Techniques for creating new types of stem cells
Generating new stem cell lines is a major focus of many CIRM funded researchers. Learn why these new lines are considered so important for the field to move forward.
- What is a stem cell line?
- What are the different ways of creating pluripotent stem cell lines?
A stem cell line is a group of identical pluripotent stem cells that can be grown and multiplied in a lab dish. A line originates with either a single iPS cell or from the cells of a five day old blastocyst, and all resulting cells in the line are replicates of the original cells. Researchers working with these lines can grow up large volumes of cells and freeze some in liquid nitrogen for future use or to share with colleagues.
Researchers are still learning the best way to grow and maintain pluripotent stem cells. The cells need nutrients and a number of biological factors in the lab dish in order to grow well. Figuring out the best combination of factors to maintain a stem cell line is the focus of several CIRM grants.
- A list of CIRM awards for generating adult stem cell lines
- A list of CIRM awards for generating embryonic stem cell lines
- A list of CIRM awards for generating iPS lines
- A list of CIRM awards for generating cancer stem cell lines
Researchers are taking many different approaches to creating new pluripotent cell lines. CIRM considers this to be such an important endeavor that it has funded $23 million in grants dedicated to the creation of new cell lines and to techniques that make the process more efficient.
All human embryonic stem cell lines in use today were created from embryos generated by vitro fertilization (IVF) and donated for research purposes after the couple had completed their family. After fertilization, the cells divide for about five days to form a ball of cells called a blastocyst. At this point the blastocyst would still be in the fallopian tube and a woman would likely not know that she is pregnant. For IVF, this is the stage when a doctor would transfer the blastocyst into a woman’s uterus.
The blastocyst is essentially a hollow ball of cells containing an inner clump that is known as the inner cell mass. This clump is what give rise to embryonic stem cells if grown in a dish. To generate an embryonic stem cell line, a researcher removes the outer layer of the five day old blastocyst then puts it on a lab dish containing factors that allow cells of the inner cell mass to grow and thrive. These cells form the basis of a new embryonic stem cell line.
Nuclear transfer to create new stem cell lines involves removing the genetic material from an egg, then injecting the genetic material from an adult person’s cell into that egg. Researchers then stimulate the egg to begin maturing. About five days later the egg develops into a hollow ball of about 150 cells called a blastocyst. This is the same type of blastocyst that would be used to create cell lines from donated IVF embryos. Researchers remove the inner cell mass from the blastocyst and grow those cells in a lab dish to create a new embryonic stem cell line.
Researchers have used nuclear transfer to create stem cell lines from a wide range of animals including non-human primates. In 2013, scientists in Oregon for the first time created human stem cell lines through nuclear transfer.
Embryonic stem cells created through nuclear transfer have the advantage of being genetically identical to a person’s own cells. If that person received a transplant of these cells to replace cells damaged by spinal cord injury or destroyed in diabetes, the cells would probably not be rejected by the immune system.
The process of using nuclear transfer to create cell lines identical to a person's own cells is sometimes referred to as therapeutic cloning. That's because those identical stem cells would be created with the intent to derive therapies.
Therapeutic cloning should not be confused with reproductive cloning, in which the intent is to create an identical human being. The California constitution, CIRM regulations and all other states that are actively supporting stem cell research expressly prohibit human reproductive cloning.
Stanford Publication: Illustration of SCNT
The first human induced pluripotent stem (iPS) cells were created by inserting four genes into the DNA of human skin cells. Those introduced genes caused the cells to revert back to a form that is similar to the very early embryonic state, rendering them pluripotent.
These cells are an exciting and valuable research tool, however, iPS cells currently face some hurdles before they can be used in clinical trials of a cell based therapy. The initial versions of the technique used a virus to shuttle the genes into the skin cell, which can integrate into the cell’s DNA and possibly cause hazardous mutations. What’s more, some of the genes used to create the iPS cells have some cancer-causing potential.
Many CIRM-funded researchers are trying to identify safer ways of creating iPS cells, which would allow researchers to create patient-specific stem cells that can be transplanted as a treatment for disease. These researchers are looking into using methods that don’t require the genes to incorporate into the cell’s DNA or finding a combination of chemicals or proteins to replace those genes as alternative ways of creating iPS cells.
UCLA Publication: Profile of Kathrin Plath