Prospective study of one- vs two-unit umbilical cord blood transplantation following reduced intensity conditioning in adults with hematological malignancies

As the threshold nucleated cell dose for one-unit umbilical cord blood (UCB) in adults has not to date been firmly established, we prospectively compared one-vs two-unit UCB transplantation after reduced intensity conditioning (RIC) in adult patients with hematological malignancies. Study design specified one-UCB unit if the cryopreserved total nucleated cell (TNC) dose was >= 2.5 x 10(7)/kg recipient weight, otherwise two units matched at minima of 4/6 HLA loci to the patient and 3/6 to each other were infused. A total of 27 patients received one unit; 23 patients received two units. Median time to ANC >500/mu L was 24 days (95% confidence interval 22-28 days), 25 days for one unit and 23 days for two units (P = 0.99). At day 100, ANC >500/mu L was 88.4 and 91.3% in the one-and two-unit groups (P = 0.99), respectively. Three-year EFS was 28.6% and 39.1% in the one-and two-unit groups (P = 0.71), respectively. Infusion of two units was associated with a significantly lower relapse risk, 30.4% vs 59.3% (P = 0.045). Infused cell doses (TNC, CD3(+), CD34(+) and CD56(+)CD3(neg)) did not impact on engraftment, OS or EFS. Taken together, one-unit UCB transplantation with a threshold cell dose >= 2.5 x 10(7)/kg recipient weight after RIC is a viable option for adults, although infusion of two units confers a lower relapse incidence. Bone Marrow Transplantation (2012) 47, 924-933; doi: 10.1038/bmt.2011.195; published online 17 October 2011