Abstract
The production of high-purity mRNA drug substances by in vitro transcription utilizing T7 RNA polymerase can be challenging due to the formation of product related impurities. These include double-stranded RNA, fragmented mRNA, and uncapped transcripts. This review examines the known mechanisms underlying the formation of the major mRNA impurities during in vitro transcription (IVT), their biological impact and strategies for their mitigation. Some companies have utilised engineered T7 RNA polymerases and optimized transcription conditions to improve mRNA purity. There is a growing focus on refining upstream and downstream processes to improve mRNA purity. The current analytical approaches for impurity detection and quantification are reviewed. These range from immunological assays to advanced chromatographic and sequencing technologies. Continued innovation is needed to develop the next generation of high-throughput, cost-efficient analytical methods for quantifying mRNA impurities. Together improved transcription, purification and analysis enable the manufacture of safe efficacious mRNA for vaccines and therapeutics.