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Human adult pluripotent stem cells, stem cells of embryonic origin and induced pluripotent stem cells (iPS) provide cellular sources for new promising regenerative medicine approaches. Because these cells can be patient-specific, they allow considering a personalized medicine appropriate to the diagnosis of each. The generation of cultured red blood cells (cRBC) derived from stem cells is emblematic of personalized medicine. Indeed, these cells have the advantage of being selected according to a blood phenotype of interest and they may provide treatments to patients in situation of impossible transfusion (alloimmunized patients, rare phenotypes). Essential progresses have established proof of concept for this approach, still a concept some years ago. From adult stem cells, all steps of upstream research were successfully achieved, including the demonstration of the feasibility of injection into human. This leads us to believe that Red Blood Cells generated in vitro from stem cells will be the future players of blood transfusion. However, although theoretically ideal, these stem cells raise many biological challenges to overcome, although some tracks are identified.

Resume Les globules rouges peuvent maintenant etre cultives in vitro a partir de plusieurs sources de cellules souches humaines: hematopoietiques, embryonnaires (ES) ou cellules matures humaines reprogrammees en cellules pluripotentes (human induced pluripotent stem cells, hiPSC). La technologie tres prometteuse des hiPSC represente une source potentiellement illimitee de GR et ouvre la voie au possible developpement d’une nouvelle generation de produits transfusionnels allogeniques. En admettant que la culture a grande echelle in vitro des GR s’opere efficacement dans un proche avenir, nous decrivons ici un scenario futuriste, mais realiste, concernant les applications potentielles pour les patients alloimmunises et ceux ayant un groupe sanguin rare. Nous avons etabli que 3 clones d’hiPSC seulement seraient suffisants pour fournir des cellules compatibles a plus que 99% des patients necessitant des transfusions de GR. L’etude du Registre national francais des personnes ayant un phenotype/genotype sanguin rare revele que 15 clones d’hiPSC couvriraient 100% des besoins des patients d’origine caucasienne. De plus, un seul clone d’hiPSC satisferait 73% des besoins des patients drepanocytaires alloimmunises qui necessitaient jusqu’ici des unites de GR rares cryopreserves. Ainsi, un nombre tres limite de clones de GR non seulement serait en mesure de couvrir les besoins de la plupart des patients alloimmunises et de ceux ayant un groupe sanguin rare, mais permettrait aussi une politique efficace de prevention de l’alloimmunisation chez les patients polytransfuses.

Resume Dans un contexte de difficulte chronique d’approvisionnement en produits sanguins, l’interet de disposer de sources complementaires de globules rouges (GR) pour la transfusion sanguine est evident. La mise au point de molecules chimiques ou naturelles qui remplaceraient l’hemoglobine se revele difficile. Le sang artificiel est encore hors d’atteinte. Ainsi au lieu de remplacer ce que fait la nature pourquoi ne pas la copier ? Pour ces raisons, tenter de generer au laboratoire des GR fait sens. Nous decrivons ici les recherches en cours qui permettront la generation massive de GR humains a partir de cellules souches hematopoietiques. Nous faisons le point sur l’etat de l’art de ce concept, evoquons les obstacles a surmonter pour passer du modele de laboratoire a la clinique et analysons les indications possibles a moyen et long terme. Si elle aboutit, cette nouvelle approche pourrait etre un progres considerable en matiere de transfusion sanguine.

