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Multiple myeloma (MM) cells express certain tumour-associated antigens (TAAs) that could serve as targets for active-specific immunotherapy. The aim of the present study was to test the MM/dendritic cell (DC) fusion as a vaccination strategy. We fused MM cells with DC to generate fusion cells (FCs) and tested their antigen presenting cell (APC) function in mixed lymphocyte reactions and cytotoxicity assays. First, the HS Sultan and SK0-007 HAT sensitive human MM cell lines and DCs generated from peripheral blood of normal donors were fused in the presence of 50% polyethylene glycol to form FCs. Next, tumour cells freshly isolated from patients were similarly fused with autologous DCs to generate FCs. The FCs demonstrated a biphenotypic profile, confirmed both by flow-cytometry and dual immunofluorescence microscopy. These FCs induced MM-specific cytotoxicity. FCs, but not MM cells or DCs alone, were potent stimulators of autologous patient T cells. More importantly, FC-primed autologous peripheral blood mononuclear cells demonstrated major histocompatibility complex-restricted MM-specific cytolysis. These studies therefore demonstrated that MM/DC FC can trigger an autologous immune response to MM cells and formed the framework for a clinical trial currently underway. [ABSTRACT FROM AUTHOR]

Despite novel treatment strategies, multiple myeloma (MM) remains an incurable disease with low immunogenicity and multiple immune defects. We developed an ex vivo strategy for inducing myeloma-specific cytotoxic T lymphocytes (CTLs) and demonstrate the possibility of identification and long-term in vivo monitoring of individual myeloma-specific T-cell clones using the most sensitive clonotypic assay that is able to detect low frequencies of T-cell clones (1 clonotypic cell in 106 cells). Ten patients with MM were examined for the presence of tumour-reactive T cells using dendritic cells loaded with autologous tumour cells. All patients had detectable myeloma-reactive T cells in vitro. Expanded myeloma-reactive T cells demonstrated specific cytotoxic effects against autologous tumour cells in vitro (median 39·6% at an effector:target ratio of 40:1). The clonality of myeloma-specific T cells was studied with a clonotypic assay, which demonstrated both oligoclonal and monoclonal populations of myeloma-specific T cells. CD8+ CTLs were the most immunodominant myeloma-specific T-cell clones and clinical responses were closely associated with the in vivo expansion and long-term persistence of individual CD8+ T-cell clones, usually at very low frequencies (10−3–10−6). We conclude that the clonotypic assay is the most sensitive tool for immunomonitoring of low-frequency T cells. [ABSTRACT FROM AUTHOR]