Human mesenchymal progenitor cells (MPCs) are considered to be of great promise for use in tissue repair and regenerative medicine. MPCs represent multipotent adherent cells, able to give rise to multiple mesenchymal lineages such as osteoblasts, adipocytes or chondrocytes. Recently, we identified and characterized human second trimester amniotic fluid (AF) as a novel source of MPCs. Herein, we found that early colonies of AF-MPCs consisted of two morphologically distinct adherent cell types, termed as spindle-shaped (SS) and round-shaped (RS). A detailed analysis of these two populations showed that SS-AF-MPCs expressed CD90 antigen in a higher level and exhibited a greater proliferation and differentiation potential. To characterize better the molecular identity of these two populations, we have generated a comparative proteomic map of SS-AF-MPCs and RS-AF-MPCs, identifying 25 differentially expressed proteins and 10 proteins uniquely expressed in RS-AF-MPCs. Furthermore, SS-AF-MPCs exhibited significantly higher migration ability on extracellular matrices, such as fibronectin and laminin in vitro, compared to RS-AF-MPCs and thus we further evaluated SS-AF-MPCs for potential use as therapeutic tools in vivo. Therefore, we tested whether GFP-lentiviral transduced SS-AF-MPCs retained their stem cell identity, proliferation and differentiation potential. GFP-SS-AF-MPCs were then successfully delivered into immunosuppressed mice, distributed in different tissues and survived longterm in vivo. In summary, these results demonstrated that AF-MPCs consisted of at least two different MPC populations. In addition, SS-AF-MPCs, isolated based on their colony morphology and CD90 expression, represented the only MPC population that can be expanded easily in culture and used as an efficient tool for future in vivo therapeutic applications.

Human spindle-shaped AF-MSCs or HPL cells might be valuable tools to induce liver repair and support liver function by cell transplantation. More importantly, the factors they release may also play an important role in cell treatment in diseases of the liver.

Amniotic fluid (AF) and amniotic membrane (AM) have been recently characterized as promising sources of stem or progenitor cells. Both not only contain subpopulations with stem cell characteristics resembling to adult stem cells, such as mesenchymal stem cells, but also exhibit some embryonic stem cell properties like (i) expression of pluripotency markers, (ii) high expansion in vitro, or (iii) multilineage differentiation capacity. Recent efforts have been focused on the isolation and the detailed characterization of these stem cell types. However, variations in their phenotype, their heterogeneity described by different groups, and the absence of a single marker expressed only in these cells may prevent the isolation of a pure homogeneous stem cell population from these sources and their potential use of these cells in therapeutic applications. In this paper, we aim to summarize the recent progress in marker discovery for stem cells derived from fetal sources such as AF and AM, using novel methodologies based on transcriptomics, proteomics, or secretome analyses.

Numerous studies have shown the presence of high levels of growth factors during the process of healing. Growth factors act by binding to the cell surface receptors and contribute to the subsequent activation of signal transduction mechanisms. Wound healing requires a complex of biological and molecular events that includes attraction and proliferation of different type of cells to the wound site, differentiation and angiogenesis. More specifically, migration of various cell types, such as endothelial cells and their precursors, mesenchymal stem/stromal cells (MSCs) or skin fibroblasts (DFs) plays an important role in the healing process. In recent years, the application of platelet rich plasma (PRP) to surgical wounds and skin ulcerations is becoming more frequent, as it is believed to accelerate the healing process. The local enrichment of growth factors at the wound after PRP application causes a stimulation of tissue regeneration. Herein, we studied: (i) the effect of autologous PRP in skin ulcers of patients of different aetiology, (ii) the proteomic profile of PRP, (iii) the migration potential of amniotic fluid MSCs and DFs in the presence of PRP extract in vitro, (iv) the use of the PRP extract as a substitute for serum in cultivating AF-MSCs. Considering its easy access, PRP may provide a valuable tool in multiple therapeutic approaches.

The concept of Regenerative Medicine combined with Cell based Therapy and Tissue Engineering represents the fourth pillar of healthcare and provides a promising approach for the treatment of serious diseases. Recently, cell based therapies are focused on the use of mesenchymal stem/stromal cells (MSCs). Human MSCs, that represent a mesoderm derived population of progenitors, are easily expanded in culture. They are capable to differentiate into osteoblasts, chondrocytes, and adipocytes and exhibit the potential to repair or regenerate damaged tissues. The best characterized source of human MSCs to date is the bone marrow; recently, fetal sources, such as amniotic fluid, umbilical cord, amniotic membranes, or placenta, have also attracted increased attention. Thus, MSCs may represent a valuable tool for tissue repair and cell therapeutic applications. To this end, the main focus of this review is to summarize and evaluate the key characteristics, the sources, and the potential use of MSCs in therapeutic approaches and modalities.

Recent studies support cell-based therapies for cancer treatment. An advantageous cell type for such therapeutic schemes are the mesenchymal stem cells (MSCs) that can be easily propagated in culture, genetically modified to express therapeutic proteins, and exhibit an innate tropism to solid tumors in vivo. Recently, we successfully isolated and expanded MSCs from second-trimester amniotic fluid (AF-MSCs). The main characteristic of AF-MSCs is their efficient and rapid expansion in vitro. Herein, we investigated the AF-MSCs tropism and capability to transport interferon beta (IFNβ) to the region of neoplasia in a bladder tumor model. To this end, we used the T24M bladder cancer cell line, previously generated from our studies, and developed a disease progression model in immunosuppressed mice, that can recapitulate the molecular events of bladder carcinogenesis. Our results documented that AF-MSCs exhibited high motility, when migrated either to T24M cells or to T24M-conditioned medium, and we further identified and studied the secreted factors which may trigger these enhanced migratory properties. Further, lentivirus-transduced AF-MSCs, expressing green fluorescent protein (GFP) or IFNβ, were intravenously administered to T24M tumor-bearing animals at multiple doses to examine their therapeutic effect. GFP- and IFNβ-AF-MSCs successfully migrated and colonized at the tumor site. Notably, significant inhibition of tumor growth as well as prolonged survival of mice were observed in the presence of IFNβ-AF-MSCs. Collectively, these results document the great potential of AF-MSCs as anti-cancer vehicles, implemented by the targeting of the tumor site and further facilitated by their high proliferation rate and expansion efficiency in culture.

The miRNA profile of mesenchymal stem cells (MSCs) derived from amniotic fluid, bone marrow (BM), and umbilical cord blood was analyzed. Initially, 67 different miRNAs were identified that were expressed in all three types of MSCs but at different levels, depending on the source. A more detailed analysis revealed that miR‐21 was expressed at higher levels in RS‐AF‐MSCs and BM‐MSCs compared with SS‐AF‐MSCs. Findings suggest that miR‐21 might function by regulating Sox2 expression in human MSCs and might also act as a key molecule determining MSC proliferation and differentiation.

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