Flaviviruses
Program Leader: Aravinda deSilva
SE-RP-004: Antibody in protective and pathogenic immunity to Dengue type 3
Aravinda deSilva and Ralph Baric
University of North Carolina
Dengue viruses (DENV) are emerging, mosquito-borne Flaviviruses and the agents of dengue fever (DF) and dengue hemorrhagic fever (DHF). The NIAID has listed dengue (DEN) as a category A priority agent with respect to Biodefense and Emerging Infections research. A large body of work has demonstrated that people infected with DENV develop long-term protective immunity to the infecting serotype but not to other serotypes. During a second infection with a different serotype, the risk of severe disease is greater because cross-reactive immunity can exacerbate the disease. Efforts to develop DEN vaccines have been hampered by the dual role of immunity in protection and pathogenesis. We know very little about the antibody repertoire in people who have been infected with dengue. The main goal of this project is to use DENV3 as a model for defining the viral epitopes engaged by human antibody and to determine the functional outcome of these interactions. Our overall hypothesis is that distinct epitopes on the DENV envelope protein are responsible for virus neutralization and enhancement. In aim 1 studies will be done to produce human monoclonal antibodies from people who have recovered from DENV infections. In aim 2 a selected subset of human MAbs will be mapped to specific epitopes and functionally characterized for neutralizing or enhancing activity using cell culture and an animal model. In aim 3 we will determine if the main antibody epitopes are conserved among DENV3 strains. This project takes advantage of a panel of reagents including well characterized virus strains, human samples and a DENV3 infectious clone available at UNC. The project also utilizes a new rodent model of DENV developed by a SERCEB investigator. We will also produce and purify large quantities of DENV antigens to support our project and other DENV projects within SERCEB. The study is expected to reveal mechanisms of antibody mediated neutralization or enhancement of DENV3. This information is directly applicable to the evaluation of the safety and efficacy of candidate dengue vaccines.
SE-RP-005: T cell response to Dengue virus serotype 3 in mice and human
LaJolla Institute of Allergy and Infectious Disease
The four serotypes of Dengue virus (DENV) cause dengue fever (DF) and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) in humans. Studies suggest that DHF/DSS is an immunopathogenic disease in which T cell responses may be dysregulated. Understanding the mechanisms that regulate the balance between T cell mediated pathology versus protection is crucial for developing therapies and, importantly, a safe dengue vaccine. By alternately passaging a DENV between mice and mosquito cells, we have naturally selected for strains that induce robust T cell responses in mice, and we have demonstrated a critical role for CD8+ T cells in limiting DENV serotype 2 (DENV2) infection in mice. Due to the broad specificity and antiviral role of the CD8+ T cell response to DENV2 in mice, we hypothesize that the murine and human CD8+ T cell response to DENV3 is broad, targeting most viral proteins, and these CD8+ T cells protect against DENV3 infection in the host. Accordingly, we have already identified CD8+ T cell epitopes in the DENV3 strain UNC3001 and have started to examine the contribution of various DENV3 epitope-specific CD8+ T cells to protection versus pathogenesis using a mouse model of DENV3 infection (Aims 1 and 2), and we are beginning to define the specificity and role of human CD8+ T cell response in the host response to DENV3 infection using HLA transgenic mice and samples derived from people who have recovered from primary DENV3 infection (Aims 3 and 4). This project focuses on DENV3 because epidemiologic studies suggest that certain DENV serotypes, genotypes, and the sequence of DENV infections may be associated with DHF/DSS, and little is known about DENV3 infection as compared with DENV2, although DENV3 co-circulates with DENV2 in endemic countries, and DENV3 has been responsible for recent epidemics in South Asia and Latin America.
Relevance
The current vaccine candidates that exploit antibody responses alone may be ineffective against new DENV variants and may enhance disease. This research may aid in generating DENV-specific vaccines that are broadly cross-reactive against all four serotypes, effectively clear virus, and increase protective immunity while avoiding immunopathology.
