Control of poorly immunogenic tumors with systemic STING agonist‐loaded liposomes targeting cross‐presenting dendritic cells

Objectives Cancer vaccines combine tumor antigen and adjuvant to drive an anti‐tumor immune response. Clec9A‐targeted nanoparticles directing CD4 and CD8 neo‐epitopes to cross‐presenting dendritic cells (DCs) stimulate adjuvant‐free therapeutically effective tumor‐specific immunity. However, personalised neo‐epitopes limit the scalability of Clec9A nanoparticles for clinical translation. Since Clec9A + DCs constitutively present relevant neoepitopes in tumors but are suppressed in tumor microenvironments, we developed Clec9A‐targeted STING or RIG‐I liposomes to enhance endogenous tumor immunity. Methods Liposomes encapsulating RIG‐I or the STING agonist MSA‐1 and functionalised with Clec9A binding peptide WH were optimised for uptake by Clec9A + conventional and plasmacytoid DCs in vivo . Biodistribution after i.v. administration was determined with in vivo imaging and cellular uptake and activation with flow cytometry. Plasma was analysed for type 1 interferon (IFN) by ELISA and liver, spleen, tumor, blood, kidney, heart and tumor draining lymph node transcriptomes were analysed with Nanostring. Effects on tumor growth and survival, and tumor‐specific T cells were evaluated using the B16 melanoma model. Results Clec9A‐targeting liposomes administered i.v. were distributed to spleen, liver and tumor and were taken up by cross‐presenting and plasmacytoid DCs. Type 1 IFN production and DC, B‐ and T‐cell activation were more effective with i.v. Clec9A‐STING than Clec9A‐RIG‐I liposomes. Intravenous Clec9A‐STING liposomes stimulated IFN‐dependent transcription in blood, lung, tumor, and draining lymph nodes. Intravenous Clec9A‐STING liposomes, or intra‐tumoral Clec9A‐RIG‐I liposomes significantly suppressed B16‐F10 melanoma growth and induced neo‐epitope and survivin‐specific CD4 + and CD8 + T‐cell responses. Conclusions Clec9A‐STING liposomes are a scalable, translatable tumor‐targeted immunotherapy platform.