Cell dose is a major limitation for umbilical cord blood (UCB) transplantation because units containing a minimum of 2.5 x 10(7) total nucleated cells (TNC)/kilogram patient body weight are frequently not available. The transplantation of 2 partially HLA-matched UCB units has been adopted as a simple approach for increasing the TNC.We sought to determine whether the relative safety and efficacy of this approach was comparable with a single UCB transplantation. Included are adults with acute leukemia who received transplants with 1 (n =106) or 2 (n =303) UCB units. All UCB units for single UCB transplantations contained TNC ≥ 2.5 x 10(7)/kg. For double UCB transplantations, the total TNC for units 1 and 2 were > 2.5 x 10(7)/kg but in approximately half of these transplantations, 1 of the 2 units contained < 2.5 x 10(7) TNC/kg. Adjusting for factors associated with outcomes, risks of neutrophil recovery (odds ratio 0.83, P =.59), transplantation-related mortality (hazard ratio [HR] 0.91, P= .63), relapse (HR 0.90, P= .64), and overall mortality (HR 0.93, P= .62) was similar after double UCB and adequate dose single UCB transplantations. These data support double UCB unit transplantation for acute leukemia when an adequately dosed single UCB unit is not available thereby extending access to nearly all patients.
Key points: Efficacy of transplanting adequately dosed 1- or 2-cord blood units.