AVANT's Partner, GlaxoSmithKline, Begins Global Launch of Rotarix in Mexico.

NEEDHAM, Mass. -- AVANT Immunotherapeutics (Nasdaq: AVAN) today announced that its partner, GlaxoSmithKline (GSK), has launched Rotarix(R) in Mexico, representing the first step in a series of global product launches. GSK plans to launch Rotarix(R) in additional Latin American countries as well as Asia Pacific countries during the course of 2005.

"We are very pleased to see the start of this global launch of Rotarix(R), which will mean increasing royalty revenues to AVANT over the next several years," said Una S. Ryan, Ph.D., AVANT President and Chief Executive Officer. "GSK is implementing a novel and unique global strategy to develop and deliver vaccines such as Rotarix(R) first to those with the greatest medical need." She noted that GSK has already filed for market approval in more than 20 countries worldwide.

"GSK has a solid track record of providing vaccines globally for more than 20 years and is constantly developing novel and unique approaches to ensure new vaccines get to those areas of the world who need them most as fast as possible," said Jean Stephenne, President and General Manager of GSK Biologicals. "In the case of Rotarix(R), we focused our clinical and regulatory strategy first on countries where the medical need for a rotavirus vaccine was amongst one of the highest in the world." Rotarix(R) obtained licensure in July 2004 from the Mexican regulatory authorities.

Rotarix(R) is an oral, two-dose, live attenuated vaccine against rotavirus disease in infants that was licensed in 1997 by AVANT Immunotherapeutics to GSK for worldwide commercialization. Dr. Richard Ward originally developed the vaccine at Cincinnati Children's Hospital Medical Center.

Rotavirus infection is the leading cause of severe diarrhea and vomiting in infants and young children between 3-24 months worldwide. Rotarix(R) is designed to provide broad protection against multiple rotavirus strains and to provide early protection before the onset of rotavirus illness. The vaccine works by stimulating the body to mimic the immune response to natural rotavirus infection, which protects against the subsequent development of moderate to severe rotavirus disease.

More than 70,000 infants have been enrolled in the global clinical development program, with studies conducted in Europe, the US, Latin America and Asia to evaluate the safety and efficacy of Rotarix(R). These studies demonstrate that Rotarix(R) is an effective, safe and well-tolerated vaccine.

About GlaxoSmithKline Biologicals

GlaxoSmithKline Biologicals (GSK Biologicals), one of the world's leading vaccine manufacturers, is located in Rixensart, Belgium, which is the centre of all GlaxoSmithKline's activities in the field of vaccine research, development and production. GSK Biologicals employs more than 1000 research scientists, who are devoted to discovering new vaccines and developing more cost-effective and convenient combination products to prevent infections that cause serious medical problems worldwide.

About AVANT Immunotherapeutics, Inc.

AVANT Immunotherapeutics, Inc. discovers, develops and sells innovative vaccines and therapeutics that harness the human immune system to prevent and treat disease. The company has developed a broad, well-staged pipeline of vaccines and therapeutics for large, high-value, under-served markets. Three of AVANT's products are marketed, including two food safety vaccines and an oral human rotavirus vaccine, which gained its first marketing approval in Mexico in July 2004. Six of AVANT's products are in clinical development, including a treatment to reduce complement-mediated tissue damage associated with cardiac bypass surgery and a novel vaccine for cholesterol management. AVANT has also assembled a technology platform that enables the creation of rapid-protecting, single-dose, oral vaccines that remain stable without refrigeration. The company is developing applications of this vaccine technology in four areas: biodefense, travelers' vaccines, global health needs, and human food safety. Further, AVANT has established a state-of-the-art vaccine manufacturing facility for the implementation of its VitriLife(R) technology and the production of its own vaccines and other companies' products. AVANT's goal is to demonstrate proof-of-concept for its products before leveraging further development through both traditional pharmaceutical partnerships and collaborations with governmental and other organizations.

Additional information on AVANT Immunotherapeutics, Inc. can be obtained through our site on the World Wide Web: http://www.avantimmune.com.

Safe Harbor Statement Under the Private Securities Litigation Reform Act of 1995: This release includes forward-looking statements which reflect AVANT's current views with respect to future events and financial performance. These forward-looking statements are based on management's beliefs and assumptions and information currently available. The words "believe", "expect", "anticipate", "intend", "estimate", "project" and similar expressions which do not relate solely to historical matters identify forward-looking statements. Investors should be cautious in relying on forward-looking statements because they are subject to a variety of risks, uncertainties, and other factors that could cause actual results to differ materially from those expressed in any such forward-looking statements. These factors include, but are not limited to: (1) the integration of multiple technologies and programs; (2) the ability to adapt AVANT's vectoring systems to develop new, safe and effective orally administered vaccines against anthrax and plague or other bioterrorism threats or emerging health care threats; (3) the ability to successfully complete development and commercialization of TP10, CETi-1, CholeraGarde(R) (Peru-15), Ty800 and other products; (4) the cost, timing, scope and results of ongoing safety and efficacy trials of TP10, CETi-1, CholeraGarde(R) (Peru-15), Ty800 and other preclinical and clinical testing; (5) the ability to successfully complete product research and further development, including animal, pre-clinical and clinical studies of TP10, CETi-1, CholeraGarde(R) (Peru-15), Ty800and other products; (6) the ability of the Company to manage multiple late stage clinical trials for a variety of product candidates; (7) the volume and profitability of product sales of Megan(R)Vac 1, Megan(R)Egg and other future products; (8) the process of obtaining regulatory approval for the sale of Rotarix(R) in major commercial markets, as well as the timing and success of worldwide commercialization of Rotarix(R) by our partner, GlaxoSmithKline; (9) changes in existing and potential relationships with corporate collaborators; (10) the availability, cost, delivery and quality of clinical and commercial grade materials supplied by contract manufacturers; (11) the timing, cost and uncertainty of obtaining regulatory approvals to use TP10, CETi-1, CholeraGarde(R) (Peru-15) and Ty800, among other purposes, for adults undergoing cardiac surgery, to raise serum HDL cholesterol levels and to protect travelers and people in endemic regions from diarrhea causing diseases, respectively; (12) the ability to obtain substantial additional funding; (13) the ability to develop and commercialize products before competitors; (14) the ability to retain certain members of management; and (15) other factors detailed from time to time in filings with the Securities and Exchange Commission. We expressly disclaim any responsibility to update forward-looking statements.