As rescue workers comb the wreckage of two of the world's largest office buildings, Americans are being asked to donate blood to help survivors. Even before yesterday's horrific terrorist attack, blood was scarce, and Americans are lining up to donate.

As much as anything else, the donations are a welcome show of solidarity with those who survived the incineration and collapse of the World Trade Center in New York City. But donated blood, even when available, is not ideal, since it must match the recipient, and it can carry disease.

Some companies are trying to bring artificial blood to the market. But biologists are also inching toward a more sophisticated source -- embryonic stem cells (ES cells).

ES cells are formed the first few days after fertilization, and have been subject of heated political wrangling in recent months. Now, a team at the University of Wisconsin-Madison has pushed undifferentiated human embryonic stem cells down a developmental pathway to become blood cells.

Writing on the blank slate
Learning to direct embryonic stem cells -- blank-slate cells that arise at the earliest stages of development -- to become blood, bone, skin, nerve and other cell types, is a key challenge for stem-cell scientists.

The Wisconsin scientists coaxed undifferentiated stem cells to become primitive blood cells that later developed into more mature, specialized blood cells.

The work shows the potential for creating blood cells for transfusions and transplants in the laboratory. "These results show an effective and efficient way to derive blood cells from these early precursors," says Dan Kaufman, a hematology fellow at the UW-Madison Medical School and the paper's lead author.

Developing a cell
The research helps illuminate the process of human development as generic embryonic cells enter developmental pathways to become any of the 220 types of cells and tissue in the human body. Learning how blood arises from ES cells would answer a fundamental question in biology.

Kaufman emphasizes that while the work shows great promise toward the goal of taming embryonic stem cells, it remains basic science, and use for transplants and transfusions is years away. Kaufman's team included James Thomson, who first grew human ES cells in the lab.

Kaufman and colleagues directed stem cells to become hematopoietic precursor cells (AKA hematopoietic colony-forming cells). These cells carry biochemical markers and gene products characteristic of blood and bone marrow cells.

The transformation was effected by exposing stem cells in tissue culture to bone marrow and other cells, and to growth factors, which emitted chemical signals that encouraged the ES cells to specialize into blood cells.

The hematopoietic precursor cells continued specializing into white blood cells, red blood cells and platelets. These, the three key types of blood cells, are normally made in human bone marrow.

Terrific transfusions
Although ES cells cannot help victims of yesterday's atrocities, the technology could greatly improve human blood supplies. "There is generally a shortage of blood," says Kaufman, and if the technology matures it "may one day be possible to augment that blood supply," by producing, on demand, properly matched, disease-free transfusions.

ES cells may also be used to treat cancers of the blood and bone marrow, such as leukemias and myelomas. Marrow transplants can treat these cancers because human blood is constantly renewed in bone marrow.

Each year, about 20,000 bone marrow transplants are conducted in the United States for these diseases. But according to Kaufman, only about 25 percent of patients with leukemia and other cancers who need blood or bone marrow from another person actually get transplants.

The reason? A scarcity of matched donor cells. ES cells, he says, could eventually provide better matches.

Some day. But technical hurdles and legal restrictions on ES research both stand in the way of progress, so don't hesitate to give blood today.

-- Terry Devitt, Dave Tenenbaum