Methods to multiply pluripotent cells for potential therapies raise worries about cancer

The therapeutic promise of human stem cells is indisputably huge, but the process of translating their potential into effective, real-world treatments involves deciphering and resolving a host of daunting complexities.

Writing in the February 25 online issue of the journal PLOS ONE, researchers at University of California, San Diego School of Medicine, with collaborators from The Scripps Research Institute (TSRI), have definitively shown for the first time that the culture conditions in which stem cells are grown and mass-produced can affect their genetic stability.

"Since genetic and epigenetic instability are associated with cancers, we worry that similar alterations in stem cells may affect their safety in therapeutic transplants. Certain mutations might make transplanted stem cells more likely to form tumors, introducing the risk of cancer where it didn't exist before," said co-corresponding author Louise Laurent, MD, PhD, assistant professor and director of perinatal research in the Department of Reproductive Medicine at UC San Diego School of Medicine.

"This study shows the importance of quality control," added Jeanne F. Loring, PhD, professor and director of the Center for Regenerative Medicine at TSRI, and adjunct professor in the UC San Diego Department of Reproductive Medicine and the study's other co-corresponding author. "It's almost certain these cells are safe, but we want to make sure they are free from any abnormalities."

To exploit the transformative powers of human pluripotent stem cells, which include embryonic stem cells and induced pluripotent stem cells, requires producing them in large numbers for transplantation into patients.

"During this culturing process, mutations can occur, and mutations that increase cell survival or proliferation may be favored, such that the cells carrying such mutations could take over the culture," said Laurent.

Human pluripotent stem cells are cultured in several different ways. Key variables are the surfaces upon which the cells are cultured, called the substrate, and the methods used to transfer cells from one culture dish into another as they grow, called the passage method.

Originally, scientists determined that stem cells grew best when cultured atop of a "feeder" layer that included other types of cells, such as irradiated mouse embryonic fibroblasts. For reasons not fully understood, these cells provide stem cells with factors that support their growth. However, concerns about the feeder cells also introducing undesirable materials into stem cells has prompted development of feeder-free cultures.

Moving cells from one culture dish to another has traditionally been done manually, with technicians physically separating the cultured cells into small clumps with an instrument. "It's very labor-intensive," said Laurent, "so new methods that use enzymes to separate individual cells were created."

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Culture clash: How stem cells are grown affects their genetic stability