AVANT Immunotherapeutics, Inc. and Celldex Therapeutics, Inc. Announce Merger Agreement

Creates NASDAQ-listed biopharmaceutical company with diversified pipeline addressing high-value indications within oncology, infectious and inflammatory diseases

Conference Call Scheduled for October Monday, October 22, 2007 at 9:00 AM EDT

NEEDHAM, Mass. & PHILLIPSBURG, N.J.--(BUSINESS WIRE)--AVANT Immunotherapeutics, Inc. (NASDAQ: AVAN) and Celldex Therapeutics, Inc., a privately-held company, announced today the signing of a definitive merger agreement. The merger creates a NASDAQ-listed, fully-integrated and diversified biopharmaceutical company with a deep pipeline of product candidates addressing high-value indications including oncology and infectious and inflammatory diseases. The all-stock transaction, approved by both companies’ Boards of Directors, will combine the two companies under the name AVANT, and is currently expected to close in the first quarter of 2008. Celldex and AVANT shareholders will own 58% and 42% of the combined company on a fully diluted basis, respectively. Closing of the merger is contingent upon a vote of approval by AVANT’s current shareholders at a special meeting of shareholders expected to take place in the first quarter of 2008.

“This proposed merger of AVANT and Celldex builds a fully-integrated, late-stage biopharmaceutical company addressing a broad spectrum of serious diseases in significant markets”

The combination of AVANT and Celldex results in a substantial pipeline of product development candidates and technology platforms focused on harnessing the human immune system, including monoclonal antibodies and vaccines. In 2008, the combined company will have three compounds in mid- to late-stage clinical development and six additional candidates in earlier-stage development. The pipeline will be fueled internally through the identification of new candidates based on Celldex’s proprietary APC Targeting Technology^™, which utilizes human monoclonal antibody (mAb) technology to directly target the immune system and AVANT’s innovative vector vaccine delivery, manufacturing and preservation technologies. The combined company expects to announce several upcoming milestones during 2008 related to these product candidates, including the following:

• Phase 2b data on CDX-110 in glioblastoma multiforme (GBM), one of the most aggressive forms of brain cancer
• Phase 2 data on infectious disease candidate Ty800 for protection against Salmonella typhi, the cause of typhoid fever
• Phase 1 data on CDX-1307 in colorectal, pancreatic, bladder and breast cancers
• Initiation of multiple Phase 1 trials for oncology, infectious and inflammatory disease treatment candidates
• Initiation of additional novel therapeutic mAb programs

“This proposed merger of AVANT and Celldex builds a fully-integrated, late-stage biopharmaceutical company addressing a broad spectrum of serious diseases in significant markets,” said Dr. Una Ryan, President and CEO of AVANT. “Merging with Celldex adds value to our existing programs and results in a robust pipeline, including several later-stage product candidates with near-term catalysts in infectious diseases and oncology. The combined company will have multiple products advancing in tandem, mitigating risk and creating a strong, diversified company focused on clinical progress and value creation.”

“This transaction forms a publicly-traded company built on our mutual expertise in developing novel immunotherapy products and backed by a widely applicable technology platform based on human monoclonal antibodies,” said Charles Schaller, Chairman of Celldex. “Since Celldex was spun out of Medarex as an independent private company, we have successfully progressed our lead oncology program into a Phase 2/3 randomized study, and advanced our first APC Targeted program into two Phase 1 trials. The merger with AVANT brings together an exceptional management team with successful experience in all aspects of drug development. In addition, this transaction extends our cGMP manufacturing capabilities, which will provide greater efficiency and flexibility to advance our current and future product candidates.”

2008 Product Pipeline:

Later-stage product candidates include:

• CDX-110, a Phase 2/3 cancer immunotherapy targeting EGFRvIII, a functional variant of the epidermal growth factor (EGFR), in glioblastoma multiforme (brain cancer)
• CholeraGarde^®, a Phase 2 single-dose oral vaccine for protection against cholera
• Ty800, a Phase 2 single-dose oral vaccine for protection against Salmonella typhi, the cause of typhoid fever

Earlier-stage product candidates include:

