Types of Stem Cells

Stem cells are the foundation for every organ and tissue in your body. There are many different types of stem cells that come from different places in the body or are formed at different times in our lives.

On the basis of origin, stem cells are divided into different categories these include;  

Embryonic stem cells (ESCs): It forms all the tissue types of the developing body

Foetal stem cells (ASCs): It forms almost all types of tissue except embryonic tissue

Adult stem cells (ASCs: It forms only a limited number of tissue types

Emberyonic Stem Cells (ESCs)

Embryonic stem cells are pluripotent, meaning they can give rise to every cell type in the fully formed body, but not the placenta & umbilical cord. these cells are incredibly valuable because they provide a renewable resource for studying normal development and disease, and for testing drugs and other therapies. Human embryonic stem cells have been derived primarily from blastocysts created by in vitro fertilization (IVF) for assisted reproduction that were no longer needed which they donated for research purposes with informed consent of the donors and ESCs are not derived from eggs fertilized in a woman’s body.   In view of the ethical and social dilemmas involved, collecting, culturing and experimenting on embryonic and foetus SCs legally restricted in many countries.  

Adult Stem Cells (Somatic Stem Cells) (ASCs)

Our body form from large number of cells, like liver cells, muscles cells, bone cells, skin cells, intestine cells and so on . Most of these cells have to be replaced every once in a while. The cells that replacing the old cells and repairing the damage tissue are the adult stem cells, also called somatic stem cells. Adult stem cells are undifferentiated (they haven’t specialized function to do but can be differentiate to many type of tissue but not all types of tissue. The term “Adult Stem Cell” is a little misleading, since these cells are actually found in infants and children as well as in adults and it’s also called Somatic Stem Cells, possess the same basic characteristics of all stem cells.

Unlike embryonic stem cells, the use of adult stem cells in research and therapy is not controversial because the production of adult stem cells does not require the destruction of an embryo. Embryonic Stem Cells, which can become any cell in the body (called pluripotent), Adult Stem Cells, can form into only a limited number of tissue types (called multipotent).

ASCs exist in the tissue for decades. It may remain not active (non-dividing) for long period of time until they are activated either; 

  • To replace dying tissue to maintain the tissue as the continuous growth for new skin, intestine and the bone marrow or
  • To regenerate damaged or lost tissue either by diseases or injury.  That mean, the ASCs main function is to maintain & repair the specific tissue where they reside. 

Researchers on adult stem cells has found it in many more tissues than they once thought possible. Scientists now have evidence that stem cell exist in the brain and the heart, two location where adult stem cells were never expected to reside. If the differentiation of adult stem cells can be controlled in the laboratory, these cells may become the basis of transplantation-based therapies.

 The use of adult stem cells and tissues derived from the patient’s own adult stem cells would mean that the cells are less likely to be rejected by the immune system. This represents a significant advantage, as immune rejection can be circumvented only by continuous administration of immunosuppressive drugs, and the drugs themselves may cause deleterious side effects. 

Where are Adult Stem Cells (ASCs) Found?

Adult stem cells have been identified in many organs and tissues, including brain, bone marrow, blood vessels, skeletal muscles, skin, teeth, heart, gut, liver, ovarian epithelium and testis. They are thought to be resides in a specific area of each tissue (called a “Stem Cell Niche”). In many tissues, current evidence suggests that some types of stem cells are pericytes, cells that compose the outmost layer of small blood vessels. Typically, there is a very small number of stem cells in each tissue and, once removed from the body, their capacity to divide is limited, making generation of large quantities of stem cells difficult till they discover the adipose tissue (fat) a rich source of it. For that, adult stem cells become the simplest type to obtain, and have the greatest importance for medical purposes

What are the Advantages of ASCs?

The following advantages are associated with the use of adult stem cells in regenerative medicine:

  1. Cells are derived entirely from mature tissues and therefore it is non-controversial, and no ethical codes are breached
  2. Even though adult Mesenchymal Stem Cells are somewhat differentiated, they are still multipotential and can form a number of new tissues
  3. Adult Mesenchymal Stem Cells are less teratogenic (in other words less prone to tumor formation)
  4. These cells are immunosuppressant in nature meaning they wouldn’t elicit a strong immune response after treatment and therefore rejection is unlikely
  5. Once a pure mesenchymal stem cell population has been obtained both inter-individual and inter-species transplants are possible
  6. There are many different sources from which these cells can be obtained

