Factors Affecting Unit Predominance In Double Umbilical Cord Blood Transplantation

Umbilical cord blood transplantation is seen as an alternative source of hematopoietic support for patients who lack suitable HLA-matched donors. Disadvantages of this method include the relatively low cellularity, late engraftment and consequently restrictive use to pediatric patients, due to the low number of hematopoietic progenitors. Transplantation of two cord blood units has been seen as a strategy to overcome the low yield, often leading to the long-term establishment of hematopoiesis supported by a single cord blood unit. Predictive factors of the predominant unit are still unclear. Total nucleated cell count, CD34⁺, CD3⁺ dose were independent factors associated with unit predominance, although this is still a controversial issue.

This retrospective study included 21 patients with hematologic malignancies and immunodeficiencies who underwent double unit cord blood transplantation. We analysed HLA mismatch, ABO group, total nucleated cell count (TNC), CD34+ dose and post-thaw viability and their correlation with the prevalent unit. Transplantations were performed from 2007 to 2013. Six patients were excluded due to incomplete information and another three died before engraftment.

Median NC and CD34⁺ doses were similar between engrafted and non-engrafted units. Nine transplantations (60%) resulted in engraftment of the higher TNC unit. TNC dose in the predominant units varied between 2.02-3.05x10⁷/kg (median dose: 2.651x10⁷/kg), and in the non-engrafted units between 1.69x10⁷/kg-4.39x10⁷/kg (median dose: 2.44x10⁷/kg), which was not statistically significant (p= 0.65). Sixty percent of the transplantations (9 patients) also resulted in engraftment of the unit with higher CD 34⁺ (median dose: 2.05x10⁶/kg), compared to 40% (6 patients) in which the lower dose unit prevailed (median dose: 1.95 x10⁶), also not statistically significant (p= 0.861). As for ABO, 26% of the units were ABO matched with the recipient, while the majority was HLA mismatched (93%).

Multiple factors related to the unit and patient influence UCB predominance. In the sample studied, no particular variant played a specific role, probably due to the limited sample size. Current evidence suggests that immunologic-related mechanisms (CD34⁺ and CD3⁺ dose) are involved, yet further studies are necessary for a better understanding of which factors lead to unit engraftment.

No relevant conflicts of interest to declare.