The Effect of Storage Time on Clinical Outcomes of Plasma Depleted (PD) Cord Blood (CB) Transplantation

CB banking and transplantation is a relatively new practice. The stability of CB units processed in different ways (e.g., PD, RBC reduction with hetastarch or buffy coat) and stored in liquid versus vapor phase liquid nitrogen (LN2) remains unclear. Previous in vitro and animal model studies have demonstrated that CB stored for 15 years showed no decline in hematopoietic stem cell function (PNAS 100:645, 2003); however, the authors noted that “final proof for the long-term engrafting capability of CB cryopreserved and stored frozen for long periods of time requires clinical results demonstrating long-term engraftment in humans…”. Storage of plasma depleted (PD) CB, in which RBC are not depleted, started at the beginning of 2001 (with storage at vapor phase of LN2), and clinical outcome data are available for products stored for over seven years. In this study, a retrospective analysis was performed on all patients transplanted with PD CB that have available survival data as of June 2008. Patients were separated into six groups based on the amount of time in storage of the CB product prior to transplantation, and their clinical outcomes were compared (Table 1, mean +/− SD). Only one out of 35 comparisons yielded a statistically significant difference (cumulative incidence of patients achieving platelet 50K engraftment is improved if CB were stored over 5 years compared to the reference group of storage for less than 1 year). It appears that storage time of longer than five years has no negative impact on these clinical outcomes of PD CB. We further investigated the effect of storage time and six other factors known to influence CB transplantation on overall survival and ANC engraftment in a multivariate setting (Table 2). Based on these two analyses, longer storage time did not correlate with poorer overall survival, disease-free survival, transplant related mortality, relapse or engraftment. Our results based on clinical outcome confirm the commonly accepted assumption derived from in vitro and animal models that CB can be stored for many years at LN2 temperatures without significantly decreased efficacy. Moreover, the lack of a storage time effect on clinical outcomes of PD CB stored in vapor phase LN2 appears to be consistent with what has been observed with CB processed using other methods or stored in liquid phase LN2.