Biopharmaceutical products are subject to downstream processes that are built on process chromatography as the main purification
agent and with membrane technologies providing clean feed streams, buffer exchange, product concentration, virus removal,
and sterile filtration. As Jungbauer notes: "Bio-separation processes are dominated by chromatographic steps. Even primary
recovery is sometimes accomplished by chromatographic separation, using a fluidized bed instead of a fixed bed."27 The expansion of chromatography as the prime tool of downstream processing is manifest in the increase of bioprocess revenues
at GE Healthcare's Life Science Division from approximately $36 million in 198641 to $461 million in 2006.42
MODERNIZATION OF PROCESS CHROMATOGRAPHY
With the development of bacterial fermentation and mammalian cell culture as the sources for new recombinant products came
a standardization of raw feed stocks with manufacturers sharing the same types of problems. The reduction of endotoxin levels
from E. coli fermentation or the reduction of host cell proteins and DNA from CHO cell culture products are prime examples. This standardization
allowed a more systematic approach to process development and is the underlying reason for the introduction of the capture–purify–polish
paradigm, now ubiquitous in downstream process design. Industry developed a new, systematic approach integrating process design,
engineering and control, process economics, hygiene, and regulatory issues, summarized by Sofer and Nyström43 in 1989 and followed by a text on validation44 in 1991. Bioprocessing systems were introduced and computerized control took over from technologies that were previously
dominated by manual operation and therefore subject to operator error.
Focus on Viral Clearance
The transmission to hemophiliacs of HIV by human plasma-derived Factor VIII renewed the focus on viral clearance and methods
of virus kill in the plasma fractionation industry. In the recombinant industry, cell cultures need to be protected from adventitious
viral contamination by viruses such as virus of mouse (MVM), epizootic hemorrhagic disease virus (EHDV), and reovirus,45 which may influence expression of the product by the host machinery. This need led to efforts to eliminate animal-derived
raw materials from the process chain and thus improved safety.
Robustness, tolerance to alkaline cleaning agents, validated viral clearance, and long-term performance over many cycles became
a focal point of adsorbents for process chromatography.46 However, the 1990s were perhaps an age of process engineering with little attention paid to improving separation media,
with the exception of the introduction of expanded bed adsorption chromatography.47 This technology, which integrates unit operations of solid–liquid separation, clarification, and recovery of the target
protein by adsorption, has met with limited success in the biopharmaceutical industry but has found large-scale application
in the dairy industry.48 Now the industry has moved to the development of platform technologies, which can be applied to monoclonal antibody (MAb)
products,49–50 but case-by-case development still remains a challenge for manufacturers with diverse product types.
INNOVATION AND THE SEARCH FOR IMPROVEMENT: 2000 AND BEYOND
Since the new millennium, the purification of MAbs—with their improved expression levels—has dominated the development of
process chromatography. Process affinity chromatography using Protein A adsorbents has received much attention with the introduction
of new products manufactured without using animal-derived raw materials, improved robustness and resistance to alkaline cleaning,
and binding capacity in the 20–30g/L range with short residence times and at flow rates between 100 and 500 cm/hr.
However, driven by increasing product titers52 the biopharmaceutical bottleneck has moved to downstream processing53 and will require even more innovation and improvement. Sofer and Chirica project the development of high flow ion exchangers
running at over 700 cm/hr in 20 cm columns and capacities of ~100 g/L at residence times of 2–6 minutes to cope with 40 kg
bioreactor batches and a product output of 1,000 kgs/year.54 Discussing the future of antibody purification, Low et al. conclude that the "true bottleneck in recovery processes is the
first adsorptive column."55