A Zika virus vaccine with E protein fusion loop mutations protects via CD8⁺ T cells

There are currently no effective vaccines against Zika virus (ZIKV). Candidate vaccines target the ZIKV envelope (E) protein, the major target of anti-ZIKV neutralizing antibodies (nAbs). Here we utilized DNA and RNA platforms to compare virus-like particle vaccines with premembrane (prM) and E expressed either in the wild-type form (Z-prM/E-WT) or with fusion loop (FL) mutations (Z-prM/E-FLM), which limit antibody-dependent enhancement of infection. Both vaccines induced effective protection against infection in C57BL/6 Ifnar1^-/- mice but with different mechanisms. The Z-prM/E-WT vaccine elicited nAbs against both immature and mature ZIKV virions, whereas mutations in the Z-prM/E-FLM vaccine impaired prM cleavage, resulting in a suboptimal antibody response failing to neutralize mature virions. Serum transfer and T cell depletion experiments in two mouse models demonstrated that CD8⁺ T cells were necessary and sufficient for short-term protection by Z-prM/E-FLM, whereas both antibodies and CD8⁺ T cells contributed to Z-prM/E-WT-induced long-term protection. Our results identify unexpected roles for CD8⁺ T cells in protection mediated by predominantly nAb-directed prM/E-based ZIKV vaccines. They also reveal that protection conferred by antibody-centric ZIKV vaccines that rely on CD8⁺ T cells alone is transient, whereas protection afforded by those that elicit both protective antibodies and CD8⁺ T cells is durable.