Classification based on level of differentiation
Totipotent stem cells
Pluripotent stem cells
Multipotent stem cells
Unipotent stem cells
Totipotent stem cells
The fertilized egg is said to be totipotent.
It has the potential to generate all the cells and tissues that make up an embryo.
It supports embryonic development in uterus.
Pluripotent stem cells
These cells develop about four days after fertilization
These cells cannot re-create a complete organism but differentiate into any cell type, except for totipotent stem cells and the cells of the placenta.
Multipotent stem cells
Can only differentiate to some types of cells.
For example, hematopoietic stem cells, which are found primarily in the bone marrow, give rise to all of the cells found in the blood, including red blood cells, white blood cells, and platelets.
Unipotent stem cells
Can differentiate along only one lineage.
What is the difference between adult and embryonic stem cells?
The function of embryonic stem cells (obtained from embryo and fetus) is to produce all the tissues of the body during development.
The function of adult stem cells (obtained from umbilical cords,
placentas, amniotic fluid, bone marrow, liver, epidermis, retina,
skeletal muscle, intestine, brain, dental pulp …..) is to maintain,
replenish and repair the tissues from which it is originated.
Comparison of embryonic and adult stem cells
Advantages of Embryonic Stem Cell
Flexible - appear to have the potential to make any cell.
Immortal - one embryonic stem cell line can potentially provide an endless supply of cells with defined characteristics.
Availability - embryos from in vitro fertilization clinics.
Disadvantages of Embryonic Stem Cell
Difficult to differentiate uniformly and homogeneously into a target tissue.
Immunogenic - embryonic stem cells from a random embryo donor are likely to be rejected after transplantation
Tumorigenic - capable of forming tumors or promoting tumor formation.
Destruction of developing human life.
Advantages of Adult Stem Cells
Adult stem cells from bone marrow and umbilical cords appear to be as flexible as the embryonic type
Somewhat specialized - inducement may be simpler.
Not immunogenic - recipients who receive the products of their own stem cells will not experience immune rejection.
Relative ease of procurement - some adult stem cells are easy to harvest (skin, muscle, marrow, fat)
Non-tumorigenic-tend not to form tumors.
No harm done to the donor.
Disadvantages of Adult stem cells
Limited quantity - can sometimes be difficult to obtain in large numbers.
Finite - may not live as long as embryonic stem cells in culture.
Less flexible - may be more difficult to reprogram to form other tissue types
