LAUSR

For several decades, a plant‐based expression system has been proposed as an alternative platform for the production of biopharmaceuticals including therapeutic monoclonal antibodies (mAbs), but the immunogenicity concerns associated with plant‐specific N‐glycans attached in plant‐based biopharmaceuticals has not been completely solved. To eliminate all plant‐specific N‐glycan structure, eight genes involved in plant‐specific N‐glycosylation were mutated in rice (Oryza sativa) using the CRISPR/Cas9 system. The glycoengineered cell lines, PhytoRice®, contained a predominant GnGn (G0) glycoform. The gene for codon‐optimized trastuzumab (TMab) was then introduced into PhytoRice® through Agrobacterium co‐cultivation. Selected cell lines were suspension cultured, and TMab secreted from cells was purified from the cultured media. The amino acid sequence of the TMab produced by PhytoRice® (P‐TMab) was identical to that of TMab. The inhibitory effect of P‐TMab on the proliferation of the BT‐474 cancer cell line was significantly enhanced at concentrations above 1 μg/mL (****P < 0.0001). P‐TMab bound to a FcγRIIIa variant, FcγRIIIa‐F158, more than 2.7 times more effectively than TMab. The ADCC efficacy of P‐TMab against Jurkat cells was 2.6 times higher than that of TMab in an in vitro ADCC assay. Furthermore, P‐TMab demonstrated efficient tumour uptake with less liver uptake compared to TMab in a xenograft assay using the BT‐474 mouse model. These results suggest that the glycoengineered PhytoRice® could be an alternative platform for mAb production compared to current CHO cells, and P‐TMab has a novel and enhanced efficacy compared to TMab.