What Is a Stem Cell?

Your body is made up of many different cells. All cells are constructed generally the same, with a nucleus, cytoplasm, and an outer membrane. The parts of a stem cell are the same as most other cells.

Most cells also have a specific function, like muscle cells, red blood cells, bone cells, or brain cells. Stem cells, on the other hand, are the building blocks of new tissue and as such, these cells are unique. Stem cells have two important characteristics, one of which can only be found in stem cells. These characteristics are:

  1. as unspecialized cells, they can renew themselves, called cell division, meaning they make copies of themselves over and over again;

  2. under the right conditions, as they divide, they can transform into different, specialized cell types, a process known as differentiation.

These stem cell functions are remarkable and no other cell type in the body has the capability to both divide and differentiate, which makes stem cells fundamentally important -- both to the body and to science. With each new stem cell, there is the potential for that stem cell to either remain a stem cell or to become another type of cell with a specialized function. By becoming a new type of cell, it replenishes cells and helps repair and replace damaged tissue. For example, a stem cell may change into a heart muscle cell to help the heart pump blood or it may change into a red blood cell to help the body transport oxygen.

Below, you will learn about the types of stem cells so you have a better understanding of what they are. Then a broader discussion will be given on stem cell therapy and stem cells used in clinical treatment.


Main Types of Stem Cell

There are many types of stem cells, but the “type” is often dependent on how stem cells are categorized. Stem cells are often categorized by:

  • Functionality

  • Potency

  • Source

Functionality: What Stem Cells Do

Stem cells can be categorized according to the types of cells they can become and the functions those cells perform. Examples of functionality and stem cell categorization include the following:

  • Hematopoietic stem cells, which refer to stem cells that can differentiate into different types of blood cells;

  • Mesenchymal stem cells, which refer to stem cells that can differentiate into cells to repair or replace damaged bone, cartilage, and/or muscle;

  • Neural stem cells; which refer to stem cells that can differentiate into neurons and glial cells (non-neuronal cells that insulate neurons and enhance the speed at which neurons send signals);

  • Epithelial stem cells, which refer to stem cells that renew the sheets of tissue that line organs and spaces within the body; and

  • Skin stem cells, which refer to stem cells that can differentiate into various cell types typically found in skin.

Potency: How Many Different Cell Types Can a Stem Cell Become

Potency is a better way to categorize stem cells as opposed to functionality. Potency is a term used to indicate the number of types of cells one stem cell can divide or differentiate into -- the further along the process of differentiation the less capability the stem cell has to differentiate into any type of other cells. There are three basic potencies:

  1. Totipotent, which refers to stem cells that have not started the process of differentiating and thus have the capability to become any cell found within the human body as well as a completely functional human;

  2. Pluripotent, which refers to stem cells that have just barely begun the process of differentiating and as such are still capable of becoming one of 200 different cells found within the human body; and

  3. Multipotent, which refers to stem cells that have started differentiating, and have predictable remaining differentiation potential and behaviors.

Source: Where Stem Cells Come From

Stem cells are most commonly categorized according to their source, meaning where (or how) they originate. There are four basic sources of stem cells:

  • Embryonic Stem Cells (ESCs)

  • Perinatal Stem Cells

  • Adult Stem Cells (ASCs)

  • Induced Pluripotent Cells (iPSCs)

These sources identify where stem cells are found in the body or, alternatively, how they are created.


Embryonic Stem Cells (ESCs)

ESCs in their native form can become a group of cells known as an embryo. They are created when a fertilized egg divides -- which is the initial stage of the development of life. ESCs supply new cells so the embryo can grow into a baby. Within three to five days of the embryo formation, the ESCs divide over and over again into a group of cells called a blastocyst. They divide into 150 to 200 unspecialized cells. After gastrulation, however, the cells can develop into pluripotent cells.

ESCs are taken from a discarded in vitro fertilization procedure (i.e., in a lab) and not from an embryo in a human body. Their differentiation patterns are difficult to predict and control, and they are not legally available for clinical use at this time due to a number of safety and efficacy concerns.

Perinatal Stem Cells

Perinatal stem cells are stem cells produced during birth, specifically immediately before and after birth. They can be found in (and extracted from):

  • The amniotic fluid, which contains a limited amount of stem cells and growth factors;

  • The umbilical cord, where multipotent stem cells are present and are genetically identical to the baby; and

  • The placenta, where there are 10 times as many multipotent stem cells that can be harvested.

