Strategies for Improving Antibody Production in CHO Cells
Biomanufacturing capacity is in demand, particularly with several biologic drugs entering final phases of the clinical pipeline. Capacity could quickly become in short supply if many of these drugs receive approval. One way to combat capacity crunches is to improve production and yield. Last week, I wrote a blog describing how CHO cells are the expression system for four out of five of the best selling biologic drugs. The blog titled “CHO Cells – the Top Expression System for Best Selling Biologic Drugs” posed a question on whether CHO production could be improved or whether we had hit peak performance. Since CHO cells are currently the top expression system for biologic drugs, it makes sense to look at ways to improve their productivity and ultimately conserve capacity.
CHO manufacturing has made continual improvements over the years, including advances in equipment, cell line development practices and media formulation. Since there are several steps in the biomanufacturing process, there are also many opportunities to make improvements. At the beginning of the bioproduction process, effective gene cloning and clone selection are a critical in selecting a CHO cell line that will be a good fit for biomanufacturing. Cell lines must grow well, have high expression, and be stable over time. One technology that provides an alternative to traditional gene cloning is gene synthesis. Several companies offer this service including GenScript, Blue Heron and Life Technologies (formerly GeneArt). Companies state that gene synthesis offers a way to quickly design and synthesize a gene sequence and that it is ultimately more cost effective than traditional cloning. In addition, gene synthesis provides sequences that are codon optimized for the host cell line, providing higher expression levels and easy protein purification.
Another area for improvement is in adjusting the cell culture media to improve cell performance. Early products produced in CHO cells were produced in media that almost always contained animal products, which are undesirable because they are undefined and yield unpredictable results due to high batch-to-batch variation. The Food and Drug Administration (FDA) and other regulatory bodies discourage use of these animal components because of the serious safety concerns involving the risk of viral and prion (the infectious causative agent associated with Mad Cow Disease) contamination. As a response to these concerns, in the early 1990’s there was a great deal of research being conducted around how to remove serum and other animal products from CHO manufacturing, but yield often suffered. Since then, serum free media has become the norm, however yield can still suffer along with cell viability and growth. The latest breakthrough has been cell culture that is completely animal-free and defined, which has paved the way for a new class of recombinant supplements that meet both criteria. Today companies including Sigma, Fisher Scientific, InVitria (CHO Cell Culture), Sheffield Bioscience and Mediatech sell recombinant albumin, transferrin, and lactoferrin that can be added to animal-free media and has been shown to improve cell growth, viability and yield of CHO cells while remaining animal-free and defined.
One area where some believe big improvements have been made is perfusion bioreactors. Perfusion bioreactors culture cells continuously, feeding and harvesting for much longer periods (sometimes months) compared with traditional bioreactors which culture cells in batches typically running between 7-21 days. Companies that manufacture perfusion systems include GE Wave Biotech, FiberCell, Xcellerex and Biovest. Proponents of perfusion state many advantages for example; there is no accumulation of waste products, which is particularly important for proteins that are less stable. Because cells in perfusion are bound to a substrate, there is less movement with no mixing necessary. This produces antibodies that are more like the native form and are more consistent resulting in higher final product quality. Additionally perfusion bioreactors are more space friendly in that they can produce the same yield in much less tank space by culturing cells at much higher concentrations. It has been shown that a 50-liter perfusion bioreactor can produce the same yield as a 1,000-liter fed-batch bioreactor. Some have questioned the cost of perfusion bioreactors due to the amount of media used in a continuous system, but estimates show that in large-scale production they should be more cost effective due to a reduction in capital and operating costs. The industry has been a bit slow to warm to perfusion bioreactors, but if manufacturers of these systems are right, it could prove to be a big improvement.
There are also great resources on the internet that discuss biomanufacturing capacity and ways to improve capacity. The Bioprocess Technology Consultants Blog is an excellent source of information on biomanufacturing capacity, identifying capacity availability and strategies for improving cost of manufacturing. High Tech Business Decisions, San Diego also has an terrific list of reports on the biomanufacturing industry.
These are just a few examples of work being done to improve CHO production and there are many others. Has anyone used any of these methods for improving their CHO production? Does anyone have any others to recommend?