Allogeneic Stem Cell Transplantation in CML With Partial T Cell Depletion

Overview

Allogeneic stem cell transplantation, the only known curative modality for CML, was abandoned in recent years for a very effective and much less toxic targeted therapy with the tyrosine kinase inhibitors (TKIs). However, approximately one third of patients still need another treatment including stem cell transplantation. The study protocol comprised a cohort of consecutive patients with CML who received allogeneic stem cell transplantation using partial T cell depletion, with no post-transplant GvHD prophylaxis. Forty consecutive patients with CML underwent allogeneic stem cell transplantation from a matched sibling using partial T cell depletion (TCD), in a single institution. Escalated dose of donor lymphocyte infusion (DLI) was given in case of either relapse or presence of minimal residual disease (MRD) as detected by cytogenetic or molecular analysis. The purpose of the study is to decrease transplant-related toxicity.

Patients were conditioned with oral busulfan 12mg/kg (days -6 to -4), cyclophosphamide 120mg/kg (days -3,-2), rabbit antithymocytic globulin, (Fresenius, Bad Hamburg, Germany) 25mg/kg (days -5 to -1) and fludarabine 200 mg/kg (days -7 to-3). Final busulfan dose was individually determined based on measurements of serum busulfan levels with a target dose of 850-1400 microM x minute. Transplants were performed in reverse isolation rooms equipped with high-efficiency particulate air filtration systems (HEPA). No post-transplant GvHD prophylaxis was given. Post-transplant infection prophylaxis consisted of acyclovir, itraconazole, trimethoprim-sulfamethoxazole and penicillin VK. Cytomegalovirus (CMV) status was determined weekly using PCR for CMV-DNA and pp65 antigenemia in blood leukocytes, followed by preemptive ganciclovir administration when positive. Donors Donors were human leukocyte antigen (HLA) A,B,C serologically matched and DR and DQ molecularly matched siblings. Donor stem cells were collected following mobilization with 10 µg/kg/day G-CSF, given subcutaneously for 5 consecutive days. CD34 cells were positively selected using anti-CD34 antibody conjugated to iron-dextran microbeads using CliniMACS device (Miltenyi Biotech, Bergisch Gladbach, Germany) with an aim to collect \> 5.0 x 106 CD34 cells/kg. Disease monitoring Following transplant, all patients were under close surveillance for the presence of minimal residual disease (MRD) using cytogenetic analysis and PCR for the detection of BCR/ABL transcripts. Bone marrow and peripheral blood samples were examined every 3 months in the first year post transplant and every 3-6 months in the subsequent years. PCR method: RQ-PCR was performed according to the Europe Against Cancer (EAC) protocol.19 The BCR-ABL and ABL copy numbers were calculated by comparing with the standard curve generated using IPSOGEN FusionQuant Standards. The results of quantifying BCR-ABL transcripts were expressed as percentage ratios relative to total ABL transcripts. A minimum number of 1x104 copies of ABL is the lower limit below which a negative RT-PCR was considered unreliable. In the molecular biology laboratory of the Rambam Health Care Campus the sensitivity for quantitative Q-PCR is (10-5). Donor leukocyte infusion (DLI). DLI was administered in escalating dose regimen starting from 3 x 106 cells/kg followed as necessary by 1 x 107 cells/kg, 5 x 107 cells/kg and 1 x 108 cells/kg. DLI was used in case of persistence/reappearance of BCR-ABL transcripts starting from 6 months post transplant onward. In instances where more than 1 DLI was administered the successive escalated dose was given at ≥ 3-month intervals as dictated by MRD follow-up.