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PDL HUMANIZED ANTIBODY FOR MYELOID LEUKEMIA IS SAFE AND CAUSES NO IMMUNE RESPONSE IN PHASE I TRIAL

 MOUNTAIN VIEW, Calif., March 29 /PRNewswire/ -- Protein Design Labs, Inc. (PDL) (NASDAQ: PDLI) today reported that none of eight patients evaluated in a multiple-dose, Phase I clinical trial for relapsed acute myeloid leukemia showed an antibody response against its humanized SMART(TM) M195 Antibody.
 David A. Scheinberg, M.D., Ph.D., chief of the Leukemia Service at Memorial Sloan-Kettering Cancer Center and principal investigator in the trial, presented preliminary results of the study Saturday at a conference on leukemia at the University of Texas M.D. Anderson Cancer Center in Houston.
 Chemotherapy often induces remissions in patients with acute myeloid or myelogenous leukemia (AML), but most patients relapse. Twelve patients with relapsed AML have been treated in the Sloan-Kettering study at four dose levels; evaluation of the last four patients is continuing. The study was designed to assess safety, biodistribution, and any human anti-mouse antibody (HAMA) or human anti-human antibody (HAHA) immune response to the SMART Antibody, which combines the binding site of a mouse antibody with 90 percent of a human antibody.
 Each patient received multiple doses, generally six, of SMART M195 over a three-week period. The first dose was trace labeled with radioactive iodine to determine biodistribution. The antibody rapidly localized to the sites of disease in all studied patients.
 Observable side effects were limited to fever, chills, or shortness of breath seen in three of the twelve patients shortly after the infusion.
 These infusion-related symptoms spontaneously resolved or were easily reversed with an antihistamine.
 Also at the M.D. Anderson conference, Dr. Scheinberg presented preliminary results of two ongoing Phase II trials of the mouse M195 antibody labeled with radioactive iodine.
 In one study, patients wit relapsed acute promyelocytic leukemia (APL), a form of AML, are being treated with labeled mouse M195 in combination with Tretinoin(TM) (trans-retinoic acid, tRA). tRA alone produced remissions in 11 patients with relapsed APL, but all patients relapsed within six months. Of the seven patients treated to date in combination therapy, only one relapsed within six months. Three in complete remission are too early to evaluate, and the outcome of this therapy cannot yet be determined.
 In the second study, AML patients who relapsed after or initially failed chemotherapy treatment (refractory) have been treated with radiolabeled mouse M195 prior to a bone marrow transplant. Without this treatment, such patients usually relapse after a bone marrow transplant. All six patients who have been treated to date went into complete remission after the bone marrow transplant, and five remain in complete remission. However, it is too early to know the duration of the remissions.
 PDL humanized the mouse M195 antibody because it causes a human anti-mouse antibody (HAMA) immune response in about half of patients after one to four doses. The encouraging results with the mouse antibody, and the preliminary data indicating good biodistribution and the absence of a HAMA response to the SMART M195 Antibody, suggest that SMART M195, possibly labeled with radioactive iodine, could be used in combination with other drugs to produce longer-lasting remissions in AML patients or prior to bone marrow transplantation. Safety and efficacy using radiolabeled SMART M195 will need to be established in additional clinical trials.
 PDL will announce its future clinical plans for SMART M195 after a complete evaluation of the Phase I trial. The trial is expected to be complete within 30 days.
 Results of early stage clinical trials may not be repeated in later stage trials. Evidence of efficacy and safety of an investigational drug must be demonstrated in larger, generally Phase III trials and still does not ensure regulatory approval.
 There are about 15,000 new cases of myeloid leukemia each year in the United States, and most are fatal within one to five years despite intensive therapy and multiple hospitalizations. The current cost of therapy is approximately $150,000 per patient.
 The SMART M195 Antibody was developed at PDL and studied in collaboration with Dr. Scheinberg and colleagues at Sloan-Kettering. PDL used its proprietary computer-based design technology to convert the mouse M195 antibody, which was developed at Sloan-Kettering, into the human-like SMART M195 Antibody. PDL has shown in laboratory experiments that SMART M195 binds and kills myeloid leukemia cells better than mouse M195.
 Protein Design Labs, founded in 1986 and with headquarters in Mountain View, Calif., is engaged in the computer-based design and manufacturing of antibodies and other novel proteins to treat autoimmune and inflammatory disease, viral infections, cancers, and other conditions.
 -0- 3/29/93
 /CONTACT: Peter Dworkin, director of corporate communications, of Protein Design Labs, Inc., 415-903-3721/


CO: Protein Design Labs, Inc. ST: California IN: MTC SU: PDT

TM-LD -- SJM005 -- 0291 03/29/93 07:00 EST
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