Stem Cells 101
Words like regeneration, rejuvenation, and regrowth conjure up hope and potential when used in a medical context. Every scientist or clinician that has harnessed the potential application of stem cells in a clinical setting for patients has pondered what the next frontier is. Even after decades of peer-reviewed, published information on stem cells, the whole issue of their use in regenerative medicine is shrouded in mystery thicker than Sir Alfred Hitchcock’s screenplays. So what is in it for patients seeking regenerative medicine, such as stem cells, as plausible treatments and therapies for their respective medical conditions? What is a stem cell? This article is not an effort to dispel or unravel the politicking on stem cells in medicine. Additionally, the myriad of complex issues of stem cell biology are beyond the scope of this publication.
Stem cells are undifferentiated biological cells which can be thought of as blank cells with great potential to differentiate into specialized cells. Undifferentiated stem cells can replicate into more stem cells, thereby providing a reservoir of even more blank cells. These blank cells can be targeted through controlled differentiation to provide specialized cells. It is this aspect of the stem cell’s controlled differentiation into certain or desired cell types that holds the potential for therapies. Mammals at the biological system level are made up of organs, tissues, and bones. Each one of these biological systems is a collection of specialized cells. Various diseases at the organ, tissue, or bone level thus have the potential to be addressed by cellular therapies.
In an effort to better explain stem cells, it is best to use the broad classification of embryonic or adult. As the name implies, embryonic stem cells (ESCs) are obtained from early stage embryos. They are harvested from a ball-like structure called the blastocyst during the early development of mammals, including humans. The cellular mass found inside the blastocyst goes on to form the embryo and is a rich source of ESCs. These embryonic cells are termed pluripotent which means that they have an unlimited potential to produce any cell type that makes up the body. As the embryo grows in to a fetus, the pluripotent capacity of the cells diminishes and progresses to a more differentiated state involved with the formation of organs. So the cell’s potency, i.e. ability to give rise to any type of cell, is greatly reduced and is restricted to the type of tissue or organ it is part of. All organs and tissues in the body possess a reservoir of stem cells whose potency is geared towards the tissue that hosts it.
Human ESCs can be used as regenerative therapies for various diseases, such as spinal cord injury, Parkinson’s disease, and diabetes. Most of the advances in the developmental biology of stem cells have been made with studies on mouse ESCs. Even though the mouse is the primary animal model for understanding mammalian embryology, there are vast differences between mice and human embryos. Namely, the formation of early structures like the placenta, embryonic membranes, and the egg cylinder all vary vastly from their counterparts in human embryo. Non-human primates, such as rhesus monkeys, are commonly used to address these scaling up problems of animal models to humans. The primary reason for using non-human primates is to prevent immune rejection of transplanted cells and to demonstrate the safety and efficacy of embryonic stem cell-based therapies comparable to humans.
Due to restrictions on human embryonic stem cell research in the U.S., it is important to have a strong grasp on the developmental biology of rhesus monkeys and their ESCs. They provide a much more accurate model and consequently aid in furthering the understanding of basic developmental biology for human ESCs. This is especially important when human embryonic stem cell research gains mainstream acceptance and government restrictions are removed for its application in medicine. Great progress has been made in the basic developmental biology of mice, rhesus monkeys, and various other animals. It is only a matter of time and thawing out politics and stigmas associated with human ESCs that will link this progress even more closely to the prevention and treatment of human disease.
Read the full article in the Spring 2015 Journal.
By Furqan Haq, PhD