A prospective investigation of cell dose in single-unit umbilical cord blood transplantation for adults with high-risk hematologic malignancies

Umbilical cord blood (UCB) as an allogeneic transplant source is generally limited to units with pre-cryopreservation total nucleated cell (TNC) doses ⩾2.5 × 10 7 NC/kg. We prospectively investigated single UCB transplantation, with cord units as low as 1 × 10 7 NC/kg, all processed with post-thaw albumin–dextran dilution. We transplanted 104 adult patients with 84% having relapsed/refractory disease. The median TNC dose was 2.1 × 10 7 NC/kg (range: 1.0–4.4 × 10 7 ) and median CD34+ cell dose was 1.0 × 10 5 /kg (range: 0.0–3.7 × 10 5 /kg). Post-manipulation cell recovery and viability were 96% and 99%, respectively. Median times to neutrophil and platelet engraftment were 16 and 43 days, respectively. Univariate factors predicting neutrophil engraftment included TNC ( P =0.03) and CD34+ cell dose ( P =0.01). CD34+ dose predicted platelet engraftment ( P <0.001). In multivariate analysis, CD34+ dose remained significant for neutrophil and platelet engraftment ( P <0.0001 and P <0.0001, respectively). The 100-day and 1-year overall survival were 70% and 46%, respectively (95% confidence interval: 36%–56% at 1 year). The subset transplanted with 1–1.5 × 10 7 NC/kg had similar 100-day and 1-year survivals of 73% and 45%, respectively. Single-unit UCB transplantation using small units, processed as described, leads to favorable engraftment and acceptable outcomes in poor prognosis patients. CD34+ cell dose (⩾1.5 × 10 5 /kg) helps predict faster engraftment and can aid in graft selection.