Umbilical cord blood transplantation: a maturing technology
Betul Oran
1and Elizabeth Shpall
11
Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas MD Anderson
Cancer Center, Houston, TX
The use of umbilical cord blood (CB) as a source of hematopoietic progenitor cells for patients with high-risk hematologic disorders receiving allogeneic hematopoietic cell transplantations (HCTs) has increased significantly. Single-institution and registry studies have shown a decreased relapse rate and an increased transplantation-related mortality rate with similar overall survival rates after allogeneic HCT with CB compared with other donor sources. The transplantation of double CB units has overcome the dose limitation inherent in a single CB unit and thus has markedly extended the use of CB to larger children and adults. Similarly, the use of reduced intensity conditioning in the CB transplantation setting has allowed the treatment of older patients who would be unable to tolerate the myeloablative regimens used in the original CB transplantation protocols.
Introduction
In recent years, there has been exciting progress in the use of umbilical cord blood (CB)– derived immune cells in the hematopoi-etic cell transplantation (HCT) setting. There are now several strategies designed to reduce graft-versus-host disease (GVHD) and to improve CB homing, engraftment, and immune reconstitution. These novel approaches will likely change the current application of CB transplantation (CBT) with the goal of producing even better clinical outcomes.
Only 30% of patients who need allogeneic HCT have a matched sibling donor. The National Marrow Donor Program (NMDP), which was established in 1986, and its cooperative international registries have 16 million volunteer donors.1It is estimated that 60%
of white patients, but only 20%-45% of African-American and other minority patients, will be able to find a suitably matched unrelated donor (MUD) and proceed to transplantation. Therefore, there are an estimated 5000 patients per year who are candidates for alternative donor HCT. Their options include mismatched related (often haploidentical), CB, or mismatched unrelated donors (MMUD).
Since the first CBT was performed in 19892to treat a child with
Fanconi anemia, CB has emerged as an alternative source of hematopoietic stem cells.3Expanding on the success in pediatric
CBT pioneered by Drs Kurtzberg, Gluckman, Wagner, Broxmeyer, and others,4,5 the field grew rapidly. As of 2011, more than
25 000 CBTs have been performed worldwide and more than 500 000 CB units have been donated for public use. CB is readily available and donors can be found for diverse patient populations.6
The use of CB for HCT provides some potential advantages compared with the use of bone marrow (BM) or mobilized peripheral blood progenitor cells (PBPCs). Advantages include ease of collection, with little to no risk to the mother or newborn; prompt availability, with patients receiving CBT a median of 25-36 days earlier than those receiving unrelated BM7; low risk of infection
transmission; decreased stringency of human leukocyte antigen (HLA)–matching requirements; and the relatively lower risk of GVHD with preserved graft-versus-malignancy effects. In contrast to BM or PBPCs, which generally require a high degree of HLA
match between donor and patient,8this reduced incidence of GVHD
with partially HLA-mismatched CB is likely due to the lower numbers of T cells and the relatively immunologically naive status of the lymphocytes in CB.9
CB is now an accepted source of allogeneic HCT. Figure 1 presents the growth in the number of BM transplantations, PBPC transplanta-tions, and CBTs facilitated by the NMDP worldwide in pediatric and adult patients over time.
CBT in pediatric patients
Although several studies have demonstrated a benefit of CBT in children with hematological malignancies,10-15the first prospective,
multicenter trial of CBT in 191 pediatric patients with hematologic malignancies was reported by Kurtzberg et al on behalf of the Cord Blood Transplantation Study (COBLT).16The overall survival (OS)
of the study population, 77% of whom had high-risk disease, was 57.3% at 1 year. Those results were compared favorably with those published from registry and single-center data showing disease-free survival (DFS) of 50%-60% in those with early-stage disease and
Figure 1. NMDP transplantations by hematopoietic cell source.In 2010, more than 1150 CBTs were facilitated by the NMDP, which represents 22% of the total number of NMDP transplantations in 2010.
10%-30% in those with more advanced and active disease. A landmark study was reported by Eapen et al on behalf of The Center for International Blood and Marrow Transplant Research (CIMBTR).17That study compared the outcomes of 503 children
under the age of 16 years with acute leukemia who had received transplantation with HLA-matched (4-6/6) CB with outcomes of 282 HLA-matched (7-8/8) unrelated donor BM recipients. CBT compared favorably to the gold standard of 8/8 allele-matched unrelated BM transplantation, supporting the use of HLA-matched or HLA-mismatched CBT in children with high-risk acute leukemia without a matched related donor (MRD). The recipients of 1-antigen– mismatched CB units with a lower cell dose had engraftment similar to 2-antigen–mismatched units, whereas 1-antigen–mismatched CB units with a higher cell dose had superior engraftment, indicating that cell dose partially compensated for the degree of HLA mismatch.
