Milestones in umbilical cord blood transplantation

historical review Milestones in umbilical cord blood transplantation Eliane Gluckman, Annalisa Ruggeri, Fernanda Volt, Renato Cunha, Karim Boudjedir and Vanderson Rocha Eurocord, Assistance publique des hôpitaux de Paris (APHP), Institut Universitaire d Hématologie (IUH) Hôpital Saint Louis, Paris, France Summary Much has been learned about umbilical cord blood (UCB) since the first human cord blood transplant was performed back in 1988. Cord blood banks have been established worldwide for the collection, cryopreservation and distribution of UCB for allogeneic haematopoietic stem cell transplantation. UCB has now become one of the most commonly used sources of haematopoietic stem cells for allogeneic transplantation. Today, a global network of cord blood banks and transplant centres has been established with a large common inventory, allowing for more than 20 000 transplants worldwide in children and adults with severe haematological diseases. Several studies have been published on UCB transplant, assessing risk factors such as cell dose and human leucocyte antigen mismatch. New strategies are ongoing to facilitate engraftment and reduce transplant-related mortality and include the use of reduced-intensity conditioning regimen, intra-bone injection of cord blood cells, double cord blood transplants or ex vivo expansion of cord blood cells. The absence of ethical concern and the unlimited supply of cells explain the increasing interest of using UCB for developing regenerative medicine. Keywords: cord blood transplantation, cord blood banks, haematological disease. Since the first human cord blood transplant, performed in 1988, cord blood banks (CBB) have been established worldwide for the collection and cryopreservation of umbilical cord blood (UCB) for allogeneic haematopoietic stem cell transplantation (HSCT) (Gluckman et al, 1989). The advantages of umbilical cord blood transplantation (UCBT) were first recognized in related donors. Later, CBB established the criteria for the standardization of the collection, banking, processing, and cryopreservation, and distribution of UCB for unrelated donor transplants in patients with various haematological malignant and non-malignant diseases (Rubinstein et al, 1993). UCB has now become one of the most commonly Correspondence: Professor Eliane Gluckman, Eurocord Hopital Saint Louis, 1 avenue Claude Vellefaux, 75475 Paris Cedex 10, France. E-mail: eliane.gluckman@sls.aphp.fr used sources of haematopoietic stem cells for allogeneic transplantation. Currently, the global network of CBB has a common inventory of an estimated 600 000 UCB units, and more than 20 000 units have already been distributed to transplant centres worldwide for the treatment of both adults and children with severe haematological diseases. The main practical advantages of using cord blood as an alternative source of stem cells are the relative ease of procurement, the absence of risk for mothers and donors, the reduced likelihood of transmitting infections, particularly cytomegalovirus, and the ability to store fully tested and human leucocyte antigen (HLA) typed transplants in the frozen state, available for immediate use. Several studies have shown that the number of cells is the most important factor for engraftment. Furthermore, studies have shown that some degree of HLA mismatch is acceptable in the UCBT setting. The last two decades of UCB research have shown clear evidence that UCB is an acceptable and promising haematopoietic stem cell source for the treatment of both adults and children with haematological malignancies. Moreover, non-haematopoietic stem cells can also be isolated from UCB, and the absence of ethical concerns surrounding this product and its unlimited supply explain the increased interest regarding the use of UCB in the developing field of regenerative medicine. Pre-clinical steps The concept of using cord blood was developed in the late 1970s, but it was the pivotal work of H.E. Broxmeyer that moved UCB from the laboratory to clinical practice. E.A. Boyse validated concept studies in mice (Yeoman et al, 1993) while H.E. Broxmeyer evaluated the haematopoietic potential of human UCB in vitro, and developed practical and efficient methods for large volume collection and storage of UCB. It was postulated at that time that UCB collected at birth might contain enough haematopoietic stem/progenitor cells for clinical use (Broxmeyer et al, 1989). This possibility was strengthened by the knowledge that haematopoietic progenitor cells from UCB could be maintained for many weeks in longterm cultures, suggesting their production from more primitive cells. Mice studies showed that, in contrast to adult blood, the use of a small quantity of neonatal blood enabled the survival of approximately half of the lethally irradiated mice First published online 5 July 2011 ª 2011 Blackwell Publishing Ltd, British Journal of Haematology, 154, 441 447 doi:10.1111/j.1365-2141.2011.08598.x

