Epimmune scientists report positive pre-clinical data on vaccine designed to combat HIV's ability to mutate

Company on track to initiate clinical trials late this year or early 2002 of epitope-based vaccine for the prevention and treatment of HIV

Keystone, CO, April 2, 2001 - Epimmune Inc. (Nasdaq: EPMN) today announced positive pre-clinical data on its HIV vaccine that is designed to directly address the problem of viral mutation. At the Keystone Symposium: "AIDS Vaccines in the New Millennium" on March 30, 2001 in Keystone, Colorado, Company scientists reported that the vaccine stimulated multiple anti-HIV cytotoxic T-cell immune responses in animal models. Epimmune has begun manufacturing the vaccine for human testing and plans to initiate clinical trials late this year or early 2002 in both non-infected volunteers and in individuals infected with HIV.

The current standard HIV therapy for Americans is a three-drug anti-retroviral combination that costs approximately $15,000 per year. While anti-retroviral drugs are effective at suppressing HIV replication in infected individuals, they do not eliminate the infection and have toxic side effects that impede their long-term use. A vaccine that can provide both preventative and therapeutic benefits has great potential to help control the AIDS epidemic and curtail the costs and side effects of anti-retroviral therapies.

"A major challenge to the development of an effective AIDS vaccine is the ability of HIV to mutate. Epimmune�s vaccine is designed to directly address this problem," said Mark Newman, Ph.D., Vice President of the Infectious Disease Program at Epimmune. "One of the unique features of Epimmune�s vaccine is that it is composed of epitopes, or protein fragments, which are strategically selected from non-mutating regions of HIV. As a result, it is expected to be harder for the virus to develop variants that can escape the vaccine-induced immune response."

Strong cellular immunity is characteristic of long-term non-progressors or HIV-positive individuals who do not progress to AIDS for long periods even without anti-retroviral drug therapy. Epimmune�s approach to vaccine development is based on epitopes from non-mutating regions of multiple virus proteins that are specifically selected for their ability to stimulate two types of cellular immunity, cytotoxic T-cells (CTLs) and helper T-cells (HTLs). Together, CTLs and HTLs comprise the body�s natural defense against HIV in which CTLs are capable of directly destroying virus-infected cells but require HTLs, which produce immune-boosting chemicals, for proper functioning.

Epimmune has designed its vaccine to provide immunity against many HIV clades (HIV strains that are common to a certain geographical region), including those that are prevalent in the United States, Europe, Africa and India. The vaccine is also designed to provide broad population coverage regardless of ethnicity.

Epimmune�s vaccine will be delivered as DNA in combination with PVP, a polymer gene delivery technology licensed from Valentis, Inc. The PVP polymer has been shown to increase the efficiency of vaccine uptake by immune cells and enhance potency in animal studies. Epimmune has also linked its HIV vaccine with its proprietary PADRE� universal helper T-cell epitope. PADRE is an HTL booster which, when combined with CTL epitopes, enhances the magnitude and duration of the immune response. Finally, the vaccine construct has also been optimized to ensure that the epitopes are processed efficiently and correctly once inside the cell. The epitopes are placed in a specific order (like beads on a string) that allows cellular enzymes to recognize the appropriate places to liberate the epitopes from the chain, thus improving the efficiency and potency of the vaccine.

In August 2000, Epimmune was awarded a National Institutes of Health (NIH) grant from the Integrated Pre-clinical/Clinical Program (IPCP) of the National Institute of Allergy and Infectious Disease (NIAID), Division of AIDS, to advance epitope-based vaccines into clinical trials. The grant funds a four-year program designed to evaluate Epimmune�s epitope-based vaccines as a therapeutic strategy for the treatment of HIV-1 infected individuals on highly active anti-retroviral therapy (HAART). The program is closely associated with the NIAID clinical trials network and represents a collaborative effort between Epimmune and academic investigators from the University of Colorado Health Services Center and the University of Wisconsin Regional Primate Center.

Epimmune Inc. is a leader in using gene maps of cancer-associated proteins and infectious agents to design vaccines that induce cellular immunity. The Company�s extensive technology platform is based on its pioneering work in deciphering the genetic code which regulates T-cell activation and identifying antigen fragments known as epitopes which can activate highly targeted T-cell responses to tumors, viruses, bacteria and parasites. This new field of pharmacology opens two significant areas of pharmaceutical development: protective vaccines that activate T-cell protection against infections, such as HIV and hepatitis C, and therapeutic vaccines designed to stimulate antigen-specific T-cell responses to infections, such as HIV, hepatitis C and hepatitis B, and tumors such as breast, colon, lung and prostate. For more information on Epimmune, visit www.epimmune.com.

This press release includes forward-looking statements that reflect management's current views of future events, including the utility of the Company�s technology, the anticipated benefits of HIV vaccine being developed by the Company and the timing for commencement of clinical trials of the HIV vaccine. 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 Company's ability to develop vaccines using epitopes, the ability of epitope-based vaccines to control HIV, the safety and efficacy of epitope-based vaccines in humans, the Company�s ability to enter into and maintain new collaborations, achievement of research and development objectives by the Company and any collaborator, 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 the Company�s 2000 Form 10-K, the most recent 10-Qs and other periodic reports filed with the Securities and Exchange Commission.