What Are Stem Cells? A Complete Guide

Stem Cell Fundamentals

What is a stem cell?
A real stem cell is a cell in the body that can divide repeatedly into two cells, with one of the two new cells always being almost identical to the cell that divided (i.e., the stem cell), while the other new cell takes on new properties that are characteristic of the tissue in which the cells reside. Stem cells preserve the DNA blueprint of tissues and organs, produce the cellular building materials for tissues and organs, but never become building materials themselves.

What are the four different types of stem cells?
There is only one type of natural stem cells.  They are tissue-specific stem cells. Every organ or tissue has one of more of them that are responsible for renewing the various parts of an organ or tissue.  For example, the eye has conjunctival stem cells, sclera stem cells, corneal stem cells, lens stem cells, and retinal stem cells. Tissue stem cells may also be called adult stem cells or somatic stem cells.  They may also be classified more specifically based on their developmental stage, as in fetal stem cells, perinatal stem cells, and postnatal stem cells.

There are other precursor cells misnamed as “stem cells”.  These include embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and primordial germ cells (PGCs).  None of these occur naturally in the body. Although each can be used to produce more mature cell types, they cannot do this without also changing their own cellular state.  So, they are not real stem cells.

What is the function of stem cells in the body?
In the body, the primary function of tissue stem cells is to continuously replace mature tissue cells, which perform the special functions of their organs and tissues of residence, but also age and die on the time scale of weeks to months.

How do doctors use stem cells?
In approved therapies, doctors use stem cells to restore tissues that have been destroyed or injured by disease or medical treatments.  For example, high dose chemotherapy or radiation therapy for cancer treatments destroys bone marrow stem cells required for blood cell production.  After such treatments for cancer, doctors transplant cancer patients with donor bone marrow stem cells to restore their loss ability to make blood cells that are required for life.

What can stem cells treat?
In theory, stem cells can treat any disease, disorder, or injury for which the primary need is to restore and maintain a normal tissue or part of an organ.  In practice, today, this includes blood cell making tissues like bone marrow and cornea. A type of stem cells found associated with many different types of tissues, called mesenchymal stem cells, are being evaluated for the possible ability to enhance healing and repair of tissues in general.

How do we get stem cells?
From a tissue specimen that is either self-derived or given by a donor.  Common specimen sources are bone marrow, umbilical cord blood, umbilical cord, fat tissue, placenta, and amniotic membrane and fluid.

What are stem cell injections?
When stem cells are re-introduced into the body of a patient, a hypodermic needle and syringe are usually used.  The stem cell suspension is place into a sterile syringe and attached to a sterile needle, which may be used to inject a joint, vein, the spine, or even the heart in some approved experimental treatments.

What are some examples of stem cells?
Liver stem cells, blood stem cells, mesenchymal stem cells, corneal stem cells, hair follicle stem cells, cord blood stem cells, pancreatic stem cells.

What are the side effects of stem cell therapy?
No side effects have been been described for stem cells themselves.  However, sometimes other cell types present in stem cell treatment preparations can cause severe side effects.  One well known example is graft versus host disease (GVHD) caused by immune cells in blood stem cell transplants attacking the tissue cells of the recipient patient.

What are the disadvantages of stem cells?
When a stem cell transplant is needed, no other treatment can substitute for it.  Therefore, there are few if any disadvantages from a successful stem cell transplant therapy.

How do you freeze stem cells?
Stem cells can be frozen with standard cell freezing techniques.  These methods freeze cells slowly after supplementation of their medium with a cryoprotectant agent to prevent ice crystal formation, which kills cells by puncturing them.  Once achieving temperatures <130^oC, the cells can be maintained viable under this condition for many years.

How long does it take for Stem Cell Therapy to work?
It takes a few weeks to begin to notice measurable effects, and a few months to be sure the treatment is stable.

How does Stem Cells work for joint pain?
There have been no well-designed clinical studies to define the effect of stem cells on joint pain.  Complicating the evaluation is the use of different sources of stem cells in different joints without a consistent administration procedure.  Even more challenging, the number of stem cells used in treatments is always unknown.

How much does it cost to buy stem cells?
First, it is important to recognize that “stem cells” are never homogenous cell populations.  The real stem cells are always a small fraction of the cells in the sample. For research purposes, vials containing 0.5 million total cells and 50-5000 stem cells, depending on the source, cost $700-$1500.  A similar vial for patient use or medical manufacturing applications could cost several thousand dollars.

What are the types of stem cell technology?
Stem cell transplantation medicine
Stem cell expansion
Stem cell counting
Stem cell regenerative medicine
Stem cell tissue engineering
Stem cell assays for drug discovery and drug development
Stem cell assays for toxicology

What is stem cell technology used for?
Number 1 is stem cell transplantation medicine: Improve existing therapies and develop new ones for treating diseases, disorders, and injuries with transplanted stem cells.

Stem cell expansion: Tissue stem cells are difficult to mass produce.  Discover methods to produce more therapeutic stem cells  from limited donor specimens. E.g., cord blood.

Stem cell counting: This newest stem cell technology was just developed since 2016.  It can be used to determine stem cell treatment dose and improve stem cell production methods.

Stem cell regenerative medicine: Take advantage of other stem cell properties like secretion of factors that accelerate healing.

Stem cell tissue engineering: Deploy stem cells in their role as tissue cell production engines to engineer artificial organs and tissues.

Stem cell assays for drug discovery and drug development: The new stem cell counting technology provides more effective assays for drug research.

Stem cell assays for toxicology: The new stem cell counting technology makes it possible to quickly evaluate environmental toxicants for bad, disease-causing effects on tissue stem cells.

What is live cell therapy?
Therapies in which living cells are injected into the body.  Bone marrow transplant is an example. The new CAR-T therapies are a newer case.

What are cell culture techniques?
These are methods developed for keeping animal cells alive and dividing in plastic dishes or flasks for either purposes of scientific research or production for use in live cell therapies.

What is the definition of cell culture?
A biologically engineered physical format that provides isolated animal cells with the nutrients and physical conditions that support their continued viability, proliferation, and development.

What are continuous cell lines?
Cell lines are isolated cell cultures that will proliferate indefinitely as long as they are provided with the required nutrients and physical conditions (e.g., temperature).  In contrast, primary cell strains are cell cultures that will eventually stop proliferation altogether, even though the required nutrients and physical conditions are maintained.

What are human cell lines?
Continuous cell lines developed from human tissue cells.

What are transformed cell lines?
Continuous cell lines that have properties of cancer cells.  These properties may be present because the lines were derived from tumor cells or because of gene mutations that occurred during culture of normal cells that resulted in cancer cell properties.

Why do we use cell lines?
Cell lines are excellent experimental models for studying cellular processes that would either be challenging or impossible to investigate in the intact body.  They can also be used to manufacture cellular factors like immune antibodies that are powerful research tools as well as therapeutic biopharmaceuticals.

What are stem cell reagents?
In general, reagents are compounds and factors used to perform experiments or other studies.  They could be specific chemicals or manufactured products. In the case of stem cells, reagents for experiments with them include culture medium, growth factors, and cell transfer agents; reagents for their analysis include viability agents like trypan blue and separation antibodies; and reagents for their treatments include dilution buffers and anesthetics.

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