Disease caused by dengue viruses, dengue fever (DF), dengue hemorrhaghic fever (DHF) and dengue shock syndrome (DSS) is of enormous importance worldwide for indigenous populations and travelers, and increasing in many parts of the world, especially in the western hemisphere. Some 2.5 billion people live in areas of the world where the dengue virus is transmitted. Over 100 million dengue infections and at least 250,000 cases of DHF/or DSS occur annually. It has been estimated that Brazil spends more than $500 million annually to try to control dengue. Dengue is a CDC category A agent in regard to the NIAID Biodefense Research Agenda. It is a hemorrhagic flavivirus for which there is a high priority to develop a vaccine. There are 4 serotypes of the virus that cause disease, dengue 1, 2, 3, and 4. There is no dengue virus vaccine, in part due to the fact that most virologists believe that unless a vaccine induces protective immune responses against all 4 serotypes, there is high likelihood of the vaccine causing severe disease (DHF/DSS). Because of the impact of dengue worldwide, a dengue virus vaccine would have a large commercial market. Maxygen has used its Molecular BreedingTM directed evolution technology to produce chimeric antigens incorporating neutralizing antibody epitopes from all 4 dengue serotypes. Immunization of mice with a DNA vaccine expressing such a chimeric protein and a transiently expressed recombinant protein induce neutralizing antibodies against all 4 dengue serotypes and protection in the mice against lethal challenge. Cross-neutralizing antibodies were also induced in non-human primates, and immunization of non-human primates elicits neutralizing antibodies. To date, DNA vaccines have not elicited significant levels of antibodies in humans, while recombinant proteins in adjuvants, and DNA prime-recombinant protein boosting strategies elicit excellent antibody responses in humans. In this project we will generate recombinant proteins and recombinant viral like particles (VLPs) based on four selected chimeric genes. These products will be assessed for capacity to induce neutralizing antibodies against all 4 dengue serotypes in mice and non-human primates. Our long-term goal of commercializing a dengue vaccine is enhanced by this collaboration among Protein Potential (recombinant protein development expertise), Maxygen (chimeric construct), and the Naval Medical Research Center (antibody and protection assessments in mice and monkeys, and eventually humans). Solving the problem of inducing neutralizing antibodies against four distinct dengue proteins using the same single recombinant protein has the potential for opening an exciting new approach to multi-valent vaccine development.
