species compared with CIP and LVX. The combination of antibacterial and antileukemic properties, coupled with selective cytostatic effects and minimal toxicity toward healthy cells, positions TP10 derivatives as promising candidates for innovative therapeutic approaches in the context of antileukemic HCT. This study highlights their potential in search of more effective leukemia treatments. SIGNIFICANCE STATEMENT: Fluoroquinolones are commonly used antibiotics, while transportan 10 (TP10) is a cell-penetrating peptide (CPP) with anticancer properties. In HCT, microbial infections are the primary cause of illness and death. Combining TP10 with fluoroquinolones enhanced their effects on different cell types. The dual pharmacological action of these conjugates offers a promising proof-of-concept solution for leukemic patients undergoing HCT. Strategically designed therapeutics, incorporating CPPs with antibacterial properties, have the potential to reduce microbial infections in the treatment of malignancies.

Population pharmacokinetic modeling of treosulfan and rationale for dose recommendation in children treated for conditioning prior to allogeneic hematopoietic stem cell transplantation

Intravenously infused treosulfan was evaluated in adult and pediatric patients for conditioning regimen prior to allogeneic hematopoietic stem cell transplantation. A population pharmacokinetic (PK) model was initially developed on 116 adult and pediatric PK profiles from historical trials, to support treosulfan dose recommendations for children in 2 prospective trials. The aim was to assess and update the initial population PK model by inclusion of additional 83 pediatric PK profiles from these 2 trials. The final population PK model was 2-compartmental with dosing in the central compartment, linear elimination, and inter-compartmental clearance. Inter-individual variability was included on clearance (CL), central volume (V1), peripheral volume (V2), and inter-compartmental clearance (Q). The final model described an effect of the body surface area (BSA) on CL, V1, V2, and Q. The final model resulted in a modified dose recommendation for children and advises treosulfan doses of 10 g/m2, 12 g/m2, and 14 g/m2 for BSAs of <0.4 m2, ≥0.4 to <0.9 m2, and ≥0.9 m2, respectively. This simplified BSA-dependent dose recommendation was developed for children, ensuring a well comparable treosulfan exposure as a dose of 14 g/m2 in adults - irrespective of their age and without applying individual therapeutic drug monitoring.

Comparative study of treosulfan plus Fludarabine (FT14) with busulfan plus Fludarabine (FB4) for acute myeloid leukemia in first or second complete remission: An analysis from the European Society for Blood and Marrow Transplantation (EBMT) Acute Leukemia Working Party (ALWP)

Different doses of treosulfan plus fludarabine have shown advantage over reduced intensity regimens. However, data comparing higher doses of treosulfan to myeloablative busulfan are limited. Thus, we compared outcomes between FT14 (fludarabine 150/160 mg/m² and treosulfan 42 g/m², or FT14) over FB4 (fludarabine 150/160 mg/m² and busulfan 12.8 mg/kg). We retrospectively studied patients from European Society for Blood and Marrow Transplantation registry: a) adults diagnosed with acute myeloid leukemia (AML), b) recipients of first allogeneic hematopoietic stem cell transplantation (HSCT) from unrelated or sibling donor (2010-2020), c) HSCT at first or second complete remission, d) conditioning with FT14 or FB4. FT14 recipients (n = 678) were older, with higher rates of secondary AML, unrelated donors, peripheral blood grafts, and adverse cytogenetics, but lower percentage of female donor to male recipient compared to FB4 (n = 2025). Analysis was stratified on age. In patients aged < 55 years, FT14 was associated with higher relapse incidence (RI) and lower Leukemia-Free Survival (LFS). In patients aged≥55 years, acute GVHD CI was higher in FB4, without significant differences in other outcomes. Although FT14 has been used for higher-risk HSCT patients, our large real-world multicenter study suggests that FB4 is associated with better outcomes compared to FT14 in younger patients.

Treosulfan compared with reduced-intensity busulfan improves allogeneic hematopoietic cell transplantation outcomes of older acute myeloid leukemia and myelodysplastic syndrome patients: Final analysis of a prospective randomized trial

The phase III study was designed to compare event-free survival (EFS) after treosulfan-based conditioning with a widely applied reduced-intensity conditioning (RIC) busulfan regimen in older or comorbid patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) undergoing allogeneic hematopoietic cell transplantation (HCT). A previously reported confirmatory interim analysis of the randomized clinical study including 476 patients demonstrated statistically significant noninferiority for treosulfan with clinically meaningful improvement in EFS. Here, the final study results and pre-specified subgroup analyses of all 570 randomized patients with completed longer-term follow-up are presented. Patients presenting HCT-specific comorbidity index >2 or aged ≥50 years were randomly assigned (1:1) to intravenous (IV) fludarabine with either treosulfan (30 g/m² IV) or busulfan (6.4 mg/kg IV) after stratification by disease risk group, donor type, and participating institution. The primary endpoint was EFS with disease recurrence, graft failure, or death from any cause as events. EFS of patients (median age 60 years) was superior after treosulfan compared to RIC busulfan: 36-months-EFS rate 59.5% (95% CI, 52.2-66.1) vs. 49.7% (95% CI, 43.3-55.7) with a hazard ratio (HR) of 0.64 (95% CI, 0.49-0.84), p = 0.0006. Likewise, overall survival (OS) with treosulfan was superior compared to busulfan: 36-month-OS rate 66.8% vs. 56.3%; HR 0.64 (95% CI, 0.48-0.87), p = 0.0037. Post hoc analyses revealed that these differences were consistent with the confirmatory interim analysis, and thereby the treosulfan regimen appears particularly suitable for older AML and MDS patients.

