Vaccine implications of folate binding protein, a novel cytotoxic T lymphocyte-recognized antigen system in epithelial cancers.

The immune system can be efficiently stimulated and targeted to specific antigens expressed exclusively or preferentially by experimental cancers. The foremost limitations to extending this vaccine technology to the prevalent epithelial-derived cancers are the lack of: (a) identified tumor-associated antigens recognized by cellular immunity; (b) antigens expressed on the majority of tumor cells during disease progression; and (c) immunogenic CTL epitopes. To date, only HER-2/neu has been shown to be the source of naturally occurring, MHC-restricted, CTL-recognized peptides in epithelial tumors. In this study, we demonstrate that the human high-affinity folate binding protein (FBP), which is a source of antigenic peptides recognized in ovarian cancer, is also recognized in breast cancer. Both immunodominant E39 (FBP, 191-199) and subdominant E41 (FBP, 245-253) epitopes are presented by HLA-A2 in these cancers. These peptides are efficient at amplifying the response of tumor-associated lymphocyte populations in terms of lytic function, enhanced proliferation, and specific IFN-gamma release. On a per cell basis, tumor-associated lymphocytes stimulated with the FBP peptides exhibit enhanced cytotoxicity not only against peptide-loaded targets but also against FBP-expressing epithelial tumors of different histologies. Furthermore, FBP peptides induced E39-specific CTLs and E39- and E41-specific IFN-gamma and IP-10 secretion in certain healthy donors. The broad distribution of FBP among >90% of ovarian and endometrial carcinomas, as well as 20-50% of breast, lung, colorectal, and renal cell carcinomas, along with pronounced differential overexpression in malignant tissues compared with the extremely limited expression in normal epithelium, suggests the exciting potential of a widely applicable FBP-based vaccine in epithelial cancers.