(Vormoor et al, 1994). These findings led to a multi institutional study that addressed the following: (i) reconstitution of cellular content by measurement of haematopoietic progenitor cells numbers in cord blood and (ii) collection, transportation and optimal cryopreservation of cord blood (Gluckman et al, 1989; Rubinstein et al, 1993). Researchers from the Indiana University School of Medicine found on 101 samples of UCB, collected in New York, that the number of progenitor cells was in the lower range of numbers associated with successful engraftment and, that the numbers were increased when erythrocyte depletion was not attempted (Broxmeyer et al, 1992). They observed that samples could be successfully frozen, stored and thawed without major loss of cells. At that time, this group believed that cord blood stem cells would be especially attractive for autologous purposes, providing a perfectly matched set of cells stored for future use. However, it was unlikely that autologous cord blood transplantation would be tested in the near future. This concept led to a long-lasting debate on patenting cord blood for clinical use and of setting up commercial cord blood banks for personal use. Next, testing the concept of allogeneic cord blood stem cell transplants, in which an HLA-identical sibling was available, was discussed. The first UCBT was made possible by an intensive collaboration between three researchers and their respective groups: A.D. Auerbach, from New York (USA), who described a method of prenatal diagnosis in Fanconi anaemia (FA) (Auerbach et al, 1990), H.. Broxmeyer, from Indianapolis (USA), who systematically analysed the number of haematopoietic cell progenitors in cord blood with the purpose of using the cells for haematopoietic reconstitution in humans (Smith & Broxmeyer, 1986), and E. Gluckman, from Paris (France), who demonstrated that the in vivo hypersensitivity of FA cells translated in an increased toxicity of the pre-transplant conditioning regimen and was the pioneer of modified attenuated dose conditioning in FA patients (Gluckman et al, 1983). Auerbach identified mothers of FA patients who were pregnant. By performing prenatal diagnosis on cultured amniotic fluid cells, she was able to select five pregnant women known to be expecting babies that were at unaffected by FA and HLA identical to their FA sibling. The UCB of the selected women were harvested and cryopreserved at birth. It was perceived by all involved in this study, including the Institutional Review Boards of the transplant centres, that the cord blood availability in these cases obviated the need for bone marrow aspiration from the infant siblings, especially with the knowledge that the siblings were available for bone marrow donation later, if necessary. From the first UCB transplant to the development of UCB banks The first UCBT was performed in 1988 in a FA patient (Gluckman et al, 1989). This patient had a healthy HLA identical sibling shown by prenatal testing to be unaffected by the disorder and to have a normal karyotype. The UCB was collected during the birth of the healthy sibiling, cryopreserved and used, after thawing, for the transplantation. The transplant conditioning consisted of low dose cyclophosphamide (20 mg/ kg instead of 200 mg/kg) and 5 Gy total lymphoid irradiation. This type of conditioning was developed specifically for the treatment of FA patients due to their extreme sensitivity to alkylating agents, such as cyclophosphamide. The cryopreserved UCB cells were transported from Indiana to Paris in a dry shipper container that maintained the temperature at )175 C. The cells were thawed without further processing on day 0. Viability and progenitor cell assays were performed on the thawed product, and the results were similar to the ones before cryopreservation. The first signs of engraftment appeared on day 22, with subsequent complete haematological reconstitution and donor chimerism. The patient never developed graft-versus-host disease (GVHD) and is currently, more than 20 years after UCBT, healthy and showing a complete long-term haematological and immunological donor reconstitution. This first successful transplantation led to a new field in the domain of allogeneic HSCT as it demonstrated the following: (i) a single UCB contained enough haematopoietic stem cells to reconstitute the host lympho-haematopoietic compartment, (ii) an UCB unit could be collected at birth without any harm to the newborn and (iii) UCB haematopoietic stem cells were able to maintain their repopulating properties post cryopreservation, thawing and, subsequently, transplantation in a myeloablated host. Since then, knowledge regarding the biological characteristics of UCB cells has increased, emphasizing the advantages of using UCB stem cells for transplant (Griffiths-Chu et al, 1984; Linch & Brent, 1989; Durandy et al, 1990). Table I lists the questions raised during the last 20 years of cord blood biology and transplantation and milestones achieved in the field. All of the listed questions have been