Summary:initially reported by Stiff et al 1 in 1983. Makino et al 2 modified this method and evaluated its clinical use for peripheral blood stem cell transplantation (PBSCT) in 1991. A simplified method for cryopreservation at −80؇C of peripheral blood stem cells (PBSC) has been increasThey reported that rates of CFU-GM remained at more than 70% during 18 months of cryopreservation and that rapid ingly used for autologous PBSC transplantation in Japan. Although this method, using 6% hydroxyethyl and sustained trilineage engraftment was obtained in 10 patients who received marrow-ablative chemotherapy and starch (HES) and 5% dimethyl sulfoxide (DMSO) as a cryoprotectant without rate-controlled freezing, has sevautotransplantation of PBSC cryopreserved by this method. While this simplified method has several advantages eral advantages over the conventional method using 10% DMSO with rate-controlled freezing, little is such as being a quick and inexpensive procedure and less clumping of the thawed cells compared with the convenknown about effects of long-term cryopreservation for years and thawing process on hematopoietic progenitional method using rate-controlled freezing with 10% DMSO and storage in liquid nitrogen, 2 little is known about tors. We examined the recovery rates of BFU-E and CFU-GM in sample tubes cryopreserved by the simplithe influence of long-term cryopreservation for years and of the thawing process on frozen-thawed hematopoietic fied method under various conditions as follows: (1) long-term storage for 1-5 years; (2) DMSO exposure stem cells. In order to assess the clinical efficacy of this simplified for 1 h after rapid thawing; and (3) thawing at a lower temperature other than 37؇C. In our study, we found method, we investigated effects of long-term cryopreservation (1-5 years), exposure of frozen-thawed cells to that the recovery rates of BFU-E and CFU-GM were not affected by the length of cryopreservation period; DMSO, and slow thawing at room temperature on hematopoietic activity of PBSC when they were cryopreserved by they remained at more than 70% on average for 16-61 months. In our hands, a 1-h exposure to DMSO after this method. rapid thawing was not toxic for hematopoietic progenitors. Furthermore, there was no significant difference in the recovery rates of BFU-E and CFU-GM between Materials and methods thawing at 37؇C and 20؇C. These observations indicate that PBSC cryopreserved for at least 5 years by the simPreparation of peripheral blood mononuclear cells plified method can be used clinically without losing hematopoietic activity, and suggest that hematopoietic Peripheral blood mononuclear cells (PBMNC) were collected by apheresis from patients with hematologic maligactivity of the thawed PBSC may be unaffected when PBSC are infused slowly within 60 min or even when nancies in remission during hematologic recovery from consolidation chemotherapy with or without G-CSF. Aph-PBSC are thawed gradually at room temperature.

Interactions of adhesion molecules among hematopoietic progenitor cells (HPC), bone marrow microvascular endothelial cells (BMMEC), and stromal cells are critical for hematopoiesis. However, most of the identified HPC receptors mediate interactions between HPC and stromal cells in the extravascular space. In order to study the interaction between HPC and BMMEC in the early period of homing, we preincubated mouse bone marrow mononuclear cells with blocking monoclonal antibodies against very late antigen-4 (VLA-4), VLA-5, leukocyte function-associated antigen-1 (LFA-1), and L-selectin before transplantation into irradiated splenectomized mice. Colony-forming units of granulocyte-macrophage (CFU-GM) seeding efficiency after preincubation with anti-VLA-5 resulted in a 54%, 67%, and 65% reduction, while that after preincubation with anti-LFA-1 resulted in a 37%, 25%, and 56% reduction, as compared with control, at 0.5, 2, and 24 h following transplantation, respectively. Similarly, the seeding efficiency was reduced by 12%, 13%, and 71% after preincubation with anti-VLA-4, and by -1%, 0%, and 18% after preincubation with anti-L-selectin. Thus, antibody blockade of VLA-5 and LFA-1 on HPC caused a significant decrease in CFU-GM seeding efficiency in the early period of homing. These observations suggest that VLA-5 and LFA-1 may play an important role in the recognition of BMMEC by HPC.

