Development of a Novel Methodology for Improving CTL Recognition of Prostate Specific Antigen (PSA) for the Immunotherapy of Prostate Cancer

Abstract

Abstract : The major goal of the proposed research is to develop a novel methodology for improving T cell epitopes. The underlying hypothesis is that T cells capable of recognizing tumor- associated antigens (TAA) are present but often difficult to activate. However, once activated such T cells might be effective against tumors due to the less stringent triggering requirements of mature effectors. We proposed to develop a novel bacterial expression system for modifying and screening the epitopes of PSA, a known TAA. In the current year, we have employed a saturation mutagenesis technique to a PSA peptide epitope we have identified. Expression libraries were constructed corresponding to each position in the peptide. These libraries were screened functionally, The clones showing enhanced activity were sequenced. From these screens, we were able to identify a number of enhanced peptide epitopes. Peptides were synthesized and tested in a functional assay. These peptides showed enhanced activity with the T cell hybridoma. The findings show that altered peptide ligands can be discovered using the novel methodology proposed. These approaches should be applicable to other tumor antigens.