• ETEC/Cholera, entering Phase 1 in 2008 as a single-dose oral vaccine for protection against enteric disease
• Two products based on APC Targeting Technology:
  • CDX-1307, a Phase 1 immunotherapy targeting the beta chain of human chorionic gonadotropin (βhCG) for colorectal, pancreatic, bladder and breast cancers
  • CDX-2401, an HIV prophylactic vaccine expected to enter Phase 1 in 2008 as part of our Bill & Melinda Gates Foundation funded collaboration with Rockefeller University
• Two preclinical candidates:
  • CDX-1401, which targets proprietary tumor target antigens for multiple solid tumors, including breast, colon, lung and prostate cancers
  • TP10, an anti-inflammatory product in development for wet and dry age-related macular degeneration (AMD), transplant or other inflammatory disease

The combined company also has a commercialized product, Rotarix^®, a novel, two-dose oral vaccine against rotavirus in collaboration with GlaxoSmithKline. Rotarix has been approved in over 90 different countries worldwide, including the European Union, and is currently under review by the U.S. Food and Drug Administration with a response expected in the second half of 2008. Upon the U.S. launch of Rotarix, the combined company will receive a $10 million milestone payment from Paul Royalty Fund.

Details of the Proposed Transaction

The estimated value of the combined company is approximately $115 million, based on the closing price of AVANT’s stock on October 19, 2007. AVANT will issue shares of AVANT common stock to Celldex stockholders such that Celldex stockholders will own approximately 58% of the combined company on a fully diluted basis and AVANT stockholders will own approximately 42% on a fully diluted basis. We will be instituting a reverse stock split to ensure our compliance with NASDAQ's listing requirements, the exact size of which is still being evaluated. The reverse stock split will be subject to a vote of approval from AVANT shareholders. The merger agreement has been approved by both Boards of Directors and requires approval by AVANT’s stockholders. AVANT expects to file a Form S-4 and related proxy statement with the U.S. Securities and Exchange Commission and any other necessary regulatory filings. Depending on the review process of the regulatory agencies, the companies currently expect the merger to close in the first quarter of 2008. Upon closing of the transaction, the combined company’s shares are expected to trade on the NASDAQ Capital Market under the symbol “AVAN.” AVANT was advised by Needham & Company, LLC and Goodwin Procter LLP, and Celldex was advised by Brean Murray, Carret & Co., LLC and Lowenstein Sandler PC.

Management and Organization

Following the closing, the combined company will have offices in Massachusetts and New Jersey, including manufacturing facilities in Fall River, MA. As a result, AVANT/Celldex will bring proprietary manufacturing of Celldex programs in-house for added cost-savings.

Executive management of the combined company will be as follows:

• Una Ryan, PhD: President and Chief Executive Officer; current President and Chief Executive Officer of AVANT
• Anthony Marucci: Executive Vice President, Corporate Development; current Vice President, Chief Financial Officer, Treasurer and Secretary of Celldex
• Chip Catlin: Senior Vice President and Chief Financial Officer; current Senior Vice President and Chief Financial Officer of AVANT
• Tibor Keler, PhD: Senior Vice President and Chief Scientific Officer; current Chief Scientific Officer, Vice President of Research and Discovery of Celldex
• Thomas Davis, MD: Senior Vice President and Chief Medical Officer; current Chief Medical Officer, Vice President of Clinical Development of Celldex
• Ronald Newbold, PhD: Senior Vice President, Business Development; current Vice President, Business Development of Celldex

The combined company’s Board of Directors will consist of four AVANT directors and four Celldex directors. The Chairman of the Board will be Charles Schaller, past Chairman of Medarex.

Conference Call Information

A joint conference call will be held on Monday, October 22 at 9:00 AM EDT to discuss the proposed merger agreement and the combined business and strategic overview of the merged companies. The conference call may be accessed by visiting www.avantimmune.com or www.celldextherapeutics.com. The webcast and telephonic replay will be available following the filing of the conference call transcript with the SEC.