Purpose To determine whether minimal residual disease (MRD) measured by Wilms' tumor gene 1 (WT1) expression is a prognostic marker in pediatric acute myeloid leukemia (AML), we quantified WT1 transcript by real-time quantitative-polymerase chain reaction in 92 AML at diagnosis and during follow-up. Patients and Methods Patients (median age, 6 years; cytogenetics, favorable 27%, intermediate 59%, poor 13%) were treated between 1995 and 2002 and enrolled in Leucémie aiguë Myéloblastique Enfant (LAME) 89/91, LAME 99 pilot study and Acute Promyelocytic Leukemia French collaborative protocols. With a median follow-up of 26 months, event-free survival was 56% with a standard deviation (SD) of 5% and overall survival of 62.5% with an SD of 6%. WT1 copy number was normalized by TATA box binding protein gene transcripts and expressed as WT1/TBP × 1,000 ratio. Median WT1 ratio in normal patient controls was 12 (range, 0 to 57). A level over two SD than normal bone marrow controls (ie, WT1 ratio > 50), was considered as significant overexpression. Results At diagnosis, WT1 overexpression was detected in 78% of patients (72 of 92 patients; median copy ratio, 2231). The WT1 values were significantly higher (P = .01) in favorable cytogenetics and lower (P < .0001) in M5-FAB subtype, 11q23 rearrangements (P < .001), and infants (P = .003) and demonstrate a strong correlation with fusion transcript AML1-ETO, PML-RARα expression. After induction treatment, WT1 ratio was analyzed in 46 of 72 patients and found above 50 in nine of 36 patients and five of 25 patients at D35-50 and 3 to 5 months, respectively. WT1 ratio > 50 after induction is an independent prognostic risk factor of relapse (P = .002) and death (P = .02). Conclusion WT1 quantification is an informative molecular marker for MRD in pediatric AML and is now performed as prospective analysis in ELAM02 protocol.

We describe here the large-scale ex vivo production of mature human red blood cells (RBCs) from hematopoietic stem cells of diverse origins. By mimicking the marrow microenvironment through the application of cytokines and coculture on stromal cells, we coupled substantial amplification of CD34(+) stem cells (up to 1.95 x 10(6)-fold) with 100% terminal differentiation into fully mature, functional RBCs. These cells survived in nonobese diabetic/severe combined immunodeficient mice, as do native RBCs. Our system for producing 'cultured RBCs' lends itself to a fundamental analysis of erythropoiesis and provides a simple in vitro model for studying important human viral or parasitic infections that target erythroid cells. Further development of large-scale production of cultured RBCs will have implications for gene therapy, blood transfusion and tropical medicine.

A hundred and eight patients less than 60 years old with de novo acute myeloid leukemia were treated between 1982 and 1994 by protocols including final intensification with a transplant using autologous bone marrow purged by mafosfamide in first remission in the absence of an HLA-matched sibling donor available for allograft. From 1989, we attempted to improve tumor control by using high-dose anthracyclines in induction, by increasing from one to two the number of consolidation courses pre-transplant and by introducing intermediate doses of cytarabine in the first consolidation course. The CR rate was 77% (33/43) before 1989 and 90% (59/65) after 1989 (P = 0.06). Forty-five out of the 59 patients (76%) who achieved CR after 1989 could undergo bone marrow grafting in CR1 vs 16/33 (48%) before 1989 (P = 0.01). In spite of the higher proportion of patients above 50 years after 1989 (32%) toxicity was mild and an adequate graft was obtained more frequently after one collection. The principal factor relating to improvement in graft feasibility was the post-1989 modification of induction and consolidation regimens. This improvement in graft feasibility was associated with a better disease-free survival (DFS) (48 +/- 7% vs 32 +/- 8%, P = 0.04) and overall survival (OS) (53 +/- 6% vs 30 +/- 7%, P = 0.007) at 5 years. By multivariate analysis four factors were associated with overall survival (OS): karyotype, white blood cell count at diagnosis, treatment regimen and bone marrow grafting in CR1. This global approach should be prospectively compared with intensive chemotherapy.

The aim of the present study was to evaluate the capacity to expand of hematopoietic stem cell (HSC) samples from eight patients with NHL, and to follow in parallel the fate of tumor cells in four of eight samples still containing bcl2/JH+ tumor cells after CD34+ or CD19-/20-/34+ cell selection. The presence of bcl2/JH+ cells was also investigated after expansion in four of eight samples, two of which were bcl2/JH at harvesting and two which were initially bcl2/JH+ but became bcl2/JH (below the level of PCR detection) after cell selection, to assess a possible reappearance of occult tumor cells after expansion culture. We used culture conditions that we previously had established to allow high level expansion of normal precursors, progenitors and LTC-ICs. In this study, particular attention was given to the role of Flt3-ligand, known to favor the growth of B cells. The expansion conditions were: 1.5 x 10(3) cells/ml in serum-free medium containing stem cell factor (SCF), interleukin-3 (IL-3), IL-6, granulocyte-stimulating factor (G-CSF), erythropoietin (Epo) +/- Flt3-ligand (Flt3-L) for 10 days. After culture, total cells, CFU-GMs, BFU-Es and LTC-ICs were expanded to a mean of 833-, 6.6-, 4.6-, and 1.8-fold, respectively with the cocktail of cytokines not including Flt3-L. When Flt3-L was added, the mean expansion values were 1095-, 31-, 15- and three-fold, respectively. Residual bcl2/JH+ cells present in four of eight samples before expansion were not detected after expansion. Similarly, no tumor cells reappeared after expansion of the two samples which had become negative after selection, as well as in the two samples which were bcl2/JH- at harvesting. These results suggest first that ex vivo expansion of hematopoietic stem cells in patients with non-Hodgkin's lymphoma is feasible without incurring the parallel risk of amplifying tumor cells; second, that Flt3-L did not stimulate the growth of tumor cells while it clearly favored the growth of normal progenitors.

