Creation of a double chimera after the transplantation of umbilical-cord blood from two partially matched unrelated donors

A new beginning: can omidubicel emerge as the next, viable alternative donor source?

Umbilical cord blood (UCB) transplantation (CBT) has been an important alternative donor option for patients lacking matched related donor (MRD) or unrelated donor (URD) grafts. Only 30% of patients with high-risk hematologic malignancies have a human leukocyte antigen (HLA)-identical sibling; subjects without a MRD option are referred for HLA-matched URD selection, or utilize alternative donor sources such as HLA-mismatched URD, UCB, or haploidentical donor grafts. While CBT demonstrates an excellent graft-versus-leukemia (GVL) effect, use of UCB as a graft source is limited due to a lower cell dose that can result in delayed engraftment and an immature immune system with increased infectious risk as a consequence. Together, increased transplant related mortality (TRM) has been associated with UCB allografts. Omidubicel is an ex vivo expanded single cord blood product that has demonstrated rapid engraftment, improved immune reconstitution, and reduced infectious complications in clinical trials. Omidubicel has now been granted U.S. Food & Drug Administration approval to enhance neutrophil recovery and decrease infectious risk. This review will focus on CBT, benefits and barriers to using this alternative donor source, and finally the potential advancements with incorporation of omidubicel in the transplant setting for malignant and non-malignant diseases.

Haploidentical versus Double-Cord Blood Stem Cells as a Second Transplantation for Relapsed Acute Myeloid Leukemia

There are limited data on second stem cell transplantation (SCT2) outcomes with alternative donors for relapsed AML after the first stem cell transplantation (SCT1). We analyzed the outcomes of 52 adult AML patients who received SCT2 from haploidentical donors (HIT, N = 32) and double-cord blood (dCBT, N = 20) between 2008 and 2021. The HIT group received T-cell-replete peripheral blood stem cells after reduced-toxicity conditioning with anti-thymocyte globulin (ATG), while the dCBT group received myeloablative conditioning. For a median follow-up of 64.9 months, the HIT group, compared to the dCBT group, had earlier engraftment, superior 2-year overall survival (OS), disease-free survival (DFS), and non-relapse mortality (NRM) with similar relapse. Multivariate analysis demonstrated that HIT was significantly associated with better OS, DFS, and lower NRM than dCBT. Both longer remission duration after SCT1 and complete remission at SCT2 were significantly associated with a lower relapse rate. In addition, bone marrow WT1 measurable residual disease (MRD) positivity was significantly associated with inferior OS and higher relapse. This study suggests that T-cell-replete HIT with ATG-based GVHD prophylaxis may be preferred over dCBT as SCT2 for relapsed AML and that WT1-MRD negativity may be warranted for better SCT2 outcomes.

Incidence and risk factors for graft failure in the modern era of cord blood transplantation

BACKGROUND AND OBJECTIVES

Graft failure (GF) after cord blood transplant (CBT) has decreased with improved supportive care and cord selection strategies. We aimed to evaluate cord blood selection and factors associated with retransplantation on the incidence of GF, determine risk factors for GF including host antibodies to Kell antigen and evaluate survival after GF.

MATERIALS AND METHODS

We retrospectively reviewed 84 patients who underwent CBT at the University of Oklahoma between 2000 and 2016 and compared outcomes in patients with/without engraftment by Day 28. The nonengraftment cohort was further divided into patients who underwent retransplantation. Kaplan-Meier curves with log-rank tests were calculated to assess the association between mortality and engraftment.

RESULTS

Engraftment following CBT was high at 81%, with 52% engrafting by Day 28 and an additional 29% engrafting by a median of 36 days. Retransplantation led to 88% engraftment at a median of 53 days. Overall, 75% of the 40 patients who did not engraft by Day 28 died. Female sex and total nucleated cell count < 3.5/kg were significantly associated with lack of engraftment and higher mortality. Antibodies to Kell fetal antigen were not identified. Retransplantation by Day 28 for primary GF conferred a survival advantage.

CONCLUSION

This study demonstrates that failure to engraft by 28 days was associated with increased mortality, and risk was mitigated with early retransplantation. Female sex and low total cell dose were associated with increased mortality. Early identification of GF coupled with early retransplantation can reduce mortality in CBT.

Evolving therapies in neuronopathic LSDs: opportunities and challenges

Lysosomal storage disorders (LSD) are multisystemic progressive disorders caused by genetic mutations involving lysosomal function. While LSDs are individually considered rare diseases, the overall true prevalence of these disorders is likely higher than our current estimates. More than two third of the LSDs have associated neurodegeneration and the neurological phenotype often defines the course of the disease and treatment outcomes. Addressing the neurological involvement in LSDs has posed a significant challenge in the rapidly evolving field of therapies for these diseases. In this review, we summarize current approaches and clinical trials available for patients with neuronopathic lysosomal storage disorders, exploring the opportunities and challenges that have emerged with each of these.

Umbilical cord blood transplantation: Still growing and improving

Umbilical cord blood transplantation (UCBT) has been performed in the clinic for over 30 years. The biological and immunological characteristics of umbilical cord blood (UCB) have been re-recognized in recent years. UCB, previously considered medical waste, is rich in hematopoietic stem cells (HSCs), which are naïve and more energetic and more easily expanded than other stem cells. UCB has been identified as a reliable source of HSCs for allogeneic hematopoietic stem cell transplantation (allo-HSCT). UCBT has several advantages over other methods, including no harm to mothers and donors, an off-the-shelf product for urgent use, less stringent HLA match, lower incidence and severity of chronic graft-vs-host disease (GVHD), and probably a stronger graft-vs-leukemia effect, especially for minimal residual disease-positive patients before transplant. Recent studies have shown that the outcome of UCBT has been improved and is comparable to other types of allo-HSCT. Currently, UCBT is widely used in malignant, nonmalignant, hematological, congenital and metabolic diseases. The number of UCB banks and transplantation procedures increased exponentially before 2013. However, the number of UCBTs increased steadily in Asia and China but decreased in the United States and Europe year-on-year from 2013 to 2019. In this review, we focus on the development of UCBT over the past 30 years, the challenges it faces and the strategies for future improvement, including increasing UCB numbers, cord blood unit selection, conditioning regimens and GVHD prophylaxis for UCBT, and management of complications of UCBT.

