The impact of donor-specific anti-HLA antibody levels on primary poor graft function and graft rejection in rituximab desensitized haploidentical stem cell transplantation

This study investigates the influence of donor-specific anti-HLA antibodies (DSA) levels on primary poor graft function (PGF) and graft rejection (GR) after haploidentical stem cell transplantation (haplo-SCT) with rituximab desensitization. A total of 155 DSA-positive haplo-SCT candidates with mean fluorescence intensity (MFI) between 2000 and 10,000 were enrolled in this prospective clinical trial. Receiver operating characteristic (ROC) curves determined the optimal DSA MFI cutoff for identifying high-risk patients. Patients were categorized into two groups: DSA low-level group (2000 ≤ DSA MFI < 5000, Group A) and high-level group (5000 ≤ DSA MFI ≤ 10,000, Group B). The incidence of primary PGF was 6.5% (2.6%-10.3%), while GR incidence was 0.6% (0.0%-1.9%). Group A had significantly lower primary PGF rates than Group B (2.3% [0.0%-5.7%] vs. 12.9% [4.8%-21.0%], p = 0.017). Only one patient in Group B experienced GR. High DSA levels (5000 ≤ MFI ≤ 10,000) were identified as the sole independent risk factor for primary PGF and GR after haplo-SCT with rituximab desensitization (HR = 7.282, 95% CI 1.517-34.953, p = 0.013). The 4-year cumulative incidence of relapse, non-relapse mortality, disease-free survival, and overall survival were 14.7% (11.6%-17.8%), 16.3% (13.1%-19.4%), 69.0% (65.9%-76.2%), and 70.6% (66.4%-74.8%), respectively. DSA levels have an impact on efficiency of rituximab desensitization, and a DSA MFI threshold is provided for predicting primary PGF and GR.

Potential Use of Mesenchymal Multipotent Cells for Hemopoietic Stem Cell Transplantation: Pro and Contra

The potential of mesenchymal multipotent (stem) cells (MSC) to modify immune reactions and mediate hematopoiesis boosted great interest for their use in allogeneic hemopoietic stem cell transplantation. Because of MSC production of a wide range of cytokines and growth factors, these cells are included in the therapy of graft-versus-host disease (GVHD). A number of clinical studies have demonstrated safety and efficacy of MSC-based therapy in acute GVHD. Japan and some other countries approved biomedical cell products on the base of allogeneic bone marrow (BM) MSCs as medical agents for acute GVHD treatment. Besides, MSCs may form BM stroma and improve hematopoiesis. Simultaneous transplantation of hematopoietic stem cells and MSCs effectively improved engraftment and prevented GVHD in transplantation of umbilical cord blood and human leukocyte antigens-incompatible BM stem cells. The review presents the analysis of clinical studies of MSCs in allogeneic hematopoietic stem cell transplantation and discusses different approaches for improvement of MSC-based GVHD treatment and prophylaxis.

Rituximab for desensitization during HLA-mismatched stem cell transplantation in patients with a positive donor-specific anti-HLA antibody

To define the efficacy of a single dose of 375 mg/m² rituximab for DSA-positive patients with 2000 ≤ MFI < 10,000, we enrolled a prospective clinical cohort including patients with positive DSA treated with rituximab (n = 55, cohort A), a matched-pair cohort including cases with negative DSA (n = 110, cohort B) and a historical cohort including subjects with 2000 ≤ MFI < 10,000 without receiving any treatment for DSA (n = 22, cohort C). The incidences of primary poor graft function (PGF) in cohort A and cohort B were 5% and 1% (P = 0.076), respectively, both of which were lower than that in cohort C (27%, P < 0.001, for all). Rituximab was associated with a reduced incidence of primary PGF (HR 0.200, P = 0.023). The 3-year nonrelapse mortality of patients in cohort A and cohort B were 23% and 24%, respectively, both of which were lower than that in the cohort C (37%), although no statistical significance was observed. These results led to a low 3-year overall survival in patients in the cohort C (58%) compared with those in the cohort A (71%) and the cohort B (73%). We suggest that a single dose of rituximab could be effectively used to prevent the onset of primary PGF. The prospective cohort of this study is registered at http://www.chictr.org.cn/ChiCTR-OPC-15006672.

PDGFB-expressing mesenchymal stem cells improve human hematopoietic stem cell engraftment in immunodeficient mice

The bone marrow (BM) niche regulates multiple hematopoietic stem cell (HSC) processes. Clinical treatment for hematological malignancies by HSC transplantation often requires preconditioning via total body irradiation, which severely and irreversibly impairs the BM niche and HSC regeneration. Novel strategies are needed to enhance HSC regeneration in irradiated BM. We compared the effects of EGF, FGF2, and PDGFB on HSC regeneration using human mesenchymal stem cells (MSCs) that were transduced with these factors via lentiviral vectors. Among the above niche factors tested, MSCs transduced with PDGFB (PDGFB-MSCs) most significantly improved human HSC engraftment in immunodeficient mice. PDGFB-MSC-treated BM enhanced transplanted human HSC self-renewal in secondary transplantations more efficiently than GFP-transduced MSCs (GFP-MSCs). Gene set enrichment analysis showed increased antiapoptotic signaling in PDGFB-MSCs compared with GFP-MSCs. PDGFB-MSCs exhibited enhanced survival and expansion after transplantation, resulting in an enlarged humanized niche cell pool that provide a better humanized microenvironment to facilitate superior engraftment and proliferation of human hematopoietic cells. Our studies demonstrate the efficacy of PDGFB-MSCs in supporting human HSC engraftment.

