New approaches for improving engraftment after cord blood transplantation

Impact of donor NKG2D and MICA gene polymorphism on clinical outcomes of adult and paediatric allogeneic cord blood transplantation for malignant diseases

OBJECTIVES

NKG2D is an activating receptor expressed by natural killer (NK) and CD8+ T cells and activation intensity varies by NKG2D expression level or nature of its ligand. An NKG2D gene polymorphism determines high (HNK1) or low (LNK1) expression. MICA is the most polymorphic NKG2D ligand and stronger effector cell activation associates with methionine rather than valine at residue 129. We investigated correlation between cord blood (CB) NKG2D and MICA genotypes and haematopoietic stem cell (HSC) transplant outcome.

METHODS

We retrospectively studied 267 CB HSC recipients (178 adult and 87 paediatric) who underwent transplant for malignant disease between 2007 and 2018, analysing CB graft DNA for NKG2D and MICA polymorphisms using Sanger sequencing. Multivariate analysis was used to correlate these results with transplant outcomes.

RESULTS

In adult patients, LNK1 homozygous CB significantly improved 60-day neutrophil engraftment (hazard ratio (HR) 0.6; 95% confidence interval (CI) 0.4-0.9; p = .003). In paediatrics, HNK1 homozygous CB improved 60-day engraftment (HR 0.4; 95% CI 0.2-0.7; p = .003), as did MICA-129 methionine+ CB grafts (HR 1.7 95% CI 1.1-2.6; p = .02).

CONCLUSION

CB NKG2D and MICA genotypes potentially improve CB HSC engraftment. However, results contrast between adult and paediatric recipients and may reflect transplant procedure disparities between cohorts.

Lentivirus-Mediated BCL-XL Overexpression Inhibits Stem Cell Apoptosis during Ex Vivo Expansion and Provides Competitive Advantage Following Xenotransplantation

Hematopoietic reconstitution after hematopoietic stem cell transplantation (HSCT) is influenced by the number of transplanted cells. However, under certain conditions donor cell counts are limited and impair clinical outcome. Hematopoietic stem and progenitor cell (HSPC) expansion prior to HSCT is a widely used method to achieve higher donor cell counts and minimize transplantation-related risks such as graft failure or delayed engraftment. Still, expansion in a non-physiological environment can trigger cell death mechanisms and hence counteract the desired effect. We have shown earlier that during HSCT a relevant amount of HSPCs were lost due to apoptosis and that cell death inhibition in donor HSPCs improved engraftment in xenotransplantation experiments. Here, we assessed the effect of combined ex vivo expansion and cell death inhibition on HSPC yield and their reconstitution potential in vivo. During expansion with cytokines and the small molecule inhibitor StemRegenin 1, concomitant lentiviral overexpression of antiapoptotic BCL-XL resulted in an increased yield of transduced HSPCs. Importantly, BCL-XL overexpression enhanced the reconstitution potential of HSPCs in xenotransplantation experiments in vivo. In contrast, treatment with caspase and necroptosis inhibitors had no favorable effects on HSPC yields nor on cell viability. We postulate that overexpression of antiapoptotic BCL-XL, both during ex vivo expansion and transplantation, is a promising approach to improve the outcome of HSCT in situations with limited donor cell numbers. However, such apoptosis inhibition needs to be transient to avoid long-term sequelae like leukemia.

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.

Intrabone transplantation of CD34+ cells with optimized delivery does not enhance engraftment in a rhesus macaque model

Intrabone (IB) injection of umbilical cord blood has been proposed as a potential mechanism to improve transplant engraftment and prevent graft failure. However, conventional IB techniques produce low retention of transplanted cells in the marrow. To overcome this barrier, we developed an optimized IB (OIB) injection method using low-volume, computer-controlled slow infusion that promotes cellular retention in the marrow. Here, we compare engraftment of CD34+ cells transplanted in a myeloablative rhesus macaque (RM) model using the OIB method compared with IV delivery. RM CD34+ cells obtained by apheresis were split equally for transduction with lentiviral vectors encoding either green fluorescent protein or yellow fluorescent protein reporters. Following conditioning, one marked autologous population of CD34+ cells was injected directly IB using the OIB method and the other was injected via slow IV push into the same animal (n = 3). Daily flow cytometry of blood quantified the proportion of engrafting cells deriving from each source. Marrow retention was examined using positron emission tomography/computed tomography imaging of 89Zirconium (89Zr)-oxine-labeled CD34+ cells. CD34+ cells injected via the OIB method were retained in the marrow and engrafted in all 3 animals. However, OIB-transplanted progenitor cells did not engraft any faster than those delivered IV and contributed significantly less to hematopoiesis than IV-delivered cells at all time points. Rigorous testing of our OIB delivery system in a competitive RM myeloablative transplant model showed no engraftment advantage over conventional IV infusion. Given the increased complexity and potential risks of IB vs IV approaches, our data do not support IB transplantation as a strategy to improve hematopoietic engraftment.

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.

GPRASP proteins are critical negative regulators of hematopoietic stem cell transplantation

Hematopoietic stem cell (HSC) transplantation (HSCT) is often exploited to treat hematologic disease. Donor HSCs must survive, proliferate, and differentiate in the damaged environment of the reconstituting niche. Illuminating molecular mechanisms regulating the activity of transplanted HSCs will inform efforts to improve HSCT. Here, we report that G-protein-coupled receptor-associated sorting proteins (GPRASPs) function as negative regulators of HSCT. Silencing of Gprasp1 or Gprasp2 increased the survival, quiescence, migration, niche retention, and hematopoietic repopulating activity of hematopoietic stem and progenitor cells (HSPCs) posttransplant. We further show that GPRASP1 and GPRASP2 promote the degradation of CXCR4, a master regulator of HSC function during transplantation. CXCR4 accumulates in Gprasp-deficient HSPCs, boosting their function posttransplant. Thus, GPRASPs negatively regulate CXCR4 stability in HSCs. Our work reveals GPRASP proteins as negative regulators of HSCT and CXCR4 activity. Disruption of GPRASP/CXCR4 interactions could be exploited in the future to enhance the efficiency of HSCT.

