SAN DIEGO, March 5, 2012 (GLOBE NEWSWIRE) -- Vical Incorporated (Nasdaq:VICL - News) today announced that the Naval Medical Research Center (NMRC) has initiated a Phase 1 human clinical trial of a tetravalent dengue DNA vaccine formulated with the company's Vaxfectin(R) adjuvant. The trial is based on exciting efficacy data from a nonhuman primate study recently published in the journal Vaccine1. Vical manufactured the vaccine and the adjuvant for both the preclinical and clinical studies, and is providing regulatory and clinical expertise to NMRC for the dengue program.

Vical completed three prior Phase 1 trials, with no safety issues and no dose-limiting toxicity, of Vaxfectin(R)-formulated DNA vaccines against H5N1 and H1N1 pandemic influenza.

Under a prior Collaborative Research and Development Agreement (CRADA) with Vical, NMRC developed a tetravalent DNA vaccine (TVDV) containing genes encoding the pre-membrane (prM) and envelope (E) proteins for all four serotypes of dengue virus, and formulated with Vical's Vaxfectin(R) adjuvant. Both Vaxfectin(R)-formulated and unformulated vaccines are now being evaluated in Phase 1 human testing. A total of 40 subjects will be assigned to three dose groups: a low dose TVDV without adjuvant, a low dose TVDV with Vaxfectin(R) adjuvant, or a high dose TVDV with Vaxfectin(R) adjuvant. Vaccines will be administered by intramuscular injections on days 0, 30 and 90, with follow-up through approximately one year. Key endpoints in the trial will be safety and immunogenicity.

The recently published preclinical TVDV immunogenicity and challenge data indicated that Vaxfectin(R) significantly improved neutralizing antibody responses and significantly enhanced protection against challenge. Nonhuman primates received the tetravalent DNA vaccine, formulated with or without the Vaxfectin(R) adjuvant, or a blank DNA control, on days 0, 28, and 84. All four (100%) rhesus macaques receiving the Vaxfectin(R)-formulated vaccine developed neutralizing antibodies to all four serotypes of dengue by one month after the second injection, compared with none of the four (0%) macaques receiving the unformulated vaccine and none of the three (0%) unvaccinated control animals. By one month after the third injection, all (100%) macaques in both vaccine groups (Vaxfectin(R)-formulated and unformulated) developed neutralizing antibodies to all four serotypes of dengue, compared with none (0%) of the unvaccinated control animals.

Macaques receiving the Vaxfectin(R)-formulated vaccine were highly protected against challenge with DEN-2, exhibiting very limited viremia (group mean 0.75 days). Macaques receiving unformulated vaccine were only partially protected against challenge (group mean 2.00 days). Unvaccinated control macaques were unprotected against challenge, exhibiting typical viremia (group mean 3.33 days).

About Dengue

According to the World Health Organization (WHO), up to 2.5 billion people across the world are at risk for dengue infections. Dengue virus infects up to 100 million and results in over 500,000 hospitalizations and 12,500 deaths each year. Its impact is magnified by the lack of effective antiviral drugs and vaccines.

Dengue fever can be caused by any one of four serotypes of dengue virus: DEN-1, DEN-2, DEN-3 and DEN-4. These viruses are part of the Flavivirus family, which includes West Nile virus and yellow fever virus. Dengue virus is spread by mosquitoes, and is most common during the rainy seasons throughout the world's tropical and subtropical regions. Dengue does not spread directly from person to person. An individual infected by one serotype of dengue virus develops lifelong immunity against that serotype, but not against other serotypes.

Symptoms of classic dengue fever include high fever, severe headache and/or pain behind the eyes, severe joint and muscle pain, nausea and vomiting. A few days after fever onset, a rash often develops over most of the body and lasts for one to two days. The rash can reappear several days later. These symptoms typically begin within a week after infection, and usually resolve without treatment.

Dengue hemorrhagic fever is a more serious form of disease which can include all of the symptoms of classic dengue fever plus leakage of blood plasma into tissues caused by noticeable damage to blood vessels and lymph vessels, bleeding from the nose and gums, and conspicuous bruising under the skin. Dengue hemorrhagic fever can lead to death. The most severe form of dengue disease is dengue shock syndrome, which includes all of the symptoms of classic dengue and dengue hemorrhagic fever, plus massive leaking of blood plasma outside of blood vessels, extensive bleeding, and shock caused by extremely low blood pressure. Dengue shock syndrome most often occurs in children infected for a second time (with a different serotype of dengue), and can be fatal.

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U.S. Navy Advances Dengue DNA Vaccine Using Vical's Vaxfectin(R) Adjuvant