PUBLIC RELEASE DATE:

30-May-2014

Contact: Krista Conger kristac@stanford.edu 650-725-5371 Stanford University Medical Center

STANFORD, Calif. For many scientists, the clinical promise of stem cells has been dampened by very real concerns that the immune system will reject the transplanted cells before they could render any long-term benefit. Previous research in mice has suggested that even stem cells produced from the subject's own tissue, called iPS cells, can trigger an immune attack.

Now researchers at the Stanford University School of Medicine have found that coaxing iPS cells in the laboratory to become more-specialized progeny cells (a cellular process called differentiation) before transplantation into mice allows them to be tolerated by the body's immune system.

"Induced pluripotent stem cells have tremendous potential as a source for personalized cellular therapeutics for organ repair," said Joseph Wu, MD, PhD, director of the Stanford Cardiovascular Institute. "This study shows that undifferentiated iPS cells are rejected by the immune system upon transplantation in the same recipient, but that fully differentiating these cells allows for acceptance and tolerance by the immune system without the need for immunosuppression."

The findings are described in a paper to be published online May 30 in Nature Communications. Wu is senior author of the paper. Postdoctoral scholars Patricia Almeida, PhD, and Nigel Kooreman, MD, and assistant professor of medicine Everett Meyer, MD, PhD, share lead authorship.

In a world teeming with microbial threats, the immune system is a necessary watchdog. Immune cells patrol the body looking not just for foreign invaders, but also for diseased or cancerous cells to eradicate. The researchers speculate that the act of reprogramming adult cells to pluripotency may induce the expression of cell-surface molecules the immune system has not seen since the animal (or person) was an early embryo. These molecules, or antigens, could look foreign to the immune system of a mature organism.

Previous studies have suggested that differentiation of iPS cells could reduce their tendency to inflame the immune system after transplantation, but this study is the first to closely examine, at the molecular and cellular level, why that might be the case.

"We've demonstrated definitively that, once the cells are differentiated, the immune response to iPS-derived cells is indistinguishable from its response to unmodified tissue derived from elsewhere in the body," said Kooreman.

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Coaxing iPS cells to become more specialized prior to transplantation cuts rejection risk