Induced Pluripotent Stem Cells (iPSCSs)

Induced pluripotent stem cells are lab-created stem cells. Embryonic genes are introduced to an adult cell, and this introduction causes the adult cell to revert to a state comparable to a pluripotent stem cell. These stem cells are still in the research stage and are not yet being used in clinical therapies.

Adult Stem Cells (ASCs)

ASCs do not refer to stem cells found only in adult humans -- infants and children have ASCs, too. The “adult” refers to stem cells found in developed tissue of the body. These stem cells may not renew for long stretches of time, at least not until they are activated by a need to renew for the purposes of repairing and maintaining tissue damaged by injuries, disease, or another reason.

The cells have a specific function throughout their lives: repairing and maintaining tissue and organs in the body. They are multipotent, and as such, divide into specific types of cells based on location in the body.

Here are a few of the places you can find adult stem cells:

  • Brain

  • Bone marrow

  • Peripheral blood

  • Blood vessels

  • Skeletal muscle

    Skin

  • Teeth

  • Heart

  • Gut

  • Liver

  • Ovarian epithelium

  • Testis

ASCs belong to a certain family of cells based on their location. Because they belong to a certain family, they differentiate into cells related to and of that specific family of cells.

The ASCs are found in specific areas of each of the above-listed (and other) tissues, and this specific area is known as “stem cell niche.” ASCs are also believed to only differentiate into cells related to and of that specific area. For instance, stem cells of the pancreas differentiate into cells specific to the pancreas, and hematopoietic stem cells differentiate only into blood cells. They cannot differentiate into any other type of cell.


Stem Cell Therapy: What Can Stem Cells Actually Do?

Stem cells are necessary for human bodies to develop, repair, and maintain themselves. Without stem cells, our ability to sustain optimal health would be severely diminished. Through research, we have been able to better understand how our bodies operate, especially under unique conditions, like when disease attacks our systems. We now understand the importance of stem cells to our health and longevity and are getting a better understanding of how stem cells actually work.

Stem cell therapy can actually improve and/or save lives, and it can do so through:

  • Regenerative medicine, where healthy unspecialized or specialized cells are created through stem cell division and/or differentiation and then used to regenerate, repair, and replace diseased or damaged cells;

  • Expanded stem cell injection, which involves replicating stem cells in a laboratory and then injecting the cells into the patient;

  • Stem cell transplant, which involves using stem cells to generate new organs that can then be transplanted into patients requiring new organs -- donated organs used today are limited and are often rejected by the receiving patient’s immune system; and

  • Stem cell treatment, which involves using adult stem cells to treat certain disorders (e.g., neuromuscular or degenerative) and medical conditions (e.g., using skin stem cells to generate new skin for patients who have suffered severe burns).

As stem cell research continues and new discoveries are made, stem cell therapy will continue to advance and improve lives.


What Stem Cells Are Used in Clinical Treatment?

Stem cells are increasingly proving their beneficial impact on patients in clinical trials and studies. Stem cell applications from reputable providers include:

  1. Intra-articular

  2. Intramuscular

  3. Intradiscal

  4. Bone grafting

  5. Cartilage grafting

  6. External wound healing

  7. Subchondral injection (into the bone)

  8. Tendon and ligament - any connective tissue graft or defect.

There are three types of stem cells most widely used in stem cell clinical treatment today:

  1. Mesenchymal stem cells;

  2. Hematopoietic stem cells; and

  3. Blood cord stem cells.

Mesenchymal stem cells are derived from bone marrow or fat tissue and are currently used for:

  • Orthopedic repair

  • Pain management

  • Arthritis

  • Asthma.

Hematopoietic stem cells are blood stem cells mostly applied to cancer patients who have undergone radiation and chemotherapy. After these harsh treatments kill the patient’s cancerous cells, the hematopoietic stem cell therapy restores the patient’s immune system. The hematopoietic stem cells do not address the cancer itself.

Cord blood stem cells are derived from the umbilical cord and are mostly used to treat children with blood cancers (e.g., leukemia) and genetic blood disease (e.g., Fanconi anemia). Treatment of adults typically requires cord blood stem cells from at least two umbilical cords as well as special permission from the FDA. Even then, such treatments haven’t proven particularly effective for adults.

Stem cell research and therapy offer a wealth of innovative and natural ways to treat patients with different types of disorders, ailments, and conditions. Continued research will help the scientific community drive down this path of discovery and treatment.