There has been an increasing interest on the use of CBT for the treatment of metabolic diseases, hemoglobinopathies, and immune deficiencies in children.18-22Kurtzberg et al has pioneered the use of
CBT with very encouraging preliminary results in children with inherited metabolic disorders,18,23 including Krabbe disease and
Hurler syndrome. Registry studies also showed acceptable out-comes after CBT in patients with severe combined immune deficiency compared with other donor sources.24
CBT in adults
The first large series of adults receiving CBT was reported by Laughlin et al in 2001.25 This analysis of 68 heavily pretreated
patients with advanced hematologic malignancies demonstrated the feasibility of performing CBTs after myeloablative conditioning (MAC) in adult patients, with an event-free survival (EFS) of 26%. Similar to what had been described in pediatric series, a higher cryopreserved nucleated cell dose (ⱖ2.4⫻107/kg) was associated
with faster and a higher probability of neutrophil recovery and a higher cryopreserved CD34⫹ cell dose (ⱖ1.2⫻105/kg) was
associated with a better EFS rate in this groundbreaking study. Neither patient age nor HLA matching appeared to influence EFS. Cornetta et al subsequently reported a 30% 6-month survival rate for the COBLT prospective study of 34 adult patients (median age, 34 years) who received MAC for advanced malignancies.26Over
time, results of CBTs have been improving. Two large registry studies compared disease outcomes for adults after CB or unrelated BM transplantation with MAC. Rocha et al observed similar leukemia free survival (LFS), transplantation related mortality (TRM) and relapse incidence despite delay of engraftment in CB recipients with acute leukemia who received MAC compared with results in recipients of MUD transplantations.27 Laughlin et al
observed higher TRM and shorter LFS with CB compared with 6 of 6 matched MUD, whereas the LFS was similar to 5/6 HLA-matched MUD.28None of those studies compared CB with PBPC
transplantations.
Recently, Eurocord and the CIBMTR performed a study comparing unrelated BM (n⫽472) or PBPC (n⫽888) transplantation with CB (n⫽165) HCT in adults with acute leukemia.29In that study,
allele-level HLA typing was performed for the adult donors at A, B, C, and DRB1 loci and either 8/8 and 7/8 matched donors were included. All CB units were HLA-typed at the antigen level for the A and B loci, with allele-level typing for DRB1. CB units matched at 4-6/6 loci were included. CB recipients received a single unit containing a minimum of 2.5⫻107 total nucleated cells/kg of
bodyweight at cryopreservation. Multiple regression analyses
re-vealed higher TRM but lower relapse and GVHD rates with CB, leading to comparable LFS rates compared with other stem cell sources (Figure 2). The results of this study and others confirmed that CBT is feasible in adults when a CB unit has a higher number of cells and should be considered an option for allogeneic HCT in patients lacking an HLA-matched donor.
Double CBT
The relatively low number of progenitor cells present in a single CB unit resulting in delayed hematopoietic recovery and an increased rate of engraftment failure initially limited the use of CBT in adults. The majority of adults do not have access to a single CB unit containing the recommended nucleated cell dose of 2.5⫻107/kg.30
To overcome the cell-dose limitation, Barker and the University of Minnesota investigators pioneered the use of double CBT (dCBT), sequentially infusing 2 CB units instead of 1 after conditioning therapy.31,32 These investigators initially reported the safety and
feasibility of dCBT in 21 adults with hematological malignancies after MAC HCT.31The results were encouraging, with all patients
engrafting neutrophils in a median of 23 days (range, 15-41). Interestingly, by day 21 in more than 80% of the patients, only 1 of the 2 CB units was detected and was responsible for the long-term hematopoiesis in those patients. In other studies, dominance of the “winning” unit as early as day 12 has also been reported.33,34 Figure 2. Probabilities of LFS by hemapoietic stem cell source and donor-recipient HLA match.The probabilities of LFS by hematopoietic stem cell source and donor-recipient HLA match for patients in remission at transplantation (A) and patients who were not in remission at transplantation (B) are shown. Reprinted with permission from Eapen et al.29
Ramirez et al showed that, in the myeloablative setting, CD3⫹cell dose was the only factor associated with unit predominance, but in the nonmyeloablative setting, CD3⫹cell dose and HLA match were independent factors associated with unit predominance.35Although
these findings suggest that immune reactivity may have a role in unit predominance, the biological mechanisms responsible for single-donor predominance after dCBT remain incompletely understood and are under investigation by many groups.
Another important observation after dCBT is the higher incidence of acute GVHD. MacMillan et al reported a higher rate of grade II-IV acute GVHD in recipients of dCBT (58%, n⫽185) compared with those of single CB units (39%, n⫽80) due to an increased rate of grade II skin GVHD.36The rates of grade III-IV GVHD were the
same for both groups and the 1-year TRM was significantly lower after dCBT compared with single CBT (24% vs 39%).
Rodrigues et al reported a significantly lower risk of relapse at 1 year after dCBT compared with single CB in a study of 104 adult patients with lymphoid malignancies (13% vs 38%).37Recently, a
study prospectively comparing single CBT versus dCBT in adult patients (assignment was based on the cell dose in the primary unit) confirmed previous findings of a lower relapse rate after dCBT versus single CBT (30.4% vs 59.3%).38The possible enhancement
of graft-versus-malignancy may be due to greater alloreactivity when 2 CB units are infused, but this finding requires confirmation and further mechanistic studies.