CNS-Targeting Therapies for Lysosomal Storage Diseases: Current Advances and Challenges

During the past decades, several therapeutic approaches have been developed and made rapidly available for many patients afflicted with lysosomal storage disorders (LSDs), inborn organelle disorders with broad clinical manifestations secondary to the progressive accumulation of undegraded macromolecules within lysosomes. These conditions are individually rare, but, collectively, their incidence ranges from 1 in 2,315 to 7,700 live-births. Most LSDs are manifested by neurological symptoms or signs, including developmental delay, seizures, acroparesthesia, motor weakness, and extrapyramidal signs. The chronic and later-onset clinical forms are at one end of the continuum spectrum and are characterized by a subtle and slow progression of neurological symptoms. Due to its inherent physiological properties, unfortunately, the blood-brain barrier (BBB) constitutes a significant obstacle for current and upcoming therapies to achieve the central nervous system (CNS) and treat neurological problems so prevalent in these conditions. To circumvent this limitation, several strategies have been developed to make the therapeutic agent achieve the CNS. This narrative will provide an overview of current therapeutic strategies under development to permeate the BBB, and address and unmet need for treatment of the progressive neurological manifestations, which are so prevalent in these inherited lysosomal disorders.

Short-Term exposure of umbilical cord blood CD34+ cells to human platelet lysate and cytokines enhances engraftment

BACKGROUND

Intra bone marrow (IBM) injection has been proposed as a strategy to bypass homing inefficiencies associated with intravenous (IV) hematopoietic progenitor stem cell (HSPC) transplantation and thus increases the number of HSPC that engraft. Despite physical delivery into the bone marrow cavity, many donor cells are rapidly redistributed by vascular perfusion. Thus, the objective of our study was to evaluate the ability of human platelet lysates (hPL) to improve HSPC retention into the bone marrow and consequently to improve engraftment.

STUDY DESIGN AND METHODS

HSPC were isolated from human umbilical cord blood. HSPC were seeded in the wells of a 24-well microplate and exposed to increasing concentrations of hPL with or without cytokines for 24 hours. Following priming, HSPC cells chemotaxis to rhSDF-1 was determined in vitro and engraftment in NSG mice was evaluated.

RESULTS

Priming of cord blood CD34+ cells to a combination of hPL and cytokines resulted in a significant increase (up to 3-fold) in the expression of the CD34 antigen on HSPC. This effect was closely correlated to a significantly increased (up to 7-fold) migration toward a rhSDF-1 concentration gradient. In addition, IBM injection of CD34+ cells previously primed with hPL+cytokines into NSG mice showed significantly increased engraftment as measured by human platelet numbers, human CD45 and human CD34+ cells for unprimed and primed cells, respectively.

CONCLUSION

The use of hPL + cytokines as a short-term priming treatment for UCB could be an advantageous strategy to improve clinical outcomes following IBM injection.

Cord blood research, banking, and transplantation: achievements, challenges, and perspectives

The first hematopoietic transplant in which umbilical cord blood (UCB) was used as the source of hematopoietic cells was performed in October 1988. Since then, significant achievements have been reported in terms of our understanding of the biology of UCB-derived hematopoietic stem (HSCs) and progenitor (HPCs) cells. Over 40,000 UCB transplants (UCBTs) have been performed, in both children and adults, for the treatment of many different diseases, including hematologic, metabolic, immunologic, neoplastic, and neurologic disorders. In addition, cord blood banking has been developed to the point that around 800,000 units are being stored in public banks and more than 4 million units in private banks worldwide. During these 30 years, research in the UCB field has transformed the hematopoietic transplantation arena. Today, scientific and clinical teams are still working on different ways to improve and expand the use of UCB cells. A major effort has been focused on enhancing engraftment to potentially reduce risk of infection and cost. To that end, we have to understand in detail the molecular mechanisms controlling stem cell self-renewal that may lead to the development of ex vivo systems for HSCs expansion, characterize the mechanisms regulating the homing of HSCs and HPCs, and determine the relative place of UCBTs, as compared to other sources. These challenges will be met by encouraging innovative research on the basic biology of HSCs and HPCs, developing novel clinical trials, and improving UCB banking both in the public and private arenas.

Delayed immune reconstitution after allogeneic transplantation increases the risks of mortality and chronic GVHD

Slow immune reconstitution is a major obstacle to the successful use of allogeneic hematopoietic cell transplantation (allo-HCT). As matched sibling donor (MSD) allo-HCT is regarded as the gold standard, we evaluated the pace of immune reconstitution in 157 adult recipients of reduced-intensity conditioning followed by MSD peripheral blood HCT (n = 68) and compared these to recipients of umbilical cord blood (UCB; n = 89). At day 28, UCB recipients had fewer natural killer (NK) cells than MSD recipients, but thereafter, NK cell numbers (and their subsets) were higher in UCB recipients. During the first 6 months to 1 year after transplant, UCB recipients had slower T-cell subset recovery, with lower numbers of CD3⁺, CD8⁺, CD8⁺ naive, CD4⁺ naive, CD4⁺ effector memory T, regulatory T, and CD3⁺CD56⁺ T cells than MSD recipients. Notably, B-cell numbers were higher in UCB recipients from day 60 to 1 year. Bacterial and viral infections were more frequent in UCB recipients, yet donor type had no influence on treatment-related mortality or survival. Considering all patients at day 28, lower numbers of total CD4⁺ T cells and naive CD4⁺ T cells were significantly associated with increased infection risk, treatment-related mortality, and chronic graft-versus-host disease (GVHD). Patients with these characteristics may benefit from enhanced or prolonged infection surveillance and prophylaxis as well as immune reconstitution-accelerating strategies.

Stable mixed double donor chimerism: Absence of war doesn't necessarily mean peace

Double cord blood transplantation has successfully been introduced to remedy the obstacle of a limited stem cell dose in a single cord blood graft. After a short initial period, the sustained hematopoiesis is derived almost exclusively from one of the donated units. In a recent publication in Clinical and Experimental Immunology we investigated two rare individuals in which both cord blood units co-existed for more than two years after transplantation.

Impact of Graft-Versus-Graft Natural Killer Cell Alloreactivity on Single Unit Dominance After Double Umbilical Cord Blood Transplantation

BACKGROUND

Natural killer (NK) cell alloreactivity is favored after double umbilical cord blood transplantation (dUCBT) in which cord blood (UCB) units and patients are often HLA class I mismatched. Generally, only 1 UCB unit persists after dUCBT. We hypothesize, that NK cell alloreactivity mediated by killer cell immunoglobulin-like receptor (KIR)-HLA interactions may explain the dominance of 1UCB unit over the other after dUCBT.

