Gamma irradiation of animal sera for inactivation of viruses and mollicutes--a review.

Animal-derived materials such as animal sera represent a low, but finite, risk for introduction of an adventitious agent (virus or mollicute) into a biological bulk harvest during upstream manufacturing processes involving mammalian cell substrates. Viral and mollicute (Mycoplasma sp. and Acholeplasma sp.) contamination events have been relatively rare, but many of those that have been reported have been attributed to use of infected animal sera in growth media during cell expansion. The risk of introduction of viruses and mollicutes may be mitigated by elimination of the use of animal sera and implementation instead of chemically defined or serum- and animal-derived material-free cell culture media. When use of animal sera is unavoidable, however, mitigation of the risk of introducing an adventitious contaminant may involve treatment of the sera to inactivate potential contaminants. Gamma irradiation is one of the most widely employed methods for viral and mollicute inactivation in animal sera. In this article, we review the inactivation results reported for viral and mollicute inactivation in frozen serum. Studies performed to assess the impact of gamma irradiation on serum quality and performance are also discussed. The available data indicate that inactivation of mollicutes in serum is essentially complete at the gamma radiation doses normally employed (25-40 kGy), while the efficacy and kinetics for viral inactivation in serum by gamma irradiation appear to be dependent in part upon the size of the target virus.

Gamma-irradiation of serum for the inactivation of adventitious contaminants.

Assurance of viral and mycoplasma safety in biopharmaceuticals is best achieved through elimination of animal-derived materials from the manufacturing process. Where this is not possible, the risk of introducing a contaminant through use of the material must be assessed and mitigated. Bovine-sourced serum represents an animal-derived material that is required for certain biopharmaceutical manufacturing processes. Gamma-irradiation of frozen bovine serum was investigated as an approach for mitigating the risk of introducing viral or mycoplasma contaminants. Mycoplasmas in frozen bovine serum were effectively inactivated by gamma-irradiation at 25-40 kGy. The larger viruses tested, respiratory enteric orphan (REO) and Cache Valley virus (CVV), were inactivated completely, while the smaller virus, simian virus type 40, was not inactivated. Gamma-irradiation of bovine-sourced serum is therefore useful for mitigating the risk of introduction of mycoplasmas and many of the viral contaminants found in biologics unprocessed bulk (e.g., CVV, REO virus, epizootic hemorrhagic disease virus). This mitigation strategy is not useful for the smaller viruses (e.g., polyomaviruses, parvoviruses, picornaviruses, caliciviruses).