Utility of the P 19 suppressor of gene‐silencing protein for production of therapeutic antibodies in N icotiana expression hosts

Summary To study how the P 19 suppressor of gene‐silencing protein can be used effectively for the production of therapeutic glycoproteins, the following factors were examined: the genetic elements used for expressing recombinant proteins; the effect of different P 19 concentrations; compatibility of P 19 with various N icotiana tabacum cultivars for transgenic expression; the glycan profile of a recombinant therapeutic glycoprotein co‐expressed with P 19 in an RNA i‐based glycomodified N icotiana benthamiana expression host. The coding sequences for the heavy and light chains of trastuzumab were cloned into five plant expression vectors (102–106) containing different 5′ and 3′ UTR s, designated as vector sets 102–106 mAb. The P 19 protein of T omato bushy stunt virus ( TBSV ) was also cloned into vector 103, which contained the C auliflower mosaic virus ( C a MV ) 35 S promoter and 5′ UTR together with the terminator region of the nopaline synthase gene of Agrobacterium. Transient expression of the antibody vectors resulted in different levels of trastuzumab accumulation, the highest being 105 and 106 mAb at about 1% of TSP . P 19 increased the concentration of trastuzumab approximately 15‐fold (to about 2.3% of TSP ) when co‐expressed with 103 mAb but did not affect antibody levels with vectors 102 and 106 mAb. When 103 mAb was expressed together with P 19 in different N . tabacum cultivars, all except L ittle C rittenden showed a marked discolouring of the infiltrated areas of the leaf and decreased antibody expression. Co‐expression of P 19 also abolished antibody accumulation in crosses between N . tabacum cv. I‐64 and L ittle C rittenden, indicating a dominant mode of inheritance for the observed P 19‐induced responses.