The risks and benefits of dCBT (n⫽128) relative to those observed after transplantations with MRD (n⫽204), MUD (n⫽152) or 1-antigen–MMUD (n⫽52) after MAC in leukemia patients were reported by the University of Minnesota in collaboration with the Fred Hutchinson Cancer Center.39Risk of relapse was significantly
lower in recipients of dCBT (15%) compared with MRD (43%), MUD (37%), and MMUD (35%) (Figure 3). However, TRM was higher for dCBT (34%) vs MRD (24%) and MUD (14%). LFS after dCBT was comparable to that observed after MRD and MUD transplantation, supporting the use of 2 partially HLA-matched CB units when patients lack an HLA-matched donor. Whether dCBT is preferable to single CBT when the cell dose in one unit is acceptable is not known. The ongoing Blood and Marrow Transplant Clinical Trials Network (BMT-CTN) 0501 study (www.clinicaltrials.gov number NCT00412360) has randomized children with leukemia to single CBT versus dCBT for MAC HCT and the results are eagerly awaited.
CBT after RIC regimens
The development of reduced-intensity conditioning (RIC) regimens was particularly important in extending HCT transplantation to adults. Barker et al reported that the fludarabine, cyclophosphamide, and low-dose total body irradiation (TBI) regimen40 was well
tolerated, with rapid neutrophil recovery, a sustained donor engraft-ment rate of 94%, and a low incidence of TRM. Rocha et al from the Eurocord Registry also reported similarly encouraging results using a RIC regimen of fludarabine, Endoxan, and TBI, with a 1-year
Figure 3. Clinical outcomes after myeloablative conditioning HCT by donor source. Clinical outcomes after dCBT, MRD, MUD, and MMUD transplantation. (A) LFS. (B) Relapse. (C) Nonrelapse mortality. (D) Neutrophil engraftment. (E) Platelet engraftment. (F) Grade 2-4 acute GVHD. Reprinted with permission from Brunstein et al.39
TRM of 24% and DFS of 50%.41Ballen et al used the RIC regimen
of fludarabine, melphalan, and rabbit antithymocyte globulin and reported a 1-year DFS of 67%.42Multiple studies supporting the use
of RIC CBT in patients who would not be able tolerate more intensive preparative regimens have subsequently been re-ported32,38,41-49and are summarized in Table 1.
Recently, CIBMTR compared the outcomes in adults with acute leukemia receiving dCBT (n⫽161) and 8/8 (n⫽313) or 7/8 (n⫽111) HLA-matched PBPCs after RIC regimens between the years 2000-2009.49 This analysis demonstrated comparable
out-comes of dCBT patients only if they were treated with TBI 200 cGy, cyclophosphamide and fludarabine (TCF). Higher TRM and lower OS and LFS were observed in recipients of dCBT if they were treated with alternative regimens. Noteworthy observations in-cluded: (1) TRM was not significantly different after dCBT-TCF and PBPC transplantations despite lower neutrophil recovery with dCBT, and (2) risk of relapse was not found to be different between stem cell sources after RIC HCT, although relapse incidence has been reported to be lower with dCBT in patients with acute leukemia after MAC.39 These results with single-center studies
supported the use of RIC CBT as a valuable strategy for broadening the application of transplantation therapy to those patients with leukemia and malignant disorders previously excluded on the basis of age, comorbidities, and the absence of an HLA MUD.
To study the reproducibility and the wider applicability of encourag-ing results after RIC dCBT and compare them with HLA-haploidentical related donor BM, the BMT-CTN completed 2 paral-lel phase 2 trials studying RIC alternative donor HCT.50 Fifty
patients were treated in each study; all patients received an RIC regimen of fludarabine, cyclophosphamide, and low-dose TBI. Nonrelapse mortality was higher after CBT (24% for CB vs 7% for haploidentical), but the relapse rate was higher after haploidentical HCT (31% for CB vs 45% for haploidentical). The 1-year progres-sion-free survival was comparable, at 46% for CBT and 48% for haploidentical HCT.