The aim of this study was to evaluate the ex vivo expansion of normal CD34 + cells in gas-permeable polypropylene bags suitable for clinical use. Cells were cultured for 14 days in serum-free medium supplemented with SCF, IL3, IL6, FLT3-1, G-CSF ± MGDF or Epo. The bags supported the expansion of hematopoietic cells in a similar manner to small scale well or flask systems, allowing mean expansions of up to 2193-fold for total nucleated cells, 140-fold for CFU-GM and 66-fold for LTC-IC. Increasing the initial cell concentration from 5 x 10 3 to 1 x 10 5 CD34 + cells/ml induced the production of granulocytic cells with terminal differentiation while simultaneously decreasing the overall extent of expansion of the white blood cells produced. We tested the phagocytic activity and oxidative metabolism of the white blood cells produced. The percentage of phagocytic cells was 39 ± 0.5% in expanded cultures derived from fractions initiated at 5 x 10 3 , 104 or 10 5 cells/ml and 45 ± 6% in cultured cells obtained from starting fractions containing 5 x 10 4 cells/ml, as compared to 58 ± 4% in normal controls. A study of the potential for oxygen-dependent microbe killing showed that the expanded cells produced H 2 O 2 , although in lesser quantities than control cells. We subsequently investigated the possibility of freezing expanded cells. Total cell recovery after thawing was 45 ± 4%, while recoveries of progenitors and stem cells ranged from 65 to 90%, without any influence of the initial cell concentration. This new approach could be of major interest for clinical practice, as it would allow evaluation of the quality of a graft prior to its infusion and employs experimental conditions which meet the criteria for potential clinical use.

Autologous bone marrow transplantation (ABMT) after high-dose chemotherapy is recognized as a curative approach to treating hematologic malignancies and some invasive solid tumors. However, tumor cells present in the bone marrow at the time of harvesting are a potential cause for relapse. Ex vivo marrow purging with very high doses of cytotoxic agents has been introduced in an attempt to remove neoplastic cells contaminating the autograft. The procedure, however, has been limited by its high toxicity to normal bone marrow progenitor cells. In their purging procedures, investigators have used agents such as amifostine, originally developed to protect against the effects of radiation and chemotherapy. In this article, the appropriateness of protecting normal cells with amifostine during various purging procedures will be reviewed.

PURPOSE To analyze retrospectively survival and prognostic factors of patients with non-Hodgkin's lymphoma (NHL) autografted from 1979 to 1995 in a single institution. PATIENTS AND METHODS A total of 120 patients, 64 with aggressive and 56 with low-grade NHL, were autografted. The carmustine (BCNU), etoposide, cytarabine, and melphalan (BEAM) regimen was used in 104. The autograft was marrow in 101 patients. Marrow was purged in vitro by mafosfamide for 63 patients (adjusted dose [AD] in 32; unique dose [UD] in 31); 27 patients received a CD34+-selected graft. Following intensification, 45 patients received additional radiotherapy on previous sites of involvement. RESULTS Outcome at 5 years for patients transplanted with low-grade NHL in first complete remission (CR1), in first partial remission (PR1), and in second complete remission (CR2) or beyond showed an event-free survival (EFS) of 75% +/- 12%, 46% +/- 18%, and 57% +/- 24%, a relapse incidence (RI) of 21% +/- 12%, 49% +/- 19%, and 43% +/- 25%, and a transplant-related mortality (TRM) of 5% +/- 5%, 10% +/- 7%, and 0%, respectively. For patients with aggressive NHL transplanted in CR1, in PR1, in CR2 or beyond, and in resistant relapse or in primary refractory disease, the EFS was of 73% +/- 9%, 58% +/- 19%, 29% +/- 16%, and 10% +/- 9%, the RI 22% +/- 9%, 14% +/- 9%, 77% +/- 18%, and 66% +/- 20%, and the TRM 6% +/- 6%, 32% +/- 21%, 11% +/- 10%, and 71% +/- 22%, respectively. In patients autografted upfront in first remission, additional radiotherapy was associated with a higher EFS, in univariate (P = .03) and multivariate analysis (P = .02, relative risk [RR] = .021). The role of graft purging with mafosfamide on the outcome reflected by the dose of colony-forming unit-granulocyte-macrophage (CFU-GM) per kilogram infused postpurging was assessed by univariate analysis: patients in first remission who received lower doses of CFU-GM had a lower RI and a higher EFS. CONCLUSION This retrospective analysis suggests that marrow purging and posttransplant radiotherapy improve the outcome of patients with NHL autografted in first remission.

