Two Chemotherapy-Based Conditioning Regimens Compared To TBI-Based Conditioning Secure Consistent Engraftment Of T-Cell Depleted Allogeneic HSCT, Similarly Low Incidences Of Gvhd and Favorable Rates Of Disease-Free Survival (DFS)

To ascertain the therapeutic potential of non-TBI-based conditioning for CD34+ HPC-selected , T cell-depleted allografts, we conducted a trial comparing our standard regimen, arm (A) 1375cGy HFTBI+ thiotepa,5 mg/kg/day x 2 days + cyclophosphamide 60 mg/kg/day x 2 days vs. arm (B) Busulfex 0.8 mg/kg/6h x12 (dose adjusted) + melphalan 70 mg/kg/day x 2 + fludarabine 25 mg/m²/day x5 and arm (C) Clofarabine 20 mg/m²/day x 5 + melphalan 70 mg/m²/day x 2 + thiotepa 5 mg/kg/day x2, as preparation for T-cell depleted CD34⁺ PBSC transplants from GCSF-mobilized leukocytes fractionated with the CliniMACS device. Primary endpoints were engraftment, GVHD, transplant-related mortality (TRM) and 2 yr OS and DFS (Confer Table). Stratification of pts to arms A (standard), B or C was based on the patient’s disease, disease stage and clinical factors such as age, prior therapy or comorbidities enhancing risks of TBI. Arm B was the non-TBI arm predominantly used for myeloid and Arm C for lymphoid malignancies. Prior to transplant, recipients of HLA-matched or non-identical transplants received rabbit thymoglobulin at 2.5 mg/kg/day x2 or 3 days respectively, to prevent graft failure. No GVHD drug prophylaxis was given post transplant. A total of 181 consecutive patients, accrued between 5/13/2010 and 6/12/2013, were analyzed (81 in arm A, 78 in arm B, 22 in arm C). These pts have been followed for a median of 12.1 months. Donors were related or unrelated and HLA-matched for 74% of the patients and 1-2 HLA allele disparate for 26%. Median age for the entire group was 50.5 years, with older pts predominating in the non-TBI groups (medians arm A ,31.9 yrs; arm B , 61.9 yrs; arm C, 44.6 yrs). The CD34+ PBSC transplants provided a mean dose of 9.7x10⁶ CD34⁺ progenitors/Kg (range 1.4-89.7) and 4.5x10³ CD3⁺ T-cells/Kg (range 0.6-25.3). All pts engrafted; but 2 pts (2.5%) in arm B experienced late graft failure, one of whom was reconstituted after a secondary graft. Overall the incidence of grade II-IV acute GVHD was 18%, and 14% for recipients of HLA-matched grafts. TRM at 1 year was 10% in Arm A, and 15% in Arms B and C. Two year OS and DFS for each arm are: arm A, 66.7% and 58.4%; arm B 62.3% and 59.5%; arm C 52% and 53%. For the 101 pts who received standard risk transplants (i.e., pts with high risk forms of AML, ALL or NHL in 1^o CR, AML in 2^o CR, MDS RA/RCMD, CML in 1^o CP or MM in CR1, VGPR or first PR ), 2 year OS and DFS are: arm A 68% and 62%; arm B 67% and 66%; arm C 86% and 86%, with relapse rates at 2 yrs of: arm A 23%, arm B 15%, and arm C 14%. These results thus identify two non-TBI-based conditioning regimens that secure consistent engraftment of rigorously T-cell depleted allogeneic HSCT and can yield favorable long-term DFS and OS with low incidences of GVHD and relapse.