Assessment of cord blood hematopoietic cell parameters before and after cryopreservation

The testing of cord blood (CB) progenitor and stem cell units for transplantation suitability involves enumeration of total nucleated cells before freezing. CD34+ cell counts may also be a means of determining suitability. Studies have been conducted to evaluate how specific storage conditions influence cell counts.

CB units were processed by hydroxyethyl starch volume reduction. Cryopreserved-thawed samples were diluted 1:3 without washing. CD34+ cells were measured with three commercially available assay methods. In specific studies, apoptosis-indicating reagents were included. CB units were analyzed for nucleated cells, aldehyde dehydrogenase-containing cells, and progenitor colonies.

CD34+ cell levels and nucleated cells were retained during storage in test tubes at 1 to 6 degrees C for 3 days. Cryopreserved-thawed samples showed a reduction in CD34+ cells relative to prefreeze levels with the largest decrease with the Stem-Kit (Beckman Coulter) restricted gating procedure. Prefreeze samples contained minimal numbers of presumed apoptotic cells detected with 7-aminoactinomycin D or SYTO16, but after cryopreservation-thawing there was an increase. Nucleated cell levels determined with a hematology analyzer or flow cytometry were reduced after thawing. Cryopreservation-thawing reduced the percentage of CD34+ cells positive for the presence of aldehyde dehydrogenase and the number of progenitor colonies. These differences were significant.

These studies indicate that CD34+ cell counts were maintained when CB samples were stored at 1 to 6 degrees C in test tubes for 3 days. Cryopreservation-thawing resulted in changes in a number of parameters including the percentage of CD34+ cells that were aldehyde dehydrogenase(+) and the number of 7-aminoactinomycin D(+) cells and SYTO16(low) cells.