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.

Human Umbilical Cord Blood Cell Transplantation in Neuroregenerative Strategies

At present there is no effective treatment of pathologies associated with the death of neurons and glial cells which take place as a result of physical trauma or ischemic lesions of the nervous system. Thus, researchers have high hopes for a treatment based on the use of stem cells (SC), which are potentially able to replace dead cells and synthesize neurotrophic factors and other molecules that stimulate neuroregeneration. We are often faced with ethical issues when selecting a source of SC. In addition to precluding these, human umbilical cord blood (hUCB) presents a number of advantages when compared with other sources of SC. In this review, we consider the key characteristics of hUCB, the results of various studies focused on the treatment of neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis), ischemic (stroke) and traumatic injuries of the nervous system and the molecular mechanisms of hUCB-derived mononuclear and stem cells.

Engineering cord blood to improve engraftment after cord blood transplant

Umbilical cord blood transplant (CBT) has traditionally been associated with slower engraftment of neutrophils, delayed immune reconstitution and consequently higher risk of infections as compared with peripheral blood progenitor cell (PBPC) or bone marrow (BM) transplants. This is primarily due to low numbers of total nucleated cells (TNCs) and the naive nature of CB immune cells. The use of double unit CB transplant (DCBT) increases the total cell dose in the graft, but it still does not produce as rapid engraftment as seen with PBPC or even BM transplants. Herein, we discuss strategies to improve engraftment after CBT. We describe methods of (I) expansion of CB graft ex vivo to increase the total cell dose; and (II) enhancement of BM homing capability of CB progenitor cells; (III) ex vivo expansion of CB derived T cells for improving T cell function against viruses, tumors and protection from graft versus host disease (GVHD). With these novel approaches, engraftment after CBT is now reaching levels comparable to that of other graft types.

Autologous Hematopoietic Stem Cell Transplantation for Adults With Acute Myeloid Leukemia

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) remains the most efficacious therapy in patients with acute leukemia. For older patients and those lacking a related HLA-compatible donor, autologous transplantation (auto-HSCT) is a valid alternative therapeutic option.

METHODS

From 1997 until 2014 in the Department of Hematooncology and Bone Marrow Transplantation, Medical University of Lublin, Poland, 29 auto-HSCT were performed in patients with acute myeloid leukemia (AML; 15 men and 14 women; median age, 52.2 years). The following FAB types of AML were diagnosed: M0, 3; M1, 4; M2, 6; M4, 10; and M5, 6. Patients with AML were classified into 3 cytogenetic prognostic groups: high risk, 9; intermediate risk, 16; and low risk, 4. Twenty-five were in first complete remission and 4 in second complete remission. The peripheral HSCs mobilized after chemotherapy (mainly second course of consolidation) and granulocyte colony-stimulating factor were the source of the stem cells in all cases. The median number of infused CD34+ cells was 3.58 × 10(6)/kg. The conditioning regimen was busulfan and cyclophosphamide in all patients with AML. The intravenous form of busulfan was applied in the last 15 patients.

RESULTS

The median time for absolute neutrophil count recovery >0.5 × 10(9)/L and for platelet count >20.0 × 10(9)/L was 12 and 16.5 days, respectively. Treatment-related mortality rate in the whole group was 3.4% (1 patient with sepsis in the aplastic period). The median follow-up time of survivors was 21.9 months (range, 11.7-142.4). The 3-year projected disease-free survival and overall survival rates were 60% and 68%, respectively.

CONCLUSIONS

Our data confirm that auto-HSCT is a valuable therapeutic option for patients with AML, especially older patients and those lacking related HLA-compatible donors.

MiRNAs and piRNAs from bone marrow mesenchymal stem cell extracellular vesicles induce cell survival and inhibit cell differentiation of cord blood hematopoietic stem cells: a new insight in transplantation

Hematopoietic stem cells (HSC), including umbilical cord blood CD34+ stem cells (UCB-CD34+), are used for the treatment of several diseases. Although different studies suggest that bone marrow mesenchymal stem cells (BM-MSC) support hematopoiesis, the exact mechanism remains unclear. Recently, extracellular vesicles (EVs) have been described as a novel avenue of cell communication, which may mediate BM-MSC effect on HSC. In this work, we studied the interaction between UCB-CD34+ cells and BM-MSC derived EVs. First, by sequencing EV derived miRNAs and piRNAs we found that EVs contain RNAs able to influence UCB-CD34+ cell fate. Accordingly, a gene expression profile of UCB-CD34+ cells treated with EVs, identified about 100 down-regulated genes among those targeted by EV-derived miRNAs and piRNAs (e.g. miR-27b/MPL, miR-21/ANXA1, miR-181/EGR2), indicating that EV content was able to modify gene expression profile of receiving cells. Moreover, we demonstrated that UCB-CD34+ cells, exposed to EVs, significantly changed different biological functions, becoming more viable and less differentiated. UCB-CD34+ gene expression profile also identified 103 up-regulated genes, most of them codifying for chemokines, cytokines and their receptors, involved in chemotaxis of different BM cells, an essential function of hematopoietic reconstitution. Finally, the exposure of UCB-CD34+ cells to EVs caused an increased expression CXCR4, paralleled by an in vivo augmented migration from peripheral blood to BM niche in NSG mice. This study demonstrates the existence of a powerful cross talk between BM-MSC and UCB-CD34+ cells, mediated by EVs, providing new insight in the biology of cord blood transplantation.

