Immunodominant structural proteins Gc and N drive T cell-mediated protection against La Crosse virus

La Crosse virus (LACV), a negative-sense RNA bunyavirus, is a major cause of pediatric encephalitis in the United States, disproportionately affecting children under the age of 16 years. Although LACV can lead to severe morbidity and mortality in this vulnerable pediatric population, no vaccines or specific antiviral therapies are currently available. Murine models recapitulate the age-dependent susceptibility observed in humans, whereby weanling mice (3 weeks old) succumb to LACV-induced neurological disease and adult mice (≥8 weeks old) exhibit resistance. In this study, we systematically characterized the T cell-mediated responses that underlie this differential susceptibility. We show that adult mice mount robust, polyfunctional LACV-specific CD4 ⁺ and CD8 ⁺ T cell responses against structural and non-structural proteins as early as 6 days post-infection (dpi), with sustained production of interferon-gamma (IFN-γ), granzyme B, interleukin-2 (IL-2), and tumor necrosis factor alpha (TNF-α). We further show that these T cells expand significantly in adult mice and display in vivo cytotoxicity against targeted cells pulsed with immunogenic antigens derived from the envelope Gc and nucleocapsid (N) proteins. In contrast, weanling mice exhibit significantly weaker T cell responses, as evidenced by reduced expansion of both CD4 ⁺ and CD8 ⁺ T cells and diminished cytokine production, correlating with 100% mortality by 7 dpi. Importantly, immunization studies with LFn-LACV-Gc and -N significantly improve in vivo T cell cytotoxicity and survival in weanlings, highlighting their potential as vaccine candidates. Collectively, our findings define key cellular correlates of protection against LACV and establish a framework for the development of pediatric vaccines designed to mitigate the public health burden of LACV-induced encephalitis.