Novel Myeloma-Specific Multiple Peptides Able to Generate Cytotoxic T Lymphocytes: Potential Therapeutic Application in Multiple Myeloma and Other Plasma Cell Disorders,

Abstract 3990

Although single antigen targeted vaccination has been evaluated in multiple myeloma (MM), its efficacy has been limited. The major challenges in developing a MM-specific immunotherapy include heterogeneity of tumor associated antigens (TAA) expression, frequent mutations of specific TAA and variability of the human T-cell repertoire. We hypothesize that peptide vaccine efficacy may be enhanced by stimulating immune cells with multiple epitopes derived from different TAA. The goal of our study was to examine the effectiveness of a combination of four immunogenic HLA-A2-specific peptides derived from multiple MM-associated antigens to induce myeloma-specific cytotoxic T lymphocytes (CTL) ex vivo. The specific target antigens, XBP1, CD138 and CS1 play a significant role in MM pathogenesis. We have identified immunogenic HLA-A2-specific epitopes: heteroclitic XBP1 US_184–192 (YISPWILAV), heteroclitic XBP1 SP_367–375 (YLFPQLISV), native CD138_260–268(GLVGLIFAV) and native CS1_239–247 (SLFVLGLFL). In this study, first we evaluated each of the four epitopes in parallel and confirmed strong HLA-A2 binding affinity of the four individual peptides and demonstrated comparable phenotypes and overall functional activity of CTL generated with each peptide against HLA-A2⁺ MM cells. We next evaluated the multipeptide-specific CTL (MP-CTL) generated using a combination of all four peptides. The MP-CTL had an increased percentage of total CD8⁺ T cells, CCR7⁻CD45RO⁺(effector memory) and CD69⁺ (activated) cells. In addition, the MP-CTL demonstrated polyfunctional immune activities [higher IFN-g production, cell proliferation and cytotoxicity] against HLA-A2⁺ primary MM cells and MM cell lines, but not to HLA-A2⁻ MM cells or HLA-A2⁺ breast cancer cells. Importantly, the MP-CTL demonstrated peptide-specific responses to all relevant epitopes including heteroclitic XBP1 US_184–192 (YISPWILAV), heteroclitic XBP1 SP_367–375 (YLFPQLISV), native CD138_260–268(GLVGLIFAV) and native CS1_239–247 (SLFVLGLFL), but not to an irrelevant CMV pp65 (NLVPMVATV) peptide in a various functional assays evaluated cytokine production and cytotoxicity. Moreover, the MP-CTL demonstrated similar or greater response against MM, compared to CTL generated using the individual peptides. Thus, targeting MM-associated antigens using a cocktail of specific peptides may provide an effective therapeutic application in patients with MM and related plasma cell disorders.