GMPs are necessary for the manufacture of biopharmaceuticals that are administered to patients enrolled in clinical trials. Gail Sofer, director of regulatory compliance at GE Healthcare, discusses the approaches for compliance in the areas of cell banking, cell culture and downstream processing.
GMP compliance is a legal requirement in most of the world, with increased emphasis on enforcement in the last several years. But what does GMP mean for clinical trial manufacturing?
Adherence to GMPs during clinical trial material manufacturing compensates for the lack of completely fixed routines, potential risks associated with cross-contamination, incomplete knowledge of product potency and toxicity, and lack of full process validation.1 In fact, process validation may be inappropriate during clinical production.2 Emphasis is placed on personnel training, which is especially critical when operators have come from R&D labs where creativity, rather than adherence to protocols, is encouraged.
Although full process validation is not appropriate (in fact, may be impossible) during manufacturing of materials for early clinical trials (for example, phase 1 and/or 2), certain aspects related to safety must be addressed. For example, as noted in the EU document, validation of the sterilisation processes is no different than for a licensed product. This means that sterility assays must also be validated, including assays for bacteriostasis and fungistasis. Viral safety should be assured as well as removal of other potentially harmful impurities. Stringent cleaning is required to minimise cross-contamination; but as noted in a FDA draft guidance, the use of disposables in early clinical manufacturing can facilitate conformance with CGMP3 (In the USA, a C is placed before GMP. GMPs should be current. Sponsors of a biotech product are expected to employ, where feasible, state of the art methods as they apply to patient safety.) Clearly, a graded approach for the implementation of GMPs is accepted by regulatory authorities as long as potential risks to patient safety are mitigated.
Cell banking, cell culture, recovery, and purification steps are unit operations used in the manufacture of biotherapeutics. The impact of each unit operation on the others should be considered early in development of clinical trial materials, with special focus on patient safety issues.
ICH Q5D addresses cell substrates used to produce biotechnological products. Establishment of a two-tiered cell banking system - master cell bank (MCB) and working cell bank (WCB) - is expected for licensed products, but it is realistic to have only an MCB for early clinical studies provided there is sufficient material to expand into WCBs at later stages. Since a new MCB is considered a new product, it is important at even the earliest stages to ensure the integrity, quantity and back-up storage for the MCB.
Although the scope statement in ICH Q5D states that it provides recommendations on information that should be present in market applications, cell line characterisation is an essential activity for patient safety. Not only should cell banks be tested prior to entering clinical studies, even earlier screening for bacteria and fungi, mycoplasma, and virus is advisable to prevent having to replace MCBs that are found to contain adventitious agents during the characterisation studies - an activity that will almost certainly result in the need to repeat earlier (and expensive) studies such as toxicology. It is also important to keep in mind that new assays and findings of new viruses require companies to periodically review cell substrate characterisation.
In a preliminary draft guidance, the FDA noted that during phase 3/pivotal studies, the stability of cells during growth should be validated. What happens if at this late development stage the cells are found to be unstable? Some companies have tried to change culture media to stabilise the cells, but this poses other risks such as alterations in product expression level, glycosylation or other post-translational modifications, and quantity and quality of host cell proteins. In reality, companies should perform a pre-study to understand if the cells will be stable under the process conditions. Companies want to obtain maximum productivity from cell culture processes and are, therefore, almost always continuing to optimise process conditions during clinical development. This has the potential to alter endogenous retrovirus expression, host cell protein expression, product modifications, and downstream processing.
The impact of a change in cell culture on downstream processing is not always obvious. Addition of an antifoam in cell culture caused increased leaching of Protein A from a chromatography column. Fortunately, the remainder of the downstream process was designed to provide a final product with sufficient Protein A removal. A change in bioreactor design caused increased cell death, which resulted in increased levels of DNA that needed to be cleared by the downstream process. A change in culture media can result in the need to redesign the downstream process to remove specific culture components. As noted above, retrovirus expression levels can be altered by changes in cell culture, notably by changes that significantly alter the metabolic state of the cells and/or rates of protein expression.4 An increase in retrovirus expression levels can require changes in the downstream process to ensure viral safety. Communication between upstream and downstream personnel is key to the design of a downstream process that will be suitable for the manufacture of clinical material.
Downstream processes are used to clear both known and potential viruses from the unprocessed bulk material derived from cell culture. Viral safety is an important issue that needs to be addressed prior to entering clinical studies, but there are different opinions around the world regarding how many viruses should be evaluated in a clearance study prior to phase 1 clinical trials. Attempts are now being made to provide guidance for companies wishing to enter clinical trials in the EU.5 For clinical trials of monoclonal antibodies in the USA, the Points to Consider provide guidance.
There is a lot to be said for designing a robust downstream process that can remove viruses within a specified range of conditions. This range of parameters defines the design space.7 Defining the design space requires robustness, also called characterisation, studies. These studies use statistical methods, such as DOE, to evaluate different parameters, their ranges, and their influence on product quality. In chromatography, the design space might include upper and lower limits for protein load, flow rate, buffer pH and conductivity. Determining the appropriate design space requires an understanding, derived from development, of why a unit operation is incorporated into the overall process.
Typically, in phase 3, processes are scaled up. Scale up usually requires some modifications, in the best case only minor ones. Understanding manufacturing's capabilities is an important element for successful scale-up. These capabilities should be considered during process development. Both production equipment and in-process controls should be evaluated. In many cases, in-process analysis capabilities are not the same at development and production scales. Once scale-up is verified and any necessary modifications made, process validation can be carried out. At this point in development, full compliance with current GMPs is required. Process validation, a GMP requirement, usually necessitates a combination of both small and manufacturing scales. Small-scale models must be demonstrated to represent manufacturing, if the data are to be meaningful and accepted by regulatory agencies.
In conclusion, it is important to keep in mind that a step-wise implementation of GMPs is accepted, but any elements related to patient safety should be implemented prior to clinical studies. Furthermore, as processes are optimised during development, some safety-related issues need to be reconsidered. This can include, for example, a repeat of viral clearance studies if the feedstream is modified during process optimisation in phase 1 and/or 2 clinical trials. The amount of risk to patient safety that is tolerated is determined by the disease which is being treated and, often, by local regulatory authorities. Getting regulatory input prior to submitting an application to begin clinical trials can be very useful.