Palmitoylated antigens as a multipurpose membrane-targeting moiety for the treatment of cancer
Horrevorts S.K.1, Schetters S.T.T.1, Stolk D.A.1, van Vliet S.J.1, Garcia-Vallejo J.J.1,
van Kooyk Y1
1Dept. of Molecular Cell Biology and Immunology, VU University Medical Center, Amsterdam, the Netherlands
Cancer immunotherapy has not been able to induce durable clinical responses in the majority of melanoma patients, despite recent successes with checkpoint inhibitors. In addition to counteract tumor-derived immune suppression, effective immunotherapies boost existing or elicit de novo, tumor-specific immune responses. Induction of these responses has been challenging, in part because of inefficient targeting of antigens to antigen presenting cells (APCs). To address this problem we made use of an endogenous mechanism of membrane targeting. Attachment and maintenance of the subcellular localization and activity of proteins are controlled by the post-translational modification, palmitoylation. Through the addition of a palmitic acid in the Golgi, proteins are targeted to the plasma membrane. We designed antigenic constructs using this method of membrane targeting to deliver exogenous tumor-associated antigens (TAA’s) for the induction of an anti-tumor response. Here, we show that synthetic mono-palmitoylated antigenic constructs target lipid membranes of a variety of carriers: cellular, vesicular and synthetic. Vaccination in vitro and in vivo with palmitoylated TAAs enhances presentation via MHC class I. Intracellular tracking of the construct revealed that binding and uptake of the palmitoylated TAAs is partly endocytosis-independent and results in localization to the cytosol. Therefore, the construct may enter the MHC class I route directly, explaining enhanced cytotoxic T cell responses. Palmitoylation of antigens provides an efficient tool to target antigens to different membranes for the induction of anti-tumor immunity. Our current research is focused on unraveling uptake and routing of the palmitoylated antigens and to identify how these vaccine-modalities are handled by DCs and Langerhans cells (LCs).