Novel immunodominant epitopes derived from MAGE-A3 and its significance in serological diagnosis of gastric cancer.

ABSTRACT

PURPOSE: To evaluate the significance of MAGE-A3 novel immunodominant epitopes in serological diagnosis of gastric cancer. METHODS: B cell, CTL, and Th epitopes of MAGE-A3 were analyzed using computer-assisted techniques. Three possible immunodominant epitope peptides located at 5aa-23aa (QRSQHCKPEEGLEARGEAL), 112aa-131aa (KVAELVHFLLLKYRAREPVT), and 232aa-246aa (EGREDSILGDPKKLL) with potential B cell-dominant epitope, high-score HLA-A2 and A24 restriction CTL epitope, and HLA-DRB restriction Th epitope were selected. After optimized by prokaryotic codon, these genes were expressed as Trx-His-tag recombinant proteins in Escherichia coli and purified by Ni-NTA agarose beads. Three recombinant proteins were identified by Western blotting using His-tag monoclonal antibody and the serum antibodies from the patient of gastric cancer. The level of specific antibodies in the sera from 210 patients with gastric cancer, 56 patients with chronic gastritis, and 116 healthy controls was further analyzed by indirect ELISA. RESULTS: Three MAGE-A3 epitope recombinant proteins about 20 kDa molecular weight were specifically recognized by His-tag monoclonal antibody and the serum of gastric cancer patients. ELISA based on the epitope recombinant protein indicated that gastric cancer patients had significantly higher reactivity to these immunodominant epitope proteins compared with chronic gastritis and healthy individuals (P < 0.05). Furthermore, the serum antibody positive rate in the gastric cancer group was also significantly higher than that in the chronic gastritis patients and healthy controls (P < 0.05), while there was no significant difference in gastritis group and the healthy control group (P > 0.05). CONCLUSIONS: These study results demonstrated that these three predictive epitopes may be potential targets for applications in the design of serological diagnosis tools for gastric cancer.