OPTIMAL CRYOPRESERVATION OF HUMAN UMBILICAL-CORD BLOOD

Cryopreservation techniques for umbilical cord blood (UCB) have been b ased on methods established for marrow (BM) and peripheral blood proge nitor cells (PBPC) with varying degrees of success. The aim of this st udy was to optimise cryopreservation of UCB haemopoietic cells based o n sound cryopreservation principles, UCB samples were cryopreserved wi th different combinations of DMSO and hydroxyethyl starch (HES) by a v ariety of freezing protocols. After cooling at 1 degrees C/min in solu tions containing 4% HES and various concentrations of DMSO there was a dramatic fall in CD34(+) recovery from 85.4% (s.d. 28.4) to 12.2% (s. d. 10.0) as DMSO concentration was reduced from 5 to 2.5%. Varying HES concentration in solutions containing 5% DMSO did not have a signific ant effect on CD34(+) cell recovery. Increasing cooling rate from 1 to 10 degrees C/min significantly reduced CD34(+) recovery (P < 0.0001) while increasing DMSO concentration up to 10% had little effect (P = 0 .8, two-way ANOVA), Good recovery of UCB CD34(+) cells can be achieved with 5-10% DMSO at a controlled cooling rate of 1 degrees C/min. Ther e was a significant difference (P < 0.0001) in the apparent recovery o f CD34(+) cells between paired aliquots thawed in the presence (recove ry = 76.8%, s.d. 26.0) and absence (32.5%, s.d. 18.7) of DNase, In con clusion, conditions for cryopreserving UCB for clinical banking that y ield optimal recovery of CD34(+) cells have been established.