Treosulfan based reduced toxicity conditioning followed by allogeneic stem cell transplantation in patients with myelofibrosis

Impact of busulfan versus treosulfan dose intensity in myelofibrosis undergoing hematopoietic cell transplantation

One key aspect of allogeneic hematopoietic cell transplantation (HCT) is pretransplant conditioning, balancing risk for relapse versus non-relapse mortality. Conditioning regimens with different alkylators at different doses can influence outcome, but data are missing for myelofibrosis, a challenging cohort of patients usually presenting at older age and with comorbidities. We evaluated in a multicenter retrospective study the comparative efficacy and safety of busulfan versus treosulfan in combination with fludarabine for myelofibrosis patients undergoing HCT. This study included 1115 patients (busulfan, n = 902; treosulfan, n = 213) receiving first HCT between 2005 and 2021. Patients were generally balanced for key patient characteristics. Overall survival at 4 years was 62% for the busulfan group versus 58% for the treosulfan group (p = .22). Impact on outcome was dose-dependent. Overall survival was 65% (95% CI, 61%-69%) for reduced intensity busulfan versus 69% (95% CI, 54%-84%) for reduced intensity treosulfan, 53% (95% CI, 44%-63%) for higher intensity busulfan, and 55% (95% CI, 46%-63%) for higher intensity treosulfan. Incidence of relapse was similar across intensity groups. In multivariable analysis, the hazard for death (with reduced intensity busulfan as reference) was 0.88 (95% CI, 0.39-2.01) for reduced intensity treosulfan (p = .77), 1.42 (95% CI, 0.96-2.10) for higher intensity busulfan (0.08), and 1.61 (95% CI, 1.14-2.26) for higher intensity treosulfan (p = .006). In terms of non-relapse mortality, comparison was not significantly different, while the hazard ratio for higher intensity treosulfan was 1.48 (95% CI, 0.98-2.23; p = .06). Here, we showed comparable outcomes and improved survival in myelofibrosis undergoing HCT with reduced intensity busulfan or treosulfan.

Treosulfan compared to busulfan in allogeneic haematopoietic stem cell transplantation for myelofibrosis: a registry-based study from the Chronic Malignancies Working Party of the EBMT

We aimed to compare outcomes following treosulfan (TREO) or busulfan (BU) conditioning in a large cohort of myelofibrosis (MF) patients from the EBMT registry. A total of 530 patients were included; 73 received TREO and 457 BU (BU ≤ 6.4 mg/kg in 134, considered RIC, BU > 6.4 mg/kg in 323 considered higher dose (HD)). Groups were compared using adjusted Cox models. Cumulative incidences of engraftment and acute GVHD were similar across the 3 groups. The TREO group had significantly better OS than BU-HD (HR:0.61, 95% CI: 0.39-0.93) and a trend towards better OS over BU-RIC (HR: 0.66, 95% CI: 0.41-1.05). Moreover, the TREO cohort had a significantly better Progression-Free-Survival (PFS) than both the BU-HD (HR: 0.57, 95% CI: 0.38-0.84) and BU-RIC (HR: 0.60, 95% CI: 0.39-0.91) cohorts, which had similar PFS estimates. Non-relapse mortality (NRM) was reduced in the TREO and BU-RIC cohorts (HR: 0.44, 95% CI: 0.24-0.80 TREO vs BU-HD; HR: 0.54, 95% CI: 0.28-1.04 TREO vs BU-RIC). Of note, relapse risk did not significantly differ across the three groups. In summary, within the limits of a registry-based study, TREO conditioning may improve PFS in MF HSCT and have lower NRM than BU-HD with a similar relapse risk to BU-RIC. Prospective studies are needed to confirm these findings.

Splenic irradiation prior to allogeneic transplant conditioning in myelofibrosis: A pilot experience

INTRODUCTION

In the era of JAK inhibitors, allogeneic stem cell transplantation (HSCT) remains the only curative treatment for patients with Myelofibrosis (MF). Splenic irradiation (SI) may be used to reduce spleen size and related symptoms.

METHODS

We conducted a retrospective analysis on 14 patients with MF who underwent HSCT with SI from any donor source at our center between June 2016 and March 2021. All patients received a conditioning backbone based on treosulfan and fludarabine, with post-transplant cyclophosphamide (PTCy) and sirolimus as graft-versus-host disease (GvHD) prophylaxis. Patients received SI with 10 Gy involved-field radiotherapy in five 2-Gy fractions over the course of a week prior to the beginning of conditioning.