To circumvent the problems inherent in allogeneic bone marrow transplantation, allogeneic cord blood has been studied as an alternative source of hematopoietic stem cells. Preliminary results with cord blood from an HLA-matched sibling are encouraging, but the experience with this procedure is limited.1–5 Although some 200 transplantations of cord blood have been performed in children,6,7 few have been performed in adults. We describe an adult with chronic myelogenous leukemia who underwent the transplantation of cord-blood stem cells successfully. Case Report A 26-year-old woman was found to have chronic myelogenous leukemia in July 1990. All the leukemic cells had . . .

IL2 infusion may benefit patients with haematological malignancies by lowering the disease burden. However, conflicting data have been reported on IL2 effects on myelopoiesis, in vitro as well as in vivo. In the present study we investigated the ability of IL2 to act on committed and primitive bone marrow progenitor cells in defined serum-free (SF) culture conditions which avoid many technical biases such as interference by exogenous stimulating or inhibiting factors. Low doses of IL2 (0.1-1000 U/ml) were studied without or in combination with recombinant IL3, GM-CSF and erythropoietin, in SF long-term marrow culture (LTMC). We report data in favour of an inhibitory activity of IL2 limited to committed progenitors and excluding more primitive haemopoietic stem cells, as shown by an alteration of CFU-GM proliferation during the first 5 weeks of LTMC, decreasing with time, unaffected BFU-E and increased nucleated cell production. Beyond week 5, no difference was observed between IL2 supplemented cultures and the SF control cultures. In parallel, IL2 induced the adherence of fibroblastic cells and their progeny. In addition to the inhibitory effect, IL2 appeared to limit the stimulating effect on granulopoiesis and erythropoiesis of myeloid growth factors (GF) such as combination of IL3, GM-CSF and EPO. Indeed, in SF-LTMC conditions, IL2 inhibitory effect is effective on CFU-GM production throughout the 7 weeks of LTMC and on BFU-E during the first 2 weeks only. These data confirm the interaction of IL2 with other GFs in the complex interplay of the cytokine network.

Background This study is the first step toward use of mesenchymal stem cells (MSCs) in therapy to alleviate the effects of radiation exposure in patients. MSCs improve repair in various organs and tissues, in particular after irradiation. However, before using MSCs in a cancer environment, for instance after radiotherapy, it must be established that MSC injections do not promote malignant cells proliferation. Methods A rat model of colorectal carcinogenesis close to human cancer was used as preclinical model. The carcinogen N-methyl-N ′ -nitro-N-nitroso-guanidine (MNNG) was instilled in rats by four intrarectal deposits within 2 weeks, and two MSC injections (10 7 cells per rat) 2 and 4 weeks after the end of carcinogen treatment. Tumours were then examined 32 and 52 weeks after initiating MNNG treatment. Another cohort of rats entered a survival experiment. Findings MSC treatment reduced cancer significantly, lowering the number of adenomas and adenocarcinomas and extending the lifespan of rats. The anti-cancer effect of MSCs was mediated by their immunological properties. In adenocarcinoma of MSC-treated rats, CD68+ monocyte/macrophage infiltration was lowered and CD3+ lymphocytes increased. MSCs induce macrophages to turn into regulatory cells involved in phagocytosis, inhibiting the production of proinflammatory cytokines. MSCs decrease NK cells and rTh17 cell activities, Treg recruitment, CD8+ lymphocytes, and endothelial cell number and restore Th17 cell activity. MiRNA mi-150 and miRNA-7 are the key effectors. Mi-150 inhibits tumour invasion and mi-RNA-7 negatively regulates the EGFR/AKT pathway, promoting cell death. Interpretation MSC infusion has a durable action on colon cancer development by modulating the immune component of the tumour microenvironment. For the first time, two mi-RNA were identified as responsible for the anti-cancer effect of MSCs. We propose that in this model of colorectal cancer early bone-marrow-derived MSC injections, by a long-term effect, reoriented tumour immune response and induced regression of colonic carcinogenesis.

