Stem Cells

What are stem cells?
The term "stem cell" was proposed for scientific use by the Russian scientist Alexander Maximov (1874–1928) at congress of hematologic society in Berlin in 1906.


Alexander Maximow was an outstanding scientist who developed and introduced the unitarian theory of hematopoiesis (i.e., "common stem cell for all blood elements"), and pioneered other concepts about stem cells and their microecological niches within bone marrow stroma. http://ctt-journal.com/1-3-maximov-1909-in-german-pdf.html

1. A stem cell “self-renews” – that is, when a stem cell is called into action, it undergoes cell division. One daughter cell remains a stem cell, while the other becomes more committed to forming a particular cell type (a “committed progenitor”) by a process called “asymmetric division”.
2. A stem cell forms multiple cell types (that is, it is “multipotent”).
3. A single stem cell completely re-forms a particular tissue when it is transplanted within the body.

Embryonic stem cells (ESCs) refer to the cells of the inner cell mass of the blastocyst during embryonic development.

Stem cells derived from the inner cell mass of blastocyst stage human embryos have been shown to differentiate into several different cell types and have the potential to one day replace or regenerate tissues. (Source: Krebsbach PH, Robey PG. Dental and skeletal stem cells: potential cellular therapeutics for craniofacial regeneration. J Dent Educ. 2002 Jun; 66(6):766-73).

Amniotic fluid-derived stem cells (AFSCs) can be isolated from aspirates of amniocentesis during genetic screening.

AFSCs were successfully isolated from second trimester amniotic fluid and analyzed for chromosomal stability to validate their safety for potential utilization as a cell therapy product. An increasing number of studies have demonstrated that AFSCs have the capacity for remarkable proliferation and differentiation into multiple lineages, such as chondrocytes, adipocytes, osteoblasts, myocytes, endothelial cells, neuron-like cells and live cells. The potential therapeutic value of AFSCs remains to be discovered.

Umbilical cord stem cells (UCSCs) derive from the blood of the umbilical cord.

There is growing interest in their capacity for self-replication and multi-lineage differentiation. UCSCs have been differentiated into several cell types, such as cells of the liver, skeletal muscle, neural tissue and immune cells. Their high capacity for multi-lineage differentiation is likely attributed to the possibility that UCSCs are chronologically closer derivatives of embryonic stem cells than adult stem cells. UCSCs are neither embryonic stem cells, nor are they viewed as adult stem cells.

Bone marrow-derived mesenchymal stem cells (BMMSCs).

The bone marrow derived (BMD) cells are a mixed population which consist of fibroblasts, osteoblast, adipocyte progenitors and up to 0.01% stem cells. BMMSCs are a subpopulation of the total BMD cells, which can be isolated from whole bone marrow aspirates. The first successful isolation of BMMSCs, then called colony-forming fibroblast-like cells, was described in 1970. BMMSCs can self-replicate and have been differentiated, under experimental conditions, into osteoblasts, chondrocytes, myoblasts, adipocytes and other cell types, such as neuron-like cells, pancreatic islet beta cells, etc. . To date, the majority of work in this area has focused on the ability of BMMSCs s to differentiate into bone. BMMSCs can be an alternative resource to regenerate adipose tissue for cosmetic purpose and for tissue repair in craniofacial reconstructive surgery.

Tooth-derived stem cells are isolated from the dental pulp, periodontal ligament - including the apical region - and other tooth structures.

Since 1980s, several studies have demonstrated the presence of progenitor cells in dental pulp. These cells become active upon injury and began to stimulate further proliferation and odontoblast differentiation to provide for dentin repair. Previous work has shown that dental pulp contains proliferating cells that are analogous to bone cells, because they express osteogenic markers and respond to many growth factors for osteo/odontogenic differentiation.Recent findings demonstrated the isolation of mesenchymal progenitors from the pulp of human deciduous incisors. These cells were named SHED (Stem cells from Human Exfoliated Deciduous teeth) and exhibited a high plasticity since they could differentiate into neurons, adipocytes, osteoblasts and odontoblasts.

Adipose-derived stem cells (ADSCs) are typically isolated from lipectomy or liposuction aspirates.

Adipose tissue can be obtained by less invasive methods and in larger quantities than bone marrow cells, making the use of ADSCs as a source of stem cells very appealing. ADSCs have been differentiated into adipocytes, chondrocytes, myocytes, neuronal and osteoblast lineages. ADSCs are also capable of expressing multiple growth factors, including vascular endothelial growth factor and hepatocyte growth factor. ADSCs can self-replicate for many passages without losing the ability to further differentiate. ADSCs were used as a potential source for cellbased therapies for healing calvarial defects.