ABSTRACT
SHUKLA: “dk3347_c014” — 2006/5/23 — 17:58 — page 419 — #1
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 14.2 Health Risk from Virus Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 14.3 Rationale and Action Plan for Viral Clearance Studies . . . . . . . . . . . . . 422 14.4 Choice of Viruses in the Viral Clearance Studies . . . . . . . . . . . . . . . . . . . 423 14.5 Selection of Steps to be Evaluated in Viral Clearance Studies . . . . . 426 14.6 Scale Down of Manufacturing Process Steps. . . . . . . . . . . . . . . . . . . . . . . . 427 14.7 Estimation of Virus Titers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 14.8 Cytotoxicity and Viral Interference Testing . . . . . . . . . . . . . . . . . . . . . . . . . 430 14.9 Design of Virus-Spiking Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 14.10 Calculation of Log Reduction Factors in a Viral
Clearance Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 14.11 Assessment of the Safety Factor in the Final Drug Product . . . . . . . . 434 14.12 Quantitative Polymerase Chain Reaction Assay for Virus
Quantitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 14.13 Identification of Worst-Case Situations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 14.14 Column Sanitization and Reuse of Chromatography Resins . . . . . . . 438 14.15 Limitations of Viral Clearance Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 14.16 Re-Evaluation of Viral Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 14.17 Bracketed Generic Approach to Virus Clearance Studies. . . . . . . . . . . 440 14.18 Multivirus-Spiking Approach for Virus Clearance Studies . . . . . . . . . 442 14.19 Virus Clearance across Membrane Adsorbers . . . . . . . . . . . . . . . . . . . . . . . 442 14.20 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 Appendix: Use of the Poisson Distribution to Determine Virus Titers . . . . . 444 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
SHUKLA: “dk3347_c014” — 2006/5/23 — 17:58 — page 420 — #2
The use of continuous cell lines of mammalian origin in the manufacture of recombinant proteins and monoclonal antibodies introduces the potential of viral contamination in the purified product. Although to date no biotech products have been implicated in the transmission of infectious viruses, there are some recent documented instances of adventitious viral contamination of cell culture based products [1,2]. In each of these cases, contamination was most likely thought to be from an adventitious source, such as the medium or the serum used in the cell culture process. Additionally, rodent cell lines that are very commonly used in the manufacturing of monoclonals are known to express multiple copies of endogenous retroviral genomes [3-5], although none of these endogenous retroviruses or retrovirus-like particles (RVLP) have been shown to be infectious to humans. Nevertheless, the regulatory agencies worldwide require the quantification of the retrovirus titers in the cell culture harvests and the validated clearance of these retrovirus-like particles in the downstream purification steps using a specific model virus such as xenotropic murine retrovirus (X-MuLV), to provide assurance that the purified drug product is free of these endogenous contaminants [6-8].