Novel strategies to improve CBT
Strategies under investigation to overcome the cell-dose limita-tion include the transplantalimita-tion of ex vivo– expanded CB units,51
direct intra-BM injection,52coinfusion of with a haploidentical
T cell–depleted graft,53,54the systemic addition of mesenchymal
stem cells (MSCs),55and the use of agents to enhance the homing
of CB to the BM.56
Improving CB engraftment
Ex vivo expansion of CB progenitors before infusion is being studied as a way to shorten time to engraftment and reduce the rate of engraftment failure. Robinson et al showed that coculture of CB cells with MSCs would yield to a 10- to 20-fold increase in total nucleated cells, a 7- to 18-fold increase in committed progenitor cells, and a 16- to 37-fold increase in CD34⫹cells.57Based on those
results, a clinical trial was initiated to evaluate the ex vivo coculture of CB mononuclear cells with either third-party haploidentical family member BM derived MSCs or off-the-shelf Stro3⫹MSCs from Mesoblastd patients (www.clinicaltrials.gov number NCT00498316). The results with either source of MSCs was similar, with prompt engraftment of neutrophils in 15 days and platelets in 40 days.58Long-term engraftment was provided by the
unexpanded unit in the majority of patients by 11 months after
Table 1. RIC regimens in CBT Reference N Disease Conditioning regimen Median age, y Median time to ANC ⬎ 500/ L, d Grade II-IV acute GVHD Chronic GVHD TRM at d 100 OS Barker 40 21 Hematological malignancies Bu/Flu/TBI 49 26 44%* 21%* 48% 39% at 1 y* 22 Cy/Flu/TBI 49 9.5 28% Miyakoshi 45 30 Hematological malignancies Flu/Mel/2-4 Gy TBI 59 18 27% 23% 27% 33% at 1 y Yuji 43 20 Lymphoma Flu/Mel/4 Gy TBI 47 20 8/15 2/11 41% 50% at 1 y Rocha 41 65 Hematological malignancies Various 47 20 27% NA 45% overall NA Brunstein 32 110 Hematological malignancies Cy/Flu/TBI ⫾ ATG 51 12 59% 23% 19% at 6 m o 45% at 3 y Miyakoshi 44 34 Hematological malignancies Flu/Mel/4 Gy TBI 57 20 45% 27% 12% 70% at 1 y Bradley 46 21 Malignant and benign hematological diseases Bu/Flu/ATG Cy/VP16/ATG 9 1 8 29% 17% 14% 60 % a t 5 y Ballen 42 21 Hematological malignancies Flu/Mel/ATG 49 20 40% 5/16 14% 71% at 2 y Cutler 47 32 Hematological malignancies Flu/Mel/ATG 53 21 9% 13% 13% 53% at 2 y Uchida 48 70 Hematological malignancies Flu/Mel/2-4 Gy TBI 61 18 61% 40% 30 of 70 23% at 2 y Kindwall-Keller 38 27 Hematological malignancies Cy/Flu/TBI/ATG single CB 50 25 19%† 22% 0 o f 2 7 36% at 3 y 23 Cy/Flu/TBI/ATG double CB 54 23 17%† 26% 7 o f 2 3 39% at 3 y Brunstein 49 121 Acute leukemia Cy/Flu/TBI ⫾ ATG 55 9 50% 34% 19% at 2 y 37% at 2 y 40 Various 48 20 33% 36% 21% at 2 y 19% at 2 y ANC indicates absolute neutrophil count; Bu, busulfan; Flu, fludarabine; Gy, Gray; Mel, melphalan; Cy, cyclophosphamide; TBI, total body irradiati on; ATG, antithymocyte globulin; VP16, etoposide; CB, cord blood; TRM, transplant-related mortality; OS, overall survival; and NA, not applicable. *The results were presented for the whole group. †Reported only grade III-IV acute GVHD.
transplantation. These results provide the rationale for a multina-tional randomized trial beginning soon that will compare unmanipu-lated dCBT with dCBT in which one of the units is expanded in MSC cocultures.
Similarly promising results have been reported by Delaney et al using Notch-mediated ex vivo expansion system for human CD34⫹ CB progenitors, with a decrease in the median time to neutrophil recovery by more than 1 week compared with results reported after infusion of 2 unmanipulated units.59The expanded cells contributed
almost exclusively to initial myeloid engraftment observed at 1 week, demonstrating an enhanced capacity of the expanded cell graft to provide rapid myeloid recovery. Furthermore, all but one evaluable subject engrafted before day 21 regardless of whether the expanded cell graft persisted in vivo.
A pivotal trial sponsored by Gamida Cell Ltd evaluated the ex vivo expansion of a fraction of a single CB unit using growth factors in conjunction with the copper chelator tetraethylenepentamine.60
Preliminary analysis revealed faster engraftment and improved survival compared with historical control recipients of single CBT reported to the international registries.51A more definitive analysis
of these data is in progress. In preclinical studies, CB CD34⫹cells cultured ex vivo with growth factors (SCF, thrombopoietin, IL-6, and FMS-related tyrosine kinase 3) and nicotinamide (pyridine-3-carboxamide) displayed increased migration toward SDF-1 and enhanced homing to BM compared with untreated CB.61A pilot
clinical trial led by Horwitz et al is in progress to evaluate this strategy in the dCBT setting (www.clinicaltrials.gov number NCT01221857). Preliminary analysis has shown rapid engraftment (10 days for neutrophils and 30 days for platelets) with, interest-ingly, sustained engraftment coming from the expanded unit in the majority of patients evaluated to date (personal communication with Dr Horwitz).
Improving CB homing to BM
Another strategy to improve engraftment is to correct the decreased fucosylation of CB cell-surface molecules, which is thought to impair homing of CB-derived progenitor cells to the BM.62 In
murine models, Robinson et al showed that CB CD34⫹cells treated with fucosyltransferase-VI led to more rapid and higher levels of engraftment.56A clinical trial in which recipients will receive dCBT
in which one of the CB units will be fucosylated before infusion was opened recently (www.clinicaltrials.gov number NCT01471067). In future trials, combining CB expansion with fucosylation may produce maximally rapid hematopoietic recovery in the patients. Prostaglandin E2 (PGE2) has been shown to enhance hematopoietic
stem cell homing, survival, and proliferation.63Based on these data,
Cutler et al are conducting a clinical trial to evaluate the ex vivo treatment of 1 of 2 CB units with dimethyl PGE2before infusion
(www.clinicaltrials.gov number NCT00890500). After optimizing the procedure, it appears that engraftment of neutrophils is prompt (17 days), with dominance of the dimethyl PGE2–modulated unit
documented in the majority of recipients.64
Broxmeyer et al have shown that inhibition of the CD34⫹ CB cell-surface protein CD26/dipeptidyl peptidase enhanced their en-graftment in sublethally irradiated NOD/SCID mice.65,66They are
conducting a pilot clinical trial of systemic sitagliptin, a United States Food and Drug Administration–approved CD26/dipeptidyl peptidase inhibitor for diabetes, to evaluate the potential for
enhancing engraftment in recipients of single CBT (www.clinical trials.gov number NCT00862719).