answered during the last 20 years thanks to the worldwide development of intense international cooperation between Europe, with Eurocord and Netcord, the USA, with the Center for International Blood and Marrow Transplant Research (CIBMTR) and National Marrow Donor Program (NMDP), Asia, with Asia Cord, Australia, with Australia Cord, and others, including single transplant centres. The international organization of cord blood transplantion Since the first UCB, more than 20 000 UCBT have been reported worldwide and more than 600 000 UCB units have been stored in more than 100 CBB (http://www.bmdw.org) (http://www.nmdp.org). The Eurocord group was established in 1995 on behalf of a European framework programme and the European Group for Blood and Marrow Transplantation, with the principal objective of collecting the clinical data regarding European patients transplanted with cord blood grafts shipped by European or 442 ª 2011 Blackwell Publishing Ltd, British Journal of Haematology, 154, 441 447

Table I. Cord blood biology and transplantation: questions answered and milestones achieved. Questions Would a single cord blood unit contain enough stem cells to sustain permanent engraftment in both children and adults? Would maternal cell contamination in cord blood also engraft and cause severe GVHD in the recipient? Would the same results be obtained in patients transplanted for conditions other than Fanconi anaemia, such as leukaemia? Would engraftment also occur in adults? Are the properties of haematopoietic cord blood cells different from adult haematopoietic cells? What are the immunological properties of cord blood cells? What is the impact of cord blood cells in GVHD, graft-versus-leukaemia, and immune reconstitution? Would the immune immaturity of cord blood lymphocytes be able to overcome the HLA barrier and allow for HLA -mismatched transplants? Would it be possible to establish CBB for both unrelated and related transplants? What would be the criteria for collection, processing, and quality control of UCB Would it be possible to collect cord blood not only for related transplants, but also for unrelated ones? What would be the necessary inventory capacity of UBC banks if it was demonstrated that HLA incompatibilities were not recognized in cord blood because of the immaturity of the immune system at birth? Milestones achieved First HLA identical sibling cord blood transplant in a patient with Fanconi anaemia (Gluckman et al, 1989) Optimization of UCB collection and storage (Gluckman et al, 1989; Rubinstein et al, 1993, 1995) Development of CBB for related and unrelated transplants (Paris, Dusseldorf, New York, Milan) First unrelated mismatched cord blood transplant in children (Kurtzberg et al, 1996) First unrelated cord blood transplant in adult (Laporte et al, 1996) Creation of the Eurocord-Netcord network (Gluckman et al, 1997) Description of donor selection criteria based on the number of nucleated cells and the possibility of using mismatched cord blood (Wagner et al, 2002; Gluckman et al, 2004) Demonstration that cord blood transplants in HLA identical siblings resulted in delayed engraftment and lower incidence of GVHD with similar survival when compared to bone marrow transplants in children (Rocha et al, 2000). Demonstration that long term leukaemia-free survival in children (Wagner et al, 1996; Locatelli et al, 1999) and adults (Cairo & Wagner, 1997; Rubinstein et al, 1998; Laughlin et al, 2001; Sanz et al, 2001) is similar for cord blood transplant recipients and matched unrelated bone marrow transplant recipients. Isolation of non-haematopoietic stem cells from cord blood as a first step for regenerative medicine (Kogler et al, 2004) Improved results, mostly in adults, with the use of double cord blood transplants and non-myeloablative conditioning regimens (Barker et al, 2005; Brunstein et al, 2007; Rocha et al, 2010) New approach on Notch-mediated ex vivo expansion system of cord blood progenitors (Delaney et al, 2010) other international cord blood banks; therefore a registry of UCBT recipients was created and, currently, more than 7000 patients have been reported. Furthermore, the Eurocord registry provides clinical outcome data on each transplanted cord blood unit to the CBB, with the goal of obtaining national and international accreditation. In addition, Eurocord has contributed to the field of UCBT with numerous publications, including guidelines for donor selection. Eurocord has also launched an online program in cord blood technology and transplantation, in order to promote education and information, providing an educational tool on the scientific, technical, clinical, and regulatory aspects of cord blood. The program (http://www.eurocord-ed.org) is easily accessible and convenient for users. Netcord was created in 1998 to establish good practices in UCB storage, facilitate donor search, improve the quality of the grafts, standardize criteria on an international scale, and, importantly, establish procedures for bank accreditation. The inventory of