Immunosuppressive effects of multipotent mesenchymal stromal cells in cultures with different O2 content in the medium

Factors Defining Human Adipose Stem/Stromal Cell Immunomodulation in Vitro

Human adipose tissue-derived stem/stromal cells (hASCs) are adult multipotent mesenchymal stem/stromal cells with immunomodulatory capacities. Here, we present up-to-date knowledge on the impact of different experimental and donor-related factors on hASC immunoregulatory functions in vitro. The experimental determinants include the immunological status of hASCs relative to target immune cells, contact vs. contactless interaction, and oxygen tension. Factors such as the ratio of hASCs to immune cells, the cellular context, the immune cell activation status, and coculture duration are also discussed. Conditioning of hASCs with different approaches before interaction with immune cells, hASC culture in xenogenic or xenofree culture medium, hASC culture in two-dimension vs. three-dimension with biomaterials, and the hASC passage number are among the experimental parameters that greatly may impact the hASC immunosuppressive potential in vitro, thus, they are also considered. Moreover, the influence of donor-related characteristics such as age, sex, and health status on hASC immunomodulation in vitro is reviewed. By analysis of the literature studies, most of the indicated determinants have been investigated in broad non-standardized ranges, so the results are not univocal. Clear conclusions cannot be drawn for the fine-tuned scenarios of many important factors to set a standard hASC immunopotency assay. Such variability needs to be carefully considered in further standardized research. Importantly, field experts' opinions may help to make it clearer.

Interaction of multipotent mesenchymal stromal and immune cells: Bidirectional effects

Adult multipotent mesenchymal stromal cells (MSCs) are considered one of the key players in physiological remodeling and tissue reparation. Elucidation of MSC functions is one of the most intriguing issues in modern cell physiology. In the present review, the interaction of MSCs and immune cells is discussed in terms of reciprocal effects, which modifies the properties of "partner" cells with special focus on the contribution of direct cell-to-cell contacts, soluble mediators and local microenvironmental factors, the most important of which is oxygen tension. The immunosuppressive phenomenon of MSCs is considered as the integral part of the response-to-injury mechanism.

Human Bone Marrow Mesenchymal Stem/Stromal Cells Preserve Their Immunomodulatory and Chemotactic Properties When Expanded in a Human Plasma Derived Xeno-Free Medium

Due to their immunomodulatory and chemotactic properties, hMSC are being explored to treat immune-related diseases. For their use in human therapies, it is necessary to culture hMSC in xeno-free conditions. In this study, the impact that a xeno-free medium based on a human plasma derivate has on these properties was analysed. Bone marrow-derived hMSC preserved their immunosuppressive and immunostimulatory properties, as observed with in vitro assays with hMSC cocultured with mixed leukocyte reactions or with mitogen-stimulated leukocytes. Moreover, hMSC expanded in xeno-free medium were recruited by macrophages in both migration and invasion assays, which indicates that the cells maintained their chemotactic properties. These data suggest that xeno-free expanded hMSC preserved their immunomodulatory and chemotactic properties, indicating that the described xeno-free medium composition is a potential candidate to culture and expand hMSC for human cell therapies.

Factors governing the immunosuppressive effects of multipotent mesenchymal stromal cells in vitro

Multipotent mesenchymal stem/stromal cells (MSCs) are of great interest to researchers because of the unique properties, such as enhanced proliferation, paracrine activity and multilineage differentiation. Their non-immunogenicity, in combination with immunomodulatory properties, opens up the opportunity for the allogeneic application of MSCs. The MSC immunomodulatory capacity is currently being actively studied in vitro using various experimental designs. However, the results are not always univocal. It was found that the outcome of the stromal/immune cell interaction depends on experimental conditions. In this review we considered the impact of different factors, such as the ratio of stromal/immune cells, interaction time, the path of immune cell activation, etc. on the MSC immunomodulation. We also accentuated the importance of local milieu, in particular, oxygen tension, for the realization of MSC immunosuppressive activity.