Ann Tsukamoto and colleagues file the landmark U.S. patent application for isolating purified human blood-forming stem cells, later granted as US 5,035,994.
On March 16, 1990, Ann Tsukamoto, together with her colleagues at SyStemix, Inc., filed a U.S. patent application titled "Human Hematopoietic Stem Cell". The application described a groundbreaking method for isolating purified, cancer-free human hematopoietic (blood-forming) stem cells from the contaminated blood or bone marrow of cancer patients.
At the time, bone marrow transplantation was hampered by the risk of reintroducing malignant cells into patients during autologous transplant procedures. Tsukamoto and her team's innovative isolation technique addressed this critical clinical problem by allowing researchers and physicians to separate healthy, functional stem cells from cancerous contaminants, a genuine scientific first in the field of hematology and oncology.
This filing represents one of the earliest formal claims to a method of isolating human hematopoietic stem cells with such precision, and it laid essential groundwork for future advances in bone marrow and blood stem cell transplantation, as well as for the broader field of regenerative medicine.
The application would be examined for over a year before being granted, a period during which the underlying science was also validated and expanded upon by Tsukamoto and her colleagues in ongoing laboratory work at SyStemix. This filing is widely regarded as a foundational milestone establishing Tsukamoto as a pioneering inventor in stem cell biology.