More Intensity Immuno-Suppression In Conditioning Regimen  may Favor Donor Stem Cell Sustained Engraftment In Allogeneic Stem Cell Transplantation For Acquired Severe Aplastic Anemia Patients

Hematopoietic stem cell transplantation (HSCT) is the first-line therapy for patients younger less than 40 years old with severe aplastic anemia (SAA). And the long-term survival for patients with SAA who received HSCT reaches to 70%-90%. Cyclophosphamide-based conditioning regimen with or without antithymocyte globulin (ATG) has been adopted in majority of HSCT for SAA patients with HLA matched related donor. However the graft rejection and graft failure in HSCT for SAA with cyclophosphamide-based conditioning regimen is still as high as 5%-16%. The aim of this study is to explore whether more immue suppression in conditioning regimen could favor the donor stem cells sustained engraftment for severe aplastic anemia patients receiving allogeneic hematopoietic stem cell transplantation. Fludarabine and busulfan were added in cyclophosphamide-based conditioning regimen to intensity immune suppression in conditioning.

To analyze the outcomes and chimeras of 40 patients with SAA who received HLA matched allo-HSCT from 2000 to 2012 with either fludarabine-based conditioning regimen or cyclophosphamide-based conditioning regimen retrospectively and to explore the relationship between the chimeras and conditioning regimen.

Forty patients with SAA who received HLA matched allo-HSCT From May, 2000 to Dec. 2012. Twelve patients ( median age 25 year old  range 13-52, male 7, femal 5) received  fludarabine-based conditioning regimen which composed of fludarabine (30 mg/m2/d ×5d), busulfan ( 3 mg/kg ×2d ), cyclophosphamide ( 60mg/kg/d×2d) and ATG (2.5mg/kg/d ×5d). Twenty patients( median age 23 year old  range 12-42, male 19, femal 9)  received  cyclophosphamide-based conditioning regimen which composed of cyclophosphamide (50mg/kg/d ×4d )and ATG (2.5mg/kg/d ×2d ). The  median dose of MNC were 4.5×108/kg (range 3.8-7.0×108/kg )and 3.58×108/kg (range 3.2-6.8×108/kg ) and CD34+ cells were  4.5×108/kg and 3.58×108/kg respectively. GVHD prophylaxis were cyclosporine and short-term course methotrexate. Donor chimera was detected on day+30, +90, +180, and 360 after HSCT by short tandem repeat polymerase chain reaction, or fluorescein in situ hybridization for X and Y chromosomes in cases when patients and donors were sex mismatched.

All patients with fludarabine-based conditioning regimen were successful Hematopoietic reconstitution and no graft failure occurred in this group patients. But two patients could not get recovery in cyclophosphamid-based conditioning regimen group. And complete donor chimeras always present when chimeras were detected by STR-PCR or FISH at day 30,day 60, day 90 and d 180 post transplantation in fludarabine-based conditioning regimen group, while seven patients with cyclophosphamide-based conditioning regimen were mixed chimeras at day 30 post transplant.  The graft was rejected in six of the seven patients at day 90 post transplant in cyclophosphamide-based conditioning regimen group. The complete donor chimera in fludarabine-based conditioning regimen group was obvious higher than that in cyclophosphamide-based conditioning regimen group ( p=0.037). The incidence of aGVHD in the fludarabine group was 16.7% and 10.7% in the cyclophosphamide-based group. There is no significant difference of aGVHD between two group (P = 0.627). The incidence of cGVHD was 8.3% and 10.7% respectively. The bacterial infections developed in 16.7% and 28.6% of patients respectively (P=0.693), The overall survival were 83.33% and 82.14% in fludarabine-based conditioning regimen group and cyclophosphamide-based group respectively (p=0.870).

More intensity immuno-suppression in conditioning regimen may favor donor stem cell sustained engraftment in allogeneic stem cell transplantation for acquired severe aplastic anemia patients.

No relevant conflicts of interest to declare.