CD8+ T cell cross-reactivity during heterologous flavivirus infection results in cross-reactive immunodomination and enhanced cytolytic capacity at the expense of virus-specific responses

Abstract

Abstract Flaviviruses constitute a genus of closely related arthropod-borne viruses including Zika virus, the four serotypes of dengue virus, and yellow fever virus, which circulate in the same geographic regions. These viruses share a substantial degree of genetic similarity and consequently, antigenic overlap has been reported by evaluating T cell and antibody responses in humans, non-human primates, and mice. However, it has not been determined how existing immunity to a heterologous flavivirus impacts functional immune responses to virus-specific and cross-reactive epitopes. We hypothesize that cross-reactive T cells from prior flavivirus exposures will expand robustly during a heterologous challenge and that these cells primed during a heterologous infection will be functionally different from cells of the same specificity primed during a homologous infection. Using various mouse models of flavivirus infection, we have identified a pan-flavivirus reactive CD8+ T cell epitope. We show in a heterologous infection model in which dengue virus exposure precedes Zika virus infection, T cell responses to the cross-reactive epitope dominate at the expense of the Zika-specific T cell responses. These cross-reactive T cells display enhanced killing capacity, in addition to other functional changes. The culmination of these features drive altered protective capacity when compared to homologously primed T cells in our mouse model of Zika infection. Our findings provide a mechanistic understanding of cross-reactive T cell control during heterologous infection and have important implications for vaccine design, as these results define the functional consequences of priming a cross-reactive T cell response for a pan-flavivirus vaccine.