Stem cells are:

• Undifferentiated cells capable of dividing indefinitely
• Cells that can differentiate, giving rise to different cell lines
• Cells with the potential to differentiate into mature cells with specialized characteristics and functions, for example nerve, cardiac, skin, blood, bone and cartilage cells

The stem cell with the biggest differentiating potential is the fertilized egg or zygote from which originate all tissues that constitute the embryo and all those essential to its development, such as the umbilical cord and placenta. Due to its capacity to differentiate into any type of cell, this cell is designated totipotent, and it is from this cell that every type of cell in an adult human being originates.

Stem cells can be divided, according to their origin, into two groups: embryonic stem cells and adult stem cells.

Embryonic stem cells exist in the blastocyst, an initial phase of the embryonic development that occurs 3 to 5 days after fertilization, before implantation in the uterus wall occurs. These cells are pluripotent and can differentiate into cells of the different embryonic germ layers (the mesoderm, endoderm and ectoderm). Each of these layers gives rise to distinct types of specialized tissues.

Adult stem cells are undifferentiated cells found in differentiated and specialized tissues. These cells are capable of self-renovation during the life-span of an organism, allowing for the regeneration of the tissues where they are present.

Adult stem cells can be found in the bone marrow, retina, cornea, gum, skin, liver, intestinal tract and pancreas.

Umbilical cord blood cells are adult stem cells with the potential to differentiate into cells of the haematopoietic and mesenchymal lineage.

• Haematopoietic stem cells are cells capable of differentiating into cells of blood lineage (white blood cells, red blood cells and platelets).
• Mesenchymal stem cells are precursors to a variety of cells such as bone, cartilage, fat (adipose tissue) and fibrous connective tissue cells.

The enormous potential that stem cells have to differentiate into distinct types of cells that constitute an organism’s tissues confers them an elevated capacity in terms of therapeutical applications in Clinical Biotechnology.

The first published reference of isolation of mesenchymal stem cells occurred in 1997. Since then, the knowledge on this type of cells has evolved considerably and it is now possible to characterize them with relative ease. Mesenchymal stem cells (MSC) can be isolated from three main sources: umbilical cord blood (CB), umbilical cord matrix (UCM) and bone marrow (BM). Cord blood is rich in haematopoietic stem cells that differentiate mainly into blood cells. There are studies that indicate that MSC may also be isolated from CB. However, the isolation of mesenchymal stem cells from this source is controversial and very inconsistent.

MSC are undifferentiated cells capable of self-renewal and intense proliferation. An important characteristic of these cells is there capacity to support haematopoietic stem cell growth and expansion, and their capacity to promote haematopoietic stem cell engraftment when applied together.

MSC can differentiate into condrocytes (cartilage cells), osteocytes (bone, tendon and ligament cells), adipocytes (fat cells) and myocytes (muscle cells).

The isolation of mesenchymal cells from bone marrow is a low yield, painful process that always implies general anaesthetic. In contrast, stem cell isolation from the umbilical cord is pain free and has a 100% yield, meaning that isolation is possible from all collected samples.

Isolation can be performed from the umbilical cord’s matrix or stroma (Wharton’s jelly) and from the subendothelium of the umbilical cord’s vein.

In the laboratory, these cells can be identified by their morphology (fibroblasts growing adherent to a surface) and by characteristic markers present on their surface.
In addition to these characteristics, MSC isolated from the umbilical cord do not possess a complete major histocompatibility complex. They lack the class II subgroup genes and a class I subgroup gene (HLA-DR). This characteristic is of major importance when compatibility between receiver and donor is an issue. In this case, even without compatibility, the probability of graft versus host disease (receptor rejection of the transplant) is practically none.

It was in fact noticed that a first injection of MSC did not produce an immune response (no antibodies were formed) and only after repeated injections was an immune response noted, but even then without transplant rejection.

DIFFERENCES BETWEEN BONE MARROW, CB AND UMBILICAL CORD MATRIX MSC:

• CB contains a lower percentage of MSC than the other sources
• The umbilical cord matrix has the highest percentage of MSC
• Umbilical cord matrix and CB cells multiply faster than bone marrow cells, indicating lesser differentiation
• MSC are isolated from 100% of umbilical cord samples whereas from only 63% of CB sample
• Isolation of MSC from CB samples can only be performed in the first 5 hours after birth

In conclusion, mesenchymal stem cells are multipotent stem cells present in various tissues of the human body. Their isolation from the umbilical cord, usually discarded after birth, is easy, painless and doesn’t imply collection costs contrary to MSC collection from the bone marrow, peripheral blood or adipose tissue. These cells can be stored/cryopreserved at the same time as the umbilical CB, widening the range of treatable diseases. Isolation of MSC from the umbilical cord has been proved to be fairly consistent, with isolation of multipliable cells always being possible.