The Important Role of FLT3-L in Ex Vivo Expansion of Hematopoietic Stem Cells following Co-Culture with Mesenchymal Stem Cells

Influential factors for optimizing and strengthening mesenchymal stem cells and hematopoietic stem cells co-culture

Mesenchymal stem cells (MSCs) and Hematopoietic stem cells (HSCs) are two types of bone marrow stem cells that can proliferate and differentiate into different cell lineages. HSCs interact with MSCs under protective conditions, called niche. Numerous studies have indicated supportive effects of MSCs on HSCs proliferation and differentiation. Furthermore, HSCs have many clinical applications and could treat different hematologic and non-hematologic diseases. For this purpose, there is a need to perform in vitro studies to optimize their expansion. Therefore, various methods including co-culture with MSCs are used to address the limitations of HSCs culture. Some parameters that might be effective for improving the MSC/ HSC co-culture systems. Manipulating culture condition to enhance MSC paracrine activity, scaffolds, hypoxia, culture medium additives, and the use of various MSC sources, have been examined in different studies. In this article, we investigated the potential factors for optimizing HSCs/ MSCs co-culture. It might be helpful to apply a suitable approach for providing high-quality HSCs and improving their therapeutic applications.

Mesenchymal Stem Cell Migration and Tissue Repair

Mesenchymal stem cells (MSCs) are multilineage cells with the ability to self-renew and differentiate into a variety of cell types, which play key roles in tissue healing and regenerative medicine. Bone marrow-derived mesenchymal stem cells (BMSCs) are the most frequently used stem cells in cell therapy and tissue engineering. However, it is prerequisite for BMSCs to mobilize from bone marrow and migrate into injured tissues during the healing process, through peripheral circulation. The migration of BMSCs is regulated by mechanical and chemical factors in this trafficking process. In this paper, we review the effects of several main regulatory factors on BMSC migration and its underlying mechanism; discuss two critical roles of BMSCs—namely, directed differentiation and the paracrine function—in tissue repair; and provide insight into the relationship between BMSC migration and tissue repair, which may provide a better guide for clinical applications in tissue repair through the efficient regulation of BMSC migration.

Generation of Organotypic Multicellular Spheres by Magnetic Levitation: Model for the Study of Human Hematopoietic Stem Cells Microenvironment

Background and Objective

The characteristics of human hematopoietic stem cells are conditioned by the microenvironment of the bone marrow, where they interact with other cell populations, such as mesenchymal stem cells and endothelial cells; however, the study of this microenvironment is complex. The objective of this work was to develop a 3D culture system by magnetic levitation that imitates the microenvironment of human HSC.

Methods and Results

Human bone marrow-mesenchymal stem cells, umbilical cord blood-hematopoietic stem cells and a non-tumoral endothelial cell line (CC2811, Lonza^Ⓡ) were used to develop organotypic multicellular spheres by the magnetic levitation method. We obtained viable structures with an average sphericity index greater than 0.6, an average volume of 0.5 mm³ and a percentage of aggregation greater than 70%. Histological studies of the organotypic multicellular spheres used hematoxylin and eosin stains, and an evaluation of vimentin expression by means of immunohistochemistry demonstrated an organized internal structure without picnotic cells and a high expression of vimentin. The functional capacity of human hematopoietic stem cells after organotypic multicellular spheres culture was evaluated by multipotency tests, and it was demonstrated that 3D structures without exogenous Flt3L are autonomous in the maintenance of multipotency of human hematopoietic stem cells.

Conclusions

We developed organotypic multicellular spheres from normal human cells that mimic the microenvironment of the human hematopoietic stem cells. These structures are the prototype for the development of complex organoids that allow the further study of the biology of normal human stem cells and their potential in regenerative medicine.

