We have identified novel CD19 and CD20 antigen-derived HLA-A2.1-specific immunogenic peptides, CD19150–158 (KLMSPKLYV) and CD20188–196 (SLFLGILSV), for generating cytotoxic T lymphocytes (CTLs) against malignant B-cell diseases. Initial testing showed that the CTLs displayed antigen-specific and HLA-A2.1-restriced cytotoxic activity against both Burkitt’s lymphoma and chronic lymphoid leukemia cell lines. The observed cytotoxic activity of the CTLs was shown to be specific to the CD19150–158 or the CD20188–196 peptides. Additionally, the CTLs displayed a distinct phenotype (majority CD69+/CD45RO+) along with a significant (p<0.05) increase in cell proliferation and IFN-γ release following re-stimulation with HLA-A2.1+/CD19+/CD20+ tumor cell lines. Based on emerging information that clonogenic myeloma cells express CD19 and/or CD20, we evaluated the activity of the CD19 and CD20 peptide specific-CTLs against several multiple myeloma cell lines. Five of 10 myeloma cell lines evaluated were HLA-A2.1-positive and expressed both CD19 and CD20 antigens. CD19 peptide specific-CTLs generated from normal donors were able to specifically lyse CD19+/HLA-A2.1+ MM cell lines (30% lysis; 10:1 E:T ratio) but did not lyse CD19/HLA-A2.1+ or CD19+/HLA-A2.1 cell lines. Similarly, the CD20-specific CTLs generated from normal donors lysed CD20+/HLA-A2.1+ MM cell lines (25% lysis; 10:1 E:T ratio), in a manner restricted to HLA-A2.1 and specific to antigens. We next showed IFN-γ production by the CTLs after exposure to CD19+/HLA-A2.1+ or CD20+/HLA-A2.1+ MM cells. Moreover, we have demonstrated the ability to expand CD20-CTLs under serum-free culture conditions while maintaining their cytotoxic activity (28–49%). In ongoing studies, we are evaluating the ability of CD19- and CD20-specific CTLs to eliminate clonogenic myeloma cells in vitro and in vivo in a SCID mouse model of myeloma. These preclinical studies strongly suggest that immunogenic CD19 and CD20 peptide-based vaccines represent a promising immunotherapeutic approach in myeloma.

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