Ex Vivo Expansion or Manipulation of Stem Cells to Improve Outcome of Umbilical Cord Blood Transplantation

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.

PLAG1 dampens protein synthesis to promote human hematopoietic stem cell self-renewal

Hematopoietic stem cell (HSC) dormancy is understood as supportive of HSC function and its long-term integrity. Although regulation of stress responses incurred as a result of HSC activation is recognized as important in maintaining stem cell function, little is understood of the preventive machinery present in human HSCs that may serve to resist their activation and promote HSC self-renewal. We demonstrate that the transcription factor PLAG1 is essential for long-term HSC function and, when overexpressed, endows a 15.6-fold enhancement in the frequency of functional HSCs in stimulatory conditions. Genome-wide measures of chromatin occupancy and PLAG1-directed gene expression changes combined with functional measures reveal that PLAG1 dampens protein synthesis, restrains cell growth and division, and enhances survival, with the primitive cell advantages it imparts being attenuated by addition of the potent translation activator, c-MYC. We find PLAG1 capitalizes on multiple regulatory factors to ensure protective diminished protein synthesis including 4EBP1 and translation-targeting miR-127 and does so independently of stress response signaling. Overall, our study identifies PLAG1 as an enforcer of human HSC dormancy and self-renewal through its highly context-specific regulation of protein biosynthesis and classifies PLAG1 among a rare set of bona fide regulators of messenger RNA translation in these cells. Our findings showcase the importance of regulated translation control underlying human HSC physiology, its dysregulation under activating demands, and the potential if its targeting for therapeutic benefit.

Guidelines for the Prevention and Management of Graft-versus-Host Disease after Cord Blood Transplantation

The incidence of graft-versus-host disease (GVHD) after cord blood (CB) transplantation (CBT) is lower than expected given the marked degree of human leukocyte antigen (HLA)-mismatch of CB grafts. While the exact mechanism that underlies this biology remains unclear, it is hypothesized to be due to the low number of mostly immature T-cells infused as part of the graft1,2, and increased tolerance of CB-derived lymphocytes induced by the state of pregnancy. Nevertheless, acute GVHD (aGVHD) is a significant complication of CBT. In contrast, the incidence of chronic GVHD (cGVHD) following CBT is lower than what is observed following matched related or unrelated donor HSC transplantation (HSCT)3-6. This review outlines the guidelines for the prevention and management of acute and chronic GVHD following CBT.

A Review of Evaluating Hematopoietic Stem Cells Derived from Umbilical Cord Blood's Expansion and Homing

Transplantation of hematopoietic stem cells (HSCs) derived from umbilical cord blood (UCB) has been taken into account as a therapeutic approach in patients with hematologic malignancies. Unfortunately, there are limitations concerning HSC transplantation (HSCT), including (a) low contents of UCB-HSCs in a single unit of UCB and (b) defects in UCB-HSC homing to their niche. Therefore, delays are observed in hematopoietic and immunologic recovery and homing. Among numerous strategies proposed, ex vivo expansion of UCB-HSCs to enhance UCB-HSC dose without any differentiation into mature cells is known as an efficient procedure that is able to alter clinical treatments through adjusting transplantation-related results and making them available. Accordingly, culture type, cytokine combinations, O2 level, co-culture with mesenchymal stromal cells (MSCs), as well as gene manipulation of UCB-HSCs can have effects on their expansion and growth. Besides, defects in homing can be resolved by exposing UCB-HSCs to compounds aimed at improving homing. Fucosylation of HSCs before expansion, CXCR4-SDF-1 axis partnership and homing gene involvement are among strategies that all depend on efficiency, reasonable costs, and confirmation of clinical trials. In general, the present study reviewed factors improving the expansion and homing of UCB-HSCs aimed at advancing hematopoietic recovery and expansion in clinical applications and future directions.

Current and future perspectives on allogeneic transplantation using ex vivo expansion or manipulation of umbilical cord blood cells

In patients with hematologic malignancies, the outcome of umbilical cord blood transplantation has improved and is now comparable to that of matched unrelated donor transplantation. However, the limitation of using umbilical cord blood has been a delay in both hematopoietic and immunologic recovery. Strategies have been proposed to overcome these limitations. One strategy involves ex vivo expansion of the umbilical cord blood unit prior to transplantation. A second strategy involves exposure of the umbilical cord blood graft to compounds aimed at improving homing and engraftment following transplantation. Many of these strategies are now being tested in late phase multi-center clinical trials. If proven cost effective and efficacious, they may alter the landscape of donor options for allogeneic stem cell transplantation.

Transient apoptosis inhibition in donor stem cells improves hematopoietic stem cell transplantation

During hematopoietic stem cell transplantation, a substantial number of donor cells are lost because of apoptotic cell death. Transplantation-associated apoptosis is mediated mainly by the proapoptotic BCL-2 family proteins BIM and BMF, and their proapoptotic function is conserved between mouse and human stem and progenitor cells. Permanent inhibition of apoptosis in donor cells caused by the loss of these BH3-only proteins improves transplantation outcome, but recipients might be exposed to increased risk of lymphomagenesis or autoimmunity. Here, we address whether transient inhibition of apoptosis can serve as a safe but efficient alternative to improve the outcome of stem cell transplantation. We show that transient apoptosis inhibition by short-term overexpression of prosurvival BCL-XL, known to block BIM and BMF, is not only sufficient to increase the viability of hematopoietic stem and progenitor cells during engraftment but also improves transplantation outcome without signs of adverse pathologies. Hence, this strategy represents a promising and novel therapeutic approach, particularly under conditions of limited donor stem cell availability.

