Development of a purification process for adenovirus: controlling virus aggregation to improve the clearance of host cell DNA.

The clearance of host cell DNA is a critical goal for purification process development for recombinant Ad5 (rAd5) based vaccines and gene therapy products. We have evaluated the clearance of DNA by a rAd5 purification process utilizing nuclease digestion, ultrafiltration, and anion exchange (AEX) chromatography and found residual host cell DNA to consistently reach a limiting value of about 100 pg/10(11) rAd5 particles. Characterization of the purified rAd5 product using serial AEX chromatography, hydroxyapatite chromatography, or nuclease treatment with and without particle disruption showed that the residual DNA was associated with virus particles. Using a variety of additional physical characterization methods, a population of rAd5 virus in an aggregated state was detected. Aggregation was eliminated using nonionic detergents to attenuate hydrophobic interactions and sodium chloride to attenuate electrostatic interactions. After implementation of these modifications, the process was able to consistently reduce host cell DNA to levels at or below 5 pg/10(11) rAd5 particles, suggesting that molecular interactions between cellular DNA and rAd5 are important determinants of process DNA clearance capability and that the co-purifying DNA was not encapsidated.