Treatment Causes Complete Remissions in Leukemia

A phase 1 trial has shown that 11 of 13 patients with hairy cell leukemia had complete remissions after receiving treatment with the recombinant immunotoxin BL22, an antibody bioengineered to recognize and deliver a deadly toxin to hairy cell leukemia cells. Conducted by scientists at the U.S. National Cancer Institute (NCI), the study was reported in the July 26, 2001, issue of The New England Journal of Medicine.

The other two patients in the trial had partial remissions. All of the trial patients had failed previous chemotherapy. The positive findings were a surprise since the trial was designed primarily to determine how to administer the drug not cure the disease. The trial also included patients with other types of leukemia, and the therapy produced a significant benefit in those with chronic lymphocytic leukemia although not as dramatic as the benefit to those with hairy cell leukemia. The most serious side effect was a decrease in platelet and red blood cell counts, associated with the clotting and breaking up of red blood cells in the kidney. After switching to a modified method of BL22 administration, this side effect was not detected in many patients treated later in the study.

The Immunotoxin therapy was developed in the NCI laboratory and is licensed to AlbaPharm, Inc. (Rockville, MD, USA). The company, in collaboration with the NCI scientists, is now planning a larger clinical trial of the immunotoxin. "We expected that some patients would respond to the treatment,” said Ira Pastan, M.D., a senior author on the paper. "But we didn't imagine in our wildest dreams that almost all of the patients would go into complete remission.”