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SummaryFetal blood collected immediately after delivery has been was the aim of this study to evaluate whether cryopreshown to contain hematopoietic progenitor cells at similar servation procedures might heavily impair the clonoor higher frequency than those in bone marrow (BM).1 genic capacity, the feasibility of CD34 ؉ selection and the Therefore, umbilical cord blood (UCB), which is normally ex vivo expansion potential of UCB progenitor cells.discarded, has been evaluated as a source of UCB samples were collected and cryopreserved as stem/progenitor cells 2-4 that can easily be collected at delivunseparated (n ‫؍‬ 21) or mononuclear (MNC) cells (n ery without any danger or inconvenience to the donor. 5,6‫؍‬ 15) within 12 h from delivery, and evaluated for Recently, UCB has been used as a source of hematopoietic viability, immunophenotype, cell and progenitor numstem cells for clinical transplantation, and is proving to be bers after a minimum stay in liquid nitrogen of 6 an acceptable alternative to BM. 7-9 Several studies have months (range 6-14 months). Viability was always demonstrated that UCB contains similar or higher pro-Ͼ97% and no statistically significant difference was portions of primitive hematopoietic progenitor cells as detected by flow cytometric analysis. Clonogenic recovcompared to adult BM 2,4 and therefore the lower number ery from unseparated cells was 80-87% for HPP-CFC, of nucleated cells, present in a single collection, might be CFU-GEMM, BFU-E and CFU-GM, and from MNC compensated by a significantly higher proportion of cells ranged from 82 to 91% for LTC-IC, CFU-GEMM, primitive cells. More recently, highly purified BFU-E and CFU-GM. CD34؉ selection (n ‫؍‬ 8) was per-CD34 capacity has made UCB-derived progenitor cells ideal cansignificant difference was detected in CFC fold-expandidates for experimental programs involving gene transfer sion for fresh or cryopreserved MNC cells and for and ex vivo stem cell expansion. Since several programs CD34 ؉ cells, either selected and cultured from fresh or throughout Europe and the USA are currently evaluating cryopreserved MNC cells. In conclusion we can state the feasibility of large-scale UCB banking for unrelated that UCB is a potential source of primitive progenitor transplants 5,12,13 cytokine-mediated ex vivo expansion of cells that can be cryopreserved unmanipulated or after UCB hematopoietic progenitor cells might increase the physical separation without major losses in clonogenic number of progenitor cells to be transplanted and facilitate capacity and immunophenotypic composition. Moreengraftment in adult patients. Therefore, it was the aim of our study to investigate whether cryopreservation can affect the clonogenic capacity, the immunophenotype, the feasi- potential of UCB progenitor cells.

Umbilical cord blood (UCB) is an attractive potential alternative to bone marrow (BM) as a source of hematopoietic progenitor cells since the number of progenitors in UCB is similar or even greater than that in normal BM. It was the aim of the present study to analyze the degree of immaturity of UCB progenitor cells. UCB mononuclear (MNC) and/or CD34 + cells were tested for surface antigen phenotype, expression of cytokines receptor, effect of stem cell factor (SCF) on colony growth, resistance to mafosfamide and replating potential. We have found that 34.9 ± 3.4% and 77.9 ± 2.6% of UCB CD34 + cells did not express CD38 and CD45RA antigens, respectively, suggesting that UCB contains a high proportion of immature progenitor cells. By means of three-color analysis, the receptor for SCF was detected on the majority of the CD34 + HLA-DR + subpopulation; in fact, 81.8% ± 4.3% of CD34 + HLA-DR + cells were defined as SCF low and 8.1 ± 1.5% as SCF high . Colony growth of MNC and CD34 + cells was enhanced by the addition of SCF to methylcellulose mixture, resulting in a statistically significant increase in CFU-GM and CFU-GEMM but not in BFU-E numbers. UCB progenitor cells showed a higher resistance to mafosfamide treatment, in comparison to BM; the addition of SCF to the culture medium resulted in a statistically significant increase in mafosfamide concentration required to inhibit 95% of colony growth (P р 0.05). Moreover, as shown by single colony transfer assays, the presence of SCF in primary cultures promoted a significantly higher replating potential for both untreated (42 ± 3.3% vs 21 ± 4.6%, P р 0.018) and mafosfamide-treated samples (62 ± 5.6% vs 44 ± 6.1%, P р 0.018). In conclusion, UCB is a source of progenitor cells with immature characteristics in terms of surface antigen expression, distribution of SCF receptor, resistance to mafosfamide and replating potential. Therefore, UCB progenitor cells represent an ideal candidate population for experimental programs involving gene transfer and ex vivo stem cell expansion.

A study was undertaken to investigate the suitability of using a high affinity (Kd = 1.1 nM) anti-CD45 monoclonal antibody for delivering the high energy beta-particle emitting isotope (90)Y to lymphohematopoietic target cells in vivo. The antibody, AHN-12, recognized the tyrosine phosphatase CD45 expressed on the surface of normal and malignant hematopoietic cells and studies showed that it reacted with both CD45-expressing normal peripheral blood cells and leukemia cells from patients. The antibody was readily labeled with (90)Y using the highly stable chelate 1B4M-DTPA and the radioimmunoconjugate was designated (90)Y-anti-CD45. The agent selectively bound to CD45(+) B cell line Daudi, but not CD45(-) control cells and significantly (p = 0.007) more bound to Daudi tumors growing in athymic nude mice than did a control non-reactive antibody. Moreover, biodistribution data correlated well to an anti-Daudi effect observed against established tumors in nude mice. The effect was dose dependent and irreversible with the best results in mice receiving a single dose of 137 microCi (90)Y-anti-CD45. These mice displayed a significantly (p < 0.0095) better anti-tumor effect than a control (90)Y-labeled antibody and survived over 135 days with no evidence of tumor. Histology studies showed no significant injury to kidney, liver, or small intestine even at 254 microCi, the highest dose tested. Because radiolabeled anti-CD45 antibody can be used to deliver radiation selectively to lymphohematopoietic tissue, these data indicate that this agent may be used to improve treatment of hematopoietic malignancies, particularly leukemia and lymphoma, when combined with hematopoietic stem cell transplantation in a future clinical trial.