Induction of HM1.24 peptide-specific cytotoxic T lymphocytes by using peripheral-blood stem-cell harvests in patients with multiple myeloma.

HM1.24 antigen is preferentially overexpressed in multiple myeloma (MM) cells but not in normal cells. To explore the potential of HM1.24 as a target for cellular immunotherapy, we selected 4 HM1.24-derived peptides that possess binding motifs for HLA-A2 or HLA-A24 by using 2 computer-based algorithms. The ability of these peptides to generate cytotoxic T lymphocytes (CTLs) was examined in 20 healthy donors and 6 patients with MM by a reverse immunologic approach. Dendritic cells (DCs) were induced from peripheral-blood mononuclear cells of healthy donors or peripheral-blood stem-cell (PBSC) harvests from patients with MM, and autologous CD8(+) T cells were stimulated with HM1.24 peptide-pulsed DCs. Both interferon-gamma-producing and cytotoxic responses were observed after stimulation with either HM1.24-126 or HM1.24-165 peptides in HLA-A2 or HLA-A24 individuals. The peptide-specific recognition of these CTLs was further confirmed by tetramer assay and cold target inhibition assay. Importantly, HM1.24-specific CTLs were also induced from PBSC harvests from patients with MM and these CTLs were able to kill MM cells in an HLA-restricted manner. These results indicate the existence of functional DCs and HM1.24-specific CTL precursors within PBSC harvests and provide the basis for cellular immunotherapy in combination with autologous PBSC transplantation in MM.