The Incorporation of Extracellular Vesicles from Mesenchymal Stromal Cells Into CD34+ Cells Increases Their Clonogenic Capacity and Bone Marrow Lodging Ability

Mesenchymal stromal cells (MSC) may exert their functions by the release of extracellular vesicles (EV). Our aim was to analyze changes induced in CD34⁺ cells after the incorporation of MSC‐EV. MSC‐EV were characterized by flow cytometry (FC), Western blot, electron microscopy, and nanoparticle tracking analysis. EV incorporation into CD34⁺ cells was confirmed by FC and confocal microscopy, and then reverse transcription polymerase chain reaction and arrays were performed in modified CD34⁺ cells. Apoptosis and cell cycle were also evaluated by FC, phosphorylation of signal activator of transcription 5 (STAT5) by WES Simple, and clonal growth by clonogenic assays. Human engraftment was analyzed 4 weeks after CD34⁺ cell transplantation in nonobese diabetic/severe combined immunodeficient mice. Our results showed that MSC‐EV incorporation induced a downregulation of proapoptotic genes, an overexpression of genes involved in colony formation, and an activation of the Janus kinase (JAK)‐STAT pathway in CD34⁺ cells. A significant decrease in apoptosis and an increased CD44 expression were confirmed by FC, and increased levels of phospho‐STAT5 were confirmed by WES Simple in CD34⁺ cells with MSC‐EV. In addition, these cells displayed a higher colony‐forming unit granulocyte/macrophage clonogenic potential. Finally, the in vivo bone marrow lodging ability of human CD34⁺ cells with MSC‐EV was significantly increased in the injected femurs. In summary, the incorporation of MSC‐EV induces genomic and functional changes in CD34⁺ cells, increasing their clonogenic capacity and their bone marrow lodging ability. stem cells2019;37:1357–1368

Immunomodulatory Effects of Placenta-derived Mesenchymal Stem Cells on T Cells by Regulation of FoxP3 Expression

The immunomodulatory effects of mesenchymal stem cells (MSCs) are an important mediator of their therapeutic effects in stem cell therapy and regenerative medicine. The regulation mechanism of MSCs is orchestrated by several factors in both intrinsic and extrinsic events. Recent studies have shown that the dynamic expression of cytokines secreted from MSCs control T cell function and maturation by regulating the expression of FoxP3, which figures prominently in T cell differentiation. However, there is no evidence that placenta-derived mesenchymal stem cells (PD-MSCs) have strong immunomodulatory effects on T cell function and maturation via FoxP3 expression. Therefore, we compared the expression of FoxP3 in activated T cells isolated from peripheral blood and co-cultured with PD-MSCs or bone marrow-derived mesenchymal stem cells (BM-MSCs) and analyzed their effect on T cell proliferation and cytokine profiles. Additionally, we verified the immunomodulatory function of PD-MSCs by siRNA-mediated silencing of FoxP3. MSCs, including PD-MSCs and BM-MSCs, promoted differentiation of naive peripheral blood T cells into CD4+CD25+FoxP3+ regulatory T (Treg) cells. Intriguingly, the population of CD4+CD25+FoxP3+ Treg cells co-cultured with PD-MSCs was significantly expanded in comparison to those co-cultured with BM-MSCs or WI38 cells (p＜0.05, p＜0.001). Dynamic expression patterns of several cytokines, including anti- and pro-inflammatory cytokines and members of the transforming growth factor-beta (TGF-β) family secreted from PD-MSCs according to FoxP3 expression were observed. The results suggest that PD-MSCs have an immunomodulatory effect on T cells by regulating FoxP3 expression.

Mesenchymal Stromal Cells: Role in the BM Niche and in the Support of Hematopoietic Stem Cell Transplantation

Mesenchymal stromal cells (MSCs) are key elements in the bone marrow (BM) niche where they interact with hematopoietic stem progenitor cells (HSPCs) by offering physical support and secreting soluble factors, which control HSPC maintenance and fate. Although necessary for their maintenance, MSCs are a rare population in the BM, they are plastic adherent and can be ex vivo expanded to reach numbers adequate for clinical use. In light of HSPC supportive properties, MSCs have been employed in phase I/II clinical trials of hematopoietic stem cell transplantation (HSCT) to facilitate engraftment of hematopoietic stem cells (HSCs). Moreover, they have been utilized to expand ex vivo HSCs before clinical use. The available clinical evidence from these trials indicate that MSC administration is safe, as no acute and long-term adverse events have been registered in treated patients, and may be efficacious in promoting hematopoietic engraftment after HSCT. In this review, we critically discuss the role of MSCs as component of the BM niche, as recent advances in defining different mesenchymal populations in the BM have considerably increased our understanding of this complex environment. Moreover, we will revise published literature on the use of MSCs to support HSC engraftment and expansion, as well as consider potential new MSC application in the clinical context of ex vivo gene therapy with autologous HSC.

