Clofarabine, Melphalan, and Thiotepa, Followed by Allogeneic Unmodified Bone Marrow or Peripheral Blood Stem Cell Transplant, by Unmodified Double Cord Blood Transplant, or by CD34+ T-Cell Depleted Stem Cell Transplant for the Treatment of Hematologic Malignancies.

Abstract 3144

Based on encouraging results with the use of clofarabine (CLO) for reinduction treatment of acute leukemias, we have developed two allograft protocols for patients with hematologic malignancies with a cytoreductive regimen, using CLO in combination with melphalan (Mel) and thiotepa (Thio). Patients on protocol #1 received unmodified bone marrow (BMT), peripheral blood stem cells (PBSCT), or unmodified double unit cord blood (dCBT). Patients on protocol #2 received CD34+ T-cell depleted stem cells (TCD-SCT). Cytoreduction consisted of CLO 20 mg/m2/day × 5, Thio 10 mg/Kg/day × 1 and Mel 70 mg/m2/day × 2. Graft-versus-host disease (GvHD) prophylaxis consisted of tacrolimus (Tacro) and methotrexate (MTX) with unmodified BMT or PBSCT, tacro and mycophenolate mofetil (MMF) with unmodified dCBT, and none with TCD-SCT. Rabbit ATG at 2.5 mg/Kg × 2 or 3 doses was used for the prevention of rejection with the TCD-SCT.

To date, 64 pts were treated with this regimen including: unmodified BMT/PBSCT 27 patients, dCBT 15 patients, and TCD-SCT 22 patients. The median age for patients was 10.2 years (range 0.9–58.7) for unmodified SCT and 41.5 (range 0.6–67.2) for TCD-SCT. This was the second SCT for 13 of 27 pts in the BMT-PBSCT group, 2 of 15 pts in the CBT group, and 4 of 22 pts in the TCD group. Patient diagnoses included acute lymphoblastic leukemia (ALL) (N=36), acute myelogenous leukemia (AML) (N=23), and myelodysplastic syndrome (MDS) (N=5). Patients with ALL or AML in first remission (CR1) or CR2 and MDS in CR1 or refractory anemia (RA) were categorized as having good risk disease (GRD), while all other pts were considered to have poor risk disease (PRD), irrespective of all other factors. There were 15 of 27 pts with PRD in the BMT/PBSCT group, 10 of 15 pts in the CBT group, and 9 of 22 pts in the TCD-SCT group.

For the unmodified BMT/PBSCT group, donors were HLA-matched related (N=11), mismatched related (N=1), matched unrelated (N=12), or mismatched unrelated (N=3). All CBT recipients received double-unit grafts from 2 mismatched unrelated donors. For the TCD-SCT group, donors were HLA-matched related (N=8), mismatched related (N=1), matched unrelated (N=4), or mismatched unrelated (N=9).

Engraftment occurred in 59 of 61 evaluable pts; three pts died before engraftment. One pt recipient of unmodified BMT/PBSCT suffered a late graft failure, and one pt recipient of CBT suffered an early graft failure in the context of sepsis. Grade 2–4 acute GvHD occurred in 8/26 (31%) evaluable pts in the BMT/PBSCT group, 5/13 (38%) evaluable pts in the CBT group, and 4/20 (20%) evaluable pts in the TCD-SCT group.

With a median follow-up of 20.5 months for the unmodified SCT groups and 15.4 months for the TCD group, the overall survival (OS) and disease-free survival (DFS) rates were: 53.7% and 41.0% for the BMT/PBSCT group, 51.3% and 41.5% for the CBT group, and 64.1% and 60.7% for the TCD-SCT group.

This cytoreductive regimen represents a promising approach for the transplantation of patients with acute leukemias without the use of total body irradiation. This regimen is also sufficiently immunosuppressive to insure consistent engraftment of T-cell depleted transplants. Lastly, it appears to be relatively well tolerated for younger pts requiring a second SCT.