Lack of impact of umbilical cord blood unit processing techniques on clinical outcomes in adult double cord blood transplant recipients

BACKGROUND AIMS

Despite widespread use of umbilical cord blood (UCB) transplantation and distinct practice preferences displayed by individual UCB banks and transplant centers, little information exists on how processing variations affect patient outcomes.

METHODS

We reviewed 133 adult double UCB transplants performed at a single center: 98 after reduced-intensity and 35 after myeloablative conditioning. Processing associated with contributing UCB banks and units was surveyed to identify differences in practice. We analyzed effect of selected variables on clinical outcomes of engraftment, dominance, transplant-related mortality, and survival.

RESULTS

Eighty-eight percent of banks queried currently practice red blood cell (RBC) depletion before cryopreservation. This reflects a shift in practice because previously 65% of banks employed RBC-replete processing methods (i.e., cryopreservation or plasma/volume reduction). Neither neutrophil nor platelet engraftment was affected by processing conditions analyzed. RBC depletion was not associated with clinical outcomes, except in 17 recipients of 2 RBC-replete units, where survival was better than that observed in 116 recipients of ≥1 RBC-depleted units (hazard ratio 3.26, P = 0.004). When analyzed by attributes of the dominant unit, RBC depletion, time in storage, bank years in existence, and inventory size did not affect clinical outcomes. Postthaw viability and CD34 dose were factors impacting engraftment. Notably, all RBC-replete units in this cohort were washed in dextran-human serum albumin before infusion.

DISCUSSION

These findings support continued utilization of the entire existing pool of cord blood units, despite recent trends in processing, and have important implications for banking resources and UCB selection practices.

Clinical-scale expansion of CD34+ cord blood cells amplifies committed progenitors and rapid scid repopulation cells

Umbilical cord blood (UCB) transplantation is associated with long periods of aplastic anaemia. This undesirable situation is due to the low cell dose available per unit of UCB and the immaturity of its progenitors. To overcome this, we present a cell culture strategy aimed at the expansion of the CD34⁺ population and the generation of granulocyte lineage-committed progenitors. Two culture products were produced after either 6 or 14days of in vitro expansion, and their characteristics compared to non-expanded UCB CD34⁺ controls in terms of phenotype, colony-forming activity and multilineage repopulation potential in NOD-scid IL2Rγ^null mice. Both expanded cell products maintained rapid SCID repopulation activity similar to the non-expanded control, but 14-day cultured cells showed impaired long term SCID repopulation activity. The process was successfully scaled up to clinically relevant doses of 89×10⁶ CD34⁺ cells committed to the granulocytic lineage and 3.9×10⁹ neutrophil precursors in different maturation stages. Cell yields and biological properties presented by the cell product obtained after 14days in culture were superior and therefore this is proposed as the preferred production setup in a new type of dual transplant strategy to reduce aplastic periods, producing a transient repopulation before the definitive engraftment of the non-cultured UCB unit. Importantly, human telomerase reverse transcriptase activity was undetectable, c-myc expression levels were low and no genetic abnormalities were found, as determined by G-banding karyotype, further confirming the safety of the expanded product.

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.

Immune reconstitution after cord blood transplantation: peculiarities, clinical implications and management strategies

Umbilical cord blood (UCB) is now widely used as an alternative hematopoietic stem cell source for patients lacking closely matched related or unrelated adult donors. UCB transplantation has traditionally been associated with delayed engraftment, poor immune reconstitution and consequent increased risk of infection. More recent clinical studies, however, suggest that conditioning regimens and in particular the omission of in vivo T-cell depletion may play a crucial role in post-transplant T-cell expansion, facilitating a uniquely rapid immune recovery after UCB transplantation. The peculiar characteristics of UCB cells, the importance of thymic function and the role of conditioning regimens and graft-versus-host disease influencing immune reconstitution are described. The last part of the review reports available data on UCB, as well as third-party peripheral blood derived anti-viral cell therapy, which provides a novel approach to rescue UCB recipients with viral complications in the post-transplant period.

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).

Haplo-cord transplantation using CD34+ cells from a third-party donor to speed engraftment in high-risk patients with hematologic disorders

Among the strategies to optimize engraftment of cord blood (CB) stem cell transplantation (SCT), single CB with the coinfusion of CD34(+) stem cells from an HLA-mismatched auxiliary donor (haplo-cord) provides a valid alternative for adult patients without a suitable donor. A total of 132 high-risk adult patients with hematological malignancies from 3 Spanish institutions underwent myeloablative haplo-cord SCT. The median age was 37 years and median weight was 70 kg; 37% had active disease. The median number of postprocessing CB total nucleated and CD34(+) cells was 2.4 × 10(7)/kg (interquartile range [IQR], 1.8 to 2.9) and 1.4 × 10(5)/kg (IQR, .9 to 2), respectively. Neutrophil engraftment occurred in a median of 11.5 days (IQR, 10.5 to 16.5) and platelet engraftment at 36 days (IQR, 25.5 to 77). Graft failure was 2% overall and only 9% for CB. Cumulative incidence of acute graft-versus-host disease (GHVD) grades II to IV was 21% and cumulative incidence of chronic GVHD was 21%. Median follow-up was 60 months (range, 3.5 to 163). Overall survival was 43.5%, event-free survival was 38.3%, nonrelapse mortality was 35%, and relapse was 20% at 5 years. Myeloablative haplo-cord SCT results in fast engraftment of neutrophils and platelets, low incidences of acute and chronic GVHD, and favorable long-term outcomes using single CB units with relatively low cell content. Moreover, CB cell dose had no impact on CB engraftment and survival in this study. Therefore, haplo-cord SCT expands donor availability while reducing CB cell dose requirements.