Serum-mediated Activation of Bone Marrow-derived Mesenchymal Stem Cells in Ischemic Stroke Patients: A Novel Preconditioning Method

Stroke induces complex and dynamic, local and systemic changes including inflammatory reactions, immune responses, and repair and recovery processes. Mesenchymal stem cells (MSCs) have been shown to enhance neurological recovery after stroke. We hypothesized that serum factors play a critical role in the activation of bone marrow (BM) MSCs after stroke such as by increasing proliferation, paracrine effects, and rejuvenation. Human MSCs (hMSCs) were grown in fetal bovine serum (FBS), normal healthy control serum (NS), or stroke patient serum (SS). MSCs cultured in growth medium with 10% SS or NS exhibited higher proliferation indices than those cultured with FBS (P < 0.01). FBS-, NS-, and SS-hMSCs showed differences in the expression of trophic factors; vascular endothelial growth factor, glial cell–derived neurotrophic factor, and fibroblast growth factor were densely expressed in samples cultured with SS (P < 0.01). In addition, SS-MSCs revealed different cell cycle– or aging-associated messenger RNA expression in a later passage, and β-galactosidase staining showed the senescence of MSCs observed during culture expansion was lower in MSCs cultured with SS than those cultured with NS or FBS (P < 0.01). Several proteins related to the activity of receptors, growth factors, and cytokines were more prevalent in the serum of stroke patients than in that of normal subjects. Neurogenesis and angiogenesis were markedly increased in rats that had received SS-MSCs (P < 0.05), and these rats showed significant behavioral improvements (P < 0.01). Our results indicate that stroke induces a process of recovery via the activation of MSCs. Culture methods for MSCs using SS obtained during the acute phase of a stroke could constitute a novel MSC activation method that is feasible and efficient for the neurorestoration of stroke.

Interferon-Gamma Impairs Maintenance and Alters Hematopoietic Support of Bone Marrow Mesenchymal Stromal Cells

Bone marrow (BM) mesenchymal stromal cells (MSCs) provide microenvironmental support to hematopoietic stem and progenitor cells (HSPCs). Culture-expanded MSCs are interesting candidates for cellular therapies due to their immunosuppressive and regenerative potential which can be further enhanced by pretreatment with interferon-gamma (IFN-γ). However, it remains unknown whether IFN-γ can also influence hematopoietic support by BM-MSCs. In this study, we elucidate the impact of IFN-γ on the hematopoietic support of BM-MSCs. We found that IFN-γ increases expression of interleukin (IL)-6 and stem cell factor by human BM-MSCs. IFN-γ-treated BM-MSCs drive HSPCs toward myeloid commitment in vitro, but impair subsequent differentiation of HSPC. Moreover, IFN-γ-ARE-Del mice with increased IFN-γ production specifically lose their BM-MSCs, which correlates with a loss of hematopoietic stem cells' quiescence. Although IFN-γ treatment enhances the immunomodulatory function of MSCs in a clinical setting, we conclude that IFN-γ negatively affects maintenance of BM-MSCs and their hematopoietic support in vitro and in vivo.

Molecular and Cellular Interactions of Allogenic and Autologus Mesenchymal Stem Cells with Innate and Acquired Immunity and Their Role in Regenerative Medicine

Mesenchymal stem cells (MSCs), as major stem cells for cell therapy, have been studied from different aspects in preclinical and clinical settings for more than a decade. These cells modulate the immune system (humoral and cellular immune responses) in vitro by producing soluble factors (anti-inflammatory molecules) and/or making cell-cell contacts. Hence, they could be used in regenerative medicine, tissue engineering and immune therapy. MSCs-based therapy have been recently used for treatment of cancer regarding the migratory potential of these cells towards tumor cells which makes them considerable candidates, also for cell therapy in both allogeneic and autologous settings. So, this review attempts to focus on the factors secreted by MSCs such as cytokines, their functional role in mounting and controlling immune responses mediated by different immune cell subpopulations and their significance in regenerative medicine in clinical trials. Although, further studies remain to be done to increase our knowledge of regulating development mechanisms, homeostasis and tissue repair in order to provide new tools to implement the efficacy of cell therapy trials. Although MSCs have been proved safe and effective for cell therapy, there are still challenges to overcome before widely applying MSCs in clinic.