Removal of neutralized model parvoviruses and enteroviruses in human IgG solutions by nanofiltration

Nanofiltration has proven to be an effective technology for virus removal. The small nonenveloped viruses, such as HAV and parvovirus B19 (B19), are evidently more difficult to remove than the larger enveloped viruses. However, since antibodies against these viruses, HAV and B19, are constantly present in large plasma pools, it is conceivable that antibody binding will lead to an increase in size of the viruses due to a corona of antibodies on the virus surfaces. These enlarged viruses should be easier to remove by nanofiltration than naked viruses. In this study, antibody-coated viruses and free virions were subjected to nanofiltration to determine whether the antibody-mediated increase in size contributes to the elimination of viruses which are otherwise too small to be retained by filters of a given nominal pore diameter.

One-percent IgG or 1-percent albumin solutions were spiked with bovine enterovirus (BEV) and filtered through 50-nm filters. This virus cross-reacts with antibodies in pooled human IgG solutions but persists as free virions in albumin solutions. Similarly, two parvoviruses, bovine parvovirus (BPV) and minute virus of mice (MVM), in 1-percent IgG solutions were filtered through 20-nm filters. BPV cross-reacts with antibodies in human IgG, whereas MVM remains unaffected. Virus removal was assessed by in vitro infectivity assays. Two methods were developed to displace the antibodies from BEV and BPV and thereby render them accessible for titration.

Antibody-coated BEV was eliminated to below detection limit by the 50-nm filters (logarithmic reduction factors [LRF] > or = 5), while free BEV virions passed without restraint through the same filters. Similarly, antibody-coated BPV was completely retained by the 20-nm filters (LRF > or = 5). MVM virions were strongly retained by the 20-nm filters; however, the virus was still detectable in the filtrate.

These results indicate that viruses with bound antibodies are efficiently eliminated by nanofiltration by use of filters having nominal pore sizes larger than the diameter of the respective free virions.