Modelling the sitagliptin effect on dipeptidyl peptidase-4 activity in adults with haematological malignancies after umbilical cord blood haematopoietic cell transplantation

BACKGROUND AND OBJECTIVES

Dipeptidyl peptidase-4 (DPP4) inhibition is a potential strategy to increase the engraftment rate of haematopoietic stem/progenitor cells. A recent clinical trial using sitagliptin, a DPP4 inhibitor approved for type 2 diabetes mellitus, has been shown to be a promising approach in adults with haematological malignancies after umbilical cord blood (UCB) haematopoietic cell transplantation (HCT). On the basis of data from this clinical trial, a semi-mechanistic model was developed to simultaneously describe DPP4 activity after multiple doses of sitagliptin in subjects with haematological malignancies after a single-unit UCB HCT.

METHODS

The clinical study included 24 patients who received myeloablative conditioning followed by oral sitagliptin with single-unit UCB HCT. Using a nonlinear mixed-effects approach, a semi-mechanistic pharmacokinetic-pharmacodynamic model was developed to describe DPP4 activity from these trial data, using NONMEM version 7.2 software. The model was used to drive Monte Carlo simulations to probe the various dosage schedules and the attendant DPP4 response.

RESULTS

The disposition of sitagliptin in plasma was best described by a two-compartment model. The relationship between sitagliptin concentrations and DPP4 activity was best described by an indirect response model with a negative feedback loop. Simulations showed that twice daily or three times daily dosage schedules were superior to a once daily schedule for maximal DPP4 inhibition at the lowest sitagliptin exposure.

CONCLUSION

This study provides the first pharmacokinetic-pharmacodynamic model of sitagliptin in the context of HCT, and provides a valuable tool for exploration of optimal dosing regimens, which are critical for improving the time to engraftment in patients after UCB HCT.

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.

Counteracting the enzymatic activity of dipeptidylpeptidase 4 for potential therapeutic advantage, with an emphasis on cord blood transplantation

Dipeptidylpeptidase (DPP) 4, also known as CD26, is an enzyme present on the surface of a number of different cell types. It is also found within cells and as a soluble protein in body fluids. It can specifically truncate proteins at the penultimate N-terminus residue for some amino acids, such as alanine, proline, serine, and perhaps others. DPP4 has been implicated in regulating the in vitro and in vivo functional activities of a number of hematopoietically active molecules, and this information, along with that on inhibition of DPP4, has been studied in efforts to enhance hematopoietic cell transplantation (HCT), hematopoiesis after stress in mouse models, and in the clinical setting of single-unit cord blood (CB) HCT. This article reviews the current status of this compound's effects on regulatory proteins, the field of CB HCT, a potential role for modulating DPP4 activity in enhancing single-unit CB HCT in adults, and future aspects in context of other cellular therapies and the area of regenerative medicine.

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.

Megakaryocytes promote murine osteoblastic HSC niche expansion and stem cell engraftment after radioablative conditioning

Successful hematopoietic stem cell (HSC) transplantation requires donor HSC engraftment within specialized bone marrow microenvironments known as HSC niches. We have previously reported a profound remodeling of the endosteal osteoblastic HSC niche after total body irradiation (TBI), defined as relocalization of surviving megakaryocytes to the niche site and marked expansion of endosteal osteoblasts. We now demonstrate that host megakaryocytes function critically in expansion of the endosteal niche after preparative radioablation and in the engraftment of donor HSC. We show that TBI-induced migration of megakaryocytes to the endosteal niche depends on thrombopoietin signaling through the c-MPL receptor on megakaryocytes, as well as CD41 integrin-mediated adhesion. Moreover, niche osteoblast proliferation post-TBI required megakaryocyte-secreted platelet-derived growth factor-BB. Furthermore, blockade of c-MPL-dependent megakaryocyte migration and function after TBI resulted in a significant decrease in donor HSC engraftment in primary and competitive secondary transplantation assays. Finally, we administered thrombopoietin to mice beginning 5 days before marrow radioablation and ending 24 hours before transplant to enhance megakaryocyte function post-TBI, and found that this strategy significantly enhanced donor HSC engraftment, providing a rationale for improving hematopoietic recovery and perhaps overall outcome after clinical HSC transplantation.

Cytomegalovirus-specific T cells are primed early after cord blood transplant but fail to control virus in vivo

A disadvantage of umbilical cord blood transplantation (UCBT) is the delay in immune reconstitution, placing patients at increased risk for infections after transplant. Cytomegalovirus (CMV) in particular has been shown to cause significant morbidity in patients undergoing UCBT. Here, we comprehensively evaluate the development of CD4(+) and CD8(+) T-cell responses to CMV in a cohort of patients that underwent double UCBT. Our findings demonstrate conclusively that a diverse polyclonal CMV-specific T-cell response derived from the UCB graft is primed to viral antigens as early as day 42 after UCBT, but these T cells fail to achieve sufficient numbers in vivo to control CMV reactivations. This is not due to an inherent inability of UCB-derived T cells to proliferate, as these T cells underwent rapid proliferation in vitro. The TCR diversity and antigen specificity of CMV-specific T cells remained remarkably stable in the first year after transplant, suggesting that later control of virus replication results from improved function of T cells primed early after transplant and not from de novo responses derived from later thymic emigrants. Ex vivo expansion and adoptive transfer of CMV-specific T cells isolated from UCBT recipients early after transplant could augment immunity to CMV.