RESULTS

At transplant all patients were transfusion-dependent and had splenomegaly (median bipolar diameter by ultrasound: 20.75 cm). Overall, 12 patients had received ruxolitinib prior to transplant. Re-evaluation of spleen dimensions was available for 13 patients: median splenic bipolar diameter after at least 3 months from transplant decreased by a median of 25%. With a median post-transplant follow-up of 25 months, 6 patients remain in CR with full-donor chimerism, 3 patients died due to NRM. Overall, 4 patients relapsed. At last follow-up, nine patients are currently alive and achieved transfusion-independence.

CONCLUSIONS

In a small cohort of mostly ruxolitinib pre-treated patients, SI and treosulfan-based conditioning appeared a safe and effective tool to reduce spleen dimensions and ameliorate symptoms. Future prospective studies with adequate sample size are warranted to further investigate the usefulness and safety of this approach in MF.

Treosulfan-Based Conditioning Regimen for Second Allograft in Patients with Myelofibrosis

Simple Summary

Currently, the only curative therapy in myelofibrosis is allogeneic hematopoietic stem cell transplantation. Donor lymphocyte infusion and second stem cell transplantation are the two main treatment options for myelofibrosis patients who relapse after the first transplantation. The optimal conditioning regimen for the second transplantation in myelofibrosis patients is not well defined. Our study aimed to address this question and showed that treosulfan-based conditioning for second allograft in relapsed myelofibrosis patients resulted in longtime freedom from disease in about 50% of the patients. This data supports the second allogeneic hematopoietic stem cell transplantation with a less toxic treosulfan-based conditioning regimen that is effective in relapsed, donor lymphocyte infusion resistant myelofibrosis patients with long term low transplant-related mortality and relapse rates.

Abstract

Relapse after allogeneic hematopoietic stem cell transplantation (AHSCT) in myelofibrosis (MF) patients remains as a significant issue despite advances in transplantation procedures and significant prolongation in survival. Second AHSCT is a potential treatment option but associated with high treatment-related mortality and novel less toxic conditioning regimens are needed. In 33 MF patients with relapse after AHSCT and failure to donor lymphocyte infusion (DLI) we investigated treosulfan (36–42 g/m²) in combination with fludarabine and anti-thymocyte globulin (ATG) as conditioning regimen for a second AHSCT with matched related (n = 2), unrelated (n = 23), or mismatched unrelated (n = 8) donors. All patients achieved leukocyte engraftment after a median of 11 days, and 56 ± 13% experienced acute GVHD grade II–IV at day 100. The therapy-related mortality at day 100 and at 3 years was 16% and 31%, respectively. The cumulative incidence of relapse at 5 years was 16%, resulting in a 5-year disease-free and overall survival of 45% and 47%, respectively. Treosulfan-based conditioning for second allograft in relapsed MF patients resulted in about 50% of the patients in long-term freedom from disease.

Splenic pooling and loss of VCAM-1 causes an engraftment defect in patients with myelofibrosis after allogeneic hematopoietic stem cell transplantation

Myelofibrosis is a myeloproliferative neoplasm that results in cytopenia, bone marrow fibrosis and extramedullary hematopoiesis. Allogeneic hematopoietic stem cell transplantation is the only curative treatment but is associated with a risk of delayed engraftment and graft failure. In this study, patients with myelofibrosis (n=31) and acute myeloid leukemia (n=31) were analyzed for time to engraftment, graft failure and engraftment-related factors. Early and late neutrophil engraftment and late thrombocyte engraftment were significantly delayed in patients with myelofibrosis as compared to acute myeloid leukemia, and graft failure only occurred in myelofibrosis (6%). Only spleen size had a significant influence on engraftment efficiency in myelofibrosis patients. To analyze the cause for the engraftment defect, clearance of hematopoietic stem cells from peripheral blood was measured and immunohistological staining of bone marrow sections was performed. Numbers of circulating CD34⁺ were significantly reduced at early time points in myelofibrosis patients, whereas CD34⁺CD38^- and colony-forming cells showed no significant difference in clearance. Staining of bone marrow sections for homing proteins revealed a loss of VCAM-1 in myelofibrosis with a corresponding significant increase in the level of soluble VCAM-1 within the peripheral blood. In conclusion, our data suggest that reduced engraftment and graft failure in myelofibrosis patients is caused by an early pooling of CD34⁺ hematopoietic stem cells in the spleen and a bone marrow homing defect caused by the loss of VCAM-1. Improved engraftment in myelofibrosis might be achieved by approaches that reduce spleen size and cleavage of VCAM-1 in these patients prior to hematopoietic stem cell transplantation.