Umbilical Cord products in Regenerative Medicine

The umbilical cord (UC) is a very good source of mesenchymal stem cells (MSCs), active biomolecules, and extracellular matrix with great potential applications in regenerative medicine. MSCs derived from the UC can be obtained from the amniotic membrane, cord lining, Wharton’s jelly, and perivascular region. UC-MSCs have several advantages for cell therapy, such as the noninvasive harvest from tissue normally discarded at birth, the relatively high cell yields, and a phenotype that parallels that of MSCs from other tissue sources. UC-MSCs possess various properties, rendering them as appealing candidates for cell based therapies. WJ-MSCs have the properties of embryonic and mature stem cells, providing both properties to cell-based therapies. WJ-MSC have capabilities for neuronal, skeletal muscle, cardiomyocyte, and endodermal lineages differentiation. The high differentiation potential and immunoregulatory properties of UC-MSCs can be envisioned to target a variety of disorders such as cancer, cardiovascular and renal diseases, diabetes wound healing, cartilage and tendon repair, neurological disorders and injuries.

Placental tissues, including UC, produce many active biologic molecules, which are able to mediate paracrine-induced anti-inflammatory responses, re-epithelialization, angiogenic properties and other biological effects. In addition to all the active biomolecules identified in whole placental tissues, there are several active biomolecules specifically derived from MSCs collectively called MSC-derived secretome. MSC-sourced secretome is defined as the set of MSC-derived bioactive factors secreted to the extracellular space. Recent reports suggest that the therapeutic activity of MSCs is mainly mediated by the paracrine effect of secretomes.

The extracellular matrix (ECM) is a dynamic and intricate three-dimensional microenvironment with excellent properties that directly or indirectly regulate cell behavior, including proliferation, adhesion, migration, and differentiation. ECMs are used to augment wound healing and tissue repair. Compared with tissue-derived ECM, cell-derived ECM has more advantages: less potential for pathogen transfer, fewer inflammatory or anti-host immune responses, and a closer resemblance to the native ECM microenvironment. The rapidly increasing interest in UC-MSCs and other active biologics from this tissue for clinical applications has already resulted in several published observations. The next several years should abound in results of clinical applications of UC-MSCs and active biomolecules, and hopefully, prove their invaluable properties.

Structure of Human Umbilical Cord

In placental mammals, the UC is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologically and genetically part of the fetus, and (in humans) normally contains two arteries (the umbilical arteries) and one vein (the umbilical vein), buried within Wharton's jelly. The umbilical vein supplies the fetus with oxygenated, nutrient-rich blood from the placenta. Conversely, the fetal heart pumps low oxygen containing blood, nutrient-depleted blood through the umbilical arteries back to the placenta. Nanaev et al. identified three regions within the term human UC, based on the distribution of extracellular matrix proteins and cytoskeletal features of the stromal cells: the subamniotic zone, Wharton’s jelly, and the combined media and adventitia of the blood vessels.

Wharton’s Jelly

Wharton’s jelly is the mucoid connective tissue, rich in proteoglycans, that surrounds the two arteries and one vein of the umbilical cord. It provides insulation and protection within the UC. It also contains some fibroblasts and macrophages. The adventitial roles, vascular support and some contractile function are considered to be fulfilled by the mucoid connective tissue that also prevents kinking of the vessels during movement of the fetus in the womb. Wharton’s jelly comprises all the tissue from the outer margins of the tunica media to the inner surface of the amniotic epithelium.