In vivo DPP-4 inhibition to enhance engraftment of single-unit cord blood transplants in adults with hematological malignancies

Delayed engraftment is a significant limitation of umbilical cord blood (UCB) transplantation due to low stem cell numbers. Inhibition of dipeptidyl peptidase (DPP)-4 enhanced engraftment in murine transplants. We evaluated the feasibility of systemic DPP-4 inhibition using sitagliptin to enhance engraftment of single-unit UCB grafts in adults with hematological malignancies. Twenty-four patients (21-58 years) received myeloablative conditioning, followed by sitagliptin 600 mg orally days -1 to +2, and single UCB grafts day 0. Seventeen receiving red cell-depleted (RCD) grafts, matched at 4 (n=10) or 5 (n=7) of 6 human leucocyte antigen (HLA) loci with median nucleated cell dose 3.6 (2.5-5.2)×10(7)/kg, engrafted at median of 21 (range, 13-50) days with cumulative incidence of 94% (95% confidence interval, 84%-100%) at 50 days. Plasma DDP-4 activity was reduced to 23%±7% within 2 h. Area under DPP-4 activity-time curve (AUCA) correlated with engraftment; 9 of 11 with AUCA <6,000 activity·h engrafted within ≤21 days, while all 6 with higher AUCA engrafted later (P=0.002). Seven patients receiving red cell replete grafts had 10-fold lower colony forming units after thawing compared with RCD grafts, with poor engraftment. Systemic DPP-4 inhibition was well tolerated and may enhance engraftment. Optimizing sitagliptin dosing to achieve more sustained DPP-4 inhibition may further improve outcome.

A soluble granulocyte colony stimulating factor decoy receptor as a novel tool to increase hematopoietic cell homing and reconstitution in mice

The relative ineffectiveness of hematopoietic stem cells in reaching the bone marrow upon transplantation combined with the limited number of these cells available is a major reason for graft failure and delayed hematopoietic recovery. Hence, the development of strategies that could enhance homing is of high interest. Here, we provide evidence that homing is severely impaired postexposure to ionizing radiation (IR) in mice, an effect we found was time dependent and could be partially rescued using mesenchymal stromal cell (MSC) therapy. In an attempt to further increase homing, we took advantage of our observation that the granulocyte colony stimulating factor (G-CSF), a cytokine known to induce cell mobilization, is increased in the marrow of mice shortly after their exposure to IR. As such, we developed a truncated, yet functional, soluble G-CSF receptor (solG-CSFR), which we hypothesized could act as a decoy and foster homing. Using MSCs or conditioned media as delivery vehicles, we show that an engineered solG-CSFR has the potential to increase homing and hematopoietic reconstitution in mice. Altogether, our results provide novel findings at the interplay of IR and stromal cell therapy and present the regulation of endogenous G-CSF as an innovative proof-of-concept strategy to manipulate hematopoietic cell homing.

Impact of donor-specific anti-HLA antibodies on graft failure and survival after reduced intensity conditioning-unrelated cord blood transplantation: a Eurocord, Société Francophone d'Histocompatibilité et d'Immunogénétique (SFHI) and Société Française de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC) analysis

Graft failure is a major complication after unrelated cord blood transplantation. Presence of HLA-antibodies before cord blood transplantation may impact graft failure. To analyze the effect of anti-HLA antibodies on unrelated cord blood transplantation outcomes, we analyzed 294 unrelated cord blood transplant recipients after reduced intensity conditioning regimen. The majority of the patients (82%) were transplanted for malignancies, 60% with double-unrelated cord blood transplant, 63% were HLA mismatched. Retrospectively, pre-unrelated cord blood transplant serum was tested for HLA-Ab using Luminex™ platform. Results were interpreted as mean fluorescence intensity (MFI) against donor-specific mismatch. Among 62 recipients (23%) who had anti-HLA antibodies before unrelated cord blood transplant, 14 patients had donor specific anti-HLA antibodies (DSA) (7 were donor-specific anti-HLA antibodies for single unrelated cord blood transplant and 7 for double unrelated cord blood transplant). Donor specific anti-HLA antibodies threshold ranged from 1620-17629 of mean fluorescence intensity (MFI). Cumulative incidence of Day-60 neutrophil engraftment was 76%: 44% for recipients with donor specific anti-HLA antibodies and 81% in those without donor specific anti-HLA antibodies (P=0.006). The cumulative incidence of 1-year transplant related mortality was 46% in patients with donor specific anti-HLA antibodies and 32% in those without antibodies (P=0.06). The presence of donor specific anti-HLA antibodies was associated with a trend for decreased survival rate (42% vs. 29%; P=0.07). Donor specific anti-HLA antibody in recipients of unrelated cord blood transplant is associated with graft failure and decreased survival. Patient's screening for donor specific anti-HLA antibodies before unrelated cord blood transplantation is recommended before choosing an HLA mismatched cord blood unit. Whenever possible it is important to avoid selecting a unit for which the patient has donor specific anti-HLA antibodies.

