Fermentation Design for the Manufacture of Therapeutic Plasmid DNA

OCTOBER 2005 P lasmid DNA production is becoming increasingly important as gene therapies make their way into clinical trials and eventually into the pharmaceutical marketplace. To date, most efforts toward process development have focused on downstream processing. However, the quality of a final product is ultimately determined by fermentation strategy. Through optimization of the growth environment for plasmid-producing organisms, improvements can be achieved in biomass yield, plasmid yield, and plasmid quality. The primary goal when designing a fermentation process for plasmids is to maximize both the volumetric (mg/L) and specific (mg/g) yields of supercoiled plasmid. Optimizing volumetric yield allows for smaller and more economical fermentations, whereas optimizing specific yield improves plasmid purity in downstream processing. It is also critical that each fermentation produces highquality plasmids. The FDA recognizes that open-circle, linear, and nicked forms may be less effective therapeutically than supercoiled DNA (1). Those other forms can be very difficult to separate from the supercoiled plasmid during purification; therefore, fermentation processes should also be optimized to produce a high percentage of supercoiled plasmid.