Virus Removal

Independent Assays for Provings Virus Removal. Retrovimses and vimses can also be present in culture fluids of mammalian cell lines (15,24). Certainly the absence of vims can be difficult to prove. Model vimses, eg, NIH Rausher leukemia vims and NZB Xenotropic vims, were spiked into fluids being purified, and their removal subsequently vaUdated when subjected to the same purification sequence as used for the product. 

Careful consideration should be given to the validation of any necessary virus removal or inactivation undertaken (see CPMP notes for guidelines). 

O Grady J, Losikoff A, Poiley J, Fickett D, Oliver C. Virus removal studies using nanofiltration membranes. Dev Biol Stand 1996 88 319-326. 

Validation Considerations. Mechanisms other then size exclusion may be operative in the removal of viruses from biological fluids. Thus virus removal must be validated within the parameters set forth for the production process and using membrane material representative of the product line of the filter. 

The virus reduction factor of an individual purification or removal—inactivation step is defined as the log10 of the ratio of the virus load in the pre-purification material divided by the virus load in the post-purification material. A clearance factor for each stage can be calculated and the overall clearance capacity of the production process assessed. Total virus reduction is calculated as the sum of individual log reduction factors. Individual manufacturing steps must possess fundamentally different mechanisms of virus removal or inactivation in order for values to be considered cumulative. Additionally, because viruses vary greatly with regard to inactivation or removal profiles, only data for the same model virus can be cumulative. 

A membrane filter which can uniformly remove all viral agents regardless of the size of the viral agent is not available. Part of the difficulty is that the efficient recovery of the biological product diminishes as the size difference between the virus and biological product lessens. Thus a balance needs to be met where virus removal and product recovery are optimized. 

Biological, medical, food processes virus removal, insecticides, algaecides, conservation, immobilization, cell fixation... 

Filters are used for clarification, removal of small molecules, exchange of buffers, and concentration of product, as well as sterilization and virus removal. A recent review of validation of filtration describes the critical validation issues [29], Filter compatibility is tested with process conditions to avoid nonspecific binding of product to the filter or addition of extractables to the process stream. Extractables are defined and limits established based on final product safety studies. Special considerations apply for sterilizing filters and those that are designed for virus removal. These filters are single use, however, which simplifies the validation effort. 

Unlike sterilizing and virus removal filters, tangential flow filtration (TFF) filters are often reused. Flow and integrity tests are necessary to ensure the filter remains the same after usage and cleaning. Consistency of filtrate and retentate streams is validated using relevant validated assays that are specific for each process and product. 

Aranha-Creado, H. Filtration virus removal in process validation. Genet Eng News 20 64 (2000). 

Zhu, B.T., Cliford, D.A., Chellam, S. (2005). Comparison of electrocoagulation and chemical coagulation pretreatment for enhanced virus removal using microfiltration membranes. Water Res. 39, 3098-3108. 

The risk associated with the presence of viruses justified clearance studies that are one of the important places of safety documentation for final pure antibodies. These studies are referred to as viral validation and are based on clearance effect of extraction-purification steps and on virus removal-inactivation steps. A comprehensive rational approach to guaranteeing a minimum risk has been reported by Berthold et al.235... 

Validation of virus removal and inactivation procedures (2/1991) Radiopharmaceuticals based on monoclonal antibodies (5/1991)... 

Committee for Proprietary Medical Products. Ad hoc working party on biotechnology/pharmacy and working party on safety medicines, EEC regulatory document, note for guidance vahdation of virus removal and inactivation procedures. Biologicals 1991,19, 247-251. 

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