The Meaning of Stem Cells

The term “stem cells” has taken on a scientific, political and conversational context over the past few years for many reasons. Scientifically, they are the origin of all cells, particularly for multicellular organisms.

There is evidence that cancer stem cells can evade conventional cancer treatment and lay dormant for long periods of time, eventually leading to cancer recurrence or progression.

While we have known for centuries that the sperm and egg are the origin of humans, the intricate details of how one cell gives rise to a whole body in a deliberate and coordinated fashion have only recently come into focus. Pluripotency is the term used for one cell being able to become any mature cell, and the most obvious situation is the sperm or egg forming an initial set of cells that becomes an embryo and then further differentiates into a fully functional newborn.

The identification of protein markers on pluri-potent stem cells, and the ability to grow these cells in the laboratory, led to a rapid proliferation of projects attempting to develop organs and tissue, and to simply further understand the biology of stem cells and the differentiation pathways that lead to specific human cell types. However, those early efforts required the use of embryos, including those obtained from abortions, which led to the politicizing of science and banning of such research that tapped federal funds. The ban was eventually lifted, but by then, stem cells were being engineered from non-embryonic cells by using specific factors or transfection of certain genes.

Once proteins and other characteristics that define stem cells were better established, different tissues were found to have their own set of stem cells—for example, bone marrow “hematopoietic stem cells,” which can give rise to all types of mature blood cells. More surprising was the discovery that cancer cells also contain a small subpopulation of stem-like cells.

In this issue, you will read more about how this information has created an explosive new field in cancer research, just as it has in regenerative medicine. The number of publications and funded grants with the word “stem cell” has skyrocketed over the past 10 years. My own institution has a Center for Regenerative Medicine and Stem Cell Research funded by the state of California, and a host of projects, including cancer clinical trials, so I have to declare a “conflict” of sorts in writing this editorial.

There is evidence that cancer stem cells can evade conventional cancer treatment and lay dormant for long periods of time, eventually leading to cancer recurrence or progression. But stem cells could also be cancer’s Achilles’ heel. We must therefore understand the biological mechanisms involved in stem cell growth and maintenance. Some of the stem cell pathways appear to have possible points of attack by specific molecules and antibodies, which are mostly in very early phases of clinical study. While many scientists and clinicians are enamored with the elegance and logic of this approach, others are skeptical and do not believe there is sufficient proof that cancer stem cells even exist.

Nevertheless, the field of cancer stem cells is currently inspiring hope and more opportunities to make a big impact in cancer. It is too soon to tell if the whole field will go by the wayside after unsuccessful clinical trials or whether serious traction will develop. Most studies are just starting, but a few promising results are being seen, as you will read in this issue. Sexy and new does not always translate into results. But the field is attracting significant funding and bright scientists—so for now, it is riding high. We will follow this story over time and track its path in history.

Debu Tripathy, MD

Editor-in-Chief

Professor of Medicine, University of Southern California

Co-Leader, Women's Cancer Program at the USC/Norris Comprehensive Cancer Center