Overall, cells from WJ fit with the minimal criteria for MSCs. Populations of the WJ-MSCs express specific mesenchymal markers such as CD 44, CD90, CD73 and CD105. The cells also reveal high level of adhesion receptors—integrin _1 (CD29) and hyaluronan receptor—CD44. Furthermore, WJ-MSCs are negative for hematopoietic and endothelial antigens: CD3, and CD34. The mesenchymal features of WJ cells have been confirmed by the expression of specific lineage cytoskeletal markers, such as SMA and Vimentin. ESC markers, such as Oct-4, SSEA4, nucleostemin, SOX-2 and Nanog, have also been revealed. The most striking feature of WJ-MSCs is their unique ability to express the HLA-G6 isoform. As mentioned previously, HLA-G6 is implicated in immune-modulation. Thus, WJ-MSCs are particularly suitable for cell-based therapy.

Umbilical Cord-Derived Active Biomolecules

Several studies have documented that UC, and other placental tissues, produce various active biologic molecules, which are able to mediate paracrine-induced anti-inflammatory responses, re-epithelialization, angiogenic properties and other biological effects.

MSC-Derived Secretome

In addition to all the active biomolecules identified in whole placental tissues, there are several active biomolecules specifically derived from MSCs isolated from various sources, including placenta, collectively called MSC-derived secretome. MSC-sourced secretome is defined as the set of MSC-derived bioactive factors (soluble proteins, nucleic acids, lipids and extracellular vesicles- EVs) secreted to the extracellular space. MSC–derived EV contains a lipid bilayer enriched in proteins (tetraspanins, integrins, ligands for cell surface receptors) enabling tracking, adhesion and the endocrine effects of EV. A large number of MSC-derived bioactive molecules, including genetic materials (DNA, RNA fragments, microRNAs-miRNAs), enzymes, signaling and signal transduction proteins, immunomodulatory and growth factors are enveloped by the bilayer membrane.

Recent reports suggest that the therapeutic activity of MSCs is mainly mediated by the paracrine effect of secretomes. Analysis of the secretome points to its influence on varied biological processes such as angiogenesis, neurogenesis, tissue repair, immunomodulation, wound healing, anti-fibrotic and anti-tumour for tissue maintenance and regeneration. However, MSC based therapy has been shown to be generally safe, from a clinical standpoint, the use of cell-free infusions can altogether circumvent the administration of viable cells for therapy. A large number of experimental studies explored therapeutic potential of MSC-sourced secretome and their findings indicated that MSC-derived conditioned medium, containing the complete milieu of MSC-sourced soluble factors and vesicular elements, managed to efficiently enhance endogenous healing process in inflamed tissues by providing pro-angiogenic and trophic factors to injured cells, and by suppressing detrimental local and systemic immune response. MSC–derived secretome showed beneficial effects in the treatment of inflammatory and degenerative diseases of hepatobiliary, respiratory, skeletal, gastrointestinal, cardiovascular and nervous system.

Future Perspectives

The UC is a good source of active biologics, including MSCs, biomolecules, and ECM, for cell therapies and tissue engineering applications. By the end of 2019, the public clinical trials database http://www.clinicaltrials.gov/ has shown more than 55 clinical trials using UC-MSC for a very wide range of therapeutic applications. Most of these trials are safety studies (Phase I) and proof of concept (Phase II) with very few in Phase III. To date, the results of most of these studies have not been published. However, the rapidly increasing interest in UC-MSCs, particularly WJ-MSCs, for clinical applications has already resulted in several published observations.

The high efficiency of WJ-MSC recovery, the minimal ethical concerns associated with its acquirement and use, low immunogenicity, and the fact that they are from healthy, young donors make them an ideal source of MSCs for autologous and allogeneic applications. Private and public banking of perinatal tissues is gaining popularity. To fulfill the promise of UC-MSCs and other active biologics found in this tissue in regenerative medicine it is imperative the observance of national and international regulations regarding standards and procedures.

The quality management systems already in place in functioning tissue/cell banks guarantee high standards for the donation, procurement, testing, processing, storage, and distribution of the WJ-MSCs and other active biologics of UC. Therefore, as the off-the-shelf product, these active biologics can be applied safely, immediately, and on demand. The next several years should abound in results of clinical applications of WJ-MSCs and hopefully, prove their invaluable properties.