American Pharmaceutical Review, December 2016
Unlike small-molecule drugs, which are made from chemical starting materials with consistent compositions, biopharmaceuticals are produced from a mixture of animal, plant and synthetic sources.
The potential for viral contamination is therefore real and must be addressed in the downstream drug manufacturing process. Doing so can be challenging, however; in many cases the potential viral contaminants may be unknown.
Removal methods and analytical techniques for virus detection must therefore be effective for both known and unknown contaminants. The 1998 International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) Q5A standard assures viral safety through testing of cell banks, raw materials and bioprocess fluids harvested from bioreactors, combined with downstream purification processes for viral clearance. Technologies for virus destruction and removal are also improving.
Why Viral Clearance Is Crucial
The number of biologic drugs under development is growing rapidly, driven by their ability to treat many chronic and other diseases that have not successfully been addressed using small-molecule drugs. Large and small biotech, as well as traditional pharmaceutical companies have biologic drugs in their pipelines. In fact, 66% of the nearly 600 pharmaceutical industry professionals responding to the 2016 Nice Insight CDMO Outsourcing Survey have new biologic entities (NBEs) in their pipelines, compared to 57% and 53% for small molecule new chemical entities (NCEs) and generics, respectively .
During the manufacture of biologic drugs, including recombinant proteins, monoclonal antibodies, hormones, etc., viral contaminants can be introduced in the cell substrates used for cell culture and the cell media and other raw materials or throughout the various stages of upstream and downstream processing. If such contamination goes undetected and is not eliminated, patient safety can be impacted, as can a company’s reputation and financial stability. Viral contamination in an existing product can lead to a production shutdown and the potential for drug shortages, while contamination of products under development can lead to costly approval delays.
Viral clearance studies are conducted to confirm that virus removal/elimination steps are effective and are thus crucial to successful approval of biopharmaceutical manufacturing processes. The global viral clearance market, including viral detection, removal and inactivation methods, was valued at $285.5 million in 2015 and is poised to grow at a CAGR of 12.3% between 2015 and 2020, reaching $510.3 million in 2020, according to market research firm Markets and Markets .
Sources of Viral Contamination
Viral contaminants can be introduced at various stages during the manufacture of biologic drug substances. Common contaminants include Mouse Minute Virus (MMV), Reovirus, Cache Valley Virus (CVV), and Vesivirus Isolate 2117 [3,4].
Raw materials, although typically now chemically defined rather than animal-derived, still have the potential for viral contamination through exposure to animal-derived materials, as they move through the supply chain. Cells produced from a contaminated master cell bank, cell culture media, other biological reagents and non-biologic reagents all have the potential to be contaminated with undesired viral species. A full understanding of the supply chain and careful characterization of all raw materials is therefore an essential component of an effective viral safety program for biologic drug products .
Viral contaminants can also be introduced during the manufacturing process, with small, non-enveloped, chemically resistant viruses being of most concern . Poor handling practices can lead to the introduction of viral contaminants into clean raw materials once they have been received at a bioprocessing facility. Use of automated systems wherever possible combined with an effective quality assurance/quality control program and Good Manufacturing Practices are further components of well-designed viral safety programs. The segregation of materials subjected to viral inactivation/removal from materials that have not been purified is also crucial during all upstream and downstream processing steps.
Taking a Holistic Approach With Risk Management
Regulatory guidelines for the prevention and control of viral con-tamination are based on a holistic style that includes responsible raw material sourcing combined with removal/activation steps, in-process testing and the use of effective methods for demonstrating viral clearance. The ICH Q8, Q9 and Q10 guidelines also refer to the need to use a risk-based approach to ensure the quality of biologic drugs .
Access to extensive knowledge about raw materials not only ensures they are of appropriate quality, but provides information on the potential viral contaminants that can be used to determine appropriate removal/inactivation methods and testing protocols. It is important to stress that viral safety programs must be designed on a product-by-product basis considering the unique risk factors presented .
In recent years, many manufacturers have expanded this approach to include viral inactivation/removal steps for key raw materials. Use of viral inactivation treatments or a filtration step to remove potential contaminants in cell culture media and media components, when combined with viral clearance studies, is an effective risk mitigation strategy. Common inactivation steps include heat treatment and exposure to ultraviolet radiation. Virus removal is typically achieved via virus retentive filtration. There is a need, however, for virus filters designed specifically for media filtration, which involves continuous operation with high throughput .
Virus Deactivation/Removal Methods
One challenge with viral activation is achieving the destruction of unwanted viral contaminants without damaging the biologic drug substance. Another is the fact that different types of viruses are degraded under different conditions (e.g., solvent/detergent treatment is effective against enveloped viruses but not non-enveloped viruses). Therefore, selection of a specific method (or typically methods) must be based on the properties of the drug substance (size, lability) and the viruses to be inactivated, as well as consideration of their cost and practicality .
