Immune Cells Save Transplanted Hearts

MONTREAL, CANADA--Transplanted organs can save lives, but they come with a catch. Without powerful immune-suppressing drugs, the recipient's body quickly rejects them. For years, doctors have been struggling for a way to give the organ without the drugs. Now researchers are hoping that a class of immune cells may be the solution: In mice, the cells, called regulatory T cells, kept newly transplanted hearts intact.

Much of the buzz at the International Congress of Immunology and conference of the Federation of Clinical Immunology Societies here this week has centered on regulatory T cells. The cells are only a small minority of T cells, but their recently discovered abilities to modulate the rest of immune system seem boundless. Although researchers don't quite understand how the cells work, they're learning that regulatory T cells can dictate the behavior many other T cells, including stopping them from mounting an immune attack. This has prompted particular interest among autoimmune disease researchers and those in the organ transplant field.

In one study, rheumatologist and immunologist Robert Horwitz of the University of Southern California in Los Angeles and his colleagues transplanted new hearts into 12 mice. Before the transplant, the group collected blood from the animals. They treated blood cells from six mice with two types of messenger proteins that can transform T cells into regulatory T cells and exposed them to cells from the donor animals. Then they injected the treated cells back into the six mice. Two of these mice kept their transplanted hearts for more than 100 days, while all six mice whose blood wasn't treated rejected the hearts within 11 days.

A second study presented by Boris Lee of the University of Toronto used a different kind of regulatory T cell in a similar mouse transplant operation. He and his colleagues, including immunologist Li Zhang, found that those cells immediately zoomed toward the new heart, bypassing other sites in the body. The fact that "they get there first," before other T cells can begin attacking the organ, could help explain why the cells are protective, says Horwitz.

The regulatory T cell approach is gaining fans. "It's clear that it works," says immunologist Karsten Mahnke of the University of Mainz in Germany. Now, he says, scientists need to figure out how to produce large numbers of these cells outside the body--and whether giving them to humans and other animals is safe and helpful.