Factors Associated with the Determination of Predominant Unit in Two Units Cord Blood Transplantation for Pediatric Acute Leukemia.

Cord blood transplantation (CBT) is a promising alternative means of allogeneic stem cell transplantation. However, limited cell doses may compromise outcome. To enhance engraftment, CBT has been conducted using two units with promising results. Our preliminary results showed the dominance of one unit which occurred early after CBT (Bone Marrow Transplant. 38:197). However, little is known about the mechanism of engraftment and factors influencing the dominancy. To improve the outcomes, CBT was performed with 2 partially HLA-matched units in pediatric acute leukemia with the analysis of factors that affect the determination of dominancy. The median age and body weight of patients (M:11, F:4) were 13 years (3–17) and 45.0 kg (10.5–62.9), respectively. Patients received various conditioning regimens according to the disease status. The median number of the infused nucleated cells by the sum of 2 units after thawing was 5.28×10⁷/kg (0.72–15.09×10⁷/kg). Engraftment achieved in 14/15 Patients. The median number of days required for ANC of more than 0.5×10⁹ or 1.0×10⁹/l were 18 days (13–31 days) and 21 days (14–34 days), respectively. Spontaneous platelet recovery to more than 20×10⁹/l required a median 50 days (19–93 days). The early engraftment kinetics reveals that dominancy of one of two units determined from the day of engraftment (ANC > 0.5×10⁹/l). The numbers of total nucleated cells, CD34⁺ cells, CD3⁺ cells, CFU-GM, order of infusion, and donor-recipient HLA disparities of the UCB units were viewed as factors that potentially influence dominancy. Among them infused CFU-GM per patient body weight was associated with the dominancy (P = 0.017). Interestingly, CFU-GM could not be found from each cord blood units in patient failed engraftment. Multiple factors associated with outcomes of CBT could influence the determination of dominancy, such as those factors that affect the recipient environment (underlying disease, previous treatment, conditioning regimen, use of ATG and the method of GVHD prophylaxis), the characteristics of each UCB unit and HLA disparity. For this reason, the selection of the two units requires consideration of the above factors. However optimal selection guidelines that take into account influencing factors are unavailable. CFU-GM was associated with the dominancy in our preliminary result but this kind of data is hard to get before CBT practically. Introducing the analysis of new parameters such as CFU-GM before freezing could help the selection of optimal cord blood unit and improve the outcomes with the consideration of cost-benefit.