Q. What are human stem cells?

A. Stem cells are the blank slates of the body that are used as the building blocks for growth, repair and replacement. As blank slates, these cells can be triggered to develop into the specific types of cells that make up tissues.

There are two different kinds of stem cells, based on their development potential. One category is known as pluripotent stem cells, meaning they have the ability to develop into any type of tissue in the body. Pluripotent stem cells can be broken into two subcategories: those that are derived from human embryos, and those that are created from human skin cells, based on pioneering research conducted at McMaster University.

The second category are adult, or somatic, stem cells, which are found in the various organs and tissues of the body. These, too, are blank slates that can be triggered to differentiate, but they can only be transformed into the cell types that are specific to that particular tissue.

“When you talk about adult stem cells, they come in different flavours and they’re very specific in their role but they don’t have the broad potential that pluripotent stem cells have,” said Dr. Mick Bhatia, director of the McMaster Stem Cell and Cancer Research Institute.

Q. Why are they considered important in medical research?

A. Somatic stem cells are important because not only can they be triggered to develop into specific cell types, they can also make copies of themselves, so there’s always a reservoir. Maintaining a fine-tuned balance is critical. “It’s analogous to an accelerator and a brake,” said Bhatia. “They have to know when to accelerate to produce new cells … and you have to know when to stop. So what are those signals and how they are orchestrated is part and parcel of understanding stem cells.” Understanding how stem cells work could help researchers better understand certain disease conditions, such as cancer.

But it’s also possible that stem cells can be used as treatments, to repair or replace damaged tissues. The trick is to trigger them to differentiate into the proper types of cells in the right places and getting them to work in harmony with the rest of the team. One advantage is that the body’s own cells are being used, so they won’t be rejected as foreign objects by the immune system.

Q. What types of conditions could potentially benefit from stem cell interventions?

A. Diabetes (replacement of insulin-producing cells in the pancreas), Parkinson’s disease, Alzheimer’s disease, spinal cord trauma, leukemia, strokes (replacement of damaged brain tissue) and other forms of cardiovascular disease.

“By understanding the stem cells, we at least have some potential to deal with these diseases,” said Bhatia. “Right now, we’re simply managing chronic disease. There are no cures.

“I think the hope with stem cells is really to fix or cure things.”

Q. Why has the issue of embryonic stem cells raised controversy, particularly in the U.S.?

A. Embryonic stem cells are derived from human embryos created through in vitro fertilization. However, the creation of a line of embryonic stem cells requires the destruction of the embryo. For religious, cultural or even philosophical reasons, some people believe human life begins when an egg is fertilized, so they believe the destruction of an embryo is equal to the destruction of a human life.

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