CB immune cells to improve outcome
CBT is associated with delayed immune reconstitution and a higher risk of morbidity and mortality due to viral and other infections after transplantation. GVHD remains a problem, particularly in the dCBT setting.36 Relapse is also of concern, particularly in high-risk
patients with disease before transplantation67 To address these
major obstacles to the widespread use of CBT, there are several exciting clinical studies in progress to evaluate several different CB-derived immune cells to improve survival.
CB-derived virus-specific cytotoxic T lymphocytes
Hanley et al developed a strategy using AD5f35pp65-transduced CB-derived antigen-presenting cells to generate autologous CB T cells specific for CMV and adenovirus.68Based on this approach,
a clinical trial led by Bollard et al at Baylor College of Medicine has been testing the use of CB-derived multivirus-specific T cells targeting EBV, CMV, and adenovirus for the prevention and treatment of viral infections after CBT (www.clinicaltrials.gov number NCT01017705).
CB-derived NK cells
Resting CB natural killer (NK) cells are reported to have signifi-cantly less cytotoxicity compared with peripheral blood NK cells.69
However, after cytokine stimulation, the cytotoxicity of CB NK cells can be rapidly increased to levels comparable to peripheral blood NK cells.70
A phase 2 trial using T cell–depleted dCBT with posttransplan-tation IL-2 is being conducted by the University of Minnesota investigators in refractory AML patients to investigate NK-cell expansion and function in vivo (www.clinicaltrials.gov number NCT01464359).
CB-derived Tregs
Regulatory T cells (Tregs) are a subset of CD4⫹ T cells that coexpress CD25 (IL-2R␣chain) and high levels of Foxp371and are
dependent on IL-2. Tregs represent a novel cell-based approach for potentially reducing the risk of GVHD.
Brunstein et al expanded Tregs obtained from a third CB unit and infused them into 23 patients undergoing dCBT.72 No severe
Treg-related acute toxicities were observed and accrual to the study continues, with refinements in the Treg-generation procedure.
Conclusions
CB is used increasingly as a source of allogeneic hematopoietic support for patients who need HCT and do not have access to an HLA-matched donor. To overcome the limitation of low cell doses in single CB units, dCBT has been adopted for many patients and is associated with outcomes comparable to those with other donor sources. There have been new strategies under development to improve engraftment with ex vivo expansion or homing and to enhance immune reconstitution with the infusion of CB-derived NK cells and cytotoxic T lymphocytes with antiviral and antileukemic specificities. Tregs are being evaluated to reduce the incidence of GVHD. Prospective, multicenter clinical trials are needed to determine the efficacy of these promising technologies that are likely to improve outcome for CBT patients.
Disclosures
Conflict-of-interest disclosure: The authors declare no competing financial interests. Off-label drug use: None disclosed.
Correspondence
Betul Oran, MD, MS, The University of Texas MD Anderson Cancer Center, Department of Stem Cell Transplant and Cell-ular Therapy, 1515 Holcombe Blvd, Unit #423, Houston, TX 77030; Phone: 713-745-2820; Fax: 713-794-4902; e-mail: boran@mdanderson.org.
References
1. Ballen KK, King RJ, Chitphakdithai P, et al. The national marrow donor program 20 years of unrelated donor hematopoi-etic cell transplantation.Biol Blood Marrow Transplant. 2008; 14:2-7.
2. Gluckman E, Broxmeyer HA, Auerbach AD, et al. Hematopoi-etic reconstitution in a patient with Fanconi’s anemia by means of umbilical-cord blood from an HLA-identical sibling.N Engl J Med. 1989;321:1174-1178.
3. Broxmeyer HE, Douglas GW, Hangoc G, et al. Human umbilical cord blood as a potential source of transplantable hematopoietic stem/progenitor cells.Proc Natl Acad Sci U S A. 1989;86:3828-3832.
4. Kurtzberg J, Laughlin M, Graham ML, et al. Placental blood as a source of hematopoietic stem cells for transplantation into unrelated recipients.N Engl J Med. 1996;335:157-166. 5. Wagner JE, Rosenthal J, Sweetman R, et al. Successful
transplantation of HLA-matched and HLA-mismatched umbili-cal cord blood from unrelated donors: analysis of engraftment and acute graft-versus-host disease.Blood.1996;88:795-802. 6. Barker JN, Byam CE, Kernan NA, et al. Availability of cord
blood extends allogeneic hematopoietic stem cell transplant access to racial and ethnic minorities. Biol Blood Marrow Transplant. 2010;16:1541-1548.
7. Barker JN, Krepski TP, DeFor TE, et al. Searching for unrelated donor hematopoietic stem cells: availability and speed of umbilical cord blood versus bone marrow.Biol Blood Marrow Transplant. 2002;8:257-260.