Netcord, the cooperative network of large experienced UCB banks, currently has more than 300 000 cryopreserved UCB units ready for clinical use for unrelated recipients and more than 8624 grafts have been shipped. In the United States, the NMDP has established a similar CBB network. Collaboration between Netcord-Eurocord and NMDP has been established with the goal of providing the most suitable and high quality cord blood unit for a specific patient. A summary of CBB activity can be seen at http:// www.wmda.org. National regulatory agencies and transplant centres are aware of the need of international standards to promote quality throughout all phases of cord blood banking with the goal of achieving a consistent production of high quality placental and UCB units for transplantation. These standards cover: (i) collection of cord blood cells, regardless of the methodology or site of collection, (ii) maternal and infant donor screening, testing, and eligibility determination in accordance with any applicable law, (iii) all phases of processing and storage, including quarantine, testing, and unit characterization, (iv) availability of the UCB unit for transplantation, either directly or through a search registry, (v) the search process for the selection of a specific UCB unit, (vi) transport and shipment of fresh and cryopreserved UCB units and (vii) UCB final disposition. All of the practical aspects of cord blood banking mentioned above have been extensively published and are detailed in the latest version of the Netcord- ª 2011 Blackwell Publishing Ltd, British Journal of Haematology, 154, 441 447 443

Table II. Number of unrelated UCBT reported to Eurocord registry according to diagnosis and recipient age. Diagnosis Children ( 18 years, n = 3566) FACT Standards (http://www.factwebsite.org). With an increasing number of cord blood units, it seemed necessary to improve the quality of the units for the cost efficiency management of the banks. The optimal number of cord blood units that should be available in CBB is not known, but it is estimated that it should approach 9 UCB units per 10 000 inhabitants. Most banks prefer to store the larger units of more than 70 ml in order to obtain a minimum of 3 10 7 nucleated cells (NC)/kg of recipient weight. The effect of increasing the inventory from 50 000 to 300 000 cord blood units with a minimum dose of 2Æ3 10 7 NC/kg results in an increment in the chances of finding a donor of 19% for children and 10% for adults. Recently, Querol et al (2009) showed that a bank containing 50 000 units is optimal for the UK and larger banks would only marginally increase the chance of finding suitable units. Clinical experience with related and unrelated UCB transplantation A survey conducted by the CIBMTR estimated that after 1998, 20% of stem cell transplants performed in young patients (<20 years old) were cord blood transplants (IBMTR Newsletter). Currently in Japan, approximately 50% of HSCT from unrelated donors are performed with UCB cells. First published large series of patients Adults (>18 years, n = 3210) Acute lymphoblastic leukaemia 1167 (32Æ7) 671 (20Æ9) Acute myeloid leukaemia 608 (17) 1208 (37Æ6) Myelodysplastic syndrome 291 (8Æ2) 428 (13Æ3) Chronic myeloid leukaemia 77 (2Æ2) 208 (6Æ5) Chronic lymphocytic leukaemia 76 (2Æ4) Hodgkin/non-Hodgkin lymphomas 64/9 (2Æ1) 290/122 (12Æ8) Myeloma 88 (2Æ7) Solid tumours 18 (0Æ5) 6 (0Æ2) Hystiocytosis 132 (3Æ7) 5 (0Æ2) Congenital and acquired bone 353 (9Æ9) 91 (2Æ8) marrow failure syndromes Haemoglobinopathies 71 (2) Primary Immunodeficiencies 412 (11Æ6) 3 (0Æ1) Metabolic diseases 353 (9Æ9) 11 (0Æ3) Other disease 11 (0Æ2) 3 (0Æ2) The values in parentheses are expressed as percentage. In 1997, Eurocord published results of cord blood transplants from related and unrelated donors (Gluckman et al, 1997). The study included 143 patients transplanted between 1988 and 1996 in 45 transplant centres. Among the 78 recipients of a related cord blood transplant, the Kaplan Mayer (KM) estimate of survival was 63%. GVHD was low at 9%. Favourable factors for engraftment were lower age and higher number of NC. Among the 60 recipients who received a mismatched unrelated UCBT, the KM estimate of survival was 29%, and the major factor associated with engraftment was the number of NC infused. In 2000, in a CIBMTR-Eurocord study, comparing paediatric bone marrow transplantation (BMT) and UCBT from an HLA identical sibling, UCBT was associated with delayed granulocyte and platelet engraftment, reduced acute and chronic GVHD and the same survival. This was the first analysis that demonstrated, unambiguously, that GVHD was reduced when UCB cells were used instead of BM (Rocha et al, 2000). This first study was the basis for advocating the use of mismatched UCBT and triggered the development of unrelated CBB. Later, Eurocord and other groups demonstrated that unrelated UCBT could be used in all current indications of allogeneic HSCT, including malignant and non-malignant diseases in children and in adults (Table