Callers may also access the call with the following dial-in information:

Domestic phone number: 1-888-396-2384 Passcode: 20038122

International phone number: 1-617-847-8711 Passcode: 20038122

Callers may access the replay with the following dial-in information:

Domestic phone number: 1-888-286-8010 Passcode: 66818661

International phone number: 1-617-801-6888 Passcode: 66818661

About AVANT Immunotherapeutics, Inc.:

AVANT Immunotherapeutics, Inc. is a Massachusetts-based NASDAQ-listed company discovering and developing innovative vaccines and therapeutics that harness the human immune system to prevent and treat disease. AVANT’s innovative bacterial vector delivery technologies with unique manufacturing and preservation processes offer the potential for a new generation of vaccines. AVANT has three commercialized products, including Rotarix^® for the treatment of rotavirus and two human food safety vaccines for reducing salmonella infection in chickens and eggs. AVANT also has four product candidates in its development pipeline, an anti-inflammatory agent, TP10, and three candidates based on its oral, rapidly-protecting, single-dose and temperature-stable vaccine technology, including combination vaccines for travelers, the military and global health needs.

About Celldex Therapeutics, Inc.:

Celldex Therapeutics, Inc. is an innovative, privately-held New Jersey-based biopharmaceutical company—spun-out of Medarex, Inc. (NASDAQ: MEDX)—developing targeted immunotherapeutics for the treatment of cancer, infectious and inflammatory diseases. Celldex focuses on the use of tumor-specific targets and human monoclonal antibodies (mAbs) to precisely deliver therapeutic agents through its novel ‘targeted immunization’ approach. Celldex’s deep product pipeline consists of products in varying stages of development, with its lead candidate currently undergoing evaluation in a Phase 2/3 clinical trial in newly diagnosed glioblastoma multiforme, one of the most aggressive forms of brain cancer. Celldex is also running clinical trials for several products based on its proprietary APC Targeting Technology^™, which delivers fully human monoclonal antibodies directly to patients to target and stimulate dendritic cells and macrophages—key cells within the immune system.

Additional Information about the Merger and Where to Find It

This communication contains “forward-looking” statements within the meaning of the Private Securities Litigation Reform Act of 1995. These statements are typically preceded by words such as “believes,” “expects,” “anticipates,” “intends,” “will,” “may,” “should,” or similar expressions. These forward-looking statements are subject to risks and uncertainties that may cause actual future experience and results to differ materially from those discussed in these forward-looking statements. Important factors that might cause such a difference include, but are not limited to, costs related to the Merger, failure of AVANT’s stockholders to approve the Merger; AVANT’s or Celldex’s inability to satisfy the conditions of the Merger; AVANT’s inability to maintain its NASDAQ listing; the risk that AVANT’s and Celldex’s businesses will not be integrated successfully; the combined company’s inability to further identify, develop and achieve commercial success for new products and technologies; the possibility of delays in the research and development necessary to select drug development candidates and delays in clinical trials; the risk that clinical trials may not result in marketable products; the risk that the combined company may be unable to successfully secure regulatory approval of and market its drug candidates; the risks associated with reliance on outside financing to meet capital requirements; risks associated with Celldex’s new and uncertain technology; risks of the development of competing technologies; risks related to the combined company’s ability to protect its proprietary technologies; risks related to patent-infringement claims; risks of new, changing and competitive technologies and regulations in the U.S. and internationally; and other events and factors disclosed previously and from time to time in AVANT’s filings with the Securities and Exchange Commission, including AVANT’s Annual Report on Form 10-K for the year ended December 31, 2006. The companies do not undertake any obligation to release publicly any revisions to such forward-looking statements to reflect events or circumstances after the date hereof or to reflect the occurrence of unanticipated events.

This communication may be deemed to be solicitation material in respect of the proposed merger of AVANT and Celldex. In connection with the proposed merger, AVANT and Celldex intend to file relevant materials with the SEC, including AVANT’s joint registration statement/proxy statement on Form S-4. SHAREHOLDERS OF AVANT ARE URGED TO READ ALL RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING AVANT’S PROXY STATEMENT, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION. Investors and security holders will be able to obtain the documents free of charge at the SEC's web site, http://www.sec.gov, and AVANT shareholders will receive information at an appropriate time on how to obtain transaction-related documents for free from AVANT. Such documents are not currently available.

Participants in the Solicitation

The directors and executive officers of AVANT and Celldex may be deemed to be participants in the solicitation of proxies from the holders of AVANT common stock in respect of the proposed transaction. Information about the directors and executive officers of AVANT is set forth in the proxy statement for AVANT’s most recent 10-K, which was filed with the SEC on March 16, 2007. Investors may obtain additional information regarding the interest of AVANT and its directors and executive officers, and Celldex and its directors and executive officers in the proposed transaction by reading the proxy statement regarding the acquisition when it becomes available.