Research to be Presented at the American Transplant Congress Examines the Role of Terminal Complement Inhibition in the Treatment of Kidney Transplantation Patients

Alexion Pharmaceuticals, Inc. (Nasdaq: ALXN) today announced that researchers are scheduled to present clinical and laboratory research on the role of terminal complement inhibition therapy in kidney transplantation patients at high risk for antibody-mediated rejection (AMR) at the American Transplant Congress, being held May 1 to 5, 2010, in San Diego. This research includes interim results from an investigator-initiated study of Soliris® (eculizumab) for the prevention of AMR in kidney transplantation patients.

Abstracts listed below can be accessed at: http://www.abstracts2view.com/atc/index.php.

Abstract #1 will be presented during a plenary session on Sun., May 2 at 8:30 a.m.:

• “Terminal Complement Inhibition Decreases Early Acute Humoral Rejection in Sensitized Renal Transplant Recipients,” Dr. Mark D. Stegall, et al.

Abstract #1510 will be presented during a poster session on Mon., May 3 from 5:30 – 6:30 p.m.:

• “Renal Transplantation in a Patient with Catastrophic Antiphospholipid Antibody Syndrome (CAPS),” Dr. Bonnie E. Lonze, et al.

Abstract #1509 will be presented during a poster session on Mon., May 3 from 5:30 – 6:30 p.m.:

• “New Therapies and Nontraditional Modalities Can Be Combined To Salvage Sensitized Patients with Exhausted Venous Access,” Dr. Bonnie E. Lonze, et al.

Abstract #288 will be presented during a concurrent session on Mon., May 3 at 5:00 p.m.

• “Chronic Humoral Rejection Despite C5 Inhibition after Positive-Crossmatch Kidney Transplantation (+XMKTx),” Dr. Lynn D. Cornell, et al.

Abstract #LB15 will be presented during a poster session on Tues., May 4 from 5:30 – 6:30 p.m.:

• “Complement Inhibitors for Treatment of Antibody-Mediated Renal Allograft Injury,” Dr. Bonnie E. Lonze, et al.

About Soliris

Soliris is not approved for the treatment of antibody-mediated rejection (AMR) in kidney transplantation patients and is being provided to patients in clinical studies on an investigational basis. Soliris is a first-in-class terminal complement inhibitor developed from the laboratory through regulatory approval by Alexion. Soliris has been approved in the United States, European Union, Japan and other countries as the first treatment for patients with paroxysmal nocturnal hemoglobinuria (PNH), an ultra-rare, debilitating and life-threatening blood disorder defined by chronic hemolysis, or the destruction of red blood cells. Prior to these approvals, there were no therapies specifically available for the treatment of patients with PNH. Alexion's innovative approach to complement inhibition has received some of the pharmaceutical industry's highest honors: the 2008 Prix Galien USA Award for Best Biotechnology Product with broad implications for future biomedical research and the 2009 Prix Galien France Award in the category of Drugs for Rare Diseases. More information on Soliris is available at www.soliris.net.

Important Safety Information

Soliris is generally well tolerated in patients with PNH. The most frequent adverse events observed in clinical studies of patients with PNH were headache, nasopharyngitis (runny nose), back pain and nausea. Treatment with Soliris should not alter anticoagulant management because the effect of withdrawal of anticoagulant therapy during Soliris treatment has not been established.

The U.S. product label for Soliris also includes a boxed warning: "Soliris increases the risk of meningococcal infections. Meningococcal infection may become rapidly life-threatening or fatal if not recognized and treated early. Vaccinate patients with a meningococcal vaccine at least two weeks prior to receiving the first dose of Soliris; revaccinate according to current medical guidelines for vaccine use. Monitor patients for early signs of meningococcal infections, evaluate immediately if infection is suspected, and treat with antibiotics if necessary." During PNH clinical studies, two out of 196 vaccinated PNH patients treated with Soliris experienced a serious meningococcal infection. Prior to beginning Soliris therapy, all patients and their prescribing physicians are encouraged to enroll in the PNH Registry, which is part of a special risk-management program that involves initial and continuing education and long-term monitoring for detection of new safety findings.

About Alexion

Alexion Pharmaceuticals, Inc. is a biopharmaceutical company working to develop and deliver life-changing drug therapies for patients with serious and life-threatening medical conditions. Alexion is engaged in the discovery, development and commercialization of therapeutic products aimed at treating patients with a wide array of severe disease states, including hematologic and kidney diseases, transplant, other inflammatory disorders, and cancer. Soliris is Alexion's first marketed product. Alexion is evaluating other potential indications for Soliris as well as other formulations of eculizumab for additional clinical indications, and is pursuing development of other antibody product candidates in early stages of development. This press release and further information about Alexion Pharmaceuticals, Inc. can be found at: www.alexionpharma.com.

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Safe Harbor Statement

This news release contains forward-looking statements, including statements related to anticipated clinical development milestones and potential health and medical benefits of Soliris (eculizumab) for the potential treatment of patients with antibody mediated rejection (AMR) of transplant organs. Forward-looking statements are subject to factors that may cause Alexion's results and plans to differ from those expected, including for example, decisions of regulatory authorities regarding marketing approval or material limitations on the marketing of Soliris for its current or potential new indications, delays in arranging satisfactory manufacturing capability and establishing commercial infrastructure, the possibility that results of published reports or clinical trials are not predictive of safety and efficacy results of Soliris in broader patient populations, the risk that clinical trials may not be completed successfully, the possibility that initial results of commercialization are not predictive of future rates of adoption of Soliris, the risk that third parties won't agree to license any necessary intellectual property to Alexion on reasonable terms or at all, the risk that third party payors will not reimburse for the use of Soliris at acceptable rates or at all, and a variety of other 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 period ended December 31, 2009, and in Alexion's other filings with the Securities and Exchange Commission. Alexion does not intend to update any of these forward-looking statements to reflect events or circumstances after the date hereof, except when a duty arises under law.