Protein Design Labs Inc. announced Tuesday that its "fullyhumanized" anti-Tac antibody has not elicited a HAMA (humananti-mouse antibody) response in any of the 17 patientsenrolled in Phase I safety trials at the Fred Hutchinson CancerCenter in Seattle.

Reporting at the 34th Annual Meeting of the American Societyof Hematology in Anaheim, Calif., Fred Hutchinson investigatorClaudio Anasetti said, "No patient developed a measurableantibody response to humanized anti-Tac." Moreover, patientsshowed no appreciable side effects from the treatment, whichconsisted of a single dose escalated from 0.5 to 1.5 milligramsper kilogram per patient over a two-hour period. And "themolecule has a long half-life (28 days) after intravenousinjection," Anasetti said.

PDL's "fully humanized" antibodies are actually 90-95 percenthuman sequences, according to Laurence Korn, president andchief executive officer of the Mountain View, Calif., company.The antibodies retain the hypervariable loops(complementarity-determining regions) of the mouse version,"plus a few extra (mouse) amino acids in the frameworkportion of the variable region," Korn told BioWorld.

The proof-of-principle -- that patients raised no antibodiesagainst PDL's "fully humanized" antibody -- is important initself, Korn told BioWorld. But so is the fact that the patientsdidn't exhibit a human anti-human antibody (HAHA) response,he said.

The patients in this group had steroid-resistant acute graft-vs.-host-disease. PDL's SMART anti-Tac antibody is beingdeveloped for preventing and treating organ transplantrejection. Hoffmann-La Roche is conducting the clinical trialsand has exclusive worldwide rights to manufacturing andmarketing the antibody product.

A parallel Phase I safety trial examining single doses of thesame anti-Tac antibody for treatment of certain blood cancersbegan simultaneously at the National Institutes of Health, ledby Thomas Waldmann, chief of the metabolism branch.

Protein Design Labs' stock (NASDAQ:PDLI) dropped 75 cents ashare on Tuesday to $12.63.

-- Jennifer Van Brunt Senior Editor

(c) 1997 American Health Consultants. All rights reserved.