Unraveling yellow fever 17D vaccine attenuation: The role of type I interferon and innate immunity

点击翻译按钮获取中文摘要

Project Summary The yellow fever 17D live-attenuated vaccine has been administered to millions of people and is a highly successful and safe vaccine providing essentially life-long protection. However, the mechanisms of attenuation are poorly understood, and rare individuals suffer from sometimes fatal severe adverse events (SAEs) including yellow fever-like viscerotropic disease, or neurologic disease. Epidemics of this mosquito-borne disease continue to occur in tropical and sub-tropical regions of South America and Africa, so understanding the mechanisms of 17D attenuation and the factors predisposing to SAEs is critical for development of safer vaccines and SAE prevention or treatment strategies. Work of others and of ours in the prior funding period determined that type I interferon (IFN) responses are greater after infection of cells with 17D compared to the virulent Asibi parental strain. New preliminary data demonstrate that the prophylactic IFN-induced antiviral state is also more effective at controlling 17D. Importantly, our work uncovered mutations in genes encoding type I IFN receptor chains (IFNAR1 and IFNAR2) and autoantibodies against type I IFNs as factors causing SAEs after 17D vaccination, thus linking the observed IFN phenotype with 17D attenuation in vivo. We also discovered a differential requirement between 17D and Asibi, mediated by the viral NS4B protein, for the host factor TMEM41B, with increased innate immune responses to 17D in TMEM41B KO cells. Prior studies have been hampered by the disparate specific infectivities of 17D and Asibi, precluding meaningful comparisons in bulk cell-based assays. New preliminary data demonstrates that 17D and Asibi harboring the 17D E protein (Asibi+17D E) have similar specific infectivities, replicate with similar kinetics in the HepG2 hepatocyte cell line, and maintain previously described differences in IFN transcription and secretion. Unexpectedly, levels of phosphorylated STAT1 are similar in 17D- and Asibi+17D E-infected cells. In this project continuation, in Aim 1 17D and Asibi+17D E will be used to examine pattern recognition receptor activation, including kinase activation and downstream transcriptional responses using phosphoproteomics and RNASeq. The mechanism by which Asibi+17D E blocks IFN secretion, the process by which STAT1 phosphorylation occurs and the consequences to infection and role of individual ISGs in controlling 17D and Asibi infection will be elucidated. In Aim 2 interactions of Asibi and 17D with both pro- and anti-viral host factors will be characterized through imaging-based methods allowing single cell resolution. We will examine responses in the infected cell and the influence of individual genes (at genome scale) on innate immunity and infection. Patient-specific mutations associated with SAEs will be functionally interrogated as we have done previously. In Aim 3 the role of NS4B in differential TMEM41B requirements will be elucidated using proteomic and mutational approaches. These studies will uncover critical host-pathogen interactions that can be exploited to develop safer vaccines, SAE treatment or prevention approaches, and new drug targets. The information gained can also be broadly applied to vaccine development for other flaviviruses.