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.
The market for protein-derived products has grown significantly in the past decade and continues to accelerate at a rapid
rate. As more recombinant therapeutic proteins enter development and get through the approval phase, more efficient large-scale
production of such proteins is necessary to meet the surging demand. 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.1 Challenges in the industry (such as competitive products for the same indication or desired cost reductions) are forcing
many to explore new production options.
In fed-batch culture, there is a gradual addition of a fresh volume of selected nutrients during the growth–culture cycle
to improve productivity and growth. The culture is subsequently harvested and the product recovered. Fed-batch culture has
been an attractive choice for large-scale production due to its operational simplicity and familiarity as a carryover process
from fermentation. However, fed-batch mode of operation typically also involves high start-up costs, resulting from the need
for larger bioreactor plant capacity.
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.
The system scales on a linear basis from 1 L to greater than 1,000 L and can be used with traditional or disposable bioreactors
and with all cell types including anchorage-dependent lines. Table 1 indicates the working volume sizes for each ATF System
in the scale-up process. The figures in the table are provided as guidelines. Actual capacity and vessel size depend on process
Table 1. Guideline working volume sizes for each ATF system
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.