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Feb 1, 2014 (Vol. 34, No. 3)

Cell-Line Development: Where Nature Meets Nurture

From our February 1 issue.

  • While nurture (process optimization, media, and feed strategies) ultimately trumps nature (cell line) for maximizing protein titer, the importance of starting out with the right cell line cannot be overstated. Volumetric productivity, product quality, and the ability to meet timelines are three factors that bioprocessors balance at different stages of a product’s lifecycle.

    During early cell-line optimization, time-to-clinic usually becomes the preeminent objective. Alison Porter, head of mammalian cell culture R&D at Fujifilm Diosynth Biotechnologies, a contract research and manufacturing firm, notes that productivity and quality attributes must eventually reach the point of commercially viability, “but ultimately it comes down to speed to reach first-in-human studies. Of course you want good titers, but you don’t have to put in all that extra work at such an early stage to get the highest possible titer. A merely good titer is satisfactory as long as clinical timelines are met.”

    While much can be said for controlling every aspect of cell-line development, sponsors generally trust their contractors to select the specific cell line, screening, and processes that will achieve the ultimate goal of timeliness. They expect well-characterized cell lines and transfection platforms with which regulators have ample experience. “In the end they’re looking for a sensible process,” Porter says.

    One of the most significant trends in cell-line development, according to Porter, is wide-scale adoption of microbioreactor and shaken microplate systems capable of fed-batch operation. “These technologies have allowed investigators to look into larger numbers of cell lines in systems that are representative of the bioreactor process. They allow better decision-making on which cell lines to progress because they transfer well to process development, where they are used in design-of-experiment to optimize cells and process conditions.”

    Before the advent of the microbioreactor, static screens and shake flasks dominated cell line and process development. But the flasks are relatively bulky and difficult to control for common process parameters. Now, shaken microplates replace static screens and microbioreactors take the place of flasks. “Microbioreactors are a step closer to bioreactors,” Porter says.

  • Ready-Made Cells

    Mark Melville, Ph.D., senior director of bioprocess development at EPIRUS Biopharmaceuticals, notes that two main avenues to cell-line development are open to virtual companies like EPIRUS.

    The more traditional approach involves working with a company that builds cell lines from the ground up using a suitable expression system and host cell line, followed by conventional screening. For biosimilars, EPIRUS’ specialty, quality endpoints would be brought into the development process as early as feasible.

    The second strategy, which has become more common since the advent of biosimilars, is to in-license cell lines optimized for the expression of specific biosimilars, for example trastuzumab (Herceptin) or bevacizumab (Avastin).

    In-licensing cells significantly has the potential to shorten development times. “But there are tradeoffs,” Dr. Melville cautions. “If you’re going that way you don’t have a wide range of cell lines to select from. By comparison, when working from scratch the sponsor can influence and shape development all along the way. In-licensing may save time, but it adds risk.”

    The risk is that, in a new set of hands, the cell line may not meet productivity or quality goals. “These vendors will provide cells, but they cannot guarantee success—that you’ll have an approvable biosimilars if you use their product,” Dr. Melville says. “There are many steps between receiving cells and achieving a commercial process.”

    An interesting analogy might be purchasing a component or ingredient for a gourmet dinner rather than making it from scratch. An inexperienced cook probably has a higher expectation of success going this route, but professional chefs know the result will be perfect if they control every “unit operation” in preparing that meal. In other words, companies inexperienced with cell-line development are probably better off in-licensing.

    For the in-licensing scenario the risk of not reaching specified quality attributes is a lot more serious than for not achieving viable productivity. “It’s not difficult to achieve commercially viable titers,” Dr. Melville explains. Quality, particularly for biosimilars developers, involves hitting a narrow target of physico-chemical similarity with the innovator drug. Factors such as culture method and medium, feed strategies, and purification all affect quality. Companies that in-license must still perform significant development on these components of a successful process. Furthermore, the analytical methods that originally qualified product-specific cells may be inadequate for demonstrating biosimilarity to regulators.

    Dr. Melville is not at liberty to divulge his company’s strategy with respect to sourcing cell-line development services. He did say, however, that most established biomanufacturers tend to keep as much control as possible over cell-line development, except for “selective” cases that make good business sense.

  • Fast, Stable Transfection

    Transient transfection provides a rapid route to modest quantities of protein for characterization and preclinical investigation. Now, a group at the National Research Council of Canada has devised a rapid, stable transfection method which, although somewhat slower than transient transfection, provides several advantages under the right circumstances.

    Yves Durocher, Ph.D., team leader for protein production at the NRC, uses a promoter developed at the NRC and a recently acquired CHO cell line. Dr. Durocher and co-workers have adapted the line to serum-free suspension, generated a master cell bank, and validated the line for use in biomanufacturing.

    Within this CHO cell line, CHOBRI/Cum2, researchers combined elements (a transactivator and repressor) that allow for cumate-regulated expression. This platform generates CHO pools that natively, stably express between 200 and 500 mg/L of protein in less than four weeks post-transfection: two weeks for clone selection, and two for production. “We have shown that the pools can be maintained for months in culture under selection pressure,” says Dr. Durocher, “and maintain productivity at 200 to 500 mg/L.”

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