News Release

Alexion's 5G1.1 drug reduces clinical signs and symptoms of rheumatoid arthritis in completed trial

Peer-Reviewed Publication

Noonan/Russo Communications

Results Presented at 63rd Annual Meeting of the American College of Rheumatology

BOSTON, MA, November 15, 1999 -- Alexion Pharmaceuticals, Inc. (Nasdaq: ALXN) reported yesterday that rheumatoid arthritis patients receiving a single dose of its anti-inflammatory complement inhibitor 5G1.1 showed a significant reduction in the signs and symptoms of the often painful joint condition as compared to placebo-treated patients.

The completed clinical trial examined the safety and biologic activity of 5G1.1 in 42 patients with mild to moderate rheumatoid arthritis, each of whom received a single dose of the drug. The company presented data at the 63rd annual American College of Rheumatology (ACR) meeting demonstrating that 50% of the patients (n=6) who received a single 8 mg/kg dose achieved an ACR20 score, as compared to 10% of the patients (n=10) treated with placebo (P=.07). ACR20 score means that a patient had a 20% improvement in tender and swollen joint count plus 20% improvement in at least 3 of 5 of the following criteria: patient pain assessment, physician global assessment, patient global assessment, patient self-assessed disability and acute phase reactant. It was previously reported in April 1999 that the single 8 mg/kg dose resulted in a 30% decrease (P<.05) in the levels of the acute phase reactant C-reactive protein, an objective measure of disease activity.

"The study's results demonstrate that rheumatoid arthritis patients who received a single dose of Alexion's anti-inflammatory C5 Complement Inhibitor drug, 5G1.1, felt less pain and were better able to function than those patients receiving placebo," said Dr. Leonard Bell, President and Chief Executive Officer of Alexion. "Further, the clinical measurement in the current study, ACR20 score, which is the same endpoint of our ongoing Phase II safety and efficacy trial with 5G1.1, was met."

The report, entitled "A Single Dose, Placebo Controlled, Double Blind, Phase I Study of the Humanized Anti-C5 Antibody h5G1.1 in Patients with Rheumatoid Arthritis," is based on a clinical trial conducted by investigators at North Shore Hospital, Gainesville Clinical Research Center and University of Alabama in collaboration with Alexion. Dr. Christopher Mojcik, a clinical rheumatologist and Senior Director of Clinical Development at Alexion, presented the clinical data.

"In follow-up to this initial single dose 5G1.1 trial in rheumatoid arthritis patients, we are currently enrolling up to 200 patients in a Phase II efficacy trial employing multiple doses of 5G1.1 in rheumatoid arthritis patients," commented Dr. Mojcik. "We are examining the safety and efficacy of multiple doses of 5G1.1 with the primary efficacy endpoint as the ACR20 score."

It is estimated that more than two million patients are affected by rheumatoid arthritis, a disease in which the immune system attacks multiple joints as well as the whole body. This chronic immune attack frequently involves multiple organs in the body leading to the onset of fatigue, severe joint destruction, pain and disfigurement.

Dr. Jacques Caldwell of Gainesville Clinical Research Center, a principal investigator in the completed trial and ongoing Phase II trial, commented, "In my experience, inhibition of the complement pathway is a unique approach to treating rheumatoid arthritis. Hopefully, these early results will be confirmed by the ongoing studies in a larger patient cohort."

Alexion's C5 complement inhibitors are designed to selectively block the production of inflammation-causing proteins in a process of the human immune system known as the complement cascade. Alexion believes that selective suppression of this immune response will provide a significant therapeutic advantage relative to existing therapies. Because of the generally beneficial effects of the components of the complement cascade prior to C5 and the greater inflammatory disease-promoting effects of the cleavage products of C5, the Company has identified C5 as a potentially effective anti-inflammatory drug target. The first two C5 Inhibitors, 5G1.1 and 5G1.1-SC, specifically and tightly bind to C5 blocking its cleavage into harmful byproducts and are designed to inhibit subsequent damage from the inflammatory process. 5G1.1 is currently being tested in Phase II safety and efficacy trials in rheumatoid arthritis and membranous nephritis patients.

Alexion Pharmaceuticals, Inc. is engaged in the development of products for the treatment of cardiovascular, autoimmune and neurologic disorders caused by the undesired effects of the human immune system. The Company is developing C5 Complement Inhibitors and Apogen T-Cell Therapeutics which together target severe cardiovascular and autoimmune disorders and xenograft cells for cell replacement therapy.

This news release contains forward-looking statements. Such statements are subject to certain factors which may cause Alexion's plans to differ or results to vary from those expected including unexpected pre-clinical or clinical results, the need for additional research and testing, delays in manufacturing, access to capital and funding, delays and adverse changes in development of commercial relationships and a variety of risks set forth from time to time in Alexion's filings with the Securities and Exchange Commission, including but not limited to the risks discussed in Alexion's Annual Report on Form 10-K for the year ended July 31, 1999. Alexion undertakes no obligation to publicly release results of any of these forward-looking statements which may be made to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

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Editor's Note:

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