Taking immunogenicity assessment of therapeutic proteins to the next level.

Therapeutic proteins provide innovative and effective therapies for numerous diseases. However, some of these products are associated with unwanted immunogenicity that may lead to clinical consequences such as reduced or loss of efficacy, altered pharmacokinetics (PK), general immune and hypersensitivity reactions, and neutralisation of the natural counterpart (e.g. the physiological hormone). Regulatory guidance on immunogenicity assessment needs to take into consideration a great diversity of products, indications and patient populations as well as constantly advancing manufacturing technologies. Such guidance needs to be sufficiently specific while, at the same time, allowing interactive discussion and adjusted benefit-risk weighing of each product on a case-by-case basis, e.g. for a unique treatment of a life threatening disease acceptable treatment risks may differ considerably from the ones in case of less serious disease. This theme was the focus of the international conference "Taking immunogenicity assessment of therapeutic proteins to the next level", held at the Paul-Ehrlich-Institut in Langen, Germany, on the 10-11. June 2010. The objectives of the conference were to highlight how the field could move from that of a mere description of risk factors to a system of risk assessment and mitigation, as well as an understanding of the impact of unwanted immunogenicity on the overall benefit/risk consideration for a medicinal product. More than 150 experts from industry, academia and regulatory authorities worldwide discussed the phenomenon of undesired immunogenicity from different perspectives. The conference focussed on issues relevant to three areas: (1) new European guidelines that are currently the subject of discussion; (2) testing strategies for immunogenicity assessment; and (3) scientific progress on the product-related factors that may contribute to the development of pathogenesis of immunogenicity, in particular in the field of protein aggregation and post-translational modifications. This report provides an overview of issues, insights, and conclusions that were discussed and achieved during the meeting.

Validation of fermentation processes.

The ability to prepare consistent biopharmaceutical products depends extensively on possession of banked and characterized cell substrates and on development of production processes which can be validated. While the attributes that define cell characterization have been extensively detailed by ICH and the regulatory agencies in the past decade, little has been specified regarding process validation for biological processes. The extent to which validation concepts can be applied to biological processes varies depending on the nature of the process, the nature of the product, and the level of knowledge regarding the relationship between process parameters and product quality. Expectations concerning the rigour of the validation programme should be adjusted accordingly. There is no single approach that is appropriate for all processes and products. At a minimum, there should be an attempt to define which process parameters are critical, and to focus the attention of validation efforts on these parameters.

Recent trends in cell substrate considerations for continuous cell lines.

Product development activity in the past five to ten years has reconstituted a version of an old debate on the safety assessment of biological products, namely whether the use of some types of continuous cell lines (CCLs) is appropriate in the preparation of some types of biological products. Since 1987, dozens of purified recombinant DNA products derived from CCLs have been developed and have received regulatory approval. In addition, several live attenuated and inactivated viral vaccines manufactured in CCLs were approved after thorough review of product safety and manufacturing issues. The current discussion revolves around the potential use of CCLs (human or not) to prepare purified protein subunit vaccines, such as for HIV, and the use of human CCLs to prepare purified protein products.

Elimination of serum from cell culture medium.

Growth of continuous cell lines for preparing biopharmaceuticals in the absence of animal serum has been attempted by many organizations to improve process and product quality, prevent exposure to adventitious agents, and reduce costs. Literature surveys suggest that substantial academic studies on serum-free medium have been pursued for many decades, with varying levels of success for different cell types and cell lines in terms of achieving cell growth while retaining cell function. Industrial research proceeded for at least three decades. Recent work with CHO cells and with some hybridomas has been successful in providing the basis for serially propagating cells on a large scale in suspension in the total absence of serum, while preserving the ability to prepare biopharmaceuticals. In some cases, this can be achieved not only without serum, but also without the use of other animal-derived proteins.

Historical reflections on cell culture engineering.

Cell culture engineering has enabled the commercial marketing of about a dozen human therapeutic products derived from rDNA technology and numerous monoclonal antibody products as well. A variety of technologies have proven useful in bringing products to the marketplace. Comparisons of the technologies available 15 years ago are contrasted with those available today. A number of improvements in unit operations have greatly improved the robustness of the processes during the past 15 years. Further evolution of the technology is expected in several directions driven by commercial and regulatory pressures. Some problems remain for the next generation of cell culture engineers to solve.

Raw material considerations.

Raw materials (RM) testing and control strategy form a major part of the foundation of a well-characterized protein (WCP) or biopharmaceutical. Raw materials may be present in the final vial as excipients or may have product contact earlier in processing. Manufacturers of WCPs should use a scientific approach to set acceptance criteria and test methods for bulk raw materials which are not present in dosage forms in substantial amounts. These methods and standards should enable the procurement of specified RMs which enable the reliable preparation of a product which consistently meets its quality attributes. Manufacturers of WCPs must use available pharmacopoeial standards for excipients and bulk process RMs which cannot be substantially removed during purification or other processing steps. Manufacturers should support efforts to harmonize pharmacopoeial standards for excipients.