Posttransplant Intramuscular Injection of PLX-R18 Mesenchymal-Like Adherent Stromal Cells Improves Human Hematopoietic Engraftment in A Murine Transplant Model

Late-term complications of hematopoietic cell transplantation (HCT) are numerous and include incomplete engraftment. One possible mechanism of incomplete engraftment after HCT is cytokine-mediated suppression or dysfunction of the bone marrow microenvironment. Mesenchymal stromal cells (MSCs) elaborate cytokines that nurture or stimulate the marrow microenvironment by several mechanisms. We hypothesize that the administration of exogenous MSCs may modulate the bone marrow milieu and improve peripheral blood count recovery in the setting of incomplete engraftment. In the current study, we demonstrated that posttransplant intramuscular administration of human placental derived mesenchymal-like adherent stromal cells [PLacental eXpanded (PLX)-R18] harvested from a three-dimensional in vitro culture system improved posttransplant engraftment of human immune compartment in an immune-deficient murine transplantation model. As measured by the percentage of CD45+ cell recovery, we observed improvement in the peripheral blood counts at weeks 6 (8.4 vs. 24.1%, p < 0.001) and 8 (7.3 vs. 13.1%, p < 0.05) and in the bone marrow at week 8 (28 vs. 40.0%, p < 0.01) in the PLX-R18 cohort. As measured by percentage of CD19+ cell recovery, there was improvement at weeks 6 (12.6 vs. 3.8%) and 8 (10.1 vs. 4.1%). These results suggest that PLX-R18 may have a therapeutic role in improving incomplete engraftment after HCT.

A reduction in CD90 (THY-1) expression results in increased differentiation of mesenchymal stromal cells

BACKGROUND

Mesenchymal stromal cells (MSCs) are multipotent progenitor cells used in several cell therapies. MSCs are characterized by the expression of CD73, CD90, and CD105 cell markers, and the absence of CD34, CD45, CD11a, CD19, and HLA-DR cell markers. CD90 is a glycoprotein present in the MSC membranes and also in adult cells and cancer stem cells. The role of CD90 in MSCs remains unknown. Here, we sought to analyse the role that CD90 plays in the characteristic properties of in vitro expanded human MSCs.

METHODS

We investigated the function of CD90 with regard to morphology, proliferation rate, suppression of T-cell proliferation, and osteogenic/adipogenic differentiation of MSCs by reducing the expression of this marker using CD90-target small hairpin RNA lentiviral vectors.

RESULTS

The present study shows that a reduction in CD90 expression enhances the osteogenic and adipogenic differentiation of MSCs in vitro and, unexpectedly, causes a decrease in CD44 and CD166 expression.

CONCLUSION

Our study suggests that CD90 controls the differentiation of MSCs by acting as an obstacle in the pathway of differentiation commitment. This may be overcome in the presence of the correct differentiation stimuli, supporting the idea that CD90 level manipulation may lead to more efficient differentiation rates in vitro.

Mesenchymal stromal cell-derived extracellular vesicles rescue radiation damage to murine marrow hematopoietic cells

Mesenchymal stromal cells (MSCs) have been shown to reverse radiation damage to marrow stem cells. We have evaluated the capacity of MSC-derived extracellular vesicles (MSC-EVs) to mitigate radiation injury to marrow stem cells at 4 h to 7 days after irradiation. Significant restoration of marrow stem cell engraftment at 4, 24 and 168 h post irradiation by exposure to MSC-EVs was observed at 3 weeks to 9 months after transplant and further confirmed by secondary engraftment. Intravenous injection of MSC-EVs to 500cGy exposed mice led to partial recovery of peripheral blood counts and restoration of the engraftment of marrow. The murine hematopoietic cell line, FDC-P1 exposed to 500cGy, showed reversal of growth inhibition, DNA damage and apoptosis on exposure to murine or human MSC-EVs. Both murine and human MSC-EVs reverse radiation damage to murine marrow cells and stimulate normal murine marrow stem cell/progenitors to proliferate. A preparation with both exosomes and microvesicles was found to be superior to either microvesicles or exosomes alone. Biologic activity was seen in freshly isolated vesicles and in vesicles stored for up to 6 months in 10% dimethyl sulfoxide at -80 °C. These studies indicate that MSC-EVs can reverse radiation damage to bone marrow stem cells.

Mesenchymal stromal cells to modulate immune reconstitution early post-hematopoietic cell transplantation

Mesenchymal stromal cells (MSCs) are multipotent progenitor cells known to modulate the immune system and to promote hematopoiesis. These dual effects make MSCs attractive for use as cellular therapy in hematopoietic cell transplantation (HCT). MSCs can be used peri-HCT or pre-engraftment to modulate immune reconstitution, promoting hematopoietic stem cell (HSC) engraftment and/or preventing graft-versus-host disease (GVHD). Pre-clinical studies have demonstrated that MSCs can potentiate HSC engraftment and prevent GVHD in a variety of animal models. Clinical trials have been small and largely non-randomized but have established safety and early evidence of efficacy, supporting the need for larger randomized trials.

Hematopoietic Support Capacity of Mesenchymal Stem Cells: Biology and Clinical Potential

Mesenchymal stem cells (MSCs) play an important role in the physiology and homeostasis of the hematopoietic system. Because MSCs generate most of the stromal cells present in the bone marrow (BM), form part of the hematopoietic stem cell (HSC) niche, and produce various molecules regulating hematopoiesis, their hematopoiesis-supporting capacity has been demonstrated. In the last decade, BM-MSCs have been proposed to be useful in some ex vivo protocols for HSC expansion, with the aim of expanding their numbers for transplant purposes (HSC transplant, HSCT). Furthermore, application of MSCs has been proposed as an adjuvant cellular therapy for promoting rapid hematopoietic recovery in HSCT patients. Although the MSCs used in preliminary clinical trials have come from the BM, isolation of MSCs from far more accessible sources such as neonatal tissues has now been achieved, and these cells have been found to possess similar biological characteristics to those isolated from the BM. Therefore, such tissues are now considered as a potential alternative source of MSCs for clinical applications. In this review, we discuss current knowledge regarding the biological characteristics of MSCs as related to their capacity to support the formation of hematopoietic stem and progenitor cells. We also describe MSC manipulation for ex vivo HSC expansion protocols used for transplants and their clinical relevance for hematopoietic recovery in HSCT patients.