Haematopoietic stem cell survival and transplantation efficacy is limited by the BH3-only proteins Bim and Bmf

Anti-apoptotic Bcl-2 family members are critical for the regulation of haematopoietic stem and progenitor cell (HSPC) survival. Little is known about the role of their pro-apoptotic antagonists, i.e. ‘BH3-only’ proteins, in this cell compartment. Based on the analysis of cytokine deprivation-induced changes in mRNA expression levels of Bcl-2 family proteins, we determined the consequences of BH3-only protein depletion on HSPC survival in culture and, for selected candidates, on engraftment in vivo. Thereby, we revealed a critical role for Bim and Bmf as regulators of HSPC dynamics both during early engraftment and long-term reconstitution. HSPCs derived from wild-type donors were readily displaced by Bim- or Bmf-deficient or Bcl-2-overexpressing HSPCs as early as 10 days after engraftment. Moreover, in the absence of Bim, significantly lower numbers of transplanted HSPCs were able to fully engraft radio-depleted recipients. Finally, we provide proof of principle that RNAi-based reduction of BIM or BMF, or overexpression of BCL-2 in human CD34⁺ cord blood cells may be an attractive therapeutic option to increase stem cell survival and transplantation efficacy.

Impact of storage temperature and processing delays on cord blood quality: discrepancy between functional in vitro and in vivo assays

BACKGROUND

Optimal conditions of cord blood (CB) storage, processing, cryopreservation, and thawing are critical for banking and transplantation. Nevertheless, standardized procedures are still awaited.

STUDY DESIGN AND METHODS

We evaluated the impact of preprocessing storage and temperature on recovery, viability, and functional differentiation capacities of hematopoietic progenitor cells. We compared units stored at room temperature (RT) or at 4 °C for 72 hours before cryopreservation to units processed shortly after collection (<12 hr).

RESULTS

Postthaw results showed similar in vitro characteristics between immediate processing and 4 °C storage for cell recovery and viability, both significantly higher than RT storage. Surprisingly, we demonstrated that storage of CB units at RT before processing and cryopreservation profoundly altered in vivo hematopoietic reconstitution in mice, although in vitro hematopoietic colony-forming unit potential was unaltered.

CONCLUSION

Our findings challenge current CB storage practices and suggest standard in vitro quality assessments may not always be indicative of CB engraftment potential.

Insights and hopes in umbilical cord blood stem cell transplantations

Over 20.000 umblical cord blood transplantations (UCBT) have been carried out around the world. Indeed, UCBT represents an attractive source of donor hematopoietic stem cells (HSCs) and, offer interesting features (e.g., lower graft-versus-host disease) compared to bone marrow transplantation (BMT). Thereby, UCBT often represents the unique curative option against several blood diseases. Recent advances in the field of UCBT, consisted to develop strategies to expand umbilical stem cells and shorter the timing of their engraftment, subsequently enhancing their availability for enhanced efficacy of transplantation into indicated patients with malignant diseases (e.g., leukemia) or non-malignant diseases (e.g., thalassemia major). Several studies showed that the expansion and homing of UCBSCs depends on specific biological factors and cell types (e.g., cytokines, neuropeptides, co-culture with stromal cells). In this review, we extensively present the advantages and disadvantages of current hematopoietic stem cell transplantations (HSCTs), compared to UBCT. We further describe the importance of cord blood content and obstetric factors on cord blood selection, and report the recent approaches that can be undertook to improve cord blood stem cell expansion as well as engraftment. Eventually, we provide two majors examples underlining the importance of UCBT as a potential cure for blood diseases.

Umbilical cord blood graft enhancement strategies: has the time come to move these into the clinic?

Umbilical cord blood (UCB) is an attractive stem cell graft option for patients who need allogeneic hematopoietic stem cell support, but lack a suitable HLA-matched donor. However, the limited number of hematopoietic progenitor cells in a single cord blood unit can lead to an increased risk of graft failure, delayed hematological recovery and prolonged immunosuppression, particularly in adult patients. Several strategies to overcome these potential limitations are being evaluated. In this review, we discuss promising ex vivo manipulations to enhance cord blood engraftment capacity such as culture of UCB cells with stimulatory cytokines and growth factors, mesenchymal cells, Notch ligand, copper chelators, prostaglandins, complement components, nicotinamide and CD26/DPPIV inhibitors. All these approaches are now in early clinical trials. However, despite the fact that several cord blood enhancement strategies have resulted in increased numbers of progenitor cells and faster neutrophil recovery, the ability of these techniques to significantly shorten engraftment time and permit the use of cord units with low numbers of total nucleated cells, or accomplish reliable engraftment with a single cord, have yet to be convincingly demonstrated. The ultimate clinical value of ex vivo cord blood expansion or manipulation has not been defined yet, and the current data do not permit predicting which technology will prove to be the optimal strategy. Nevertheless, expectations remain high that eventually ex vivo enhancement will be able to improve clinical outcomes and significantly extend the applicability of UCB transplantation.

Enhancing engraftment of cord blood cells via insight into the biology of stem/progenitor cell function

Cord blood (CB) transplantation has been used over the last 24 years to treat patients with malignant and nonmalignant disorders. CB has its advantages and disadvantages compared with other sources of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) for transplantation. More knowledge of the cytokines and intracellular signaling molecules regulating HSCs and HPCs could be used to modulate these regulators for clinical benefit. This review provides information about the general field of CB transplantation and about studies from the author's laboratory that focus on regulation of HSCs and HPCs by CD26/DPPIV, SDF-1/CXCL12, the Rheb2-mTOR pathway, SIRT1, DEK, cyclin-dependent kinase inhibitors, and cytokines/growth factors. Cryopreservation of CB HSCs and HPCs is also briefly discussed.

