The onconeural antigens appear to serve as tumor rejection antigens in the paraneoplastic neurologic disorders. Here, we used an unbiased peptide binding screen, followed by studies in HLA-A2.1 transgenic mice to identify naturally processed HLA-A2.1 restricted epitopes of the paraneoplastic cerebellar degeneration breast/ovarian cancer antigen cdr2. These mice were used to clone high-avidity cdr2-specific CD8⁺ T cells that recognize human tumor cells presenting endogenously loaded MHC class I-cdr2 peptide. T cells with this specificity were detected in the peripheral blood of two HLA-A2.1⁺ paraneoplastic cerebellar degeneration patients. We cloned T cell receptor (TCR) α and β genes from cdr2-specific T cells; electroporation of RNA encoding this TCR turned nonreactive donor T cells into efficient killers of human cdr2-expressing tumor cells. Cloned cdr2-specific TCR genes provide a clinically relevant means for immunologic targeting of human gynecologic cancers.