Differential ability of MSCs isolated from placenta and cord as feeders for supporting ex vivo expansion of umbilical cord blood derived CD34(+) cells

INTRODUCTION

Ex vivo expansion of umbilical cord blood (UCB) is attempted to increase cell numbers to overcome the limitation of cell dose. Presently, suspension cultures or feeder mediated co-cultures are performed for expansion of hematopoietic stem cells (HSCs). Mesenchymal stem cells (MSCs) have proved to be efficient feeders for the maintenance of HSCs. Here, we have established MSCs-HSCs co-culture system with MSCs isolated from less invasive and ethically acceptable sources like umbilical cord tissue (C-MSCs) and placenta (P-MSCs). MSCs derived from these tissues are often compared with bone marrow derived MSCs (BM-MSCs) which are considered as a gold standard. However, so far none of the studies have directly compared C-MSCs with P-MSCs as feeders for ex vivo expansion of HSCs. Thus, we for the first time performed a systematic comparison of hematopoietic supportive capability of C and P-MSCs using paired samples.

METHODS

UCB-derived CD34(+) cells were isolated and co-cultured on irradiated C and P-MSCs for 10 days. C-MSCs and P-MSCs were isolated from the same donor. The cultures comprised of serum-free medium supplemented with 25 ng/ml each of SCF, TPO, Flt-3 L and IL-6. After 10 days cells were collected and analyzed for phenotype and functionality.

RESULTS

C-MSCs and P-MSCs were found to be morphologically and phenotypically similar but exhibited differential ability to support ex vivo hematopoiesis. Cells expanded on P-MSCs showed higher percentage of primitive cells (CD34(+)CD38(-)), CFU (Colony forming unit) content and LTC-IC (Long term culture initiating cells) ability. CD34(+) cells expanded on P-MSCs also exhibited better in vitro adhesion to fibronectin and migration towards SDF-1α and enhanced NOD/SCID repopulation ability, as compared to those grown on C-MSCs. P-MSCs were found to be closer to BM-MSCs in their ability to expand HSCs. P-MSCs supported expansion of functionally superior HSCs by virtue of reduction in apoptosis of primitive HSCs, higher Wnt and Notch activity, HGF secretion and cell-cell contact. On the other hand, C-MSCs facilitated expansion of progenitors (CD34(+)CD38(+)) and differentiated (CD34(-)CD38(+)) cells by secretion of IL1-α, β, MCP-2, 3 and MIP-3α.

CONCLUSIONS

P-MSCs were found to be better feeders for ex vivo maintenance of primitive HSCs with higher engraftment potential than the cells expanded with C-MSCs as feeders.

Direct Comparison of Wharton's Jelly and Bone Marrow-Derived Mesenchymal Stromal Cells to Enhance Engraftment of Cord Blood CD34(+) Transplants

Cotransplantation of CD34(+) hematopoietic stem and progenitor cells (HSPCs) with mesenchymal stromal cells (MSCs) enhances HSPC engraftment. For these applications, MSCs are mostly obtained from bone marrow (BM). However, MSCs can also be isolated from the Wharton's jelly (WJ) of the human umbilical cord. This source, regarded to be a waste product, enables a relatively low-cost MSC acquisition without any burden to the donor. In this study, we evaluated the ability of WJ MSCs to enhance HSPC engraftment. First, we compared cultured human WJ MSCs with human BM-derived MSCs (BM MSCs) for in vitro marker expression, immunomodulatory capacity, and differentiation into three mesenchymal lineages. Although we confirmed that WJ MSCs have a more restricted differentiation capacity, both WJ MSCs and BM MSCs expressed similar levels of surface markers and exhibited similar immune inhibitory capacities. Most importantly, cotransplantation of either WJ MSCs or BM MSCs with CB CD34(+) cells into NOD SCID mice showed similar enhanced recovery of human platelets and CD45(+) cells in the peripheral blood and a 3-fold higher engraftment in the BM, blood, and spleen 6 weeks after transplantation when compared to transplantation of CD34(+) cells alone. Upon coincubation, both MSC sources increased the expression of adhesion molecules on CD34(+) cells, although stromal cell-derived factor-1 (SDF-1)-induced migration of CD34(+) cells remained unaltered. Interestingly, there was an increase in CFU-GEMM when CB CD34(+) cells were cultured on monolayers of WJ MSCs in the presence of exogenous thrombopoietin, and an increase in BFU-E when BM MSCs replaced WJ MSCs in such cultures. Our results suggest that WJ MSC is likely to be a practical alternative for BM MSC to enhance CB CD34(+) cell engraftment.

Potential functional applications of extracellular vesicles: a report by the NIH Common Fund Extracellular RNA Communication Consortium

The NIH Extracellular RNA Communication Program's initiative on clinical utility of extracellular RNAs and therapeutic agents and developing scalable technologies is reviewed here. Background information and details of the projects are presented. The work has focused on modulation of target cell fate by extracellular vesicles (EVs) and RNA. Work on plant-derived vesicles is of intense interest, and non-mammalian sources of vesicles may represent a very promising source for different therapeutic approaches. Retro-viral-like particles are intriguing. Clearly, EVs share pathways with the assembly machinery of several other viruses, including human endogenous retrovirals (HERVs), and this convergence may explain the observation of viral-like particles containing viral proteins and nucleic acid in EVs. Dramatic effect on regeneration of damaged bone marrow, renal, pulmonary and cardiovascular tissue is demonstrated and discussed. These studies show restoration of injured cell function and the importance of heterogeneity of different vesicle populations. The potential for neural regeneration is explored, and the capacity to promote and reverse neoplasia by EV exposure is described. The tremendous clinical potential of EVs underlies many of these projects, and the importance of regulatory issues and the necessity of general manufacturing production (GMP) studies for eventual clinical trials are emphasized. Clinical trials are already being pursued and should expand dramatically in the near future.