Types of Adult Stem Cells ASCs

  • Hemopoietic Stem Cells (HSCs):It found in the bone marrow and umbilical cord blood and give rise to all the blood cell types plus all the tissues types of the developing body.
  • Mesenchymal Stem Cells (MSCs): It form only a limited number of tissue types and it have been isolated from placenta, adipose tissue, lung, bone marrow and blood, Wharton’s jelly from the umbilical cord and teeth. 
  • Mammary Stem Cells (MSCs):provide the source of cells for growth of the mammary gland during puberty and gestation. It has been isolated from human and mouse tissue as well as from cell lined derived from the mammary glands
  • Intestinal Stem Cells:Can divide continuously throughout life and use a complex genetic program to produce the cells lining the surface of the small and large intestine. 
  • Endothelial Stem Cells: are found in the bone marrow. they are rare.
  • Neural Stem Cells:The presence of stem cells in the mature primate brain was first reported in 1967.Neural stem cells are commonly cultured in vitro as so called neurosphere, it share many properties with haematopoietic stem cells (HSCs). Remarkably, when injected into the blood, neurosphere-derived cells differentiate into various cell types of the immune system
  • Olfactory Stem Cells: Olfactory adult stem cells have been successfully harvested from the human olfactory mucosa cells, which are found in the lining of the nose and are involved in the sense of smell. Olfactory stem cells hold the potential for therapeutic applications and, in contrast to neural stem cells, can be harvested with ease without harm to the patient.  This means they can be easily obtained from all individuals, including older patients who might be most in need of stem cell therapies.
  • Testicular Stem CellsMultipotent adult stem cells have been derived from the germ cells found in human testicles.

Adult Mesenchymal Stem Cells (MSCs)

Mesenchymal stem cells (MSCs) are adult stem cells which can be isolated from human & animal sources. Human MSCs (hMSCs) are the non-haematopoietic, multipotent stem cells with the capacity to differentiate into mesodermal lineage such as osteocytes, adipocytes and chondrocytes as well ectodermal (neurocytes) and endodermal lineages (hepatocytes). Since the first description of hMSCs derived from bone marrow, they have been isolated from almost all tissues including perivascular area.

Human MSCs are a favorite choice of stem cells due to its self-renewal ability, multi-potency, easily accessible and culturally expandable in vitro with exceptional genomic stability and few ethical issues, marking its importance in cell therapy, regenerative medicine and tissue replacement

Sources: 

The first time reported in the bone marrow and till now have been isolated from various tissues, including; Adipose tissue, amniotic fluid & membrane , endometrium, menstrual blood, peripheral blood, dental tissues, salivary glands, in skin & foreskin, synovial fluid, umbilical cord & Wharton’s jelly which harbours potential MSCs.

Characteristic of Mesenchymal Stem Cells (MSCs)

Today, Mesenchymal Stem Cells (MSCs) are one of the most famous stem cell type used in medicine. They have been shown to be effective for a wide range of diseases with a minimal risk profile. At the same time several hundred clinical studies are ongoing to investigate their regenerative abilities in greater detail. From a biological point-of-view, they are progenitor cells of connective tissues. This means that they are important for building and maintaining the healthy status of connective tissues throughout the whole body & are known as Stromal Stem Cells, they possess the ability to differentiate into a spectrum of other cell types, including chondrocytes (cartilage cells), osteoblasts (bone cells), adipocytes (fat cells), etc.

This property classifies them as “multipotent stem cells” (being able to transform into many cell types). 

There are several reasons of why they are the leading stem cell type in medical applications and clinical trials on humans:

  1. They are relatively easy to harvest & can be isolated from: 

             Fat tissue, known as ADMSCs (Adipose-Derived MSCs)

             Bone Marrow, known as BmMSCs (Bone marrow MSCs)

             Umbilical Cord, known as UcMSC (Umbilical cord MSCs)

  1. MSCs are relatively stable to culture and expand in the laboratory.
  2. They can go through relatively many division cycles without losing their expression profile, health and division potential
  3. They possess little to no potential to grow into cancer cells

Bone marrow-Mesenchymal Stem Cells
(Bm-MSCs)

Bone Marrow Concentrate (BMC) is one of the most commonly applied source of stem cells. Despite the fact that the actual number of stem cells in BMC is biologically limited, several other (regenerative) factors in BMC have been shown to deliver promising results in the treatment of numerous diseases.

