U.S. Patent 5,035,994 is granted, co-invented by Ann Tsukamoto, disclosing the first method to isolate human blood-forming stem cells.
On July 30, 1991, the United States Patent and Trademark Office granted U.S. Patent 5,035,994, titled "Human Hematopoietic Stem Cell," co-invented by Ann Tsukamoto and her colleagues at SyStemix, Inc. This patent disclosed, for the first time, a reliable method for isolating human hematopoietic stem cells—the rare progenitor cells responsible for generating all types of blood cells.
The significance of this achievement cannot be overstated: prior to this discovery, scientists lacked a dependable technique to separate these stem cells from the complex mixture of cells found in bone marrow and blood. Tsukamoto's method enabled researchers to isolate cancer-free hematopoietic stem cells even from the contaminated tissue of cancer patients, opening the door to safer and more effective bone marrow and blood stem cell transplants.
This patent became one of the most cited and foundational intellectual property assets in the field of regenerative medicine, influencing subsequent research into leukemia treatment, immune system reconstitution, and broader stem cell therapies. It also cemented Tsukamoto's reputation as a leading inventor in biotechnology, at a time when women, and especially Asian American women, were significantly underrepresented among named patent holders in the life sciences.
The grant of this patent represents a genuine scientific first: the first successful isolation and patenting of a method to purify human hematopoietic stem cells, a milestone that continues to underpin modern hematology and oncology research decades later.