Treosulfan plus fludarabine versus TEAM as conditioning treatment before autologous stem cell transplantation for B-cell Non-Hodgkin lymphoma

Conditioning with treosulfan and fludarabine (Treo/Flu) has been proven to be feasible and efficient in several types of malignancies before allogeneic hematopoietic stem cell transplantation (allo-HSCT). Given its favorable reduced toxicity profile, we introduced Treo/Flu as conditioning before autologous HSCT (auto-HSCT) in patients with B-cell Non-Hodgkin lymphoma (NHL). The aim of this study was to evaluate the efficacy and safety of Treo/Flu in comparison to TEAM. Fifty-seven patients with NHL received auto-HSCT after conditioning with either Treo/Flu (n = 22) or TEAM (n = 35). All patients achieved sustained engraftment. PFS, EFS and OS were not significant in both groups. Of note is that patients in the Treo/Flu group were less dependent on thrombocyte transfusions (p = 0.0082), significantly older (in median 11 years, p < 0.0001) and suffered less frequently from infectious complications (p = 0.0105), mucositis and stomatitis (p < 0.0001). This study is the first to present efficacy, feasibility, and safety of conditioning with Treo/Flu preceding auto-HSCT in patients with NHL. Since it demonstrated a lack of significant difference in comparison to TEAM conditioning it might be a valuable alternative especially in elderly patients with B-cell NHL and comorbidities. Further evaluation by prospective clinical trials is warranted.

Clinical experience with venetoclax in patients with newly diagnosed, relapsed, or refractory acute myeloid leukemia

Background

Diagnosis of acute myeloid leukemia (AML) is associated with poor outcome in elderly and unfit patients. Recently, approval of the BCL-2 inhibitor venetoclax (VEN) in combination with hypo-methylating agents (HMA) led to a significant improvement of response rates and survival. Further, application in the relapsed or refractory (r/r) AML setting or in context of allogeneic stem cell transplantation (alloHSCT) seems feasible.

Methods and patients

Fifty-six consecutive adult AML patients on VEN from January 2019 to June 2021 were analyzed retrospectively. Patients received VEN either as first-line treatment, as subsequent therapy (r/r AML excluding prior alloHSCT), or at relapse after alloHSCT. VEN was administered orally in 28-day cycles either combined with HMA or low-dose cytarabine (LDAC).

Results

After a median follow-up of 11.5 (range 6.1–22.3) months, median overall survival (OS) from start of VEN treatment was 13.3 (2.2–20.5) months, 5.0 (0.8–24.3) months and 4.0 (1.5–22.1) months for first-line, subsequent line treatment and at relapse post-alloHSCT, respectively. Median OS was 11.5 (10–22.3) months from start of VEN when subsequent alloHSCT was carried out. Relapse-free survival (RFS) for the total cohort was 10.2 (2.2 – 24.3) months. Overall response rate (composite complete remission + partial remission) was 51.8% for the total cohort (61.1% for VEN first-line treatment, 52.2% for subsequent line and 42.8% at relapse post-alloHSCT). Subgroup analysis revealed a significantly reduced median OS in FLT3-ITD mutated AML with 3.4 (1.9–4.9) months versus 10.4 (0.8–24.3) months for non-mutated cases, (HR 4.45, 95% CI 0.89–22.13, p = 0.0002). Patients harboring NPM1 or IDH1/2 mutations lacking co-occurrence of FLT3-ITD showed a survival advantage over patients without those mutations (11.2 (5–24.3) months versus 5.0 (0.8–22.1) months, respectively, (HR 0.53, 95% CI 0.23 – 1.21, p = 0.131). Multivariate analysis revealed mutated NPM1 as a significant prognostic variable for achieving complete remission (CR) (HR 19.14, 95% CI 2.30 – 436.2, p < 0.05). The most common adverse events were hematological, with grade 3 and 4 neutropenia and thrombocytopenia reported in 44.6% and 14.5% of patients, respectively.

Conclusion

Detailed analyses on efficacy for common clinical scenarios, such as first-line treatment, subsequent therapy (r/r AML), and application prior to and post-alloHSCT, are presented. The findings suggest VEN treatment combinations efficacious not only in first-line setting but also in r/r AML. Furthermore, VEN might play a role in a subgroup of patients with failure to conventional chemotherapy as a salvage regimen aiming for potential curative alloHSCT.

Combination of treosulfan, fludarabine and cytarabine as conditioning in patients with acute myeloid leukemia, myelodysplastic syndrome and myeloproliferative neoplasms

PURPOSE

Treosulfan and fludarabine (Treo/Flu) were successfully introduced into toxicity-reduced conditioning for SCT. However, the risk of post-SCT relapse remains a matter of concern. We report the results of a novel individual treatment approach with Treo/Flu and cytarabine (Treo/Flu/AraC) conditioning prior to allogeneic SCT in patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or myeloproliferative neoplasms (MPN).

METHODS

Seventy-seven patients (median age 54 years) at high risk of disease relapse due to unfavorable cytogenetics or failure to achieve complete remission prior to SCT were included. Median follow-up was 3.2 years.

RESULTS

The 1-, 2- and 3-year RFS rates were 49.4%, 41.7%, and 37.6% and OS rates were 59.3%, 49.3%, and 45.4%, respectively. Cumulative incidence of NRM was 10% at 100 days, 18.8% at 1 year and 20.1% at 2 years. The cumulative incidence of relapse increased from 31% at 1 year to 38.5% after 3 years. The cumulative incidences of engraftment, chimerism, graft-versus-host disease (GvHD) and toxicities were acceptable and comparable with similar patients conditioned with Treo/Flu or FLAMSA-RIC.

