Stem cells form blood vessels

Many scientists have found new ways to repair damaged arteries and ailing hearts have coaxed stem cells from a human embryo into forming tiny blood vessels. According to Robert Langer, leader of a laboratory team at the Massachusetts Institute of Technology, this is the first time human embryonic stem cells have been nurtured to the point where they will organize into blood vessels that could nourish the body.

But it is not likely to be the last, as scientists continue their research into uses for stem cells despite debate over the ethics of using the cells. The new development is reported in Tuesday's online issue of Proceedings of the National Academy of Sciences.

Dr. John Gearhart of the Hopkins School of Medicine felt that the research was a nice illustration of how stem cells can serve as a source of various types of cells, in this case for blood vessels. It's another good example of the isolation of an important cell type from human embryonic stem cells.

According to Langer the work shows that endothelial cells can be made from human embryonic stem cells. Endothelial cells line veins, arteries and lymph tissue and are the key to the structures that carry blood throughout the body.

He said if the technique is refined, scientists may eventually be able to make in the laboratory blood vessels that could be used to replace diseased arteries in the body. ``There are thousands of operations a year now where doctors take vessels from one part of the body and transplant them to another,'' said Langer. Eventually, such vessels might be made outside the body from embryonic stem cells.

Langer said 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. The research was conducted under a private grant, but Langer said the cell culture used is one of 55 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 already existed and 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 money to continue research using the same stem cell cultures, which were obtained from 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 develop 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 blood vessels. He said some of the vessels 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.