Clinical stem-cell sources contain CD8+CD3+ T-cell receptor-negative cells that facilitate bone marrow repopulation with hematopoietic stem cells. Blood. 2008;111:1735-1738. [PMID: 17984314 DOI: 10.1182/blood-2007-02-076000]

Differential CXCR4 expression on hematopoietic progenitor cells versus stem cells directs homing and engraftment

Gene therapy involves a substantial loss of hematopoietic stem and progenitor cells (HSPC) during processing and homing. Intra-BM (i.b.m.) transplantation can reduce homing losses, but prior studies have not yielded promising results. We studied the mechanisms involved in homing and engraftment of i.b.m. transplanted and i.v. transplanted genetically modified (GM) human HSPC. We found that i.b.m. HSPC transplantation improved engraftment of hematopoietic progenitor cells (HPC) but not of long-term repopulating hematopoietic stem cells (HSC). Mechanistically, HPC expressed higher functional levels of CXCR4 than HSC, conferring them a retention and homing advantage when transplanted i.b.m. Removing HPC and transplanting an HSC-enriched population i.b.m. significantly increased long-term engraftment over i.v. transplantation. Transient upregulation of CXCR4 on GM HSC-enriched cells, using a noncytotoxic portion of viral protein R (VPR) fused to CXCR4 delivered as a protein in lentiviral particles, resulted in higher homing and long-term engraftment of GM HSC transplanted either i.v. or i.b.m. compared with standard i.v. transplants. Overall, we show a mechanism for why i.b.m. transplants do not significantly improve long-term engraftment over i.v. transplants. I.b.m. transplantation becomes relevant when an HSC-enriched population is delivered. Alternatively, CXCR4 expression on HSC, when transiently increased using a protein delivery method, improves homing and engraftment specifically of GM HSC.

Schwann cells secrete extracellular vesicles to promote and maintain the proliferation and multipotency of hDPCs

OBJECTIVES

Schwann cells (SCs) are the principal glial cells in peripheral nerve system, involved in neuropathies with great regenerative potential. Dental pulp cells have been reported to maintain neurogenic potential. In contrast, the regulatory role of SCs on human dental pulp cells (hDPCs) development remains undefined.

MATERIALS AND METHODS

SC secretion and SC-derived extracellular vesicles (EVs) were collected and used to treat hDPCs; and proliferation and multiple differentiation of hDPCs were detected after EVs treatments. Finally, we analysed the proteomes of SC-EVs and SCs through mass spectrum.

RESULTS

In this study, we found SC secretion showed a predominantly regulatory role on the development of hDPCs. Further, we identified EVs from SC secretion with similar function as SC secretion in regulating hDPCs proliferation and multipotency. And expression of transcription factor Oct4 was upregulated after treatment of both SC secretion and EVs, as well as Sox2 and Nanog. We detected abundant enrichment of Oct4 in EVs, which might be responsible for the upregulation of stem cell-related genes in hDPCs. Through proteome and western blot analysis, we found enriched TGFβs in EVs, indicating that accelerated hDPCs proliferation may be mediated by activated TGFβ-Samd and TGFβ-MAPK signalling.

CONCLUSIONS

In summary, our study sheds light on critical regulatory ability of SC-derived EVs on hDPCs proliferation and multipotency, suggesting great implications for seeding cells used in tissue engineering.

Impact of T cells on hematopoietic stem and progenitor cell function: Good guys or bad guys?

When hematopoietic stem and progenitor cells (HSPC) are harvested for transplantation, either from the bone marrow or from mobilized blood, the graft contains a significant number of T cells. It is these T cells that are the major drivers of graft-vs-host disease (GvHD). The risk for GvHD can simply be reduced by the removal of these T cells from the graft. However, this is not always desirable, as this procedure also decreases the engraftment of the transplanted HSPCs and, if applicable, a graft-vs-tumor effect. This poses an important conundrum in the field: T cells act as a double-edged sword upon allogeneic HSPC transplantation, as they support engraftment of HSPCs and provide anti-tumor activity, but can also cause GvHD. It has recently been suggested that T cells also enhance the engraftment of autologous HSPCs, thus supporting the notion that T cells and HSPCs have an important functional interaction that is highly beneficial, in particular during transplantation. The underlying reason on why and how T cells contribute to HSPC engraftment is still poorly understood. Therefore, we evaluate in this review the studies that have examined the role of T cells during HSPC transplantation and the possible mechanisms involved in their supporting function. Understanding the underlying cellular and molecular mechanisms can provide new insight into improving HSPC engraftment and thus lower the number of HSPCs required during transplantation. Moreover, it could provide new avenues to limit the development of severe GvHD, thus making HSPC transplantations more efficient and ultimately safer.