CONCLUSION

In conclusion, Treo/Flu/AraC provides tolerable, feasible, and effective conditioning for patients with AML, MDS or MPN, even in advanced disease states. The incidence of NRM and relapse is acceptable in this heavily pre-treated population with high-risk disease. Future research will aim to confirm these initial findings and include a larger number of participants in a prospective trial.

Outcome of patients with relapsed or refractory acute myeloid leukemia treated with Mito-FLAG salvage chemotherapy

PURPOSE

Curative intended treatment is challenging in patients with relapsed or refractory acute myeloid leukemia (r/r AML) and associated with a dismal prognosis for long-term survival. Despite novel treatment options, the majority of patients are treated with chemotherapy-based regimens. Although widely used, little data exist on the combination of fludarabine, cytarabine, granulocyte colony stimulating factor (FLAG) and mitoxantrone as salvage strategy for r/r AML.

MATERIALS AND METHODS

Sixty-six patients receiving Mito-FLAG for r/r AML treated at a German tertiary care center between 2009 and 2019 were analyzed with regard to response rates, survival and safety profile.

RESULTS

Overall response rate was 75.8% with 56.1% of patients achieving complete remission (CR) and 19.7% partial remission (PR). After a median follow-up of 54 months, median overall survival (OS) was 13 months. Patients transitioned to allogeneic hematopoietic stem cell transplantation (alloHSCT) (75.8%) showed a significant improvement in OS with a median OS of 17 (95% CI 8.5-25.4) months vs 3 (95% CI 1.7-4.3) months (p < 0.001). 30- and 60-day mortality rates for all patients after the initial cycle of Mito-FLAG were 4.5% and 7.6%, respectively.

CONCLUSION

The Mito-FLAG salvage protocol represents an effective and feasible treatment regimen for r/r AML. Importantly, a high rate of transition to successful alloHSCT with the aim of long-term disease-free survival has been shown.

Treosulfan-Based Conditioning Regimen Prior to Allogeneic Stem Cell Transplantation: Long-Term Results From a Phase 2 Clinical Trial

Introduction

Reducing toxicities while preserving efficacy in allogeneic stem cell transplant (allo-HCT) remains a particularly challenging problem. Different strategies to enhance the antitumor activity without increasing early and late adverse toxicities of the conditioning regimens have been investigated.

Methods

The aim of “AlloTreo” prospective phase 2 clinical trial was to evaluate the efficacy and safety of a conditioning regimen based on Treosulfan (42 g/m²) and fludarabine (https://clinicaltrials.gov/ct2/show/NCT00598624). We enrolled 108 patients with hematological diseases who received a first allo-HCT between June 2005 and January 2011, inside the frame of this trial at our center. Median age at allo-HCT was 49 (21–69) years. Disease Risk Index was low in 14 (13%) patients, intermediate in 73 (67.7%), high in 17 (15.7%), and very high in 4 (3.7%). Donors were human leukocyte antigen (HLA)-matched related in 50 cases, 10/10-matched unrelated in 36, and 9/10-mismatched unrelated in 22. Graft-versus-host disease (GvHD) prophylaxis consisted of cyclosporine-A and methotrexate. Anti-T-lymphocyte globulin (ATLG) was administered in patients receiving unrelated allo-HCT. Stem cell source was mainly peripheral blood stem cells (95%).

Results

Conditioning regimen was well tolerated. Full donor chimerism was documented for most patients (88%) at day +30. At 12 years, overall survival (OS) was 41.7% (32.2%–50.9%), progression-free survival (PFS) was 31.7% (23%–40.7%), GvHD-free/relapse-free survival was 20.9% (13.7%–29.1%), cumulative incidence (CI) of relapse was 44.5% (34.9%–53.6%), and transplant-related mortality (TRM) was 22.5% (15.1%–30.9%). CI of acute GvHD grades II–IV was 27.8% (19.7%–36.5%) at 100 days; 12-year CI of chronic GvHD was 40.7% (31.3%–49.9%). Relevant long-term adverse effects were 10 secondary malignancy, 3 fatal cardiovascular events, and 1 late-onset transplant-associated thrombotic microangiopathy. Ten successful pregnancies were reported after allo-HCT. In multivariate analysis, older age (≥60 years) at transplant [hazard ratio (HR), 2.157; p = 0.004] and a high/very high disease risk index (HR, 1.913; p = 0.026) were significantly associated with a lower OS.

Conclusions

Overall, our data confirmed the myeloablative potential and safe toxicity profile of full dose Treo (42 g/m²) especially for the younger population.

Survival Advantage of Treosulfan Plus Fludarabine Before Allogeneic Hematopoietic Cell Transplantation for Older or Comorbid Patients With Myeloid Malignancies