8. Petersdorf EW, Gooley TA, Anasetti C, et al. Optimizing outcome after unrelated marrow transplantation by comprehen-sive matching of HLA class I and II alleles in the donor and recipient.Blood.1998;92:3515-3520.
9. Garderet L, Dulphy N, Douay C, et al. The umbilical cord blood alphabeta T-cell repertoire: characteristics of a polyclonal and naive but completely formed repertoire.Blood. 1998;91:340-346.
10. Hu JY, Wang S, Zhu JG, et al. Expression of B7 costimulation molecules by colorectal cancer cells reducestumorigenicity and induces anti-tumor immunity.World J Gastroenterol. 1999;5: 147-151.
11. Locatelli F, Rocha V, Chastang C, et al. Factors associated with outcome after cord blood transplantation in children with acute leukemia. Eurocord-Cord Blood Transplant Group. Blood.
2009;93:3662-3671.
12. Michel G, Rocha V, Chevret S, et al. Unrelated cord blood transplantation for childhood acute myeloid leukemia: a Euro-cord Group analysis.Blood.2003;102:4290-4297.
13. Ohnuma K, Isoyama K, Ikuta K, et al. Cord blood transplanta-tion from HLA-mismatched unrelated donors as a treatment for children with haematological malignancies. Br J Haematol. 2001;112:981-987.
14. Gluckman E, Rocha V. Cord blood transplantation for children with acute leukaemia: a Eurocord registry analysis.Blood Cells Mol Dis. 2004;33:271-273.
15. Wall DA, Carter SL, Kernan NA, et al. Busulfan/melphalan/ antithymocyte globulin followed by unrelated donor cord blood transplantation for treatment of infant leukemia and leukemia in young children: the Cord Blood Transplantation study (COBLT) experience.Biol Blood Marrow Transplant. 2005;11:637-646. 16. Kurtzberg J, Prasad VK, Carter SL, et al. Results of the Cord Blood Transplantation Study (COBLT): clinical outcomes of unrelated donor umbilical cord blood transplantation in pediat-ric patients with hematologic malignancies.Blood.2008;112: 4318-4327.
17. Eapen M, Rubinstein P, Zhang MJ, et al. Outcomes of transplantation of unrelated donor umbilical cord blood and bone marrow in children with acute leukaemia: a comparison study.Lancet. 2007;369:1947-1954.
18. Escolar ML, Poe MD, Provenzale JM, et al. Transplantation of umbilical-cord blood in babies with infantile Krabbe’s disease.
N Engl J Med. 2005;352:2069-2081.
19. Staba SL, Escolar ML, Poe M, et al. Cord-blood transplants from unrelated donors in patients with Hurler’s syndrome.
N Engl J Med. 2004;350:1960-1969.
20. Kamani NR, Walters MC, Carter S, et al. Unrelated donor cord blood transplantation for children with severe sickle cell disease: results of one cohort from the phase II Study from the Blood and Marrow Transplant Clinical Trials Network (BMT CTN).Biol Blood Marrow Transplant. 2012;18(8):1265–1272. 21. Adamkiewicz TV, Szabolcs P, Haight A, et al. Unrelated cord blood transplantation in children with sickle cell disease: review of four-center experience.Pediatr Transplant. 2007;11: 641-644.
22. Knutsen AP, Wall DA. Umbilical cord blood transplantation in severe T-cell immunodeficiency disorders: two-year experi-ence.J Clin Immunol. 2000;20:466-476.
23. Prasad VK, Mendizabal A, Parikh SH, et al. Unrelated donor umbilical cord blood transplantation for inherited metabolic disorders in 159 pediatric patients from a single center: influence of cellular composition of the graft on transplantation outcomes.Blood.2008;112:2979-2989.
24. Fernandes JF, Rocha V, Labopin M, et al. Transplantation in patients with SCID: mismatched related stem cells or unrelated cord blood?Blood.2012;119:2949-2955.
25. Laughlin MJ, Barker J, Bambach B, et al. Hematopoietic engraftment and survival in adult recipients of umbilical-cord blood from unrelated donors.N Engl J Med. 2001;344:1815-1822.
26. Cornetta K, Laughlin M, Carter S, et al. Umbilical cord blood transplantation in adults: results of the prospective Cord Blood Transplantation (COBLT). Biol Blood Marrow Transplant. 2005;11:149-160.
27. Rocha V, Labopin M, Sanz G, et al. Transplants of umbilical-cord blood or bone marrow from unrelated donors in adults with acute leukemia.N Engl J Med. 2004;351:2276-2285. 28. Laughlin MJ, Eapen M, Rubinstein P, et al. Outcomes after
transplantation of cord blood or bone marrow from unrelated donors in adults with leukemia.N Engl J Med. 2004;351:2265-2275.
29. Eapen M, Rocha V, Sanz G, et al. Effect of graft source on unrelated donor haemopoietic stem-cell transplantation in adults with acute leukaemia: a retrospective analysis.Lancet Oncol. 2010;11:653-660.
transplantation: HLA matching, cell dose and other graft- and transplantation-related factors.Br J Haematol. 2009;147:262-274.
