Cord blood banking and transplantation

The availability of umbilical cord blood (UCB) as a source of haematopoietic stem cells (HSC) for transplantation has met an important niche in the field of HSC transplantation (HSCT) as patients unable to find a HLA-matched sibling or unrelated donor have been able to receive less well-matched UCB transplantation (UCBT) with equivalent outcomes. This has led to significant growth in this field resulting in more than 20 000 unrelated donor UCBTs performed to date with about 3000 more performed annually. Growth of UCBT has been further supported by the proliferation of public cord blood banks throughout the world which store UCB at no cost to the donor, making these available for patients all round the world through global search registries like the US National Marrow Donor Program (NMDP), NetCord and the Bone Marrow Donors Worldwide (BMDW). International organizations like the World Marrow Donor Association have also helped to steer these efforts through the formulation and distribution of guidelines and protocols for these cord blood banks and bone marrow registries. The US Food and Drug Administration (FDA) has also stepped in to regulate publicly banked UCB as an Investigational New Drug (IND). The key limiting factor in UCBT is in the limited number of cells for transplantation (about 10-fold less than donated bone marrow) resulting in delayed engraftment and even non-engraftment, particularly for adult patients for whom UCB cell doses may be insufficient relative to the patient’s body size. Efforts to overcome this barrier include the use of concurrent infusion of two differing cord blood units in order to raise the cumulative cell dose. Interestingly, this does not lead to mutual rejection of the CBUs, but appears to result in an additive effect on enhancing engraftment. Other efforts to overcome cell dose constraints of cord blood include direct bone marrow injection, use of homing molecules and ex vivo cord blood expansion. Cell dose is also an important consideration for cord blood banking as donated UCB that is collected with cell count <800 million nucleated cells has very low chance of utilization by many transplant centres which demand the best cell doses for their patients. As such, not all UCB collected is banked, although many of the low volume cords can still be reassigned to research. Strategies to increase the number of cells collected from each delivery include the use of ex utero devices which apply suction, perfusion or pressure to delivered placenta and umbilical cord in order to maximize HSC collection. Devices which enhance cell recovery during cord blood processing also help to minimize cell loss. Other strategies which might influence obstetric practice are not advised. As the worldwide experience in UCBT and UCB banking grows, patient outcomes have continued to improve such that UCBT now has a firm place in the HSCT spectrum of care with even greater potential for growth in the years to come. The challenge is for these advances to stay cost-effective so that the majority of patients can still have access to them.     

