The Toxoplasma Effector GRA4 Hijacks Host TBK1 to Oppositely Regulate Anti‐T. Gondii Immunity and Tumor Immunotherapy

Abstract Toxoplasma gondii (T. gondii)‐associated polymorphic effector proteins are crucial in parasite development and regulating host anti‐T. gondii immune responses. However, the mechanism remains obscure. Here, it is shown that Toxoplasma effector dense granules 4 (GRA4) restricts host IFN‐I activation. Infection with Δgra4 mutant T. gondii strain induces stronger IFN‐I responses and poses a severe threat to host health. Mechanistically, GRA4 binds to phosphorylated TBK1 to promote TRIM27‐catalyzed K48‐ubiquitination at Lys251/Lys372 residues, which enhances its recognition by autophagy receptor p62, ultimately leading to TBK1 autophagic degradation. Furthermore, an avirulent Δgra4 strain (ME49Δompdc/gra4) is constructed for tumor immunotherapy due to its ability to enhance IFN‐I production. Earlier vaccination with ME49Δompdc/gra4 confers complete host resistance to the tumor compared with the classical ME49Δompdc treatment. Notably, ME49Δompdc/gra4 vaccination induces a specific CD64+MAR‐1+CD11b+ dendritic cell subset, thereby enhancing T cell anti‐tumor responses. Overall, these findings identify the negative role of T. gondii GRA4 in modulating host IFN‐I signaling and suggest that GRA4 can be a potential target for the development of T. gondii vaccines and tumor immunotherapy.