No Synergistic Effect of Cotransplantation of MSC and Ex Vivo TPO-Expanded CD34(+) Cord Blood Cells on Platelet Recovery and Bone Marrow Engraftment in NOD SCID Mice

After cord blood (CB) transplantation, early platelet recovery in immune-deficient mice is obtained by expansion of CB CD34(+) cells with thrombopoietin (TPO) as single growth factor. Moreover, improvement of hematopoietic engraftment has been shown by cotransplantation of mesenchymal stem cells (MSC). We investigated whether a combination of both approaches would further enhance the outcome of CB transplantation in NOD SCID mice. NOD SCID mice were transplanted with either CB CD34(+) cells, CD34(+) cells with MSC, TPO-expanded CD34(+) cells or TPO-expanded CD34(+) cells with MSC. We analyzed human platelet recovery in the peripheral blood (PB) from day 4 after transplantation onward and human bone marrow (BM) engraftment at week 6. The different transplants were assessed in vitro for their migration capacity and expression of CXCR4. TPO expansion improved the early platelet recovery in the PB of the mice. Cotransplantation of MSC with CD34(+) cells improved BM engraftment and platelet levels in the PB 6 weeks after transplantation. Combining TPO expansion and MSC cotransplantation, however, neither resulted in a more efficient early platelet recovery, nor in a better BM engraftment, nor even very low or absent BM engraftment occurred. In vitro, MSC boosted the migration of CD34(+) cells, suggesting a possible mechanism for the increase in engraftment. Our results show that cotransplantation of MSC with TPO-expanded CD34(+) cells at most combines, but does not increase the separate advantages of these different strategies. A combination of both strategies even adds a risk of non engraftment.

Concise review: the surface markers and identity of human mesenchymal stem cells

The concept of mesenchymal stem cells (MSCs) is becoming increasingly obscure due to the recent findings of heterogeneous populations with different levels of stemness within MSCs isolated by traditional plastic adherence. MSCs were originally identified in bone marrow and later detected in many other tissues. Currently, no cloning based on single surface marker is capable of isolating cells that satisfy the minimal criteria of MSCs from various tissue environments. Markers that associate with the stemness of MSCs await to be elucidated. A number of candidate MSC surface markers or markers possibly related to their stemness have been brought forward so far, including Stro-1, SSEA-4, CD271, and CD146, yet there is a large difference in their expression in various sources of MSCs. The exact identity of MSCs in vivo is not yet clear, although reports have suggested they may have a fibroblastic or pericytic origin. In this review, we revisit the reported expression of surface molecules in MSCs from various sources, aiming to assess their potential as MSC markers and define the critical panel for future investigation. We also discuss the relationship of MSCs to fibroblasts and pericytes in an attempt to shed light on their identity in vivo.

Effects of MSC Coadministration and Route of Delivery on Cord Blood Hematopoietic Stem Cell Engraftment

Hematopoietic stem cell transplantation (HSCT) using umbilical cord blood (UCB) progenitors is increasingly being used. One of the problems that may arise after UCB transplantation is an impaired engraftment. Either intrabone (IB) injection of hematopoietic progenitors or mesenchymal stem cell (MSC) coadministration has been proposed among the strategies to improve engraftment. In the current study, we have assessed the effects of both approaches. Thus, NOD/SCID recipients were transplanted with human UCB CD34+ cells administered either intravenously (IV) or IB, receiving or not bone marrow (BM)-derived MSCs also IV or IB (in the right femur). Human HSC engraftment was measured 3 and 6 weeks after transplantation. Injected MSCs were tracked weekly by bioluminescence. Also, lodgment within the BM niche was assessed at the latter time point by immunofluorescence. Our study shows regarding HSC engraftment that the number of BM human CD45+ cells detected 3 weeks after transplantation was significantly higher in mice cotransplanted with human MSCs. Moreover, these mice had a higher myeloid (CD13+) engraftment and a faster B-cell (CD19+) chimerism. At the late time point evaluated (6 weeks), human engraftment was higher in the group in which both strategies were employed (IB injection of HSC and MSC coadministration). When assessing human MSC administration route, we were able to track MSCs only in the injected femurs, whereas they lost their signal in the contralateral bones. These human MSCs were mainly located around blood vessels in the subendosteal region. In summary, our study shows that MSC coadministration can enhance HSC engraftment in our xenogenic transplantation model, as well as IB administration of the CD34+ cells does. The combination of both strategies seems to be synergistic. Interestingly, MSCs were detected only where they were IB injected contributing to the vascular niche.