Umbilical cord blood as a source of stem cells

Umbilical cord blood (UCB) is a source of the rare but precious primitive hematopoietic stem cells (HSC) and progenitor cells that can reconstitute the hematopoietic system in patients with malignant and nonmalignant disorders treated with myeloablative therapy. UCB cells possess an enhanced capacity for progenitor cell proliferation and self-renewal in vitro. UCB is usually discarded, and it exists in almost limitless supply. The blood remaining in the delivered placenta is safely and easily collected and stored. The predominant collection procedure currently practiced involves a relatively simple venipuncture, followed by gravity drainage into a standard sterile anti-coagulant-filled blood bag, using a closed system, similar to the one utilized on whole blood collection. After aliquots have been removed for routine testing, the units are cryopreserved and stored in liquid nitrogen. UCB banks are being established throughout the world and UCB units are collected for allogeneic unrelated and related HSC transplantation. In unrelated cord blood banks donated UCB units are collected and stored for allogeneic use in patients who do not have an identified HLA matched relative. UCB banks report available units to national and international donor registries. The second model of UCB banking is referred to as family banking, where UCB is stored for the benefit of the donor or their family members. After more than one decade of clinical experience, it is currently accepted that UCB transplants, related and unrelated, are equivalent to or might compare favorably with bone marrow (BM) transplants, especially in children. Initial studies of long-term survival in children with both malignant and non-malignant hematologic disorders, who were transplanted with UCB from a sibling donor, demonstrated comparable or superior survival to children who received BM transplantation. One factor that limits the use of UCB transplantation in adult patients is the relatively limited number of HSC that may be harvested from umbilical cord, resulting in a slower time to engraftment and higher transplant related mortality, mainly due to the long aplasia period after transplantation and susceptibility to viral and fungal infections. Despite prolonged periods of aplasia, the apparent reduction in the incidence and severity of graft versus host disease (GVHD) may in turn underline comparable rates of survival in some series comparing UCB to adult-donor sources. The "naive" nature of UCB lymphocytes may explain the lower incidence and severity of GVHD encountered in UCB transplantation compared to the allogeneic BM transplant setting. UCB transplantation does not seem to be associated with increased rates of disease relapse. The available data suggest that nucleated cell dose in UK unit should be the primary criterion for donor selection. In 1991, the UCB transplantation program was established at the Zagreb University Hospital Center for related transplants, and until now 4 UCB transplantations have been performed successfully. In order to speed up the engraftment rate, several strategies such as multiple UCB transplants and ex vivo expansion of HSC have been assayed. The current strategies are focused on the development of much more efficient technologies for ex vivo production of progenitor cells, but whether expansion will speed engraftment and improve outcome after UCB remains to be determined. UCB is known to contain extremely immature stem cells. Consequently, such pluripotent or, perhaps, multipotent stem cells have been proposed as elements suitable for cellular therapy and regenerative medicine. Up to date there are no conclusive data regarding these possibilities but preliminary in vitro and animal studies in the field of tissue regeneration suggest some degree of plasticity and/or transdifferentiation. UCB cells are showing their unique qualities and potential, and consequently UCB banks might dramatically increase the scope of their clinical application.     

Mismatched Related and Unrelated Donors for Allogeneic Hematopoietic Cell Transplantation for Adults with Hematologic Malignancies

Two parallel phase II trials in adults with hematologic malignancies demonstrated comparable survival after reduced-intensity conditioning and transplantation of either 2 HLA-mismatched umbilical cord blood (UCB) units or bone marrow from HLA-haploidentical relatives. Donor choice is often subject to physician practice and institutional preference. Despite clear preliminary evidence of equipoise between HLA-haploidentical related donor and double unrelated donor UCB transplantation, the actual prospect of being randomized between these 2 very different donor sources is daunting to patients and their treating physicians alike. Under these circumstances, it is challenging to conduct a phase III randomized trial in which patients are assigned to the UCB or haploidentical bone marrow arms. Therefore, we aimed to provide an evidence-based review and recommendations for selecting donors for adults without an HLA-matched sibling or an HLA-matched adult unrelated donor.     

Status of umbilical cord blood transplantation in the year 2001

Umbilical cord blood (UCB) transplantation is limited to small recipients because of the low haemopoietic cell dose. Children from ethnic minority groups may benefit most from cord blood transplantation. Cohort controlled retrospective data indicate that there is significantly less acute and chronic graft versus host disease associated with the transplantation of human major histocompatibility complex (HLA) identical sibling cord blood compared with HLA identical sibling marrow. Controlled data are not yet available to confirm this observation in unrelated donor cord blood transplantation. The difference in leukaemic relapse seen after cord blood compared with bone marrow transplantation is also unknown. Tentative recommendations for the use of umbilical cord blood for transplantation are as follows. Collection is indicated from healthy newborn siblings when urgent transplantation is required for an older child in a family. The haematologist responsible for the older child, with the approval of the family and the obstetric team, should contact the medical director of the nearest cord blood bank to discuss arrangements for the UCB to be collected and HLA typed. Antenatal blood sampling to HLA type the fetus is not recommended. Umbilical cord blood should be considered when allogeneic transplantation is the treatment of choice for a child who does not have an HLA identical sibling, or a well matched unrelated adult volunteer donor. The potential advantages and disadvantages of using an HLA haplotype matched peripheral blood stem cell family donor rather than an unrelated cord blood donation should be discussed. There are no comparative data available as yet. At present, UCB transplantation should only be considered if a suitably matched donation contains at least 2 x 10(7)/kg nucleated cells. Effectively, this means that most adults and larger children are not suitable recipients.     