We have previously shown an advantage of a myeloablative conditioning regimen with reduced toxicity (Fludarabine 150 mg/m², Treosulfan 42 g/m², FluTreo) compared to a reduced-intensity regimen. We aimed to determine long-term safety and efficacy of FluTreo. We prospectively studied consecutive patients who received FluTreo in our center (2014-2019) on the basis of age (≥50 years), hematopoietic cell transplantation comorbidity index (HCT-CI) ≥2, or both. FluTreo recipients were then compared to a historical control group. We studied 68 FluTreo recipients, with a median age of 58.5 years and HCT-CI of 3. We calculated cumulative incidence (CI) of acute (grade 2-4) and moderate/severe chronic graft-versus-host disease (GVHD) (29.9% and 25%, respectively). The 3-year CI of treatment-related mortality was 19.1%, associated only with acute GVHD (P < .001). With a median follow-up of 27.3 (range 5.7-84.5) months in surviving patients, the 3-year overall survival (OS) was 56.6%, and disease-free survival (DFS) was 54.9%. Median survival has not yet been reached. Among pretransplantation and transplantation factors, only HCT-CI was associated with DFS and OS (P = .022 and P = .043, respectively). FluTreo recipients aged ≥50 with HCT-CI ≤ 2 had favorable DFS and OS compared with patients aged ≥50 with HCT-CI ≤2 after myeloablative conditioning. Our real-world study confirms that HCT with FluTreo expands the transplant population with favorable outcomes compared to previously used conditions. The choice of HCT in patients of a rather older age and comorbidity index needs to be revisited.

Impact of induction chemotherapy with intermediate-dosed cytarabine and subsequent allogeneic stem cell transplantation on the outcome of high-risk acute myeloid leukemia

Background

Acute myeloid leukemia (AML) with antecedent hematological disease (s-AML) and treatment-related AML (t-AML) predicts poor prognosis. Intensive treatment protocols of those high-risk patients should consider allogeneic stem cell transplantation (allo-HSCT) in first complete remission (CR). Despite allo-HSCT, relapse rate remains high. Induction chemotherapy with liposomal cytarabine and daunorubicin (CPX-351) has been approved for patients with AML with myeloid-related changes (AML-MRC) or t-AML based on improved survival and remission rates compared to standard 7 + 3 induction.

Patients and methods

110 patients with newly diagnosed s-AML or t-AML at a university hospital were analyzed retrospectively. Median age was 62 years (24–77 years). A total of 65 patients with s-AML after MDS (59%) and 23 patients (20.9%) with t-AML were included. Induction chemotherapy consisted of intermediate-dosed cytarabine (ID-AraC) in combination with idarubicin (patients up to 60 years) or mitoxantrone (patients over 60 years). In patients subsequently undergoing allo-HSCT, reduced conditioning regimens (RIC) were applied prior to transplantation in 47 of 62 patients (76%).

Results

Induction chemotherapy with ID-AraC resulted in an overall response rate of 83% including complete remission (CR/CRi) in 69 patients (63%) with a low rate of early death (2.7%). Most relevant non-hematologic toxicity consisted of infectious complications including sepsis with need of intensive care treatment in five patients (4.5%) and proven or probable invasive fungal disease in eight patients (7.2%). Relapse-free survival (RFS), event-free survival (EFS) and overall survival (OS) of the whole cohort were 19 months (0–167), 10 months (0–234) and 15 months (0–234), respectively (p < 0.0001). A significant improvement of OS was observed in patients who underwent allo-HSCT compared to those without subsequent allo-HSCT: 9 vs. 46 months, p < 0.0001. Rate of transplantation-related mortality (TRM) in the early phase post allo-HSCT was low (0.9% at day 30 and 1.8% at day 90, respectively). RIC conditioning results in OS rate of 60% after 60 months post allo-HSCT (median OS not reached).

Conclusion

S-AML and t-AML patients receiving induction chemotherapy with intermediate-dosed cytarabine showed satisfactory response rate and consolidation therapy with allo-HSCT after full or reduced-intensity conditioning further improved survival in these patients with similar outcome as reported for CPX-351.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00432-021-03733-0.

Long-Term Outcomes of Treosulfan- vs. Busulfan-Based Conditioning Regimen for Patients With Myelodysplastic Syndrome and Acute Myeloid Leukemia Before Hematopoietic Cell Transplantation: A Systematic Review and Meta-Analysis

Background

Many studies aimed to evaluate the efficacy and safety of treosulfan-based conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT) compared with other regimens, but different outcomes were reported across studies.

Aim

To determine the long-term survival outcomes of treosulfan-based vs. busulfan-based conditioning regimens in myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML) patients.

Methods

PubMed, Embase, and Cochrane library were searched for studies published prior to December 6, 2019. The fixed-effects model was applied for overall survival (OS), leukemia-free survival (LFS), non-relapse mortality (NRM), acute and chronic graft versus host disease (GvHD). Relapse incidence (RI) was pooled by the use of the random-effects model.

Results

Six studies were included (3,982 patients; range, 57-1,956). The pooled HR for OS favored treosulfan (HR=0.80, 95%CI: 0.71-0.90). There was no significant difference in NRM between the two regimens (HR=0.84, 95%CI=0.71-1.01). There was no significant difference in LFS between the two regimens (HR=0.98, 95%CI=0.87-1.12). Treosulfan-based regimens showed a lower risk of aGvHD (HR=0.70, 95%CI=0.59-0.82), but there was no difference for cGvHD (HR=0.94, 95%CI=0.81-1.09). There was no significant difference in RI between the two regimens (HR=0.96, 95%CI=0.71-1.31). There was no publication bias among these studies.

Conclusion

The current meta-analysis determined that treosulfan-based conditioning regimens could improve the OS in patients with MDS and AML, with lower acute graft-versus-host disease incidence, compared with busulfan-based regimens.