The work on human embryonic stem cells is being performed with a variety of cell lines using a variety of culture conditions; a situation that makes standardisation between projects and publications very difficult. Clearly the consequence of using such cells would be wasted time and resources but, more seriously, the generation of erroneous data in the literature which could both confuse and delay scientific progress in this area. This guidance document represents the outcome of the first meeting of the group named The International Stem Cell Banking Initiative held in October 2007. The document has been prepared from the perspective of hESC culture but, in many respects, is broadly applicable to all human stem cell lines including induced pluripotent stem cell lines.

THE MAIN DISADVANTAGES of transplantation of cord blood (CB) hematopoietic stem or progenitor cells (HSPC) are the delayed neutrophil and platelet reconstitution coupled with the difficulty in obtaining a large enough graft for patients weighing more than 30 kg (1). Both problems could be overcome by ex vivo expansion of CB progenitors. In most CB banks, the whole CB samples are stored in individual or double bags. The ex vivo expansion of progenitors in whole blood samples is inefficient; thus, a CD341 selection before an expansion procedure is a prerequisite. However, this selection using frozen-thawed blood samples is impaired by aggregate formation (“clumping”). To overcome this problem, addition of recombinant human deoxyribonuclease (DNase) has been proposed during thawing of CB cells prior to transplantation (2) or expansion (3). We have extended this procedure to clinical-grade conditions incorporating subsequent CD341 cell selection and expansion in two-step culture conditions. Two bags [(Macopharma, Lille, France) GSR 7000 A), each containing 125 ml of CB and 125 ml of cryoprotecting solution 20% dimethylsulfoxide (DMSO), from a single CB and frozen by using a controlled-rate procedure and stored in liquid nitrogen, were thawed in a water bath at 37°C. DNase (Pulmozyme Roche, Neuilly, France) (3750 units) and the MgCl2 solution (Cooper, Mellin, France) (0.5 M, 250 ml) were added to each bag. Two samples were pooled and then rehydrated slowly (10 min at 20–22°C) by adding 250 ml of Dextran 40-sorbitol solution (Braun Medical, Boulogne, France) and 3.3 ml of Gamma IV (0.5 g LFB). The cell suspension was filtered, incubated with anti-CD34, and transferred into the separation chamber (system Isolex 300i, Baxter, Deerfield, IL). An additional 7500 Units of DNase and 500 ml of MgCl2 were added before the addition of immunomagnetic microbeads (Baxter kit). The suspension was processed on Isolex 300i. The CD341 cells were transferred into 50-ml conical tubes and centrifuged for 10 min at 1500 rpm. The supernatant was removed, and the cells were resuspended in 10 ml of serum-free culture medium (Irvine Scientific, Santa Ana, CA). The CD341 cells were expanded in the same serum-free medium (200 ml; 10,000 cells/ml) in gas-permeable bags (Opticyte 390 cm2, Baxter, Maurepas, France) in the presence of stem cell factor (SCF; Amgen, Thousand Oaks, CA), megakaryocyte growth and development factor (MGDF) (Amgen), Flt3 ligand (RD Median 3.333 106 n 5 5) CD341 cells per sample (Fig. 1A), i.e., a mean recovery of 48.5% with respect to the values found in fresh CB samples (Fig. 1B). The purity of these

