Rice cell culture as an alternative production system for functional diagnostic and therapeutic antibodies

We investigated the suitability of transformed rice cell lines as a system for the production of therapeutic recombinant antibodies. Expression constr ucts encoding a single-chain Fv fragment (scFvT84.66, specific for CEA, the carcinoembryonic antigen present on many human tumours) were introduced in to rice tissue by particle bombardment. We compared antibody production lev els when antibodies were either secreted to the apoplast or retained in the endoplasmic reticulum (ER) using a KDEL retention signal. Production level s were up to 14 times higher when antibodies were retained in the ER. Addit ionally, we compared constructs encoding different leader peptides (plant c odon optimised murine immunoglobulin heavy and light chain leader peptides) and carrying alternative 5' untranslated regions (the petunia chalcone syn thase gene 5' UTR and the tobacco mosaic virus omega sequence). We observed no significant differences in antibody production levels among cell lines transformed with these constructs. The highest level of antibody production we measured was 3.8 mu g g(-1) callus (fresh weight). Immunological analys is of transgenic rice callus confirmed the presence of functional scFvT84.6 6. We discuss the potential merits of cell culture for the production of re combinant antibodies and other valuable macromolecules.