Stem Cell Nomenclature

This section is not meant to provide an exhaustive explanation of all stem cell terminology. Rather, it is meant to offer clarification to a handful of important terms over which confusion commonly exists throughout the lay public.


  • Adult Stem Cells — These are the stem cells found in tissue after birth has occurred.

Fetal stem cells and embryonic stem cells are not adult stem cells.

Some types of adult stem cells are floating around in your body right now. Adult stem cells are masters at healing and regenerating all the tissue types of the body, whether as a result of injury or as part of ongoing natural, daily, physiological processes.

Adult stem cells have been in use by the conventional medical establishment for over 60 years, ever since the first successful bone marrow transplant was performed in 1956.1

Although the nomenclature is not precise, stem cells that are derived from umbilical cord blood are actually classified as “adult” stem cells (not as embryonic stem cells, nor as fetal stem cells).

Adult stem cells are harvested through entirely safe, ethical, noncontroversial means. Nobody is harmed in any way by the harvesting of adult stem cells.

Adult stem cells pose no problems, neither scientifically, nor medically, nor politically, nor ethically.

Adult stem cells are entirely safe, efficacious, and ethical.

Both the Baptist Church2 and the Roman Catholic Church3 fully and officially endorse research and treatment with adult stem cells. In fact, the Catholic Church has been funding adult stem cell research for quite some time.

However, both the Baptist and Catholic Churches are strongly and officially against any type of research or medical treatment involving embryonic or fetal stem cells.2, 3 (See Embryonic Stem Cells, and Fetal Stem Cells).

Another important, and desirable, characteristic of adult stem cells is that they are not pluripotent. (See Pluripotency).

  • Blastocyst — The early developmental structure that exists in mammalian gestation. It is the inner cell mass (ICM) of the blastocyst which later develops into the embryo, while the outer-layer cells of the blastocyst, which collectively form the trophoblast, will develop into the extra-embryonic tissue, such as the placenta.

The ICM is the source of embryonic stem cells that are harvested for research, resulting therefore in the destruction of the blastocyst.

The blastocyst stage exists between the morula and the embryonic stages. (See Morula, and Embryonic Stem Cells).

  • Charlie’s Law / HB 810 — House Bill 810, the historic piece of legislation which makes adult stem cell therapy legal for the first time ever in the U.S., but only in the state of Texas.

Named in honor of former Texas State Representative Charlie Howard, HB 810 passed both the Texas Senate and the Texas House of Representatives unanimously in each case, and was signed into law by Texas Governor Greg Abbott on June 12th, 2017, taking effect on September 1st, 2017.

HB 810 allows, for the first time ever in the United States, the legal medical treatment of patients with expanded adult stem cells, but only in the state of Texas. 

Read more about HB 810, or Charlie’s law, here.

  • Embryonic Stem Cells — These are stem cells that exist only in an embryo. (See Adult Stem Cells, and Fetal Stem Cells).

In humans, the embryonic stage of development is defined as beginning at implantation (when the blastocyst, or fertilized ovum, adheres to the wall, or endometrium, of the uterus) and lasting through the 8th week of gestation. After the 8th week, the developing human is known as a fetus, until birth.

In order to harvest embryonic stem cells from an embryo, the embryo must be destroyed.

Embryonic stem cells are pluripotent, and therefore, by definition — like all pluripotent stem cells — they form a particular type of tumor known as a teratoma. For this as well as a multitude of other reasons, embryonic stem cells are highly problematic scientifically, highly dangerous medically, and ethically as well as politically they are highly controversial. (See Teratoma).

Despite decades of research, embryonic stem cells have never successfully been used to treat any medical condition. On the contrary, embryonic stem cells cause a myriad of problems, not the least of which is the formation of tumors (teratomas) in the recipient patients, a significant problem which shows no indication of being resolved.

To reiterate: medically, embryonic stem cells are extremely unsafe and ineffective; ethically and politically, embryonic stem cells are extremely controversial.

  • Fetal Stem Cells — These are the stem cells that exist in a fetus. (See Embryonic Stem Cells, and Adult Stem Cells).

The human fetal stage is defined as beginning on the last day of the 8th week after fertilization, and continues until birth.

Fetal stem cells are derived from fetuses obtained from abortions, even as late as the third trimester.12

Like embryonic stem cells, fetal stem cells are scientifically and medically extremely problematic, and ethically and politically extremely controversial.12

As with embryonic stem cells, both the Baptist Church2 and the Roman Catholic Church3 are strongly and officially against any research or clinical use of fetal stem cells.

