BTI scientists involved in the study: Dr. Lin Pao Chun (right) and Dr. Song Zhiwei (left).
Dr. Song contributed to the conceptualization and design of the study. Dr. Lin designed and performed the experiments, as well as co-wrote the manuscript.
Cells that are most commonly used for producing protein drugs were originally obtained from the ovary of a Chinese hamster (CHO) more than 60 years ago. For decades, CHO cells have been used to make some of the proteins that exist in our bodies. These protein products can be used to treat human diseases including cancers. To reduce production costs, biotech companies around the world have tried many methods to make these cells produce more proteins.
Each CHO cell has about 24,000 genes. Studies have shown that about one-tenth of these genes are absolutely required for the cells to survive and grow. Scientists at BTI and their industry collaborator, MSD, explored if the remaining ninety percent of the genes would affect protein production in CHO cells. The team studied 3,000 genes and identified a new way to make CHO cells produce more antibody products—by repressing some of these genes.
Manipulating the expression of specific genes that are known to be involved in protein synthesis, folding, and secretion for the purpose of increasing productivity has been intensively investigated. However, there have been no reports on CHO cell‐specific functional screens to identify novel gene targets that may impact the production of secreted recombinant proteins. Therefore, we performed the first large-scale CHO cell‐specific siRNA screen using seven different recombinant CHO lines in which different antibodies were produced. From the screen, several genes were consistently identified to be able to enhance antibody production when silenced in different CHO cell lines. Four genes were selected for further evaluation by permanently inactivating them with CRISPR‐Cas9 in another antibody-producing CHO cell line. Single knockout of 3 out of the 4 genes resulted in more than 90% increase in specific antibody productivity.
Over the last five years, antibodies have become the best-selling drugs in the pharmaceutical market. In 2018, eight of the top ten best-selling drugs worldwide were biologics and many of them are produced in CHO cells. The global therapeutic monoclonal antibody (mAb) market was estimated at US$115 billion in 2018 and is expected to reach US$300 billion by 2025. By the end of 2019, 79 therapeutic mAbs have been approved by the United States Food & Drug Administration and many more are in the pipeline. Between 2013 and 2019, global production of mAbs more than doubled to nearly 25 metric tons a year. These mAb products are used to treat various human diseases, including cancers, autoimmune and metabolic disorders. Most of these diseases are age-related, and the market still has significant growth potential as ageing populations in both developing and industrialized countries are growing rapidly. With limited production capacity, increased specific productivity of each cell line is a top priority to meet the fast-growing demand.
Lin PC, Liu R, Alvin K, Wahyu S, Murgolo N, Ye J, Du Z, Song Z. (2020) Improving Antibody Production in Stably Transfected CHO Cells by CRISPR-Cas9-Mediated Inactivation of Genes Identified in a Large-Scale Screen with Chinese Hamster-Specific siRNAs. Biotechnol J. 2020 Oct 20;e2000267. doi: 10.1002/biot.202000267.