Antiviral Treatments

Ever since the transmission of HIV infection to haemophiliac patients through contaminated blood-based products in the early 1980s, there have been stricter controls and scrutiny of the methods of viral inactivation utilised during bioprocessing. This is of particular concern when using mammalian cells to produce biotherapeutic products, as there is clear potential to host harmful viruses. Current good practice therefore dictates that products destined for use as therapeutics are submitted to antiviral treatments with two different viral-inactivation steps each of which gives a four to five log reduction in virus load. To achieve this level of reduction, several steps with viral removal functionality are required, although some of these steps may have dual functions. The methods employed to achieve this are varied and the regulatory bodies do not require specific viral inactivation treatments but rather judge the validity of the approach used for each product on its own merits.
The most commonly used methods to reduce viral load are the heating of protein solutions and lyophilisates, nanofiltration, low-pH hold steps, UV irradiation, solvent/detergent treatments and those process removal steps that are part of the purification methodology or the production of the protein of interest. Of these treatments, heat treatment is the current ‘gold standard’ and many therapeutic protein preparations are treated in this way (e.g. albumin, Factor VIII, Factor IX, thrombin, fibrinogen, IgG). Further, heat treatment has the advantage of being one of the few methods that can be applied to a given product in the vial without the need for disruption of the product. Typical heat treatment in the liquid state consists of 60 1C for 10 h, whereas in the lyophilised state samples are typically subjected to temperatures of 90 1C for 10 h or 80 1C for 72 h. The disadvantage of heat treatment is that as proteins denature and undergo deleterious reactions upon heat stress, it is necessary to formulate the protein of interest in stabilising excipients such as sucrose to prevent such reactions. It has been shown that the excipients themselves can break down and react with the protein of interest under certain heat
treatment conditions, resulting in disadvantageous side reactions that compromise the authenticity of the protein product.