Clonogenic capacity and ex vivo expansion potential of umbilical cord blood progenitor cells are not affected by cryopreservation

Umbilical cord blood (UCB) has been used as a source of hematopoietic progenitors for clinical transplantation, and is proving to be an acceptable alternative to bone marrow. Since a number of UCB banks for unrelated transplant are currently being developed, we investigated whether cryoprescrvation can affect the clonogenic capacity and the ex vivo expansion potential of UCB progenitors. Mononuclear (MNC) cells (n=l 3) were tested for viability, cell and progenitor numbers before and after cryopreservation. According to our previous studies MNC fractions were obtained after sedimentation on pol igelt ne (Emagel, Behringwerke) followed by separation on Ficoll/Hypaque (d=l,077 g/ml). Progenitor cells recovery was evaluated by means of short- (CFU-GEMM, BFU-E, CFU-GM) and long-term cultures (CPU 5 weeks). Cell recovery after freezing was 73+11%, with a viability >97%, while progenitors recovery was 82% for CFU-GEMM, 94% for BFU-E, 82% for CFU-GM and 90% for more primitive progenitors after five weeks in long term culture. By means of single colonies replating experiments we have shown similar results for recloning efficiency (41±3 vs 39±4%, pa}.375) and colony numbers in secondary cultures (13+5 vs 12±3, p<0.375) before and after cryopreservation. Ex vivo expansion potential was tested in presence of different combinations of cytokines; SCF+IL-3+IL-6 showed 47.8- and 45-fold expansion in colony numbers, respectively before and after cryopreservation. !n conclusion we can state that: 1 ) UCB is a potential source of primitive progenitors; 2) cryopreservation doesn't affect neither the clonogenic capacity nor the ex vivo expansion potential of UCB progenitors. These results may have important implication in the large scale banking of UCB. in view of future applications in the transplantation of adult patients.