Acute toxicity and outcome among pediatric allogeneic hematopoietic transplant patients conditioned with treosulfan-based regimens

Treosulfan-based regimens constitute a feasible and increasingly used, but still myeloablative, conditioning in pediatric allogeneic hematopoietic stem cell transplantation (HSCT). We retrospectively analyzed the acute toxicity and outcome of all consecutive (2004-2015) pediatric HSCT patients prepared for HSCT with treosulfan in a single-center setting. We included HSCTs performed for both nonmalignant (n = 23) and malignant diseases (n = 11). The controls were patients with nonmalignant diseases or hematological malignancies conditioned with cyclophosphamide (Cy)-total body irradiation (TBI)-based (39 patients) or busulfan-based regimens (11 patients). The major toxicities of the treosulfan-based regimens were limited to oral mucosa and skin. 50% of the patients needed IV morphine for severe mucositis compared to 31% in patients conditioned with Cy-TBI (P = 0.02). Other toxicities were rare. The disease-free survival (DFS) of patients transplanted for nonmalignant disorders was 88.9 ± 7.5% at 2 years. The event-free survival (EFS) at 2 years in this small cohort for those with a malignant disease and a treosulfan-based conditioning was 54.5 ± 1.5%. We conclude that a treosulfan-based conditioning regimen gives excellent DFS in pediatric HSCT performed for a nonmalignant disorder but with substantial mucosal toxicity. In a malignant disorder a treosulfan-based regimen looks promising but larger, preferably randomized, studies are needed to prove efficacy.

Extra-medullary recurrence of myeloid leukemia as myeloid sarcoma after allogeneic stem cell transplantation: impact of conditioning intensity

Myeloid sarcoma (MS) as a solid extra-medullary (EM) manifestation of acute myeloid leukemia (AML), myeloproliferative or myelodysplastic syndromes is a rare presentation of relapse after allogeneic hematopoietic stem cell transplantation (HSCT). The databases of the Departments of Hematology and Oncology of the University Hospitals of Jena and Rostock were screened for patients aged 18 years or older for onset of MS after HSCT for myeloid malignancies between 2002 and 2019. Nineteen patients with MS were identified, the majority of whom had received reduced-intensity conditioning (RIC). The median onset of MS was 425 days after HSCT and the median overall survival since MS was 234 days. Although MS is associated with a poor prognosis, three patients survived more than two years and one more than 11 years after MS onset. These results indicate that RIC protocols may be associated with a higher risk of EM relapse. Since EM relapse occurred in the presence of Graft-versus-host-disease, these observations also demonstrate the limitations of graft-versus-tumor effects after HSCT. In conclusion, occurrence of MS after HSCT is associated with a poor prognosis, as multimodal curative concepts including intensive chemotherapy and another HSCT are often not viable.

Knockout of LASP1 in CXCR4 expressing CML cells promotes cell persistence, proliferation and TKI resistance

Chronic myeloid leukaemia (CML) is a clonal myeloproliferative stem cell disorder characterized by the constitutively active BCR-ABL tyrosine kinase. The LIM and SH3 domain protein 1 (LASP1) has recently been identified as a novel BCR-ABL substrate and is associated with proliferation, migration, tumorigenesis and chemoresistance in several cancers. Furthermore, LASP1 was shown to bind to the chemokine receptor 4 (CXCR4), thought to be involved in mechanisms of relapse. In order to identify potential LASP1-mediated pathways and related factors that may help to further eradicate minimal residual disease (MRD), the effect of LASP1 on processes involved in progression and maintenance of CML was investigated. The present data indicate that not only overexpression of CXCR4, but also knockout of LASP1 contributes to proliferation, reduced apoptosis and migration as well as increased adhesive potential of K562 CML cells. Furthermore, LASP1 depletion in K562 CML cells leads to decreased cytokine release and reduced NK cell-mediated cytotoxicity towards CML cells. Taken together, these results indicate that in CML, reduced levels of LASP1 alone and in combination with high CXCR4 expression may contribute to TKI resistance.

Clofarabine and Treosulfan as Conditioning for Matched Related and Unrelated Hematopoietic Stem Cell Transplantation: Results from the Clo3o Phase II Trial

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) can be curative for patients with hematologic malignancies. The ideal conditioning regimen before allo-HSCT has not been established. We conducted a Phase II study to evaluate the tolerability and efficacy of clofarabine and treosulfan as conditioning regimen before allo-HSCT. The primary objective was to evaluate the cumulative incidence of nonrelapse mortality (NRM) on day +100. Forty-four patients (36 with acute myelogenous leukemia, 5 with acute lymphoblastic leukemia, 3 with myelodysplastic syndromes) were enrolled. The median patient age was 47 years, and the median duration of follow-up was 27 months. The conditioning regimen was based on clofarabine 40 mg/m² (days -6 to -2) and treosulfan 14 g/m² (days -6 to -4). Allogeneic hematopoietic stem cells were derived from a sibling (n = 22) or a well-matched unrelated donor (n = 22). Graft-versus-host disease (GVHD) prophylaxis consisted of antithymocyte globulin, rituximab, cyclosporine, and a short-course of methotrexate. The regimen allowed for rapid engraftment and a 100-day NRM of 18%, due mainly to bacterial infections. The incidences of grade II-IV acute GVHD and chronic GVHD were 16% and 19%, respectively. The rates of overall survival (OS), progression-free survival, and relapse at 2 years were 51%, 31%, and 50%, respectively. Significantly different outcomes were observed between patients with low-intermediate and patients with high-very high Disease Risk Index (DRI) scores (1-year OS, 78% and 24%, respectively). Our findings show that the use of treosulfan and clofarabine as a conditioning regimen for allo-HSCT is feasible, with a 78% 1-year OS in patients with a low-intermediate DRI score. However, 1-year NRM was 18%, and despite the intensified conditioning regimen, relapse incidence remains a major issue in patients with poor prognostic risk factors.

