Cross-presentation of epitopes on virus-like particles via the MHC I receptor recycling pathway.

Effective vaccines and immunotherapies against cancer require professional antigen-presenting cells to cross-present exogenous antigen to initiate cytotoxic T-cell responses to destroy tumors. Virus-like particles (VLPs), containing tumor antigens, which can immunize against cancers, are cross-presented by dendritic cell (DC) but the mechanism by which this occurs is not fully understood. Here, we used VLPs, derived from rabbit hemorrhagic disease virus (RHDV) with both murine and human DCs, to elucidate these pathways. We have employed inhibitors to demonstrate that these VLPs are taken up by clathrin-dependent macropinocytosis and phagocytosis before being degraded in acidic lysosomal compartments. VLP-derived peptides are loaded onto major histocompatibility complex I that have been recycled from the cell surface. Antigen-coupled VLPs and murine ovalbumin-specific and human melanoma-associated antigen recognized by T cells (MART-1)-specific CD8(+) T cells were used to demonstrate cross-presentation via this alternate, receptor recycling pathway, which operated independently of the proteasome and the transporter-associated with antigen presentation. Finally, we found that cross-presentation of VLPs in vivo was not confined to CD8α(+) DC subsets. These data define the cross-presentation pathway for RHDV VLPs and may lead to improved cancer immunotherapies.