Immunomodulation of endothelial differentiated mesenchymal stromal cells: impact on T and NK cells.

Wharton's jelly mesenchymal stromal cells (WJ-MSCs) are promising candidates for tissue engineering, as their immunomodulatory activity allows them to escape immune recognition and to suppress several immune cell functions. To date, however, few studies have investigated the effect of differentiation of the MSCs on this immunomodulation. To address this question, we sought to determine the impact of differentiation toward endothelial cells on immunoregulation by WJ-MSCs. Following differentiation, the endothelial-like cells (ELCs) were positive for CD31, vascular endothelial cadherin and vascular endothelial growth factor receptor 2, and able to take up acetylated low-density lipoproteins. The expression of HLA-DR and CD86, which contribute to MSCs immunoprivilege, was still weak after differentiation. We then co-cultured un- and differentiated MSCs with immune cells, under conditions of both direct and indirect contact. The proliferation and phenotype of the immune cells were analyzed and the mediators secreted by both ELCs and WJ-MSCs quantified. Interleukin (IL)-6, IL-1ß, prostaglandin E2 and in particular indoleamine-2,3-dioxygenase expression were upregulated in ELCs on stimulation by T and NK cells, suggesting the possible involvement of these factors in allosuppression. ELCs co-cultured with T cells were able to generate CD25(+) T cells, which were shown to be of the CD4(+)CD25(+)FoxP3(+) regulatory subset. Direct contact between NK cells and ELCs or WJ-MSCs decreased the level of NK-activating receptor natural-killer group 2, member D. Moreover, direct co-culturing with ELCs stimulates CD73 acquisition on NK cells, a mechanism which may induce adenosine secretion by the cells and lead to an immunosuppressive function. Taken together, our results show that ELCs obtained following differentiation of WJ-MSCs remain largely immunosuppressive.

Diversity and heterogeneity of extracellular RNA in human plasma.

Extracellular RNAs (exRNAs) are secreted by nearly all cell types and are now known to play multiple physiological roles. In humans, exRNA populations are found in nearly any physiological liquid and are attracting growing interest as a potential source for biomarker discovery. Human plasma, a readily available sample for biomedical analysis, reported to contain various subpopulations of exRNA, some of which are most likely components of plasma ribonucleoproteins (RNPs), while others are encapsulated into extracellular vesicles (EVs) of different size, origin and composition. This variation explains the extreme complexity of the human exRNA fraction in plasma. In this work, we aimed to characterize exRNA species from blood samples of healthy human donors to achieve the most comprehensive overview of the species, sizes and origins of the exRNA present in plasma fractions. Unbiased analysis of exRNA composition was performed with prefractionation of plasma exRNA followed by library preparation, sequencing and bioinformatics analysis. Our results demonstrate that, in addition to "mature", adaptor ligation-competent RNA species (5'-P/3'-OH), human plasma contains a substantial proportion of degraded RNA fragments (5'-OH/3'-P or cycloP), which can be made competent for ligation using appropriate treatments. These degraded RNAs represent the major fraction in the overall population and mostly correspond to rRNA, in contrast to mature products, which mostly contain miRNAs and hY4 RNA fragments. Precipitation polyethylene glycol (PEG)-based kits for EV isolation yield a fraction that is highly contaminated by large RNPs and by RNA loosely bound to EVs. Purer EV preparations are obtained by using proteinase K and RNase A treatment, as well as by size-exclusion chromatography (SEC). These samples have rather distinct RNA compositions compared to PEG-precipitated EV preparations and contain a substantial proportion of exRNA of non-human origin, arising from human skin and gut microbiota, including viral microbiota. These exogenous exRNAs represent up to 75-80% of total RNA reads in highly purified extracellular vesicles, paving the way for biomedical exploitation of these non-human biomarkers.

How Do Mesenchymal Stem Cells Influence or Are Influenced by Microenvironment through Extracellular Vesicles Communication?

Mesenchymal stem cells (MSCs) are widely used in cell therapy and tissue engineering thanks to their self-renewal, their multipotency, and their immunomodulatory properties that make them an attractive tool for regenerative medicine. A large part of MSCs positive effects is due to their secretion products which participate in creating a favorable microenvironment and closely relate these cells to other cell types. Extracellular vesicles (EVs) belong to cellular secretions. They are produced by cells continuously or after stimulation (e.g., calcium flux, cellular stress) and act in tissue homeostasis and intercellular communication. The understanding of the role of EVs is growing, more particularly their impact on cell migration, differentiation, or immunomodulation. EVs derived from MSCs show these interesting properties that may be considered in therapeutics, although they can have adverse effects by facilitating cancer propagation. Moreover, MSC behavior may also be influenced (proliferation, differentiation) by EVs derived from other donor cells. The aim of this mini review is to summarize the two-way communication between MSCs and other cell types, and how they can affect each other with their microenvironment through EVs. On the one hand, the manuscript presents the influence of MSC-derived EVs on diverse recipient cells and on the other hand, the effects of EVs derived from various donor cells on MSCs. The discrepancies between cancer cells and MSCs communication according to the sources of MSCs but also the tumor origins are also mentioned.