In vitro production of red blood cells (RBCs) from stem cells (SCs) for transfusion is emblematic of what regenerative medicine could be in the near future [1]. This project of proposing an alternative to conventional transfusion, includes four challenges – scientific, technological, public health and social – that must be overcome to attain large-scale clinical development. First, a scientific challenge: recreate in vitro a fundamental physiological mechanism – the complete and terminal maturation of RBCs from a SC population. The goal is to reach the ultimate stage of the erythroid lineage, cells that specialize in oxygen transport to the point of losing all other functions, even eliminating their nucleus. The complexity of this concept resides in that we need to identify the best source of SCs to attain a double goal: qualitative (mature and functional cells) and quantitative (massive amplification allowing transfusion applications). When this project was initiated in early 2000, the target population was limited to hematopoietic SCs from bone marrow, blood or umbilical cord. Today, other major SCs are putative candidates, the pluripotent, embryonic SCs or adults SCs (induced pluripotent SCs; iPSCs) [2]. Immortalized lines of CD34 cells will probably soon be available also. Indeed, while hematopoietic SCs theoretically allow our quantitative goal of RBC production for transfusion to be reached, their availability is dependent on donors and is thus limited. These are the limitations. Because iPSCs can proliferate indefinitely, they are potential candidates to provide complementary sources of RBCs for transfusion. Proof of concept for generating human RBCs from SCs has been performed, but the procedures need to be optimized to lead to clinical application in blood transfusion [3]. Several crucial points remain to be resolved. Notably, these include: the choice of the initial cell type to generate iPSCs; the method of reprogramming to ensure their safety as clinical-grade cells; the optimization of erythrocyte differentiation; and the definition of GMP conditions for industrial production. Thus, while we know the goal to attain, we do not know yet from where to start. It is a paradox! Fundamental science moves faster than industrial development. This problem is common to all fields of regenerative medicine. Let us take the example of cardiac regeneration. Who can say today which is the appropriate target: total bone marrow cells, hematopoietic CD34 cells, CD133 cells, mesenchymal SCs, endothelial cells, embryonic SCs or iPSCs? All leads must be investigated without exclusion or bias.

New sources of red blood cells (RBCs) would improve the transfusion capacity of blood centers. Our objective was to generate cells for transfusion by inducing a massive proliferation of hematopoietic stem and progenitor cells, followed by terminal erythroid differentiation. We describe here a procedure for amplifying hematopoietic stem cells (HSCs) from human cord blood (CB) by the sequential application of specific combinations of growth factors in a serum-free culture medium. The procedure allowed the ex vivo expansion of CD34+ progenitor and stem cells into a pure erythroid precursor population. When injected into nonobese diabetic, severe combined immunodeficient (NOD/SCID) mice, the erythroid cells were capable of proliferation and terminal differentiation into mature enucleated RBCs. The approach may eventually be useful in clinical transfusion applications.

In vivo expansion of reinfused autologous peripheral blood stem cells after a myeloablative regimen, as an alternative to ex vivo expansion pretransplantation: an intriguing observation in a patient autografted twice

We report a stimulating effect of leukaemic B-lymphocytes from anaemic and non-anaemic patients with CLL on the proliferation of normal peripheral blood BFU-E. Coculture of leukaemic B-cells at various concentrations (2.5 X 10(3)-10(6)) with 2.5 X 10(5) mononuclear cells from normal peripheral blood increased the number of BFU-E derived erythroid colonies. The same effect was observed when the number of target cells was varied in the presence of a fixed number of B-lymphocytes, with a clear linear relationship. B-cell conditioned medium gave a similar increase when added to the culture instead of B-cells. At high concentration of B-cells from anaemic patients, the size of the colonies was increased and a large number of macroscopic colonies was seen. The place of the B-cells in the regulation of erythroid progenitors in relation to monocytes and T-lymphocytes has still to be established.

Prolonged in vitro maintenance of human bone marrow progenitor cells was achieved using a serum-free (SF) liquid culture system. Culture medium was based on Iscove's medium supplemented with bovine serum albumin, human transferrin, bovine insulin, soybean lecithin, cholesterol, hydrocortisone and alpha-thioglycerol. Under these standardized culture conditions, CFU-GM were maintained for up to 4 weeks, as is the case when using conventional serum-dependent medium. Erythropoiesis exhibited a slower decline than that found using serum containing medium. Development of normal haematopoiesis was effective in spite of poor stromal cell development--a confluent adherent layer as classically described in serum conditions was never achieved. Our newly defined system provides a reliable technique for studying human haematopoietic stem cell proliferation and differentiation in vitro; it allows for rational utilization of currently available purified recombinant growth factors. It may be a promising tool in the clinical use of cultured haematopoietic stem cells.