Contaminant-clearance validation

Contaminant-clearance validation studies are of special signibcance in biopharmaceutical manufacture. As discussed in Section 7.6.4, downstream processing must be capable of removing contaminants such as viruses, DNA and endotoxin from the product steam. Contaminant-clearance validation studies normally entail spiking the raw material (from which the product is to be purihed) with a known level of the chosen contaminant and subjecting the contaminated material to the complete downstream processing protocol. This allows determination of the level of clearance of the contaminant achieved after each purihcation step, and the contaminant reduction factor for the overall process. 

Arindam Bose (Pfizer Central Research) further discussed the ICH documents and presented a rationale for the recommended combination of test procedures and process clearance validations required to demonstrate that marketed biopharmaceuticals are free of adventitious agents. He showed that testing of Pre-Seed Stock (PSS), the Master Cell Bank (MCB), and the Working Cell Bank (WCB) is required to demonstrate that they are free from contamination by mycoplasma, bacteria, molds, and yeasts. In addition, viral clearance validation studies must be performed on scaled down versions of each chromatographic step and the viral inactivation/removal step employed in the product purification scheme. Finally, clearance studies must be conducted with a panel of relevant and model viruses (typically three to four) to establish that the purification scheme will indeed purge any viruses that may be inadvertently introduced during processing. 

Plasma-derived therapeutic proteins are parenteral biologies that are purified on an industrial scale. All biologies derived from human sources, such as plasma, carry the risk of viral contamination. Thus, in order to market a medicinal product derived from human plasma, manufacturers must assure the absence of specific viral contamination. Virus validation studies are performed to evaluate the capacity of a manufacturing process to remove viral contaminants. Virus clearance across three different terminal inactivation steps, low pH incubation of immunoglobulins (IgG), pasteurization of albumin, and freeze dry/dry heat treatment of plasma-derived products (Factor VIII and Protein G), is discussed in this article. The data show that, like all other upstream virus reduction steps, the methods used for terminal inactivation are process and product dependent, and that the reduction factors for an individual step may be overestimated or underestimated due to inherent limitations or inadequate designs of viral validation studies. 

For more comprehensive validation studies, the molecular mass profile of the DNA spike should roughly approximate to the molecular mass range of endogenous contaminant DNA in the crude product. Obviously, the true DNA clearance rate attained by downstream processing procedures (e.g. gel filtration) will depend to some extent on the molecular mass characteristics of the contaminant DNA. 

Consistency of product quality is demonstrated by showing operating consistency and product quality from batch-to-batch, processing with only buffer (blank runs) with assays for contaminants, examination of cleaned surfaces and materials, and extended scale-down clearance studies on reused materials. Disposable processing components that eliminate the need for cleaning validation are increasingly used at small scale. 

The equipment supplier will therefore aim to offer versatile, multi-purpose equipment that can be used in a range of processes. Most of it will be stainless steel or glass-lined to avoid problems with contamination or corrosion. In spite of its versatility, however, the plant, once built, will rarely be changed. Any new process or important modification of an existing process must be validated, and critical phases of an existing manufacturing process must be regularly revalidated. If the manufacturer wants to add a recycle stream, for example, clearance must first be obtained. 

Steps to be Validated for Viral Clearance. Process validation for viral clearance is conducted only on robust steps that can (1) be scaled down accurately and (2) reproducibly and effectively remove and/or inactivate a wide variety of potential viral contaminants under a wide variety of process conditions [5,41]. The number of steps selected for validation depends on estimated viral clearance effectiveness based on historical data and target clearance values [5]. The FDA demands at least two different steps for virus reduction to guarantee safety and efficacy [7]. Potentially only two steps are required for antibody processes that use serum-free medium, but additional steps might be required if viral contamination risk is increased by using serum-containing medium [7]. Due to the use of live viruses to perform clearance studies, this work usually is outsourced to reduce cross-contamination issues [14]. 

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