Development of a mock hemopoietic stem cell component suitable for the validation of cryopreservation procedures.

We developed a laboratory model of a unit of hemopoietic progenitor cells (mock-HPC unit) suitable for the validation of HPC cryopreservation procedures. The project was prompted by the practical and ethical difficulty of using real HPC units collected from healthy donors and patients for validation purposes. Mock-HPC units of different volumes ranging from about 120 to about 540mL were prepared by pooling a routinely discarded by product of our procedure to prepare platelet concentrates from buffy-coats, a standard procedure in most blood centers in Europe. Five ABO/Rh identical buffy coats each of 50mL volume, obtained from 450mL whole blood units by hard spin, were pooled with 300mL of a commercial platelet additive solution. After soft spin, the supernatant platelet concentrate pool was removed. The bottom fraction of this procedure, which contains RBC, WBC, HPC and platelets, constitutes a mock-HPC unit of about 120mL volume. Several bottom fractions may be pooled to obtain a mock-HPC unit of the desired volume. We used 20 mock-HPC units to validate an automatic procedure of HPC cryopreservation with a controlled rate freezer. In particular, we documented the standardization of critical points of the cooling profile, such as the correspondence of the crystallization phase with the theoretical freezing temperature of the product, the temperature peak rise above the theoretical freezing temperature of -5.7 degrees C and the automatic achievement in the chamber of a constant minimum temperature during supercooling (about -37 degrees C) with mean chamber loading volumes ranging from 231.8 to 1027.2mL.