Presentation of a major histocompatibility complex class 1–binding peptide by monocyte-derived dendritic cells incorporating hydrophobized polysaccharide–truncated HER2 protein complex: implications for a polyvalent immuno-cell therapy

Abstract

Recognition of the essential role of dendritic cells (DCs) as professional antigen-presenting cells has prompted investigators to search for methods to use DCs as natural adjuvants in immunotherapy. A number of antigenic oligopeptides, recognized by CD8⁺cytotoxic T lymphocytes (CTLs) specific for cancer cells, have been applied in clinical trials using DCs. Such a monovalent vaccine with a single epitope for a particular type of HLA class 1 molecule would be effective. However, a polyvalent vaccine might be more potent. We designed a novel protein delivery system consisting of hydrophobized polysaccharides complexed with target proteins. The truncated HER2 protein encompassing 147 N-terminal amino acids, including the 9-mer HER2p63-71 peptide (HER2p63), TYLPTNASL, the human homologue of an antigenic murine tumor rejection peptide, was prepared. We report here that HLA-A2402⁺ DCs could incorporate hydrophobized polysaccharide–truncated HER2 protein complexes and process the protein to present major histocompatibility complex class 1-binding HER2p63 peptide. The complexes enter DCs by phagocytosis, and then the truncated protein is processed through a pathway similar to that for endogenous proteins. DCs sensitized by these complexes primed and boosted HER2p63-specific CD8⁺T cells in the context of HLA-A2402. Vaccination with DCs incorporating these complexes completely suppressed lung metastases in a HER2-expressing murine tumor model. We also generated 3 CD4⁺ clones reactive with different HER2- derived 25-mer peptides from lymph node cells in mice treated with CHP/HER2-147. Thus, hydrophobized polysaccharide–protein complexes are promising candidates for the construction of polyvalent vaccines.