Vaccination with single plasmid DNA encoding IL-12 and antigens of severe fever with thrombocytopenia syndrome virus elicits complete protection in IFNAR knockout mice

Jun-Gu Kang; Kyeongseok Jeon; Hooncheol Choi; Yuri Kim; Hong-Il Kim; Hyo-Jin Ro; Yong Bok Seo; Jua Shin; Junho Chung; Yoon Kyung Jeon; Yang Soo Kim; Keun Hwa Lee; Nam-Hyuk Cho

leukocytopenia, and thrombocytopenia [3, 4] . Disease mortality of SFTS patients has been 88 estimated to be 5 ~ 20% [3] . Even though the majority of SFTS cases has been reported from 89 China [3] , Korea [4] , and Japan [5] , SFTSV infections in southern Asia, including Vietnam, 90 have been recently reported in a retrospective survey [6] . Currently, no specific viral therapy 91 nor vaccine is available. An effective vaccine is needed to combat its relatively high mortality, 92 especially in elderly patients, and spread of SFTSV between humans [7, 8] . 93 Vaccine development for SFTS is at an early discovery phase and there have only been a few 94 studies on vaccine candidates using animal infection models [8] [9] [10] [11] . Immunization of NS 95 antigen with Freund's adjuvant in C57BL/6 mice, which are naturally resistant to SFTSV but 96 partially mimic human infections [12] , failed to enhance viral clearance, although it induced The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/787879 doi: bioRxiv preprint 5 103 attenuated recombinant vesicular stomatitis virus (rVSV) vaccine expressing the SFTSV 104 Gn/Gc glycoproteins elicited high titers of protective neutralizing antibodies in both wild type 105 and interferon α/β receptor knockout (IFNAR KO) mice [11] . They clearly showed that a 106 single dose rVSV carrying SFTSV Gn/Gc could provide complete protection against lethal 107 challenge with SFTSV in young and old IFNAR KO mice, a promising infection model for 108 severe human infection of SFTSV [11, 13, 14] . Nevertheless, the potential role of cellular 109 immunity against the viral antigens in complete protection was not examined in this study, 110 although adoptive transfer of immune sera from mice immunized with rVSV-Gn/Gc to naïve 111 IFNAR KO mice provide partial (~ 60%) protection against lethal SFTSV challenge [11] . 112 In this study, we developed a recombinant plasmid DNA (pSFTSV) encoding extracellular 113 domains of Gn and Gc, and NP-NS fusion antigen as a DNA vaccine candidate. We 114 examined whether it could provide protective immunity against lethal SFTSV infection in 115 IFNAR KO mice. In order to facilitate the processing and presentation of the SFTSV antigens 116 by dendritic cells (DCs) and enhance antigen-specific T cell responses, these recombinant 117 antigens were fused with Fms-like tyrosine kinase-3 ligand (Flt3L) [15, 16] . Moreover, we 118 generated a recombinant DNA encoding IL-12 and  in addition to the recombinant viral 119 antigens (pSFTSV-IL12) to further enhance cell-mediated immunity [17] . Vaccination of 120 pSFTSV-IL12 provided complete protection of IFNAR KO mice upon lethal SFTSV 121 challenge, whereas immunization with pSFTSV elicits only partial protection, indicating that 122 antigen-specific cellular immune responses enhanced by co-expression of IL-12 could play a 123 significant role in protection against lethal SFTSV infection. We confirmed significantly 124 higher levels of Gn and NP-specific CD4 + and CD8 + T cell responses in mice vaccinated with 125 pSFTSV-IL12 when compared to those in mock vector-immunized mice. Therefore, our 126 results indicate that enhanced antigen-specific T cell immunity against multiple SFTVS In order to generate plasmids for DNA vaccination, genes encoding ectodomains of Gn, Gc 141 (from Genebank accession no. AJO16082.1), and NP/NS fusion protein (from Genebank 142 accession no. AJO16088.1 and AKI34