Small-molecule inhibitors of TBK1 serve as an adjuvant for a plasmid-launched live-attenuated yellow fever vaccine

Plasmid-launched live-attenuated vaccines (PLLAV), also called infectious DNA (iDNA) vaccines, combine the assets of genetic immunization with the potency of replication-competent live viral vaccines. However, due to their origin as bacterial plasmid DNA, efficient delivery of PLLAV may be hampered by innate signaling pathways such as the cGAS-STING-mediated sensing of cytosolic DNA, resulting in an unfavorable proinflammatory and antiviral response locally at the site of immunization. Employing several complementary cell-based systems and using the yellow fever vaccine (YF17D) and the respective PLLAV-YF17D, we screened a panel of small molecules known to interfere with antiviral signaling for their proviral activity and identified two potent inhibitors of the TANK-binding kinase 1 (TBK1), BX795 and CYT387, to enhance YF17D replication and hence efficacy of PLLAV-YF17D transfection. In tissue culture, BX795 could fully revert the block that plasmid transfection poses on YF17D infection in a type I interferon dependent manner, as confirmed by (i) a marked change in gene expression signatures, (ii) a rescue of full YF17D replication, and (iii) a massively increased virus yield. Inhibitors of TBK1 may hence be considered an adjuvant to potentiate novel PLLAV vaccines, which might boost PLLAV delivery toward their use in vivo.