Intravenous Busulfan Compared with Treosulfan-Based Conditioning for Allogeneic Stem Cell Transplantation in Acute Myeloid Leukemia: A Study on Behalf of the Acute Leukemia Working Party of European Society for Blood and Marrow Transplantation

Dose intensity of the conditioning regimen has significant impact on the outcomes after stem cell transplantation (SCT) for acute myeloid leukemia. Most studies have shown more relapse, less nonrelapse mortality (NRM), and similar overall survival after reduced-intensity and myeloablative conditioning. There are limited data on the dose equivalence and expected outcomes of treosulfan-based compared with busulfan-based conditioning. We compared SCT outcomes after fludarabine with either intravenous busulfan at a myeloablative dose (FB4, 12.8 mg/kg, n = 1265) or a reduced dose (FB2, 6.4 mg/kg, n = 1456) or treosulfan at 42 g/m² (FT14, n = 403) or 36 g/m² (FT12, n = 168). Median patient age was 48, 60, 57, and 60 years in the FB4, FB2, FT14, and FT12 groups, respectively (P < .0001). Two-year overall survival was 58%, 53%, 53%, and 51%, respectively (P = .25). Multivariate analysis identified advanced age, advanced disease status, and secondary leukemia to be associated with worse survival. Relapse rate was 30%, 35%, 34%, and 40%, respectively. Relapse was more common after FB2, advanced age and disease status, secondary leukemia, and sibling donors. NRM was 17%, 18%, 21%, and 16%, respectively. NRM was least common after FT12 and more common with advanced age and disease status and unrelated donors. Treosulfan-based regimens were associated with lower rates of graft-versus-host disease. There was no difference in any outcome among patients in first complete remission at transplantation. However, there was better survival with treosulfan-based conditioning in advanced leukemia. In conclusion, survival is determined mostly by disease biology and is similar after various regimens. Treosulfan-based conditioning is more similar to myeloablative than to reduced-intensity conditioning but can be administered safely in older patients, with lower rates of graft-versus-host disease and possibly better outcomes in patients with active leukemia.

Missing HLA C group 1 ligand in patients with AML and MDS is associated with reduced risk of relapse and better survival after allogeneic stem cell transplantation with fludarabine and treosulfan reduced toxicity conditioning

Reduced-toxicity conditioning with fludarabine and treosulfan is a dose-intensive regimen with enhanced anti-leukemia effect and acceptable toxicity in AML/MDS. HLA-C regulates natural-killer (NK) cell function by inhibiting Killer immunoglobulin-like receptors (KIR) and is divided into C1 and C2 epitopes. The missing-ligand theory suggests that missing recipient KIR ligands drives NK-alloreactivity after SCT, in the absence of HLA-mismatch by activating unlicensed donor NK cells. We analyzed SCT outcomes in 203 patients with AML/MDS, median age 58 years, given SCT from matched-siblings (n = 97) or matched-unrelated donors (n = 106), using two treosulfan doses (total 36 or 42 g/m² ). 34% expressed one HLA-C group 1 allele (C1C1), 19% one HLA-C group 2 allele (C2C2), and 48% both KIR ligands (C1C2). Median follow-up was 48 months. 5-year relapse, nonrelapse mortality (NRM) and leukemia-free survival (LFS) rates were 38%, 27%, and 36%, respectively. Relapse rates were 43%, 45%, and 26% in patients expressing C1C1, C1C2, and C2C2 ligands, respectively (P = .03). Multivariate-analysis identified chemo-refractory disease (HR 3.1, P = .003), poor cytogenetics (HR 1.7, P = .08), female donor to male recipient (HR 0.4, P = .01) and C2C2 ligands (HR 0.4, P = .04) as independent factors predicting relapse. HLA-C ligands were not associated with GVHD or NRM. LFS was 33%, 30%, and 46%, respectively (P = .07). Chemorefractory disease (HR 3.1, P = .0004) and C2C2 group ligand (HR 0.6, P = .06) independently predicted LFS. Treosulfan dose did not predict any SCT outcome. In conclusion, missing HLA-C group 1 ligand is associated with reduced relapse risk, similar NRM and improved LFS, after HLA-matched SCT with treosulfan conditioning in AML/MDS.

Ocular disposition of treosulfan and its active epoxy-transformers following intravenous administration in rabbits

Treosulfan (TREO) has an established position in chemotherapy of advanced ovarian cancer but has been also applied in uveal melanoma patients. Moreover, it is used as an orphan drug for a myeloablative conditioning prior to stem cell transplantation. In this paper, biodistribution of prodrug TREO and its active monoepoxide (S,S-EBDM) and diepoxide (S,S-DEB) into aqueous humor of the eye was studied for the first time. For that purpose, alone TREO and the mixture of TREO, S,S-EBDM and S,S-DEB were administered intravenously to New Zealand White rabbits. The three analytes were determined in plasma and aqueous humor by validated HPLC methods and pharmacokinetic calculations were performed in WinNonlin. After the infusion of TREO, the aqueous humor/plasma C_max ratio and area under the curve ratio amounted 0.04 and 0.10 for TREO, and 1.1 and 2.2 for S,S-EBDM, respectively. Following the bolus injection of the mixture of the prodrug and its epoxides, the aqueous humor/plasma C_max ratios for TREO, S,S-EBDM and S,S-DEB were 0.05, 0.66, and 4.0, respectively. The presented results indicate a poor penetration of TREO into the eye, which may impair systemic treatment of ocular tumors but is beneficial in terms of a lack of clinically relevant ophthalmic adverse effects.

