Stem cells are primitive, non-specialised cells characterized by their limitless potential to proliferate and their unique ability to differentiate into specialised cells whereby tissues are formed. Their properties have been used to renew or replace damaged cells. Stem cells can be retrieved, among others, from the umbilical cord blood.
Bone marrow was the primary source of stem cells (bone marrow transplantation involves transplanting stem cells derived from the bone marrow), whereas nowadays, the umbilical cord blood stem cells are more frequently applied for therapeutic uses. Other sources include the peripheral blood drawn from donors who underwent pharmacological mobilisation.
Each living organism, through the course of its life, systematically produces new cells which subsequently mature and differentiate into more specialised cells. Eventually, these cells perish after a specific period of time, as inscribed in their genetic code. Specific stem cells are cells which directly replace dead cells with new ones. All stem cells, even if transiently present in the body, can be subdivided into the following four categories:
Stem cell types
- Totipotent cells – are the only cells found in a living organism which have the ability to divide and produce all the differentiated cells of an organism, in other words they are capable of developing into a complete organism. Examples of totipotent cells include zygotes - produced in the event of fertilisation and blastomeres - formed in subsequent developmental stages.
- Pluripotent cells – are cells formed in the course of subsequent developmental stages of the fertilised cell – zygote. These cells have the potential to differentiate into any of the three types of components occurring in a human being during antenatal development – germ layers: mesoderm, ectoderm and endoderm. These cells can give rise to any type of cell – the only restriction being their inability to transform back into totipotent cells – occurring in the initial stage of human development.
- Multipotent cells – arise from a single germ layer. These cells have the potential to transform into several types of distinct cells, however they are limited by the germ layer they originate from. For instance, within the mesoderm, these cells can give rise to bone marrow, blood or muscle cells. These types of cells include haematopoietic stem cells, for which human umbilical cord blood is a rich source.
- Unipotent cells – occur in the final stage of development and have shown to be capable of differentiating into only one specific adult cell type (e.g. epithelium cells). These cells retain the capacity to divide, as opposed to the adult cells.