Robust inactivation methods such as heat treatment, treatment under low/high pH conditions and solvent/detergent (S/D) treatment are generally effective regardless of the buffer or protein concentration . They also are the most-well-understood methods in use today. Each, however, is only effective against certain viruses. Filtration is also a robust process and is widely used for viral clearance in many biomanufacturing processes .
Less robust processes, notably precipitation and chromatography, which are partitioning processes, were not initially designed for virus removal. They can, however, be effective in some cases. It is worth noting that chromatography has the advantage of being able to remove both enveloped and non-enveloped viruses. Other technologies for viral inactivation include γ–irradiation, UV-C irradiation and HTST (High Temperature — Short Time/Treatment) .
For virus removal, nanofiltration is becoming increasingly important in biopharmaceutical processing, in part because it can remove most small and large enveloped and non-enveloped viral contaminants . Improvements in conventional filtration technology, including increased fluxes and capacities (and in some cases the ability to perform steam-in-place, which allows their use in closed systems) are also improving virus removal operations .
In addition, membrane absorbers are finding use as easy-to-install secondary or back-up viral clearance tools, particularly disposable solutions that eliminate the need for cleaning and cleaning validation and the risk of cross-contamination between different processes . To meet the need for higher log reduction values at high flux rates, new membrane structures involving selective layers, a laid-over pleat filter construction with narrower cores and asymmetric hollow-fibers have been introduced respectively by EMD Millipore, Sartorius and Pall Life Sciences .
Viral Clearance Studies
Removal of viral contaminants must be confirmed using viral clearance studies, which involve “spiking” or “challenging” scale-down models of each process step with appropriate test viruses. Demonstration that each scale-down model closely mimics the production-scale process it is intended to represent is an important aspect of the overall clearance study. The most effective clearance studies are designed to evaluate performance under both typical operating conditions and during possible process excursions (temperature, pressure, poor mixing, etc.) to confirm the robustness of the virus removal/inactivation method . It is also important on an ongoing basis to confirm that the current commercial manufacturing process is still the same as that used for the viral clearance study.
Selection of the appropriate test viruses to be used in a viral clearance study is also crucial. Both the potential viral contaminants and the specific removal method must be considered when selecting the model virus (or viruses) to be used in viral clearance studies for different biopharmaceutical processes. Preparation of the virus spikes must be done very carefully as well, with particular attention paid to the purity of the viruses, as impurities in virus spikes and result in incorrect sizing of filters and unnecessarily higher operating costs .
The development and manufacture of novel drug substances and products involves not only the applications of advanced synthetic and biologic technologies, but state-of-the-art risk management strategies. For biopharmaceuticals, minimization of the risk for virus contamination is a key component of such a risk management strategy. The most effective programs involve the use of virus reduction/inactivation methods combined with the performance of vial clearance studies for both upstream raw materials and downstream processes, as well as careful sourcing of raw materials.
In addition, there is increasing recognition in the industry that viral clearance must be treated like any other process, and as a result more emphasis is being placed on developing optimized solutions. A greater understanding of virus reduction/inactivation technologies is also leading to improvements in available methods and the regulatory process .
- The 2016 Nice Insight Contract Development & Manufacturing Survey.
- Markets and Markets, “Viral Clearance Market by Application (Stem Cell, Blood, Tissue, Cell & Gene Therapy), Method (Inactivation, Removal (Precipitation), Detection (PCR, ELISA)) & End User (Pharmaceutical & Biotechnology, CROs, Research Institute) - Global Forecast to 2020,” Press Release, April 2016, http://www.marketsandmarkets.com/Market-Reports/viral-clearance-market-62681197.html.
- Remington, K.M. “Fundamental Strategies for Viral Clearance – Part 1: Exploring the Regulatory Implications.” Bioprocess Intl. January 13, 2015. http://www.bioprocessintl.com/downstream-processing/viral-clearance/fundamental-strategies-viral-clearance-part-1-exploring-regulatory-implications/.
- Remington, K.M. “Fundamental Strategies for Viral Clearance – Part 2: Technical Approaches.” Bioprocess Intl. May 12, 2015. http://www.bioprocessintl.com/downstream-processing/viral-clearance/fundamental-strategies-for-viral-clearance-part-2-technical-approaches/.
- Challener, C.A. “Viral Clearance Challenges in Bioprocessing.” BioPharm Intl. Volume 27, Issue 11, Nov. 01, 2014. http://www.biopharminternational.com/viral-clearance-challenges-bioprocessing.
- Challener, C.A. “Selecting the Right Viral Clearance Technologies.” BioPharm Intl. Volume 28, Issue 11, Nov. 01, 2015. http://www.biopharminternational.com/selecting-right-viral-clearance-technology.
- Challener, C.A. “Filtration Technologies Advance to Meet Bioprocessing Needs.” BioPharm Intl. Volume 28, Issue 5, May 01, 2015. http://www.biopharminternational.com/filtration-technologies-advance-meet-bioprocessing-needs.