Researchers make blood vessels from human embryonic stem cells

Monday, March 25th 2002, 12:00 am

By: News On 6

WASHINGTON (AP) _ Cells extracted from a human embryo have been nurtured into tiny blood vessels, a key step toward someday using embryonic stem cells to aid ailing hearts or fix blocked arteries, researchers say.

For the first time, researchers have demonstrated that human embryonic stem cells can be coaxed to spontaneously form blood vessels and organize themselves so they could nourish tissue in the body, said Robert Langer, leader of a laboratory team at the Massachusetts Institute of Technology.

Langer said that if the technique is refined, scientists may eventually be able to make in the laboratory blood vessels that could replace diseased arteries.

``There are thousands of operations a year now where doctors take vessels from one part of the body and transplant them to another,'' Langer said. Eventually, he said, such vessels might be made outside the body from embryonic stem cells.

``This shows that you can make endothelial cells from human embryonic stem cells,'' said Langer. Endothelial cells line veins, arteries and lymph tissue. They are key to the formation of vascular structures that carry blood throughout the body.

Langer said that endothelial cells also might be used to restore circulation to cells damaged by heart attacks. He said the processed stem cells may be able to re-establish blood flow to hearts failing due to blocked arteries.

Dr. John Gearhart of the Johns Hopkins School of Medicine said the research is a ``nice illustration'' of how stem cells can serve as a source of various types of cells, in this case for blood vessels.

``I think this is terrific,'' said Gearhart, who was not part of the research team. ``It's another good example of the isolation of an important cell type from human embryonic stem cells.''

The work is reported in Tuesday's online issue of Proceedings of the National Academy of Sciences.

The research was conducted under a private grant, but Langer said the cell culture used is one of 61 worldwide that have been approved by the National Institutes of Health for federally funded research.

The use of embryonic stem cells is controversial because extracting the cells kills a living human embryo. President Bush last summer decided that federal funding would be permitted only for stem cell cultures that then existed and which were made from embryos that were to be discarded by fertility clinics. The aim was to prevent further killing for research purposes of other human embryos.

Langer said his lab will seek federal funding to continue research using the same stem cell cultures. They were taken from a stem cell colony isolated from a human embryo by the Rambam Medical Center in Haifa, Israel.

Embryonic stem cells are the ancestral cells of every cell in the body. In a developing embryo, they transform into cells that make up the organs, bone, skin and other tissues. Researchers hope to direct the transformation of such cells to treat ailing hearts, livers, brains and other organs.

Langer said his team cultured the cells in such a way that they were allowed to differentiate, or change, into the various types of cells that are precursors to mature tissue. From this colony, the researchers extracted cells that were following a linage that would lead to mature endothelial cells.

These were further cultured and some eventually formed primitive vascular structures.

Some of the cells were injected into laboratory rodents, called SCID mice, whose immune system will not reject foreign tissue.

Langer said the cells continued to transform themselves and after 14 days they developed the tiny tubes and structure of capillaries, the small vessels in the vascular system.

He said an examination of the vessels showed that some contained mouse blood cells, suggesting that they had actually incorporated themselves into the mouse circulation system.

The result, said Langer, shows that embryonic stem cells can spontaneously transform to vessels and organize themselves into a pattern like that which occurs during the formation of an embryo.

``This is the first time this has been done with human cells,'' said Langer.