Fed-batch and perfusion culture are the two dominant modes of operation for mammalian-cell-culture based processes, especially for the production of glycosylated proteins required in large amounts. This article provides an economic comparison for the production of a typical glycosylated protein using the fed-batch, concentrated fed-batch (CFB), and concentrated perfusion (CP) technologies. The CFB and CP processes are based on the ATF System, a platform technology developed by Refine Technology for biologics production.
In perfusion culture, a continuous supply of fresh media is fed into the bioreactor while growth-inhibitory by-products are constantly removed. The increasing interest in the use of perfusion culture can be attributed to the higher product output from a reduced reactor size (hence, simplifying operation, cleaning, and sterilization). The cell densities achieved in perfusion culture (30–100 x 106 cells/mL) are typically higher than for fed-batch modes (5–25 x 106 cells/mL).2 The principal aspect of perfusion operation, which is different from fed-batch, is the added requirement of a cell-retention device. Cell-retention systems add a level of complexity to the process, requiring management, control, and maintenance for successful operation. Perfusion bioreactors can suffer operational difficulties such as malfunction or failure of the cell-separation device, which can lead to shortening of the production run, leading further, to increased operating costs. This has previously limited their attractiveness.
In recent years, a platform technology has been developed for biologics production—the ATF System, introduced by Refine Technology (Pine Brook, NJ). Used in the alternating tangential flow mode, it is a low shear filtration system that inhibits filter-membrane fouling. This external cell-separation system is able to maintain continuous culture for extended periods of time and offers the capability of rapid filter change without compromising the culture run.3 The ATF System allows increased volumetric productivity and reduced bioreactor size.
Concentrated fed-batch and concentrated perfusion are two production techniques based on the ATF System, which simultaneously nourishes the culture and concentrates the product within the bioreactor. These manufacturing methods permit great increases in cell and product concentrations as compared with fed-batch and perfusion. For example, in the concentrated fed-batch production platform, one of Refine Technology's pharmaceutical clients has reported a protein product titer of 17 g/L with an unoptimized Chinese hamster ovary (CHO) cell process.4 Higher titers are expected as process optimization continues. In the concentrated fed-batch operation, ultra-high cell densities of (70–200) x 106 cells/mL have been achieved; similarly, extremely high cell densities in the region of (70–100) x 106 cells/mL have been achieved in systems using the concentrated perfusion mode.
This article compares the economic feasibility of a typical glycosylated protein manufactured using three production techniques—fed-batch (FB), concentrated fed-batch (CFB), and concentrated perfusion (CP). The Excel-based process-cost modeling tool, BioSolve from BioPharm Services (Chesham, Buckinghamshire, UK), was used for the economic assessment. The methodology, assumptions, and key results of the cost model are described. The analysis will use the cost of goods (CoG) metric expressed on a per gram basis for comparability.