31. Barker JN, Weisdorf DJ, DeFor TE, et al. Transplantation of 2 partially HLA-matched umbilical cord blood units to enhance engraftment in adults with hematologic malignancy. Blood.
2005;105:1343-1347.
32. Brunstein CG, Barker JN, Weisdorf DJ, et al. Umbilical cord blood transplantation after nonmyeloablative conditioning: im-pact on transplantation outcomes in 110 adults with hemato-logic disease.Blood.2007;110:3064-3070.
33. Delaney C, Gutman JA, Appelbaum FR. Cord blood transplan-tation for haematological malignancies: conditioning regimens, double cord transplant and infectious complications. Br J Haematol. 2009;147:207-216.
34. Gutman JA, Turtle CJ, Manley TJ, et al. Single-unit dominance after double-unit umbilical cord blood transplantation coincides with a specific CD8⫹T-cell response against the nonengrafted unit.Blood.2010;115:757-765.
35. Ramirez P, Wagner JE, Defor TE, et al. Factors predicting single-unit predominance after double umbilical cord blood transplantation.Bone Marrow Transplant. 2012;47:799-803. 36. MacMillan ML, Weisdorf DJ, Brunstein CG, et al. Acute
graft-versus-host disease after unrelated donor umbilical cord blood transplantation: analysis of risk factors.Blood.2009;113: 2410-2415.
37. Rodrigues CA, Sanz G, Brunstein CG, et al. Analysis of risk factors for outcomes after unrelated cord blood transplantation in adults with lymphoid malignancies: a study by the Eurocord-Netcord and lymphoma working party of the European group for blood and marrow transplantation.J Clin Oncol. 2009;27: 256-263.
38. Kindwall-Keller TL, Hegerfeldt Y, Meyerson HJ, et al. Prospec-tive study of one- vs two-unit umbilical cord blood transplanta-tion following reduced intensity conditransplanta-tioning in adults with hematological malignancies.Bone Marrow Transplant. 2012; 47(7):924 –933.
39. Brunstein CG, Gutman JA, Weisdorf DJ, et al. Allogeneic hematopoietic cell transplantation for hematologic malignancy: relative risks and benefits of double umbilical cord blood.
Blood.2010;116:4693-4699.
40. Barker JN, Weisdorf DJ, DeFor TE, et al. Rapid and complete donor chimerism in adult recipients of unrelated donor umbili-cal cord blood transplantation after reduced-intensity condition-ing.Blood.2003;102:1915-1919.
41. Rocha V, Rio B, Garnier F, et al. Reduced intensity condition-ing regimen in scondition-ingle unrelated cord blood transplantation in adults with hematological malignant disorders. A Eurocord-Netcord and SFGM-TC Survey [abstract].Blood(ASH Annual Meeting Abstracts).2006;108(11):3143.
42. Ballen KK, Spitzer TR, Yeap BY, et al. Double unrelated reduced-intensity umbilical cord blood transplantation in adults.
Biol Blood Marrow Transplant. 2007;13:82-89.
43. Yuji K, Miyakoshi S, Kato D, et al. Reduced-intensity unrelated cord blood transplantation for patients with advanced malignant lymphoma.Biol Blood Marrow Transplant. 2005;11:314-318. 44. Miyakoshi S, Kami M, Tanimoto T, et al. Tacrolimus as prophylaxis for acute graft-versus-host disease in reduced intensity cord blood transplantation for adult patients with advanced hematologic diseases.Transplantation. 2007;84:316-322.
45. Miyakoshi S, Yuji K, Kami M, et al. Successful engraftment after reduced-intensity umbilical cord blood transplantation for
adult patients with advanced hematological diseases. Clin Cancer Res. 2004;10:3586-3592.
46. Bradley MB, Satwani P, Baldinger L, et al. Reduced intensity allogeneic umbilical cord blood transplantation in children and adolescent recipients with malignant and non-malignant dis-eases.Bone Marrow Transplant. 2007;40:621-631.
47. Cutler C, Stevenson K, Kim HT, et al. Double umbilical cord blood transplantation with reduced intensity conditioning and sirolimus-based GVHD prophylaxis.Bone Marrow Transplant. 2011;46:659-667.
48. Uchida N, Wake A, Takagi S, et al. Umbilical cord blood transplantation after reduced-intensity conditioning for elderly patients with hematologic diseases.Biol Blood Marrow Trans-plant. 2008;14:583-590.
49. Brunstein CG, Eapen M, Ahn KW, et al. Reduced intensity conditioning transplantation in acute leukemia: the effect of source of unrelated donor stem cells on outcomes. Blood.
2012;119(23):5591–5598.
50. Brunstein CG, Fuchs EJ, Carter SL, et al. Alternative donor transplantation after reduced intensity conditioning: results of parallel phase 2 trials using partially HLA-mismatched related bone marrow or unrelated double umbilical cord blood grafts.
Blood.2011;118:282-288.
51. de Lima M, McMannis J, Gee A, et al. Transplantation of ex vivo expanded cord blood cells using the copper chelator tetraethylenepentamine: a phase I/II clinical trial.Bone Marrow Transplant. 2008;41:771-778.
