Cell dose is a critical determinant of outcomes in unrelated cord blood (CB) transplantation. We investigated a strategy in which CB units should contain at least 2 × 107 total nucleated cells/ kg of recipient weight, otherwise a second unit had to be added. We report the results of a study that was prematurely closed owing to toxicity. Patients with advanced hematologic malignancies without a human leukocyte antigen-matched sibling or unrelated donor were eligible. Conditioning regimen consisted of fludarabine and 12Gy of total body irradiation (n=11), or melphalan (n=4), with antithymocyte globulin. Graft-versus-host disease prophylaxis was tacrolimus and methotrexate. Fifteen patients with acute leukemia (n=9), chronic myelogenous leukemia (n=2), multiple myeloma (n=2) and lymphoma (n=2) were treated; 60% had relapsed disease at transplantation. Three patients received double CB transplants. The 100-day and 1-year treatment-related mortality rates were 40 and 53%, respectively. Median time to neutrophil and platelet engraftment was 22 days (n=10) and 37 days (n=10), respectively. One patient had secondary graft failure and five patients failed to engraft. Two patients are alive and disease free; 4-year actuarial survival is 33 versus 0% for patients transplanted in remission versus in relapse. We concluded that disease status was the main determinant of treatment failure in this study.
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