Types of stem cells present in the blood of the umbilical cord

Stem cells are progenitor cells with a high potential for proliferation, capable of self-renewal (i.e., able of producing daughter cells equal to themselves) and of generating more than on specialised cells types (totipotent stem cells are capable of giving rise to all the specialised cells which constitute the various tissues and organs). A fundamental role seems to be played by the so-called "niche", i.e., by the micro-environment of the stem cell in situ: such a micro-environment would maintain the cells in their state of stemness, by mean so biochemical signals which inhibit their maturation. In man four sources of stem cells have been identified so far:

  • Embryonic stem cells (derived from the inner mass of the blastocysts)
  • Germ cells derived from the foetus
  • Stem cells from the umbilical cords
  • "Adult" or "Somatic" stem cells (identified in all tissues of the adult organism, such as bone marrow, pancreas, bone, cartilage, liver, skin, nervous system and fat tissue)

Different types of stem cells are contained in the blood of the umbilical cord: haemapoetic stem cells, mesenchymal stem cells and progenitor endothelial cells. At present cord blood cells have:

  • A clinical application for hematologic purposes
  • A prospect of use in the context of regenerative medicine

01. Haematopoetic Stem Cells

Haematopoetic stem cells are cells which are able to give rise to all the cellular elements of peripheral blood (red blood cells, white blood cells and platelets). These cells are able to regenerate the cellular content of the bone in all those cases in which it has been damaged as a result of pathologies, accidental exposure to ionising radiation or chemo-radio-therapy treatment for cancer. They are present in the bone marrow (where they constitute 1-3% of the cell population present), in peripheral blood (0.01-0.1%) and in cord blood (0.1-0.4%).

Initially, in 1974, S. Knudtzon demonstrated the existence of mature haematopoetic stem cells in the blood of the umbilical cord, while about ten years further on M. Ogawa and collaborators demonstrated the existence of primitive progenitor haemapoetic cells. On the basis of these studies umbilical cord blood has been recognised as a rich source of haematopoetic stem cells. Numerous other studies have demonstrated that such cells are capable of reproducing haematopoesis in vitro and can be preserved by freezing. The wealth of stem cells in umbilical cord blood explains very well, from a scientific point of view, their efficacy in the treatment of haematological diseases.

02. Mesenchymal Stem Cells

Mesenchymal stem cells are cells which are able to give rise to fat, cartilage and bone tissue. They are contained inside the medullary stroma. They constitute a population of pluripotent cells, so that, if they are properly directed, they can given rise to cells with the characteristics of various tissues.

Their presence has initially been suggested from the discovery of a therapeutic potential of cord blood beyond its haematopoetic effect. Cord blood, in fact, offers an excellent alternative to bone marrow as a source of mesenchymal stem cells. Such cells have been studied in depth in comparison with the mesenchymal stem cells of bone marrow and it has emerged that, while being morphologically and immunologically similar to the latter, they present a greater versatility for differentiation, being capable of giving rise to cells proper to the mesoderm (osteocytes, chondrocytes, adipocytes, skeletal myoblatsts), of the neuro-ectoderm (neuron and glia) and of the endoderm (hepatocytes). The presence of mesenchymal stem cells has been demonstrated also in Wharton’s jelly (the mucoid connective tissue which support the two arteries and the vein within the umbilical cord and which, until now, has been considered as a tissue without any use): such cells have been differentiated in osteoblasts, chondrocytes, adipocytes, hepatocytes and in cells producing insulin.

03. Endothelial Progenitor Cells

Endothelial progenitor cells are stem cells originating in the marrow, involved in the repair of the endothelial and in angiogenesis.

Also present in umbilical cord blood these cells contribute to the haematopoetic environment. According to some researchers, such cells could play a role in angiogenetic therapy and in endothelisation of transplanted bio-engineered tissues.

Besides, some research is being directed towards the study of cells of the immune system, in view of their possible application in the context of immuno-therapy and in the diagnostic forecasting of certain diseases.

One relevant characteristic of cord blood stem cells is that they are young (the length of their telomeres is relatively long) and immature. Different groups of researchers, using a cell depletion technology have recently isolated from human cord blood some pluripotent stem cells very similar to embryonic stem cells, in a way which can be reproduced and in significant quantities. Some other researchers have found a specific type of pluripotent stem cells derived from umbilical cord blood that they named USSCs (unrestricted somatic stem cells).