Scientists Grow Thymus From Stem Cells in Mice

By Richard Woodman

LONDON (Reuters) - Scientists said on Wednesday they had successfully used stem cells in mice to create a thymus, the linchpin of the body's immune system.

The team, at the University of Edinburgh's Center for Genome Research, said they had identified a unique type of stem cell -- a thymic epithelial progenitor cell -- which can grow into a functioning thymus, the small but vital organ that makes the body's infection-fighting white blood T-cells.

The discovery could lead to improved treatment for patients with low levels of T-cells as a result of an organ transplant, chemotherapy or AIDS , team leader Clare Blackburn said.

The research, published in the journal Immunity, was carried out in mice but she said work to confirm a human thymus could also be generated would start within a few months.

"Our findings show very clearly that we are able to generate a thymus, starting from this tiny population of cells. We can implant these cells into mice lacking a thymus. The mice then develop a thymus and gain a functioning immune system," she said.

"Evidence suggests that the human thymus will develop in the same way as in mice, but we need to find the specific markers that define these unique cells in humans before we know for sure," she added.

In a statement, the team said it might be possible to use these stem cells to generate supplies of T-cells in the laboratory which are specific to a particular patient.

This could have a range of clinical applications, including improving the outcome of bone marrow transplants, often required by leukemia sufferers.

The thymus is vital to the immune system. Without it, the white blood cells called T-cells which fight viruses and infection cannot be produced. The organ atrophies after puberty, so people are then dependent on the number of T-cells already produced.

The thymus ensures that only the T-cells with the correct immune response survive. It does this by programming the cells to recognize which cells are foreign and should be attacked, and which are the body's own tissue and should be left alone.

Researchers hope doctors can use the thymus stem cells discovered by the Edinburgh team to program T-cells created in the laboratory to only attack foreign cells.

"This is a really exciting scientific discovery that has a number of implications," said David Grant, scientific director of the Leukemia Research Fund, which funded the research.

"Importantly, it presents the possibility that scientists could create a veritable assembly line generating patient specific immune cells."

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This article posted September 27, 2002.