A novel high-yield volume-reduction method for the cryopreservation of UC blood units

For the application of umbilical cord blood (UCB) units as hematopoietic grafts, a dose of 3.7 x 10(7) nucleated cells (NC)/kg body weight is required. NC can be lost during volume-reduction processing and during thawing. A novel modification of the double-processing protocol with the aim of minimizing NC loss is described and evaluated.

One-hundred and fifty UCB were collected. The volume was reduced by a centrifugation step following double-processing in the presence of 2% HES 200/0.5. Pre- and post-processing cell counts and platelet parameters were measured with an automatic counter. The number of viable CD34+ hemopoietic stem cells was measured by flow cytometry. In 25 of the samples, colony-forming units (CFU) were also determined. The same samples were thawed 6 months after cryopreservation and re-evaluated.

The volume was reduced to 6 +/- 1.5 mL. The recovery of NC, MNC, CD34+ hemopoietic stem cells, RBC depletion and CFU following double-processing was 93.6 +/- 3.2%, 95.8 +/- 2.2%, 98.4 +/- 1.5%, 96.8 +/- 1.1% and 107.1 +/- 6.1% (for 25 samples), respectively. The post-thaw recoveries of NC, MNC, CD34+ hemopoietic stem cells and CFU (for 25 samples) were 78.6 +/- 5.4%, 90.8 +/- 4.4%, 96.4 +/- 2.5%, 89.1 +/- 4.1%, respectively. No post-thaw cell aggregation was observed. A significant (P<0.05) post-thaw loss of platelets and signs of platelet activation was observed.

The protocol uses non-expensive equipment and clinically approved materials and results in samples that can be used in patients with a mean weight of 32.7 kg.