  • Gamete — Either of the mature haploid male or female germ cells (ovum or sperm), capable of uniting with the gamete of the opposite sex to produce a zygote. (See Zygote).
  • Germ Layer — In the early embryo, a germ layer is group of cells that is responsible for the formation of specific tissues and organs.

Some species are diploblastic, that is, they have two primary germ layers; mammals are triploblastic, with three germ layers.

Regardless of the species, all germ layers together will give rise to every type of tissue in the entire mature organism.

The human body develops entirely from the three germ layers, which give rise to everything from bones and hair to skin and internal organs. This is why the formation of a teratoma (which contains cells from all 3 germ layers) is a required capability, by formal medical definition, of human pluripotent stem cells. (See Teratoma, and Pluripotency).

The three human germ layers are:

1/ Endoderm (internal layer): this layer gives rise to the gastrointestinal and respiratory tracts, endocrine glands, liver, and pancreas.

2/ Mesoderm (middle layer): this layer gives rise to bone and skeletal muscle, cartilage, cardiac muscle cells, red blood cells and most of the circulatory system, smooth muscle cells in the gut, and connective tissue.

3/ Ectoderm (external layer): this layer gives rise to the epidermis (skin cells), pigment cells, neuronal brain and nervous system cells.

The human germ layers develop early in the embryonic stage, through the process of gastrulation, during which the blastula reorganizes itself into two primary germ layers, the inner layer (the endoderm) and the outer layer (the ectoderm), both of which proceed to interact with each other to produce the third, and middle, germ layer (the mesoderm).

Germ layers were first observed and described by Christian Pander in a doctoral dissertation at the University of Würzburg in Germany in 1817.4

Read more about germ layers here.

  • Induced Pluripotent Stem Cells (iPSCs) — These are ordinary skin or blood cells, taken from adult humans, which have been reprogrammed backwards, or de-differentiated, to their more primitive, embryonic-like pluripotent state. The mature, specialized cells have been altered in the laboratory to regress to an earlier, simpler form. (See Pluripotency).

iPSC technology was pioneered by Dr. Shinya Yamanaka and his laboratory team in Kyoto, Japan in 2006, using transcription factors encoded from four specific genes. Dr. Yamanaka would later receive the 2012 Nobel Prize in Physiology or Medicine, along with Sir John Gurdon, for this method of turning ordinary cells into pluripotent stem cells.

In an effort to circumvent the ethical and political controversies surrounding embryonic and fetal stem cells, scientists originally had high hopes for iPSCs. But this new type of genetically manipulated cell has not been without its challenges. Now, more than a decade after their discovery, iPSCs are understood to be highly problematic, and not merely for their pluripotency – a feature which in and of itself is sufficient to render the cells dangerous for therapeutic use.

iPSCs have never been successfully used to treat any medical condition. Additionally, the ease with which they form teratomas makes them highly unstable and unsuitable for any medical therapy.5

  • Morula — The developing zygote, once it has divided into 16 cells, after which it proceeds by cavitation to enter the blastula stage. (See Blastocyst, and Zygote).
  • MSCs: Mesenchymal Stem Cells / Medicinal Signaling Cells — Dr. Arnold Caplan, the scientist who first isolated these cells from bone marrow and expanded them in culture, originally named them “mesenchymal stem cells” because it was thought at the time that the cells came from the stroma of the bone marrow. It is now known, however, that the cells are not part of the stroma or marrow, and, in fact, they are not stem cells. They are perivascular cells that exhibit extremely powerful paracrine activity. Dr. Caplan, renowned throughout the world as “The Father of the MSC,” has therefore suggested that they be renamed Medicinal Signaling Cells

Click here to read more about Medicinal Signaling Cells. Click here to read Dr. Caplan’s testimony about MSCs before the U.S. FDA in September of 2016.

MSCs are among the most important type of “adult stem cell” — even though, technically, they are not stem cells. Nevertheless, they are masters at doing everything that stem cells are expected to do, namely, regenerating tissue. Additionally, MSCs go above and beyond mere regeneration by performing a wide range of other beneficial functions which include modulating the immune system and calming inflammation, to name but a few.

MSCs are safe, efficacious, and ethical.