52. Frassoni F, Gualandi F, Podesta M, et al. Direct intrabone transplant of unrelated cord-blood cells in acute leukaemia: a phase I/II study.Lancet Oncol. 2008;9:831-839.
53. Ferna´ndez MN, Regidor C, Cabrera R, et al. Unrelated umbili-cal cord blood transplants in adults: Early recovery of neutro-phils by supportive co-transplantation of a low number of highly purified peripheral blood CD34⫹ cells from an HLA-haploidentical donor.Exp Hematol. 2003;31:535-544. 54. Bautista G, Cabrera JR, Regidor C, et al. Cord blood transplants
supported by co-infusion of mobilized hematopoietic stem cells from a third-party donor.Bone Marrow Transplant. 2009;43: 365-373.
55. Macmillan ML, Blazar BR, DeFor TE, et al. Transplantation of ex-vivo culture-expanded parental haploidentical mesenchymal stem cells to promote engraftment in pediatric recipients of unrelated donor umbilical cord blood: results of a phase I-II clinical trial.Bone Marrow Transplant. 2009;43:447-454. 56. Robinson SN, Simmons PJ, Thomas MW, et al. Ex vivo
fucosylation improves human cord blood engraftment in NOD-SCID IL-2Rgamma(null) mice.Exp Hematol. 2012;40(6):445– 456.
57. Robinson SN, Ng J, Niu T, et al. Superior ex vivo cord blood expansion following co-culture with bone marrow-derived mesenchymal stem cells.Bone Marrow Transplant. 2006;37: 359-366.
58. de Lima M, Robinson S, McManins J, et al. Mesenchymal stem cells (MSC) based cord blood (CB) expansin (Exp) leads to rapid engraftment of platelets and neutrophils [abstract].Blood
(ASH Annual Meeting Abstracts).2010;116(21):362.
59. Delaney C, Heimfeld S, Brashem-Stein C, et al. Notch-mediated expansion of human cord blood progenitor cells capable of rapid myeloid reconstitution.Nat Med. 2010;16:232-236.
60. Peled T, Mandel J, Goudsmid RN, et al. Pre-clinical develop-ment of cord blood-derived progenitor cell graft expanded ex
vivo with cytokines and the polyamine copper chelator tetraeth-ylenepentamine.Cytotherapy. 2004;6:344-355.
61. Peled A, Adi S, Peleg I, et al. Nicotinamide modulates ex-vivo expansion of cord blood derived CD34⫹ cells cultured with cytokines and promotes their homing and engraftment in SCID mice [abstract].Blood(ASH Annual Meeting Abstracts).2006; 108(11):725.
62. Xia L, McDaniel JM, Yago T, et al. Surface fucosylation of human cord blood cells augments binding to P-selectin and E-selectin and enhances engraftment in bone marrow.Blood.
2004;104:3091-3096.
63. Hoggatt J, Singh P, Sampath J, et al. Prostaglandin E2 enhances hematopoietic stem cell homing, survival, and proliferation.
Blood.2009;113:5444-5455.
64. Cutler CS, Shoemaker D, Ballen KK, et al. FT1050 (16,16-dimethyl Prostaglandin E2)-enhanced umbilical cord blood accelerates hematopoietic engraftment after reduced intensity conditioning and double umbilical cord blood transplantation [abstract]. Blood (ASH Annual Meeting Abstracts). 2011; 118(21):653.
65. Christopherson KW 2nd, Hangoc G, Broxmeyer HE: Cell surface peptidase CD26/dipeptidylpeptidase IV regulates CXCL12/stromal cell-derived factor-1 alpha-mediated che-motaxis of human cord blood CD34⫹progenitor cells.J Immu-nol. 2002;169:7000-7008.
66. Christopherson KW 2nd, Hangoc G, Mantel CR, et al.
Modula-tion of hematopoietic stem cell homing and engraftment by CD26.Science.2004;305:1000-1003.
67. Oran B, Wagner JE, DeFor TE, et al. Effect of conditioning regimen intensity on acute myeloid leukemia outcomes after umbilical cord blood transplantation. Biol Blood Marrow Transplant. 2011;17:1327-1334.
68. Hanley PJ, Cruz CR, Savoldo B, et al. Functionally active virus-specific T cells that target CMV, adenovirus, and EBV can be expanded from naive T-cell populations in cord blood and will target a range of viral epitopes.Blood. 2009;114:1958-1967.
69. Verneris MR, Miller JS. The phenotypic and functional charac-teristics of umbilical cord blood and peripheral blood natural killer cells.Br J Haematol. 2009;147:185-191.
70. Xing D, Ramsay AG, Gribben JG, et al. Cord blood natural killer cells exhibit impaired lytic immunological synapse formation that is reversed with IL-2 ex vivo expansion.
J Immunother. 2010;33:684-696.
71. Godfrey WR, Spoden DJ, Ge YG, et al. Cord blood CD4(⫹)CD25(⫹)-derived T regulatory cell lines express FoxP3 protein and manifest potent suppressor function.Blood.2005; 105:750-758.
72. Brunstein CG, Miller JS, Cao Q, et al. Infusion of ex vivo expanded T regulatory cells in adults transplanted with umbili-cal cord blood: safety profile and detection kinetics. Blood.