Summary:Despite the therapeutic efficacy of allogeneic bone marrow transplantation (allo-BMT), circulating hematopoietic progenitor cells after bone marrow transplantation have not been well characterized. In the present study, we focused on these 'post-transplant circulating progenitor cells (PTCPC)' which may be on their way to bone marrow. We analyzed the number of myeloid progenitor cells (CFU-GM) per 10 ml of peripheral blood (PB) on days 0 (just before transplantation), 1 (8-15 h after the completion of transplantation), 2, 3, 5, 7, 10, 14, 17, 21, 28 and 35 after allo-BMT in five transplant patients using a standard methylcellulose assay. In addition, high proliferative potential colony-forming cells (HPP-CFC) of the harvested donor bone marrow (BM) and day 1 PB of recipients were assayed in five patients. The origin of HPP-CFC from day 1 PB was analyzed by polymerase chain reaction of a DNA region containing a variable number of tandem repeats. The replating potential of these HPP-CFC was evaluated by a secondary colony assay. The proportion of CD38 negative cells among CD34 ؉ cells in the harvested BM and day 1 PB was evaluated by two-color flow cytometric analysis. The number of CFU-GM on day 1 ranged from 6 to 73/10 ml PB, and became undetectable on day 5. The reappearance of PTCPC was observed on day 14, along with hematopoietic recovery. The proportion of HPP-CFC among myeloid colonies from day 1 PB was significantly higher than that from harvested BM (44.3 ؎ 10.4% vs 11.3 ؎ 2.1%, respectively, n = 5, P = 0.0030). These HPP-CFC from day 1 PB were confirmed to be of donor origin. More than 90% of these HPP-CFC had replating potential. Two-color flow cytometric analysis revealed that the proportion of CD34 ؉ CD38 negative cells was significantly higher in day 1 PB than in the harvested BM (61.0 ؎ 16.5% vs 9.3 ؎ 3.5%, respectively, n = 7, P = 0.0002). These observations suggest that both primitive and committed transplanted myeloid progeniCorrespondence: Dr Y Katayama, Kobe West City Hospital, 2-4 Ichibancho, Nagata-ku, Kobe, Hyogo 653-0013, Japan Received 17 August 1998; accepted 19 October 1998 tor cells may circulate in the very early period following allo-BMT.

Ex vivo expansion systems of hematopoietic progenitor cells (HPC) have been extensively studied and their clinical application is under investigation. However, it is not known whether HPC expanded ex vivo will be able to retain their replating potential. CD34+ cells isolated from cord blood were cultured in Iscove's modified Dulbecco's medium supplemented with 10% fetal bovine serum, 1.0% bovine serum albumin, 50 ng/ml stem cell factor, 50 ng/ml interleukin-3 (IL-3), 50 ng/ml IL-6, 100 ng/ml granulocyte colony-stimulating factor, and 3 U/ml erythropoietin for 0, 5, 7, 10, 14, and 21 days. After the expansion cultures, granulocyte/macrophage progenitor cells (CFU-GM) were assayed from each culture by the standard methylcellulose method. After 14 days of culture, CFU-GM-derived colonies were randomly picked up and processed for the replating assay. The fold increase of CFU-GM peaked at day 7 of the expansion culture (29.8 +/- 7.7-fold, n = 5), followed by a decline until day 21. In the replating assay of CFU-GM from freshly isolated CD34+ cells, the mean replating efficiency was 91.2 +/- 4.7%. The replating efficiency decreased gradually with the time of the expansion culture. At day 7 when the fold increase of CFU-GM reached its peak, the replating efficiency had dropped to 47.5 +/- 2.3%, followed by a further decline to 5.3 +/- 3.4% at day 21. Furthermore, the addition of 100 ng/ml thrombopoietin to this expansion system failed to prevent the decline of replating efficiency. These observations suggest that the replating potential of CFU-GM may decrease in the ex vivo expansion system, even when their fold increase reaches its peak. This should be taken into consideration when HPC expanded ex vivo are used in clinical transplantation.

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