Mesenchymal Stem Cell Insights: Prospects in Hematological Transplantation

Adult stem cells have been proven to possess tremendous potential in the treatment of hematological disorders, possibly in transplantation. Mesenchymal stem cells (MSCs) are a heterogeneous group of cells in culture, with hypoimmunogenic character to avoid alloreactive T-cell recognition as well as inhibition of T-cell proliferation. Numerous experimental findings have shown that MSCs also possess the ability to promote engraftment of donor cells and to accelerate the speed of hematological recovery. Despite that the exact mechanism remains unclear, the therapeutic ability of MSCs on hematologic transplantation have been tested in preclinical trials. Based on encouraging preliminary findings, MSCs might become a potentially efficacious tool in the therapeutic options available to treat and cure hematological malignancies and nonmalignant disorders. The molecular mechanisms behind the real efficacy of MSCs on promoting engraftment and accelerating hematological recovery are awaiting clarification. It is hypothesized that direct cell-to-cell contact, paracrine factors, extracellular matrix scaffold, BM homing capability, and endogenous metabolites of immunologic and nonimmunologic elements are involved in the interactions between MSCs and HSCs. This review focuses on recent experimental and clinical findings related to MSCs, highlighting their roles in promoting engraftment, hematopoietic recovery, and GvHD/graft rejection prevention after HSCT, discussing the potential clinical applications of MSC-based treatment strategies in the context of hematological transplantation.

Placenta as a reservoir of stem cells: an underutilized resource?

INTRODUCTION

Both embryonic and adult tissues are sources of stem cells with therapeutic potential but with some limitations in the clinical practice such as ethical considerations, difficulty in obtaining and tumorigenicity. As an alternative, the placenta is a foetal tissue that can be obtained during gestation and at term, and it represents a reservoir of stem cells with various potential.

SOURCES OF DATA

We reviewed the relevant literature concerning the main stem cells that populate the placenta.

AREAS OF AGREEMENT

Recently, the placenta has become useful source of stem cells that offer advantages in terms of proliferation and plasticity when compared with adult cells and permit to overcome the ethical and safety concern inherent in embryonic stem cells. In addition, the placenta has the advantage of containing epithelia, haematopoietic and mesenchymal stem cells. These stem cells possess immunosuppressive properties and have the capacity of suppress in vivo inflammatory responses.

AREAS OF CONTROVERSY

Some studies describe a subpopulation of placenta stem cells expressing pluripotency markers, but for other studies, it is not clear whether pluripotent stem cells are present during gestation beyond the first few weeks. Particularly, the expression of some pluripotency markers such as SSEA-3, TRA-1-60 and TRA-1-81 has been reported by us, but not by others.

GROWING POINTS

Placenta stem cells could be of great importance after delivery for banking for autologous and allogeneic applications. The beneficial effects of these cells may be due to secretion of bioactive molecules that act through paracrine actions promoting beneficial effects.

AREAS TIMELY FOR DEVELOPING RESEARCH

Understanding the role of placenta stem cells during pregnancy and their paracrine actions could help in the study of some diseases that affect the placenta during pregnancy.

Immunosuppressive properties of mesenchymal stem cells

Mesenchymal stem cells (MSC) can be isolated from different adult tissues including bone marrow, adipose tissue, cord blood and placenta. MSCs modulate the immune function of the major immune cell populations involved in alloantigen recognition and elimination, including antigen presenting cells, T cells, B cells and natural killer cells. Many clinical trials are currently underway that employ MSCs to treat human immunological diseases. However, the molecular mechanism that mediates the immunosuppressive effect of MSCs is still unclear and the safety of using MSC in patient needs further confirmation. Here, we review the cytokines that activate MSCs and the soluble factors produced by MSCs, which allow them to exert their immunosuppressive effects. We review the mechanism responsible, at least in part, for the immune suppressive effects of MSCs and highlight areas of research required for a better understanding of MSC immune modulation.

The immunomodulatory and neuroprotective effects of mesenchymal stem cells (MSCs) in experimental autoimmune encephalomyelitis (EAE): a model of multiple sclerosis (MS)

Mesenchymal stem cells (MSCs) are multipotent cells that differentiate into the mesenchymal lineages of adipocytes, osteocytes and chondrocytes. MSCs can also transdifferentiate and thereby cross lineage barriers, differentiating for example into neurons under certain experimental conditions. MSCs have anti-proliferative, anti-inflammatory and anti-apoptotic effects on neurons. Therefore, MSCs were tested in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), for their effectiveness in modulating the pathogenic process in EAE to develop effective therapies for MS. The data in the literature have shown that MSCs can inhibit the functions of autoreactive T cells in EAE and that this immunomodulation can be neuroprotective. In addition, MSCs can rescue neural cells via a mechanism that is mediated by soluble factors, which provide a suitable environment for neuron regeneration, remyelination and cerebral blood flow improvement. In this review, we discuss the effectiveness of MSCs in modulating the immunopathogenic process and in providing neuroprotection in EAE.

Therapeutic potential of intravenously administered human mesenchymal stromal cells

Mesenchymal stem cells (MSC) represent a stem and progenitor cell population that has been shown to promote tissue recovery in pre-clinical and clinical studies. The study of MSC migration following systemic infusion of exogenous MSC is difficult. The challenges facing these efforts are due to a number of factors, including defining culture conditions for MSC, the phenotype of cultured MSC, the differences observed between cultured MSC and freshly isolated MSC. However, even if, MSC populations consist of a mixture of stem and more committed multipotent progenitors, it remains probable that these cell populations are still useful in the clinic as discussed in this review.