Umbilical cord blood transplantation: basic biology and clinical challenges to immune reconstitution

Allogeneic stem cell transplantation has continued to evolve as a common procedure for the treatment of hematological malignancies and bone marrow failure. Donor bone marrow and mobilized peripheral stem cells are routinely employed for the reconstitution of immune function in leukemia and lymphoma patients following radiation and/or chemotherapy. Unfortunately, only 30% of patients have an HLA-identical sibling donor and the identification of matched unrelated donors, particularly for minorities, can present an exceptional challenge. The transplantation of umbilical cord blood (UCB) represents the most recent strategy to expand the potential donor pool while maintaining an acceptable level of treatment-related complications. First utilized in children, UCB transplantation permits a higher degree of HLA disparity while demonstrating a reduction in the incidence and severity of graft-versus-host disease (GvHD) compared to previous transplantation modalities. Despite the apparent decrease in GvHD, relapse rates remain comparable to transplantation with bone marrow or mobilized peripheral blood suggesting a strong graft-versus-leukemia/lymphoma (GvL) effect. However, several issues complicate the use of UCB transplantation and its extension to the treatment of adults. Many infections that afflict transplant patients are particularly frequent and more severe in the context of UCB transplantation. UCB T-cells are naive and therefore display less proliferation and IFN-γ production in response to cognate antigen and also appear to demonstrate defects in signal transduction mechanisms. In addition, UCB contains T regulatory cells (Treg) with more potent suppressor function than adult Treg. Furthermore, adult patients often require more total cells and CD34+ progenitors for transplantation than a single UCB unit can provide. Thus, strategies to expand selected subpopulations from UCB and the use of multi-unit transplantation are areas of active research. This review will provide a condensed summary of the clinical history of UCB transplantation and emphasize the advantages and disadvantages of this approach to hematological malignancies in comparison to other methods of hematopoietic stem cell transplantation. Subsequently, it will mainly focus on the current challenges to immune reconstitution presented by UCB transplantation, recent research into their cellular and molecular mechanisms, and experimental approaches to overcome them.     

Patients benefit from the addition of KIR repertoire data to the donor selection procedure for unrelated haematopoietic stem cell transplantation

Killer cell immunoglobulin-like receptors (KIRs) expressed on donor natural killer (NK) cells are important for induction of NK cell alloreactivity in haematopoietic stem cell transplantation (HSCT). Current criteria in the selection procedure of an unrelated donor do not account for this potential NK alloresponse. In this study the KIR gene repertoire of 21 HSCT patients and all their potential, unrelated donors (N=64) has been identified by the sequence-specific priming (SSP) procedure. KIR genotype characteristics are correlated with HLA and clinical data. These data show that for 16 cases an HLA compatible alternative donor was available. Among those 16 were 8 donors with a favourable predicted NK alloreactivity directed against the leukaemic cells. In conclusion, it is feasible and clinically relevant to add the KIR repertoire to the unrelated donor selection procedure.     

