Altered peptide ligand vaccination with Flt3 ligand expanded dendritic cells for tumor immunotherapy

Most tumor-associated antigens represent self-proteins and as a result are poorly immunogenic due to immune tolerance. Here we show that tolerance to carcinoembryonic antigen (CEA), which is overexpressed by the majority of l ethal malignancies, can be reversed by immunization with a CEA-derived pept ide. This peptide was altered to make it a more potent T cell antigen and l oaded onto dendritic cells (DCs) for delivery as a cellular vaccine. Althou gh DCs are rare in the blood, we found that treatment of advanced cancer pa tients with Flt3 ligand, a hematopoietic growth factor, expanded DCs 20-fol d in vivo. Immunization with these antigen-loaded DCs induced CD8 cytotoxic T lymphocytes that recognized tumor cells expressing endogenous CEA, Stain ing with peptide-MHC tetramers demonstrated the expansion of CD8 T cells th at recognize both the native and altered epitopes and possess an effector c ytotoxic T lymphocyte phenotype (CD45RA(+)CD27(-)CCR7(-)). After vaccinatio n, two of 12 patients experienced dramatic tumor regression, one patient ha d a mixed response, and two had stable disease. Clinical response correlate d with the expansion of CD8 tetramer(+) T cells, confirming the role of CD8 T cells in this treatment strategy.