A safe insect-based chikungunya fever vaccine affords rapid and durable protection in cynomolgus macaques

Eilat (EILV)/chikungunya virus (CHIKV), an insect-based chimeric alphavirus was previously reported to protect mice months after a single dose vaccination. The underlying mechanisms of host protection are not clearly defined. Here, we assessed the capacity of EILV/CHIKV to induce quick and durable protection in cynomolgus macaques. Both EILV/CHIKV and the live attenuated CHIKV 181/25 vaccine protected macaques from wild-type (WT) CHIKV infection 1 year after a single dose vaccination. Transcriptome and functional analyses reveal that EILV/CHIKV triggered T cell, memory B cell and antibody responses in a dose-dependent manner. EILV/CHIKV induced more robust, durable, and broader repertoire of CHIKV-specific T cell responses than CHIKV 181/25; whereas the latter group induced more durable memory B cells and comparable or higher CHIKV -specific neutralization and binding antibodies. EILV/CHIKV and an inactivated WT CHIKV protected macaques from WT CHIKV infection and CHIK fever (CHIKF) within 6 days post vaccination. Transcriptome analysis showed that the chimeric virus induced multiple innate immune pathways, including Toll-like receptor signaling, antigen presenting cell activation, and NK receptor signaling. EILV/CHIKV triggered quicker and more robust type I interferon and NK cell responses than the inactivated WT virus vaccine. Lastly, we developed a guinea pig sensitization model and demonstrated that the chimeric virus produced in insect cells, did not cause skin hypersensitivity reactions. Overall, EILV/CHIKV is safe, and confers rapid and long-lasting protection in cynomolgus macaques via preferential induction of robust innate immune signaling and superior T cell immunity.