Frequently Asked Questions - Bioprocess Monitoring

The test article supernatant, whether from a large or a small test article, is clarified by filtration or centrifugation, then concentrated by density gradient ultracentrifugation techniques.

The concentrated test article is then prepared by mixing a known concentration of latex spheres with the unknown number of virus particles from the test article. This mixture is mounted onto grids, negatively stained, and examined in the transmission electron microscope. Both latex spheres and virus particles are enumerated, and the concentration of virus particles in the test article is determined by using ratio formulas.

Test articles from cell banks, master seed stocks, or production seed stocks are examined using ultra-thin sectioning.  Test articles are prepared following standard written protocols, then examined by transmission electron microscope for the presence of virus or other microbial contaminants.  Examination is conducted at low and high magnifications appropriate for the test articles.

This assay allows for the determination and identification of viruses present within, or secreted from, the cells used to produce biopharmaceuticals.