Intrabone cord blood hematopoietic stem cell transplantation in a subset of very high-risk pediatric patients: a safety and feasibility pilot study

The main limit of umbilical cord blood hematopoietic stem cell transplantation is a more difficult engraftment related to the number of cells infused per kilogram of recipient body weight. This limit makes the cord blood a suboptimal source of hematopoietic stem cells for transplantation in case of difficult engraftment situations. Direct intrabone cord blood (CB) injection has been recently investigated as a solution to cell dose problem in the adults population, but there is a lack of data concerning this approach in pediatric patients. Here, we describe 5 pediatric patients undergoing intrabone cord blood transplantation (IBCBT) for different diseases characterized by a high risk of posttransplant graft failure. The conditioning regimen differed according to the disease, whereas the GvHD prophylaxis consisted of cyclosporine, mycophenolate, and ATG. The median numbers of total nucleated cells infused and CD34(+) cells were 3.3 × 10(7)/kg, 2 × 10(5)/kg. All the patients showed complete hematological recovery and complete donor engraftment. No patient had secondary graft failure, whereas 1 patient relapsed 6 months after IBCBT. No patient died of transplant-related complications. Our results show that IBCBT is safe and feasible in pediatrics as well, and suggest that IBCBT might be an attractive option to overcome some limits of umbilical cord blood hematopoietic stem cell transplantation.

Irradiated allogeneic cells enhance umbilical cord blood stem cell engraftment in immunodeficient mice

Umbilical cord blood (UCB) is a readily available source of hematopoietic stem cells for transplantation. UCB hematopoietic SCT for average- and large-sized patients is often limited by the number of cells available in a single unit. To address this limitation, we performed experiments to determine if adjunctive therapy with third-party human allogeneic cells enhances the engraftment of human UCB in immunodeficient mice. UCB cells with or without sequential infusion of irradiated third-party allogeneic cells were used in transplantation studies of NOD/SCID and NOD/SCID-IL2Rγ null mice. We studied the impact of irradiated allogeneic cells on colony formation in vitro using long-term culture assays also. Our studies demonstrate that short- and long-term UCB engraftment of immunodeficient mice is enhanced by irradiated allogeneic cells. Secondary transplants demonstrate the durability of engraftment. These preclinical studies support the further development of irradiated allogeneic cells as an adjunct to single UCB transplantation when limiting numbers of cells are available.

Hematopoietic, CNS and skeletal muscle stem cells as drug targets: opportunities, progress and challenges

Lineage-committed stem and progenitor cells are currently targeted by a handful of medicines, mainly to treat conditions involving the immune and hematopoietic systems. Knowledge of new stem and progenitor cell populations in the body is accumulating at a rapid pace and a new era of targeting resident stem cell populations for therapeutic ends is coming into focus. Small-molecule regulators of body-resident stem and progenitor cell assess are now a reality both in the clinic and as promising new drugs in the development pipeline. This review will explore the current state of the art with an emphasis on emerging concepts and experimental systems in the therapeutic regulation of endogenous stem and progenitor cell populations.

Ex vivo expansion of umbilical cord blood: where are we?

Since the first successful clinical use of umbilical cord blood (UCB) in 1988, UCB grafts have been used for over 20,000 patients with both malignant and non-malignant diseases. UCB has several practical advantages over other transplantable graft sources. For example, the ease of procurement, the absence of donor risks, the reduced risk of transmissible infections, and the availability for immediate use make UCB an appealing graft choice. However, UCB grafts suffer from a few limitations related to the limited cell dose available for transplantation in each UCB unit and to defects in UCB stem cell homing. These limitations lead to increased post-transplant complications. In this review, we focus on the issue of limited cell dose in UCB units and discuss the possible approaches to overcome this limitation. We also summarize the various cellular pathways that have been explored to expand UCB units.

Comparison of outcomes after HLA-matched sibling and unrelated donor transplantation for children with high-risk acute lymphoblastic leukemia

We compared outcomes after 94 HLA-matched sibling, 168 unrelated donor bone marrow (BM; n = 81 matched and n = 88 mismatched), and 86 cord blood transplantations in patients age 1 to 15 years with acute lymphoblastic leukemia (ALL) in second complete remission (CR). All patients had their first BM relapse within 3 years from diagnosis. Cox regression models were constructed to examine for differences in transplant outcome by donor source. Risks of grade 2 to 4 acute graft-versus-host disease (aGVHD) and chronic graft-versus-host disease (cGVHD), when compared to HLA-matched sibling transplants, were higher after matched unrelated donor BM (relative risk [RR], 2.42; P = .001; RR, 5.12; P < .001, respectively), mismatched BM (RR, 3.24; P < .001; RR, 5.19; P < .001, respectively), and cord blood (RR, 2.67; P < .001; RR, 2.54; P = .024, respectively) transplants. Although nonrelapse mortality was higher after transplantation of mismatched unrelated donor BM and cord blood, there were no differences in leukemia-free survival (LFS) between HLA-matched sibling and any of the unrelated donor transplantations. The 3-year probabilities of LFS were 50% after HLA-matched sibling and 44% after matched unrelated BM, and 44% after mismatched unrelated BM and 43% after cord blood transplantation. Our observations support transplantation of BM or cord blood from a suitably matched unrelated donor or cord blood for patients without an HLA-matched sibling with ALL in second CR.

