To perform mechanistic studies on the T

To perform mechanistic studies on the T cell response to DENV, a manipulable and tractable animal model is required in which the exact infecting viral strain, as well as the order and times of infection, are known. Wild-type mice are highly resistant to infection with DENV, as the virus is able to block type I Interferon (IFN) receptor signaling in human but not murine order conotoxin (Ashour et al., 2010; Yu et al., 2012; Aguirre et al., 2012). The antiviral IFN response must be disrupted in mice to make them susceptible to DENV infection. Therefore, we previously developed a model of DENV infection in IFN-α/βR−/− mice lacking the type I IFN receptor (Perry et al., 2009; Zellweger et al., 2010). Our group has used this mouse model to identify protective roles for T cells in the context of various DENV infection settings, including heterotypic reinfection (Yauch et al., 2009; Yauch et al., 2010; Zellweger et al., 2010; Zellweger et al., 2015; Zellweger et al., 2014; Zellweger et al., 2013). To link the findings obtained from the IFN-α/βR−/− mouse model studies to the human situation, we have also developed an IFN-α/βR−/− HLA transgenic mouse model. This mouse model has been used to map the DENV2- and DENV3-specific T cell response restricted by HLA B*0702 (Weiskopf et al., 2011; Weiskopf et al., 2014), which is associated with high response frequency and magnitude and decreased susceptibility to severe dengue disease in humans (Weiskopf et al., 2013). Additionally, the HLA B*0702-transgenic IFN-α/βR−/− mouse model has been validated by following observations: (i) The epitopes identified were also recognized by human Peripheral Blood Mononuclear Cells (PBMC) from DENV-exposed donors (Weiskopf et al., 2011; Weiskopf et al., 2014); (ii) A dominance of HLA B*0702-restricted response was detected in both mice and human peripheral blood mononuclear cell (PBMC) donors (Weiskopf et al., 2013); and (iii), The finding that CD8 T cell response targets both structural and NS proteins in DENV3 but only NS proteins in DENV2 was observed in both mice and humans (Weiskopf et al., 2015b; Weiskopf et al., 2015c). In the present study, we explore the role of cross-reactive T cells in vivo during DENV infection using the HLA-B*0702-transgenic IFN-α/βR−/− mouse model. We show that HLA-B*0702-transgenic IFN-α/βR−/− mice infected with DENV2 mount a poly-functional antiviral immune response. In particular, CD8 T cells from DENV2-infected mice produce IFNγ, TNFα, or both cytokines when re-stimulated with DENV2 or variant peptides from other serotypes, DENV1/3/4. Although cross-reactive T cells elicit a weaker T cell response in vitro, immunization with cross-reactive peptides confers protection against DENV infection by reducing viral load. Our results do not provide support for “original T cell antigenic sin;” instead, they demonstrate that cross-reactive T cells can play a protective role against DENV infection.
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Results
Discussion Epidemiological studies have highlighted an increase of severe disease manifestations (DHF/DSS) during secondary infections with different DENV serotype (Halstead, 2007). To explain this epidemiological observation, two dominant hypotheses have been postulated: ADE and T cell original antigenic sin. The relevance of ADE to DHF/DSS pathogenesis had been controversial until the demonstration of ADE in vivo in 2010, when our laboratory and another group independently demonstrated that subneutralizing levels of antibody can turn a mild illness into a lethal disease in mice lacking IFN-α/β receptor alone or both IFN-α/β and γ receptors (Zellweger et al., 2010; Balsitis et al., 2010). Unlike wild-type mice, the IFN receptor-deficient mice support high levels of DENV replication and in the ADE model of infection, develop signs of disease that mimic DHF/DSS in humans (Zellweger et al., 2010). In contrast, no study to date has provided direct evidence in support of the original T cell antigenic sin hypothesis. As a step towards addressing this hypothesis, in this study, we investigated the contribution of DENV serotype-specific vs. cross-reactive CD8 T cells to protection against DENV infection using an HLA transgenic mouse model of human relevance. Our results demonstrated that both serotype-specific and cross-reactive CD8 T cells could reduce DENV burden in tissues, providing no direct evidence for the original T cell antigenic sin hypothesis. Instead, our findings support recent data implicating HLA-linked protective role for CD8 T cells against DENV infection in humans (Weiskopf et al., 2013).