Dengue fever and its more severe forms, Dengue hemorrhagic fever and Dengue shock syndrome, are the most prevalent vector-born viral diseases in humans. Dengue virus is typically found in tropical and subtropical regions. Over the course of the past fifty years, the Dengue virus has spread to more areas of the world and is now prevalent in over one hundred countries, including some parts of the United States. The World Health Organization (WHO) estimates that approximately 40% of the world's population, i.e., over 2.5 billion people, lives in areas at risk of Dengue infection, resulting in 100 million cases of Dengue fever and 500,000 cases of Dengue hemorrhagic fever annually. In addition to the residents of these countries, especially those who live in poverty, travelers and military personnel are at risk of exposure. A growing population, along with an increase in global travel and urbanization, suggest that infection rates will continue to rise (see, e.g., Guha-Sapir and Schimmer, Emerging Themes in Epidemiology, 2: 1-10 (2005)).
The Dengue virus is transmitted to humans by the bite of an Aedes aegypti mosquito. Human infections range from asymptomatic to the life-threatening Dengue hemorrhagic fever and Dengue shock syndrome. Dengue fever is an influenza-like disease, frequently resulting in high fever, headache, rash, abdominal pain, and myalgia after an incubation period of four to seven days. In addition to the Dengue fever symptoms, Dengue hemorrhagic fever and Dengue shock syndrome can result in thrombocytopenia, plasma leakage, bleeding, and hypovolemic shock, resulting in shock and eventual death.
Dengue viruses are members of the genus Flavivirus and the family Flaviviridae. The Dengue virus consists of four different serotypes, DV1, DV2, DV3, and DV4. Although infection with one serotype typically confers future protective immunity with respect to that serotype, it does not confer long term immunity to any of the other three serotypes. In addition, prior immunity to one serotype of the Dengue virus may increase the severity of symptoms upon infection of a different serotype of the virus, thus increasing the likelihood that the subject will develop the more severe Dengue hemorrhagic fever or Dengue shock syndrome (see, e.g., Mota and Rico-Hesse, J. Virol., 83(17): 8638-8645 (2009); and Appanna et al., Clinical and Vaccine Immunology, 14(8): 969-977 (2007)). There is no specific treatment for Dengue virus. In order to combat Dengue virus infections, the focus has been primarily on mosquito control. However, due to mosquito drug resistance coupled with climate change and the reduction in public health programs, these efforts have been unsuccessful in curtailing the spread of Dengue virus.
Vaccines are the most cost effective and efficient therapeutic interventions for infectious diseases. Research and development directed to a Dengue virus vaccine have not proven successful. Recent efforts have focused primarily on developing vaccines using live attenuated or inactivated virus (see, e.g., U.S. Pat. No. 7,718,359). The current status of Dengue virus vaccine development is reviewed in, for example, Whitehead et al., Nature Reviews Microbiology, 5: 518-528 (2007), and Webster et al., Lancet, 9(11): 678-687 (2009). DNA-based vaccines such as adenoviral vector vaccines, have been considered (see, e.g., Raviprakash et al., J. Virol., 82(14): 6927-6934 (2008)). However, these vaccines have been unsuccessful due in part to problems with viremia, pre-existing immunity in humans to adenoviral vectors, and concerns associated with an adenoviral vaccine trial associated with HIV (see, e.g., Webster et al., Lancet, 9(11): 678-687 (2009)).
Pre-existing immunity results from the generation of antibodies to antigenic epitopes on adenoviral capsid proteins. If sufficient in titer, the antibodies can limit the ability of the vector to be used more than once as an effective gene transfer vehicle. For instance, animal studies demonstrate that intravenous or local administration (e.g., to the lung, heart, or peritoneum) of an adenoviral type 2 or 5 gene transfer vector can result in the production of antibodies directed against the vector which prevent expression from the same serotype vector administered 1 to 2 weeks later (see, e.g., Yei et al., Hum. Gene Ther., 5: 731-744 (1994); Zabner, Nat. Genet., 6: 75-83 (1994); Setoguchi et al., Am. J. Respir. Cell. Mol. Biol., 10: 369-377 (1994); Kass-Eisler et al., Gene Therapy, 1: 395-402 (1994); Kass-Eisler et al., Gene Therapy, 3: 154-162 (1996)). This is a drawback in adenoviral-mediated gene therapy, since many uses of an adenoviral vector (e.g., for prolonged gene therapy) require repeat administration, inasmuch as the vector does not stably integrate into the host cell genome. The mechanism by which antibodies directed against an adenovirus are able to prevent or reduce expression of an adenoviral-encoded gene is unclear. This phenomenon is loosely referred to as “neutralization,” and the responsible antibodies are termed “neutralizing antibodies.”
Hexon proteins are the largest and most abundant proteins in the adenovirus capsid, making them a primary target for modification in order to reduce neutralization of adenoviral vectors (see, e.g., Gall et al., J. Virol., 72: 10260-264 (1998), and Rux et al., J. Virol., 77(17): 9553-9566 (2003)). However, many of the hexon modifications made to date have not been successful in sufficiently reducing the neutralizing antibody response. These failures are due, at least in part, to the disruption of structural interactions between the loops of the hexon protein, which interferes with the stability of the hexon structure itself, and likely impedes the ability of the hexon region to interact with other capsid proteins. In addition, many of the hexon modification made to date have adversely affected adenovirus growth. Problems associated with virus growth impede the ability to manufacture commercial quantities of adenoviral vectors for, e.g., therapeutic use.
Thus, there remains a need for a composition to effectively deliver Dengue virus antigens to human hosts so as to prevent the onset of disease and/or protect human hosts from further infections. The invention provides such a composition.