THE DEVELOPMENT OF THERAPEUTIC MONOCLONAL ANTIBODY PRODUCTS
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Excerpt of Chapter 7

… The development of a suitable recovery and purification process for a monoclonal antibody focuses on two main technical aspects – the effectiveness of the removal of impurities and contaminants (i.e. the product purity) and the yield of the product (the percent of the active antibody product present in the bioreactor batch that is recovered in the final bulk drug substance). All processes involve tradeoffs between yield and purity so that the major overall goal of downstream process development is to insure that the purity is sufficient for the monoclonal antibody product to be safe for its intended use, while simultaneously maximizing yield. Meeting the necessary purity levels is an absolute regulatory requirement, while product yield is primarily an economic concern for the Sponsor.

…Three basic modes of chromatography are used for intermediate and polishing purification: ion exchange, hydrophobic interaction, and mixed mode chromatography. Less frequently used is size exclusion chromatography, which typically requires lower flow rates and larger column sizes, reducing its attractiveness for large-scale process use.

Chromatographic separations used for intermediate and polishing purification can be run either as bind/elute (B/E) operations or flow-through (FT) operations. In the B/E mode, the antibody is bound to the column under one set of conditions, the column is washed under these same or different conditions to remove the contaminants and impurities, and then the monoclonal antibody product is selectively eluted from the column under another set of conditions, leaving more tightly bound contaminants and impurities behind on the column. FT separations are designed so that the antibody does not bind to the column but the contaminants and impurities do bind and are retained on the column. Conditions for FT operation must be optimized for each antibody so that the maximum possible amount of contaminants and impurities are bound and removed from the solution while the maximum amount of antibody flows through into the eluate. B/E steps are generally more flexible for removing a wider range of contaminants and impurities, but require large columns to bind the large mass of the antibody product and are relatively complex to develop and operate. FT steps are operationally much simpler and, because only the trace levels of contaminants bind to the column, usually require much smaller column volumes.

By far the most common is ion exchange chromatography, in which a resin with immobilized charge groups is used to bind molecules in the feedstream with the opposite surface charge through electrostatic forces. The bound molecules are then selectively washed off and eluted by changing the pH and/or ionic strength. The process may be done with either anion exchange media (in which positive charge groups such as quaternary amines on the column bind negatively charged molecules in the feedstream) or cation exchange media (which are the reverse, in which negatively charged groups such as sulfonates on the column bind positively charged molecules in the feedstream)…

…Monoclonal antibodies are unusual among biopharmaceutical products in that antibodies as a class share a large fraction of common molecular structure, with the primary variability for antibodies within a specific subclass being in the two binding sites on the Fab portion of the molecule. Because of this commonality of structure, it is possible to develop a common platform purification process which can be used, with only minor variations and optimization, for a wide range of antibody products. The platform purification process approach is so powerful that it has been adopted in recent years by most of the major therapeutic antibody producers and contract manufacturers. One of the obvious advantages is the use of common facilities, equipment, materials, and unit operations for all products, which speeds process development and facilitates the introduction of new products. A more subtle but equally important advantage is that because process performance and optimization information gathered for one antibody product in a platform process can often be applied to other antibodies in the same process, it is worthwhile to do the kind of detailed characterization and optimization that result in more robust processes for all the antibody products. Finally, some organizations with many antibody products in development or on the market have been able use process validation information for one product to support validation of subsequent products.

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