After processing, PBSC are then cryopreserved for later infusion. Controlled-rate freezing with temperature curve monitoring is typically used. Products are stored in the vapor phase of liquid nitrogen until they are required for infusion. Usually the storage period is weeks to months, but stem cell products have provided adequate engraftment when infused 8-10 years after cryopreservation (Attarian et al. 1996). After thawing, PBSC again are checked for viability. Granulocytes do not survive cryopreservation, so loss of this cell fraction from the collection is expected. In order to allow cells to survive freezing and thawing, they are placed in a medium containing 7.5-10% dimethyl sulfoxide. Stem and progenitor cells lose viability over time in this medium (Rowley and Anderson 1993), so it is important to infuse the cells immediately after thawing.

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