Definition of optimal conditions for collection and cryopreservation of umbilical cord hematopoietic cells.

Prior studies have shown that human umbilical cord blood cells can restore hematopoiesis and be used as a source of stem cells for hematopoietic transplantation. We have performed a study of the best conditions of collection and cryopreservation of blood from eight umbilical cords. We compared the influence of cell separation and of delay between collection and cryopreservation on the numbers of nucleated cells and of hematopoietic progenitors recovered before and after cryopreservation. Ficoll separation resulted in the loss of more than 50% of nucleated cells, but also of a significant number of progenitors before freezing. Unseparated cells could be kept at 25 degrees C as long as 24 h before freezing with minimal loss of progenitors before and after freezing and thawing. In contrast, there was a significant decrease in the number of viable cells and progenitors when cells were maintained at 4 degrees C before freezing. Our data show that cord blood banking is feasible with simple collection and cryopreservation procedures.