METHODS

We investigated the impact of KIR NK cell alloreactivities on the dominance of 1 full UCB unit in 50 dUCBT. We analyzed the effects of the KIR/HLA genetic incompatibilities and studied cord blood cells at both the phenotypic and functional levels.

RESULTS

The genetic combination of KIR3DL1 loser UCB unit/Bw4 winner UCB unit determined both the dominance of 1 UCB unit (hazards ratio, 2.88 [1.32-6.27], P = 0.0077) and correlated with an increased incidence of relapse (hazards ratio, 4.91 [1.39-17.3], P = 0.0134). It is interesting to note that cord blood cells exhibited extremely low HLA class I expression. Moreover, resting cord blood KIR3DL1 NK cells exhibited a basal alloreactivity against Bw4 target cells that increased upon activation, thus triggering death by apoptosis.

CONCLUSIONS

Our unicentric study suggests, for the first time, the significant impact of KIR NK cell alloreactivity in the determination of which UCB unit will dominate in dUCBT.

Directing Stem Cell Fate: The Synthetic Natural Product Connection

Stem cells possess remarkable potential for the treatment of a broad array of diseases including many that lack therapeutic options. However, the use of cell-based products derived from stem cells as therapeutics has limitations including rejection, sufficient availability, and lack of appropriate engraftment. Chemical control of stem cells provides potential solutions for overcoming many of the current limitations in cell-based therapeutics. The development of exogenous molecules to control stem cell self-renewal or differentiation has arrived at natural product-based agents as an important class of modulators. The ex vivo production of cryopreserved cellular products for use in tissue repair is a relatively new area of medicine in which the conventional hurdles to implementing chemicals to effect human health are changed. Translational challenges centered on chemistry, such as pharmacokinetics, are reduced. Importantly, in many cases the desired human tissues can be evaluated against new chemicals, and approaches to cellular regulation can be validated in the clinically applicable system. As a result linking new and existing laboratory syntheses of natural products with findings of the compounds' unique abilities to regulate stem cell fate provides opportunities for developing improved methods for tissue manufacture, accessing probe compounds, and generating new leads that yield manufactured cells with improved properties. This review provides a summary of natural products that have shown promise in controlling stem cell fate and which have also been fully synthesized thereby providing chemistry platforms for further development.

Phase II study of intrabone single unit cord blood transplantation for hematological malignancies

The outcomes of cord blood transplantation with non‐irradiated reduced‐intensity conditioning for hematological malignancies need to be improved because of graft failure and delayed engraftment. Intrabone infusion of cord blood cells has the potential to resolve the problems. In this phase II study, 21 adult patients with hematological malignancy received intrabone transplantation of serological HLA‐A, B, and DR ≥4/6 matched single cord blood with a median number of cryopreserved total nucleated cells of 2.7 × 10⁷/kg (range, 2.0–4.9 × 10⁷/kg) following non‐irradiated fludarabine‐based reduced‐intensity conditioning. Short‐term methotrexate and tacrolimus were given as graft‐versus‐host disease prophylaxis, and granulocyte colony‐stimulating factor was given after transplantation. No severe adverse events related to intrabone injection were observed. The cumulative incidences of neutrophils ≥0.5 × 10⁹/L, reticulocytes ≥1%, and platelets ≥20 × 10⁹/L recoveries were 76.2%, 71.4%, and 76.2%, respectively, with median time to recoveries of 17, 28, and 32 days after transplantation, respectively. The probability of survival with neutrophil engraftment on day 60 was 71.4%, and overall survival at 1 year after transplantation was 52.4%. The incidences of grade II–IV and III–IV acute graft‐versus‐host disease were 44% and 19%, respectively, with no cases of chronic graft‐versus‐host disease. The present study showed the safety of direct intrabone infusion of cord blood. Further analysis is required to confirm the efficacy of intrabone single cord blood transplantation with non‐irradiated reduced‐intensity conditioning for adult patients with hematological malignancy. This study was registered with UMIN‐CTR, number 000000865.

Outcomes of UCB transplantation are comparable in FLT3+ AML: results of CIBMTR, EUROCORD and EBMT collaborative analysis

Allogeneic hematopoietic cell transplantation (HCT) from siblings or unrelated donors (URD) during complete remission (CR) may improve leukemia-free survival (LFS) in FLT3+ acute myeloid leukemia (AML) that has poor prognosis due to high relapse rates. Umbilical cord blood (UCB) HCT outcomes are largely unknown in this population. We found that compared with sibling HCT, relapse risks were similar after UCB (n=126), (HR 0.86, p=0.54) and URD (n=91) (HR 0.81, p=0.43). UCB HCT was associated with statistically higher non-relapse mortality compared with sibling HCT (HR 2.32, p=0.02), but not vs. URD (HR 1.72, p=0.07). All three cohorts had statistically not significant 3-year LFS: 39% (95% CI 30–47) after UCB, 43% (95% CI 30–54) after sibling, and 50% (95% CI 40–60) after URD. Chronic GVHD rates were significantly lower after UCB compared with either sibling (HR 0.59, p=0.03) or URD (HR 0.49, p=0.001). Adverse factors for LFS included high leukocyte count at diagnosis and HCT during CR2. UCB is a suitable option for adults with FLT3+AML in the absence of an HLA-matched sibling and its immediate availability may be particularly important for FLT3+ AML where early relapse is common thus allowing HCT in CR1 when outcomes are best.

Novel strategies for improving hematopoietic reconstruction after allogeneic hematopoietic stem cell transplantation or intensive chemotherapy

INTRODUCTION

High-dose conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT) as well as intensive poly-chemotherapy for acute myeloid leukemia (AML) induce prolonged periods of neutropenia. The duration of the neutropenia is particularly long following umbilical cord blood transplantation (UCBT). Areas covered: After briefly reviewing the impact of hematopoietic growth factors administration to hasten hematologic reconstitution after allo-HCT or intensive AML chemotherapy, this article summarizes recent approaches that have been investigated to prompt hematologic reconstruction after UCBT or intensive AML chemotherapy. Expert opinion: In the allo-HCT setting, administration of G-CSF or GM-CSF shortened the duration of the neutropenia but failed to decrease infection-related mortality or to improve survival. Novel approaches to hasten hematological reconstruction after UCBT such as double UCBT with expansion of one of the 2 UCB units with Notch ligand, mesenchymal stromal cells, nicotinamide, or StemRegenin 1, co-transplanting a single UCB unit with HLA-haploidentical CD34+ cells, or increasing UCB HSC homing to marrow niches via direct intra bone UCB administration, pulse treatment with dmPGE2 or enforced fucosylation are promising and deserve further investigations in prospective phase III studies. In the AML setting, G-CSF or GM-CSF administration after intensive chemotherapy decreased the duration of the neutropenia without improving survival.