II) (Laughlin et al, 2001; Wagner et al, 2002; Gluckman et al, 2004). Since 2005, further results have been obtained with the use of double cord blood transplant (ducbt) (Barker et al, 2005; Ballen et al, 2007). The objective of using double CB units was to increase the cell dose using the same criteria of HLA compatibility (no more than two out of six HLA disparities between UCB unit and patient) for patients who could not find a single unit with enough cells. This new strategy has extended UCBT to many adults who could not safely undergo single UCBT. To date, the Eurocord registry now includes more adult patients who have received a ducbt than those transplanted with a single unit. In 2005, the Minnesota group published the safety and feasibility of the first 21 cases of ducbt (Barker et al, 2005). In spite of the fact that ducbt recipients are heavier than patients receiving a single unit, the cumulative incidence (CI) of neutrophil recovery does not statistically differ between the two groups. This observation suggests a booster effect from the non-engrafting unit. Chimerism data from these studies reveal that, typically, only one cord blood engrafts. In this series of 21 patients, the winner unit was the one with the higher CD3 + cell dose. However, this observation was not confirmed in a larger series of ducbt recipients from the same group (Brunstein et al, 2007). Another group has suggested that the first unit infused was the winner unit (Ballen et al, 2007), but this observation still needs to be confirmed. Also, the Minnesota group has evaluated the efficacy of ducbt in the setting of a non-myeloablative regimen (Brunstein et al, 2007). In this study, 110 patients with haematological diseases were analysed. Neutrophil recovery was achieved in 92% at a median of 12 d. Overall survival and leukaemia-free survival (LFS) at 3 years were 45% and 38% respectively. More recently, ducbt has been associated with a higher incidence of acute GVHD (MacMillan et al, 2009), but lower relapse incidence when compared to single 444 ª 2011 Blackwell Publishing Ltd, British Journal of Haematology, 154, 441 447

cord blood unit transplantation. Interestingly, in an analysis of 177 patients with acute leukaemia, relapse was significantly lower for early stage (first or second complete remission) patients who received two UCB units, suggesting a greater graft-versus-leukaemia (GVL) effect. LFS was 40% and 51% for single and double unit recipients, respectively (P = 0Æ35) (Verneris et al, 2009). Comparisons with other sources of stem cells In children with malignant diseases, two studies were performed that compared the outcome of unrelated UCBT and BMT. Eurocord published a study comparing the outcomes of matched unrelated BMT (HLA 6 out of 6) either unmanipulated or T-depleted to mismatched UCBT. Results showed that after UCBT, engraftment was delayed, GVHD was reduced similarly as in after T-cell depleted BMT and relapse and LFS was the same in both groups (Rocha et al, 2004). Eapen et al (2007), on behalf of the CIBMTR and the New York CBB (NYCBB), compared the outcomes of 503 acute leukaemia paediatric patients receiving an unrelated mismatched UCBT with 282 unrelated BM transplant recipients (116 HLA allele matched 8 out of 8). The study showed that HLA allele-mismatched BM recipients developed more acute and chronic GVHD without decreasing LFS. Importantly, they demonstrated that the LFS for HLA allele-matched BMT recipients was not statistically different than the LFS for recipients of UCBT with one or two HLA mismatches and that HLA matched UCBT recipient had better outcomes. However, an increased transplant related mortality (TRM) was observed in children transplanted with low NCdose (<3 10 7 /kg) and one HLA mismatched UCB grafts or in children given a two HLA mismatched UCBT, independently of the cell dose infused. The same types of studies were performed in adults with malignancies. A study conducted by Eurocord compared acute leukaemia adult patients receiving either a matched unrelated bone marrow transplant (HLA 6 out of 6) or a mismatched cord blood transplant. Results showed that LFS was similar in both groups even if engraftment was delayed in the UCBT recipients (Rocha et al, 2004). At the same time, the CIBMTR and NYCBB showed that LFS in adults with malignancies was similar to the LFS in UCB recipients and one antigen mismatched unrelated BMT recipients (Laughlin et al, 2004). Later, a Japanese study showed better results for UCBT than for matched unrelated BMT (Takahashi et al, 2007). In a metaanalysis, combining the published studies, 161 children and 316 adults undergoing UCBT (mostly one or two antigenmismatched), along with 316 children and 996 adults undergoing BMT (mostly fully HLA matched), were analysed. Pooled comparisons of studies of UCBT and BMT in children demonstrated that the incidence of chronic GVHD was lower post-ucbt, but the incidence of grade III IV acute GVHD did not differ, and there was no difference in the 2-year overall survival in children (Hwang et al, 2007). Eurocord and CIBMTR performed a study comparing outcomes of unrelated HLA matched, one to two antigens mismatched bone marrow (n = 364) or granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood (n = 728) transplants to mismatched cord blood transplants (n = 148) in acute leukaemia adults (Eapen et al, 2010). In a multivariate analysis, UCBT recipients showed higher TRM and lower incidence of relapse and GVHD, while LFS was similar when compared with results of recipients transplanted with a different source of stem cells. Recent results after ducbt have been comparable to HLAidentical sibling transplants (Brunstein et al, 2010). This study analysed 536 patients with leukaemia who were transplanted with a HLA-matched sibling (n = 204), 8/8-HLA (n = 152) or 7/8-HLA (n = 52) matched unrelated donor or ducbt (n = 128). When transplant outcomes were compared, ducbt was associated with slower haematopoietic recovery compared to other stem cell sources. While the incidence of acute GVHD was similar to that observed after sibling HSCT, ducbt was associated with less acute GVHD and a trend toward less chronic GVHD relative to unrelated donors. Despite a reduced risk of GVHD after ducbt, the risk of relapse was remarkably low while TRM was elevated, resulting in similar LFS. The results of these comparative studies and the metaanalysis, combined confirm that: (i) UCBT is feasible in adults when a cord blood unit contains a higher number of NC or double UCB units are used and it should be considered an option as an allogeneic stem cell source for patients lacking an HLA matched bone marrow donor; (ii) despite increased HLA disparities, UCB from unrelated donors offers sufficiently promising comparable results to matched BMT in adults with haematological malignancies leading to the conclusion that the donor search process for BM and UCB from unrelated donors should be started simultaneously for both children and adults, especially in patients with acute leukaemia, where the time factor is crucial. Criteria of donor choice In 2004, Eurocord analysed data from 550 patients with haematological malignancies who received an UCBT. Neutrophil and platelet recovery was associated with the number of HLA mismatches, the number of NC collected and infused, and the use of G-CSF after transplant. Coexistence of HLA class I and II disparities and high CD34 + cell dose in the graft were associated with higher rate of mild GVHD, but not with severe GVHD. Disease relapse was higher in matched transplants, demonstrating the GVL effect (Gluckman et al, 2004). Following this and others studie (Rubinstein et al, 1998; Wagner et al, 2002; Barker et al, 2010), the current recommendations to select cord blood units with 2 HLA disparities and >3 10 7 NC/kg or 2 10 5 CD34 + cells/kg before freezing. In non-malignant diseases, where the risk of rejection is higher, the cell dose should be increased and units with 3Æ5 10 7 NC/kg and/or two or more HLA mismatches must be avoided. If a single unit with these characteristics is not ª 2011 Blackwell Publishing Ltd, British Journal of Haematology, 154, 441 447 445

identified, the recommendation is to search for two units with a combined total dose of 3 10 7 NC/kg and, if possible, no more than one HLA mismatch between the two units and the patient. Future directions Much has been learned in a relatively short time about the UCB progenitor cells properties and their clinical applications. However, UCBT is still evolving. Several methods, such as the addition of mesenchymal stem cells (MSC), cord blood intrabone infusion (Frassoni et al, 2008) and Notch mediated ex vivo UCB expansion (Delaney et al, 2010) are under investigation to improve engraftment. Other strategies are also showing promising results to enhance immune reconstitution (Komanduri et al, 2007) and reduce GVHD, such as with infusion of expanded T regulatory cells (Godfrey et al, 2005; Brunstein et al, 2010). More interestingly, non-haematopoietic stem cells have been isolated from cord blood and placenta (Kogler et al, 2004). These cells can be cultured, and they have the potential of differentiating in various tissue types, including MSC, bone, cartilage, liver, pancreas, neurons, endothelial cells, muscle, keratinocytes etc. The advantages of using UCB over other stem cell sources such as embryonic (ES) and induced pluripotent (ips) stem cells are multiple: the supply of UCB stem cells is unlimited, they can be used in both the autologous and allogeneic settings, they require minimal manipulation, and they raise no ethical concerns. Future studies will test the potential of cord blood cells for the treatment of several diseases, including, among other possibilities, diabetes, arteritis, burns, neurological disorders and myocardial infarction. Acknowledgement This work was funded by Eurocord FP5 program and Inserm grant TGIR0805. References Auerbach, A.D., Liu, Q., Ghosh, R., Pollack, M.S., Douglas, G.W. & Broxmeyer, H.E. 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