Cytel discovers potent immunostimulant for use in vaccine development.

SAN DIEGO--(BUSINESS WIRE)--April 16, 1997--Cytel Corporation (NASDAQ: CYTL) today announced the discovery of a potent universal immunostimulant, known as PADRE (TM), that could enable the development of synthetic vaccines. In a scientific paper published recently in the journal "Vaccine," Cytel scientists and their collaborators showed that immune responses stimulated with the PADRE synthetic vaccine exhibited hallmarks of protective immunity, with high titers of antibody consisting mainly of IgG which persist longer than twelve months. Based on these results and other work at Cytel, the Company believes the use of its PADRE technology may enable the development of synthetic vaccines that are highly immunogenic, straightforward to manufacture and well characterized.

Cytel recently announced that it is restructuring operations and spinning off its vaccine program to form a new company that will be independently managed and financed. "PADRE is one of the assets that will be transferred to the new vaccine company when it is formed," said Virgil Thompson, Cytel's President and Chief Executive Officer. "We believe there are significant opportunities to use PADRE in the development of synthetic therapeutic and prophylactic vaccines."

The "Vaccine" paper is entitled "Potent Immunogenic Short Linear Peptide Constructs Composed of B Cell Epitopes and Pan DR T Helper Epitopes (PADRE) for Antibody Responses in vivo." "We have shown that a monovalent construct using PADRE effectively induces a long-lived IgG antibody response," said senior author Dr. Alessandro Sette, Director of Immunology at Cytel. "The response is as potent as that generated using larger, complex constructs, but PADRE is easier to manufacture and it does not induce an antibody response to the PADRE which would inhibit its function."

Prophylactic vaccines in use today consist of killed or disabled microbes, or "subunit" vaccines containing whole proteins isolated from infectious organisms or recombinant sources. These types of vaccines stimulate protective antibody responses, but are complex to make and sometimes have side effects that limit their use. Synthetic peptide vaccines, which use chemically-synthesized pieces of proteins, offer advantages over subunit or killed microbe vaccines in that they are well-defined chemical entities which are easy to manufacture and characterize, and they present no pathogen contamination concerns.

While synthetic vaccines offer many potential advantages, their use has been limited by their inability to elicit appropriate antibody responses. Linking the antigens to immunogenic proteins, such as KLH, or making large, cross-linked peptide constructs can increase the immunogenicity of a synthetic antigen. However, these approaches present other problems, including manufacturing difficulties and loss of effectiveness associated with repeated use of the same carrier. As reported in the "Vaccine" paper, the problems with synthetic vaccines can be greatly diminished by using the PADRE construct: PADRE effectively induces a long-lived IgG antibody response; manufacturing the PADRE construct is straightforward; there is no carrier-suppression effect since PADRE alone does not induce an anti-PADRE antibody response.

Cytel Corporation is a leader in the discovery and development of cell adhesion inhibitors for treatment of acute and chronic inflammation, and its Glytec (TM) unit is a leader in the manufacture of bioactive carbohydrates for use in medical and consumer products. The company is in the process of restructuring its operations and spinning off its vaccine program to form a new company. The newly formed vaccine company will focus on the discovery of novel vaccines for the treatment and prevention of cancer and infectious diseases.

Actual results may differ materially from the above forward-looking statements due to a number of important factors, including but not limited to the risks associated with the timing and cost of conducting human clinical trials, the regulatory approval process and the possibility that testing may reveal undesirable and unintended side effects or other characteristics that may prevent or limit the commercial use of proposed products. These factors are more fully discussed in Cytel's most recent Form 10-K.

CONTACT: Cytel Corporation, San Diego

Deborah A. Schueren

Vice President, Chief Financial Officer

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