Umbilical cord blood cells from unrelated donor as an alternative source of hematopoietic stem cells for transplantation in children and adults

Umbilical cord blood (CB) is an alternative source of hematopoietic stem cells (HSC) for patients requiring allogeneic HSC transplantation but lacking a suitable human leukocyte antigen (HLA)-matched donor. Using CB has many advantages, including lower HLA-matching requirements, increased donor availability, and low rates of graft-versus-host disease. Furthermore, with over 630,000 cryopreserved volunteer CB units currently stored in international CB banks worldwide, CB is rapidly available for those patients requiring urgent transplantation. However, concern remains over the low HSC doses available in CB grafts, resulting in delayed engraftment and poor immune reconstitution. This article reviews the current use and future developments of unrelated allogeneic CB transplantation (CBT). An overview of the encouraging results of CBT and the comparisons with other HSC sources and transplant strategies both in children and adults with malignant and non-malignant diseases are shown. We will discuss important factors that need to be considered when selecting CB units for transplantation to further improve the results of CBT.

Ectopic miR-125a Expression Induces Long-Term Repopulating Stem Cell Capacity in Mouse and Human Hematopoietic Progenitors

Umbilical cord blood (CB) is a convenient and broadly used source of hematopoietic stem cells (HSCs) for allogeneic stem cell transplantation. However, limiting numbers of HSCs remain a major constraint for its clinical application. Although one feasible option would be to expand HSCs to improve therapeutic outcome, available protocols and the molecular mechanisms governing the self-renewal of HSCs are unclear. Here, we show that ectopic expression of a single microRNA (miRNA), miR-125a, in purified murine and human multipotent progenitors (MPPs) resulted in increased self-renewal and robust long-term multi-lineage repopulation in transplanted recipient mice. Using quantitative proteomics and western blot analysis, we identified a restricted set of miR-125a targets involved in conferring long-term repopulating capacity to MPPs in humans and mice. Our findings offer the innovative potential to use MPPs with enhanced self-renewal activity to augment limited sources of HSCs to improve clinical protocols.

Human leukocyte antigen supertype matching after myeloablative hematopoietic cell transplantation with 7/8 matched unrelated donor allografts: a report from the Center for International Blood and Marrow Transplant Research

The diversity of the human leukocyte antigen (HLA) class I and II alleles can be simplified by consolidating them into fewer supertypes based on functional or predicted structural similarities in epitope-binding grooves of HLA molecules. We studied the impact of matched and mismatched HLA-A (265 versus 429), -B (230 versus 92), -C (365 versus 349), and -DRB1 (153 versus 51) supertypes on clinical outcomes of 1934 patients with acute leukemias or myelodysplasia/myeloproliferative disorders. All patients were reported to the Center for International Blood and Marrow Transplant Research following single-allele mismatched unrelated donor myeloablative conditioning hematopoietic cell transplantation. Single mismatched alleles were categorized into six HLA-A (A01, A01A03, A01A24, A02, A03, A24), six HLA-B (B07, B08, B27, B44, B58, B62), two HLA-C (C1, C2), and five HLA-DRB1 (DR1, DR3, DR4, DR5, DR9) supertypes. Supertype B mismatch was associated with increased risk of grade II-IV acute graft-versus-host disease (hazard ratio =1.78, P=0.0025) compared to supertype B match. Supertype B07-B44 mismatch was associated with a higher incidence of both grade II-IV (hazard ratio=3.11, P=0.002) and III-IV (hazard ratio=3.15, P=0.01) acute graft-versus-host disease. No significant associations were detected between supertype-matched versus -mismatched groups at other HLA loci. These data suggest that avoiding HLA-B supertype mismatches can mitigate the risk of grade II-IV acute graft-versus-host disease in 7/8-mismatched unrelated donor hematopoietic cell transplantation when multiple HLA-B supertype-matched donors are available. Future studies are needed to define the mechanisms by which supertype mismatching affects outcomes after alternative donor hematopoietic cell transplantation.

Methods of ex vivo expansion of human cord blood cells: challenges, successes and clinical implications

More than 40,000 unrelated cord blood transplantations (UCBT) have been performed worldwide as treatment for patients with malignant or non-malignant life threatening hematologic disorders. However, low absolute numbers of hematopoietic stem and progenitor cells (HSPCs) within a single cord blood unit has remained a limiting factor for this transplantation modality, particularly in adult recipients. Further, because UCB contains low numbers of mostly naïve T cells, immune recovery after UCBT is slow, predisposing patients to severe infections. Other causes of UCBT failure has included graft-versus-host disease (GVHD) and relapse of the underlying disease. In this article, we first review the current landscape of cord blood engineering aimed at improving engraftment. This includes approaches of UCB-HSPCs expansion and methods aimed at improving UCB-HSCPs homing. We then discuss recent approaches of cord blood engineering developed to prevent infection [generation of multivirus-specific cytotoxic T cells (VSTs) from UCB], relapse [transduction of UCB-T cells with tumor-specific chimeric receptor antigens (CARs)] and GVHD (expansion of regulatory T cells from UCB). Although many of these techniques of UCB engineering remain currently technically challenging and expensive, they are likely to revolutionize the field of UCBT in the next decades.

Alternative donors: cord blood for adults

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment for patients with hematological diseases. The probability of finding a human leukocyte antigen (HLA)- identical donor among family members is around 25% and 30% that of having a full matched unrelated donor in the registry. Patients in need may also benefit of a HLA-mismatched HSCT either from an haploidentical donors or from umbilical cord blood (UCB). Much has been learned about UCB transplant (UCBT) since the first human UCBT was performed back in 1988. Cord blood banks have been established worldwide for the collection, cryopreservation, and distribution of UCB for HSCT. Today, a global network of cord blood banks and transplant centers has been established with a large common inventory of more than 650,000 UCB units available, allowing for more than 40,000 UCBT worldwide in children and adults with severe hematological diseases. Several studies have been published on UCBT, assessing risk factors such as cell dose and HLA mismatch. Outcomes of several retrospective comparative studies showed similar results using other stem cell sources both in pediatric and adult setting. New strategies are ongoing to facilitate engraftment and reduce transplant-related mortality. In this issue, we review the current results of UCBT in adults with hematological malignancies and the clinical studies comparing UCBT with other transplant strategies. We provide guidelines for donor algorithm selection in UCBT setting.