Potential therapeutic applications of mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are a non-homogeneous population of plastic-adherent cells which were initially isolated from post-natal bone marrow. They have the capacity to differentiate to multiple mesodermal lineages including bone, cartilage and adipose tissue. In stringent culture conditions, MSCs can also be induced to differentiate into different cell types of endoderm and neuroectoderm lineages. To date, no specific marker identifies MSCs, although a number of cell surface antigens have been described which enrich for MSCs. Mesenchymal stromal cells possess a number of properties which have generated considerable interest in diverse cellular therapeutic applications. The capacity of MSCs to differentiate into multiple different cell lineages has seen them actively explored for tissue repair, particularly in cardiac, orthopaedic and neurological applications. A large body of data indicates that MSCs possess immunomodulatory properties. Mesenchymal stromal cells are immunosuppressive, interacting with T lymphocytes, antigen presenting cells, B lymphocytes, and natural killer cells. In addition, they are immunoprivileged, allowing transplantation across allogeneic barriers. These immunomodulatory properties have seen infusion of MSCs for the treatment of steroid refractory graft versus host disease, a life threatening complication of haemopoietic cell transplantation, with promising results. Furthermore, these immune functions may lead to roles in the facilitation of engraftment, induction of tolerance and as therapy in autoimmune disease.

Application of mesenchymal stromal cells in bone marrow transplantation for sensitized recipients

Sensitized patients are at high risk for graft rejection during transplantation. It is of interest to investigate the effect of mesenchymal stromal cells (MSCs) in sensitized hematopoietic stem cell transplantation. MSCs were generated from bone marrow cells of BALB/c mice. The molecular markers of MSCs were detected by flow cytometry. MSCs labeled with green fluorescent dye were transplanted into nonsensitized and sensitized recipients, respectively. Homing of MSCs in vivo was monitored at different time points post-transplantation. Additionally, sensitized BALB/c mice under irradiation were transplanted with syngeneic MSCs and allogeneic bone marrow cells, and the rate of survival was monitored daily. The fourth passage of MSCs presented a typical spindle-shaped morphology and met the identification criteria of MSCs. Forty-eight hours post-transplantation, the homing of MSCs was found mainly in the bone morrow of nonsensitized recipients and the spleen of sensitized recipients, respectively. Moreover, all of the sensitized recipients died 12-16 days after receiving syngeneic MSCs and allogeneic bone marrow cells, with a median of 14 days. Our results suggest that the MSCs mainly homed to the spleen of sensitized recipients post-transplantation. MSCs could not enhance the engraftment of allogeneic bone marrow cells in sensitized recipients.

Bone marrow mesenchymal stem cells for improving hematopoietic function: an in vitro and in vivo model. Part 2: Effect on bone marrow microenvironment

The aim of the present study was to determine how mesenchymal stem cells (MSC) could improve bone marrow (BM) stroma function after damage, both in vitro and in vivo. Human MSC from 20 healthy donors were isolated and expanded. Mobilized selected CD34⁺ progenitor cells were obtained from 20 HSCT donors. For in vitro study, long-term bone marrow cultures (LTBMC) were performed using a etoposide damaged stromal model to test MSC effect in stromal confluence, capability of MSC to lodge in stromal layer as well as some molecules (SDF1, osteopontin,) involved in hematopoietic niche maintenance were analyzed. For the in vivo model, 64 NOD/SCID recipients were transplanted with CD34+ cells administered either by intravenous (IV) or intrabone (IB) route, with or without BM derived MSC. MSC lodgement within the BM niche was assessed by FISH analysis and the expression of SDF1 and osteopontin by immunohistochemistry. In vivo study showed that when the stromal damage was severe, TP-MSC could lodge in the etoposide-treated BM stroma, as shown by FISH analysis. Osteopontin and SDF1 were differently expressed in damaged stroma and their expression restored after TP-MSC addition. Human in vivo MSC lodgement was observed within BM niche by FISH, but MSC only were detected and not in the contralateral femurs. Human MSC were located around blood vessels in the subendoestal region of femurs and expressed SDF1 and osteopontin. In summary, our data show that MSC can restore BM stromal function and also engraft when a higher stromal damage was done. Interestingly, MSC were detected locally where they were administered but not in the contralateral femur.

Immunomodulatory properties of human adult and fetal multipotent mesenchymal stem cells

In recent years, a large number of studies have contributed to our understanding of the immunomodulatory mechanisms used by multipotent mesenchymal stem cells (MSCs). Initially isolated from the bone marrow (BM), MSCs have been found in many tissues but the strong immunomodulatory properties are best studied in BM MSCs. The immunomodulatory effects of BM MSCs are wide, extending to T lymphocytes and dendritic cells, and are therapeutically useful for treatment of immune-related diseases including graft-versus-host disease as well as possibly autoimmune diseases. However, BM MSCs are very rare cells and require an invasive procedure for procurement. Recently, MSCs have also been found in fetal-stage embryo-proper and extra-embryonic tissues, and these human fetal MSCs (F-MSCs) have a higher proliferative profile, and are capable of multilineage differentiation as well as exert strong immunomodulatory effects. As such, these F-MSCs can be viewed as alternative sources of MSCs. We review here the current understanding of the mechanisms behind the immunomodulatory properties of BM MSCs and F-MSCs. An increase in our understanding of MSC suppressor mechanisms will offer insights for prevalent clinical use of these versatile adult stem cells in the near future.

Hematopoietic stromal cells and megakaryocyte development

The hematopoietic microenvironment, and in particular the hematopoietic stromal cell element, are intimately involved in megakaryocyte development. The process of megakaryocytopoiesis occurs within a complex bone marrow microenvironment where adhesive interactions, chemokines, as well as cytokines play a pivotal role. Here we review the effect of stromal cells and cytokines on megakaryocytopoiesis with the aim of exploring new therapeutic strategies for platelet recovery after hematopoietic stem cell transplantation (HSCT).

Mesenchymal stromal cells: a novel and effective strategy for facilitating engraftment and accelerating hematopoietic recovery after transplantation?