Current issues in viral assays and viral clearance evaluation.

Viral contaminants are less amenable then chemical contaminants to analytical detection due to the lower sensitivity, specificity and precision of existing assays. In combination with the potential for biological amplification of viral contaminants in cell substrates or product recipients these analytical limitations lead directly to potential risk of virus infection of product recipients. While less than perfect, a broad spectrum of assays is available to characterize cell banks for the presence of adventitious and endogenous agents. Each product lot can be tested by an appropriate subset of assays for selected viruses of concern. Engineering and procedural controls over facilities, equipment and operations are necessary to minimize the possibility of viral contamination. Processes can be designed to include unit operations to remove or inactivate specific viruses of potential concern; the efficacy of these measures can be evaluated. While each of these measures has value, each also has limitations. None is solely adequate by itself to the task of preventing potential exposure to viral contaminants in product recipients. Biopharmaceuticals (purified characterizable macromolecules) are prepared by using a combination of such preventive measures. Specific measures will vary from product to product, depending on the nature and origin of the cell substrate, cell bank characterization results, raw materials used, physicochemical properties of the biopharmaceutical, effectiveness of assays, available facilities, and the agents of concern. Thus, flexibility in approach is necessary, resulting in different combinations of measures for each set of circumstances. So far, this approach has been successful in preventing viral infection in large populations treated to date with cell culture-derived biopharmaceuticals. Current issues for discussion include appropriate assays for adventitious and endogenous agents, appropriateness of current control systems and the scientific basis for standards.

Viral validation strategy for recombinant products derived from established animal cell lines.

For products derived from continuous cell lines, regulatory agencies worldwide require that the purification process be validated for its ability to remove or inactivate potential contaminants such as viruses and virus-like particles. New guidance suggests a requirement for statistical evaluation of these studies but the industry has yet to develop such standards. The task of estimating excess capacity is also complicated by variable assays, accumulation of variability in clearance estimates over unit operations, dependence of clearance capacity on operating parameters, and expense of experiments. We propose an experimental strategy to determine the excess clearance capacity of a biopharmaceutical process and to provide statistical estimation of excess capacity in an efficient way. Clearance estimates and their variances are calculated for each orthogonal unit operation and estimates are combined to form an interval estimate of overall process clearance capacity. Poisson regression is suggested as an efficient technique for data analysis of clearance studies. We believe that this approach should meet regulatory guidelines in a cost effective way, while clarifying the roles of qualitative and quantitative components in setting requirements.

Purified protein products of rDNA technology expressed in animal cell culture.

During the past 7 years, 14 versions of 7 rDNA proteins have been licensed which are derived from animal cell culture expression systems. These medically useful products have included hormones, coagulation factors, enzymes and a vaccine. Aspects of the molecular complexity, manufacture, control and utilization of these products are discussed. In contrast to previous generations of biological production technology, the technology for production of rDNA-derived proteins in animal cells appears to be safe.

Genetic stability and recombinant product consistency.

A committee of U.S. industry scientists from the Pharmaceutical Manufacturers Association has reviewed the recent suggestions of Galibert and Center for Biologics Evaluation and Research (CBER) regarding assurances of product consistency by cloning and sequencing efforts. We disagree that their proposals will achieve this goal, and estimate that such efforts will be very costly in terms of regulatory agency time examining artifactual errors as well as industry resources. We feel that current analytical and manufacturing technology is adequate to assure recombinant product consistency without the suggested cloning and sequencing measures.

Effects of fermentation on product consistency.

A variety of different fermentation processes has been successfully employed to produce consistent protein-based biopharmaceuticals from genetically engineered animal cells. Chinese hamster ovary (CHO) cells were genetically modified to produce recombinant human soluble CD4, tissue plasminogen activator (tPA) or erythropoietin (EPO). Soluble CD4 was collected from extended perfused fermentations of several months' duration, during which some quantitative loss of DNA copy level, mRNA expression level, and fermentation titer were observed. In one extended run, a novel contaminant appeared in intermediates purified from later harvests. However, in all cases, the final soluble CD4 product was consistent in terms of purity and potency. Evaluation of genetic stability for tPA examined both biological traits at the cellular level as well as potency, purity and structure of product derived from cells at various levels of in vitro age; no significant cell age effects were observed. Similarly, evaluation of the EPO product showed that genetically-determined and process-determined traits such as potency, tryptic peptide mapping, and sialylation were consistent from lot to lot. These data exemplified how process design, process validation, and in-process and quality control assays can be used effectively to ensure the consistency of recombinant products derived from cell culture fermentations.

Process validation for cell culture-derived pharmaceutical proteins.

Principles of process validation are extremely powerful tools in assurance of product quality. They are especially useful for reducing those risks not easily measured routinely during production. When combined with effective process and facility design principles, characterization of cell banks and products, appropriate lot release tests, and adherence to cGMP, safe cell culture biologicals can be prepared in a reliable manner.