Cross-presentation of NY-ESO-1 cytotoxic T lymphocyte epitope fused to human heat shock cognate protein 70 by dendritic cells

The cancer-testis antigen NY-ESO-1 has been implicated as one of the most attractive candidates for a cancer vaccine. However, a protein vaccine generally meets inefficient antigen presentation to CD8⁺ T cells, which could be overcome by combination with an appropriate adjuvant. Heat shock protein is a natural adjuvant and activates the antigen-presenting cells to channel exogenous antigens into the classical major histocompatibility complex class I antigen-processing pathway (cross-presentation). Therefore, we genetically fused a minigene encompassing the NY-ESO-1 cytotoxic T lymphocyte (CTL) epitope 157-165 (ESO p157-165) to the human heat shock cognate protein 70 (hsc70) and expressed the resulting fusion proteins in Escherichia coli. By using a human leukocyte antigen-A*0201-restricted NY-ESO-1-specific CTL clone, the cross-presentation of ESO p157-165 by monocyte-derived dendritic cells (mo-DC) pulsed with the fusion protein was evaluated. The fusion protein-pulsed mo-DC activates the CTL clone much more efficiently than the free NY-ESO-1 protein-pulsed mo-DC. Moreover, the magnitude of the CTL activity was comparable between ESO p157-165 and the fusion protein of hsc70 and ESO p157-165 (hsc70-ESO p157-165 fusion protein). In addition, the CTL activation induced by the fusion protein, but not by the epitope, was inhibited by paraformaldehyde fixation of the mo-DC and by treatment with lactacystin, a specific inhibitor for the proteasome. Finally, the hsc70-ESO p157-165 fusion protein-pulsed DC was able to induce an antigen-specific T-cell response. These results suggest that the hsc70-ESO p157-165 fusion protein is therefore considered to be a promising candidate as a cancer vaccine.