Cord blood transplant: strategy of alternative donor search

Unrelated cord blood transplantation has been used to treat patients with malignant and non-malignant hematopoietic disorders for whom an HLA-compatible hematopoietic stem cell donor is not available. The establishment of cord blood banks worldwide, the increased number of cord blood units frozen, and the shorter time to find a donor, have made it possible to use this source of hematopoietic stem cells to treat more than 2,500 patients. The Eurocord registry was established to study the clinical results of cord blood transplantation and to compare the outcomes of unrelated transplants using either cord blood or bone marrow. Briefly, we have found, in two distinct retrospective analyses of children or adults with acute leukemia given either an unrelated cord blood or bone marrow transplant, that leukemia-free survival and relapse were similar in both types of graft (with adjustment for confounding clinical factors). Cord blood recipients experienced a decreased incidence of acute graft-versus-host disease and delayed hematopoietic recovery compared to bone marrow recipients. To improve the delayed hematopoietic recovery after cord blood transplantation, certain approaches have been investigated such as ex vivo expansion of cord blood cells, double cord blood transplantation and reduced intensity conditioning regimen. We have also attempted to establish some guidelines for cord blood-donor choice based on cord blood cell dose and number of HLA disparities that have been found to be associated with hematopoietic recovery. In conclusion, an unrelated hematopoietic stem cell donor should be simultaneously searched for in cord blood banks and in bone marrow donor registries for patients lacking an HLA-identical sibling hematopoietic stem cell donor. The option of performing cord blood transplants should be based on urgency of the transplant, cord blood cell dose and number of HLA disparities.     

Hematopoietic engraftment in recipients of unrelated donor umbilical cord blood is affected by the CD34+ and CD8+ cell doses.

Umbilical cord blood (UCB) transplantation is limited by the low number of hematopoietic stem cells in UCB units, which results in a low engraftment rate in transplant recipients. Here, we measured the total nucleated cell count and CD34(+), CD3(+), CD4(+), CD8(+), CD14(+), and CD16(+)/56(+) cell doses in each UCB unit and evaluated their influence on engraftment and other outcomes in 146 recipients. Multivariate analysis showed a significant association between a higher incidence of successful engraftment and a dose of CD34(+) and CD8(+) cells above the median (1.4 x 10(5) and 15.7 x 10(5) cells/kg, respectively). Engraftment occurred 4 days earlier in patients who received UCB with more than the median dose of CD34(+) cells than those receiving UCB at or below the median. Stratification of the group according to CD34(+) cell dose revealed a significant influence of the CD8(+) cell dose on the time to achieve neutrophil engraftment in patients receiving a lower CD34(+) cell dose, whereas there was no significant influence in the patients receiving a higher CD34(+) cell dose. These results suggest that consideration of CD34(+) and CD8(+) cell doses in UCB units may improve the engraftment in recipients of UCB transplantation.     

Stem cells: you can't tell a cell by its cover

Embryonic stem (ES) cells are capable of unlimited self-renewal and have the ability to give rise to all tissue types in the body. The use of human ES cells for tissue and cell therapeutics has been suggested, but is limited by ethical concerns as these cells are derived from the inner cell mass of human embryos. In addition, the need for HLA matching of ES cell-derived tissues for allogeneic transplantation would require a bank of several thousand ES cell lines to make tissue therapeutics practical. Recently, adult stem cells-of which those in bone marrow are the best studied-have been shown to be capable of multilineage differentiation into cells of various non-blood tissues. Umbilical cord blood (UCB) haematopoietic stem cells have been shown to be equivalent to bone marrow stem cells for reconstitution of the haematopoietic system. Preliminary studies have also demonstrated that UCB haematopoietic stem cells are multipotent and capable of differentiating into non-blood cell types. This observation raises the exciting possibility of replacing human ES cells for tissue and cell therapeutics with UCB blood haematopoietic stem cells that are normally discarded with the placenta after delivery.     

