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Definition of an Immunogenic Region Within the Ovarian Tumor Antigen Stratum Corneum Chymotryptic Enzyme

Authors' Affiliations: Departments of ¹ Microbiology and Immunology and ² Obstetrics and Gynecology, University of Arkansas for Medical Sciences, Little Rock, Arkansas

Requests for reprints: Martin J. Cannon, University of Arkansas for Medical Sciences, 4301 West Markham, Little Rock, AR 72205. Phone: 501-296-1254; Fax: 501-686-5359; E-mail: mjcannon{at}uams.edu.

Purpose: The serine protease stratum corneum chymotryptic enzyme (SCCE) is overexpressed by ovarian tumor cells, but is not expressed by normal tissues, suggesting that SCCE may be an attractive target for immunotherapy. In this study, we tested the hypothesis that dendritic cells loaded with SCCE peptides will induce ovarian tumor antigen–specific CD8⁺ CTL responses and antigen-specific CD4⁺ helper T cell responses.

Experimental Design: Computer algorithms were used to identify candidate HLA-A2.1-restricted CD8⁺ CTL epitopes and HLA-DR-binding CD4⁺ helper T cell epitopes within SCCE. CD8⁺ CTL stimulated with peptide-loaded dendritic cells were tested against targets expressing endogenous SCCE, including HLA-A2.1-matched ovarian tumor cells. Dendritic cells were also loaded with an extended SCCE peptide, SCCE 110-139, which encompassed a defined CD8⁺ CTL epitope and multiple candidate CD4⁺ T helper cell epitopes.

Results: CD8⁺ CTL specific for SCCE 123-131 lysed autologous macrophages infected with an SCCE-expressing recombinant adenovirus, and also lysed HLA-A2.1-matched, SCCE-expressing ovarian tumor cells. Dendritic cells loaded with SCCE 5-13 peptide stimulated an HLA-A2.1-restricted CD8⁺ CTL response, but with a reduced level of lysis against ovarian tumor cells. Dendritic cells loaded with SCCE 110-139 induced antigen-specific CD4⁺ T cell and CD8⁺ T cell responses. Although SCCE 110-139-loaded dendritic cells processed and presented the 123-131 epitope, the dominant CD8⁺ CTL response was directed against alternative epitopes within SCCE 110-139.

Conclusions: The 110-139 region of SCCE incorporates multiple CD8⁺ CTL and CD4⁺ helper T cell epitopes, and represents an attractive target antigen for immunotherapy of ovarian cancer.

Key Words: SCCE • dendritic cells • CD4⁺ T lymphocytes • CTL

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