Phase I/II Trial of StemRegenin-1 Expanded Umbilical Cord Blood Hematopoietic Stem Cells Supports Testing as a Stand-Alone Graft

Clinical application of umbilical cord blood (UCB) as a source of hematopoietic stem cells for transplantation is limited by low CD34+ cell dose, increased risk of graft failure, and slow hematopoietic recovery. While the cell dose limitation is partially mitigated by using two UCB units, larger-dosed single units would be preferable. We have evaluated the feasibility and safety of StemRegenin-1 (SR-1), an aryl hydrocarbon receptor antagonist that expands CD34+ cells, by placing one of the two units in expansion culture. SR-1 produced a 330-fold increase in CD34+ cells and led to engraftment in 17/17 patients at a median of 15 days for neutrophils and 49 days for platelets, significantly faster than in patients treated with unmanipulated UCB. Taken together, the marked expansion, absence of graft failure, and enhanced hematopoietic recovery support testing of SR-1 expansion as a stand-alone graft and suggest it may ameliorate a limitation of UCB transplant.

A robust potency assay highlights significant donor variation of human mesenchymal stem/progenitor cell immune modulatory capacity and extended radio-resistance

The inherent immunomodulatory capacity of mesenchymal stem/progenitor cells (MSPCs) encouraged initiation of multiple clinical trials. Release criteria for therapeutic MSPCs cover identity, purity and safety but appropriate potency assessment is often missing. Reports on functional heterogeneity of MSPCs created additional uncertainty regarding donor and organ/source selection. We established a robust immunomodulation potency assay based on pooling responder leukocytes to minimize individual immune response variability. Comparing various MSPCs revealed significant potency inconsistency and generally diminished allo-immunosuppression compared to dose-dependent inhibition of mitogenesis. Gamma-irradiation to block unintended MSPC proliferation did not prohibit chondrogenesis and osteogenesis in vivo, indicating the need for alternative safety strategies.

Cellular engineering and therapy in combination with cord blood allografting in pediatric recipients

Cord blood (CB) transplantation is an alternate source of human hematopoietic progenitor cells for allogeneic stem cell transplantation in children and adolescents with both malignant and nonmalignant diseases. Current limitations included delay in hematopoietic reconstitution, increased incidence of primary graft failure and slow cellular immunoreconstitution. These limitations lead to a significant increase in primary graft failure, infectious complications and increased transplant-related mortality. There is a number of experimental approaches currently under investigation including cellular engineering to circumvent these limitations. In this review, we summarize the recent findings of utilizing ex vivo CB expansion with Notch1 ligand Delta 1, mesenchymal progenitor cells, the use of human placenta-derived stem cells and CB-derived natural killer cells. Early and preliminary results suggest some of these experimental cellular strategies may in part ameliorate the incidence of primary graft failure, delays in hematopoietic reconstitution and/or slowness in cellular immune reconstitution following unrelated CB transplantation.

Better allele-level matching improves transplant-related mortality after double cord blood transplantation

Cord blood transplant requires less stringent human leukocyte antigen matching than unrelated donors. In 133 patients with hematologic malignancies who engrafted after double cord blood transplantation with a dominant unit, we studied the effect of high resolution testing at 4 loci (-A, -B, -C, -DRB1) for its impact on 2-year transplant-related mortality. Ten percent of the dominant cord blood units were matched at 7-8/8 alleles using HLA-A, -B, -C, and -DRB1; 25% were matched at 6/8, 40% at 5/8, and 25% at 4/8 or less allele. High resolution typing at 4 loci showed that there was no 2-year transplant-related mortality in 7-8/8 matched patients. Patients with 5-6/8 matched dominant cord blood units had 2-year transplant-related mortality of 39% while patients with 4/8 or less matched units had 60%. Multivariate regression analyses confirmed the independent effect of high resolution typing on the outcome when adjusted for age, diagnosis, CD34(+) cell dose infused, graft manipulation and cord to cord matching. The worst prognostic group included patients aged over 32 years with 4/8 or less matched cord blood units compared with patients who were either younger than 32 years old independent of allele-level matching, or aged over 32 years but with 5-6/8 matched cord blood units (Hazard Ratio 2.2; 95% confidence interval: 1.3-3.7; P<0.001). Patients with 7-8/8 matched units remained the group with the best prognosis. Our data suggest that high resolution typing at 4 loci and selecting cord blood units matched at at least 5/8 alleles may reduce transplant-related mortality after double cord blood transplantation.

Making a little go a long way

In this issue of Blood, Popat et al report the results of a clinical trial designed to test the safety and feasibility of a novel strategy, enforced fucosylation, intended to improve engraftment after donor unrelated cord blood (UCB) transplantation in adults. The data show that the strategy is safe, and that engraftment of platelets and neutrophils is faster in recipients of the modified cord blood (CB) unit when compared with historical controls

Alternative Donor Transplantation for Acute Myeloid Leukemia

Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative therapy for adult patients with acute myeloid leukemia (AML), but its use for consolidation therapy after first remission with induction chemotherapy used to be limited to younger patients and those with suitable donors. The median age of AML diagnosis is in the late 60s. With the introduction of reduced-intensity conditioning (RIC), many older adults are now eligible to receive allo-HCT, including those who are medically less fit to receive myeloablative conditioning. Furthermore, AML patients commonly have no human leukocyte antigen (HLA)-identical or medically suitable sibling donor available to proceed with allo-HCT. Technical advances in donor matching, suppression of alloreactivity, and supportive care have made it possible to use alternative donors, such as unrelated umbilical cord blood (UCB) and partially HLA-matched related (haploidentical) donors. Outcomes after alternative donor allo-HCT are now approaching the outcomes observed for conventional allo-HCT with matched related and unrelated donors. Thus, with both UCB and haploidentical donors available, lack of donor should rarely be a limiting factor in offering an allo-HCT to adults with AML.

