Cytoplasmic Transduction Peptide-Fused Recombinant Tumor-Associated Antigens Elicit Potent Myeloma-Specific Cytotoxic T Lymphocytes By Loading Onto Dendritic Cells: Implications of Feasible Tumor Antigens for Clinical Application Against Multiple Myeloma

Dendritic cell (DC)-based vaccines are one of promising tools in patients with multiple myeloma (MM). However, the source of tumor antigens is still challenging in this field. Here, we evaluated the feasibility of tumor-associated antigens (TAAs) to be loaded onto DCs for improving the efficacy of immunotherapy against MM. Quantitative PCR was performed to evaluate the expression of TAAs from malignant plasma cells isolated from bone marrow mononuclear cells of MM patients. Based on quantitative PCR analysis, 4 cancer testis antigens (SSX2, SSX4, MAGE-A3 and MAGE-C2), hTERT, BCMA, and CD38 were selected to make CTP-fused recombinant TAAs. Then, we made cytoplasm transduction peptide (CTP)-fused recombinant proteins (CTP-SSX2, CTP-SSX4, CTP-MAGEA3, CTP-MAGEC2, CTP-hTERT, CTP-BCMA, and CTP-CD38) for the efficient delivery of TAAs to DCs. After determination of optimal protein dose for loading onto DCs, several functional studies were performed by the DCs. The CTP-fused recombinant TAAs did not deteriorate the function of DCs in terms of phenotype expressions and cytokine productions, including a Th1-polarizing capacity of naïve T cells. DCs loaded with each CTP-fused recombinant TAA had successfully generated a myeloma-specific cytotoxic T lymphocyte (CTL) to kill myeloma cell lines and primary myeloma cells. This study showed that CTP-fused recombinant myeloma-associated proteins were a useful tumor antigen source to be loaded onto DCs for generation of myeloma-specific CTLs in vitro . Therefore, CTP-fused recombinant TAAs will become a feasible tumor antigen for the clinical application of DC-based cancer immunotherapy in the field of MM.