Virus tangential-flow filtration

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. 

Currently, there are many examples of cell processing in the industrial environment using tangential flow filtration. To illustrate the breadth of microbial types which may be processed by this technology, we will discuss three applications which have been in routine operation under production conditions. The applications include cell/growth medium separations directly from fermentors (Escherichia coli and Mycoplasma species) and the concentration/washing of influenza virus used in the production of flu vaccines. 

The unique features of tangential-flow filtration include the ability to remove cells and cell debris from the growth medium, which contains the product of interest, to concentrate the product of interest and to fractionate solutes of different size. These features have lead to numerous applications of tangential flow filtration in the purification of protein products. These same features could be exploited both for virus purification and validation of vims clearance as described in the following sections. 

TABLE 20.1 Examples of Tangential Flow Filtration for Purification of Viruses... 

Comparing Figures 20.5a and 20.5b it can be seen that the sharpness of the virus particle fractionation is better with the 0.1-pm pore size membrane. Since membranes have a pore size distribution, development of a practical membrane-based fractionation step will depend on careful selection of an appropriate membrane pore size and pore size distribution. Further it is likely that operating methods such as high-performance tangential-flow filtration may improve the sharpness of the fractionation. 

Tangential-flow filtration could also be used to validate virus clearance. Today most virus clearance filters are operated in normal flow mode. However, when the size of the model virus particle for which clearance is being validated, and the desired product are within an order of magnimde of each other, tangential-flow filtration may be the preferred mode of operation. 

The concentration of viruses in water is much lower than that of bacteria therefore their preconcentration and separation from other suspended matter is important in virological analysis. Viruses may be enriched by UF by use of tangential-flow or hollow-fiber filtration units most suitable for preconcentration from large-volume water samples. Another possibility consists in adsorption of the viruses on the microfilter matrix followed by elution with diluents containing cell extracts, serum, or surfactants. 

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