212P - Dual T lymphocyte suppression with antithymocyte globulin and post-transplant cyclophosphamide as graft-versus-host disease prophylaxis in haploidentical hematopoietic stem cell transplant for acute leukemias and myelodysplastic syndrome

Background

Allogeneic stem cell transplantation (SCT) offers the chance of cure for various hematologic malignancies, but graft-versus-host disease (GVHD) remains a major impediment. Especially, with increasing numbers of haploidentical SCT in light of donor’s immediate availability, the interest in better GVHD prophylactic regimens is also on the rise. Antithymocyte globulin (ATG) has traditionally been used for prophylactic T cell depletion and GVHD prevention. Recently, the success of post-transplant cyclophosphamide (PTCy) has been reported by several groups. At Seoul National University Hospital, we designed a busulfan and fludararbine (BuFlu) conditioning combined with rabbit-ATG, PTCy, cyclosporine (CsA) and mycophenolate mofetil (MMF) for the prevention of GVHD.

Methods

We conducted a single-center retrospective longitudinal cohort study of 23 acute leukemia and MDS patients over 18 years old undergoing haplo-SCT. Bu (3.2mg/kg for 2 days for reduced intensity; for 3 days for myeloablative) Flu (40mg/m² for 4 days) conditioning was used. Rabbit ATG was given from D-3 to D-1 and was adjusted per absolute lymphocyte count (ALC) on D-3: for ALC > 1,000, total of 4.0mg/kg was used; for ALC 500 – 1,000, total of 3.5mg/kg; and for ALC < 500, total of 3.5mg/kg. CsA and MMF were given from D+5.

Results

The median age of all patients was 51. The most common underlying disease was AML (39.1%) followed by ALL (26.1%) and MDS (26.1%). There were 14 patients (60.9%) who had modified EBMT score between 1-3. 19 patients (82.6%) underwent reduced intensity conditioning, and the median infused CD34 cell amount was 5.14 x 10⁶/kg. The neutrophil engraftment was achieved in 91.3% with median time of 15 days (range 14-20). The platelet engraftment was achieved in 87% with median time of 13.5 days (range 10-114). The cumulative incidence of any acute GVHD at day 100 was 43.5%, and grade III-IV acute GVHD 8.7%. The cumulative incidence of any chronic GVHD at 1 year was 34.8%, and there were no moderate to severe chronic GVHD.

Conclusions

Combining ATG with PTCy is ideal for building an immunologic platform for reduced GVHD and relapse.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Seoul National University Hospital.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.