What are adult stem cells?
We are all the result of one of our father’s sperm cells entering our mother’s egg cell (oocyte), fertilizing it, and stimulating the fertilized egg to implant into the side of our mother’s womb (uterus) and begin dividing. After many cell divisions the fertilized egg assumes a spherical shape called a blastocyst, and a group of cells called the inner cell mass forms. These cells are “pluripotential”, meaning that they can become any tissue in the body. All of our organs are derived from these pluripotential cells by a process called differentiation.
The inner cell mass can be removed from a human embryo and cultured. The resulting cells, known as “human embryonic stem cells”, or hESC, remain pluripotential and can be differentiated into various mature cells such as skin, muscle, bone, heart, etc. Because an embryo must be destroyed to access the inner cell mass, some find this procedure to be morally objectionable, and use of hESC’s in research has become controversial.
In 2009 the Nobel Prize in Medicine was awarded to investigators who developed a technology to create pluripotential stem cells from adult differentiated cells, such as those in skin punch biopsies or blood samples. These differentiated cells were taken from adults and induced with viruses to transform into pluripotential stem cells. The creation of “iPSC’s”, or induced pluripotential stem cells, represents a major advance in studying how primitive cells change into the tissues of our bodies.
How do we make iPSC’s?
We have adapted a procedure reported in 2012 to make iPSC’s from human blood mononuclear white blood cells. We can easily isolate these cells from a standard blood sample. After collecting the mononuclear cells, we put them into cell culture for 3 weeks and then use electric current to punch small holes in the cell membranes. This process of “electroporation” allows a small piece of circular DNA known as a plasmid to enter the cells and reproduce itself. This plasmid also carries genes for 5 proteins known as “reprogramming” proteins. As the plasmid makes increasing quantities of these reprogramming proteins, the “clock is turned back” in the cells and they become pluripotent, very much like (but not identical to) how they were at the time the person who donated the blood sample was an embryo.
What do we do with the iPSC’s?
We can differentiate the iPSC’s into neural stem cells that then can be changed into non-dividing nerve cells (neurons) or glial cells (astrocytes). Neural stem cells are attractive because they represent a non-tumor, human cell line that spontaneously divides and can be propagated in cell culture. We use the neural stem cells to screen drug effects as well as a source of neurons and glia.
Will iPSC’s allow us to pursue personalized pharmacology?
We have every reason to expect that iPSC’s derived from a person with a degenerative brain disease can be changed into neurons or glia that reflect how the brain disease is manifested in that individual. It is unrealistic to expect that all people who look alike in terms of a clinical brain disease will be the same at the molecular level. Simple genetic reasoning tells us that if someone with light skin, red hair and blue eyes, as well as a different person with dark skin, black hair and brown eyes can both develop the same brain condition, there is no reason to assume that they have the same underlying molecular genetic disturbances. iPSC’s changed into neurons or glia will likely reflect the specific molecular disturbances of individuals. And screening a drug against the iPSC-derived neural stem cells or neurons and glia should predict how a specific individual’s brain disease would respond to that drug. That is how we will pursue personalized pharmacology.