MSCs are easily harvested, and have been in use by the standard medical community for over 60 years.1

Click here for information on two important books about MSCs, one of which contains compelling accounts of patients who have recently been safely and efficaciously treated with MSCs, and the other of which spans more than 50 years of research and clinical trials, drawing from more than 800 unique references, and citing MSCs in the treatment of 44 different medical conditions.

  • MTFs: Mesenchymal Trophic Factors — see “Secretome,” below.
  • Multipotency — The ability of a stem cell to differentiate into more than one type of specialized cell or tissue, but not all types. (See Pluripotency, and Totipotency).

Adult stem cells are multipotent.

  • Paracrine Signaling — A form of cell-to-cell communication, in which a cell releases molecules that induce changes in nearby cells.

Paracrine, from the Greek, “para,” meaning “beside,” and “krino,” “to separate.”

Paracrine activity is similar to, yet different from, endocrine activity (from the Greek “endo,” meaning “within”) in which hormones secreted by a gland exhibit influences over cells at a further distance, by transportation through the circulatory system.

MSCs exhibit especially powerful paracrine signaling, so much so that the scientist who discovered and named these cells has suggested that their name be changed from “mesenchymal stem cell” to “medicinal signaling cell.”

Learn more about the importance of MSC paracrine signaling here.

  • Pluripotency — The ability of a stem cell to differentiate into all tissue types, from all 3 of the germ layers: the ectoderm, the mesoderm, and the endoderm. (See Germ Layer).

In other words, a pluripotent cell must be able to differentiate into all the various types of tissue that form the entire organism. A human pluripotent stem cell, therefore, is capable of forming the entire human body.

Teratoma formation is the means by which pluripotency is determined. In other words, the laboratory test for determining whether or not a cell is pluripotent is to see if it forms the type of tumor known as a teratoma. Preferably, the test is conducted in vivo, rather than in vitro, by injecting the cell into a mouse. If the mouse develops a teratoma at the site of injection, then the injected cell is determined to have been pluripotent; if no teratoma forms, then the injected cell is determined not to have been pluripotent.8 (See Teratoma).

One of the different types of potency (totipotent, pluripotent, multipotent), pluripotency is characteristic of embryonic stem cells and of iPSCs (induced pluripotent stem cells). (See Multipotency, and Totipotency).

By contrast, adult stem cells are not pluripotent.

It was originally believed, in the early years of stem cell research, that pluripotency was a desirable trait of stem cells, and a necessary condition for the stem cells to be an efficacious medical therapy. We now know that the opposite is true. Pluripotency is neither necessary nor desirable, as a medical therapy. In fact, for the medical therapy to be safe, the stem cells should not be pluripotent, because there must not be any risk at all to the patient of teratoma formation.

  • Secretome — The totality of bioactive molecules secreted by a particular cell, tissue, organ, or organism.

The MSC secretome is particularly rich in regenerative, healing, beneficial substances such as trophic factors, growth factors, cytokines, ECM (extracellular matrix) proteases, hormones, lipid mediators, and neurovascular supportive factors (including FGF2 and VEGF-A), all of which exhibit a wide range of beneficial effects, including neuro-protective, cardiovascular-protective, musculoskeletal-protective, anti-inflammatory, immunomodulatory benefits, to name just a few. 6, 7

MSCs are masters of cellular regulation, precisely through their powerful secretome and paracrine signaling.

Bioactive molecules in the MSC secretome are also known as MTFs (mesenchymal trophic factors).

Read more about MTFs and the MSC secretome here.

  • Teratoma — A particularly hideous type of tumor, often containing hair, teeth, bone, muscle, and organ-like structures, among other abnormal characteristics. Teratomas contain components of the human body, but in an entirely random and disorganized manner.

The term is from the ancient Greek “téras,” meaning “monster,” with the suffix “-oma” which indicates “tumor” or “cancer.” The related medical prefix “terato-“ is used to mean “pertaining to birth defects.”

Contrary to widespread misconception, a teratoma can be both malignant and benign. The malignant form is known as a teratocarcinoma.

Pluripotent stem cells are required, by definition, to form a teratoma. If a cell is not capable of forming a teratoma, then it cannot be classified as pluripotent.(See Pluripotency).

All embryonic stem cells, therefore, as well as all iPSCs (induced pluripotent stem cells), form teratomas, because of their pluripotency. In fact, iPSCs form teratomas even “More Efficiently and Faster Than Human Embryonic Stem Cells Regardless the Site of Injection.” 5

By contrast, adult stem cells do not form teratomas, for the simple reason that adult stem cells are not pluripotent.

