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Endothelial progenitor cells (EPCs) has been shown to be present in umbilical cord blood (UCB) in addition to hematopoietic stem cells. Cryopreservation is the accepted method for long-term storage of UCB. However, whether EPCs can be derived from cryopreserved UCB samples is unclear. The aim of this study was to investigate the differentiation potential of EPCs from cryopreserved CB samples. CD34+ cells were isolated from fresh or frozen and thawed UCB using magnetic beads. Cells were then cultured on fibronectin-coated plates containing endothelial differentiation medium. After 4-5 weeks in culture, endothelial-like cells were generated from fresh UCB samples, but not cryopreserved UCB samples. Examining this further, both fresh and frozen/thawed UCB MNCs were stained with Annexin V-PE and 7-actinomycin D (7-AAD) using flow cytometry. We found that there were a significant number of apoptotic cells in cryopreserved UCB samples compared to fresh UCB samples. In conclusion, cryopreservation induced UCB cell apoptosis and impaired EPC differentiation.

Summary. Post-transplant lymphoproliferative disorder (PTLD) is a well-recognized complication of organ transplant and has been associated with high mortality using conventional chemotherapy. We have investigated 11 cases of PTLD for alterations to the interferon alpha (IFNA) and p16 genes on chromosome 9p using archival material. 4/9 (44%) cases had deletions of the IFNA genes, in contrast to 1/59 (1 . 7%) cases of intermediate/high-grade de novo NHL drawn from the same geographical region. PTLD may therefore represent a distinct NHL subgroup exhibiting distinct gene pathology.

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