Multiple unit HLA-unmatched sex-mismatched umbilical cord blood transplantation for advanced hematological malignancy

We investigated the effect of multiple-unit umbilical cord blood (UCB) transplantation on engraftment in the setting of severe human leukocyte antigen (HLA) mismatch. Ten poor-risk adult patients with hematological malignancy received multiple unit, HLA-unmatched, sex-mismatched, unrelated UCB transplantation after a reduced intensity-conditioning regimen (RICR) with engraftment as the primary endpoint. The median age of the patients was 55 years with a range of 28-67. Patients received one unit of UCB per 10 kg of recipient body weight (5-7 units). The median number of nucleated cells and CD34(+) cells per kilogram of recipient body weight infused was 6.3 x 10(7) (range 3.8-10.0) (NC/kg) and 5.7 x 10(5) (range 1.1-11.9) (CD34/kg), respectively. Three patients expired before day 28 and were not evaluable for engraftment. Five of the remaining 7 patients showed increasing neutrophil counts. Fluorescent in situ hybridization (FISH) for the Y chromosome or HLA-typing showed only donor cells in the peripheral blood. After engraftment, HLA typing was done on 3 patients and their infused UCB units. All revealed the presence of a single HLA type concordant with one of the infused units. Moreover, the order of infusion did not influence which UCB unit engrafted. The engrafting UCB units were infused first or second in one case and fourth in the other two. One patient transplanted for refractory acute lymphoblastic leukemia (ALL) survives in continuous complete remission 4 years after transplant. He engrafted with one UCB unit, is fully hematologically reconstituted, has no evidence of graft-versus-host disease (GVHD), and takes no immunosuppressive medication. HLA typing reveals that the recipient and the engrafted cord blood match at only one HLA-B locus using conventional 6 antigen typing (A, B, and DR). Although engraftment was not accelerated, it did occur in the majority of evaluable patients. Long-term disease-free survivorship without debilitating GVHD is possible in patients with refractory hematological malignancy who receive unmatched multiple unit UCB.     

Umbilical Cord Blood Transplantation in Severe T-Cell Immunodeficiency Disorders: Two-Year Experience

Hematopoietic stem cell transplantation is the treatment of choice for severe primary T-cell immunodeficiencies. When an HLA-identical sibling as the donor is not available, an alternative donor stem cell source is needed. In primary T-cell immunodeficiencies, T-cell-depleted HLA-haploidentical bone marrow transplantation has been particularly successful in reconstituting the immune system in many but not all of the severe T-cell immune deficiency disorders. This study reports the use of umbilical cord blood (UCB) stem cell transplantation in severe T-cell immune deficiency.Umbilical cord blood was evaluated as a stem cell source for immune reconstitution in children with severe primary T-cell immunodeficiency disorders, such as severe combined immunodeficiency syndrome (SCID), reticular dysgenesis, thymic dysplasia, combined immunodeficiency disease (CID), and Wiskott–Aldrich syndrome (WAS) when a matched sibling donor was unavailable. From 1/96 through 5/98, eight children received unrelated cord blood stem cell transplantation following a preparative regimen for the treatment of combined immunodeficiency diseases. The patients ranged in age from 2 weeks to 8 years. The cord blood units were 3/6 HLA antigen matches in two children, 4/6 in four children, and 5/6 in two child, with molecular HLA-DR mismatch in three of the children. The average time for neutrophil engraftment (absolute neutrophil count >500/mm³) was 12 days (range 10–15 days) and the average time for platelet engraftment (platelet count >20,000/mm³) was 36 days (range 24–50 days). A patient with reticular dysgenesis failed to engraft following her first transplant, but fully engrafted after a second unrelated donor cord blood transplantation. Five of six patients exhibited grade I graft-versus-host disease (GvHD), while one child had grade IV skin and gut GvHD. Immunologic reconstitution demonstrated that cord blood stem cell transplantation resulted in consistent and stable T-, B- and natural killer (NK) cell development. The kinetics of development were such that T-cell development occurred between 60 to 100 days. Initial T-cell engraftment consisted predominantly of CD45RO+, CD3+, and CD4+ T cells, and at 12 to 24 months changed to CD45RA+, CD3+, and CD4+ T cells, indicatingde novomaturation of T cells. NK cell development occurred at approximately 180 days. B cells engrafted early, and study of functional B-cell antibody responses revealed that five of six patients in whom intravenous immune globulin has been discontinued have low detectable antibody responses to tetanus and diphtheria toxoid immunizations at 18 to 24 months posttransplantation.Unrelated umbilical donor cord blood is an alternative source of stem cells for transplantation in children with severe T-cell immune deficiency disorders when a suitable HLA-matched donor is not available and when a T-depleted haploidentical preparation is not beneficial. Benefits of UCB include rapid and reliable recovery of immune function, low risk of GvHD, and low viral transmission rate.     