MSCs are multipotent cells that can be isolated from several human tissues and expanded ex vivo for clinical use. They comprise a heterogeneous population of cells, which, through production of growth factors, cell-to-cell interactions and secretion of matrix proteins, has a role in the regulation of hematopoiesis. In recent years, several experimental studies have shown that MSCs are endowed with immunomodulatory properties and with the capacity to promote graft survival in animal models. In view of these properties, MSCs have been tested in pilot studies aimed at preventing/treating graft rejection and at accelerating recovery after hematopoietic cell transplantation (HCT). The available clinical evidence deriving from these studies indicates that MSC infusion is safe and promising in terms of capacity of preventing graft failure. More debated is the effect of MSCs for what concerns their capacity of accelerating hematopoietic reconstitution after HCT. Whether the favorable effect of MSCs largely depends on the type of transplantation remains also a field of future investigation. Moreover, future researches should be oriented to gain more insights on MSC biological and functional mechanisms relevant for exploiting their use in the modulation of alloreactivity and in the promotion of hematopoietic reconstitution.

Tissue regeneration potential in human umbilical cord blood

Regenerative medicine is the process of creating functional tissue with the aid of stem cells, to repair loss of organ function. Possible targets for regenerative medicine include orthopaedic, cardiac, hepatic, pancreatic and central nervous system (CNS) applications. Umbilical cord blood (CB) has established itself as a legitimate source for haematopoietic stem cell transplantation. It is also considered an accessible and less immunogenic source for mesenchymal, unrestricted somatic and for other stem cells with pluri/multipotent properties. The latter are capable of differentiating into a wide variety of cell types including bone, cartilage, cardiomyocytes and neural. They also possess protective abilities that may contribute to tissue repair even if in vitro differentiation is excluded. In view of the absence of treatment for many devastating diseases, the elucidation of non-haematopoietic applications for CB will facilitate the development of pioneering relevant cell therapy approaches. This review focusses on current studies using human CB-derived cells for regenerative medicine.

Review: Preclinical studies on placenta-derived cells and amniotic membrane: an update

Recent years have seen considerable advances in our knowledge of the biology and properties of stem/progenitor cells isolated from placental tissues. This has encouraged researchers to address the potential effects of these cells in animal models of different diseases, resulting in increasing expectations regarding their possible utility for cell-based therapeutic applications. This rapidly evolving research field is also enriched by studies aimed at expanding the use of the whole amniotic membrane (AM), a well-known surgical material, for pathological conditions other than those tested so far and for which clinical applications already exist. In this review, we provide an update on studies that have been performed with placenta-derived cells and fragments of the entire AM to validate their potential clinical applications in a variety of diseases, in particular those associated with degenerative processes induced by inflammatory and fibrotic mechanisms. We also offer, as far as possible, insight into the interpretation and suggested mechanisms to explain the most important outcomes achieved to date.

Mesenchymal stromal cells from human perinatal tissues: From biology to cell therapy

Cell-based regenerative medicine is of growing interest in biomedical research. The role of stem cells in this context is under intense scrutiny and may help to define principles of organ regeneration and develop innovative therapeutics for organ failure. Utilizing stem and progenitor cells for organ replacement has been conducted for many years when performing hematopoietic stem cell transplantation. Since the first successful transplantation of umbilical cord blood to treat hematological malignancies, non-hematopoietic stem and progenitor cell populations have recently been identified within umbilical cord blood and other perinatal and fetal tissues. A cell population entitled mesenchymal stromal cells (MSCs) emerged as one of the most intensely studied as it subsumes a variety of capacities: MSCs can differentiate into various subtypes of the mesodermal lineage, they secrete a large array of trophic factors suitable of recruiting endogenous repair processes and they are immunomodulatory.Focusing on perinatal tissues to isolate MSCs, we will discuss some of the challenges associated with these cell types concentrating on concepts of isolation and expansion, the comparison with cells derived from other tissue sources, regarding phenotype and differentiation capacity and finally their therapeutic potential.

Toward cell therapy using placenta-derived cells: disease mechanisms, cell biology, preclinical studies, and regulatory aspects at the round table

Among the many cell types that may prove useful to regenerative medicine, mounting evidence suggests that human term placenta-derived cells will join the list of significant contributors. In making new cell therapy-based strategies a clinical reality, it is fundamental that no a priori claims are made regarding which cell source is preferable for a particular therapeutic application. Rather, ongoing comparisons of the potentiality and characteristics of cells from different sources should be made to promote constant improvement in cell therapies, and such comparisons will likely show that individually tailored cells can address disease-specific clinical needs. The principle underlying such an approach is resistance to the notion that comprehensive characterization of any cell type has been achieved, neither in terms of phenotype nor risks-to-benefits ratio. Tailoring cell therapy approaches to specific conditions also requires an understanding of basic disease mechanisms and close collaboration between translational researchers and clinicians, to identify current needs and shortcomings in existing treatments. To this end, the international workshop entitled "Placenta-derived stem cells for treatment of inflammatory diseases: moving toward clinical application" was held in Brescia, Italy, in March 2009, and aimed to harness an understanding of basic inflammatory mechanisms inherent in human diseases with updated findings regarding biological and therapeutic properties of human placenta-derived cells, with particular emphasis on their potential for treating inflammatory diseases. Finally, steps required to allow their future clinical application according to regulatory aspects including good manufacturing practice (GMP) were also considered. In September 2009, the International Placenta Stem Cell Society (IPLASS) was founded to help strengthen the research network in this field.