We have compared the efficiencyof the different strategies allowingfor a longterm storage of a human CD34+ bone marrow cells. Accordingly,the aliquots of CD34+ cells isolated from bone marrow were frozen using: controlled rate freezing equipment, or freezer unprogrammed in a -8O°C mechanical freezer. After freezing, CD34+ cells were subsequently stored for one month in a liquidnitrogen tank at -196°Cor in mechanicalfreezer at -80°C. We have found that both the viability and the recovery of clonogeneic progenitors of CD34+ cells samples stored at different temperature were similar. Therefore, regarding the costs and simplicity, we recommend the unprogrammed freezing and storage of human CD34+ cells at -8O°C in a mechanical freezer as a convenient, inexpensive, and reliable method for storing marrow for transplantation. This data also indirectly indicate that the aliquots of the CD34+ cells can be shipped frozen on dry ice (- 8O°C), and that these cells will maintain viability under this conditions. Furthermore, in this study we have confirmed validity of our earlier observation that human CFU-Meg progenitors are more sensitive to cryopreservation.

Keywords: CD34+ cells, Cryopreservation, unprogrammed rate freezing