Donor cell origin of multiple myeloma occurring after allogeneic haematopoietic stem cell transplantation in a patient with refractory anaemia with ring sideroblast

Post-transplant lymphoproliferative disorder (PTLD) is a rare but life-threatening complication after solid organ and haematopoietic stem cell transplantation. A 40-year-old woman who was diagnosed as having refractory anaemia with ring sideroblast 6 years ago took an ABO mismatched, unrelated allogeneic haematopoietic stem cell transplantation (HSCT) from a 32-year-old healthy male donor. The bone marrow (BM) study was carried out because of progressing pancytopenia, serum biclonal gammopathy and a distorted ratio of serum level of free κ and λ light chain 138 days after HSCT. The BM examination showed an increased number of plasma cells (12% of total marrow cells) comprising mainly CD45-CD19-CD138+ malignant plasma cells with an immunoglobulin heavy-chain gene rearrangement. Conventional cytogenetics and molecular personal identification studies revealed that all BM cells were totally replaced by donor cells, thus indicating the donor cell origin of PTLD-multiple myeloma. The BM microenvironment of the recipient might be associated with the development of PTLD-multiple myeloma.     

Unlicensed Umbilical Cord Blood Units Provide a Safe and Effective Graft Source for a Diverse Population: A Study of 2456 Umbilical Cord Blood Recipients

Umbilical cord blood (UCB) transplantation (UCBT) is a curative procedure for patients with hematologic malignancies and genetic disorders and expands access to transplantation for non-Caucasian patients unable to find a fully matched unrelated donor. In 2011, the US Food and Drug Administration required that unrelated UCBT be performed using either licensed UCB or unlicensed UCB under the Investigational New Drug (IND) program. The National Marrow Donor Program manages an IND under which 2456 patients (1499 adults and 957 children, 564 with malignant diseases and 393 with nonmalignant diseases) underwent single or double UCBT between October 2011 and December 2016. The median patient age was 31 years (range, <1 to 81 years), and 50% of children and 36% of adults were non-Caucasian. The median time to neutrophil engraftment (ie, absolute neutrophil count ≥500/mm³) was 22 days for adults, 20 days for pediatric patients with malignant diseases, and 19 days for pediatric patients with nonmalignant diseases, with corresponding rates of engraftment at 42 days of 89%, 88%, and 90%. In these 3 groups of patients, the incidence of acute graft-versus-host disease (GVHD) grade II-IV was 35%, 32%, and 24%; the incidence of chronic GVHD was 24%, 26%, and 24%; and 1-year overall survival (OS) was 57%, 71%, and 79%, respectively. In multivariate analysis, younger age, lower Hematopoietic Cell Transplantation-Specific Comorbidity Index, early-stage chemotherapy-sensitive disease, and higher performance score were predictive of improved OS for adults. In a subset analysis of children with malignancies undergoing single UCBT, the use of either licensed UCB (n = 48) or unlicensed UCB (n = 382) was associated with similar engraftment and survival. The use of unlicensed UCB units is safe and effective and provides an important graft source for a diverse population.     

Searching for unrelated donor hematopoietic stem cells: availability and speed of umbilical cord blood versus bone marrow.

