Construction, Safety, and Immunogenicity in Nonhuman Primates of a Chimeric Yellow Fever-Dengue Virus Tetravalent Vaccine

Dengue is a mosquito-borne flavivirus infection, causing significant morbidity and mortality in tropical areas worldwide (12). There are four dengue virus (DEN) serotypes (1 to 4), all of which cause human illness. Over 2.5 billion people live in areas at risk of the disease worldwide, and 100 million people are affected annually (35, 36, 47). The severe immunopathological form of the disease, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), is the leading cause of hospitalization of children in Asia. The disease is expanding in distribution and incidence, particularly in the Americas. The United States, infested with Aedes aegypti, is vulnerable to introduction of Dengue. The most recent incursion and autochthonous outbreak of dengue occurred in Texas in 1999. Areas of the world recently invaded or at imminent risk include the southern cone (Argentina and Chile), Australia, parts of Africa, southern Europe, and the Middle East. Mosquito control, as a means of preventing dengue, has been a failure due to expanding urbanization, human population increases, degraded sanitation, competition for financial resources, pesticide resistance, and airline travel, which facilitates movement of viremic travelers. Vaccination has the highest potential as a public health approach that is likely to blunt the increasing incidence and geographic expansion of the disease. The development of a vaccine against DEN has been a high priority of the World Health Organization for decades (4). An effective vaccine would be used for (i) universal immunization of children in areas of Asia, Latin America, and the Caribbean where dengue is endemic; (ii) protection of foreign travelers and military personnel; and (iii) control of epidemics. Because of the importance of a DEN vaccine for travelers and military personnel in developed countries, DEN vaccines are of interest to the pharmaceutical industry. However, the need for a vaccine extends far beyond such markets, to the people of the most impoverished countries. Development of a DEN vaccine has been an elusive goal, principally because of the need to simultaneously immunize and induce long-lasting protection against all four DEN serotypes. An incompletely immunized individual, or one in whom antibody titers wanes, may be sensitized to a severe immunopathological disease (DHS/DSS) (15, 26, 45). The ChimeriVax technology offers a good probability of successful DEN vaccine development. The vaccine attributes include the potential for single-dose application, absent or minimal reactogenicity, extremely durable immunity, reduced potential for interference between the individual components in a tetravalent formulation, and low cost of manufacture. ChimeriVax is a live, attenuated genetically engineered virus, prepared by replacing the genes encoding two structural proteins, the premembrane (prM) and envelope (E) proteins of the yellow fever virus (YF) 17D vaccine strain (YF-VAX) with the corresponding genes of the vaccine target virus, e.g., DEN. Construction and characterization of YF/DEN2 (in which prME genes of YF 17D were exchanged with those of the PUO218, a Thai strain of DEN serotype 2 [DEN2]) have been described previously (10). In this paper, we describe the construction of chimeric viruses incorporating the prME genes of DEN serotypes 1, 3, and 4. The safety and immunogenicity of these viruses were evaluated in animal models. Studies in rhesus monkeys demonstrated effective simultaneous immunization with all four YF/DEN serotypes.