Characterization of Human CD8(+)TCR(-) Facilitating Cells In Vitro and In Vivo in a NOD/SCID/IL2rγ(null) Mouse Model

CD8(+)/TCR(-) facilitating cells (FCs) in mouse bone marrow (BM) significantly enhance engraftment of hematopoietic stem/progenitor cells (HSPCs). Human FC phenotype and mechanism of action remain to be defined. We report, for the first time, the phenotypic characterization of human FCs and correlation of phenotype with function. Approximately half of human FCs are CD8(+)/TCR(-)/CD56 negative (CD56(neg)); the remainder are CD8(+)/TCR(-)/CD56 bright (CD56(bright)). The CD56(neg) FC subpopulation significantly promotes homing of HSPCs to BM in nonobese diabetic/severe combined immunodeficiency/IL-2 receptor γ-chain knockout mouse recipients and enhances hematopoietic colony formation in vitro. The CD56(neg) FC subpopulation promotes rapid reconstitution of donor HSPCs without graft-versus-host disease (GVHD); recipients of CD56(bright) FCs plus HSPCs exhibit low donor chimerism early after transplantation, but the level of chimerism significantly increases with time. Recipients of HSPCs plus CD56(neg) or CD56(bright) FCs showed durable donor chimerism at significantly higher levels in BM. The majority of both FC subpopulations express CXCR4. Coculture of CD56(bright) FCs with HSPCs upregulates cathelicidin and β-defensin 2, factors that prime responsiveness of HSPCs to stromal cell-derived factor 1. Both FC subpopulations significantly upregulated mRNA expression of the HSPC growth factors and Flt3 ligand. These results indicate that human FCs exert a direct effect on HSPCs to enhance engraftment. Human FCs offer a potential regulatory cell-based therapy for enhancement of engraftment and prevention of GVHD.

Evolving approaches of hematopoietic stem cell-based therapies to induce tolerance to organ transplants: the long road to tolerance

The immunoregulatory properties of hematopoietic stem cells (HSCs) have been recognized for more than 60 years, beginning in 1945, when Owen reported that genetically disparate freemartin cattle sharing a common placenta were red blood cell chimeras. In 1953, Billingham, Brent, and Medawar demonstrated that murine neonatal chimeras prepared by infusion of donor-derived hematopoietic cells exhibited donor-specific tolerance to skin allografts. Various approaches using HSCs in organ transplantation have gradually brought closer to reality the dream of inducing donor-specific tolerance in organ transplant recipients. Several hurdles needed to be overcome, especially the risk of graft-versus-host disease (GVHD), the toxicity of ablative conditioning, and the need for close donor-recipient matching. For wide acceptance, HSC therapy must be safe and reproducible in mismatched donor-recipient combinations. Discoveries in other disciplines have often unexpectedly and synergistically contributed to progress in this area. This review presents a historic perspective of the quest for tolerance in organ transplantation, highlighting current clinical approaches.

Ex vivo expanded hematopoietic stem cells overcome the MHC barrier in allogeneic transplantation

The lack of understanding of the interplay between hematopoietic stem cells (HSCs) and the immune system has severely hampered the stem cell research and practice of transplantation. Major problems for allogeneic transplantation include low levels of donor engraftment and high risks of graft-versus-host disease (GVHD). Transplantation of purified allogeneic HSCs diminishes the risk of GVHD but results in decreased engraftment. Here we show that ex vivo expanded mouse HSCs efficiently overcame the major histocompatibility complex barrier and repopulated allogeneic-recipient mice. An 8-day expansion culture led to a 40-fold increase of the allograft ability of HSCs. Both increased numbers of HSCs and culture-induced elevation of expression of the immune inhibitor CD274 (B7-H1 or PD-L1) on the surface of HSCs contributed to the enhancement. Our study indicates the great potential of utilizing ex vivo expanded HSCs for allogeneic transplantation and suggests that the immune privilege of HSCs can be modulated.

Comparison of unmobilized and mobilized graft characteristics and the implications of cell subsets on autologous and allogeneic transplantation outcomes

Autologous and allogeneic hematopoietic stem cell transplantation (HSCT) are considered the standard of care for many malignancies, including lymphoma, myeloma, and some leukemias. In many cases, mobilized peripheral blood has become the preferred source of hematopoietic stem cells. The efficacy of different mobilization regimens and transplantation outcomes based on cell doses has been well studied; however, the characteristics of the stem cell graft may be of equal importance with respect to patient outcomes following autologous or allogeneic HSCT. This review summarizes available preclinical and clinical data for bone marrow and mobilized peripheral blood HSCT characteristics, defined as the cell types found in the graft as well as their gene expression profiles. It also explores how graft characteristics can affect bone marrow homing, engraftment, immune reconstitution, and other posttransplantation outcomes in both the allogeneic and autologous HSCT settings.