  • Totipotency — The ability of a single cell not merely to generate all the cells of the body (developing into all types of tissue from all 3 germ layers), but also its ability to differentiate into the extra-embryonic, e.g., placental, cells — and, in addition, most importantly, its ability to organize the entire bodily cells into a fully integrated, functional, living organism.

The term comes from the Latin “totus,” meaning “all” or “entirely.”

In mammalian gestation, only the earliest zygote is totipotent. (See Multipotency, Pluripotency, and Zygote).

Widespread confusion has resulted, even within the scientific community, from the inaccurate use of the term according to contradictory definitions. One author and scientist has even proposed the new term, “plenipotency,” to alleviate this confusion, and to distinguish between the totipotency that is correctly reserved strictly for living organisms, and the weaker potency characteristic of individual cells and tumors (teratomas) that produce all cell types but lack the genetic ability to organize the cells into a living body.9

  • Umbilical Cord Blood — A particularly rich source of the type of adult stem cell known as an MSC.

Although the nomenclature is not precise, stem cells which are derived from umbilical cord blood are classified as adult stem cells (not as embryonic stem cells, nor as fetal stem cells).

Rather than discard the umbilical cord, along with the rest of the afterbirth, it can be collected and processed for its highly therapeutic cells, the safety and efficacy of which have already been demonstrated in numerous studies, for the treatment of a wide variety of diseases, injuries, and other conditions.10

Click here to learn about two important books documenting the numerous cases of patient success stories with MSC treatment.

Umbilical cord blood MSCs are only collected from the umbilical cord blood of full-term, live, healthy births, from mothers who give their full consent for the collection and who have been carefully screened to make sure the delivery is free of disease and genetic abnormalities. 

Scientifically and medically, umbilical cord blood is one of the best sources for the safest, most efficacious type of adult stem cell therapy.

Ethically and politically, like adult stem cells in general, the adult stem cells harvested from umbilical cord blood are entirely noncontroversial, and are fully endorsed by both the Baptist2 and Catholic3 Churches, as well as by a number of other religious organizations.

MSCs from bone marrow and umbilical cord blood have already been in widespread medical use for years, and the trend continues to grow. As of 2015, the number of marrow donors and cord blood units registered on the Bone Marrow Donors Worldwide database surpassed 25 million.11

  • Zygote — The pre-embryonic, diploid eukaryotic single cell resulting from the fertilization of the female haploid gamete (the ovum, or egg cell) by the male haploid gamete (the sperm cell). (See Gamete). As a diploid cell, the zygote possesses half the DNA of each of its two parents (in humans, 23 chromosomes from each parent). The single-celled zygote divides by mitosis to produce a multicellular organism, a later result of which is an embryo.

In mammals, the zygote develops into an embryo through a precise series of stages which encompass the morula, blastula, gastrula, and organogenesis stages. (See Blastocyst, and Morula).

After fertilization yet prior to implantation, the developing cells are known as a “pre-implantation conceptus.” Although there is some usage of the term “proembryo” to refer to the developing human prior to implantation, the U.S. National Institutes of Health have designated the term “pre-implantation embryo” as the proper classification for this stage of development.

Embryonic stem cells that are harvested for research are usually derived from the zygote, during the blastocyst stage – resulting, therefore, in the destruction of the blastocyst, i.e., the death of the zygote.


See also:



5 “Human Induced Pluripotent Stem Cells Develop Teratoma More Efficiently and Faster Than Human Embryonic Stem Cells Regardless the Site of Injection,” Ivan Gutierrez-Aranda et al., Stem Cells, Sept. 2010, 28(9): 1568–1570.


See also:

Maureen L. Condic, “Totipotency: What It Is and What It Is Not,” Stem Cells Dev., April 2014, 23(8): 796-812.

10 Please see the two books: Stem Cell Therapy, A Rising Tide — How Stem Cells are Disrupting Medicine and Transforming Lives, by Neil Riordan, PA, PhD, and MSC, Mesenchymal Stem Cells – Clinical Evidence Leading Medicine’s Next Frontier, by Neil Riordan, PA, PhD, and Thomas E. Ichim, PhD.


12 The Truth About Fetal Tissue Research, Nature, December 2015,