Current Stem Cell Research & Therapy, 2011, 6, 221-228 221 1574-888X/11 $58.00+.00 © 2011 Bentham Science Publishers . Mesenchymal Stem Cells in the Umbilical Cord: Phenotypic Characteriza- tion, Secretome and Applications in Central Nervous System Regenerative Medicine Miguel M. Carvalho #,1,2 , Fábio G. Teixeira #,1,2 , Rui L. Reis 2,3 , Nuno Sousa 1,2 and António J. Salgado* ,1,2 1 Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal; 2 3B's Research Group - Biomaterials, Biodegradables, Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark, Taipas, Guimarães, Portugal; 3 Institute for Biotechnology and Bioengeneering, PT Government Associated Lab, Guimarães, Portugal Abstract: Mesenchymal Stem Cells (MSCs), have been defined and characterized by: 1) their ability to adhere to plastic culture flasks; 2) the positive expression of CD105, CD73, CD90 membrane antigens, and the lack of expression of others (e.g CD45 and CD34) and 3) the ability of differentiation under adequate conditions along the osteogenic, chondrogenic and adipogenic lineages. In recent years, cells with these characteristics have been isolated from the Wharton’s jelly of the Umbilical Cord (UC). Similarly to bone marrow MSCs, they have shown multilineage differentiation potential and to be able to provide trophic support to neighboring cells. According to the literature, there are two main populations of cells with a mesenchymal character within the human UC: Wharton's jelly Mesenchymal Stem Cells (WJ-MSCs) and Human Umbilical Cord Perivascular Cells (HUCPVCs). In the present work our aim is to make a comprehensive review on MSC populations of the UC and how these cell populations may be used for future applications in CNS regenerative medicine. Following a brief insight on the general characteristics of MSC like cells, we will discuss the possible sources of stem cells within the WJ and the cord itself (apart UC blood), as well as their phenotypic character. As it has already been shown that these cells hold a strong trophic support to neighbouring cell populations, we will then focus on their secre- tome, namely which molecules have already been identified within it and their role in phenomena such as immunomodu- lation. The possible applications of these cell populations to CNS regenerative medicine will be addressed by critically reviewing the work that has been performed so far in this field. Finally, a brief insight will be made on what in the authors’ opinion are the major challenges in the field for the future application of these cell populations in CNS regenerative medicine. Keywords: Mesenchymal stem cells, umbilical cord, Wharton’s jelly, secretome. 1. INTRODUCTION The identification of Mesenchymal Stem Cells (MSCs) followed the pioneering work of Alexander Friedenstein and colleagues, who discovered that within the bone marrow compartment existed a population of non-hematopoietic cells with osteogenic potential [1]. Furthermore, he developed a method of isolating these cells based on their adherence to plastic surfaces, reporting that they developed into fibro- blast-shaped cell cultures with high replicative and clono- genic potential [2]. Since then, human MSCs (hMSCs), or cells with a MSC-like phenotype have been identified and isolated from several adult and fetal tissues, namely bone marrow [3-5], adipose tissue [6, 7], circulating blood [4, 8], dental pulp [9-11], placenta [12, 13], amniotic fluid [14, 15], umbilical cord blood [16], subendothelial layer of umbilical cord vein [17], umbilical cord Wharton’s jelly (WJ) [18, 19], umbilical cord perivascular layer [20], pancreas [21], *Address correspondence to this author at the Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal; Tel: +351 253 60 49 47; Fax: +351 253 60 48 20; E-mail: asalgado@ecsaude.uminho.pt # M.M. Carvalho and F.G. Teixeira contributed equally to the work. liver [4, 5], lung and spleen [5]. They are commonly charac- terized by: 1) the ability to adhere to plastic culture flasks; 2) the expression in 95% of the MSC population of CD105, CD73 and CD90 membrane antigens, and the lack of expres- sion of CD45, CD34, CD14, CD11b, CD79 or CD19 and HLA class II; and 3) the ability of differentiation under ade- quate conditions into at least osteoblasts, chondrocytes and adipocytes [22, 23]. Despite these common traits, these cells do present subtle changes in their expression profile. Such changes can be the result of tissue-specific environments; however, as already pointed by others, one should also take into account that dif- ferences in culture protocols may influence the identity of MSC populations [24, 25]. In addition to CD105, CD73 and CD90, other membrane antigens, namely CD29, CD44, CD51, CD71, CD106, CD166 and Stro-1, have been associ- ated with a MSC-like identity [24, 26]. Besides the deriva- tion towards the osteogenic, chondrogenic and adipogenic lineages [24, 26, 27], the derivation of other mesenchymal cell types, namely myocytes and tenocytes, from MSCs, has also been documented [26, 27]. Interestingly, several reports argued that MSCs can be derived into cell types without a mesoderm/mesenchymal origin, namely neurons or epithelial