Reduced Intensity Conditioning (RIC) with Cladribine, Busulfan and 4 Gy Total Body Irradiation (TBI) for Bone Marrow Transplantation (BMT) from an HLA-Matched Unrelated Donor (URD): A Prospective Multi-Institutional Clinical Trial.

[Background] We report the results of a prospective multi-institutional clinical trial of BMT from an HLA-matched URD following RIC.

[Patients and Methods] The conditioning regimen included cladribine 0.11 mg/kg on day -8 to day -3, busulfan 4 mg/kg po on day -6 and day -5, and 4 Gy TBI on day -1. GVHD prophylaxis included cyclosporine and short-term methotrexate. Patients with hematologic diseases were eligible for this study if they were either older than 50 years or had significant medical contraindications to undergo conventional transplantation. Primary endpoints were neutrophil engraftment and achievement of complete donor-type chimerism (CD3⁺ cells >90%) on day 90. Regimen-related toxicities (RRT) between day -8 and day 28 were assessed by the NCI-CTC v2.0. A total of 27 patients were registered, but one patient was removed before transplant because of severe fungal infection.

[Results] The median follow-up time was 722 days (range, 324–996) among survivors. The median age of patients was 56.5 years (36–64). Nine of the 26 patients (36%) had advanced-stage diseases and 3 (11%) had failed previous high-dose autologous or allogeneic transplantation. The diagnoses included AML (n=9), MDS/MPD (n=7), NHL (n=3), ALL (n=2), CML, ATLL, PCL, biphenotypic acute leukemia, and severe aplastic anemia (n=1). The median number of infused nucleated cells was 2.2 × 10⁸/kg. After transplant, while one patient experienced engraftment failure and subsequent sepsis, and died on day 34, the remaining 25 patients achieved neutrophil engraftment (median, 17th day). Another patient was censored from the study due to grade 4 liver dysfunction, which developed on day 19, which left 24 patients for the chimerism analysis. The percentage of donor chimerism in CD3⁺ cells on days 28, 56 and 90 was, respectively, 88% (21/24), 100% (24/24) and 100% (24/24). Grade 3 RRT included arrhythmia (n=1), hypoxia (n=3), hyperbilirubinemia or hypertransaminasemia (n=7), stomatitis (n=18) and diarrhea (n=4), and grade 4 RRT included hypoxia (n=1) and hyperbilirubinemia (n=1). Acute GVHD of grade II, III and IV occurred in 27%, 27% and 4%, respectively. Ten of 15 evaluable patients (67%) had extensive chronic GVHD. CMV reactivation occurred in 23 patients (89%); 4 had histologically confirmed CMV colitis, 1 had CMV pneumonitis and 1 had CMV hepatitis, while the remaining patients had asymptomatic viremia. Of the 16 patients with measurable disease at the time of BMT, 15 achieved complete remission. The 100-day and 1-year cumulative incidences of non-relapse mortality (NRM) estimated by the Kaplan-Meier method were 20% and 54%, respectively. The cause of death that contributed to NRM was infection, with grade 0–I acute GVHD in 29% and grade II–IV acute GVHD in 71%. The 100-day and 1-year cumulative incidences of relapse were 8% and 35%, respectively, and the 1-year overall and progression-free survival rates were 42% and 30%, respectively.

[Conclusions] The results support the feasibility of this procedure with a high response rate, but there is still a problem with the high NRM due to uncontrollable infections primarily associated with GVHD.