Immunization with tumor-associated epitopes fused to an endoplasmic reticulum translocation signal sequence affords protection against tumors with down-regulated expression of MHC and peptide transporters

Treatment of human cancers with an inherent antigen-processing defect due t o a loss of peptide transporters (TAP-1 and TAP-2) and/or MHC class I antig en expression remains a considerable challenge. There is now an increasing realization that tumor cells with down-regulated expression of TAP and/or M HC class I antigens display strong resistance to cytotoxic T lymphocyte (CT L)mediated immune control, and often fail to respond to the conventional im munotherapeutic protocols based on active immunization with tumor-associate d epitopes (TAE) or adoptive transfer of tumor-specific T cells, In the pre sent study, we describe a novel approach based on immunization with either genetically modified tumor cells or naked DNA vectors encoding TAE fused to an endoplasmic reticulum (ER) signal sequence (ER-TAE) which affords prote ction against challenge by melanoma cells with down-regulated expression of TAP-1/2 and MHC class I antigens. In contrast, animals immunized with a va ccine based on TAE alone showed no protection against tumor challenge. Alth ough MHC-peptide tetramer analysis showed a similar frequency of antigen-sp ecific CTL in both ER-TAE- and TAE-immunized mice, functional analysis reve aled that CTL activated following immunization with ER-TAE displayed signif icantly higher avidity for TAE when compared to animals immunized with the TAE alone, These observations provide a new strategy in anti-cancer vaccine design that allows activation of a highly effective and well-defined CTL r esponse against tumors with down-regulated expression of TAP and MHC class I antigens.