Bicistronic expression of the genes encoding the trastuzumab monoclonal antibody in tobacco using an internal ribosome entry site sequence

Monoclonal antibodies are heterotetramers consisting of four peptide chains—two identical light (L) chains and two identical heavy (H) chains and simultaneous equimolar expression of the corresponding genes is required to stable produce and assembly into a functional antibody. In order to co-express of multiple genes, different systems have been developed such as internal ribosome entry site (IRES) based vectors. IRES sequences are genetic elements that can drive cap-independent translation initiation of cistrons located downstream of the element. In this study, we constructed a bicsitronic vector for co-expression of genes encoding the H and L chains of the anti-breast cancer antibody trastuzumab (Herceptin®) using an IRES sequence derived from the Nicotiana tabacum heat-shock factor 1 (NtHSF1). The effectiveness of construction was evaluated in Nicotina tabacum using agroinfiltration method. Bisictronic expression of transgenes at the RNA transcription level was detected by semi-quantitative RT-PCR analysis. Western blot analyses revealed the efficient accumulation of tetrameric form of trastuzumab in tobacco leaf tissues and antibody content were ca. 0.44% of total soluble protein within 7 days after infiltration. The results of this study demonstrate the efficacy of a plant derived IRES element for bicistronic expression of heteromultimeric proteins.