Identification of a novel cancer-testis antigen CRT2 frequently expressed in various cancers using representational differential analysis

Purpose: Cancer-testis antigens are promising targets for cancer immunotherapy. Identification of additional cancer-testis antigens with frequent expression in various cancers was attempted using representational differential analysis (RDA) and immunogenicity evaluation. Experimental Design: cDNAs preferentially expressed in testis were enriched using RDA by subtraction between testis and normal tissues. Thirty clones showing cancer-testis - like expression based on EST database analysis were evaluated by reverse transcription-PCR. A potential antigen, CRT2, was identified and its expression was analyzed with a newly generated anti-CRT2 antibody. The immunogenicity of CRT2 was examined based on reactivity with serum immunoglobulin G (IgG) from cancer patients, using Western blot and ELISA analysis, and on in vitro induction of tumor-reactive CTLs from HLA-A24 transgenic mice and human peripheral blood lymphocytes. Results: CRT2 was expressed in elongated spermatids of testis among normal tissues and in various cancer cell lines and tissues. The recombinant CRT2 protein was recognized by serum IgG from patients with various cancers in Western blot and ELISA analyses. ACRT2-derived peptide was identified as an HLA-A24-restricted T-cell epitope that induced tumor-reactive CTLs. Conclusion: CRT2 was identified as a new cancer-testis antigen expressed in elongated spermatids of testis and in cancer tissues (particularly melanoma) that is recognized by serum IgG from cancer patients. An HLA-A24-restricted T-cell epitope capable of inducing tumor-reactive CTLs was identified, suggesting that CRT2 may be useful for cancer diagnosis and immunotherapy.