Dickkopf-1 (DKK1) is a widely expressed and potent tumor-associated antigen in multiple myeloma

The identification of novel tumor-associated antigens, especially those shared among patients, is urgently needed to improve the efficacy of immunotherapy for multiple myeloma (MM). In this study, we examined whether Dickkopf-1 (DKK1), a protein that is not expressed in most normal tissues but is expressed by tumor cells from almost all patients with myeloma, could be a good candidate. We identified and synthesized DKK1 peptides for human leukocyte antigen (HLA)-A*0201 and confirmed their immunogenicity by in vivo immunization in HLA-A*0201 transgenic mice. We detected, using peptidetetramers, low frequencies of DKK1 peptide-specific CD8-positive (CD8(+)) T cells in patients with myeloma and generated peptide-specific T-cell lines and clones from HLA-A*0201-positive (HLA-A*0201(+)) blood donors and patients with myeloma. These T cells efficiently lysed peptide-pulsed but not unpulsed T2 or autologous dendritic cells, DKK1-positive (DKK1(+))/HLA-A*0201(+) myeloma cell lines U266 and IM-9, and, more importantly, HLA-A*0201(+) primary myeloma cells from patients. No killing was observed on DKK1(+)/HLA-A*0201-negative (HLA-A*0201(-)) myeloma cell lines and primary myeloma cells or HLA-A*0201(+) normal lymphocytes, including B cells. These results indicate that these T cells were potent cytotoxic T cells and recognized DKK1 peptides naturally presented by myeloma cells in the context of HLA-A*0201 molecules. Hence, our study identifies DKK1 as a potentially important antigen for immunotherapy in MM.