Assessing the efficacy of allogeneic hematopoietic stem cells transplantation (allo-HSCT) by analyzing survival end points in defined groups of acute myeloid leukemia patients: a retrospective, multicenter Polish Adult Leukemia Group study

The importance of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for survival outcomes in patients with acute myeloid leukemia (AML) currently remains unclear. The study aimed to compare measures of clinical treatment for patients with AML in CR1 (the first complete remission) with or without being subjected to allo-HSCT. These consisted of leukemia-free survival (LFS), overall survival (OS), cumulative incidence of relapse (CIR), and non-relapse mortality disease (NRM). Subjects were 622 patients, median age of 44, forming part of the prospective, randomized, and multicenter clinical Polish Adult Leukemia Group trials during 1999-2008. The Mantel-Byar approach was used to assess allo-HSCT on survival endpoints, accounting for a changing transplant status. Undergoing allo-HSCT significantly improved the LFS and OS for the entire group of patients with AML in CR1, along with the DAC induction subgroup and for the group with unfavorable cytogenetics aged 41-60. The CIR demonstrated that allo-HSCT reduced the risk of relapse for patients with AML in CR1 and those with an unfavorable cytogenetic risk. In addition, the NRM analysis showed that allo-HSCT significantly reduced the risk of death unrelated to relapse for the entire group of AML patients in CR1 and aged 41-60. The allo-HSCT treatment particularly benefitted survival for the AML in CR1 group having an unfavorable cytogenetic prognosis.

Penetration of Treosulfan and its Active Monoepoxide Transformation Product into Central Nervous System of Juvenile and Young Adult Rats

Treosulfan (TREO) is currently investigated as an alternative treatment of busulfan in conditioning before hematopoietic stem cell transplantation. The knowledge of the blood-brain barrier penetration of the drug is still scarce. In this paper, penetration of TREO and its active monoepoxide (S,S-EBDM) and diepoxide (S,S-DEB) into the CNS was studied in juvenile (JR) and young adult rats (YAR) for the first time. CD rats of both sexes (n = 96) received an intravenous dose of TREO 500 mg/kg b.wt. Concentrations of TREO, S,S-EBDM, and S,S-DEB in rat plasma, brain, and cerebrospinal fluid (CSF, in YAR only) were determined by validated bioanalytical methods. Pharmacokinetic calculations were performed in WinNonlin using a noncompartmental analysis and statistical evaluation was done in Statistica software. In male JR, female JR, male YAR, and female YAR, the brain/plasma area under the curve (AUC) ratio for unbound TREO was 0.14, 0.17, 0.10, and 0.07 and for unbound S,S-EBDM, it was 0.52, 0.48, 0.28, and 0.22, respectively. The CSF/plasma AUC ratio in male and female YAR was 0.12 and 0.11 for TREO and 0.66 and 0.64 for S,S-EBDM, respectively. Elimination rate constants of TREO and S,S-EBDM in all the matrices were sex-independent with a tendency to be lower in the JR. No quantifiable levels of S,S-DEB were found in the studied samples. TREO and S,S-EBDM demonstrated poor and sex-independent penetration into CNS. However, the brain exposure was greater in juvenile rats, so very young children might potentially be more susceptible to high-dose TREO-related CNS exposure than young adults.

Reduced-intensity conditioned allogeneic SCT in adults with AML

AML is currently the most common indication for reduced-intensity conditioned (RIC) allo-SCT. Reduced-intensity regimens allow a potent GVL response to occur with minimized treatment-related toxicity in patients of older age or with comorbidities that preclude the use of myeloablative conditioning. Whether RIC SCT is appropriate for younger and more standard risk patients is not well defined and the field is changing rapidly; a prospective randomized trial of myeloablative vs RIC (BMT-CTN 0901) was recently closed when early results indicated better outcomes for myeloablative regimens. However, detailed results are not available, and all patients in that study were eligible for myeloablative conditioning. RIC transplants will likely remain the standard of care as many patients with AML are not eligible for myeloablative conditioning. Recent publication of mature results from retrospective and prospective cohorts provide contemporary efficacy and toxicity data for these attenuated regimens. In addition, recent studies explore the use of alternative donors, introduce regimens that attempt to reduce toxicity without reducing intensity, and identify predictive factors that pave the way to personalized approaches. These studies paint a picture of the future of RIC transplants. Here we review the current status of RIC allogeneic SCT in AML.

Treosulfan-based conditioning and hematopoietic cell transplantation for nonmalignant diseases: a prospective multicenter trial

Hematopoietic cell transplantation is an effective treatment for patients with nonmalignant diseases and for many is the only known cure. Conventional myeloablative regimens have been associated with unacceptably high early transplant-related mortality (TRM), particularly in patients with comorbid conditions. This prospective multicenter trial was designed to determine the safety and engraftment efficacy of treosulfan-based conditioning in patients with nonmalignant diseases. Thirty-one patients received HLA-matched related (n = 4) or unrelated (n = 27) grafts after conditioning with treosulfan (total dose, 42 g/m(2)), fludarabine (total dose, 150 mg/m(2)), ± thymoglobulin (6 mg/kg; n = 22). Graft-versus-host disease (GVHD) prophylaxis consisted of tacrolimus and methotrexate. All patients engrafted. Day-100 TRM was 0%. With a median follow-up of 2 years, the 2-year survival was 90%. Three patients died of GVHD, recurrent hemophagocytic lymphohistiocytosis, and a surgical complication, respectively. The cumulative incidences of grades II to IV and III to IV acute GVHD at day 100 and chronic GVHD at 2 years were 62%, 10%, and 21%, respectively. Patients who received thymoglobulin had a significantly lower incidence of grades III to IV acute GVHD (0% versus 33%; P = .005). These results indicate that the combination of treosulfan, fludarabine, and thymoglobulin is effective at establishing donor engraftment with low toxicity and improved survival in patients with nonmalignant diseases and support the need for future disease-specific clinical trials.

