Development and evaluation of transgenic rice seeds accumulating a type II-collagen tolerogenic peptide.

Type II collagen (CII) in joint cartilage is known to be a major auto-antigen in human rheumatoid arthritis. Several animal model- and clinical-studies on tolerance-based immunotherapy for the arthritis have been conducted by administrating synthetic immunodominant peptides through an oral route. In the present study, to produce a tolerogenic peptide with therapeutic potential in transgenic rice plants, a gene construct producing glutelin fusion protein with tandem four repeats of a CII250–270 peptide (residues 250–270) (GluA-4XCII250–270) containing a human T-cell epitope was introduced with a selection marker, hygromycin phosphotransferase gene (hygromycin-resistance gene) (hph), by co-transformation. Several transgenic plants with high and stable expression of gluA-4XCII 250–270 , but no hph, were selected based on both DNA and protein analyses. The GluA-4XCII250–270 fusion proteins were detected as both precursor and processed forms mainly in a glutelin fraction of rice endosperm protein extracts and in protein-body rich fractions prepared by density gradient ultracentrifugation. The amount of accumulated CII250–270 peptide was immunochemically estimated to be about 1 μg per seed. Feeding DBA/1 mice the transgenic rice seeds (25 μg of the peptide per mouse a day) for 2 weeks showed tendencies lowering and delaying serum specific-IgG2a response against subsequent and repeated intraperitoneal-injection of type II collagen. Taken these together, the CII-immunodominant peptide could effectively be produced and accumulated as a glutelin-fusion protein in the transgenic rice seeds, which might be useful as pharmaceutical materials and functional food for prevention and therapy for anti-CII autoimmune diseases like human rheumatoid arthritis.