T‐cell activation by transgenic rice seeds expressing the genetically modified Japanese cedar pollen allergens

Transgenic rice seeds that contain genetically modified Cry j 1 and Cry j 2, the two major allergens of Cryptomeria japonica (Japanese cedar; JC), have been developed as immunotherapeutic candidates for JC pollinosis. Because the transgenic rice (TG‐rice) seeds express allergens containing whole amino acid sequences of Cry j 1 and Cry j 2 in the endosperm tissue (edible part of rice grain), they can potentially target all Cry j 1‐ and Cry j 2‐specific T‐cells. However, it was unknown whether antigenicity of Cry j 1 and Cry j 2 could be completely preserved in TG‐rice seeds. We verified the antigenicity of TG‐rice seeds to T‐cells through the analysis of the proliferative responses of T‐cells in Cry j 1‐ or Cry j 2‐immunized mice or T‐cell lines to TG‐rice seed extract. First, four mouse strains were immunized with Cry j 1 or Cry j 2. T‐cells in the immunized mice proliferated on treatment with TG‐rice seed extract, but not non‐transgenic wild‐type rice (WT‐rice) seed extract. Furthermore, T‐cell lines were established from the spleen cells of the immunized mice. Each T‐cell line resulted in a proliferative response to TG‐rice seed extract, but not to WT‐rice seed extract, suggesting that TG‐rice seeds certainly express T‐cell epitopes corresponding to T‐cell lines. Considering the modified amino acid sequences of Cry j 1 and Cry j 2 in TG‐rice seeds, the expression of specific T‐cell epitopes suggested that TG‐rice seeds express all possible T‐cell epitope repertoires of Cry j 1 and Cry j 2.