Umbilical Cord Blood Processing Techniques and Their Comparative Advantages: A Review

Background: Umbilical Cord Blood (UCB) has steadily gained prominence in haematopoietic stem cell transplantation (HSCT). Despite UCB advantages, the main disadvantage of UCB in haematopoietic stem cell transplantation (HSCT) is its limited cell dose. Initially, UCB used to be processed and then made to undergo cryopreservation as whole cord blood banking leading to the problem of storing sufficiently large number of cryoprotected UCB units which requires vast amounts of costly storage space in liquid nitrogen. The sole purpose of processing is to concentrates the stem cells and reduce the volume for storage. Different UCB processing methods have been developed.

Aim: This review is aimed at bringing together the literature on the different processing methods and highlighting the underlying principles of each method, the relative efficiency and advantages of the methods.

Methodology: The work involved mainly the critical review of all available academic, professional and industry documents on cord blood processing. The relevant information was obtained from textbooks, academic journals, conference proceedings, the internet among others. The major UCB processing methods include Plasma Depletion, Density Gradient Centrifugation (DGC), Hetastarch, PrepaCyte-CB and Sepax. A study of the potential impact of Hetastarch and PrepaCyte processing methods on transplantation outcomes revealed no difference that was significant was observed between patients receiving cells after the processing regimens were compared.

Results: A comparison of the engraftment time of PrepaCyte-CB with five other processing methods revealed a quicker engraftment time for PrepaCyte-CB processed cord blood units compared to other processing methods. PrepaCyte-CB also recovers significantly more viable stem cells than AutoXpress (AXP) and hydroxyethyl starch (HES) processing methods. Other workers demonstrated that Sepax depletion produces higher recovery of cells that are nucleated. The effect initial volume of cord blood had on the recovery of nucleated cells for the different method of processing were also compared. Recovery when using Sepax is reduced as the unit size processed increases. Hetastarch, which is a density gradient, and plasma depletion separation is also affected in like manner, however, processing done using PrepaCyte-CB was not affected by the initial volume of the collected unit. The advantage of Sepax is that it is fully automated and this allows for mass processing of samples, suitable for bigger cord blood banks. For erythrocyte removal, density gradient separation is a better method that is effective. PrepaCyte-CB is the second most efficient method for removing RBC. The result of Total Nucleated Cells (TNC) and Mono Nucleated Cells (MNC) recovery rate of Hespan and Sepax against AXP processing methods shows that both Hespan and Sepax reproducibly recover greater than 95% of the cord blood stem cells in a typical collection and result in a reduced final volume for final storage.

Conclusion: The five most popular processing techniques are Plasma Depletion, Density Gradient, Hetastarch, PrepaCyte-CB and Automated Centrifugal Machine (Sepax). Most methods involve centrifugation, sedimentation and/or filtration for reducing the red cell content, plasma volume, or both. The different UCB processing methods each has its advantages and disadvantages.