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.