High-Yield Production of pBR322-Derived Plasmids Intended for Human Gene Therapy by Employing a Temperature-Controllable Point Mutation

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Abstract
Production of large quantities of highly purified plasmid DNA is essential for gene therapy. A low-copy-number pBR322-derived plasmid (VCL1005) was converted to a high-copy-number plasmid (VCL1005G/A) by incorporating a G → A mutation that affects initiation of DNA replication from the CoIE1 origin of replication. Because the phenotypic effect of this mutation is enhanced at an elevated temperature, a further increase in yield was achieved by changing the growth temperature from 37°C to 42°C at mid-log phase during batch and fed-batch fermentation. The combined effect of the single base-pair change and the elevated growth temperature produced an overall yield of 2.2 grams of plasmid DNA available for recovery from a 10-liter fed-batch fermentation compared to 0.03 grams from a 10-liter batch fermentation, a 70-fold increase in yield. The plasmid DNA isolated from this process contained lower levels of RNA and chromosomal DNA contaminants, simplifying downstream processing. This paper describes a method for increasing the overall plasmid DNA yield from any pBR322-derived plasmid by employing a temperature-sensitive single point mutation that affects the negative regulation of replication from the CoIE1 origin of replication. The change reported facilitates low volume, high-yield manufacturing of plasmid DNA intended for human gene therapy.