The potential of cytotherapeutics in hematologic reconstitution and in the treatment and prophylaxis of graft-versus-host disease. Chapter I: current practice and remaining unmet medical needs

Hematopoietic stem cell transplantation is a life-saving treatment for inherited anemias, immunodeficiencies or hematologic malignancies. When using partially HLA-matched allografts, a major complication is graft-versus-host disease (GvHD). The ideal attributes of a transformational new GvHD treatment include improved survival, decreased corticosteroids, decreased antifungals, improved quality of life through decreased infections, reduced number of hospital stay days, reduced risks of developing chronic GvHD impact on lower GI tract and liver, prophylactic benefits and decreased GvHD relapses, but, in the case of cancer, without negatively impacting beneficial graft-versus-tumor effects. The current practice of hematopoietic stem cell transplantation, its incidence and its unmet medical needs are reviewed here and discussed.

Advances in umbilical cord blood manipulation-from niche to bedside

The use of umbilical cord blood (UCB) as an alternative haematopoietic cell source in lieu of bone marrow for haematopoietic reconstitution is increasingly becoming a mainstay treatment for both malignant and nonmalignant diseases, as most individuals will have at least one available, suitably HLA-matched unit of blood. The principal limitation of UCB is the low and finite number of haematopoietic stem and progenitor cells (HSPC) relative to the number found in a typical bone marrow or mobilized peripheral blood allograft, which leads to prolonged engraftment times. In an attempt to overcome this obstacle, strategies that are often based on native processes occurring in the bone marrow microenvironment or 'niche' have been developed with the goal of accelerating UCB engraftment. In broad terms, the two main approaches have been either to expand UCB HSPC ex vivo before transplantation, or to modulate HSPC functionality to increase the efficiency of HSPC homing to the bone marrow niche after transplant both of which enhance the biological activities of the engrafted HSPC. Several early phase clinical trials of these approaches have reported promising results.

Harnessing immunosurveillance: current developments and future directions in cancer immunotherapy

Despite improved methods of cancer detection and disease management over the last few decades, cancer remains a major public health problem in many societies. Conventional therapies, such as chemotherapy, radiation, and surgery, are not usually sufficient to prevent disease recurrence. Therefore, efforts have been focused on developing novel therapies to manage metastatic disease and to prolong disease-free and overall survival, by modulating the immune system to alleviate immunosuppression, and to enhance antitumor immunity. This review discusses protumor mechanisms in patients that circumvent host immunosurveillance, and addresses current immunotherapy modalities designed to target these mechanisms. Given the complexity of cancer immunosuppressive mechanisms, we propose that identification of novel disease biomarkers will drive the development of more targeted immunotherapy. Finally, administration of different classes of immunotherapy in combination regimens, will be the ultimate route to impact low survival rates in advanced cancer patients.

Decreased nonrelapse mortality after unrelated cord blood transplantation for acute myeloid leukemia using reduced-intensity conditioning: a prospective phase II multicenter trial

A prospective phase II multicenter trial was performed with the aim to obtain less than 25% nonrelapse mortality (NRM) after unrelated cord blood transplantation (UCBT) for adults with acute myeloid leukemia (AML) using a reduced-intensity conditioning regimen (RIC) consisting of total body irradiation (2 Gy), cyclophosphamide (50 mg/kg), and fludarabine (200 mg/m(2)). From 2007 to 2009, 79 UCBT recipients were enrolled. Patients who underwent transplantation in first complete remission (CR1) (n = 48) had a higher frequency of unfavorable cytogenetics and secondary AML and required more induction courses of chemotherapy to achieve CR1 compared with the others. The median infused total nucleated cells (TNC) was 3.4 × 10(7)/kg, 60% received double UCBT, 77% were HLA mismatched (4/6), and 40% had major ABO incompatibility. Cumulative incidence of neutrophil recovery at day 60 was 87% and the cumulative incidence of 100-day acute graft-versus-host disease (II to IV) was 50%. At 2 years, the cumulative incidence of NRM and relapse was 20% and 46%, respectively. In multivariate analysis, major ABO incompatibility (P = .001) and TNC (<3.4 × 10(7)/kg; P = .001) were associated with increased NRM, and use of 2 or more induction courses to obtain CR1 was associated with increased relapse incidence (P = .04). Leukemia-free survival (LFS) at 2 years was 35%, and the only factor associated with decreased LFS was secondary AML (P = .04). In conclusion, despite the decreased NRM observed, other RIC regimens with higher myelosuppression should be evaluated to decrease relapse in high-risk AML. (EUDRACT 2006-005901-67).

One-unit versus two-unit cord-blood transplantation for hematologic cancers

BACKGROUND

Umbilical-cord blood has been used as the source of hematopoietic stem cells in an estimated 30,000 transplants. The limited number of hematopoietic cells in a single cord-blood unit prevents its use in recipients with larger body mass and results in delayed hematopoietic recovery and higher mortality. Therefore, we hypothesized that the greater numbers of hematopoietic cells in two units of cord blood would be associated with improved outcomes after transplantation.

METHODS

Between December 1, 2006, and February 24, 2012, a total of 224 patients 1 to 21 years of age with hematologic cancer were randomly assigned to undergo double-unit (111 patients) or single-unit (113 patients) cord-blood transplantation after a uniform myeloablative conditioning regimen and immunoprophylaxis for graft-versus-host disease (GVHD). The primary end point was 1-year overall survival.

RESULTS

Treatment groups were matched for age, sex, self-reported race (white vs. nonwhite), performance status, degree of donor-recipient HLA matching, and disease type and status at transplantation. The 1-year overall survival rate was 65% (95% confidence interval [CI], 56 to 74) and 73% (95% CI, 63 to 80) among recipients of double and single cord-blood units, respectively (P=0.17). Similar outcomes in the two groups were also observed with respect to the rates of disease-free survival, neutrophil recovery, transplantation-related death, relapse, infections, immunologic reconstitution, and grade II-IV acute GVHD. However, improved platelet recovery and lower incidences of grade III and IV acute and extensive chronic GVHD were observed among recipients of a single cord-blood unit.

CONCLUSIONS

We found that among children and adolescents with hematologic cancer, survival rates were similar after single-unit and double-unit cord-blood transplantation; however, a single-unit cord-blood transplant was associated with better platelet recovery and a lower risk of GVHD. (Funded by the National Heart, Lung, and Blood Institute and the National Cancer Institute; ClinicalTrials.gov number, NCT00412360.).

