Combined real time PCR and immunohistochemical evaluation of sperm protein 17 as a cancer-testis antigen

We previously identified sperm protein 17 (Sp17) as a normal testicular protein aberrantly expressed in a proportion of multiple myeloma (MM). However, recent studies have generated controversies on the normal tissue expression of Sp17 and whether or not it is a suitable target for immunotherapy. In this study, we have used a combination of real time polymerase chain reaction and immunohistochemistry on a large panel of normal tissues. Although Sp17 transcripts could be detected in some normal tissues, the levels of expression were <2% of those in normal testis. In contrast, Sp17+ myeloma cells expressed 3-18% of normal testis levels of Sp17 transcript. Immunohistochemistry using two Sp17 murine monoclonal antibodies, each directed at a non-overlapping B-cell epitope, showed Sp17 protein to be expressed only in testis and not any other normal tissues. Specificity of binding of the antibodies to testis was also confirmed in competitive binding assays. Our results therefore further suggest Sp17 as a cancer-testis antigen in MM and support its suitability as a target for immunotherapy.