Biological therapies are rapidly gaining acceptance in the treatment of a wide spectrum of diseases. While many complex diseases such as rheumatologic disorders are routinely addressed by biologics, applications to non-rheumatic diseases such as psoriasis, inflammatory bowel disease, diabetes, and multiple sclerosis are currently in development. (Bell et. al. 2011). However, on some occasions, treatment regimens can lead to paradoxical effects such as an actual worsening of the disease.
The mechanism behind this unexpected outcome has been documented in at least two studies where biological therapy was administered. In the first example, antibody associated pure red cell aplasia was discovered in patients who had undergone treatment with recombinant human erythropoietin (EPO). (Bennett et. al. 2004) It was determined that a convergence of factors related to production, handling, and route of administration may have accounted for the EPO associated pure red cell aplasia. Processes and formulations that facilitate oxidation or aggregation of the protein can enhance immunogenicity. In another example, TGN1412 was an anti-CD28 Monoclonal antibody (MAb) initially developed for the treatment of B cell chronic lymphocytic leukemia (B-CLL) and rheumatoid arthritis. In its first human clinical trials, it caused catastrophic systemic organ failure in the subjects, despite being administered at a supposed sub-clinical dose of 0.1 mg per kg; some 500 times lower than the dose found safe in animals (Coghlan 2006). Six patients presented evidence of “cytokine storm”, a potentially fatal immune reaction consisting of a positive feedback loop between cytokines and immune cells (http://en.wikipedia.org/wiki/Cytokine_storm) , with highly elevated levels of various cytokines (Suntharalingam et. al. 2006). While physicians at the time declared that it was impossible to anticipate such severe reactions, particularly in the light of convincing animal safety data, one has to wonder whether a particular variant of TGN1412 may have been the culprit and in fact, this has led to a proposal for guidelines on immunogenicity of biotherapeutics in the EU.
Although MAbs present a different set of challenges from other product classes, the level of risk associated with first administration to humans can be effectively mitigated through appropriate pre-clinical strategies addressing product safety. The analysis of contributing risk factors for safety must include a thorough analytical profile of the product. Product aggregates and process related impurities could alter immunogenic potential. Further, the presence of product variants that have different biological activities could significantly influence the overall benefit-to-risk for humans (Chamberlain 2011) .
Most approved biopharmaceuticals have shown some immunogenicity although the percentage of patients developing antibodies upon treatment with protein-based drugs varies widely. Factors influencing the immunogenicity of proteins are manifold and include amino acid variations, modification of amino acid side chains, variation in glycosylation, as well as the presence of unseen contaminants. It is therefore imperative that manufacturers identify and hopefully eliminate these issues early in development. Apart from the need for a consistent manufacturing process, immunogenicity must be monitored-either directly or by a reliable surrogate method.
The use of displacement chromatography provides a platform for analysis of biological therapeutics and has been used to identify charge related variants in an IgG1 MAb preparation ( Zhang et. al. 2011). In this paper , Genentech scientists demonstrated the value of including displacement chromatography in MAb characterization and highlighted the potential to greatly enhance the information available regarding the development of complex biological therapeutics. As a preparative technique, cation exchange displacement chromatography allowed for significant enrichment of charge variants with high purity and recovery. Using displacement, one can generate a ‘fingerprint” of each processed batch based upon presence of variants encountered during manufacturing. This fingerprint can provide useful information to help correlate product efficacy with manufacturing protocol and could possibly help compensate for lack of predictability of human immunogenicity based on animal studies alone.
REFERENCES:
Bell, et. al Nature Reviews in Rheumatology (2011) 7: 507-516
Bennett, et. al. New England Journal of Medicine (2004) 351: 1403-1408
Chamberlain New Biotechnology (2011) 10.1016: 1-8
Coghlan, New Scientist (2006) 12: 14-16
Suntharalingam, et. al. New England Journal of Medicine (2006) 355: 1018-1028
Zhang et. al. Journ. Chromatog A (2011) 1218: 5079-5086