Optimal Recovery of SSEA-4+/OCT-4+/CD133+/CXCR4+/Lin-/CD45- Very Small Embryonic-Like (VSEL) Stem Cells From Umbilical Cord Blood (CB) Using Plasma Depletion/Reduction (PDR) Compared to Red Cell Reduction (RCR)

We previously reported the presence of VSEL stem cells (SC) in CB which are capable of tri-lineage differentiation, and the techniques to identify and isolate these cells (Leukemia 2007;21:297-303). Because of their small size (< 6 μm) and different cell density, 42.5±12.6% of these VSEL SC in CB are lost upon red cell reduction (RCR) processing with AXP™ AutoXpress technology, and significant percentages of VSEL SC are also lost with Ficoll-Paque and red cell lysis techniques (Europ. J. Hematology 2009;84:34-46). Moreover, after thawing, 82.7±17.3% of the VSELs cyopreserved after RCR are recovered. Since these CB VSELs may be important for regenerative medicine applications and contribute to CB hematopoiesis and possess potential of long term repopulating hematopoietic stem cells (LT-HSCs), we sought to optimize recovery of these cells with different CB volume reduction techniques. Previously, it was reported that plasma depletion/reduction (PDR) of CB loses less than 0.01% of nucleated cells in the discarded plasma portion (Biol. Blood Marrow Transplant 2007;13:1346-57), so we performed 3 parallel comparisons using CB products that were divided into two equal portions processed using either hetastarch (HES) RCR or PDR. As can be seen in the table below, there is essentially no loss of VSEL SCs that we can detect after PDR processing, compared to 44.7±3.9% VSEL SC loss with RCR. Post-thaw, the two types of products appear to yield similar recoveries of VSELs compared to post-processing and pre-freeze samples (85.2% PDR versus 86.8% RCR). We conclude that (1) we confirmed our previous observations of significant CB VSEL SC loss with standard RCR techniques, this time using a manual HES RCR method, (2) PDR offers essentially 100% recovery of VSEL SCs in CB, and (3) even after thawing, PDR retains 85.2% of the collected VSELs compared to 50.9% for HES RCR. Whether these observations extend to the outstanding transplant-related mortality (TRM), overall (OS) and disease free survival (DFS) seen with PDR CB transplants, and whether VSELs are responsible for the effect seen with post-thaw wash versus direct infusion on chronic GvHD, TRM, OS and DFS are the subjects of current investigations.Table 1Optimal Recovery of CB VSEL by PDR versus HES RCR Processing% VSEL LossHES RCRPDRPost-Processing vs. Pre-Processing (Processing Loss)44.7±3.9%0%Post-Thaw vs. Post-Processing (Thaw Loss)13.2±7.1%14.8±5.3%Post-Thaw vs. Pre-Processing (Total Loss)49.1±9.1%14.8±5.3% Open table in a new tab