Cell based therapy for Duchenne muscular dystrophy

Mutations in the dystrophin gene cause an X-linked genetic disorder: Duchenne muscular dystrophy (DMD). Stem cell therapy is an attractive method to treat DMD because a small number of cells are required to obtain a therapeutic effect. Here, we discussed about multiple types of myogenic stem cells and their possible use to treat DMD. The identification of a stem cell population providing efficient muscle regeneration is critical for the progression of cell therapy for DMD. We speculated that the most promising possibility for the treatment of DMD is a combination of different approaches, such as gene and stem cell therapy.

Human acute myeloid leukemia CD34+CD38- stem cells are susceptible to allorecognition and lysis by single KIR-expressing natural killer cells

The concept of tumor immunosurveillance has raised prospects for natural killer cell-based immunotherapy of human cancer. The cure of acute myeloid leukemia may depend on eradication of leukemic stem cells, the self-renewing component of leukemia. Whether natural killer cells can recognize and lyse leukemic stem cells is not known. To develop strategies that effectively target acute myeloid leukemia-leukemic stem cells, we investigated anti-leukemic effects of human alloreactive single KIR(+) natural killer cells. Natural killer effectors with KIR specificity mismatched with respect to HLA class I allotype of target cells effectively recognized acute myeloid leukemia-leukemic stem cells defined phenotypically as CD34(+)CD38(-), while healthy bone marrow-derived CD34(+)CD38(-) hematopoietic stem cells were spared, as demonstrated by cytotoxicity and hematopoietic colony-forming assays. The HDAC inhibitor valproic acid increased the activating NKG2D ligand-dependent lysis of acute myeloid leukemia-CD34(+)CD38(-) leukemic stem cells. These results show that alloreactive natural killer cells have the potential to detect and target leukemic stem cells, and thus to improve the treatment outcome in acute myeloid leukemia.

Megadose CD34(+) cell grafts improve recovery of T cell engraftment but not B cell immunity in patients with severe combined immunodeficiency disease undergoing haplocompatible nonmyeloablative transplantation

To determine whether T cell engraftment and recovery of B cell immunity could be improved, we prospectively treated 15 children with severe combined immunodeficiency disease (SCID) with megadoses of haplocompatible CD34(+) cells and a fixed number of CD3(+) cells without previous myeloablative chemotherapy. Evidence of T cell engraftment was seen in 73% of patients (95% confidence interval [CI] = 48%-90%). Engraftment was more likely in patients with X-linked SCID and in those with evidence of maternal engraftment at the time of diagnosis. In patients with T cell engraftment, the median time to development of a CD4 count > 200 cells/mm(3) and a phytohemagglutinin response > 50% of control was 1.2 and 4.9 months, respectively. Clearance of preexisting infections occurred after a median of 2.8 months. B cell function developed in 33% of engrafted patients (95% CI = 14%-61%). The 1-year event-free survival (EFS) rate was 60% (95% CI = 36%-80%), and the overall survival (OS) rate was 87% (95% CI = 61%-98%), with a median follow-up of 39 months. The use of megadoses of CD34(+) cells with a fixed number of CD3(+) cells in nonmyeloablative hematopoietic stem cell transplantation (HSCT) in patients with SCID is associated with excellent engraftment, T cell recovery, and OS; however, B cell function does not recover in most patients.

Plasmacytoid precursor dendritic cells from NOD mice exhibit impaired function: are they a component of diabetes pathogenesis?

OBJECTIVE

Plasmacytoid precursor dendritic cell facilitating cells (p-preDC FCs) play a critical role in facilitation of syngeneic and allogeneic hematopoietic stem cell (HSC) engraftment. Here, we evaluated the phenotype and function of CD8(+)/TCR(-) FCs from NOD mice.

RESEARCH DESIGN AND METHODS

The phenotype of CD8(+)/TCR(-) FCs was analyzed by flow cytometry using sorted FCs from NOD, NOR, or B6 mice. The function of NOD FCs was evaluated by colony-forming cell (CFC) assay in vitro and syngeneic or allogeneic HSC transplantation in vivo.

RESULTS

We report for the first time that NOD FCs are functionally impaired. They fail to facilitate engraftment of syngeneic and allogeneic HSCs in vivo and do not enhance HSC clonogenicity in vitro. NOD FCs contain subpopulations similar to those previously described in B6 FCs, including p-preDC, CD19(+), NK1.1(+)DX5(+), and myeloid cells. However, the CD19(+) and NK1.1(+)DX5(+) subpopulations are significantly decreased in number in NOD FCs compared with disease-resistant controls. Removal of the CD19(+) or NK1.1(+)DX5(+) subpopulations from FCs did not significantly affect facilitation. Notably, Flt3 ligand (FL) treatment of NOD donors expanded FC total in peripheral blood and restored facilitating function in vivo.

CONCLUSIONS

These data demonstrate that NOD FCs exhibit significantly impaired function that is reversible, since FL restored production of functional FCs in NOD mice and suggest that FL plays an important role in the regulation and development of FC function. FCs may therefore be linked to diabetes pathogenesis and prevention.