Cationic liposome-mediated CXCR4 gene delivery into hematopoietic stem/progenitor cells: implications for clinical transplantation and gene therapy

The chemokine stromal cell-derived factor (SDF)-1α/CXCL12 and its receptor CXC chemokine receptor 4 (CXCR4) play a crucial role in the homing/engraftment and retention of hematopoietic stem/progenitor cells (HSPCs) in the bone marrow. It has been shown using the viral gene transfer technique that CXCR4 overexpression on human CD34(+) HSPC significantly improves their engraftment in murine models. However, clinical trials with gene therapy have revealed safety concerns related to the immunogenicity of the viral carriers, due to the random integration of viral genes into the host genome. Therefore, a method for CXCR4 gene delivery into HSPC that is safe, nonviral, and highly efficient is needed to improve clinical transplantation and gene therapies. In this work, we investigated the nonviral CXCR4 gene delivery into HSPC using the cationic liposome agent IBAfect. We used CD34(+) cells from cord blood and the models of immature hematopoietic cells expressing CD34 antigen, namely, leukemic cell lines KG-1a and KG-1. Transfection efficiency was determined by flow cytometric analysis 12, 24, 48, and 72 h after transfection, and the viability of cells analyzed by trypan blue exclusion and MTS assays. The functional response of CXCR4-transfected HSPC toward an SDF-1α gradient was determined by chemotaxis assay. We found that ~25% transfection is achieved for KG-1a and KG-1 cells and 20% for HSPC, and that the viability of CXCR4-transfected HSPC is not significantly altered. More importantly, overexpression of CXCR4 using IBAfect significantly increased the chemotaxis of KG-1 cells and HSPC toward SDF-1α. However, we tested 2 other commercially available cationic liposomes (Lipofectamine 2000 and 1,2-dioleoyl-3-trimethylammonium-propane [DOTAP]) in parallel, and we found that they failed to deliver the CXCR4 gene into cells under the same conditions. These results suggest that IBAfect-mediated in vitro gene delivery to overexpress CXCR4 on HSPC is a safe and efficient technique with great potential for improving the efficacy of HSPC transplantation and gene therapy protocols.

Hematopoietic stem cell homing to injured tissues

The use of stem cells is considered a promising therapy for tissue regeneration and repair, particularly for tissues injured through degeneration, ischemia and inflammation. Bone marrow (BM)-derived haematopoietic stem cells (HSCs) are rare populations of multipotent stem cells that have been identified as promising potential candidates for treating a broad range of conditions. Although research into the use of stem cells for regenerative medicine is on a steep upward slope, clinical success has not been as forthcoming. This has been primarily attributed to a lack of information on the basic biology of stem cells, which remains insufficient to justify clinical studies. In particular, while our knowledge on the molecular adhesive mechanisms and local environmental factors governing stem cell homing to BM is detailed, our understanding of the mechanisms utilized at injured sites is very limited. For instance, it is unclear whether mechanisms used at injured sites are location specific or whether this recruitment can be modulated for therapeutic purposes. In addition, it has recently been suggested that platelets may play an important role in stem cell recruitment to sites of injury. A better understanding of the mechanisms used by stem cells during tissue homing would allow us to develop strategies to improve recruitment of these rare cells. This review will focus on the status of our current understanding of stem cell homing to injured tissues, the role of platelets and directions for the future.

Prospective study of one- vs two-unit umbilical cord blood transplantation following reduced intensity conditioning in adults with hematological malignancies

As the threshold nucleated cell dose for one-unit umbilical cord blood (UCB) in adults has not to date been firmly established, we prospectively compared one- vs two-unit UCB transplantation after reduced intensity conditioning (RIC) in adult patients with hematological malignancies. Study design specified one-UCB unit if the cryopreserved total nucleated cell (TNC) dose was 2.5 × 10(7)/kg recipient weight, otherwise two units matched at minima of 4/6 HLA loci to the patient and 3/6 to each other were infused. A total of 27 patients received one unit; 23 patients received two units. Median time to ANC >500/μL was 24 days (95% confidence interval 22-28 days), 25 days for one unit and 23 days for two units (P=0.99). At day 100, ANC >500/μL was 88.4 and 91.3% in the one- and two-unit groups (P=0.99), respectively. Three-year EFS was 28.6% and 39.1% in the one- and two-unit groups (P=0.71), respectively. Infusion of two units was associated with a significantly lower relapse risk, 30.4% vs 59.3% (P=0.045). Infused cell doses (TNC, CD3(+), CD34(+) and CD56(+)CD3(neg)) did not impact on engraftment, OS or EFS. Taken together, one-unit UCB transplantation with a threshold cell dose 2.5 × 10(7)/kg recipient weight after RIC is a viable option for adults, although infusion of two units confers a lower relapse incidence.

Ex vivo rapamycin treatment of human cord blood CD34+ cells enhances their engraftment of NSG mice

Since cord blood (CB) has become a commonly used source of transplantable hematopoietic stem (HSC) and hematopoietic progenitor cells (HPC), there has been a need to overcome the limited HSC and HPC numbers available to transplant from a single CB, especially for adult recipients. Our laboratory previously demonstrated that Rheb2 overexpression significantly impaired the repopulating ability of HSC. Since overexpression of Rheb2 leads to increased signaling through mTOR, we examined the effect of the mTOR inhibitor rapamycin ex vivo on cytokine expanded CD34(+) CB cells for the engraftment of these cells in non-obese diabetic, severe combined immunodeficient, IL-2 receptor γ chain null (NSG) mice. We observed significant enhancement in engraftment of the CB treated ex vivo with cytokines in the presence of rapamycin prior to transplant, effects seen in primary as well as secondary transplants. These pre-clinical results suggest a positive role for rapamycin during ex vivo culture of CB SCID repopulating cells/HSC.