Los Angeles, CA - The California Science Center has announced the selection of Irving L. Weissman, MD, as the 2002 California Scientist of the Year. Dr. Weissman, professor of pathology and cancer biology at Stanford University, is credited with being among the first to isolate the hematopoietic stem cell in both mouse and man. His groundbreaking research has paved the way for dozens of experiments that explore the cell's power to fight illnesses as diverse as cancer and Parkinson's disease.

The California Science Center established the California Scientist of the Year Award in recognition of the prominent role California plays in the areas of scientific and technological development. A blue-ribbon panel selects a nominee whose work is current and advances the boundaries of any field of science. Of those selected, eleven have earned the California Scientist of the Year honors before becoming Nobel Laureates.

Weissman's interest in lymphocytes, the disease-fighting white blood cells of the immune system, led him to explore how they go awry to produce lymphomas such as Hodgkin's. His work came to focus on the two types of lymphocytes - T cells and B cells. He knew it would be important to learn where these cells came from, so he began searching for a common ancestor.

In 1988 after years of research, Weissman and his colleagues devised a process of elimination to isolate the blood-forming stem cell from a pool of bone marrow cells.

This was accomplished by building up as many blood-cell binding antibodies as possible and using the antibodies to select out non-stem cells. When an antibody attached to a cell, that cell was eliminated from the group. Finally, two antibodies known from previous research to bind to stem cells were added to the small group that remained. The few cells left in the pool were tested to see if they were really stem cells by injecting them into mice whose blood systems had been destroyed by lethal radiation. The researchers found that as few as 30 of these cells saved half of the mice, renewing these survivor's entire blood supplies.

Weissman's next challenge was to identify the stem cell in humans. Since humans could not be subjected to the same types of experiments as mice, Weissman and his research team set out to make mice more like humans. They created a special mouse, known as Hu-SCID, that had all the components of the human immune system.

By April 1992, Weissman and his collaborators reported in the Proceedings of the National Academy of Sciences that they had found a candidate for the human blood-forming stem cell. In 1996, Weissman and his colleagues at StemCells, Inc. a company he help found, initiated several clinical trials using the newly discovered stem cells in patients with various forms of cancer. One trial involved women with late stage breast cancer that had spread throughout their bodies. The study addressed a problem observed in many cancer patients treated with bone marrow transplants that relied on the patient's own tissues for transplant material: Tumor cells remained in the blood. In the trial, the researchers extracted bone-marrow material from the women, purified the stem cells and reinfused them back into the patients after they had been given chemotherapy. The purified stem cells were tested after treatment and no residual cancer cells were found. Results of the study were published in December 2000 in Biology of Blood and Marrow Transplantation.

Weissman was described in statements supporting his nomination as being "treasured throughout the world for his love of life and science, his wonderful capacity to communicate ideas and the excitement of science" and that "there is no predicting what he might accomplish but it will surely be pathfinding."

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