Unrelated donor (URD) umbilical cord blood (UCB) has several potential advantages over URD BM for hematopoietic stem cell transplantation. To examine the efficiency of donor identification for each of these URD stem cell sources, we reviewed the search processes for all pediatric and adult URD transplantation referrals to the University of Minnesota during a period of 1 year. Of 171 consecutive referrals for URD transplantation, 108 patients proceeded to a formal URD search with selection of at least 1 donor. Significantly more formal UCB searches(54%) than BM searches (21%) were performed for patients who required urgent transplantation (P < .01). At least one 4-6/6 HLA-antigen matched UCB graft but no suitable BM graft was identified for 21 of the 108 patients (19%). The median time required to obtain a URD BM donor (from formal search to clearance of a BM donor) was 49 days (range, 32-293 days) compared to a UCB search time (from formal search to a donor unit chosen) of only 13.5 days (range, 2-387 days). For patients undergoing both BM and UCB searches, 29 more days (95% confidence interval, 21-37 days) were required to identify and clear a URD BM donor than a UCB donor (P < .01). For the 76 patients who proceeded to transplantation, patients receiving UCB received a transplant a median of 25 days more rapidly than did those receiving BM (P < .01). These data confirm that the availability of banked cryopreserved URD UCB grafts allows transplantations for patients with no available BM donor and that URD UCB grafts areavailable considerably faster than are URD BM grafts. Faster availability is a particular advantage for patients requiring urgent transplantation. These unique features of UCB transplantation must be considered in comparisons of the outcomes of UCB versus BM transplant recipients and in the design of prospective trials comparing URD sources.     

Umbilical cord blood transplantation in adults using myeloablative and nonmyeloablative preparative regimens.

Unrelated umbilical cord blood (UCB) transplantation has recently been explored in an increasing number of adult patients. The relative ease of procurement and the lower-than-anticipated risk of severe acute graft-versus-host disease has made UCB transplantation an appealing alternative to bone marrow-derived hematopoietic stem cells. The use of reduced-intensity or nonmyeloablative preparative regimens to allow engraftment of UCB broadens the scope of patients who may benefit from allogeneic immunotherapy, including elderly and medically infirm patients with no matched sibling donor. This review summarizes the available data on the use of UCB as an alternative source of hematopoietic stem cell transplantation in adult patients.     

Directed sibling cord blood banking for transplantation: the 10-year experience in the national blood service in England

Umbilical cord blood (UCB) is an important source of hematopoietic stem cells for transplantation. Although UCB is often collected from unrelated donors, directed umbilical cord blood (DCB) from sibling donors also provides an important source of UCB for transplantation. This report summarizes the experience in collection, testing, storage, and transplantation of DCB units by the National Blood Service for England and North Wales over 10 years. Eligibility for collection was based on an existing sibling suffering from a disease that may be treated by stem cell transplantation or a family history that could result in the birth of a sibling with a disease that could be treated by stem cell transplantation. Collections were made on the provision that the sibling's clinician was willing to financially support the collection and to take responsibility for medical review of the mother and potential recipient. Given the high investment in UCB banking and the introduction of new regulations and mandatory licensing under the European Union Tissues and Cells Directive and those proposed in the U.S., this report details the procedures that we have used for DCB donations, the outcome data where donations have been used for transplantation, and it provides some timely recommendations for best practices. Disclosure of potential conflicts of interest is found at the end of this article.     

A modified cord blood collection method achieves sufficient cell levels for transplantation in most adult patients

