Functionalisation of virus-like particles enhances antitumour immune responses

Virus-like particles (VLP) from the rabbit haemorrhagic disease virus (RHDV) can deliver tumour antigens to induce anticancer immune responses. In this study, we explored how RHDV VLP can be functionalised to enhance the immune response by increasing antigen loading, incorporating linkers to enhance epitope processing, and targeting receptor-mediated internalisation of VLP. RHDV VLP were developed to deliver up to three copies of gp100 ₂₅ - ₃₃ which contained proteasome cleavable linkers to target the correct processing of the epitope. Addition of mono- and dimannosides, conjugated to the surface of the gp100 VLP, would utilise a second pathway of internalisation, mannose receptor mediated, to further augment antigen internalised by phagocytosis/macropinocytosis. In vitro cell culture studies showed that a processing linker at the C-terminus of the epitope (gp100.1LC) induced enhanced T-cell activation (7.3 ng/ml interferon- (IFN-) γ release) compared to no linker (3.0 ng/ml IFN-γ) or the linker at the N-terminus (0.8 ng/ml IFN-γ). VLP delivering two (gp100.2L) or three (gp100.3L) gp100 epitopes induced similar high T-cell activation (7.6 ng/ml IFN-γ) compared to gp100.1LC. An in vivo cytotoxicity assay and a therapeutic tumour trial confirmed that mice vaccinated with either gp100.2L or gp100.3L induced a specific antitumour immune response. Mannosylation of the gp100.2L VLP further enhanced the generated immune response, demonstrated by prolonged survival of mice vaccinated with dimannosylated gp100.2L VLP (D-gp100.2L) by 22 days compared to gp100.2L-vaccinated mice. This study showed that functionalisation of RHDV VLP by addition of an epitope-processing linker and mannosylation of the surface facilitates the efficacy of VLP as vaccination vectors for tumour immunotherapy.