Adipose-Derived Mesenchymal Stem Cells
(ADSCs)

Fat (adipose) derived Mesenchymal Stem Cells (ADSCs | ADMSCs) are a commonly used source of stem cells. ADSCs share many of the characteristics of bone marrow-derived mesenchymal stem cells (BMSC), they can be obtained more easily with a 100–1000 times greater cellular yield, and in practice, many patients are eager for the harvest of unwanted fat. A number of preclinical and clinical trials have established the safety and efficacy of ADSCs and range from breast reconstruction and correction of defects to neural regeneration in spinal cord injuries. ADSCs have the ability to produce a range of tissue types and are an ideal cell source for the clinical application of tissue engineering.

Induced pluripotent stem cells (iPSCs)

Scientists have recently discovered how to turn adult stem cells into pluripotent stem cells. These new types of cells are called induced pluripotent stem cells (iPSCs). They can differentiate into all types of specialized cells in the body. This means they can potentially produce new cells for any organ or tissue.

To create iPSCs, scientists genetically reprogram the adult stem cells so they behave like embryonic stem cells.

The breakthrough has created a way to “de-differentiate” the stem cells. This may make them more useful in understanding how diseases develop. Scientists are hoping that the cells can be made from someone’s own skin to treat a disease. This will help prevent the immune system from rejecting an organ transplant. Research is underway to find ways to produce iPSCs safely.

Read More-References:

  1. Bourin P, Bunnell BA, Casteilla L et al. 2013; Stromal cells from the adipose tissue-derived stromal vascular fraction and culture expanded adipose tissue-derived stromal/stem cells: a joint statement of the International Federation for Adipose Therapeutics and Science (IFATS) and the International Society for Cellular Therapy (ISCT). Cytotherapy 15(6): 641–648. Click Here for PDF
  2. Castro-Manrreza ME, Montesinos JJ. Immunoregulation by Mesenchymal Stem Cells: Biological Aspects and Clinical Applications. Journal of Immunology Research. 2015;2015:394917. doi:10.1155/2015/394917. Click here for PDF
  3. Diederichs S, Tuan RS. Functional Comparison of Human-Induced Pluripotent Stem Cell-Derived Mesenchymal Cells and Bone Marrow-Derived Mesenchymal Stromal Cells from the Same Donor. Stem Cells and Development. 2014;23(14):1594-1610. Click here for PDF
  4. Giai Via A, Frizziero A, Oliva F. Biological properties of mesenchymal Stem Cells from different sources. Muscles, Ligaments and Tendons Journal. 2012;2(3):154-162. Click here for PDF
  5. J.A. Dahl, S. Duggal, N. Coulston, et al., (2008) Genetic and epigenetic instability of human bone marrow mesenchymal stem cells expanded in autologous serum or fetal bovine serum, Int. J. Dev. Biol. 52 1033e1042.  Click Here for PDF
  6. Kingham E, Oreffo ROC. Embryonic and Induced Pluripotent Stem Cells: Understanding, Creating, and Exploiting the Nano-Niche for Regenerative Medicine. ACS Nano. 2013;7(3):1867-1881. doi:10.1021/nn3037094. Click here for PDF
  7. Lansdorp PM. 1995; Telomere length and proliferation potential of hematopoietic stem cells. J Cell Sci 108 (Pt 1): 1–6. Click Here for PDF
  8. Mizuno H, Tobita M, Uysal AC. 2012; Concise review: adipose-derived stem cells as a novel tool for future regenerative medicine. Stem Cells 30(5): 804–810. Click Here for PDF
  9. Strong AL, Neumeister MW, Levi B. Stem cells and tissue engineering: regeneration of the skin and its contents. Clinics in plastic surgery. 2017;44(3):635-650. doi:10.1016/j.cps.2017.02.020.
  10. Vogel H, Niewisch H, Matioli G. 1968; The self-renewal probability of hemopoietic stem cells. J Cell Physiol 72(3): 221–228. Click Here for PDF
  11. Yang B, Qiu Y, Zhou N, et al. Application of Stem Cells in Oral Disease Therapy: Progresses and Perspectives. Frontiers in Physiology. 2017;8:197. doi:10.3389/fphys.2017.00197. Click here for PDF
  12. Yoshimura K, Shigeura T, Matsumoto D et al. 2006; Characterization of freshly isolated and cultured cells derived from the fatty and fluid portions of liposuction aspirates. J Cell Physiol 208(1): 64–76. Click Here for PDF
  13. Zuk PA, Zhu M, Mizuno H et al. 2001; Multilineage cells from human adipose tissue: implications for cell-based therapies. Tissue Eng 7(2): 211–228. Click Here for PDF
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