In March 1991, Immunex announced it had received U.S. Food and Drug Administration (FDA) approval to market Leukine (GM-CSF in the U.S. to treat bone marrow transplant patients. GM-CSF (marketed as Leukine), was a blood-growth stimulator that enhanced the body’s production of white blood cells.

In 2018, Boston-based cancer company Partner Therapeutics acquired the global rights to develop, manufacture, and commercialize Leukine (sargramostim) from Sanofi.