Selection And Identification Of Mimic Epitope Of Gastric Cancer Associated Antigen And Construction Of A Phage Display Library Of Human Antibodies

Tumor antigens and epitopes play important roles in inducing immune responses against tumor. The ideal epitope vaccine includes a group of optimized CTL epitopes, Th epitopes and B-cell epitopes. Selection and identification of B-cell epitopes are important for tumor vaccine designing. Filamentous bacteriophages have been used extensively in recent years for the display on their surface of large repertoires of peptides. Phage display system has many advantages: efficacy of biopanning, the ability for amplification and the linkage of the displayed peptide with its encoding DNA sequence within the phage particle, enabling quick and simple elucidation of binding sequences. Many papers have shown that it is possible to select phage display peptides that mimic the original characteristic of antigen binding to specific antibodies, without previous knowledge of the antigen structure. In this respect, phage display technology is well established as an important experimental approach in the development of -5- novel vaccines and drugs. In the present study, to select the possible mimic epitope of gastric cancer, a random phage display peptide library constructed on pill was biopanned using MGb 1 -Ab as selective molecule. After three biopanning procedures , there was remarkable enrichment for the titer of bound phages in each biopanning procedure. Then, 10 phage clones were selected from the third biopannirtg with ELISA. Single chains of DNA were sequenced and amino acid sequences were deduced. According to the homology of amino acid sequences of displayed peptides, preserved epitope information was obtained. Most of the positive phage dons had motifs of H(x)Q or L(x)S. ELISA showed that the positive phage clones had activity of specific binding to MGbI-Ab and could inhibit the binding of MGbl-Ab to gastric cancer cell KATOæ¡°Il. After immunization of Babl/c mice with different purified positive phage display peptides, î–’ISA and FACS were conducted. The results showed that one phage display peptide could induce specific serum which could bind to gastric cancer cell KIATOæ¡°II.