Umbilical cord matrix derived mesenchymal stem cells can change the cord blood transplant scenario

BACKGROUND AND OBJECTIVES

The field of Umbilical cord blood (UCB) hematopoietic stem cell transplantation has had an amazing run since 1988. UCB is being increasing used in related and unrelated transplant settings. A major hurdle, however, in the use of UCB is its low cell dose, which is largely responsible for an elevated risk of graft failure and significantly delayed neutrophils and platelet engraftment. Strategies to increase CD34(+) HSC/HPC dose are under development as a direct correlation has been shown between these counts and time for engraftment. One strategy includes the ex vivo expansion of UCB derived CD34(+) cells.

METHODS AND RESULTS

We show that the umbilical cord derived mesenchymal stem cells (UCMSCs) can be used as supporting cells for ex vivo expansion of CD34(+) cells using low concentrations of cytokine cocktail. The UCMSCs release the cytokines required for maintenance and proliferation of CD34(+) cells in the ex vivo culture conditions. More than 25 fold increase in total nucleated cell count (TNC) and more than 20 fold increase in CD34(+) cell count has been obtained using this co-culture system.

CONCLUSIONS

UCMSCs from both, autologous and allogeneic origin can be used for expansion of UCB derived CD34(+) cells. The ease of availability and immunoprivileged nature of UCMSCs further holds promise in their use in an allogeneic transplant setting.

Clinical utilization of cord blood over human health: experience of stem cell transplantation and cell therapy using cord blood in Korea

Cord blood (CB) has been used as an important and ethical source for hematopoietic stem cell transplantation (SCT) as well as cell therapy by manufacturing mesenchymal stem cell, induced pleuripotential stem cell or just isolating mononuclear cell from CB. Recently, the application of cell-based therapy using CB has expanded its clinical utility, particularly, by using autologous CB in children with refractory diseases. For these purposes, CB has been stored worldwide since mid-1990. In this review, I would like to briefly present the historical development of clinical uses of CB in the fields of SCT and cell therapy, particularly to review the experiences in Korea. Furthermore, I would touch the recent banking status of CB.

Low rate of infusional toxicity after expanded cord blood transplantation

BACKGROUND AIMS

Umbilical cord blood (CB) is used with increasing frequency to restore hematopoiesis in patients with bone marrow transplant who lack a suitable human leukocyte antigen-matched donor. CB transplantation is limited by low cell doses and delays in neutrophil and platelet engraftment. CB progenitors expanded ex vivo before transplantation provide more rapid hematopoietic and immune reconstitution as well as less engraftment failure compared with unmanipulated CB. However, the safety of infusing double and ex vivo-expanded CB has not been systematically examined.

METHODS

We reviewed the immediate adverse events (AE) associated with the infusion of CB occurring within 24 hours in 137 patients enrolled in clinical CB transplant trials at the MD Anderson Cancer Center from February 2004 to May 2010. All patients received an unmanipulated CB unit followed by infusion of a second unmanipulated CB unit or a second CB unit expanded ex vivo with the use of cytokines in a liquid culture system or in mesenchymal stromal cell co-cultures.

RESULTS

A total of three grade 2 and two grade 3 infusion reactions occurred within 24 hours of CB transplantation. This resulted in an AE rate of 3.7%. The majority of AEs manifested as signs of hypertension. No association with patient age, sex, disease status, premedication, ABO compatibility or total infusion volume was observed. In summary, the incidence of infusion-related toxicities in patients who receive unmanipulated and ex vivo-expanded double CB transplantation is low.

CONCLUSIONS

We conclude that the infusion of unmanipulated followed by expanded CB products is a safe procedure associated with a low probability of inducing severe reactions.

Improving engraftment and immune reconstitution in umbilical cord blood transplantation

Umbilical cord blood (UCB) is an important source of hematopoietic stem cells (HSC) for allogeneic transplantation when HLA-matched sibling and unrelated donors (MUD) are unavailable. Although the overall survival results for UCB transplantation are comparable to the results with MUD, UCB transplants are associated with slow engraftment, delayed immune reconstitution, and increased opportunistic infections. While this may be a consequence of the lower cell dose in UCB grafts, it also reflects the relative immaturity of cord blood. Furthermore, limited cell numbers and the non-availability of donor lymphocyte infusions currently prevent the use of post-transplant cellular immunotherapy to boost donor-derived immunity to treat infections, mixed chimerism, and disease relapse. To further develop UCB transplantation, many strategies to enhance engraftment and immune reconstitution are currently under investigation. This review summarizes our current understanding of engraftment and immune recovery following UCB transplantation and why this differs from allogeneic transplants using other sources of HSC. It also provides a comprehensive overview of promising techniques being used to improve myeloid and lymphoid recovery, including expansion, homing, and delivery of UCB HSC; combined use of UCB with third-party donors; isolation and expansion of natural killer cells, pathogen-specific T cells, and regulatory T cells; methods to protect and/or improve thymopoiesis. As many of these strategies are now in clinical trials, it is anticipated that UCB transplantation will continue to advance, further expanding our understanding of UCB biology and HSC transplantation.

Cord Blood Transplantation: Can We Make it Better?

Umbilical cord blood is an established source of hematopoietic stem cells for transplantation. It enjoys several advantages over bone marrow or peripheral blood, including increased tolerance for Human Leukocyte Antigen mismatches, decreased incidence of graft-versus-host disease, and easy availability. Unrelated cord blood does have limitations, however, especially in the treatment of adults. In the 24 years since the first umbilical cord blood transplant was performed, significant progress has been made, but delayed hematopoietic engraftment and increased treatment-related mortality remain obstacles to widespread use. Here we summarize the latest results of unrelated cord blood transplants, and review strategies under investigation to improve clinical outcomes.