3D models of the hematopoietic stem cell niche under steady-state and active conditions

Hematopoietic stem cells (HSCs) in the bone marrow are able to differentiate into all types of blood cells and supply the organism each day with billions of fresh cells. They are applied to cure hematological diseases such as leukemia. The clinical need for HSCs is high and there is a demand for being able to control and multiply HSCs in vitro. The hematopoietic system is highly proliferative and thus sensitive to anti-proliferative drugs such as chemotherapeutics. For many of these drugs suppression of the hematopoietic system is the dose-limiting toxicity. Therefore, biomimetic 3D models of the HSC niche that allow to control HSC behavior in vitro and to test drugs in a human setting are relevant for the clinics and pharmacology. Here, we describe a perfused 3D bone marrow analog that allows mimicking the HSC niche under steady-state and activated conditions that favor either HSC maintenance or differentiation, respectively, and allows for drug testing.

Outcomes after Umbilical Cord Blood Transplantation for Myelodysplastic Syndromes

For patients with hematologic malignancies undergoing allogeneic hematopoietic cell transplantation, umbilical cord blood transplantation (UCBT) has become an acceptable alternative donor source in the absence of a matched sibling or unrelated donor. To date, however, there have been few published series dedicated solely to describing the outcomes of adult patients with myelodysplastic syndrome (MDS) who have undergone UCBT. Between 2004 and 2013, 176 adults with MDS underwent UCBT as reported to the Center for International Blood and Marrow Transplant Research. Median age at the time of transplantation was 56 years (range, 18-73 years). The study group included 10% with very low, 23% with low, 19% with intermediate, 19% with high, and 13% with very high-risk Revised International Prognostic Scoring System (IPSS-R) scores. The 100-day probability of grade II-IV acute graft-versus-host disease (GVHD) was 38%, and the 3-year probability of chronic GVHD was 28%. The probabilities of relapse and transplantation-related mortality (TRM) at 3 years were 32% and 40%, respectively, leading to a 3-year disease-free survival (DFS) of 28% and an overall survival (OS) of 31%. In multivariate analysis, increasing IPSS-R score at the time of HCT was associated with inferior TRM (P = .0056), DFS (P = .018), and OS (P = .0082), but not with GVHD or relapse. The presence of pretransplantation comorbidities was associated with TRM (P = .001), DFS (P = .02), and OS (P = .001). Reduced-intensity conditioning was associated with increased risk of relapse (relative risk, 3.95; 95% confidence interval, 1.78-8.75; P < .001), and although a higher proportion of myeloablative UCBTs were performed in patients with high-risk disease, the effect of conditioning regimen intensity was the same regardless of IPSS-R score. For some individuals who lack a matched sibling or unrelated donor, UCBT can result in long-term DFS; however, the success of UCBT in this population is hampered by a high rate of TRM.

Heterogeneous Niche Activity of Ex-Vivo Expanded MSCs as Factor for Variable Outcomes in Hematopoietic Recovery

Ex-vivo expanded mesenchymal stromal cells (MSCs) are increasingly used for paracrine support of hematopoietic stem cell (HSC) regeneration, but inconsistent outcomes have hindered ongoing clinical trials. Here, we show that significant heterogeneity in the niche activity of MSCs is created during their culture in various serum-supplemented media. The MSCs cultured under stimulatory or non-stimulatory culture conditions exhibited differences in colony forming unit-fibroblast contents, expression levels of cross-talk molecules (Jagged-1 and CXCL-12) and their support for HSC self-renewal. Accordingly, the enhancing effects of MSCs on hematopoietic engraftment were only visible when HSCs were co-transplanted with MSCs under stimulatory conditions. Of note, these differences in MSCs and their effects on HSCs were readily reversed by switching the cultures, indicating that the difference in niche activity can be caused by distinct functional state, rather than by clonal heterogeneity. Supporting the findings, transcriptomic analysis showed distinct upstream signaling pathways such as inhibition of P53 and activation of ER-stress response gene ATF4 for MSCs under stimulatory conditions. Taken together, our study shows that the niche activity of MSCs can vary rapidly by the extrinsic cues during culture causing variable outcomes in hematopoietic recoveries, and point to the possibility that MSCs can be pre-screened for more predictable efficacy in various cell therapy trials.

A Novel High-Throughput Screening Platform Reveals an Optimized Cytokine Formulation for Human Hematopoietic Progenitor Cell Expansion

The main limitations of hematopoietic cord blood (CB) transplantation, viz, low cell dosage and delayed reconstitution, can be overcome by ex vivo expansion. CB expansion under conventional culture causes rapid cell differentiation and depletion of hematopoietic stem and progenitor cells (HSPCs) responsible for engraftment. In this study, we use combinatorial cell culture technology (CombiCult^®) to identify medium formulations that promote CD133⁺ CB HSPC proliferation while maintaining their phenotypic characteristics. We employed second-generation CombiCult screens that use electrospraying technology to encapsulate CB cells in alginate beads. Our results suggest that not only the combination but also the order of addition of individual components has a profound influence on expansion of specific HSPC populations. Top protocols identified by the CombiCult screen were used to culture human CD133⁺ CB HSPCs on nanofiber scaffolds and validate the expansion of the phenotypically defined CD34⁺CD38^lo/-CD45RA^-CD90⁺CD49f⁺ population of hematopoietic stem cells and their differentiation into defined progeny.