MAD-CT-2 Identified as a Novel Melanoma Cancer-testis Antigen Using Phage Immunoblot Analysis

One focus in the field of tumor immunology is the identification of cancer-specific antigens that might be exploited as therapeutic targets or as immunologic diagnostic markers. Cancer-testis antigens (CTAs) are of particular interest as potential target antigens given that their expression is typically restricted to germ cells among normal tissues, but aberrantly expressed in multiple tumor types. In the current report, we sought to evaluate serum antibody immune responses to a defined panel of CTA from multiple antigen families to identify potential tumor-specific antigens that could potentially serve as candidate target antigens for immunotherapy or diagnostic purposes. This was conducted by screening sera from male patients with metastatic melanoma (n=44) and volunteer blood donors (n=50) against a panel of λ phage-encoded CTA. We found that IgG antibody responses occurred in 39% of patients with melanoma to at least one of these antigens compared with 4% of controls (P<0.001). We found antibody responses to one antigen, MAD-CT-2, occurred in 27% of patients compared with 0/50 controls (P<0.0001). These findings, along with the demonstration that MAD-CT-2 is expressed in melanoma cell lines, identified MAD-CT-2 as a novel melanoma CTA.