**4. Mesenchymal stem cells**

MSCs were firstly characterized by Friedenstein's group as being phenotypically identical to fibroblasts and capable to adhere to plastic surfaces [1]. These cells are defined by the International Society for Cellular Therapy as cells that express specific surface markers (CD73, CD90, and CD105), do not exhibit the hematopoietic markers (CD45, CD34, CD14, CD19, CD11b, CD79a, and others), and have the ability to adhere to plastic surfaces when in culture and multipotential ability to differentiate in at least osteoblasts, chondrocytes, and adipocytes under specific *in vitro* conditions [14]. MSCs can be isolated from various sources such as adipose tissue, bone marrow, umbilical cord, dental pulp, olfactory mucosa, and muscle [15, 16].

In addition to their ability to differentiate into various types of tissues, MSCs can be used to produce secretome, which is composed by a wide variety of secreted