Advances in hematopoietic stem cell transplantation for primary immunodeficiency

The transplantation of hematopoietic stem cells in patients with primary immunodeficiencies has improved significantly over the last 40 years. In favorable circumstances when there is minimal or no infection present, no end-organ damage and the availability of a well HLA-matched donor, survival and cure reaches 90%. Barriers to further success include late identification of disease, with accumulation of infection- and inflammation-related organ damage, stem cell manipulation when there is no HLA-matched donor, toxicity of conditioning regimens and prediction and treatment of graft-versus-host disease. This review will outline recent developments in conditioning regimens, stem cell source manipulation and early detection and treatment of graft-versus-host disease, with a particular emphasis on patients with primary immunodeficiency.

Rapid and sensitive liquid chromatography-tandem mass spectrometry method for determination of protein-free pro-drug treosulfan and its biologically active monoepoxy-transformer in plasma and brain tissue

For the first time a high performance liquid chromatography method with tandem mass spectrometry detection (HPLC-MS/MS) was developed for simultaneous determination of a pro-drug treosulfan (TREO) and its active monoepoxide (S,S-EBDM) in biological matrices. Small volumes of rat plasma (50 μL) and the brain homogenate supernatant (100 μL), equivalent to 0.02 g of brain tissue, were required for the analysis. Protein-free TREO, S,S-EBDM and acetaminophen, internal standard (IS), were isolated from the samples by ultrafiltration. Complete resolution of the analytes and the IS was accomplished on Zorbax Eclipse column using an isocratic elution with a mobile phase composed of ammonium formate - formic acid buffer pH 4.0 and acetonitrile. Detection was performed on a triple-quadrupole MS via multiple-reaction-monitoring following electrospray ionization. The developed method was fully validated according to the current guidelines of the European Medicines Agency. Calibration curves were linear in ranges: TREO 0.2-5720 μM and S,S-EBDM 0.9-175 μM for plasma, and TREO 0.2-29 μM and S,S-EBDM 0.4-44 μM for the brain homogenate supernatant. The limits of quantitation of TREO and S,S-EBDM in the studied matrices were much lower in comparison to the previously used bioanalytical methods. The HPLC-MS/MS method was adequately precise (coefficient of variation≤12.2%), accurate (relative error≤8.6%), and provided no carry-over, acceptable matrix effect as well as dilution integrity. The analytes were stable in acidified plasma and the brain homogenate supernatant samples for 4 h at room temperature, for 4 months at-80°C as well as within two cycles of freezing and thawing, and demonstrated 18-24h autosampler stability. The validated method enabled determination of low concentrations of TREO and S,S-EBDM in incurred brain samples of the rats treated with TREO, which constitutes a novel bioanalytical application.

Treosulfan, fludarabine, and 2-Gy total body irradiation followed by allogeneic hematopoietic cell transplantation in patients with myelodysplastic syndrome and acute myeloid leukemia

Allogeneic hematopoietic cell transplantation (HCT) offers curative therapy for many patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). However, post-HCT relapse remains a major problem, particularly in patients with high-risk cytogenetics. In this prospective phase II trial, we assessed the efficacy and toxicity of treosulfan, fludarabine, and 2 Gy total body irradiation (TBI) as conditioning for allogeneic HCT in patients with MDS or AML. Ninety-six patients with MDS (n = 36: 15 refractory cytopenia with multilineage dysplasia, 10 refractory anemia with excess blasts type 1, 10 refractory anemia with excess blasts type 2, 1 chronic myelomonocytic leukemia type 1) or AML (n = 60: 35 first complete remission [CR], 18 second CR, 3 advanced CR, 4 refractory relapse) were enrolled; median age was 51 (range, 1 to 60) years. Twelve patients had undergone a prior HCT with high-intensity conditioning. Patients received 14 g/m(2)/day treosulfan i.v. on days -6 to -4, 30 mg/m(2)/day fludarabine i.v. on days -6 to -2, and 2 Gy TBI on day 0, followed by infusion of hematopoietic cells from related (n = 27) or unrelated (n = 69) donors. Graft-versus-host disease prophylaxis consisted of tacrolimus and methotrexate. With a median follow-up of 30 months, the 2-year overall survival (OS), relapse incidence, and nonrelapse mortality were 73%, 27%, and 8%, respectively. The incidences of grades II to IV (III to IV) acute and chronic graft-versus-host disease were 59% (10%) and 47%, respectively. Two-year OS was not significantly different between MDS patients with poor-risk and good/intermediate-risk cytogenetics (69% and 85%, respectively) or between AML patients with unfavorable and favorable/intermediate-risk cytogenetics (64% and 76%, respectively). In AML patients, minimal residual disease (MRD; n = 10) at the time of HCT predicted higher relapse incidence (70% versus 18%) and lower OS (41% versus 79%) at 2 years, when compared with patients without MRD. In conclusion, treosulfan, fludarabine, and low-dose TBI provided effective conditioning for allogeneic HCT in patients with MDS or AML and resulted in low relapse incidence, regardless of cytogenetic risk. In patients with AML, MRD at the time of HCT remained a risk factor for post-HCT relapse.