Umbilical cord blood transplantation (UCBT) has been used increasingly in both pediatric and adult patients. The total nucleated cell (NC) dose infused is the most critical factor in determining speed of engraftment and survival. Using standard collection techniques, the mean NC content of UCB units is about 10 x 10(8) and only 25% of these units reach the target cell dose of 2 x 10(7)/kg in UCBT patients weighing 50-70 kg. We have designed a modified placental/umbilical two-step collection method in which a standard blood fraction obtained by umbilical venipuncture is combined with a second fraction harvested after placental perfusion with 50 ml heparinized 0.9% saline. This second fraction contributed 32% volume and 15% NCs to the whole UCB unit (123.7 +/- 50.1 ml and 1.26 +/- 0.52 x 10(9) NC). The proportion of progenitor cells in both fractions was not significantly different, indicating that the hematopoietic potential of these larger units is 20% (range, 2%-100%) higher than UCB units collected by standard methods. In addition, the bacterial contamination rate associated with this novel collection method (2.78%) compares favorably. Since 1998 we have further enriched our units by processing only UCB units over 0.8 x 10(9) NCs, resulting in a 36% cell increment (1.46 +/- 0.52 x 10(9) NCs). Thus, 84% and 54% of the Madrid UCB Bank inventory would fulfill the target cell dose of 2 x 10(7)/kg in patients weighing 50 and 65 kg, respectively. This significant UCB banking improvement gives larger pediatric and adult patients a greater chance of finding adequate grafts in order to achieve better clinical outcomes after UCBT.     

Mobilization and collection of peripheral blood stem cells in healthy donors: Risks,adverse events and follow-up

Allogeneic haematopoietic stem cell transplantation is the choice treatment for many haematological malignancies. Granulocyte-colony-stimulating factor (G-CSF) has been widely used to mobilize stem cells into the peripheral blood from healthy siblings or volunteer unrelated donors. To a large extent, the use of mobilized peripheral blood haematopoietic stem cells has replaced marrow-derived stem cells as the preferred source of donor haematopoietic stem cells. Clinicians have been aware since the first clinical use, that administration of G-CSF, even in a single short course, could possibly be a risk for healthy donors either in short-term or as a delayed effect. The immediate side effects of G-CSF have been established for a long time, most of them are frequent but transient, self-limited and without long-term consequences. Questions have been raised about potential long-term adverse effects such as an elevated risk of haematological malignancies after G-CSF administration. More long-term safety data from registries are needed to adequately evaluate such a relationship. Our objective in this article is to provide an in-depth review of reported adverse events associated with the use of G-CSF in healthy donors and to focus attention on unanswered questions related to their long-term follow-up.     

Optimal Donor Selection: Beyond HLA

Worldwide >10 million adults and 250 000 cord blood units are available for unrelated HCT. HLA matching and, in the case of cord blood units, cell dose are critical determinants for selecting among these donors. Once a list of suitable adult donors or cord blood units is established, the transplantation physician must choose the optimal donor. We review factors that go into making that decision. We conclude that for adults the optimal donor is a male who is younger and has a larger body weight. When selecting among female adults, the optimal donor is also younger with a larger body weight and has never been pregnant. Additional factors, which can be considered and are relevant particularly for cord blood units, include family and medical histories, risk-exposure history, collection site characteristics, and geographic location.     

Characterization of long-term mixed donor�Cdonor chimerism after double cord blood transplantation

Double cord blood transplantation (DCBT) with two matched or partially matched cord blood units has been implemented successfully to circumvent the limitations of graft cell dose associated with single CBT. After DCBT, sustained haematopoiesis is derived almost exclusively from only one of the donated units. None the less, we previously observed two of six evaluable DCBT patients still having mixed donor–donor chimerism at 28 and 45 months post‐transplantation, respectively. In the present study we utilize flow cytometry techniques to perform the first thorough analysis of phenotype and functionality of cord blood units in patients with mixed donor–donor chimerism. Our results suggest that the two stable cord blood units are different phenotypically and functionally: one unit shows more naive T cells, lower T cell cytokine production and higher frequencies of natural killer cells, the other shows higher frequencies of well‐differentiated and functional lymphocytes. Additionally, in comparison with control patients having a single prevailing cord blood unit, the patients with donor–donor chimerism exhibit less overall T cell cytokine production and a smaller fraction of memory T cells. Furthermore, our results indicate that human leucocyte antigen‐C match of donor units may partly explain the development of a donor–donor mixed chimerism.