Mixed effects of long-term frozen storage on cord tissue stem cells

Cord tissue (CT) storage is promoted as an opportunity to preserve a source of mesenchymal stromal cells (MSCs) for future use. We analyzed maximal MSC yields from fresh and frozen CT including functional capacity after long-term cryopreservation as a means of assessing potential utility.

CT was evaluated immediately upon harvest or frozen and banked for 5 years before analysis. Upon thawing, cell viability and yield were determined, as were growth characteristics and the ability to differentiate into various tissues. After thawing, enzymatic digestion of CT to release MSCs resulted in poor cell recoveries and few viable cells, requiring explant cultures to recover sufficient cell numbers for analysis. Upon expansion of surviving cells, fluorescence-activated cell sorter analysis showed the cells to be MSCs based on phenotype (CD34-, 45-, 44+, 90+, 105+) and function (ability to form adipocytes and osteoblasts). Frozen CT, however, exhibited decreased plating efficiency, increased doubling times but near equivalent maximum cell expansion, compared with fresh CT.

Poor cell yields and recoveries, along with slower growth characteristics, make frozen CT a less-than-optimal choice for MSC banking, despite good functional recovery. In addition, because the amount of fresh CT available at birth is limited and total MSC yields are low, even fresh CT-MSC requires extensive in vitro expansion before clinical use, which limits it application.