Comparison of outcomes after single or double cord blood transplantation in adults with acute leukemia using different types of myeloablative conditioning regimen, a retrospective study on behalf of Eurocord and the Acute Leukemia Working Party of EBMT

We report outcomes after single (s) and double (d) umbilical cord blood transplantation (UCBT) after myeloablative conditioning (MAC) regimen for 239 patients transplanted for acute leukemia in first complete remission (CR1). All sUCBT patients received a total nucleated cell dose >2.5 × 10(7)/kg. Conditioning regimen for sUCBT was total body irradiation (TBI)12 Gy- or busulfan (BU)-based ± fludarabine (Flu) (n=68, group 1), thiotepa+BU+Flu (TBF) (n=88, group 2), and for dUCBT it was TBI12 Gy+cyclophosphamide ± Flu (n=83, group 3). dUCBT recipients were younger, received higher cell dose and less frequently antithymocyte globulin. In multivariate analysis, we found similar neutrophil recovery among the three groups; however, acute graft-versus-host disease II-IV was higher in dUCBT compared with others. Non-relapse mortality and relapse incidence were not statistically different among the three groups. Leukemia-free survival was 30% for sUCBT using TBI- or BU-based MAC compared with 48% for sUCBT TBF and 48% for dUCBT (P=0.02 and P=0.03, respectively), and it was not statistically different between sUCBT with TBF and dUCBT. In conclusion, use of sUCBT with adequate cell dose (>2.5 × 10(7)/kg) and a specific conditioning regimen in the MAC setting results in similar outcomes as dUCBT. The choice of TBF conditioning regimen for sUCBT may improve results, and whether this regimen may be effective in dUCBT should be further analyzed.

Prostaglandin-modulated umbilical cord blood hematopoietic stem cell transplantation

Umbilical cord blood (UCB) is a valuable source of hematopoietic stem cells (HSCs) for use in allogeneic transplantation. Key advantages of UCB are rapid availability and less stringent requirements for HLA matching. However, UCB contains an inherently limited HSC count, which is associated with delayed time to engraftment, high graft failure rates, and early mortality. 16,16-Dimethyl prostaglandin E2 (dmPGE2) was previously identified to be a critical regulator of HSC homeostasis, and we hypothesized that brief ex vivo modulation with dmPGE2 could improve patient outcomes by increasing the "effective dose" of HSCs. Molecular profiling approaches were used to determine the optimal ex vivo modulation conditions (temperature, time, concentration, and media) for use in the clinical setting. A phase 1 trial was performed to evaluate the safety and therapeutic potential of ex vivo modulation of a single UCB unit using dmPGE2 before reduced-intensity, double UCB transplantation. Results from this study demonstrated clear safety with durable, multilineage engraftment of dmPGE2-treated UCB units. We observed encouraging trends in efficacy, with accelerated neutrophil recovery (17.5 vs 21 days, P = .045), coupled with preferential, long-term engraftment of the dmPGE2-treated UCB unit in 10 of 12 treated participants.

Double umbilical cord blood transplantation for hematological malignancies: a long-term analysis from the SFGM-TC registry

Allogeneic hematopoietic stem cell (HSC) transplantation is a curative treatment for many hematologic malignancies for which umbilical cord blood (UCB) represents an alternative source of HSCs. To overcome the low cellularity of one UCB unit, double UCB transplantation (dUCBT) has been developed in adults. We have analyzed the outcome of 136 patients who underwent dUCBT reported to the SFGM-TC registry between 2005 and 2007. Forty-six patients received myeloablative regimens, and 90 patients received reduced-intensity conditioning regimens. There were 84 cases of leukemia, 17 cases of non-Hodgkin lymphoma, 11 cases of myeloma, and 24 other hematologic malignancies. At transplantation, 40 (29%) patients were in complete remission. At day 60 after transplantation, the cumulative incidence of neutrophil recovery was 91%. We observed one UCB unit domination in 88% of cases. The cumulative incidence of day 100 acute graft-versus-host disease, chronic graft-versus-host disease, transplant-related mortality, and relapse at 2 years were 36%, 23%, 27%, and 28% respectively. After a median follow-up of 49.5 months, the 3-year probabilities of overall and progression-free survival were 41% and 35%, respectively, with a significant overall survival advantage when male cord engrafted male recipients. We obtained a long-term plateau among patients in complete remission, which makes dUCBT a promising treatment strategy for these patients.

Comparison of outcomes after two standards-of-care reduced-intensity conditioning regimens and two different graft sources for allogeneic stem cell transplantation in adults with hematologic diseases: a single-center analysis

Recent advances in allogeneic stem cell transplantation (allo-HSCT) have included the advent of reduced-intensity conditioning (RIC) regimens to decrease the toxicity of myeloablative allo-SCT and the use of double umbilical cord blood (dUCB) units as a graft source in adults lacking a suitable donor. The FB2A2 regimen (fludarabine 30 mg/kg/day for 5-6 days + i.v. busulfan 3.6 mg/kg/day for 2 days + rabbit antithymocyte globulin 2.5 mg/kg/day for 2 days) supported by peripheral blood stem cells (PBSCs) and the TCF regimen (fludarabine 200 mg/m² for 5 days + cyclophosphamide 50 mg/kg for 1 day + low-dose [2 Gy] total body irradiation) supported by dUCB units are currently the most widely used RIC regimens in many centers and could be considered standard of care in adults eligible for an RIC allo-SCT. Here we compared, retrospectively, the outcomes of adults patients who received the FB2A2-PBSC RIC regimen (n = 52; median age, 59 years; median follow-up, 19 months) and those who received the dUCB-TCF RIC regimen (n = 39; median age, 56 years; median follow-up, 20 months) for allo-SCT between January 2007 and November 2010. There were no significant between-group differences in patient and disease characteristics. Cumulative incidences of engraftment, acute grade II-IV and chronic graft-versus-host disease were similar in the 2 groups. The median time to platelet recovery, incidence of early death (before day +100), and 2-year nonrelapse mortality were significantly higher in the dUCB-TCF group (38 days versus 0 days [P <.0001]; 20.5% versus 4% [P = .05], and 26.5% versus 6% [P = .02], respectively). The groups did not differ in terms of 2-year overall survival (62% for FB2A2-PBSC versus 61% for dUCB-TCF), disease-free survival (59% versus 50.5%), or relapse incidence (35.5% versus 23%). In multivariate analysis, the presence of a lymphoid disorder was associated with a significantly higher 2-year overall survival (hazard ratio, 0.42; 95% confidence interval, 0.20-0.87; P = .02), whereas patients receiving a FB2A2-PBSC allo-SCT had a significantly lower 2-year nonrelapse mortality (hazard ratio, 0.24; 95% confidence interval, 0.1-0.7; P = .01). There were no factors associated with higher 2-year disease-free survival or lower relapse incidence. This study suggests that the dUCB-TCF regimen provides a valid alternative in adults lacking a suitable donor and eligible for RIC allo-SCT. Prospective and randomized studies are warranted to establish the definitive role of dUCB RIC allo-SCT in adults. In addition, strategies for decreasing nonrelapse mortality after dUCB RIC allo-SCT are urgently needed.