The sperm-derived SPANX family proteins can be found expressed in human tumors. Here, we aimed to perform a comprehensive study to evaluate immunotherapeutic relevance of one of its members, SPANX-B. We wanted to test its expression pattern in human tumors; and to evaluate CD4+ and CD8+ T cell responses in healthy humans after in vitro immunizations.
The Experimental Design
Expression of SPANX-B in human malignancies, including a multi-tumor tissue array of 145 primary tumors, was assessed utilizing RT/PCR, western blotting and immunohistochemical analysis. T cell immunogenicity and immunodominant epitopes of SPANX-B were studied using in vitro immunizations of healthy human donor-derived leukocytes.
SPANX-B was abundantly expressed in melanoma and carcinomas of lung, ovary, colon and breast. In melanoma, tissue array data indicated that it was expressed in advanced and metastatic disease. Unlike most tumor-associated antigens, SPANX-B was an immunogenic antigen that was recognized by circulating T cell precursors in healthy humans. Importantly, these T cells were readily expanded to generate SPANX-B –specific helper CD4+ and cytolytic CD8+ T cells that recognized unique immunodominant epitopes: at least one HLA-DR-restricted Pep-9 epitope (SPANX-B12–23) and two HLA-A2-restricted Pep-2 and Pep-4 epitopes (respectively, SPANX-B23–31 and SPANX-B57–65). The CD8+ T cells were fully functional to recognize and lyse HLA-A2-expressing tumors, including primary human melanomas.
SPANX-B is an immunogenic sperm-derived antigen that is expressed in a number of human tumors. SPANX-B is also efficiently recognized by the human T cell immune arm, indicating its significant value for the development of protective and therapeutic cancer vaccines.