Phase II Prospective Multicenter Study of Treosulfan Based Reduced Intensity Conditioning In Allogeneic Hematopoietic Stem Cell Transplantation for Hematological Malignancies From 10/10 HLA Identical Unrelated Donor
Authors: Michallet Mauricette , Sobh Mohamad , Morisset Stephane , Tedone Nathalie , Bay Jacques-Olivier , Harousseau Jean-Luc , Mohty Mohamad , Yakoub-Agha Ibrahim , Buzyn Agnes , Milpied Noel , Nicolini Franck E , Labussiere Helene , Baumgart Joachim , Raus Nicole , Tabrizi Reza , Blaise Didier 
Published: October 2019

Abstract
Abstract 2353

Background:
The key point in allogeneic hematopoietic stem cell transplantation (allo-HSCT) is to find the optimal balance between the graft-versus-host disease (GVHD) and the graft-versus-leukemia (GVL) effect particularly in the unrelated HSCT settings, without forgetting the important role of conditioning.

Objective:
To evaluate the toxicity and efficacy of a new reduced intensity conditioning regimen including Treosulfan, followed by allo-HSCT from a 10/10 HLA identical unrelated donor.

Materials and Methods:
This prospective study included adult patients presenting a hematological malignancy in need of allo-HSCT using a 10/10 HLA identical unrelated donor. Accepted diagnoses were: CML in 1st chronic phase (CP) resistant to imatinib, in 2nd CP or in complete remission (CR) after blast crisis. Multiple myeloma (MM) or chronic lymphocytic leukemia (CLL) in stage B or C in response after relapse post-auto-HSCT. Acute lymphocytic or myeloid leukemia (ALL, AML) patients in CR1 at high risk or <CR1. Myelodysplasic syndrome (MDS) with poor prognostic factors.

The conditioning included:
Treosulfan 12g/m2/day intra-venous (day-6 to day-4), fludarabine 30mg/m2/day intra-venous (day-6 to day -2) and ATG 2.5 mg/kg/day (day-2 to day-1). GVHD prophylaxis used cyclosporine A oral (5mg/kg/day) or iv. (3mg/kg/day) from day-1. Peripheral stem cells after mobilization by G-CSF were used as HSC source.

Results:
Between February 2005 and July 2009, 56 patients were included in 5 different French centers, 30 (54%) males and 26 females with a median age of 57 years (18-65.5). There were 38 (68%) myeloproliferative disorders [29 AML (14 in CR1, 14 CR2 & 1<CR), 8 MDS (1CR1 and 7<CR) and 1 CML in CR1] and 18 (32%) lymphoprolifative disorders [9 MM in PR, 6 CLL (2CR1 & 4PR) and 3 ALL(1CR1 & 2CR2)]. Among 45 explored for cytogenetics, 23 (51%) were normal and 22 with poor prognostic. Before transplantation, two patients did not receive any previous treatment, 21 received 1 line, 22 two lines and 11 > 2 lines. For sex-matching, 49% of patients were sex-mismatched (half of them were F>M). For CMV, 43% were -/-, 25% +/+, 28% +/&minus; and 1% -/+. For ABO matching, 52% were compatible, 24% major incomp. & 24% minor incopm. The median time between diagnosis and allograft was 15 months (4-168). The median number of infused CD34+ cells was 6.5 × 106/Kg(1-17.2)
Fifty-four (96%) patients engrafted with a median time to neutrophils (>0.5G/l), and platelets (>50G/l) recovery of 16 days (4-86), 11 (4-82) respectively. Seventeen patients developed aGVHD grade ≥II (8 grade II, 2 grade III & 7 grade IV) with a cumulative incidence at 3 months of 31% (25-38). The cumulative incidence of cGVHD was, at 12 months: 32% (25-39) limited and 6% (2-10) extensive; at 18 months: 34% (27-47) limited and 8% (5-12) extensive. After a median follow-up of 13 months (1-57), the median overall survival (OS) was not reached with a 3 years probability of 52% (38-71). The median time of event free survival (EFS) was 15 months (8 - 57) with a 3-years probability of 47% (35-64). The cumulative incidence of relapse at 3 years was 25% (19-31) and the cumulative incidence of transplant-related mortality (TRM) at 12, 18 and 36 months was 20% (16-27), 23% (16-29) (same at 18 & 36 months) respectively. At the last follow-up, 22 patients died, 7 due to relapse and 15 due to TRM (5 pneumonia, 4 GVHD, 1 secondary malignancy and 6 other causes). We showed in a univariate analysis a higher 3-years OS of patients in CR1 (65%) compared to those <CR1 (44%) at transplantation with a significant better benefit for AML patients (76%). Patients with active cGVHD seem to benefit for the GVL effect on OS with a high significant difference (HR=0.2 (0.1-0.6) p=0.002). The multivariate analysis studying age, sex matching, ABO compatibility, CMV matching, type of disease, CD34+ cells number, cytogenetics, number of previous treatments, disease status and interval diagnosis-allo-HSCT showed: a negative significant impact of both minor ABO incompatibility (p<0.001) and CMV+/&minus; (p=0.01) on OS, a negative significant impact of patients <CR (p=0.03) on relapse. There was no impact of studied factors on TRM.

Conclusion:
We showed very promising results in terms of OS, relapse and TRM with an impressive GVL effect, in heavily pre-treated patients and transplanted using unrelated donors. Treosulfan appears to be a good choice for conditioning especially with a better outcome in AML patients in CR1.

Disclosures:
No relevant conflicts of interest to declare.