Undifferentiated cells found throughout the body after embryonic development, that multiply by cell division to replenish dying cells and regenerate damaged tissue. They can be found in juvenile as well as adult animals and humans. Stem cells of adult organisms can be unipotent (give rise to one specific cell type) or multipotent (give rise to different specific cell types). Unlike embryonic stem cells, the use of adult stem cells is not considered too controversial, as they are derived from adult tissue samples rather than destroyed human embryos.

Alleles are different versions of the same gene. Each allele differs by one or more differences in the sequence of nucleotides (structural unit of DNA). These differences arise by mutation in the history of the species, or genetic recombination. All alleles of a gene occupy the same locus (position) on a single chromosome.

Cells from a donor, another person, in contrast with autologous cells, which are derived from one’s own body.

An antigen can be “self” and “ non-self”. A “non-self” antigen is a substance/molecule that, when introduced into the body triggers the production of an antibody by the immune system, which will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as pollen or cells such as bacteria. “Self” antigens are usually tolerated by the immune system.

Cells from one’s own body, in contrast to cells from a donor.

Blood in the placenta and umbilical cord.

Placental blood collected from an umbilical cord allows the preparation of a unit of placental blood. Grafting centres speak of cord blood units used by transplant recipients. The use of placental blood to perform transplants was initially limited to children. Today, it becomes possible to use two units of cord blood to form a graft in an adult.

Cells resulting from an embryo of 5 to 7 days, capable of giving rise to more than 200 cell types representative of all body tissues. These stem cells can be totipotent or pluripotent.

Stands for "Graft Versus Host Disease". It is a post-transplantation complication that occurs when the donor immune system cells recognize the patient’s body as foreign and attacks it. It is much lower incidence in umbilical cord blood transplants compared to bone marrow transplants, which is a great advantage as GVHD has a high mortality and morbidity.

Cells that give rise to blood cells.

HLA stands for Human Leukocyte Antigens. Human Leukocyte Antigens are expressed on the cell surface and allow the identification of cells by the immune system.

The HLA system or Major Histocompatibility Complex (MHC) is the system that allows the body and its immune system to recognize the self (e.g. tissue) of non-self (virus, bacteria and grafts). An item that does not have the correct tissue type HLA will be attacked by the immune system. Each human body has an HLA of its own, and is highly polymorphic between individuals.During a transplant, HLA matching is crucial to prevent graft rejection. Stem cells v4.0 - 5/45

Induced pluripotent stem cell, or IPS cell, is a stem cell that has been created from an adult cell such as a skin, liver, stomach or other mature cell through the introduction of genes that reprogram the cell and transform it into a cell that has all the characteristics of an embryonic stem cell. The term pluripotent connotes the ability of a cell to give rise to multiple cell types, including all three embryonic lineages forming the body’s organs, nervous system, skin, muscle and skeleton. So far, induced pluripotent stem cells appear to exhibit the same key features of embryonic stem cells.

Mesenchymal stem cells, or MSC, are non-hematopoietic multipotent progenitor cells. They are capable of differentiating into many cell types (adipose, cartilage, bone, muscle, nerve ...) and capable of reducing immune responses. Mesenchymal stem cells were initially identified in bone marrow and can also be obtained from other tissues: adipose tissue, placental blood, umbilical cord, amniotic fluid, synovium, periosteum, and perichondrium. These are adherent cells with a fibroblastic look, not phagocytic and their number decreases with age.

Multipotent stem cells are unspecialized cells that have the ability to self-renew for long periods of time and differentiate into specialized cells with specific functions. Their specialization potential is limited and they are committed to produce specific cell types. They vary from stem cells such as pluripotent ones which can give rise to almost any cell type.

Pluripotent stem cells are often termed 'true' stem cells because they have the potential to differentiate into almost any cell in the body. This means that under the right circumstances, a stem cell that is isolated from an embryo can produce almost all of the cells in the body. Yet after this embryonic development stage is over, the stem cells no longer have this unlimited potential to develop into all cell types. Their pluripotency is thus lost and they can only become certain types of cells (multipotent).

Progenitor cell is a biological cell that, like a stem cell, has a tendency to differentiate into a specific type of cell, but is already more specific than a stem cell and is pushed to differentiate into its "target" cell. The most important difference between stem cells and progenitor cells is that stem cells can replicate indefinitely, whereas progenitor cells can only divide a limited number of times. Controversy about the exact definition remains and the concept is still evolving.

Biological cells that can divide and differentiate into diverse specialized cell types, capable of self-renewal, differentiate into other cell types and to proliferate in culture. The stem cells are derived either from the embryo or fetus (embryonic stem cells), or adult tissue (adult stem cells). They can also be obtained by nuclear transfer.
Totipotent stem cells: undifferentiated cells that can theoretically give rise to a whole organism; cells from the first divisions of the fertilized egg (up to 4th day).

The umbilical cord connects the baby to the placenta in the mother's womb. It helps carry oxygen to the baby through the cord blood. Initially, it was thought that the cord contained only blood vessels. However, scientists have shown that the tissue between the skin and the blood vessels - known as "Wharton's Jelly" - is one of the human body's richest sources of mesenchymal stem cells.

Cells that are be responsible for only one type of differentiated cell.